                        The Origin of Species

                by means of Natural Selection  or  the

        Preservation of Favoured Races in the Struggle for Life 

                   By Charles Darwin  M A   F R S  
                Author of  The Descent of Man   etc   etc 


Sixth London Edition  with all Additions and Corrections 
The 6th Edition is often considered the definititive edition 
Also see Project Gutenberg Etext  1228 for an earlier edition 


 But with regard to the material world  we can at least go so far as this  
we can perceive that events are brought about not by insulated
interpositions of Divine power  exerted in each particular case  but by the
establishment of general laws    Whewell   Bridgewater Treatise  

 The only distinct meaning of the word  natural  is STATED  FIXED or
SETTLED  since what is natural as much requires and presupposes an
intelligent agent to render it so  i e   to effect it continually or at
stated times  as what is supernatural or miraculous does to effect it for
once    Butler    Analogy of Revealed Religion  


 To conclude  therefore  let no man out of a weak conceit of sobriety  or
an ill applied moderation  think or maintain  that a man can search too far
or be too well studied in the book of God s word  or in the book of God s
works  divinity or philosophy  but rather let men endeavour an endless
progress or proficience in both    Bacon   Advancement of Learning  


AN HISTORICAL SKETCH

OF THE PROGRESS OF OPINION ON THE ORIGIN OF SPECIES 

PREVIOUSLY TO THE PUBLICATION OF THE FIRST EDITION OF THIS WORK 

I will here give a brief sketch of the progress of opinion on the Origin of
Species   Until recently the great majority of naturalists believed that
species were immutable productions  and had been separately created   This
view has been ably maintained by many authors   Some few naturalists  on
the other hand  have believed that species undergo modification  and that
the existing forms of life are the descendants by true generation of pre
existing forms   Passing over allusions to the subject in the classical
writers  Aristotle  in his  Physicae Auscultationes   lib 2  cap 8  s 2  
after remarking that rain does not fall in order to make the corn grow  any
more than it falls to spoil the farmer s corn when threshed out of doors 
applies the same argument to organisation  and adds  as translated by Mr 
Clair Grece  who first pointed out the passage to me    So what hinders the
different parts  of the body  from having this merely accidental relation
in nature  as the teeth  for example  grow by necessity  the front ones
sharp  adapted for dividing  and the grinders flat  and serviceable for
masticating the food  since they were not made for the sake of this  but it
was the result of accident   And in like manner as to other parts in which
there appears to exist an adaptation to an end   Wheresoever  therefore 
all things together  that is all the parts of one whole  happened like as
if they were made for the sake of something  these were preserved  having
been appropriately constituted by an internal spontaneity  and whatsoever
things were not thus constituted  perished and still perish    We here see
the principle of natural selection shadowed forth  but how little Aristotle
fully comprehended the principle  is shown by his remarks on the formation
of the teeth    the first author who in modern times has treated it in a
scientific spirit was Buffon   But as his opinions fluctuated greatly at
different periods  and as he does not enter on the causes or means of the
transformation of species  I need not here enter on details 

Lamarck was the first man whose conclusions on the subject excited much
attention   This justly celebrated naturalist first published his views in
1801  he much enlarged them in 1809 in his  Philosophie Zoologique   and
subsequently  1815  in the Introduction to his  Hist  Nat  des Animaux sans
Vertebres    In these works he up holds the doctrine that all species 
including man  are descended from other species   He first did the eminent
service of arousing attention to the probability of all change in the
organic  as well as in the inorganic world  being the result of law  and
not of miraculous interposition   Lamarck seems to have been chiefly led to
his conclusion on the gradual change of species  by the difficulty of
distinguishing species and varieties  by the almost perfect gradation of
forms in certain groups  and by the analogy of domestic productions   With
respect to the means of modification  he attributed something to the direct
action of the physical conditions of life  something to the crossing of
already existing forms  and much to use and disuse  that is  to the effects
of habit   To this latter agency he seems to attribute all the beautiful
adaptations in nature  such as the long neck of the giraffe for browsing on
the branches of trees   But he likewise believed in a law of progressive
development  and as all the forms of life thus tend to progress  in order
to account for the existence at the present day of simple productions  he
maintains that such forms are now spontaneously generated    I have taken
the date of the first publication of Lamarck from Isidore Geoffroy Saint 
Hilaire s   Hist  Nat  Generale   tom  ii  page 405  1859  excellent
history of opinion on this subject   In this work a full account is given
of Buffon s conclusions on the same subject   It is curious how largely my
grandfather  Dr  Erasmus Darwin  anticipated the views and erroneous
grounds of opinion of Lamarck in his  Zoonomia   vol  i  pages 500 510  
published in 1794   According to Isid  Geoffroy there is no doubt that
Goethe was an extreme partisan of similar views  as shown in the
introduction to a work written in 1794 and 1795  but not published till
long afterward  he has pointedly remarked   Goethe als Naturforscher   von
Dr  Karl Meding  s  34  that the future question for naturalists will be
how  for instance  cattle got their horns and not for what they are used  
It is rather a singular instance of the manner in which similar views arise
at about the same time  that Goethe in Germany  Dr  Darwin in England  and
Geoffroy Saint Hilaire  as we shall immediately see  in France  came to the
same conclusion on the origin of species  in the years 1794 5  

Geoffroy Saint Hilaire  as is stated in his  Life   written by his son 
suspected  as early as 1795  that what we call species are various
degenerations of the same type   It was not until 1828 that he published
his conviction that the same forms have not been perpetuated since the
origin of all things   Geoffroy seems to have relied chiefly on the
conditions of life  or the  monde ambiant  as the cause of change   He was
cautious in drawing conclusions  and did not believe that existing species
are now undergoing modification  and  as his son adds   C est donc un
probleme a reserver entierement a l avenir  suppose meme que l avenir doive
avoir prise sur lui  

In 1813 Dr  W C  Wells read before the Royal Society  An Account of a White
Female  part of whose skin resembles that of a Negro   but his paper was
not published until his famous  Two Essays upon Dew and Single Vision 
appeared in 1818   In this paper he distinctly recognises the principle of
natural selection  and this is the first recognition which has been
indicated  but he applies it only to the races of man  and to certain
characters alone   After remarking that negroes and mulattoes enjoy an
immunity from certain tropical diseases  he observes  firstly  that all
animals tend to vary in some degree  and  secondly  that agriculturists
improve their domesticated animals by selection  and then  he adds  but
what is done in this latter case  by art  seems to be done with equal
efficacy  though more slowly  by nature  in the formation of varieties of
mankind  fitted for the country which they inhabit   Of the accidental
varieties of man  which would occur among the first few and scattered
inhabitants of the middle regions of Africa  some one would be better
fitted than others to bear the diseases of the country   This race would
consequently multiply  while the others would decrease  not only from their
in ability to sustain the attacks of disease  but from their incapacity of
contending with their more vigorous neighbours   The colour of this
vigorous race I take for granted  from what has been already said  would be
dark   But the same disposition to form varieties still existing  a darker
and a darker race would in the course of time occur   and as the darkest
would be the best fitted for the climate  this would at length become the
most prevalent  if not the only race  in the particular country in which it
had originated    He then extends these same views to the white inhabitants
of colder climates   I am indebted to Mr  Rowley  of the United States  for
having called my attention  through Mr  Brace  to the above passage of Dr 
Wells  work 

The Hon  and Rev  W  Herbert  afterward Dean of Manchester  in the fourth
volume of the  Horticultural Transactions   1822  and in his work on the
 Amaryllidaceae   1837  pages 19  339   declares that  horticultural
experiments have established  beyond the possibility of refutation  that
botanical species are only a higher and more permanent class of varieties   
He extends the same view to animals   The dean believes that single species
of each genus were created in an originally highly plastic condition  and
that these have produced  chiefly by inter crossing  but likewise by
variation  all our existing species 

In 1826 Professor Grant  in the concluding paragraph in his well known
paper   Edinburgh Philosophical Journal   vol  XIV  page 283  on the
Spongilla  clearly declares his belief that species are descended from
other species  and that they become improved in the course of modification  
This same view was given in his Fifty fifth Lecture  published in the
 Lancet  in 1834 

In 1831 Mr  Patrick Matthew published his work on  Naval Timber and
Arboriculture   in which he gives precisely the same view on the origin of
species as that  presently to be alluded to  propounded by Mr  Wallace and
myself in the  Linnean Journal   and as that enlarged in the present
volume   Unfortunately the view was given by Mr  Matthew very briefly in
scattered passages in an appendix to a work on a different subject  so that
it remained unnoticed until Mr  Matthew himself drew attention to it in the
 Gardeners  Chronicle   on April 7  1860   The differences of Mr  Matthew s
views from mine are not of much importance   he seems to consider that the
world was nearly depopulated at successive periods  and then restocked  and
he gives as an alternative  that new forms may be generated  without the
presence of any mold or germ of former aggregates    I am not sure that I
understand some passages  but it seems that he attributes much influence to
the direct action of the conditions of life   He clearly saw  however  the
full force of the principle of natural selection 

The celebrated geologist and naturalist  Von Buch  in his excellent
 Description Physique des Isles Canaries   1836  page 147   clearly
expresses his belief that varieties slowly become changed into permanent
species  which are no longer capable of intercrossing 

Rafinesque  in his  New Flora of North America   published in 1836  wrote
 page 6  as follows    All species might have been varieties once  and many
varieties are gradually becoming species by assuming constant and peculiar
characters   but further on  page 18  he adds   except the original types
or ancestors of the genus  

In 1843 44 Professor Haldeman   Boston Journal of Nat  Hist  U  States  
vol  iv  page 468  has ably given the arguments for and against the
hypothesis of the development and modification of species   he seems to
lean toward the side of change 

The  Vestiges of Creation  appeared in 1844   In the tenth and much
improved edition  1853  the anonymous author says  page 155     The
proposition determined on after much consideration is  that the several
series of animated beings  from the simplest and oldest up to the highest
and most recent  are  under the providence of God  the results  FIRST  of
an impulse which has been imparted to the forms of life  advancing them  in
definite times  by generation  through grades of organisation terminating
in the highest dicotyledons and vertebrata  these grades being few in
number  and generally marked by intervals of organic character  which we
find to be a practical difficulty in ascertaining affinities  SECOND  of
another impulse connected with the vital forces  tending  in the course of
generations  to modify organic structures in accordance with external
circumstances  as food  the nature of the habitat  and the meteoric
agencies  these being the  adaptations  of the natural theologian    The
author apparently believes that organisation progresses by sudden leaps 
but that the effects produced by the conditions of life are gradual   He
argues with much force on general grounds that species are not immutable
productions   But I cannot see how the two supposed  impulses  account in a
scientific sense for the numerous and beautiful coadaptations which we see
throughout nature  I cannot see that we thus gain any insight how  for
instance  a woodpecker has become adapted to its peculiar habits of life  
The work  from its powerful and brilliant style  though displaying in the
early editions little accurate knowledge and a great want of scientific
caution  immediately had a very wide circulation   In my opinion it has
done excellent service in this country in calling attention to the subject 
in removing prejudice  and in thus preparing the ground for the reception
of analogous views 

In 1846 the veteran geologist M J  d Omalius d Halloy published in an
excellent though short paper   Bulletins de l Acad  Roy  Bruxelles   tom 
xiii  page 581  his opinion that it is more probable that new species have
been produced by descent with modification than that they have been
separately created   the author first promulgated this opinion in 1831 

Professor Owen  in 1849   Nature of Limbs   page 86   wrote as follows  
 The archetypal idea was manifested in the flesh under diverse such
modifications  upon this planet  long prior to the existence of those
animal species that actually exemplify it   To what natural laws or
secondary causes the orderly succession and progression of such organic
phenomena may have been committed  we  as yet  are ignorant    In his
address to the British Association  in 1858  he speaks  page li  of  the
axiom of the continuous operation of creative power  or of the ordained
becoming of living things    Further on  page xc   after referring to
geographical distribution  he adds   These phenomena shake our confidence
in the conclusion that the Apteryx of New Zealand and the Red Grouse of
England were distinct creations in and for those islands respectively  
Always  also  it may be well to bear in mind that by the word  creation 
the zoologist means  a process he knows not what     He amplifies this idea
by adding that when such cases as that of the Red Grouse are  enumerated by
the zoologist as evidence of distinct creation of the bird in and for such
islands  he chiefly expresses that he knows not how the Red Grouse came to
be there  and there exclusively  signifying also  by this mode of
expressing such ignorance  his belief that both the bird and the islands
owed their origin to a great first Creative Cause    If we interpret these
sentences given in the same address  one by the other  it appears that this
eminent philosopher felt in 1858 his confidence shaken that the Apteryx and
the Red Grouse first appeared in their respective homes  he knew not how  
or by some process  he knew not what  

This address was delivered after the papers by Mr  Wallace and myself on
the Origin of Species  presently to be referred to  had been read before
the Linnean Society   When the first edition of this work was published  I
was so completely deceived  as were many others  by such expressions as
 the continuous operation of creative power   that I included Professor
Owen with other palaeontologists as being firmly convinced of the
immutability of species  but it appears   Anat  of Vertebrates   vol  iii 
page 796  that this was on my part a preposterous error   In the last
edition of this work I inferred  and the inference still seems to me
perfectly just  from a passage beginning with the words  no doubt the type 
form   etc  Ibid   vol  i  page xxxv   that Professor Owen admitted that
natural selection may have done something in the formation of a new
species  but this it appears  Ibid   vol  iii  page 798  is inaccurate and
without evidence   I also gave some extracts from a correspondence between
Professor Owen and the editor of the  London Review   from which it
appeared manifest to the editor as well as to myself  that Professor Owen
claimed to have promulgated the theory of natural selection before I had
done so  and I expressed my surprise and satisfaction at this announcement 
but as far as it is possible to understand certain recently published
passages  Ibid   vol  iii  page 798  I have either partially or wholly
again fallen into error   It is consolatory to me that others find
Professor Owen s controversial writings as difficult to understand and to
reconcile with each other  as I do   As far as the mere enunciation of the
principle of natural selection is concerned  it is quite immaterial whether
or not Professor Owen preceded me  for both of us  as shown in this
historical sketch  were long ago preceded by Dr  Wells and Mr  Matthews 

M  Isidore Geoffroy Saint Hilaire  in his lectures delivered in 1850  of
which a Resume appeared in the  Revue et Mag  de Zoolog    Jan   1851  
briefly gives his reason for believing that specific characters  sont
fixes  pour chaque espece  tant qu elle se perpetue au milieu des memes
circonstances   ils se modifient  si les circonstances ambiantes viennent a
changer   En resume  L OBSERVATION des animaux sauvages demontre deja la
variabilite LIMITEE des especes   Les EXPERIENCES sur les animaux sauvages
devenus domestiques  et sur les animaux domestiques redevenus sauvages  la
demontrent plus clairment encore   Ces memes experiences prouvent  de plus 
que les differences produites peuvent etre de VALEUR GENERIQUE    In his
 Hist  Nat  Generale   tom  ii  page 430  1859  he amplifies analogous
conclusions 

 From a circular lately issued it appears that Dr  Freke  in 1851   Dublin
Medical Press   page 322   propounded the doctrine that all organic beings
have descended from one primordial form   His grounds of belief and
treatment of the subject are wholly different from mine  but as Dr  Freke
has now  1861  published his Essay on the  Origin of Species by means of
Organic Affinity   the difficult attempt to give any idea of his views
would be superfluous on my part 

Mr  Herbert Spencer  in an Essay  originally published in the  Leader  
March  1852  and republished in his  Essays   in 1858   has contrasted the
theories of the Creation and the Development of organic beings with
remarkable skill and force   He argues from the analogy of domestic
productions  from the changes which the embryos of many species undergo 
from the difficulty of distinguishing species and varieties  and from the
principle of general gradation  that species have been modified  and he
attributes the modification to the change of circumstances   The author
 1855  has also treated Psychology on the principle of the necessary
acquirement of each mental power and capacity by gradation 

In 1852 M  Naudin  a distinguished botanist  expressly stated  in an
admirable paper on the Origin of Species   Revue Horticole   page 102 
since partly republished in the  Nouvelles Archives du Museum   tom  i 
page 171   his belief that species are formed in an analogous manner as
varieties are under cultivation  and the latter process he attributes to
man s power of selection   But he does not show how selection acts under
nature   He believes  like Dean Herbert  that species  when nascent  were
more plastic than at present   He lays weight on what he calls the
principle of finality   puissance mysterieuse  indeterminee  fatalite pour 
les uns  pour les autres volonte providentielle  dont l action incessante
sur les etres vivantes determine  a toutes les epoques de l existence du
monde  la forme  le volume  et la duree de chacun d eux  en raison de sa
destinee dans l ordre de choses dont il fait partie   C est cette puissance
qui harmonise chaque membre a l ensemble  en l appropriant a la fonction
qu il doit remplir dans l organisme general de la nature  fonction qui est
pour lui sa raison d etre     From references in Bronn s  Untersuchungen
uber die Entwickelungs Gesetze   it appears that the celebrated botanist
and palaeontologist Unger published  in 1852  his belief that species
undergo development and modification   Dalton  likewise  in Pander and
Dalton s work on Fossil Sloths  expressed  in 1821  a similar belief  
Similar views have  as is well known  been maintained by Oken in his
mystical  Natur Philosophie    From other references in Godron s work  Sur
l Espece   it seems that Bory St  Vincent  Burdach  Poiret and Fries  have
all admitted that new species are continually being produced   I may add 
that of the thirty four authors named in this Historical Sketch  who
believe in the modification of species  or at least disbelieve in separate
acts of creation  twenty seven have written on special branches of natural
history or geology  

In 1853 a celebrated geologist  Count Keyserling   Bulletin de la Soc 
Geolog    2nd Ser   tom  x  page 357   suggested that as new diseases 
supposed to have been caused by some miasma have arisen and spread over the
world  so at certain periods the germs of existing species may have been
chemically affected by circumambient molecules of a particular nature  and
thus have given rise to new forms 

In this same year  1853  Dr  Schaaffhausen published an excellent pamphlet
  Verhand  des Naturhist  Vereins der Preuss  Rheinlands   etc    in which
he maintains the development of organic forms on the earth   He infers that
many species have kept true for long periods  whereas a few have become
modified   The distinction of species he explains by the destruction of
intermediate graduated forms    Thus living plants and animals are not
separated from the extinct by new creations  but are to be regarded as
their descendants through continued reproduction  

A well known French botanist  M  Lecoq  writes in 1854   Etudes sur
Geograph  Bot  tom  i  page 250    On voit que nos recherches sur la fixite
ou la variation de l espece  nous conduisent directement aux idees emises
par deux hommes justement celebres  Geoffroy Saint Hilaire et Goethe   
Some other passages scattered through M  Lecoq s large work make it a
little doubtful how far he extends his views on the modification of
species 

The  Philosophy of Creation  has been treated in a masterly manner by the
Rev  Baden Powell  in his  Essays on the Unity of Worlds   1855   Nothing
can be more striking than the manner in which he shows that the
introduction of new species is  a regular  not a casual phenomenon   or  as
Sir John Herschel expresses it   a natural in contradistinction to a
miraculous process  

The third volume of the  Journal of the Linnean Society  contains papers 
read July 1  1858  by Mr  Wallace and myself  in which  as stated in the
introductory remarks to this volume  the theory of Natural Selection is
promulgated by Mr  Wallace with admirable force and clearness 

Von Baer  toward whom all zoologists feel so profound a respect  expressed
about the year 1859  see Prof  Rudolph Wagner   Zoologisch Anthropologische
Untersuchungen   1861  s  51  his conviction  chiefly grounded on the laws
of geographical distribution  that forms now perfectly distinct have
descended from a single parent form 

In June  1859  Professor Huxley gave a lecture before the Royal Institution
on the  Persistent Types of Animal Life    Referring to such cases  he
remarks   It is difficult to comprehend the meaning of such facts as these 
if we suppose that each species of animal and plant  or each great type of
organisation  was formed and placed upon the surface of the globe at long
intervals by a distinct act of creative power  and it is well to recollect
that such an assumption is as unsupported by tradition or revelation as it
is opposed to the general analogy of nature   If  on the other hand  we
view  Persistent Types  in relation to that hypothesis which supposes the
species living at any time to be the result of the gradual modification of
pre existing species  a hypothesis which  though unproven  and sadly
damaged by some of its supporters  is yet the only one to which physiology
lends any countenance  their existence would seem to show that the amount
of modification which living beings have undergone during geological time
is but very small in relation to the whole series of changes which they
have suffered  

In December  1859  Dr  Hooker published his  Introduction to the Australian
Flora    In the first part of this great work he admits the truth of the
descent and modification of species  and supports this doctrine by many
original observations 

The first edition of this work was published on November 24  1859  and the
second edition on January 7  1860 



CONTENTS 


INTRODUCTION


CHAPTER I 

VARIATION UNDER DOMESTICATION 

Causes of Variability    Effects of Habit and the use or disuse of Parts   
Correlated Variation    Inheritance    Character of Domestic Varieties   
Difficulty of distinguishing between Varieties and Species    Origin of
Domestic Varieties from one or more Species    Domestic Pigeons  their
Differences and Origin    Principles of Selection  anciently followed 
their Effects    Methodical and Unconscious Selection    Unknown Origin of
our Domestic Productions    Circumstances favourable to Man s power of
Selection 


CHAPTER II 

VARIATION UNDER NATURE 

Variability    Individual Differences    Doubtful species    Wide ranging 
much diffused  and common species  vary most    Species of the larger
genera in each country vary more frequently than the species of the smaller
genera    Many of the species of the larger genera resemble varieties in
being very closely  but unequally  related to each other  and in having
restricted ranges 


CHAPTER III 

STRUGGLE FOR EXISTENCE 

Its bearing on natural selection    The term used in a wide sense   
Geometrical ratio of increase    Rapid increase of naturalised animals and
plants    Nature of the checks to increase    Competition universal   
Effects of climate    Protection from the number of individuals    Complex
relations of all animals and plants throughout nature    Struggle for life
most severe between individuals and varieties of the same species  often
severe between species of the same genus    The relation of organism to
organism the most important of all relations 


CHAPTER IV 

NATURAL SELECTION  OR THE SURVIVAL OF THE FITTEST 

Natural Selection    its power compared with man s selection    its power
on characters of trifling importance    its power at all ages and on both
sexes    Sexual Selection    On the generality of intercrosses between
individuals of the same species    Circumstances favourable and
unfavourable to the results of Natural Selection  namely  intercrossing 
isolation  number of individuals    Slow action    Extinction caused by
Natural Selection    Divergence of Character  related to the diversity of
inhabitants of any small area and to naturalisation    Action of Natural
Selection  through Divergence of Character and Extinction  on the
descendants from a common parent    Explains the Grouping of all organic
beings    Advance in organisation    Low forms preserved    Convergence of
character    Indefinite multiplication of species    Summary 


CHAPTER V 

LAWS OF VARIATION 

Effects of changed conditions    Use and disuse  combined with natural
selection  organs of flight and of vision    Acclimatisation    Correlated
variation    Compensation and economy of growth    False correlations   
Multiple  rudimentary  and lowly organised structures variable    Parts
developed in an unusual manner are highly variable  specific characters
more variable than generic  secondary sexual characters variable    Species
of the same genus vary in an analogous manner    Reversions to long lost
characters    Summary 


CHAPTER VI 

DIFFICULTIES OF THE THEORY 

Difficulties of the theory of descent with modification    Absence or
rarity of transitional varieties    Transitions in habits of life   
Diversified habits in the same species    Species with habits widely
different from those of their allies    Organs of extreme perfection   
Modes of transition    Cases of difficulty    Natura non facit saltum   
Organs of small importance    Organs not in all cases absolutely perfect   
The law of Unity of Type and of the Conditions of Existence embraced by the
theory of Natural Selection 


CHAPTER VII 

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION 

Longevity    Modifications not necessarily simultaneous    Modifications
apparently of no direct service    Progressive development    Characters of
small functional importance  the most constant    Supposed incompetence of
natural selection to account for the incipient stages of useful structures
   Causes which interfere with the acquisition through natural selection of
useful structures    Gradations of structure with changed functions   
Widely different organs in members of the same class  developed from one
and the same source    Reasons for disbelieving in great and abrupt
modifications 


CHAPTER VIII 

INSTINCT 

Instincts comparable with habits  but different in their origin   
Instincts graduated    Aphides and ants    Instincts variable    Domestic
instincts  their origin    Natural instincts of the cuckoo  molothrus 
ostrich  and parasitic bees    Slave making ants    Hive bee  its cell 
making instinct    Changes of instinct and structure not necessarily
simultaneous    Difficulties on the theory of the Natural Selection of
instincts    Neuter or sterile insects    Summary 


CHAPTER IX 

HYBRIDISM 

Distinction between the sterility of first crosses and of hybrids   
Sterility various in degree  not universal  affected by close
interbreeding  removed by domestication    Laws governing the sterility of
hybrids    Sterility not a special endowment  but incidental on other
differences  not accumulated by natural selection    Causes of the
sterility of first crosses and of hybrids    Parallelism between the
effects of changed conditions of life and of crossing    Dimorphism and
Trimorphism    Fertility of varieties when crossed and of their mongrel
offspring not universal    Hybrids and mongrels compared independently of
their fertility    Summary 


CHAPTER X 

ON THE IMPERFECTION OF THE GEOLOGICAL RECORD 

On the absence of intermediate varieties at the present day    On the
nature of extinct intermediate varieties  on their number    On the lapse
of time  as inferred from the rate of denudation and of deposition    On
the lapse of time as estimated in years    On the poorness of our
palaeontological collections    On the intermittence of geological
formations    On the denudation of granitic areas    On the absence of
intermediate varieties in any one formation    On the sudden appearance of
groups of species    On their sudden appearance in the lowest known
fossiliferous strata    Antiquity of the habitable earth 


CHAPTER XI 

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 

On the slow and successive appearance of new species    On their different
rates of change    Species once lost do not reappear    Groups of species
follow the same general rules in their appearance and disappearance as do
single species    On extinction    On simultaneous changes in the forms of
life throughout the world    On the affinities of extinct species to each
other and to living species    On the state of development of ancient forms
   On the succession of the same types within the same areas    Summary of
preceding and present chapter 


CHAPTER XII 

GEOGRAPHICAL DISTRIBUTION 

Present distribution cannot be accounted for by differences in physical
conditions    Importance of barriers    Affinity of the productions of the
same continent    Centres of creation    Means of dispersal by changes of
climate and of the level of the land  and by occasional means    Dispersal
during the Glacial period    Alternate Glacial periods in the north and
south 


CHAPTER XIII 

GEOGRAPHICAL DISTRIBUTION    CONTINUED 

Distribution of fresh water productions    On the inhabitants of oceanic
islands    Absence of Batrachians and of terrestrial Mammals    On the
relation of the inhabitants of islands to those of the nearest mainland   
On colonisation from the nearest source with subsequent modification   
Summary of the last and present chapter 


CHAPTER XIV 

MUTUAL AFFINITIES OF ORGANIC BEINGS   MORPHOLOGY    EMBRYOLOGY    
RUDIMENTARY ORGANS 

Classification  groups subordinate to groups    Natural system    Rules and
difficulties in classification  explained on the theory of descent with
modification    Classification of varieties    Descent always used in
classification    Analogical or adaptive characters    Affinities  general 
complex and radiating    Extinction separates and defines groups   
Morphology  between members of the same class  between parts of the same
individual    Embryology  laws of  explained by variations not supervening
at an early age  and being inherited at a corresponding age    Rudimentary
Organs  their origin explained    Summary 


CHAPTER XV 

RECAPITULATION AND CONCLUSION 

Recapitulation of the objections to the theory of Natural Selection   
Recapitulation of the general and special circumstances in its favour   
Causes of the general belief in the immutability of species    How far the
theory of Natural Selection may be extended    Effects of its adoption on
the study of Natural history    Concluding remarks 


GLOSSARY OF SCIENTIFIC TERMS 


INDEX 




ORIGIN OF SPECIES 


INTRODUCTION 

When on board H M S  Beagle  as naturalist  I was much struck with certain
facts in the distribution of the organic beings inhabiting South America 
and in the geological relations of the present to the past inhabitants of
that continent   These facts  as will be seen in the latter chapters of
this volume  seemed to throw some light on the origin of species  that
mystery of mysteries  as it has been called by one of our greatest
philosophers   On my return home  it occurred to me  in 1837  that
something might perhaps be made out on this question by patiently
accumulating and reflecting on all sorts of facts which could possibly have
any bearing on it   After five years  work I allowed myself to speculate on
the subject  and drew up some short notes  these I enlarged in 1844 into a
sketch of the conclusions  which then seemed to me probable   from that
period to the present day I have steadily pursued the same object   I hope
that I may be excused for entering on these personal details  as I give
them to show that I have not been hasty in coming to a decision 

My work is now  1859  nearly finished  but as it will take me many more
years to complete it  and as my health is far from strong  I have been
urged to publish this abstract   I have more especially been induced to do
this  as Mr  Wallace  who is now studying the natural history of the Malay
Archipelago  has arrived at almost exactly the same general conclusions
that I have on the origin of species   In 1858 he sent me a memoir on this
subject  with a request that I would forward it to Sir Charles Lyell  who
sent it to the Linnean Society  and it is published in the third volume of
the Journal of that Society   Sir C  Lyell and Dr  Hooker  who both knew of
my work  the latter having read my sketch of 1844  honoured me by thinking
it advisable to publish  with Mr  Wallace s excellent memoir  some brief
extracts from my manuscripts 

This abstract  which I now publish  must necessarily be imperfect   I
cannot here give references and authorities for my several statements  and
I must trust to the reader reposing some confidence in my accuracy   No
doubt errors may have crept in  though I hope I have always been cautious
in trusting to good authorities alone   I can here give only the general
conclusions at which I have arrived  with a few facts in illustration  but
which  I hope  in most cases will suffice   No one can feel more sensible
than I do of the necessity of hereafter publishing in detail all the facts 
with references  on which my conclusions have been grounded  and I hope in
a future work to do this   For I am well aware that scarcely a single point
is discussed in this volume on which facts cannot be adduced  often
apparently leading to conclusions directly opposite to those at which I
have arrived   A fair result can be obtained only by fully stating and
balancing the facts and arguments on both sides of each question  and this
is here impossible 

I much regret that want of space prevents my having the satisfaction of
acknowledging the generous assistance which I have received from very many
naturalists  some of them personally unknown to me   I cannot  however  let
this opportunity pass without expressing my deep obligations to Dr  Hooker 
who  for the last fifteen years  has aided me in every possible way by his
large stores of knowledge and his excellent judgment 

In considering the origin of species  it is quite conceivable that a
naturalist  reflecting on the mutual affinities of organic beings  on their
embryological relations  their geographical distribution  geological
succession  and other such facts  might come to the conclusion that species
had not been independently created  but had descended  like varieties  from
other species   Nevertheless  such a conclusion  even if well founded 
would be unsatisfactory  until it could be shown how the innumerable
species  inhabiting this world have been modified  so as to acquire that
perfection of structure and coadaptation which justly excites our
admiration   Naturalists continually refer to external conditions  such as
climate  food  etc   as the only possible cause of variation   In one
limited sense  as we shall hereafter see  this may be true  but it is
preposterous to attribute to mere external conditions  the structure  for
instance  of the woodpecker  with its feet  tail  beak  and tongue  so
admirably adapted to catch insects under the bark of trees   In the case of
the mistletoe  which draws its nourishment from certain trees  which has
seeds that must be transported by certain birds  and which has flowers with
separate sexes absolutely requiring the agency of certain insects to bring
pollen from one flower to the other  it is equally preposterous to account
for the structure of this parasite  with its relations to several distinct
organic beings  by the effects of external conditions  or of habit  or of
the volition of the plant itself 

It is  therefore  of the highest importance to gain a clear insight into
the means of modification and coadaptation   At the commencement of my
observations it seemed to me probable that a careful study of domesticated
animals and of cultivated plants would offer the best chance of making out
this obscure problem   Nor have I been disappointed  in this and in all
other perplexing cases I have invariably found that our knowledge 
imperfect though it be  of variation under domestication  afforded the best
and safest clue   I may venture to express my conviction of the high value
of such studies  although they have been very commonly neglected by
naturalists 

 From these considerations  I shall devote the first chapter of this
abstract to variation under domestication   We shall thus see that a large
amount of hereditary modification is at least possible  and  what is
equally or more important  we shall see how great is the power of man in
accumulating by his selection successive slight variations   I will then
pass on to the variability of species in a state of nature  but I shall 
unfortunately  be compelled to treat this subject far too briefly  as it
can be treated properly only by giving long catalogues of facts   We shall 
however  be enabled to discuss what circumstances are most favourable to
variation   In the next chapter the struggle for existence among all
organic beings throughout the world  which inevitably follows from the high
geometrical ratio of their increase  will be considered   This is the
doctrine of Malthus  applied to the whole animal and vegetable kingdoms  
As many more individuals of each species are born than can possibly
survive  and as  consequently  there is a frequently recurring struggle for
existence  it follows that any being  if it vary however slightly in any
manner profitable to itself  under the complex and sometimes varying
conditions of life  will have a better chance of surviving  and thus be
NATURALLY SELECTED   From the strong principle of inheritance  any selected
variety will tend to propagate its new and modified form 

This fundamental subject of natural selection will be treated at some
length in the fourth chapter  and we shall then see how natural selection
almost inevitably causes much extinction of the less improved forms of
life  and leads to what I have called divergence of character   In the next
chapter I shall discuss the complex and little known laws of variation   In
the five succeeding chapters  the most apparent and gravest difficulties in
accepting the theory will be given   namely  first  the difficulties of
transitions  or how a simple being or a simple organ can be changed and
perfected into a highly developed being or into an elaborately constructed
organ  secondly the subject of instinct  or the mental powers of animals 
thirdly  hybridism  or the infertility of species and the fertility of
varieties when intercrossed  and fourthly  the imperfection of the
geological record   In the next chapter I shall consider the geological
succession of organic beings throughout time  in the twelfth and
thirteenth  their geographical distribution throughout space  in the
fourteenth  their classification or mutual affinities  both when mature and
in an embryonic condition   In the last chapter I shall give a brief
recapitulation of the whole work  and a few concluding remarks 

No one ought to feel surprise at much remaining as yet unexplained in
regard to the origin of species and varieties  if he make due allowance for
our profound ignorance in regard to the mutual relations of the many beings
which live around us   Who can explain why one species ranges widely and is
very numerous  and why another allied species has a narrow range and is
rare   Yet these relations are of the highest importance  for they
determine the present welfare and  as I believe  the future success and
modification of every inhabitant of this world   Still less do we know of
the mutual relations of the innumerable inhabitants of the world during the
many past geological epochs in its history   Although much remains obscure 
and will long remain obscure  I can entertain no doubt  after the most
deliberate study and dispassionate judgment of which I am capable  that the
view which most naturalists until recently entertained  and which I
formerly entertained  namely  that each species has been independently
created  is erroneous   I am fully convinced that species are not
immutable  but that those belonging to what are called the same genera are
lineal descendants of some other and generally extinct species  in the same
manner as the acknowledged varieties of any one species are the descendants
of that species   Furthermore  I am convinced that natural selection has
been the most important  but not the exclusive  means of modification 


CHAPTER I 

VARIATION UNDER DOMESTICATION 

Causes of Variability    Effects of Habit and the use and disuse of Parts
   Correlated Variation    Inheritance    Character of Domestic Varieties
   Difficulty of distinguishing between Varieties and Species    Origin of
Domestic Varieties from one or more Species    Domestic Pigeons  their
Differences and Origin    Principles of Selection  anciently followed 
their Effects    Methodical and Unconscious Selection    Unknown Origin of
our Domestic Productions    Circumstances favourable to Man s power of
Selection 

CAUSES OF VARIABILITY 

When we compare the individuals of the same variety or sub variety of our
older cultivated plants and animals  one of the first points which strikes
us is  that they generally differ more from each other than do the
individuals of any one species or variety in a state of nature   And if we
reflect on the vast diversity of the plants and animals which have been
cultivated  and which have varied during all ages under the most different
climates and treatment  we are driven to conclude that this great
variability is due to our domestic productions having been raised under
conditions of life not so uniform as  and somewhat different from  those to
which the parent species had been exposed under nature   There is  also 
some probability in the view propounded by Andrew Knight  that this
variability may be partly connected with excess of food   It seems clear
that organic beings must be exposed during several generations to new
conditions to cause any great amount of variation  and that  when the
organisation has once begun to vary  it generally continues varying for
many generations   No case is on record of a variable organism ceasing to
vary under cultivation   Our oldest cultivated plants  such as wheat  still
yield new varieties   our oldest domesticated animals are still capable of
rapid improvement or modification 

As far as I am able to judge  after long attending to the subject  the
conditions of life appear to act in two ways  directly on the whole
organisation or on certain parts alone and in directly by affecting the
reproductive system   With respect to the direct action  we must bear in
mind that in every case  as Professor Weismann has lately insisted  and as
I have incidently shown in my work on  Variation under Domestication  
there are two factors   namely  the nature of the organism and the nature
of the conditions   The former seems to be much the more important  for
nearly similar variations sometimes arise under  as far as we can judge 
dissimilar conditions  and  on the other hand  dissimilar variations arise
under conditions which appear to be nearly uniform   The effects on the
offspring are either definite or in definite   They may be considered as
definite when all or nearly all the offspring of individuals exposed to
certain conditions during several generations are modified in the same
manner   It is extremely difficult to come to any conclusion in regard to
the extent of the changes which have been thus definitely induced   There
can  however  be little doubt about many slight changes  such as size from
the amount of food  colour from the nature of the food  thickness of the
skin and hair from climate  etc   Each of the endless variations which we
see in the plumage of our fowls must have had some efficient cause  and if
the same cause were to act uniformly during a long series of generations on
many individuals  all probably would be modified in the same manner   Such
facts as the complex and extraordinary out growths which variably follow
from the insertion of a minute drop of poison by a gall producing insect 
shows us what singular modifications might result in the case of plants
from a chemical change in the nature of the sap 

In definite variability is a much more common result of changed conditions
than definite variability  and has probably played a more important part in
the formation of our domestic races   We see in definite variability in the
endless slight peculiarities which distinguish the individuals of the same
species  and which cannot be accounted for by inheritance from either
parent or from some more remote ancestor   Even strongly marked differences
occasionally appear in the young of the same litter  and in seedlings from
the same seed capsule   At long intervals of time  out of millions of
individuals reared in the same country and fed on nearly the same food 
deviations of structure so strongly pronounced as to deserve to be called
monstrosities arise  but monstrosities cannot be separated by any distinct
line from slighter variations   All such changes of structure  whether
extremely slight or strongly marked  which appear among many individuals
living together  may be considered as the in definite effects of the
conditions of life on each individual organism  in nearly the same manner
as the chill effects different men in an in definite manner  according to
their state of body or constitution  causing coughs or colds  rheumatism 
or inflammation of various organs 

With respect to what I have called the in direct action of changed
conditions  namely  through the reproductive system of being affected  we
may infer that variability is thus induced  partly from the fact of this
system being extremely sensitive to any change in the conditions  and
partly from the similarity  as Kolreuter and others have remarked  between
the variability which follows from the crossing of distinct species  and
that which may be observed with plants and animals when reared under new or
unnatural conditions   Many facts clearly show how eminently susceptible
the reproductive system is to very slight changes in the surrounding
conditions   Nothing is more easy than to tame an animal  and few things
more difficult than to get it to breed freely under confinement  even when
the male and female unite   How many animals there are which will not
breed  though kept in an almost free state in their native country   This
is generally  but erroneously attributed to vitiated instincts   Many
cultivated plants display the utmost vigour  and yet rarely or never seed  
In some few cases it has been discovered that a very trifling change  such
as a little more or less water at some particular period of growth  will
determine whether or not a plant will produce seeds   I cannot here give
the details which I have collected and elsewhere published on this curious
subject  but to show how singular the laws are which determine the
reproduction of animals under confinement  I may mention that carnivorous
animals  even from the tropics  breed in this country pretty freely under
confinement  with the exception of the plantigrades or bear family  which
seldom produce young  whereas  carnivorous birds  with the rarest
exception  hardly ever lay fertile eggs   Many exotic plants have pollen
utterly worthless  in the same condition as in the most sterile hybrids  
When  on the one hand  we see domesticated animals and plants  though often
weak and sickly  breeding freely under confinement  and when  on the other
hand  we see individuals  though taken young from a state of nature
perfectly tamed  long lived  and healthy  of which I could give numerous
instances   yet having their reproductive system so seriously affected by
unperceived causes as to fail to act  we need not be surprised at this
system  when it does act under confinement  acting irregularly  and
producing offspring somewhat unlike their parents   I may add that as some
organisms breed freely under the most unnatural conditions  for instance 
rabbits and ferrets kept in hutches  showing that their reproductive organs
are not easily affected  so will some animals and plants withstand
domestication or cultivation  and vary very slightly  perhaps hardly more
than in a state of nature 

Some naturalists have maintained that all variations are connected with the
act of sexual reproduction  but this is certainly an error  for I have
given in another work a long list of  sporting plants   as they are called
by gardeners  that is  of plants which have suddenly produced a single bud
with a new and sometimes widely different character from that of the other
buds on the same plant   These bud variations  as they may be named  can be
propagated by grafts  offsets  etc   and sometimes by seed   They occur
rarely under nature  but are far from rare under culture   As a single bud
out of many thousands produced year after year on the same tree under
uniform conditions  has been known suddenly to assume a new character  and
as buds on distinct trees  growing under different conditions  have
sometimes yielded nearly the same variety  for instance  buds on peach 
trees producing nectarines  and buds on common roses producing moss roses  
we clearly see that the nature of the conditions is of subordinate
importance in comparison with the nature of the organism in determining
each particular form of variation  perhaps of not more importance than the
nature of the spark  by which a mass of combustible matter is ignited  has
in determining the nature of the flames 

EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS  CORRELATED VARIATION 
INHERITANCE 

Changed habits produce an inherited effect as in the period of the
flowering of plants when transported from one climate to another   With
animals the increased use or disuse of parts has had a more marked
influence  thus I find in the domestic duck that the bones of the wing
weigh less and the bones of the leg more  in proportion to the whole
skeleton  than do the same bones in the wild duck  and this change may be
safely attributed to the domestic duck flying much less  and walking more 
than its wild parents   The great and inherited development of the udders
in cows and goats in countries where they are habitually milked  in
comparison with these organs in other countries  is probably another
instance of the effects of use   Not one of our domestic animals can be
named which has not in some country drooping ears  and the view which has
been suggested that the drooping is due to disuse of the muscles of the
ear  from the animals being seldom much alarmed  seems probable 

Many laws regulate variation  some few of which can be dimly seen  and will
hereafter be briefly discussed   I will here only allude to what may be
called correlated variation   Important changes in the embryo or larva will
probably entail changes in the mature animal   In monstrosities  the
correlations between quite distinct parts are very curious  and many
instances are given in Isidore Geoffroy St  Hilaire s great work on this
subject   Breeders believe that long limbs are almost always accompanied by
an elongated head   Some instances of correlation are quite whimsical  thus
cats which are entirely white and have blue eyes are generally deaf  but it
has been lately stated by Mr  Tait that this is confined to the males  
Colour and constitutional peculiarities go together  of which many
remarkable cases could be given among animals and plants   From facts
collected by Heusinger  it appears that white sheep and pigs are injured by
certain plants  while dark coloured individuals escape   Professor Wyman
has recently communicated to me a good illustration of this fact  on asking
some farmers in Virginia how it was that all their pigs were black  they
informed him that the pigs ate the paint root  Lachnanthes   which coloured
their bones pink  and which caused the hoofs of all but the black varieties
to drop off  and one of the  crackers   i e  Virginia squatters  added   we
select the black members of a litter for raising  as they alone have a good
chance of living    Hairless dogs have imperfect teeth  long haired and
coarse haired animals are apt to have  as is asserted  long or many horns 
pigeons with feathered feet have skin between their outer toes  pigeons
with short beaks have small feet  and those with long beaks large feet  
Hence if man goes on selecting  and thus augmenting  any peculiarity  he
will almost certainly modify unintentionally other parts of the structure 
owing to the mysterious laws of correlation 

The results of the various  unknown  or but dimly understood laws of
variation are infinitely complex and diversified   It is well worth while
carefully to study the several treatises on some of our old cultivated
plants  as on the hyacinth  potato  even the dahlia  etc   and it is really
surprising to note the endless points of structure and constitution in
which the varieties and sub varieties differ slightly from each other   The
whole organisation seems to have become plastic  and departs in a slight
degree from that of the parental type 

Any variation which is not inherited is unimportant for us   But the number
and diversity of inheritable deviations of structure  both those of slight
and those of considerable physiological importance  are endless   Dr 
Prosper Lucas  treatise  in two large volumes  is the fullest and the best
on this subject   No breeder doubts how strong is the tendency to
inheritance  that like produces like is his fundamental belief   doubts
have been thrown on this principle only by theoretical writers   When any
deviation of structure often appears  and we see it in the father and
child  we cannot tell whether it may not be due to the same cause having
acted on both  but when among individuals  apparently exposed to the same
conditions  any very rare deviation  due to some extraordinary combination
of circumstances  appears in the parent  say  once among several million
individuals  and it reappears in the child  the mere doctrine of chances
almost compels us to attribute its reappearance to inheritance   Every one
must have heard of cases of albinism  prickly skin  hairy bodies  etc  
appearing in several members of the same family   If strange and rare
deviations of structure are truly inherited  less strange and commoner
deviations may be freely admitted to be inheritable   Perhaps the correct
way of viewing the whole subject would be  to look at the inheritance of
every character whatever as the rule  and non inheritance as the anomaly 

The laws governing inheritance are for the most part unknown  no one can
say why the same peculiarity in different individuals of the same species 
or in different species  is sometimes inherited and sometimes not so  why
the child often reverts in certain characteristics to its grandfather or
grandmother or more remote ancestor  why a peculiarity is often transmitted
from one sex to both sexes  or to one sex alone  more commonly but not
exclusively to the like sex   It is a fact of some importance to us  that
peculiarities appearing in the males of our domestic breeds are often
transmitted  either exclusively or in a much greater degree  to the males
alone   A much more important rule  which I think may be trusted  is that 
at whatever period of life a peculiarity first appears  it tends to
reappear in the offspring at a corresponding age  though sometimes earlier  
In many cases this could not be otherwise  thus the inherited peculiarities
in the horns of cattle could appear only in the offspring when nearly
mature  peculiarities in the silk worm are known to appear at the
corresponding caterpillar or cocoon stage   But hereditary diseases and
some other facts make me believe that the rule has a wider extension  and
that  when there is no apparent reason why a peculiarity should appear at
any particular age  yet that it does tend to appear in the offspring at the
same period at which it first appeared in the parent   I believe this rule
to be of the highest importance in explaining the laws of embryology  
These remarks are of course confined to the first APPEARANCE of the
peculiarity  and not to the primary cause which may have acted on the
ovules or on the male element  in nearly the same manner as the increased
length of the horns in the offspring from a short horned cow by a
long horned bull  though appearing late in life  is clearly due to the male
element 

Having alluded to the subject of reversion  I may here refer to a statement
often made by naturalists  namely  that our domestic varieties  when run
wild  gradually but invariably revert in character to their aboriginal
stocks   Hence it has been argued that no deductions can be drawn from
domestic races to species in a state of nature   I have in vain endeavoured
to discover on what decisive facts the above statement has so often and so
boldly been made   There would be great difficulty in proving its truth  
we may safely conclude that very many of the most strongly marked domestic
varieties could not possibly live in a wild state   In many cases we do not
know what the aboriginal stock was  and so could not tell whether or not
nearly perfect reversion had ensued   It would be necessary  in order to
prevent the effects of intercrossing  that only a single variety should be
turned loose in its new home   Nevertheless  as our varieties certainly do
occasionally revert in some of their characters to ancestral forms  it
seems to me not improbable that if we could succeed in naturalising  or
were to cultivate  during many generations  the several races  for
instance  of the cabbage  in very poor soil  in which case  however  some
effect would have to be attributed to the DEFINITE action of the poor soil
  that they would  to a large extent  or even wholly  revert to the wild
aboriginal stock   Whether or not the experiment would succeed is not of
great importance for our line of argument  for by the experiment itself the
conditions of life are changed   If it could be shown that our domestic
varieties manifested a strong tendency to reversion  that is  to lose their
acquired characters  while kept under the same conditions and while kept in
a considerable body  so that free intercrossing might check  by blending
together  any slight deviations in their structure  in such case  I grant
that we could deduce nothing from domestic varieties in regard to species  
But there is not a shadow of evidence in favour of this view   to assert
that we could not breed our cart and race horses  long and short horned
cattle  and poultry of various breeds  and esculent vegetables  for an
unlimited number of generations  would be opposed to all experience 

CHARACTER OF DOMESTIC VARIETIES  DIFFICULTY OF DISTINGUISHING BETWEEN
VARIETIES AND SPECIES  ORIGIN OF DOMESTIC VARIETIES FROM ONE OR MORE
SPECIES 

When we look to the hereditary varieties or races of our domestic animals
and plants  and compare them with closely allied species  we generally
perceive in each domestic race  as already remarked  less uniformity of
character than in true species   Domestic races often have a somewhat
monstrous character  by which I mean  that  although differing from each
other and from other species of the same genus  in several trifling
respects  they often differ in an extreme degree in some one part  both
when compared one with another  and more especially when compared with the
species under nature to which they are nearest allied   With these
exceptions  and with that of the perfect fertility of varieties when
crossed  a subject hereafter to be discussed   domestic races of the same
species differ from each other in the same manner as do the closely allied
species of the same genus in a state of nature  but the differences in most
cases are less in degree   This must be admitted as true  for the domestic
races of many animals and plants have been ranked by some competent judges
as the descendants of aboriginally distinct species  and by other competent
judges as mere varieties   If any well marked distinction existed between a
domestic race and a species  this source of doubt would not so perpetually
recur   It has often been stated that domestic races do not differ from
each other in characters of generic value   It can be shown that this
statement is not correct  but naturalists differ much in determining what
characters are of generic value  all such valuations being at present
empirical   When it is explained how genera originate under nature  it will
be seen that we have no right to expect often to find a generic amount of
difference in our domesticated races 

In attempting to estimate the amount of structural difference between
allied domestic races  we are soon involved in doubt  from not knowing
whether they are descended from one or several parent species   This point 
if it could be cleared up  would be interesting  if  for instance  it could
be shown that the greyhound  bloodhound  terrier  spaniel and bull dog 
which we all know propagate their kind truly  were the offspring of any
single species  then such facts would have great weight in making us doubt
about the immutability of the many closely allied natural species  for
instance  of the many foxes  inhabiting the different quarters of the
world   I do not believe  as we shall presently see  that the whole amount
of difference between the several breeds of the dog has been produced under
domestication  I believe that a small part of the difference is due to
their being descended from distinct species   In the case of strongly
marked races of some other domesticated species  there is presumptive or
even strong evidence that all are descended from a single wild stock 

It has often been assumed that man has chosen for domestication animals and
plants having an extraordinary inherent tendency to vary  and likewise to
withstand diverse climates   I do not dispute that these capacities have
added largely to the value of most of our domesticated productions  but how
could a savage possibly know  when he first tamed an animal  whether it
would vary in succeeding generations  and whether it would endure other
climates   Has the little variability of the ass and goose  or the small
power of endurance of warmth by the reindeer  or of cold by the common
camel  prevented their domestication   I cannot doubt that if other animals
and plants  equal in number to our domesticated productions  and belonging
to equally diverse classes and countries  were taken from a state of
nature  and could be made to breed for an equal number of generations under
domestication  they would on an average vary as largely as the parent
species of our existing domesticated productions have varied 

In the case of most of our anciently domesticated animals and plants  it is
not possible to come to any definite conclusion  whether they are descended
from one or several wild species   The argument mainly relied on by those
who believe in the multiple origin of our domestic animals is  that we find
in the most ancient times  on the monuments of Egypt  and in the lake 
habitations of Switzerland  much diversity in the breeds  and that some of
these ancient breeds closely resemble  or are even identical with  those
still existing   But this only throws far backward the history of
civilisation  and shows that animals were domesticated at a much earlier
period than has hitherto been supposed   The lake inhabitants of
Switzerland cultivated several kinds of wheat and barley  the pea  the
poppy for oil and flax  and they possessed several domesticated animals  
They also carried on commerce with other nations   All this clearly shows 
as Heer has remarked  that they had at this early age progressed
considerably in civilisation  and this again implies a long continued
previous period of less advanced civilisation  during which the
domesticated animals  kept by different tribes in different districts 
might have varied and given rise to distinct races   Since the discovery of
flint tools in the superficial formations of many parts of the world  all
geologists believe that barbarian men existed at an enormously remote
period  and we know that at the present day there is hardly a tribe so
barbarous as not to have domesticated at least the dog 

The origin of most of our domestic animals will probably forever remain
vague   But I may here state that  looking to the domestic dogs of the
whole world  I have  after a laborious collection of all known facts  come
to the conclusion that several wild species of Canidae have been tamed  and
that their blood  in some cases mingled together  flows in the veins of our
domestic breeds   In regard to sheep and goats I can form no decided
opinion   From facts communicated to me by Mr  Blyth  on the habits  voice 
constitution and structure of the humped Indian cattle  it is almost
certain that they are descended from a different aboriginal stock from our
European cattle  and some competent judges believe that these latter have
had two or three wild progenitors  whether or not these deserve to be
called species   This conclusion  as well as that of the specific
distinction between the humped and common cattle  may  indeed  be looked
upon as established by the admirable researches of Professor Rutimeyer  
With respect to horses  from reasons which I cannot here give  I am
doubtfully inclined to believe  in opposition to several authors  that all
the races belong to the same species   Having kept nearly all the English
breeds of the fowl alive  having bred and crossed them  and examined their
skeletons  it appears to me almost certain that all are the descendants of
the wild Indian fowl  Gallus bankiva  and this is the conclusion of Mr 
Blyth  and of others who have studied this bird in India   In regard to
ducks and rabbits  some breeds of which differ much from each other  the
evidence is clear that they are all descended from the common duck and wild
rabbit 

The doctrine of the origin of our several domestic races from several
aboriginal stocks  has been carried to an absurd extreme by some authors  
They believe that every race which breeds true  let the distinctive
characters be ever so slight  has had its wild prototype   At this rate
there must have existed at least a score of species of wild cattle  as many
sheep  and several goats  in Europe alone  and several even within Great
Britain   One author believes that there formerly existed eleven wild
species of sheep peculiar to Great Britain   When we bear in mind that
Britain has now not one peculiar mammal  and France but few distinct from
those of Germany  and so with Hungary  Spain  etc   but that each of these
kingdoms possesses several peculiar breeds of cattle  sheep  etc   we must
admit that many domestic breeds must have originated in Europe  for whence
otherwise could they have been derived   So it is in India   Even in the
case of the breeds of the domestic dog throughout the world  which I admit
are descended from several wild species  it cannot be doubted that there
has been an immense amount of inherited variation  for who will believe
that animals closely resembling the Italian greyhound  the bloodhound  the
bull dog  pug dog  or Blenheim spaniel  etc   so unlike all wild
Canidae  ever existed in a state of nature   It has often been loosely said
that all our races of dogs have been produced by the crossing of a few
aboriginal species  but by crossing we can only get forms in some degree
intermediate between their parents  and if we account for our several
domestic races by this process  we must admit the former existence of the
most extreme forms  as the Italian greyhound  bloodhound  bull dog  etc  
in the wild state   Moreover  the possibility of making distinct races by
crossing has been greatly exaggerated   Many cases are on record showing
that a race may be modified by occasional crosses if aided by the careful
selection of the individuals which present the desired character  but to
obtain a race intermediate between two quite distinct races would be very
difficult   Sir J  Sebright expressly experimented with this object and
failed   The offspring from the first cross between two pure breeds is
tolerably and sometimes  as I have found with pigeons  quite uniform in
character  and every thing seems simple enough  but when these mongrels are
crossed one with another for several generations  hardly two of them are
alike  and then the difficulty of the task becomes manifest 

BREEDS OF THE DOMESTIC PIGEON  THEIR DIFFERENCES AND ORIGIN 

Believing that it is always best to study some special group  I have  after
deliberation  taken up domestic pigeons   I have kept every breed which I
could purchase or obtain  and have been most kindly favoured with skins
from several quarters of the world  more especially by the Hon  W  Elliot
from India  and by the Hon  C  Murray from Persia   Many treatises in
different languages have been published on pigeons  and some of them are
very important  as being of considerable antiquity   I have associated with
several eminent fanciers  and have been permitted to join two of the London
Pigeon Clubs   The diversity of the breeds is something astonishing  
Compare the English carrier and the short faced tumbler  and see the
wonderful difference in their beaks  entailing corresponding differences in
their skulls   The carrier  more especially the male bird  is also
remarkable from the wonderful development of the carunculated skin about
the head  and this is accompanied by greatly elongated eyelids  very large
external orifices to the nostrils  and a wide gape of mouth   The
short faced tumbler has a beak in outline almost like that of a finch  and
the common tumbler has the singular inherited habit of flying at a great
height in a compact flock  and tumbling in the air head over heels   The
runt is a bird of great size  with long  massive beak and large feet  some
of the sub breeds of runts have very long necks  others very long wings and
tails  others singularly short tails   The barb is allied to the carrier 
but  instead of a long beak  has a very short and broad one   The pouter
has a much elongated body  wings  and legs  and its enormously developed
crop  which it glories in inflating  may well excite astonishment and even
laughter   The turbit has a short and conical beak  with a line of reversed
feathers down the breast  and it has the habit of continually expanding 
slightly  the upper part of the oesophagus   The Jacobin has the feathers
so much reversed along the back of the neck that they form a hood  and it
has  proportionally to its size  elongated wing and tail feathers   The
trumpeter and laugher  as their names express  utter a very different coo
from the other breeds   The fantail has thirty or even forty tail feathers 
instead of twelve or fourteen  the normal number in all the members of the
great pigeon family   these feathers are kept expanded and are carried so
erect that in good birds the head and tail touch   the oil gland is quite
aborted   Several other less distinct breeds might be specified 

In the skeletons of the several breeds  the development of the bones of the
face  in length and breadth and curvature  differs enormously   The shape 
as well as the breadth and length of the ramus of the lower jaw  varies in
a highly remarkable manner   The caudal and sacral vertebrae vary in
number  as does the number of the ribs  together with their relative
breadth and the presence of processes   The size and shape of the apertures
in the sternum are highly variable  so is the degree of divergence and
relative size of the two arms of the furcula   The proportional width of
the gape of mouth  the proportional length of the eyelids  of the orifice
of the nostrils  of the tongue  not always in strict correlation with the
length of beak   the size of the crop and of the upper part of the
oesophagus  the development and abortion of the oil gland  the number of
the primary wing and caudal feathers  the relative length of the wing and
tail to each other and to the body  the relative length of the leg and
foot  the number of scutellae on the toes  the development of skin between
the toes  are all points of structure which are variable   The period at
which the perfect plumage is acquired varies  as does the state of the down
with which the nestling birds are clothed when hatched   The shape and size
of the eggs vary   The manner of flight  and in some breeds the voice and
disposition  differ remarkably   Lastly  in certain breeds  the males and
females have come to differ in a slight degree from each other 

Altogether at least a score of pigeons might be chosen  which  if shown to
an ornithologist  and he were told that they were wild birds  would
certainly be ranked by him as well defined species   Moreover  I do not
believe that any ornithologist would in this case place the English
carrier  the short faced tumbler  the runt  the barb  pouter  and fantail
in the same genus  more especially as in each of these breeds several
truly inherited sub breeds  or species  as he would call them  could be
shown him 

Great as are the differences between the breeds of the pigeon  I am fully
convinced that the common opinion of naturalists is correct  namely  that
all are descended from the rock pigeon  Columba livia   including under
this term several geographical races or sub species  which differ from each
other in the most trifling respects   As several of the reasons which have
led me to this belief are in some degree applicable in other cases  I will
here briefly give them   If the several breeds are not varieties  and have
not proceeded from the rock pigeon  they must have descended from at least
seven or eight aboriginal stocks  for it is impossible to make the present
domestic breeds by the crossing of any lesser number   how  for instance 
could a pouter be produced by crossing two breeds unless one of the
parent stocks possessed the characteristic enormous crop   The supposed
aboriginal stocks must all have been rock pigeons  that is  they did not
breed or willingly perch on trees   But besides C  livia  with its
geographical sub species  only two or three other species of rock pigeons
are known  and these have not any of the characters of the domestic breeds  
Hence the supposed aboriginal stocks must either still exist in the
countries where they were originally domesticated  and yet be unknown to
ornithologists  and this  considering their size  habits and remarkable
characters  seems improbable  or they must have become extinct in the wild
state   But birds breeding on precipices  and good flyers  are unlikely to
be exterminated  and the common rock pigeon  which has the same habits with
the domestic breeds  has not been exterminated even on several of the
smaller British islets  or on the shores of the Mediterranean   Hence the
supposed extermination of so many species having similar habits with the
rock pigeon seems a very rash assumption   Moreover  the several
above named domesticated breeds have been transported to all parts of the
world  and  therefore  some of them must have been carried back again into
their native country  but not one has become wild or feral  though the
dovecot pigeon  which is the rock pigeon in a very slightly altered state 
has become feral in several places   Again  all recent experience shows
that it is difficult to get wild animals to breed freely under
domestication  yet on the hypothesis of the multiple origin of our pigeons 
it must be assumed that at least seven or eight species were so thoroughly
domesticated in ancient times by half civilized man  as to be quite
prolific under confinement 

An argument of great weight  and applicable in several other cases  is 
that the above specified breeds  though agreeing generally with the wild
rock pigeon in constitution  habits  voice  colouring  and in most parts of
their structure  yet are certainly highly abnormal in other parts  we may
look in vain through the whole great family of Columbidae for a beak like
that of the English carrier  or that of the short faced tumbler  or barb 
for reversed feathers like those of the Jacobin  for a crop like that of
the pouter  for tail feathers like those of the fantail   Hence it must be
assumed  not only that half civilized man succeeded in thoroughly
domesticating several species  but that he intentionally or by chance
picked out extraordinarily abnormal species  and further  that these very
species have since all become extinct or unknown   So many strange
contingencies are improbable in the highest degree 

Some facts in regard to the colouring of pigeons well deserve
consideration   The rock pigeon is of a slaty blue  with white loins  but
the Indian sub species  C  intermedia of Strickland  has this part bluish   
The tail has a terminal dark bar  with the outer feathers externally edged
at the base with white   The wings have two black bars   Some semi domestic
breeds  and some truly wild breeds  have  besides the two black bars  the
wings chequered with black   These several marks do not occur together in
any other species of the whole family   Now  in every one of the domestic
breeds  taking thoroughly well bred birds  all the above marks  even to the
white edging of the outer tail feathers  sometimes concur perfectly
developed   Moreover  when birds belonging to two or more distinct breeds
are crossed  none of which are blue or have any of the above specified
marks  the mongrel offspring are very apt suddenly to acquire these
characters   To give one instance out of several which I have observed   I
crossed some white fantails  which breed very true  with some black barbs  
and it so happens that blue varieties of barbs are so rare that I never
heard of an instance in England  and the mongrels were black  brown and
mottled   I also crossed a barb with a spot  which is a white bird with a
red tail and red spot on the forehead  and which notoriously breeds very
true  the mongrels were dusky and mottled   I then crossed one of the
mongrel barb fantails with a mongrel barb spot  and they produced a bird of
as beautiful a blue colour  with the white loins  double black wing bar 
and barred and white edged tail feathers  as any wild rock pigeon   We can
understand these facts  on the well known principle of reversion to
ancestral characters  if all the domestic breeds are descended from the
rock pigeon   But if we deny this  we must make one of the two following
highly improbable suppositions   Either  first  that all the several
imagined aboriginal stocks were coloured and marked like the rock pigeon 
although no other existing species is thus coloured and marked  so that in
each separate breed there might be a tendency to revert to the very same
colours and markings   Or  secondly  that each breed  even the purest  has
within a dozen  or at most within a score  of generations  been crossed by
the rock pigeon   I say within a dozen or twenty generations  for no
instance is known of crossed descendants reverting to an ancestor of
foreign blood  removed by a greater number of generations   In a breed
which has been crossed only once the tendency to revert to any character
derived from such a cross will naturally become less and less  as in each
succeeding generation there will be less of the foreign blood  but when
there has been no cross  and there is a tendency in the breed to revert to
a character which was lost during some former generation  this tendency 
for all that we can see to the contrary  may be transmitted undiminished
for an indefinite number of generations   These two distinct cases of
reversion are often confounded together by those who have written on
inheritance 

Lastly  the hybrids or mongrels from between all the breeds of the pigeon
are perfectly fertile  as I can state from my own observations  purposely
made  on the most distinct breeds   Now  hardly any cases have been
ascertained with certainty of hybrids from two quite distinct species of
animals being perfectly fertile   Some authors believe that long continued
domestication eliminates this strong tendency to sterility in species  
 From the history of the dog  and of some other domestic animals  this
conclusion is probably quite correct  if applied to species closely related
to each other   But to extend it so far as to suppose that species 
aboriginally as distinct as carriers  tumblers  pouters  and fantails now
are  should yield offspring perfectly fertile  inter se  seems to me rash
in the extreme 

 From these several reasons  namely  the improbability of man having
formerly made seven or eight supposed species of pigeons to breed freely
under domestication  these supposed species being quite unknown in a wild
state  and their not having become anywhere feral  these species presenting
certain very abnormal characters  as compared with all other Columbidae 
though so like the rock pigeon in most other respects  the occasional
reappearance of the blue colour and various black marks in all the breeds 
both when kept pure and when crossed  and lastly  the mongrel offspring
being perfectly fertile  from these several reasons  taken together  we may
safely conclude that all our domestic breeds are descended from the rock 
pigeon or Columba livia with its geographical sub species 

In favour of this view  I may add  firstly  that the wild C  livia has been
found capable of domestication in Europe and in India  and that it agrees
in habits and in a great number of points of structure with all the
domestic breeds   Secondly  that although an English carrier or a
short faced tumbler differs immensely in certain characters from the
rock pigeon  yet that by comparing the several sub breeds of these two
races  more especially those brought from distant countries  we can make 
between them and the rock pigeon  an almost perfect series  so we can in
some other cases  but not with all the breeds   Thirdly  those characters
which are mainly distinctive of each breed are in each eminently variable  
for instance  the wattle and length of beak of the carrier  the shortness
of that of the tumbler  and the number of tail feathers in the fantail  and
the explanation of this fact will be obvious when we treat of selection  
Fourthly  pigeons have been watched and tended with the utmost care  and
loved by many people   They have been domesticated for thousands of years
in several quarters of the world  the earliest known record of pigeons is
in the fifth Aegyptian dynasty  about 3000 B C   as was pointed out to me
by Professor Lepsius  but Mr  Birch informs me that pigeons are given in a
bill of fare in the previous dynasty   In the time of the Romans  as we
hear from Pliny  immense prices were given for pigeons   nay  they are come
to this pass  that they can reckon up their pedigree and race    Pigeons
were much valued by Akber Khan in India  about the year 1600  never less
than 20 000 pigeons were taken with the court    The monarchs of Iran and
Turan sent him some very rare birds   and  continues the courtly historian 
 His Majesty  by crossing the breeds  which method was never practised
before  has improved them astonishingly    About this same period the Dutch
were as eager about pigeons as were the old Romans   The paramount
importance of these considerations in explaining the immense amount of
variation which pigeons have undergone  will likewise be obvious when we
treat of selection   We shall then  also  see how it is that the several
breeds so often have a somewhat monstrous character   It is also a most
favourable circumstance for the production of distinct breeds  that male
and female pigeons can be easily mated for life  and thus different breeds
can be kept together in the same aviary 

I have discussed the probable origin of domestic pigeons at some  yet quite
insufficient  length  because when I first kept pigeons and watched the
several kinds  well knowing how truly they breed  I felt fully as much
difficulty in believing that since they had been domesticated they had all
proceeded from a common parent  as any naturalist could in coming to a
similar conclusion in regard to the many species of finches  or other
groups of birds  in nature   One circumstance has struck me much  namely 
that nearly all the breeders of the various domestic animals and the
cultivators of plants  with whom I have conversed  or whose treatises I
have read  are firmly convinced that the several breeds to which each has
attended  are descended from so many aboriginally distinct species   Ask 
as I have asked  a celebrated raiser of Hereford cattle  whether his cattle
might not have descended from Long horns  or both from a common parent 
stock  and he will laugh you to scorn   I have never met a pigeon  or
poultry  or duck  or rabbit fancier  who was not fully convinced that each
main breed was descended from a distinct species   Van Mons  in his
treatise on pears and apples  shows how utterly he disbelieves that the
several sorts  for instance a Ribston pippin or Codlin apple  could ever
have proceeded from the seeds of the same tree   Innumerable other examples
could be given   The explanation  I think  is simple   from long continued
study they are strongly impressed with the differences between the several
races  and though they well know that each race varies slightly  for they
win their prizes by selecting such slight differences  yet they ignore all
general arguments  and refuse to sum up in their minds slight differences
accumulated during many successive generations   May not those naturalists
who  knowing far less of the laws of inheritance than does the breeder  and
knowing no more than he does of the intermediate links in the long lines of
descent  yet admit that many of our domestic races are descended from the
same parents  may they not learn a lesson of caution  when they deride the
idea of species in a state of nature being lineal descendants of other
species 

PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED  AND THEIR EFFECTS 

Let us now briefly consider the steps by which domestic races have been
produced  either from one or from several allied species   Some effect may
be attributed to the direct and definite action of the external conditions
of life  and some to habit  but he would be a bold man who would account by
such agencies for the differences between a dray and race horse  a
greyhound and bloodhound  a carrier and tumbler pigeon   One of the most
remarkable features in our domesticated races is that we see in them
adaptation  not indeed to the animal s or plant s own good  but to man s
use or fancy   Some variations useful to him have probably arisen suddenly 
or by one step  many botanists  for instance  believe that the fuller s
teasel  with its hooks  which can not be rivalled by any mechanical
contrivance  is only a variety of the wild Dipsacus  and this amount of
change may have suddenly arisen in a seedling   So it has probably been
with the turnspit dog  and this is known to have been the case with the
ancon sheep   But when we compare the dray horse and race horse  the
dromedary and camel  the various breeds of sheep fitted either for
cultivated land or mountain pasture  with the wool of one breed good for
one purpose  and that of another breed for another purpose  when we compare
the many breeds of dogs  each good for man in different ways  when we
compare the game cock  so pertinacious in battle  with other breeds so
little quarrelsome  with  everlasting layers  which never desire to sit 
and with the bantam so small and elegant  when we compare the host of
agricultural  culinary  orchard  and flower garden races of plants  most
useful to man at different seasons and for different purposes  or so
beautiful in his eyes  we must  I think  look further than to mere
variability   We can not suppose that all the breeds were suddenly produced
as perfect and as useful as we now see them  indeed  in many cases  we know
that this has not been their history   The key is man s power of
accumulative selection   nature gives successive variations  man adds them
up in certain directions useful to him   In this sense he may be said to
have made for himself useful breeds 

The great power of this principle of selection is not hypothetical   It is
certain that several of our eminent breeders have  even within a single
lifetime  modified to a large extent their breeds of cattle and sheep   In
order fully to realise what they have done it is almost necessary to read
several of the many treatises devoted to this subject  and to inspect the
animals   Breeders habitually speak of an animal s organisation as
something plastic  which they can model almost as they please   If I had
space I could quote numerous passages to this effect from highly competent
authorities   Youatt  who was probably better acquainted with the works of
agriculturalists than almost any other individual  and who was himself a
very good judge of animals  speaks of the principle of selection as  that
which enables the agriculturist  not only to modify the character of his
flock  but to change it altogether   It is the magician s wand  by means of
which he may summon into life whatever form and mould he pleases    Lord
Somerville  speaking of what breeders have done for sheep  says    It would
seem as if they had chalked out upon a wall a form perfect in itself  and
then had given it existence    In Saxony the importance of the principle of
selection in regard to merino sheep is so fully recognised  that men follow
it as a trade   the sheep are placed on a table and are studied  like a
picture by a connoisseur  this is done three times at intervals of months 
and the sheep are each time marked and classed  so that the very best may
ultimately be selected for breeding 

What English breeders have actually effected is proved by the enormous
prices given for animals with a good pedigree  and these have been exported
to almost every quarter of the world   The improvement is by no means
generally due to crossing different breeds  all the best breeders are
strongly opposed to this practice  except sometimes among closely allied
sub breeds   And when a cross has been made  the closest selection is far
more indispensable even than in ordinary cases   If selection consisted
merely in separating some very distinct variety and breeding from it  the
principle would be so obvious as hardly to be worth notice  but its
importance consists in the great effect produced by the accumulation in one
direction  during successive generations  of differences absolutely
inappreciable by an uneducated eye  differences which I for one have vainly
attempted to appreciate   Not one man in a thousand has accuracy of eye and
judgment sufficient to become an eminent breeder   If gifted with these
qualities  and he studies his subject for years  and devotes his lifetime
to it with indomitable perseverance  he will succeed  and may make great
improvements  if he wants any of these qualities  he will assuredly fail  
Few would readily believe in the natural capacity and years of practice
requisite to become even a skilful pigeon fancier 

The same principles are followed by horticulturists  but the variations are
here often more abrupt   No one supposes that our choicest productions have
been produced by a single variation from the aboriginal stock   We have
proofs that this is not so in several cases in which exact records have
been kept  thus  to give a very trifling instance  the steadily increasing
size of the common gooseberry may be quoted   We see an astonishing
improvement in many florists  flowers  when the flowers of the present day
are compared with drawings made only twenty or thirty years ago   When a
race of plants is once pretty well established  the seed raisers do not
pick out the best plants  but merely go over their seed beds  and pull up
the  rogues   as they call the plants that deviate from the proper
standard   With animals this kind of selection is  in fact  likewise
followed  for hardly any one is so careless as to breed from his worst
animals 

In regard to plants  there is another means of observing the accumulated
effects of selection  namely  by comparing the diversity of flowers in the
different varieties of the same species in the flower garden  the diversity
of leaves  pods  or tubers  or whatever part is valued  in the
kitchen garden  in comparison with the flowers of the same varieties  and
the diversity of fruit of the same species in the orchard  in comparison
with the leaves and flowers of the same set of varieties   See how
different the leaves of the cabbage are  and how extremely alike the
flowers  how unlike the flowers of the heartsease are  and how alike the
leaves  how much the fruit of the different kinds of gooseberries differ in
size  colour  shape  and hairiness  and yet the flowers present very slight
differences   It is not that the varieties which differ largely in some one
point do not differ at all in other points  this is hardly ever  I speak
after careful observation  perhaps never  the case   The law of correlated
variation  the importance of which should never be overlooked  will ensure
some differences  but  as a general rule  it cannot be doubted that the
continued selection of slight variations  either in the leaves  the
flowers  or the fruit  will produce races differing from each other chiefly
in these characters 

It may be objected that the principle of selection has been reduced to
methodical practice for scarcely more than three quarters of a century  it
has certainly been more attended to of late years  and many treatises have
been published on the subject  and the result has been  in a corresponding
degree  rapid and important   But it is very far from true that the
principle is a modern discovery   I could give several references to works
of high antiquity  in which the full importance of the principle is
acknowledged   In rude and barbarous periods of English history choice
animals were often imported  and laws were passed to prevent their
exportation   the destruction of horses under a certain size was ordered 
and this may be compared to the  roguing  of plants by nurserymen   The
principle of selection I find distinctly given in an ancient Chinese
encyclopaedia   Explicit rules are laid down by some of the Roman classical
writers   From passages in Genesis  it is clear that the colour of domestic
animals was at that early period attended to   Savages now sometimes cross
their dogs with wild canine animals  to improve the breed  and they
formerly did so  as is attested by passages in Pliny   The savages in South
Africa match their draught cattle by colour  as do some of the Esquimaux
their teams of dogs   Livingstone states that good domestic breeds are
highly valued by the negroes in the interior of Africa who have not
associated with Europeans   Some of these facts do not show actual
selection  but they show that the breeding of domestic animals was
carefully attended to in ancient times  and is now attended to by the
lowest savages   It would  indeed  have been a strange fact  had attention
not been paid to breeding  for the inheritance of good and bad qualities is
so obvious 

UNCONSCIOUS SELECTION 

At the present time  eminent breeders try by methodical selection  with a
distinct object in view  to make a new strain or sub breed  superior to
anything of the kind in the country   But  for our purpose  a form of
selection  which may be called unconscious  and which results from every
one trying to possess and breed from the best individual animals  is more
important   Thus  a man who intends keeping pointers naturally tries to get
as good dogs as he can  and afterwards breeds from his own best dogs  but
he has no wish or expectation of permanently altering the breed  
Nevertheless we may infer that this process  continued during centuries 
would improve and modify any breed  in the same way as Bakewell  Collins 
etc   by this very same process  only carried on more methodically  did
greatly modify  even during their lifetimes  the forms and qualities of
their cattle   Slow and insensible changes of this kind could never be
recognised unless actual measurements or careful drawings of the breeds in
question have been made long ago  which may serve for comparison   In some
cases  however  unchanged  or but little changed  individuals of the same
breed exist in less civilised districts  where the breed has been less
improved   There is reason to believe that King Charles  spaniel has been
unconsciously modified to a large extent since the time of that monarch  
Some highly competent authorities are convinced that the setter is directly
derived from the spaniel  and has probably been slowly altered from it   It
is known that the English pointer has been greatly changed within the last
century  and in this case the change has  it is believed  been chiefly
effected by crosses with the foxhound  but what concerns us is  that the
change has been effected unconsciously and gradually  and yet so
effectually that  though the old Spanish pointer certainly came from Spain 
Mr  Borrow has not seen  as I am informed by him  any native dog in Spain
like our pointer 

By a similar process of selection  and by careful training  English race 
horses have come to surpass in fleetness and size the parent Arabs  so that
the latter  by the regulations for the Goodwood Races  are favoured in the
weights which they carry   Lord Spencer and others have shown how the
cattle of England have increased in weight and in early maturity  compared
with the stock formerly kept in this country   By comparing the accounts
given in various old treatises of the former and present state of carrier
and tumbler pigeons in Britain  India  and Persia  we can trace the stages
through which they have insensibly passed  and come to differ so greatly
from the rock pigeon 

Youatt gives an excellent illustration of the effects of a course of
selection which may be considered as unconscious  in so far that the
breeders could never have expected  or even wished  to produce the result
which ensued  namely  the production of the distinct strains   The two
flocks of Leicester sheep kept by Mr  Buckley and Mr  Burgess  as Mr 
Youatt remarks   Have been purely bred from the original stock of Mr 
Bakewell for upwards of fifty years   There is not a suspicion existing in
the mind of any one at all acquainted with the subject that the owner of
either of them has deviated in any one instance from the pure blood of Mr 
Bakewell s flock  and yet the difference between the sheep possessed by
these two gentlemen is so great that they have the appearance of being
quite different varieties  

If there exist savages so barbarous as never to think of the inherited
character of the offspring of their domestic animals  yet any one animal
particularly useful to them  for any special purpose  would be carefully
preserved during famines and other accidents  to which savages are so
liable  and such choice animals would thus generally leave more offspring
than the inferior ones  so that in this case there would be a kind of
unconscious selection going on   We see the value set on animals even by
the barbarians of Tierra del Fuego  by their killing and devouring their
old women  in times of dearth  as of less value than their dogs 

In plants the same gradual process of improvement through the occasional
preservation of the best individuals  whether or not sufficiently distinct
to be ranked at their first appearance as distinct varieties  and whether
or not two or more species or races have become blended together by
crossing  may plainly be recognised in the increased size and beauty which
we now see in the varieties of the heartsease  rose  pelargonium  dahlia 
and other plants  when compared with the older varieties or with their
parent stocks   No one would ever expect to get a first rate heartsease or
dahlia from the seed of a wild plant   No one would expect to raise a
first rate melting pear from the seed of a wild pear  though he might
succeed from a poor seedling growing wild  if it had come from a
garden stock   The pear  though cultivated in classical times  appears 
from Pliny s description  to have been a fruit of very inferior quality   I
have seen great surprise expressed in horticultural works at the wonderful
skill of gardeners in having produced such splendid results from such poor
materials  but the art has been simple  and  as far as the final result is
concerned  has been followed almost unconsciously   It has consisted in
always cultivating the best known variety  sowing its seeds  and  when a
slightly better variety chanced to appear  selecting it  and so onwards  
But the gardeners of the classical period  who cultivated the best pears
which they could procure  never thought what splendid fruit we should eat 
though we owe our excellent fruit in some small degree to their having
naturally chosen and preserved the best varieties they could anywhere find 

A large amount of change  thus slowly and unconsciously accumulated 
explains  as I believe  the well known fact  that in a number of cases we
cannot recognise  and therefore do not know  the wild parent stocks of the
plants which have been longest cultivated in our flower and kitchen
gardens   If it has taken centuries or thousands of years to improve or
modify most of our plants up to their present standard of usefulness to
man  we can understand how it is that neither Australia  the Cape of Good
Hope  nor any other region inhabited by quite uncivilised man  has afforded
us a single plant worth culture   It is not that these countries  so rich
in species  do not by a strange chance possess the aboriginal stocks of any
useful plants  but that the native plants have not been improved by
continued selection up to a standard of perfection comparable with that
acquired by the plants in countries anciently civilised 

In regard to the domestic animals kept by uncivilised man  it should not be
overlooked that they almost always have to struggle for their own food  at
least during certain seasons   And in two countries very differently
circumstanced  individuals of the same species  having slightly different
constitutions or structure  would often succeed better in the one country
than in the other  and thus by a process of  natural selection   as will
hereafter be more fully explained  two sub breeds might be formed   This 
perhaps  partly explains why the varieties kept by savages  as has been
remarked by some authors  have more of the character of true species than
the varieties kept in civilised countries 

On the view here given of the important part which selection by man has
played  it becomes at once obvious  how it is that our domestic races show
adaptation in their structure or in their habits to man s wants or fancies  
We can  I think  further understand the frequently abnormal character of
our domestic races  and likewise their differences being so great in
external characters  and relatively so slight in internal parts or organs  
Man can hardly select  or only with much difficulty  any deviation of
structure excepting such as is externally visible  and indeed he rarely
cares for what is internal   He can never act by selection  excepting on
variations which are first given to him in some slight degree by nature  
No man would ever try to make a fantail till he saw a pigeon with a tail
developed in some slight degree in an unusual manner  or a pouter till he
saw a pigeon with a crop of somewhat unusual size  and the more abnormal or
unusual any character was when it first appeared  the more likely it would
be to catch his attention   But to use such an expression as trying to make
a fantail is  I have no doubt  in most cases  utterly incorrect   The man
who first selected a pigeon with a slightly larger tail  never dreamed what
the descendants of that pigeon would become through long continued  partly
unconscious and partly methodical  selection   Perhaps the parent bird of
all fantails had only fourteen tail feathers somewhat expanded  like the
present Java fantail  or like individuals of other and distinct breeds  in
which as many as seventeen tail feathers have been counted   Perhaps the
first pouter pigeon did not inflate its crop much more than the turbit now
does the upper part of its oesophagus  a habit which is disregarded by all
fanciers  as it is not one of the points of the breed 

Nor let it be thought that some great deviation of structure would be
necessary to catch the fancier s eye   he perceives extremely small
differences  and it is in human nature to value any novelty  however
slight  in one s own possession   Nor must the value which would formerly
have been set on any slight differences in the individuals of the same
species  be judged of by the value which is now set on them  after several
breeds have fairly been established   It is known that with pigeons many
slight variations now occasionally appear  but these are rejected as faults
or deviations from the standard of perfection in each breed   The common
goose has not given rise to any marked varieties  hence the Toulouse and
the common breed  which differ only in colour  that most fleeting of
characters  have lately been exhibited as distinct at our poultry shows 

These views appear to explain what has sometimes been noticed  namely  that
we know hardly anything about the origin or history of any of our domestic
breeds   But  in fact  a breed  like a dialect of a language  can hardly be
said to have a distinct origin   A man preserves and breeds from an
individual with some slight deviation of structure  or takes more care than
usual in matching his best animals  and thus improves them  and the
improved animals slowly spread in the immediate neighbourhood   But they
will as yet hardly have a distinct name  and from being only slightly
valued  their history will have been disregarded   When further improved by
the same slow and gradual process  they will spread more widely  and will
be recognised as something distinct and valuable  and will then probably
first receive a provincial name   In semi civilised countries  with little
free communication  the spreading of a new sub breed will be a slow
process   As soon as the points of value are once acknowledged  the
principle  as I have called it  of unconscious selection will always
tend  perhaps more at one period than at another  as the breed rises or
falls in fashion  perhaps more in one district than in another  according
to the state of civilisation of the inhabitants  slowly to add to the
characteristic features of the breed  whatever they may be   But the chance
will be infinitely small of any record having been preserved of such slow 
varying  and insensible changes 

CIRCUMSTANCES FAVOURABLE TO MAN S POWER OF SELECTION 

I will now say a few words on the circumstances  favourable or the reverse 
to man s power of selection   A high degree of variability is obviously
favourable  as freely giving the materials for selection to work on  not
that mere individual differences are not amply sufficient  with extreme
care  to allow of the accumulation of a large amount of modification in
almost any desired direction   But as variations manifestly useful or
pleasing to man appear only occasionally  the chance of their appearance
will be much increased by a large number of individuals being kept   Hence
number is of the highest importance for success   On this principle
Marshall formerly remarked  with respect to the sheep of part of Yorkshire 
 As they generally belong to poor people  and are mostly IN SMALL LOTS 
they never can be improved    On the other hand  nurserymen  from keeping
large stocks of the same plant  are generally far more successful than
amateurs in raising new and valuable varieties   A large number of
individuals of an animal or plant can be reared only where the conditions
for its propagation are favourable   When the individuals are scanty all
will be allowed to breed  whatever their quality may be  and this will
effectually prevent selection   But probably the most important element is
that the animal or plant should be so highly valued by man  that the
closest attention is paid to even the slightest deviations in its qualities
or structure   Unless such attention be paid nothing can be effected   I
have seen it gravely remarked  that it was most fortunate that the
strawberry began to vary just when gardeners began to attend to this plant  
No doubt the strawberry had always varied since it was cultivated  but the
slight varieties had been neglected   As soon  however  as gardeners picked
out individual plants with slightly larger  earlier  or better fruit  and
raised seedlings from them  and again picked out the best seedlings and
bred from them  then  with some aid by crossing distinct species  those
many admirable varieties of the strawberry were raised which have appeared
during the last half century 

With animals  facility in preventing crosses is an important element in the
formation of new races  at least  in a country which is already stocked
with other races   In this respect enclosure of the land plays a part  
Wandering savages or the inhabitants of open plains rarely possess more
than one breed of the same species   Pigeons can be mated for life  and
this is a great convenience to the fancier  for thus many races may be
improved and kept true  though mingled in the same aviary  and this
circumstance must have largely favoured the formation of new breeds  
Pigeons  I may add  can be propagated in great numbers and at a very quick
rate  and inferior birds may be freely rejected  as when killed they serve
for food   On the other hand  cats  from their nocturnal rambling habits 
can not be easily matched  and  although so much valued by women and
children  we rarely see a distinct breed long kept up  such breeds as we do
sometimes see are almost always imported from some other country   Although
I do not doubt that some domestic animals vary less than others  yet the
rarity or absence of distinct breeds of the cat  the donkey  peacock 
goose  etc   may be attributed in main part to selection not having been
brought into play   in cats  from the difficulty in pairing them  in
donkeys  from only a few being kept by poor people  and little attention
paid to their breeding  for recently in certain parts of Spain and of the
United States this animal has been surprisingly modified and improved by
careful selection  in peacocks  from not being very easily reared and a
large stock not kept  in geese  from being valuable only for two purposes 
food and feathers  and more especially from no pleasure having been felt in
the display of distinct breeds  but the goose  under the conditions to
which it is exposed when domesticated  seems to have a singularly
inflexible organisation  though it has varied to a slight extent  as I have
elsewhere described 

Some authors have maintained that the amount of variation in our domestic
productions is soon reached  and can never afterward be exceeded   It would
be somewhat rash to assert that the limit has been attained in any one
case  for almost all our animals and plants have been greatly improved in
many ways within a recent period  and this implies variation   It would be
equally rash to assert that characters now increased to their utmost limit 
could not  after remaining fixed for many centuries  again vary under new
conditions of life   No doubt  as Mr  Wallace has remarked with much truth 
a limit will be at last reached   For instance  there must be a limit to
the fleetness of any terrestrial animal  as this will be determined by the
friction to be overcome  the weight of the body to be carried  and the
power of contraction in the muscular fibres   But what concerns us is that
the domestic varieties of the same species differ from each other in almost
every character  which man has attended to and selected  more than do the
distinct species of the same genera   Isidore Geoffroy St  Hilaire has
proved this in regard to size  and so it is with colour  and probably with
the length of hair   With respect to fleetness  which depends on many
bodily characters  Eclipse was far fleeter  and a dray horse is comparably
stronger  than any two natural species belonging to the same genus   So
with plants  the seeds of the different varieties of the bean or maize
probably differ more in size than do the seeds of the distinct species in
any one genus in the same two families   The same remark holds good in
regard to the fruit of the several varieties of the plum  and still more
strongly with the melon  as well as in many other analogous cases 

To sum up on the origin of our domestic races of animals and plants  
Changed conditions of life are of the highest importance in causing
variability  both by acting directly on the organisation  and indirectly by
affecting the reproductive system   It is not probable that variability is
an inherent and necessary contingent  under all circumstances   The greater
or less force of inheritance and reversion determine whether variations
shall endure   Variability is governed by many unknown laws  of which
correlated growth is probably the most important   Something  but how much
we do not know  may be attributed to the definite action of the conditions
of life   Some  perhaps a great  effect may be attributed to the increased
use or disuse of parts   The final result is thus rendered infinitely
complex   In some cases the intercrossing of aboriginally distinct species
appears to have played an important part in the origin of our breeds   When
several breeds have once been formed in any country  their occasional
intercrossing  with the aid of selection  has  no doubt  largely aided in
the formation of new sub breeds  but the importance of crossing has been
much exaggerated  both in regard to animals and to those plants which are
propagated by seed   With plants which are temporarily propagated by
cuttings  buds  etc   the importance of crossing is immense  for the
cultivator may here disregard the extreme variability both of hybrids and
of mongrels  and the sterility of hybrids  but plants not propagated by
seed are of little importance to us  for their endurance is only temporary  
Over all these causes of change  the accumulative action of selection 
whether applied methodically and quickly  or unconsciously and slowly  but
more efficiently  seems to have been the predominant power 


CHAPTER II 

VARIATION UNDER NATURE 

Variability    Individual differences    Doubtful species    Wide ranging 
much diffused  and common species  vary most    Species of the larger
genera in each country vary more frequently than the species of the smaller
genera    Many of the species of the larger genera resemble varieties in
being very closely  but unequally  related to each other  and in having
restricted ranges 

Before applying the principles arrived at in the last chapter to organic
beings in a state of nature  we must briefly discuss whether these latter
are subject to any variation   To treat this subject properly  a long
catalogue of dry facts ought to be given  but these I shall reserve for a
future work   Nor shall I here discuss the various definitions which have
been given of the term species   No one definition has satisfied all
naturalists  yet every naturalist knows vaguely what he means when he
speaks of a species   Generally the term includes the unknown element of a
distinct act of creation   The term  variety  is almost equally difficult
to define  but here community of descent is almost universally implied 
though it can rarely be proved   We have also what are called
monstrosities  but they graduate into varieties   By a monstrosity I
presume is meant some considerable deviation of structure  generally
injurious  or not useful to the species   Some authors use the term
 variation  in a technical sense  as implying a modification directly due
to the physical conditions of life  and  variations  in this sense are
supposed not to be inherited  but who can say that the dwarfed condition of
shells in the brackish waters of the Baltic  or dwarfed plants on Alpine
summits  or the thicker fur of an animal from far northwards  would not in
some cases be inherited for at least a few generations   And in this case I
presume that the form would be called a variety 

It may be doubted whether sudden and considerable deviations of structure 
such as we occasionally see in our domestic productions  more especially
with plants  are ever permanently propagated in a state of nature   Almost
every part of every organic being is so beautifully related to its complex
conditions of life that it seems as improbable that any part should have
been suddenly produced perfect  as that a complex machine should have been
invented by man in a perfect state   Under domestication monstrosities
sometimes occur which resemble normal structures in widely different
animals   Thus pigs have occasionally been born with a sort of proboscis 
and if any wild species of the same genus had naturally possessed a
proboscis  it might have been argued that this had appeared as a
monstrosity  but I have as yet failed to find  after diligent search  cases
of monstrosities resembling normal structures in nearly allied forms  and
these alone bear on the question   If monstrous forms of this kind ever do
appear in a state of nature and are capable of reproduction  which is not
always the case   as they occur rarely and singly  their preservation would
depend on unusually favourable circumstances   They would  also  during the
first and succeeding generations cross with the ordinary form  and thus
their abnormal character would almost inevitably be lost   But I shall have
to return in a future chapter to the preservation and perpetuation of
single or occasional variations 

INDIVIDUAL DIFFERENCES 

The many slight differences which appear in the offspring from the same
parents  or which it may be presumed have thus arisen  from being observed
in the individuals of the same species inhabiting the same confined
locality  may be called individual differences   No one supposes that all
the individuals of the same species are cast in the same actual mould  
These individual differences are of the highest importance for us  for they
are often inherited  as must be familiar to every one  and they thus afford
materials for natural selection to act on and accumulate  in the same
manner as man accumulates in any given direction individual differences in
his domesticated productions   These individual differences generally
affect what naturalists consider unimportant parts  but I could show  by a
long catalogue of facts  that parts which must be called important  whether
viewed under a physiological or classificatory point of view  sometimes
vary in the individuals of the same species   I am convinced that the most
experienced naturalist would be surprised at the number of the cases of
variability  even in important parts of structure  which he could collect
on good authority  as I have collected  during a course of years   It
should be remembered that systematists are far from being pleased at
finding variability in important characters  and that there are not many
men who will laboriously examine internal and important organs  and compare
them in many specimens of the same species   It would never have been
expected that the branching of the main nerves close to the great central
ganglion of an insect would have been variable in the same species  it
might have been thought that changes of this nature could have been
effected only by slow degrees  yet Sir J  Lubbock has shown a degree of
variability in these main nerves in Coccus  which may almost be compared to
the irregular branching of the stem of a tree   This philosophical
naturalist  I may add  has also shown that the muscles in the larvae of
certain insects are far from uniform   Authors sometimes argue in a circle
when they state that important organs never vary  for these same authors
practically rank those parts as important  as some few naturalists have
honestly confessed  which do not vary  and  under this point of view  no
instance will ever be found of an important part varying  but under any
other point of view many instances assuredly can be given 

There is one point connected with individual differences which is extremely
perplexing   I refer to those genera which have been called  protean  or
 polymorphic   in which species present an inordinate amount of variation  
With respect to many of these forms  hardly two naturalists agree whether
to rank them as species or as varieties   We may instance Rubus  Rosa  and
Hieracium among plants  several genera of insects  and of Brachiopod
shells   In most polymorphic genera some of the species have fixed and
definite characters   Genera which are polymorphic in one country seem to
be  with a few exceptions  polymorphic in other countries  and likewise 
judging from Brachiopod shells  at former periods of time   These facts are
very perplexing  for they seem to show that this kind of variability is
independent of the conditions of life   I am inclined to suspect that we
see  at least in some of these polymorphic genera  variations which are of
no service or disservice to the species  and which consequently have not
been seized on and rendered definite by natural selection  as hereafter to
be explained 

Individuals of the same species often present  as is known to every one 
great differences of structure  independently of variation  as in the two
sexes of various animals  in the two or three castes of sterile females or
workers among insects  and in the immature and larval states of many of the
lower animals   There are  also  cases of dimorphism and trimorphism  both
with animals and plants   Thus  Mr  Wallace  who has lately called
attention to the subject  has shown that the females of certain species of
butterflies  in the Malayan Archipelago  regularly appear under two or even
three conspicuously distinct forms  not connected by intermediate
varieties   Fritz Muller has described analogous but more extraordinary
cases with the males of certain Brazilian Crustaceans   thus  the male of a
Tanais regularly occurs under two distinct forms  one of these has strong
and differently shaped pincers  and the other has antennae much more
abundantly furnished with smelling hairs   Although in most of these cases 
the two or three forms  both with animals and plants  are not now connected
by intermediate gradations  it is possible that they were once thus
connected   Mr  Wallace  for instance  describes a certain butterfly which
presents in the same island a great range of varieties connected by
intermediate links  and the extreme links of the chain closely resemble the
two forms of an allied dimorphic species inhabiting another part of the
Malay Archipelago   Thus also with ants  the several worker castes are
generally quite distinct  but in some cases  as we shall hereafter see  the
castes are connected together by finely graduated varieties   So it is  as
I have myself observed  with some dimorphic plants   It certainly at first
appears a highly remarkable fact that the same female butterfly should have
the power of producing at the same time three distinct female forms and a
male  and that an hermaphrodite plant should produce from the same seed 
capsule three distinct hermaphrodite forms  bearing three different kinds
of females and three or even six different kinds of males   Nevertheless
these cases are only exaggerations of the common fact that the female
produces offspring of two sexes which sometimes differ from each other in a
wonderful manner 

DOUBTFUL SPECIES 

The forms which possess in some considerable degree the character of
species  but which are so closely similar to other forms  or are so closely
linked to them by intermediate gradations  that naturalists do not like to
rank them as distinct species  are in several respects the most important
for us   We have every reason to believe that many of these doubtful and
closely allied forms have permanently retained their characters for a long
time  for as long  as far as we know  as have good and true species  
Practically  when a naturalist can unite by means of intermediate links any
two forms  he treats the one as a variety of the other  ranking the most
common  but sometimes the one first described as the species  and the other
as the variety   But cases of great difficulty  which I will not here
enumerate  sometimes arise in deciding whether or not to rank one form as a
variety of another  even when they are closely connected by intermediate
links  nor will the commonly assumed hybrid nature of the intermediate
forms always remove the difficulty   In very many cases  however  one form
is ranked as a variety of another  not because the intermediate links have
actually been found  but because analogy leads the observer to suppose
either that they do now somewhere exist  or may formerly have existed  and
here a wide door for the entry of doubt and conjecture is opened 

Hence  in determining whether a form should be ranked as a species or a
variety  the opinion of naturalists having sound judgment and wide
experience seems the only guide to follow   We must  however  in many
cases  decide by a majority of naturalists  for few well marked and
well known varieties can be named which have not been ranked as species by
at least some competent judges 

That varieties of this doubtful nature are far from uncommon cannot be
disputed   Compare the several floras of Great Britain  of France  or of
the United States  drawn up by different botanists  and see what a
surprising number of forms have been ranked by one botanist as good
species  and by another as mere varieties   Mr  H C  Watson  to whom I lie
under deep obligation for assistance of all kinds  has marked for me 182
British plants  which are generally considered as varieties  but which have
all been ranked by botanists as species  and in making this list he has
omitted many trifling varieties  but which nevertheless have been ranked by
some botanists as species  and he has entirely omitted several highly
polymorphic genera   Under genera  including the most polymorphic forms 
Mr  Babington gives 251 species  whereas Mr  Bentham gives only 112  a
difference of 139 doubtful forms   Among animals which unite for each
birth  and which are highly locomotive  doubtful forms  ranked by one
zoologist as a species and by another as a variety  can rarely be found
within the same country  but are common in separated areas   How many of
the birds and insects in North America and Europe  which differ very
slightly from each other  have been ranked by one eminent naturalist as
undoubted species  and by another as varieties  or  as they are often
called  geographical races   Mr  Wallace  in several valuable papers on the
various animals  especially on the Lepidoptera  inhabiting the islands of
the great Malayan Archipelago  shows that they may be classed under four
heads  namely  as variable forms  as local forms  as geographical races or
sub species  and as true representative species   The first or variable
forms vary much within the limits of the same island   The local forms are
moderately constant and distinct in each separate island  but when all from
the several islands are compared together  the differences are seen to be
so slight and graduated that it is impossible to define or describe them 
though at the same time the extreme forms are sufficiently distinct   The
geographical races or sub species are local forms completely fixed and
isolated  but as they do not differ from each other by strongly marked and
important characters   There is no possible test but individual opinion to
determine which of them shall be considered as species and which as
varieties    Lastly  representative species fill the same place in the
natural economy of each island as do the local forms and sub species  but
as they are distinguished from each other by a greater amount of difference
than that between the local forms and sub species  they are almost
universally ranked by naturalists as true species   Nevertheless  no
certain criterion can possibly be given by which variable forms  local
forms  sub species and representative species can be recognised 

Many years ago  when comparing  and seeing others compare  the birds from
the closely neighbouring islands of the Galapagos Archipelago  one with
another  and with those from the American mainland  I was much struck how
entirely vague and arbitrary is the distinction between species and
varieties   On the islets of the little Madeira group there are many
insects which are characterized as varieties in Mr  Wollaston s admirable
work  but which would certainly be ranked as distinct species by many
entomologists   Even Ireland has a few animals  now generally regarded as
varieties  but which have been ranked as species by some zoologists  
Several experienced ornithologists consider our British red grouse as only
a strongly marked race of a Norwegian species  whereas the greater number
rank it as an undoubted species peculiar to Great Britain   A wide distance
between the homes of two doubtful forms leads many naturalists to rank them
as distinct species  but what distance  it has been well asked  will
suffice if that between America and Europe is ample  will that between
Europe and the Azores  or Madeira  or the Canaries  or between the several
islets of these small archipelagos  be sufficient 

Mr  B D  Walsh  a distinguished entomologist of the United States  has
described what he calls Phytophagic varieties and Phytophagic species  
Most vegetable feeding insects live on one kind of plant or on one group of
plants  some feed indiscriminately on many kinds  but do not in consequence
vary   In several cases  however  insects found living on different plants 
have been observed by Mr  Walsh to present in their larval or mature state 
or in both states  slight  though constant differences in colour  size  or
in the nature of their secretions   In some instances the males alone  in
other instances  both males and females  have been observed thus to differ
in a slight degree   When the differences are rather more strongly marked 
and when both sexes and all ages are affected  the forms are ranked by all
entomologists as good species   But no observer can determine for another 
even if he can do so for himself  which of these Phytophagic forms ought to
be called species and which varieties   Mr  Walsh ranks the forms which it
may be supposed would freely intercross  as varieties  and those which
appear to have lost this power  as species   As the differences depend on
the insects having long fed on distinct plants  it cannot be expected that
intermediate links connecting the several forms should now be found   The
naturalist thus loses his best guide in determining whether to rank
doubtful forms as varieties or species   This likewise necessarily occurs
with closely allied organisms  which inhabit distinct continents or
islands   When  on the other hand  an animal or plant ranges over the same
continent  or inhabits many islands in the same archipelago  and presents
different forms in the different areas  there is always a good chance that
intermediate forms will be discovered which will link together the extreme
states  and these are then degraded to the rank of varieties 

Some few naturalists maintain that animals never present varieties  but
then these same naturalists rank the slightest difference as of specific
value  and when the same identical form is met with in two distant
countries  or in two geological formations  they believe that two distinct
species are hidden under the same dress   The term species thus comes to be
a mere useless abstraction  implying and assuming a separate act of
creation   It is certain that many forms  considered by highly competent
judges to be varieties  resemble species so completely in character that
they have been thus ranked by other highly competent judges   But to
discuss whether they ought to be called species or varieties  before any
definition of these terms has been generally accepted  is vainly to beat
the air 

Many of the cases of strongly marked varieties or doubtful species well
deserve consideration  for several interesting lines of argument  from
geographical distribution  analogical variation  hybridism  etc   have been
brought to bear in the attempt to determine their rank  but space does not
here permit me to discuss them   Close investigation  in many cases  will
no doubt bring naturalists to agree how to rank doubtful forms   Yet it
must be confessed that it is in the best known countries that we find the
greatest number of them   I have been struck with the fact that if any
animal or plant in a state of nature be highly useful to man  or from any
cause closely attracts his attention  varieties of it will almost
universally be found recorded   These varieties  moreover  will often be
ranked by some authors as species   Look at the common oak  how closely it
has been studied  yet a German author makes more than a dozen species out
of forms  which are almost universally considered by other botanists to be
varieties  and in this country the highest botanical authorities and
practical men can be quoted to show that the sessile and pedunculated oaks
are either good and distinct species or mere varieties 

I may here allude to a remarkable memoir lately published by A  de
Candolle  on the oaks of the whole world   No one ever had more ample
materials for the discrimination of the species  or could have worked on
them with more zeal and sagacity   He first gives in detail all the many
points of structure which vary in the several species  and estimates
numerically the relative frequency of the variations   He specifies above a
dozen characters which may be found varying even on the same branch 
sometimes according to age or development  sometimes without any assignable
reason   Such characters are not of course of specific value  but they are 
as Asa Gray has remarked in commenting on this memoir  such as generally
enter into specific definitions   De Candolle then goes on to say that he
gives the rank of species to the forms that differ by characters never
varying on the same tree  and never found connected by intermediate states  
After this discussion  the result of so much labour  he emphatically
remarks    They are mistaken  who repeat that the greater part of our
species are clearly limited  and that the doubtful species are in a feeble
minority   This seemed to be true  so long as a genus was imperfectly
known  and its species were founded upon a few specimens  that is to say 
were provisional   Just as we come to know them better  intermediate forms
flow in  and doubts as to specific limits augment    He also adds that it
is the best known species which present the greatest number of spontaneous
varieties and sub varieties   Thus Quercus robur has twenty eight
varieties  all of which  excepting six  are clustered round three sub 
species  namely Q  pedunculata  sessiliflora and pubescens   The forms
which connect these three sub species are comparatively rare  and  as Asa
Gray again remarks  if these connecting forms which are now rare were to
become totally extinct the three sub species would hold exactly the same
relation to each other as do the four or five provisionally admitted
species which closely surround the typical Quercus robur   Finally  De
Candolle admits that out of the 300 species  which will be enumerated in
his Prodromus as belonging to the oak family  at least two thirds are
provisional species  that is  are not known strictly to fulfil the
definition above given of a true species   It should be added that De
Candolle no longer believes that species are immutable creations  but
concludes that the derivative theory is the most natural one   and the most
accordant with the known facts in palaeontology  geographical botany and
zoology  of anatomical structure and classification  

When a young naturalist commences the study of a group of organisms quite
unknown to him he is at first much perplexed in determining what
differences to consider as specific and what as varietal  for he knows
nothing of the amount and kind of variation to which the group is subject 
and this shows  at least  how very generally there is some variation   But
if he confine his attention to one class within one country he will soon
make up his mind how to rank most of the doubtful forms   His general
tendency will be to make many species  for he will become impressed  just
like the pigeon or poultry fancier before alluded to  with the amount of
difference in the forms which he is continually studying  and he has little
general knowledge of analogical variation in other groups and in other
countries by which to correct his first impressions   As he extends the
range of his observations he will meet with more cases of difficulty  for
he will encounter a greater number of closely allied forms   But if his
observations be widely extended he will in the end generally be able to
make up his own mind  but he will succeed in this at the expense of
admitting much variation  and the truth of this admission will often be
disputed by other naturalists   When he comes to study allied forms brought
from countries not now continuous  in which case he cannot hope to find
intermediate links  he will be compelled to trust almost entirely to
analogy  and his difficulties will rise to a climax 

Certainly no clear line of demarcation has as yet been drawn between
species and sub species  that is  the forms which in the opinion of some
naturalists come very near to  but do not quite arrive at  the rank of
species  or  again  between sub species and well marked varieties  or
between lesser varieties and individual differences   These differences
blend into each other by an insensible series  and a series impresses the
mind with the idea of an actual passage 

Hence I look at individual differences  though of small interest to the
systematist  as of the highest importance for us  as being the first step
towards such slight varieties as are barely thought worth recording in
works on natural history   And I look at varieties which are in any degree
more distinct and permanent  as steps toward more strongly marked and
permanent varieties  and at the latter  as leading to sub species  and then
to species   The passage from one stage of difference to another may  in
many cases  be the simple result of the nature of the organism and of the
different physical conditions to which it has long been exposed  but with
respect to the more important and adaptive characters  the passage from one
stage of difference to another may be safely attributed to the cumulative
action of natural selection  hereafter to be explained  and to the effects
of the increased use or disuse of parts   A well marked variety may
therefore be called an incipient species  but whether this belief is
justifiable must be judged by the weight of the various facts and
considerations to be given throughout this work 

It need not be supposed that all varieties or incipient species attain the
rank of species   They may become extinct  or they may endure as varieties
for very long periods  as has been shown to be the case by Mr  Wollaston
with the varieties of certain fossil land shells in Madeira  and with
plants by Gaston de Saporta   If a variety were to flourish so as to exceed
in numbers the parent species  it would then rank as the species  and the
species as the variety  or it might come to supplant and exterminate the
parent species  or both might co exist  and both rank as independent
species   But we shall hereafter return to this subject 

 From these remarks it will be seen that I look at the term species as one
arbitrarily given  for the sake of convenience  to a set of individuals
closely resembling each other  and that it does not essentially differ from
the term variety  which is given to less distinct and more fluctuating
forms   The term variety  again  in comparison with mere individual
differences  is also applied arbitrarily  for convenience sake 

WIDE RANGING  MUCH DIFFUSED  AND COMMON SPECIES VARY MOST 

Guided by theoretical considerations  I thought that some interesting
results might be obtained in regard to the nature and relations of the
species which vary most  by tabulating all the varieties in several
well worked floras   At first this seemed a simple task  but Mr  H C 
Watson  to whom I am much indebted for valuable advice and assistance on
this subject  soon convinced me that there were many difficulties  as did
subsequently Dr  Hooker  even in stronger terms   I shall reserve for a
future work the discussion of these difficulties  and the tables of the
proportional numbers of the varying species   Dr  Hooker permits me to add
that after having carefully read my manuscript  and examined the tables  he
thinks that the following statements are fairly well established   The
whole subject  however  treated as it necessarily here is with much
brevity  is rather perplexing  and allusions cannot be avoided to the
 struggle for existence    divergence of character   and other questions 
hereafter to be discussed 

Alphonse de Candolle and others have shown that plants which have very wide
ranges generally present varieties  and this might have been expected  as
they are exposed to diverse physical conditions  and as they come into
competition  which  as we shall hereafter see  is a far more important
circumstance  with different sets of organic beings   But my tables further
show that  in any limited country  the species which are the most common 
that is abound most in individuals  and the species which are most widely
diffused within their own country  and this is a different consideration
from wide range  and to a certain extent from commonness   oftenest give
rise to varieties sufficiently well marked to have been recorded in
botanical works   Hence it is the most flourishing  or  as they may be
called  the dominant species  those which range widely  are the most
diffused in their own country  and are the most numerous in
individuals  which oftenest produce well marked varieties  or  as I
consider them  incipient species   And this  perhaps  might have been
anticipated  for  as varieties  in order to become in any degree permanent 
necessarily have to struggle with the other inhabitants of the country  the
species which are already dominant will be the most likely to yield
offspring  which  though in some slight degree modified  still inherit
those advantages that enabled their parents to become dominant over their
compatriots   In these remarks on predominence  it should be understood
that reference is made only to the forms which come into competition with
each other  and more especially to the members of the same genus or class
having nearly similar habits of life   With respect to the number of
individuals or commonness of species  the comparison of course relates only
to the members of the same group   One of the higher plants may be said to
be dominant if it be more numerous in individuals and more widely diffused
than the other plants of the same country  which live under nearly the same
conditions   A plant of this kind is not the less dominant because some
conferva inhabiting the water or some parasitic fungus is infinitely more
numerous in individuals  and more widely diffused   But if the conferva or
parasitic fungus exceeds its allies in the above respects  it will then be
dominant within its own class 

SPECIES OF THE LARGER GENERA IN EACH COUNTRY VARY MORE FREQUENTLY THAN THE
SPECIES OF THE SMALLER GENERA 

If the plants inhabiting a country as described in any Flora  be divided
into two equal masses  all those in the larger genera  i e   those
including many species  being placed on one side  and all those in the
smaller genera on the other side  the former will be found to include a
somewhat larger number of the very common and much diffused or dominant
species   This might have been anticipated  for the mere fact of many
species of the same genus inhabiting any country  shows that there is
something in the organic or inorganic conditions of that country favourable
to the genus  and  consequently  we might have expected to have found in
the larger genera  or those including many species  a larger proportional
number of dominant species   But so many causes tend to obscure this
result  that I am surprised that my tables show even a small majority on
the side of the larger genera   I will here allude to only two causes of
obscurity   Fresh water and salt loving plants generally have very wide
ranges and are much diffused  but this seems to be connected with the
nature of the stations inhabited by them  and has little or no relation to
the size of the genera to which the species belong   Again  plants low in
the scale of organisation are generally much more widely diffused than
plants higher in the scale  and here again there is no close relation to
the size of the genera   The cause of lowly organised plants ranging widely
will be discussed in our chapter on Geographical Distribution 

 From looking at species as only strongly marked and well defined varieties 
I was led to anticipate that the species of the larger genera in each
country would oftener present varieties  than the species of the smaller
genera  for wherever many closely related species  i e   species of the
same genus  have been formed  many varieties or incipient species ought  as
a general rule  to be now forming   Where many large trees grow  we expect
to find saplings   Where many species of a genus have been formed through
variation  circumstances have been favourable for variation  and hence we
might expect that the circumstances would generally still be favourable to
variation   On the other hand  if we look at each species as a special act
of creation  there is no apparent reason why more varieties should occur in
a group having many species  than in one having few 

To test the truth of this anticipation I have arranged the plants of twelve
countries  and the coleopterous insects of two districts  into two nearly
equal masses  the species of the larger genera on one side  and those of
the smaller genera on the other side  and it has invariably proved to be
the case that a larger proportion of the species on the side of the larger
genera presented varieties  than on the side of the smaller genera  
Moreover  the species of the large genera which present any varieties 
invariably present a larger average number of varieties than do the species
of the small genera   Both these results follow when another division is
made  and when all the least genera  with from only one to four species 
are altogether excluded from the tables   These facts are of plain
signification on the view that species are only strongly marked and
permanent varieties  for wherever many species of the same genus have been
formed  or where  if we may use the expression  the manufactory of species
has been active  we ought generally to find the manufactory still in
action  more especially as we have every reason to believe the process of
manufacturing new species to be a slow one   And this certainly holds true
if varieties be looked at as incipient species  for my tables clearly show 
as a general rule  that  wherever many species of a genus have been formed 
the species of that genus present a number of varieties  that is  of
incipient species  beyond the average   It is not that all large genera are
now varying much  and are thus increasing in the number of their species 
or that no small genera are now varying and increasing  for if this had
been so  it would have been fatal to my theory  inasmuch as geology plainly
tells us that small genera have in the lapse of time often increased
greatly in size  and that large genera have often come to their maxima 
declined  and disappeared   All that we want to show is  that where many
species of a genus have been formed  on an average many are still forming 
and this certainly holds good 

MANY OF THE SPECIES INCLUDED WITHIN THE LARGER GENERA RESEMBLE VARIETIES IN
BEING VERY CLOSELY  BUT UNEQUALLY  RELATED TO EACH OTHER  AND IN HAVING
RESTRICTED RANGES 

There are other relations between the species of large genera and their
recorded varieties which deserve notice   We have seen that there is no
infallible criterion by which to distinguish species and well marked
varieties  and when intermediate links have not been found between doubtful
forms  naturalists are compelled to come to a determination by the amount
of difference between them  judging by analogy whether or not the amount
suffices to raise one or both to the rank of species   Hence the amount of
difference is one very important criterion in settling whether two forms
should be ranked as species or varieties   Now Fries has remarked in regard
to plants  and Westwood in regard to insects  that in large genera the
amount of difference between the species is often exceedingly small   I
have endeavoured to test this numerically by averages  and  as far as my
imperfect results go  they confirm the view   I have also consulted some
sagacious and experienced observers  and  after deliberation  they concur
in this view   In this respect  therefore  the species of the larger genera
resemble varieties  more than do the species of the smaller genera   Or the
case may be put in another way  and it may be said  that in the larger
genera  in which a number of varieties or incipient species greater than
the average are now manufacturing  many of the species already manufactured
still to a certain extent resemble varieties  for they differ from each
other by a less than the usual amount of difference 

Moreover  the species of the larger genera are related to each other  in
the same manner as the varieties of any one species are related to each
other   No naturalist pretends that all the species of a genus are equally
distinct from each other  they may generally be divided into sub genera  or
sections  or lesser groups   As Fries has well remarked  little groups of
species are generally clustered like satellites around other species   And
what are varieties but groups of forms  unequally related to each other 
and clustered round certain forms  that is  round their parent species  
Undoubtedly there is one most important point of difference between
varieties and species  namely  that the amount of difference between
varieties  when compared with each other or with their parent species  is
much less than that between the species of the same genus   But when we
come to discuss the principle  as I call it  of divergence of character  we
shall see how this may be explained  and how the lesser differences between
varieties tend to increase into the greater differences between species 

There is one other point which is worth notice   Varieties generally have
much restricted ranges   This statement is indeed scarcely more than a
truism  for if a variety were found to have a wider range than that of its
supposed parent species  their denominations would be reversed   But there
is reason to believe that the species which are very closely allied to
other species  and in so far resemble varieties  often have much restricted
ranges   For instance  Mr  H C  Watson has marked for me in the well sifted
London catalogue of Plants  4th edition  sixty three plants which are
therein ranked as species  but which he considers as so closely allied to
other species as to be of doubtful value   these sixty three reputed
species range on an average over 6 9 of the provinces into which Mr  Watson
has divided Great Britain   Now  in this same catalogue  fifty three
acknowledged varieties are recorded  and these range over 7 7 provinces 
whereas  the species to which these varieties belong range over 14 3
provinces   So that the acknowledged varieties have very nearly the same
restricted average range  as have the closely allied forms  marked for me
by Mr  Watson as doubtful species  but which are almost universally ranked
by British botanists as good and true species 

SUMMARY 

Finally  varieties cannot be distinguished from species  except  first  by
the discovery of intermediate linking forms  and  secondly  by a certain
indefinite amount of difference between them  for two forms  if differing
very little  are generally ranked as varieties  notwithstanding that they
cannot be closely connected  but the amount of difference considered
necessary to give to any two forms the rank of species cannot be defined  
In genera having more than the average number of species in any country 
the species of these genera have more than the average number of varieties  
In large genera the species are apt to be closely but unequally allied
together  forming little clusters round other species   Species very
closely allied to other species apparently have restricted ranges   In all
these respects the species of large genera present a strong analogy with
varieties   And we can clearly understand these analogies  if species once
existed as varieties  and thus originated  whereas  these analogies are
utterly inexplicable if species are independent creations 

We have also seen that it is the most flourishing or dominant species of
the larger genera within each class which on an average yield the greatest
number of varieties  and varieties  as we shall hereafter see  tend to
become converted into new and distinct species   Thus the larger genera
tend to become larger  and throughout nature the forms of life which are
now dominant tend to become still more dominant by leaving many modified
and dominant descendants   But  by steps hereafter to be explained  the
larger genera also tend to break up into smaller genera   And thus  the
forms of life throughout the universe become divided into groups
subordinate to groups 


CHAPTER III 

STRUGGLE FOR EXISTENCE 

Its bearing on natural selection    The term used in a wide sense   
Geometrical ratio of increase    Rapid increase of naturalised animals and
plants    Nature of the checks to increase    Competition universal   
Effects of climate    Protection from the number of individuals    Complex
relations of all animals and plants throughout nature    Struggle for life
most severe between individuals and varieties of the same species   often
severe between species of the same genus    The relation of organism to
organism the most important of all relations 

Before entering on the subject of this chapter I must make a few
preliminary remarks to show how the struggle for existence bears on natural
selection   It has been seen in the last chapter that among organic beings
in a state of nature there is some individual variability   indeed I am not
aware that this has ever been disputed   It is immaterial for us whether a
multitude of doubtful forms be called species or sub species or varieties 
what rank  for instance  the two or three hundred doubtful forms of British
plants are entitled to hold  if the existence of any well marked varieties
be admitted   But the mere existence of individual variability and of some
few well marked varieties  though necessary as the foundation for the work 
helps us but little in understanding how species arise in nature   How have
all those exquisite adaptations of one part of the organisation to another
part  and to the conditions of life and of one organic being to another
being  been perfected   We see these beautiful co adaptations most plainly
in the woodpecker and the mistletoe  and only a little less plainly in the
humblest parasite which clings to the hairs of a quadruped or feathers of a
bird  in the structure of the beetle which dives through the water  in the
plumed seed which is wafted by the gentlest breeze  in short  we see
beautiful adaptations everywhere and in every part of the organic world 

Again  it may be asked  how is it that varieties  which I have called
incipient species  become ultimately converted into good and distinct
species  which in most cases obviously differ from each other far more than
do the varieties of the same species   How do those groups of species 
which constitute what are called distinct genera and which differ from each
other more than do the species of the same genus  arise   All these
results  as we shall more fully see in the next chapter  follow from the
struggle for life   Owing to this struggle  variations  however slight and
from whatever cause proceeding  if they be in any degree profitable to the
individuals of a species  in their infinitely complex relations to other
organic beings and to their physical conditions of life  will tend to the
preservation of such individuals  and will generally be inherited by the
offspring   The offspring  also  will thus have a better chance of
surviving  for  of the many individuals of any species which are
periodically born  but a small number can survive   I have called this
principle  by which each slight variation  if useful  is preserved  by the
term natural selection  in order to mark its relation to man s power of
selection   But the expression often used by Mr  Herbert Spencer  of the
Survival of the Fittest  is more accurate  and is sometimes equally
convenient   We have seen that man by selection can certainly produce great
results  and can adapt organic beings to his own uses  through the
accumulation of slight but useful variations  given to him by the hand of
Nature   But Natural Selection  we shall hereafter see  is a power
incessantly ready for action  and is as immeasurably superior to man s
feeble efforts  as the works of Nature are to those of Art 

We will now discuss in a little more detail the struggle for existence   In
my future work this subject will be treated  as it well deserves  at
greater length   The elder De Candolle and Lyell have largely and
philosophically shown that all organic beings are exposed to severe
competition   In regard to plants  no one has treated this subject with
more spirit and ability than W  Herbert  Dean of Manchester  evidently the
result of his great horticultural knowledge   Nothing is easier than to
admit in words the truth of the universal struggle for life  or more
difficult  at least I found it so  than constantly to bear this conclusion
in mind   Yet unless it be thoroughly engrained in the mind  the whole
economy of nature  with every fact on distribution  rarity  abundance 
extinction  and variation  will be dimly seen or quite misunderstood   We
behold the face of nature bright with gladness  we often see superabundance
of food  we do not see or we forget that the birds which are idly singing
round us mostly live on insects or seeds  and are thus constantly
destroying life  or we forget how largely these songsters  or their eggs 
or their nestlings  are destroyed by birds and beasts of prey  we do not
always bear in mind  that  though food may be now superabundant  it is not
so at all seasons of each recurring year 

THE TERM  STRUGGLE FOR EXISTENCE  USED IN A LARGE SENSE 

I should premise that I use this term in a large and metaphorical sense 
including dependence of one being on another  and including  which is more
important  not only the life of the individual  but success in leaving
progeny   Two canine animals  in a time of dearth  may be truly said to
struggle with each other which shall get food and live   But a plant on the
edge of a desert is said to struggle for life against the drought  though
more properly it should be said to be dependent on the moisture   A plant
which annually produces a thousand seeds  of which only one of an average
comes to maturity  may be more truly said to struggle with the plants of
the same and other kinds which already clothe the ground   The mistletoe is
dependent on the apple and a few other trees  but can only in a far fetched
sense be said to struggle with these trees  for  if too many of these
parasites grow on the same tree  it languishes and dies   But several
seedling mistletoes  growing close together on the same branch  may more
truly be said to struggle with each other   As the mistletoe is
disseminated by birds  its existence depends on them  and it may
metaphorically be said to struggle with other fruit bearing plants  in
tempting the birds to devour and thus disseminate its seeds   In these
several senses  which pass into each other  I use for convenience sake the
general term of Struggle for Existence 

GEOMETRICAL RATIO OF INCREASE 

A struggle for existence inevitably follows from the high rate at which all
organic beings tend to increase   Every being  which during its natural
lifetime produces several eggs or seeds  must suffer destruction during
some period of its life  and during some season or occasional year 
otherwise  on the principle of geometrical increase  its numbers would
quickly become so inordinately great that no country could support the
product   Hence  as more individuals are produced than can possibly
survive  there must in every case be a struggle for existence  either one
individual with another of the same species  or with the individuals of
distinct species  or with the physical conditions of life   It is the
doctrine of Malthus applied with manifold force to the whole animal and
vegetable kingdoms  for in this case there can be no artificial increase of
food  and no prudential restraint from marriage   Although some species may
be now increasing  more or less rapidly  in numbers  all cannot do so  for
the world would not hold them 

There is no exception to the rule that every organic being naturally
increases at so high a rate  that  if not destroyed  the earth would soon
be covered by the progeny of a single pair   Even slow breeding man has
doubled in twenty five years  and at this rate  in less than a thousand
years  there would literally not be standing room for his progeny  
Linnaeus has calculated that if an annual plant produced only two
seeds  and there is no plant so unproductive as this  and their seedlings
next year produced two  and so on  then in twenty years there would be a
million plants   The elephant is reckoned the slowest breeder of all known
animals  and I have taken some pains to estimate its probable minimum rate
of natural increase  it will be safest to assume that it begins breeding
when thirty years old  and goes on breeding till ninety years old  bringing
forth six young in the interval  and surviving till one hundred years old 
if this be so  after a period of from 740 to 750 years there would be
nearly nineteen million elephants alive descended from the first pair 

But we have better evidence on this subject than mere theoretical
calculations  namely  the numerous recorded cases of the astonishingly
rapid increase of various animals in a state of nature  when circumstances
have been favourable to them during two or three following seasons   Still
more striking is the evidence from our domestic animals of many kinds which
have run wild in several parts of the world  if the statements of the rate
of increase of slow breeding cattle and horses in South America  and
latterly in Australia  had not been well authenticated  they would have
been incredible   So it is with plants  cases could be given of introduced
plants which have become common throughout whole islands in a period of
less than ten years   Several of the plants  such as the cardoon and a tall
thistle  which are now the commonest over the wide plains of La Plata 
clothing square leagues of surface almost to the exclusion of every other
plant  have been introduced from Europe  and there are plants which now
range in India  as I hear from Dr  Falconer  from Cape Comorin to the
Himalaya  which have been imported from America since its discovery   In
such cases  and endless others could be given  no one supposes that the
fertility of the animals or plants has been suddenly and temporarily
increased in any sensible degree   The obvious explanation is that the
conditions of life have been highly favourable  and that there has
consequently been less destruction of the old and young and that nearly all
the young have been enabled to breed   Their geometrical ratio of increase 
the result of which never fails to be surprising  simply explains their
extraordinarily rapid increase and wide diffusion in their new homes 

In a state of nature almost every full grown plant annually produces seed 
and among animals there are very few which do not annually pair   Hence we
may confidently assert that all plants and animals are tending to increase
at a geometrical ratio  that all would rapidly stock every station in which
they could any how exist  and that this geometrical tendency to increase
must be checked by destruction at some period of life   Our familiarity
with the larger domestic animals tends  I think  to mislead us  we see no
great destruction falling on them  and we do not keep in mind that
thousands are annually slaughtered for food  and that in a state of nature
an equal number would have somehow to be disposed of 

The only difference between organisms which annually produce eggs or seeds
by the thousand  and those which produce extremely few  is  that the slow
breeders would require a few more years to people  under favourable
conditions  a whole district  let it be ever so large   The condor lays a
couple of eggs and the ostrich a score  and yet in the same country the
condor may be the more numerous of the two   The Fulmar petrel lays but one
egg  yet it is believed to be the most numerous bird in the world   One fly
deposits hundreds of eggs  and another  like the hippobosca  a single one  
But this difference does not determine how many individuals of the two
species can be supported in a district   A large number of eggs is of some
importance to those species which depend on a fluctuating amount of food 
for it allows them rapidly to increase in number   But the real importance
of a large number of eggs or seeds is to make up for much destruction at
some period of life  and this period in the great majority of cases is an
early one   If an animal can in any way protect its own eggs or young  a
small number may be produced  and yet the average stock be fully kept up 
but if many eggs or young are destroyed  many must be produced or the
species will become extinct   It would suffice to keep up the full number
of a tree  which lived on an average for a thousand years  if a single seed
were produced once in a thousand years  supposing that this seed were never
destroyed and could be ensured to germinate in a fitting place  so that  in
all cases  the average number of any animal or plant depends only
indirectly on the number of its eggs or seeds 

In looking at Nature  it is most necessary to keep the foregoing
considerations always in mind  never to forget that every single organic
being may be said to be striving to the utmost to increase in numbers  that
each lives by a struggle at some period of its life  that heavy destruction
inevitably falls either on the young or old during each generation or at
recurrent intervals   Lighten any check  mitigate the destruction ever so
little  and the number of the species will almost instantaneously increase
to any amount 

NATURE OF THE CHECKS TO INCREASE 

The causes which check the natural tendency of each species to increase are
most obscure   Look at the most vigorous species  by as much as it swarms
in numbers  by so much will it tend to increase still further   We know not
exactly what the checks are even in a single instance   Nor will this
surprise any one who reflects how ignorant we are on this head  even in
regard to mankind  although so incomparably better known than any other
animal   This subject of the checks to increase has been ably treated by
several authors  and I hope in a future work to discuss it at considerable
length  more especially in regard to the feral animals of South America  
Here I will make only a few remarks  just to recall to the reader s mind
some of the chief points   Eggs or very young animals seem generally to
suffer most  but this is not invariably the case   With plants there is a
vast destruction of seeds  but from some observations which I have made it
appears that the seedlings suffer most from germinating in ground already
thickly stocked with other plants   Seedlings  also  are destroyed in vast
numbers by various enemies  for instance  on a piece of ground three feet
long and two wide  dug and cleared  and where there could be no choking
from other plants  I marked all the seedlings of our native weeds as they
came up  and out of 357 no less than 295 were destroyed  chiefly by slugs
and insects   If turf which has long been mown  and the case would be the
same with turf closely browsed by quadrupeds  be let to grow  the more
vigorous plants gradually kill the less vigorous  though fully grown
plants  thus out of twenty species grown on a little plot of mown turf
 three feet by four  nine species perished  from the other species being
allowed to grow up freely 

The amount of food for each species  of course  gives the extreme limit to
which each can increase  but very frequently it is not the obtaining food 
but the serving as prey to other animals  which determines the average
number of a species   Thus  there seems to be little doubt that the stock
of partridges  grouse  and hares on any large estate depends chiefly on the
destruction of vermin   If not one head of game were shot during the next
twenty years in England  and  at the same time  if no vermin were
destroyed  there would  in all probability  be less game than at present 
although hundreds of thousands of game animals are now annually shot   On
the other hand  in some cases  as with the elephant  none are destroyed by
beasts of prey  for even the tiger in India most rarely dares to attack a
young elephant protected by its dam 

Climate plays an important part in determining the average numbers of a
species  and periodical seasons of extreme cold or drought seem to be the
most effective of all checks   I estimated  chiefly from the greatly
reduced numbers of nests in the spring  that the winter of 1854 5 destroyed
four fifths of the birds in my own grounds  and this is a tremendous
destruction  when we remember that ten per cent  is an extraordinarily
severe mortality from epidemics with man   The action of climate seems at
first sight to be quite independent of the struggle for existence  but in
so far as climate chiefly acts in reducing food  it brings on the most
severe struggle between the individuals  whether of the same or of distinct
species  which subsist on the same kind of food   Even when climate  for
instance  extreme cold  acts directly  it will be the least vigorous
individuals  or those which have got least food through the advancing
winter  which will suffer the most   When we travel from south to north  or
from a damp region to a dry  we invariably see some species gradually
getting rarer and rarer  and finally disappearing  and the change of
climate being conspicuous  we are tempted to attribute the whole effect to
its direct action   But this is a false view  we forget that each species 
even where it most abounds  is constantly suffering enormous destruction at
some period of its life  from enemies or from competitors for the same
place and food  and if these enemies or competitors be in the least degree
favoured by any slight change of climate  they will increase in numbers 
and as each area is already fully stocked with inhabitants  the other
species must decrease   When we travel southward and see a species
decreasing in numbers  we may feel sure that the cause lies quite as much
in other species being favoured  as in this one being hurt   So it is when
we travel northward  but in a somewhat lesser degree  for the number of
species of all kinds  and therefore of competitors  decreases northward 
hence in going northward  or in ascending a mountain  we far oftener meet
with stunted forms  due to the DIRECTLY injurious action of climate  than
we do in proceeding southward or in descending a mountain   When we reach
the Arctic regions  or snow capped summits  or absolute deserts  the
struggle for life is almost exclusively with the elements 

That climate acts in main part indirectly by favouring other species we
clearly see in the prodigious number of plants which in our gardens can
perfectly well endure our climate  but which never become naturalised  for
they cannot compete with our native plants nor resist destruction by our
native animals 

When a species  owing to highly favourable circumstances  increases
inordinately in numbers in a small tract  epidemics  at least  this seems
generally to occur with our game animals  often ensue  and here we have a
limiting check independent of the struggle for life   But even some of
these so called epidemics appear to be due to parasitic worms  which have
from some cause  possibly in part through facility of diffusion among the
crowded animals  been disproportionally favoured   and here comes in a sort
of struggle between the parasite and its prey 

On the other hand  in many cases  a large stock of individuals of the same
species  relatively to the numbers of its enemies  is absolutely necessary
for its preservation   Thus we can easily raise plenty of corn and
rape seed  etc   in our fields  because the seeds are in great excess
compared with the number of birds which feed on them  nor can the birds 
though having a superabundance of food at this one season  increase in
number proportionally to the supply of seed  as their numbers are checked
during the winter  but any one who has tried knows how troublesome it is to
get seed from a few wheat or other such plants in a garden  I have in this
case lost every single seed   This view of the necessity of a large stock
of the same species for its preservation  explains  I believe  some
singular facts in nature such as that of very rare plants being sometimes
extremely abundant  in the few spots where they do exist  and that of some
social plants being social  that is abounding in individuals  even on the
extreme verge of their range   For in such cases  we may believe  that a
plant could exist only where the conditions of its life were so favourable
that many could exist together  and thus save the species from utter
destruction   I should add that the good effects of intercrossing  and the
ill effects of close interbreeding  no doubt come into play in many of
these cases  but I will not here enlarge on this subject 

COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO EACH OTHER IN THE STRUGGLE
FOR EXISTENCE 

Many cases are on record showing how complex and unexpected are the checks
and relations between organic beings  which have to struggle together in
the same country   I will give only a single instance  which  though a
simple one  interested me   In Staffordshire  on the estate of a relation 
where I had ample means of investigation  there was a large and extremely
barren heath  which had never been touched by the hand of man  but several
hundred acres of exactly the same nature had been enclosed twenty five
years previously and planted with Scotch fir   The change in the native
vegetation of the planted part of the heath was most remarkable  more than
is generally seen in passing from one quite different soil to another   not
only the proportional numbers of the heath plants were wholly changed  but
twelve species of plants  not counting grasses and carices  flourished in
the plantations  which could not be found on the heath   The effect on the
insects must have been still greater  for six insectivorous birds were very
common in the plantations  which were not to be seen on the heath  and the
heath was frequented by two or three distinct insectivorous birds   Here we
see how potent has been the effect of the introduction of a single tree 
nothing whatever else having been done  with the exception of the land
having been enclosed  so that cattle could not enter   But how important an
element enclosure is  I plainly saw near Farnham  in Surrey   Here there
are extensive heaths  with a few clumps of old Scotch firs on the distant
hill tops   within the last ten years large spaces have been enclosed  and
self sown firs are now springing up in multitudes  so close together that
all cannot live   When I ascertained that these young trees had not been
sown or planted I was so much surprised at their numbers that I went to
several points of view  whence I could examine hundreds of acres of the
unenclosed heath  and literally I could not see a single Scotch fir  except
the old planted clumps   But on looking closely between the stems of the
heath  I found a multitude of seedlings and little trees  which had been
perpetually browsed down by the cattle   In one square yard  at a point
some hundred yards distant from one of the old clumps  I counted thirty two
little trees  and one of them  with twenty six rings of growth  had  during
many years tried to raise its head above the stems of the heath  and had
failed   No wonder that  as soon as the land was enclosed  it became
thickly clothed with vigorously growing young firs   Yet the heath was so
extremely barren and so extensive that no one would ever have imagined that
cattle would have so closely and effectually searched it for food 

Here we see that cattle absolutely determine the existence of the Scotch
fir  but in several parts of the world insects determine the existence of
cattle   Perhaps Paraguay offers the most curious instance of this  for
here neither cattle nor horses nor dogs have ever run wild  though they
swarm southward and northward in a feral state  and Azara and Rengger have
shown that this is caused by the greater number in Paraguay of a certain
fly  which lays its eggs in the navels of these animals when first born  
The increase of these flies  numerous as they are  must be habitually
checked by some means  probably by other parasitic insects   Hence  if
certain insectivorous birds were to decrease in Paraguay  the parasitic
insects would probably increase  and this would lessen the number of the
navel frequenting flies  then cattle and horses would become feral  and
this would certainly greatly alter  as indeed I have observed in parts of
South America  the vegetation   this again would largely affect the
insects  and this  as we have just seen in Staffordshire  the insectivorous
birds  and so onwards in ever increasing circles of complexity   Not that
under nature the relations will ever be as simple as this   Battle within
battle must be continually recurring with varying success  and yet in the
long run the forces are so nicely balanced that the face of nature remains
for long periods of time uniform  though assuredly the merest trifle would
give the victory to one organic being over another   Nevertheless  so
profound is our ignorance  and so high our presumption  that we marvel when
we hear of the extinction of an organic being  and as we do not see the
cause  we invoke cataclysms to desolate the world  or invent laws on the
duration of the forms of life 

I am tempted to give one more instance showing how plants and animals 
remote in the scale of nature  are bound together by a web of complex
relations   I shall hereafter have occasion to show that the exotic Lobelia
fulgens is never visited in my garden by insects  and consequently  from
its peculiar structure  never sets a seed   Nearly all our orchidaceous
plants absolutely require the visits of insects to remove their
pollen masses and thus to fertilise them   I find from experiments that
humble bees are almost indispensable to the fertilisation of the heartsease
 Viola tricolor   for other bees do not visit this flower   I have also
found that the visits of bees are necessary for the fertilisation of some
kinds of clover  for instance twenty heads of Dutch clover  Trifolium
repens  yielded 2 290 seeds  but twenty other heads  protected from bees 
produced not one   Again  100 heads of red clover  T  pratense  produced
2 700 seeds  but the same number of protected heads produced not a single
seed  Humble bees alone visit red clover  as other bees cannot reach the
nectar   It has been suggested that moths may fertilise the clovers  but I
doubt whether they could do so in the case of the red clover  from their
weight not being sufficient to depress the wing petals   Hence we may infer
as highly probable that  if the whole genus of humble bees became extinct
or very rare in England  the heartsease and red clover would become very
rare  or wholly disappear   The number of humble bees in any district
depends in a great measure upon the number of field mice  which destroy
their combs and nests  and Colonel Newman  who has long attended to the
habits of humble bees  believes that  more than two thirds of them are thus
destroyed all over England    Now the number of mice is largely dependent 
as every one knows  on the number of cats  and Colonel Newman says   Near
villages and small towns I have found the nests of humble bees more
numerous than elsewhere  which I attribute to the number of cats that
destroy the mice    Hence it is quite credible that the presence of a
feline animal in large numbers in a district might determine  through the
intervention first of mice and then of bees  the frequency of certain
flowers in that district 

In the case of every species  many different checks  acting at different
periods of life  and during different seasons or years  probably come into
play  some one check or some few being generally the most potent  but all
will concur in determining the average number  or even the existence of the
species   In some cases it can be shown that widely different checks act on
the same species in different districts   When we look at the plants and
bushes clothing an entangled bank  we are tempted to attribute their
proportional numbers and kinds to what we call chance   But how false a
view is this   Every one has heard that when an American forest is cut
down  a very different vegetation springs up  but it has been observed that
ancient Indian ruins in the Southern United States  which must formerly
have been cleared of trees  now display the same beautiful diversity and
proportion of kinds as in the surrounding virgin forests   What a struggle
must have gone on during long centuries between the several kinds of trees 
each annually scattering its seeds by the thousand  what war between insect
and insect  between insects  snails  and other animals with birds and
beasts of prey  all striving to increase  all feeding on each other  or on
the trees  their seeds and seedlings  or on the other plants which first
clothed the ground and thus checked the growth of the trees   Throw up a
handful of feathers  and all fall to the ground according to definite laws 
but how simple is the problem where each shall fall compared to that of the
action and reaction of the innumerable plants and animals which have
determined  in the course of centuries  the proportional numbers and kinds
of trees now growing on the old Indian ruins 

The dependency of one organic being on another  as of a parasite on its
prey  lies generally between beings remote in the scale of nature   This is
likewise sometimes the case with those which may strictly be said to
struggle with each other for existence  as in the case of locusts and
grass feeding quadrupeds   But the struggle will almost invariably be most
severe between the individuals of the same species  for they frequent the
same districts  require the same food  and are exposed to the same dangers  
In the case of varieties of the same species  the struggle will generally
be almost equally severe  and we sometimes see the contest soon decided  
for instance  if several varieties of wheat be sown together  and the mixed
seed be resown  some of the varieties which best suit the soil or climate 
or are naturally the most fertile  will beat the others and so yield more
seed  and will consequently in a few years supplant the other varieties  
To keep up a mixed stock of even such extremely close varieties as the
variously coloured sweet peas  they must be each year harvested separately 
and the seed then mixed in due proportion  otherwise the weaker kinds will
steadily decrease in number and disappear   So again with the varieties of
sheep   it has been asserted that certain mountain varieties will starve
out other mountain varieties  so that they cannot be kept together   The
same result has followed from keeping together different varieties of the
medicinal leech   It may even be doubted whether the varieties of any of
our domestic plants or animals have so exactly the same strength  habits 
and constitution  that the original proportions of a mixed stock  crossing
being prevented  could be kept up for half a dozen generations  if they
were allowed to struggle together  in the same manner as beings in a state
of nature  and if the seed or young were not annually preserved in due
proportion 

STRUGGLE FOR LIFE MOST SEVERE BETWEEN INDIVIDUALS AND VARIETIES OF THE SAME
SPECIES 

As the species of the same genus usually have  though by no means
invariably  much similarity in habits and constitution  and always in
structure  the struggle will generally be more severe between them  if they
come into competition with each other  than between the species of distinct
genera   We see this in the recent extension over parts of the United
States of one species of swallow having caused the decrease of another
species   The recent increase of the missel thrush in parts of Scotland has
caused the decrease of the song thrush   How frequently we hear of one
species of rat taking the place of another species under the most different
climates   In Russia the small Asiatic cockroach has everywhere driven
before it its great congener   In Australia the imported hive bee is
rapidly exterminating the small  stingless native bee   One species of
charlock has been known to supplant another species  and so in other cases  
We can dimly see why the competition should be most severe between allied
forms  which fill nearly the same place in the economy of nature  but
probably in no one case could we precisely say why one species has been
victorious over another in the great battle of life 

A corollary of the highest importance may be deduced from the foregoing
remarks  namely  that the structure of every organic being is related  in
the most essential yet often hidden manner  to that of all other organic
beings  with which it comes into competition for food or residence  or from
which it has to escape  or on which it preys   This is obvious in the
structure of the teeth and talons of the tiger  and in that of the legs and
claws of the parasite which clings to the hair on the tiger s body   But in
the beautifully plumed seed of the dandelion  and in the flattened and
fringed legs of the water beetle  the relation seems at first confined to
the elements of air and water   Yet the advantage of the plumed seeds no
doubt stands in the closest relation to the land being already thickly
clothed with other plants  so that the seeds may be widely distributed and
fall on unoccupied ground   In the water beetle  the structure of its legs 
so well adapted for diving  allows it to compete with other aquatic
insects  to hunt for its own prey  and to escape serving as prey to other
animals 

The store of nutriment laid up within the seeds of many plants seems at
first sight to have no sort of relation to other plants   But from the
strong growth of young plants produced from such seeds  as peas and beans 
when sown in the midst of long grass  it may be suspected that the chief
use of the nutriment in the seed is to favour the growth of the seedlings 
whilst struggling with other plants growing vigorously all around 

Look at a plant in the midst of its range   Why does it not double or
quadruple its numbers   We know that it can perfectly well withstand a
little more heat or cold  dampness or dryness  for elsewhere it ranges into
slightly hotter or colder  damper or drier districts   In this case we can
clearly see that if we wish in imagination to give the plant the power of
increasing in numbers  we should have to give it some advantage over its
competitors  or over the animals which prey on it   On the confines of its
geographical range  a change of constitution with respect to climate would
clearly be an advantage to our plant  but we have reason to believe that
only a few plants or animals range so far  that they are destroyed
exclusively by the rigour of the climate   Not until we reach the extreme
confines of life  in the Arctic regions or on the borders of an utter
desert  will competition cease   The land may be extremely cold or dry  yet
there will be competition between some few species  or between the
individuals of the same species  for the warmest or dampest spots 

Hence we can see that when a plant or animal is placed in a new country 
among new competitors  the conditions of its life will generally be changed
in an essential manner  although the climate may be exactly the same as in
its former home   If its average numbers are to increase in its new home 
we should have to modify it in a different way to what we should have had
to do in its native country  for we should have to give it some advantage
over a different set of competitors or enemies 

It is good thus to try in imagination to give any one species an advantage
over another   Probably in no single instance should we know what to do  
This ought to convince us of our ignorance on the mutual relations of all
organic beings  a conviction as necessary  as it is difficult to acquire  
All that we can do is to keep steadily in mind that each organic being is
striving to increase in a geometrical ratio  that each  at some period of
its life  during some season of the year  during each generation  or at
intervals  has to struggle for life and to suffer great destruction   When
we reflect on this struggle we may console ourselves with the full belief
that the war of nature is not incessant  that no fear is felt  that death
is generally prompt  and that the vigorous  the healthy  and the happy
survive and multiply 


CHAPTER IV 

NATURAL SELECTION  OR THE SURVIVAL OF THE FITTEST 

Natural Selection    its power compared with man s selection    its power
on characters of trifling importance    its power at all ages and on both
sexes    Sexual Selection    On the generality of intercrosses between
individuals of the same species    Circumstances favourable and
unfavourable to the results of Natural Selection  namely  intercrossing 
isolation  number of individuals    Slow action    Extinction caused by
Natural Selection    Divergence of Character  related to the diversity of
inhabitants of any small area and to naturalisation    Action of Natural
Selection  through Divergence of Character and Extinction  on the
descendants from a common parent    Explains the Grouping of all organic
beings    Advance in organisation    Low forms preserved    Convergence of
character    Indefinite multiplication of species    Summary 

How will the struggle for existence  briefly discussed in the last chapter 
act in regard to variation   Can the principle of selection  which we have
seen is so potent in the hands of man  apply under nature   I think we
shall see that it can act most efficiently    Let the endless number of
slight variations and individual differences occurring in our domestic
productions  and  in a lesser degree  in those under nature  be borne in
mind  as well as the strength of the hereditary tendency   Under
domestication  it may truly be said that the whole organisation becomes in
some degree plastic   But the variability  which we almost universally meet
with in our domestic productions is not directly produced  as Hooker and
Asa Gray have well remarked  by man  he can neither originate varieties nor
prevent their occurrence  he can only preserve and accumulate such as do
occur   Unintentionally he exposes organic beings to new and changing
conditions of life  and variability ensues  but similar changes of
conditions might and do occur under nature   Let it also be borne in mind
how infinitely complex and close fitting are the mutual relations of all
organic beings to each other and to their physical conditions of life  and
consequently what infinitely varied diversities of structure might be of
use to each being under changing conditions of life   Can it then be
thought improbable  seeing that variations useful to man have undoubtedly
occurred  that other variations useful in some way to each being in the
great and complex battle of life  should occur in the course of many
successive generations   If such do occur  can we doubt  remembering that
many more individuals are born than can possibly survive  that individuals
having any advantage  however slight  over others  would have the best
chance of surviving and procreating their kind   On the other hand  we may
feel sure that any variation in the least degree injurious would be rigidly
destroyed   This preservation of favourable individual differences and
variations  and the destruction of those which are injurious  I have called
Natural Selection  or the Survival of the Fittest   Variations neither
useful nor injurious would not be affected by natural selection  and would
be left either a fluctuating element  as perhaps we see in certain
polymorphic species  or would ultimately become fixed  owing to the nature
of the organism and the nature of the conditions 

Several writers have misapprehended or objected to the term Natural
Selection   Some have even imagined that natural selection induces
variability  whereas it implies only the preservation of such variations as
arise and are beneficial to the being under its conditions of life   No one
objects to agriculturists speaking of the potent effects of man s
selection  and in this case the individual differences given by nature 
which man for some object selects  must of necessity first occur   Others
have objected that the term selection implies conscious choice in the
animals which become modified  and it has even been urged that  as plants
have no volition  natural selection is not applicable to them   In the
literal sense of the word  no doubt  natural selection is a false term  but
who ever objected to chemists speaking of the elective affinities of the
various elements   and yet an acid cannot strictly be said to elect the
base with which it in preference combines   It has been said that I speak
of natural selection as an active power or Deity  but who objects to an
author speaking of the attraction of gravity as ruling the movements of the
planets   Every one knows what is meant and is implied by such metaphorical
expressions  and they are almost necessary for brevity   So again it is
difficult to avoid personifying the word Nature  but I mean by nature  only
the aggregate action and product of many natural laws  and by laws the
sequence of events as ascertained by us   With a little familiarity such
superficial objections will be forgotten 

We shall best understand the probable course of natural selection by taking
the case of a country undergoing some slight physical change  for instance 
of climate   The proportional numbers of its inhabitants will almost
immediately undergo a change  and some species will probably become
extinct   We may conclude  from what we have seen of the intimate and
complex manner in which the inhabitants of each country are bound together 
that any change in the numerical proportions of the inhabitants 
independently of the change of climate itself  would seriously affect the
others   If the country were open on its borders  new forms would certainly
immigrate  and this would likewise seriously disturb the relations of some
of the former inhabitants   Let it be remembered how powerful the influence
of a single introduced tree or mammal has been shown to be   But in the
case of an island  or of a country partly surrounded by barriers  into
which new and better adapted forms could not freely enter  we should then
have places in the economy of nature which would assuredly be better filled
up if some of the original inhabitants were in some manner modified  for 
had the area been open to immigration  these same places would have been
seized on by intruders   In such cases  slight modifications  which in any
way favoured the individuals of any species  by better adapting them to
their altered conditions  would tend to be preserved  and natural selection
would have free scope for the work of improvement 

We have good reason to believe  as shown in the first chapter  that changes
in the conditions of life give a tendency to increased variability  and in
the foregoing cases the conditions the changed  and this would manifestly
be favourable to natural selection  by affording a better chance of the
occurrence of profitable variations   Unless such occur  natural selection
can do nothing   Under the term of  variations   it must never be forgotten
that mere individual differences are included   As man can produce a great
result with his domestic animals and plants by adding up in any given
direction individual differences  so could natural selection  but far more
easily from having incomparably longer time for action   Nor do I believe
that any great physical change  as of climate  or any unusual degree of
isolation  to check immigration  is necessary in order that new and
unoccupied places should be left for natural selection to fill up by
improving some of the varying inhabitants   For as all the inhabitants of
each country are struggling together with nicely balanced forces  extremely
slight modifications in the structure or habits of one species would often
give it an advantage over others  and still further modifications of the
same kind would often still further increase the advantage  as long as the
species continued under the same conditions of life and profited by similar
means of subsistence and defence   No country can be named in which all the
native inhabitants are now so perfectly adapted to each other and to the
physical conditions under which they live  that none of them could be still
better adapted or improved  for in all countries  the natives have been so
far conquered by naturalised productions that they have allowed some
foreigners to take firm possession of the land   And as foreigners have
thus in every country beaten some of the natives  we may safely conclude
that the natives might have been modified with advantage  so as to have
better resisted the intruders 

As man can produce  and certainly has produced  a great result by his
methodical and unconscious means of selection  what may not natural
selection effect   Man can act only on external and visible characters  
Nature  if I may be allowed to personify the natural preservation or
survival of the fittest  cares nothing for appearances  except in so far as
they are useful to any being   She can act on every internal organ  on
every shade of constitutional difference  on the whole machinery of life  
Man selects only for his own good  Nature only for that of the being which
she tends   Every selected character is fully exercised by her  as is
implied by the fact of their selection   Man keeps the natives of many
climates in the same country   He seldom exercises each selected character
in some peculiar and fitting manner  he feeds a long and a short beaked
pigeon on the same food  he does not exercise a long backed or long legged
quadruped in any peculiar manner  he exposes sheep with long and short wool
to the same climate  does not allow the most vigorous males to struggle for
the females  he does not rigidly destroy all inferior animals  but protects
during each varying season  as far as lies in his power  all his
productions   He often begins his selection by some half monstrous form  or
at least by some modification prominent enough to catch the eye or to be
plainly useful to him   Under nature  the slightest differences of
structure or constitution may well turn the nicely balanced scale in the
struggle for life  and so be preserved   How fleeting are the wishes and
efforts of man  How short his time  and consequently how poor will be his
results  compared with those accumulated by Nature during whole geological
periods   Can we wonder  then  that Nature s productions should be far
 truer  in character than man s productions  that they should be infinitely
better adapted to the most complex conditions of life  and should plainly
bear the stamp of far higher workmanship 

It may metaphorically be said that natural selection is daily and hourly
scrutinising  throughout the world  the slightest variations  rejecting
those that are bad  preserving and adding up all that are good  silently
and insensibly working  WHENEVER AND WHEREVER OPPORTUNITY OFFERS  at the
improvement of each organic being in relation to its organic and inorganic
conditions of life   We see nothing of these slow changes in progress 
until the hand of time has marked the long lapse of ages  and then so
imperfect is our view into long past geological ages that we see only that
the forms of life are now different from what they formerly were 

In order that any great amount of modification should be effected in a
species  a variety  when once formed must again  perhaps after a long
interval of time  vary or present individual differences of the same
favourable nature as before  and these must again be preserved  and so
onward  step by step   Seeing that individual differences of the same kind
perpetually recur  this can hardly be considered as an unwarrantable
assumption   But whether it is true  we can judge only by seeing how far
the hypothesis accords with and explains the general phenomena of nature 
On the other hand  the ordinary belief that the amount of possible
variation is a strictly limited quantity  is likewise a simple assumption 

Although natural selection can act only through and for the good of each
being  yet characters and structures  which we are apt to consider as of
very trifling importance  may thus be acted on   When we see leaf eating
insects green  and bark feeders mottled grey  the alpine ptarmigan white in
winter  the red grouse the colour of heather  we must believe that these
tints are of service to these birds and insects in preserving them from
danger   Grouse  if not destroyed at some period of their lives  would
increase in countless numbers  they are known to suffer largely from birds
of prey  and hawks are guided by eyesight to their prey   so much so that
on parts of the continent persons are warned not to keep white pigeons  as
being the most liable to destruction   Hence natural selection might be
effective in giving the proper colour to each kind of grouse  and in
keeping that colour  when once acquired  true and constant   Nor ought we
to think that the occasional destruction of an animal of any particular
colour would produce little effect  we should remember how essential it is
in a flock of white sheep to destroy a lamb with the faintest trace of
black   We have seen how the colour of hogs  which feed on the  paint root 
in Virginia  determines whether they shall live or die   In plants  the
down on the fruit and the colour of the flesh are considered by botanists
as characters of the most trifling importance  yet we hear from an
excellent horticulturist  Downing  that in the United States smooth skinned
fruits suffer far more from a beetle  a Curculio  than those with down 
that purple plums suffer far more from a certain disease than yellow plums 
whereas another disease attacks yellow fleshed peaches far more than those
with other coloured flesh   If  with all the aids of art  these slight
differences make a great difference in cultivating the several varieties 
assuredly  in a state of nature  where the trees would have to struggle
with other trees and with a host of enemies  such differences would
effectually settle which variety  whether a smooth or downy  a yellow or a
purple fleshed fruit  should succeed 

In looking at many small points of difference between species  which  as
far as our ignorance permits us to judge  seem quite unimportant  we must
not forget that climate  food  etc   have no doubt produced some direct
effect   It is also necessary to bear in mind that  owing to the law of
correlation  when one part varies and the variations are accumulated
through natural selection  other modifications  often of the most
unexpected nature  will ensue 

As we see that those variations which  under domestication  appear at any
particular period of life  tend to reappear in the offspring at the same
period  for instance  in the shape  size and flavour of the seeds of the
many varieties of our culinary and agricultural plants  in the caterpillar
and cocoon stages of the varieties of the silkworm  in the eggs of poultry 
and in the colour of the down of their chickens  in the horns of our sheep
and cattle when nearly adult  so in a state of nature natural selection
will be enabled to act on and modify organic beings at any age  by the
accumulation of variations profitable at that age  and by their inheritance
at a corresponding age   If it profit a plant to have its seeds more and
more widely disseminated by the wind  I can see no greater difficulty in
this being effected through natural selection  than in the cotton planter
increasing and improving by selection the down in the pods on his
cotton trees   Natural selection may modify and adapt the larva of an
insect to a score of contingencies  wholly different from those which
concern the mature insect  and these modifications may affect  through
correlation  the structure of the adult   So  conversely  modifications in
the adult may affect the structure of the larva  but in all cases natural
selection will ensure that they shall not be injurious   for if they were
so  the species would become extinct 

Natural selection will modify the structure of the young in relation to the
parent and of the parent in relation to the young   In social animals it
will adapt the structure of each individual for the benefit of the whole
community  if the community profits by the selected change   What natural
selection cannot do  is to modify the structure of one species  without
giving it any advantage  for the good of another species  and though
statements to this effect may be found in works of natural history  I
cannot find one case which will bear investigation   A structure used only
once in an animal s life  if of high importance to it  might be modified to
any extent by natural selection  for instance  the great jaws possessed by
certain insects  used exclusively for opening the cocoon  or the hard tip
to the beak of unhatched birds  used for breaking the eggs   It has been
asserted  that of the best short beaked tumbler pigeons a greater number
perish in the egg than are able to get out of it  so that fanciers assist
in the act of hatching   Now  if nature had to make the beak of a
full grown pigeon very short for the bird s own advantage  the process of
modification would be very slow  and there would be simultaneously the most
rigorous selection of all the young birds within the egg  which had the
most powerful and hardest beaks  for all with weak beaks would inevitably
perish   or  more delicate and more easily broken shells might be selected 
the thickness of the shell being known to vary like every other structure 

It may be well here to remark that with all beings there must be much
fortuitous destruction  which can have little or no influence on the course
of natural selection   For instance  a vast number of eggs or seeds are
annually devoured  and these could be modified through natural selection
only if they varied in some manner which protected them from their enemies 
Yet many of these eggs or seeds would perhaps  if not destroyed  have
yielded individuals better adapted to their conditions of life than any of
those which happened to survive   So again a vast number of mature animals
and plants  whether or not they be the best adapted to their conditions 
must be annually destroyed by accidental causes  which would not be in the
least degree mitigated by certain changes of structure or constitution
which would in other ways be beneficial to the species   But let the
destruction of the adults be ever so heavy  if the number which can exist
in any district be not wholly kept down by such causes  or again let the
destruction of eggs or seeds be so great that only a hundredth or a
thousandth part are developed  yet of those which do survive  the best
adapted individuals  supposing that there is any variability in a
favourable direction  will tend to propagate their kind in larger numbers
than the less well adapted   If the numbers be wholly kept down by the
causes just indicated  as will often have been the case  natural selection
will be powerless in certain beneficial directions  but this is no valid
objection to its efficiency at other times and in other ways  for we are
far from having any reason to suppose that many species ever undergo
modification and improvement at the same time in the same area 

SEXUAL SELECTION 

Inasmuch as peculiarities often appear under domestication in one sex and
become hereditarily attached to that sex  so no doubt it will be under
nature   Thus it is rendered possible for the two sexes to be modified
through natural selection in relation to different habits of life  as is
sometimes the case  or for one sex to be modified in relation to the other
sex  as commonly occurs   This leads me to say a few words on what I have
called sexual selection   This form of selection depends  not on a struggle
for existence in relation to other organic beings or to external
conditions  but on a struggle between the individuals of one sex  generally
the males  for the possession of the other sex   The result is not death to
the unsuccessful competitor  but few or no offspring   Sexual selection is 
therefore  less rigorous than natural selection   Generally  the most
vigorous males  those which are best fitted for their places in nature 
will leave most progeny   But in many cases victory depends not so much on
general vigour  but on having special weapons  confined to the male sex   A
hornless stag or spurless cock would have a poor chance of leaving numerous
offspring   Sexual selection  by always allowing the victor to breed  might
surely give indomitable courage  length of spur  and strength to the wing
to strike in the spurred leg  in nearly the same manner as does the brutal
cockfighter by the careful selection of his best cocks   How low in the
scale of nature the law of battle descends I know not  male alligators have
been described as fighting  bellowing  and whirling round  like Indians in
a war dance  for the possession of the females  male salmons have been
observed fighting all day long  male stag beetles sometimes bear wounds
from the huge mandibles of other males  the males of certain hymenopterous
insects have been frequently seen by that inimitable observer M  Fabre 
fighting for a particular female who sits by  an apparently unconcerned
beholder of the struggle  and then retires with the conqueror   The war is 
perhaps  severest between the males of polygamous animals  and these seem
oftenest provided with special weapons   The males of carnivorous animals
are already well armed  though to them and to others  special means of
defence may be given through means of sexual selection  as the mane of the
lion  and the hooked jaw to the male salmon  for the shield may be as
important for victory as the sword or spear 

Among birds  the contest is often of a more peaceful character   All those
who have attended to the subject  believe that there is the severest
rivalry between the males of many species to attract  by singing  the
females   The rock thrush of Guiana  birds of paradise  and some others 
congregate  and successive males display with the most elaborate care  and
show off in the best manner  their gorgeous plumage  they likewise perform
strange antics before the females  which  standing by as spectators  at
last choose the most attractive partner   Those who have closely attended
to birds in confinement well know that they often take individual
preferences and dislikes   thus Sir R  Heron has described how a pied
peacock was eminently attractive to all his hen birds   I cannot here enter
on the necessary details  but if man can in a short time give beauty and an
elegant carriage to his bantams  according to his standard of beauty  I can
see no good reason to doubt that female birds  by selecting  during
thousands of generations  the most melodious or beautiful males  according
to their standard of beauty  might produce a marked effect   Some
well known laws  with respect to the plumage of male and female birds  in
comparison with the plumage of the young  can partly be explained through
the action of sexual selection on variations occurring at different ages 
and transmitted to the males alone or to both sexes at corresponding ages 
but I have not space here to enter on this subject 

Thus it is  as I believe  that when the males and females of any animal
have the same general habits of life  but differ in structure  colour  or
ornament  such differences have been mainly caused by sexual selection  
that is  by individual males having had  in successive generations  some
slight advantage over other males  in their weapons  means of defence  or
charms  which they have transmitted to their male offspring alone   Yet  I
would not wish to attribute all sexual differences to this agency   for we
see in our domestic animals peculiarities arising and becoming attached to
the male sex  which apparently have not been augmented through selection by
man   The tuft of hair on the breast of the wild turkey cock cannot be of
any use  and it is doubtful whether it can be ornamental in the eyes of the
female bird  indeed  had the tuft appeared under domestication it would
have been called a monstrosity 

ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION  OR THE SURVIVAL OF THE
FITTEST 

In order to make it clear how  as I believe  natural selection acts  I must
beg permission to give one or two imaginary illustrations   Let us take the
case of a wolf  which preys on various animals  securing some by craft 
some by strength  and some by fleetness  and let us suppose that the
fleetest prey  a deer for instance  had from any change in the country
increased in numbers  or that other prey had decreased in numbers  during
that season of the year when the wolf was hardest pressed for food   Under
such circumstances the swiftest and slimmest wolves have the best chance of
surviving  and so be preserved or selected  provided always that they
retained strength to master their prey at this or some other period of the
year  when they were compelled to prey on other animals   I can see no more
reason to doubt that this would be the result  than that man should be able
to improve the fleetness of his greyhounds by careful and methodical
selection  or by that kind of unconscious selection which follows from each
man trying to keep the best dogs without any thought of modifying the
breed   I may add that  according to Mr  Pierce  there are two varieties of
the wolf inhabiting the Catskill Mountains  in the United States  one with
a light greyhound like form  which pursues deer  and the other more bulky 
with shorter legs  which more frequently attacks the shepherd s flocks 

Even without any change in the proportional numbers of the animals on which
our wolf preyed  a cub might be born with an innate tendency to pursue
certain kinds of prey   Nor can this be thought very improbable  for we
often observe great differences in the natural tendencies of our domestic
animals  one cat  for instance  taking to catch rats  another mice  one
cat  according to Mr  St  John  bringing home winged game  another hares or
rabbits  and another hunting on marshy ground and almost nightly catching
woodcocks or snipes   The tendency to catch rats rather than mice is known
to be inherited   Now  if any slight innate change of habit or of structure
benefited an individual wolf  it would have the best chance of surviving
and of leaving offspring   Some of its young would probably inherit the
same habits or structure  and by the repetition of this process  a new
variety might be formed which would either supplant or coexist with the
parent form of wolf   Or  again  the wolves inhabiting a mountainous
district  and those frequenting the lowlands  would naturally be forced to
hunt different prey  and from the continued preservation of the individuals
best fitted for the two sites  two varieties might slowly be formed   These
varieties would cross and blend where they met  but to this subject of
intercrossing we shall soon have to return   I may add  that  according to
Mr  Pierce  there are two varieties of the wolf inhabiting the Catskill
Mountains in the United States  one with a light greyhound like form  which
pursues deer  and the other more bulky  with shorter legs  which more
frequently attacks the shepherd s flocks 

It should be observed that in the above illustration  I speak of the
slimmest individual wolves  and not of any single strongly marked variation
having been preserved   In former editions of this work I sometimes spoke
as if this latter alternative had frequently occurred   I saw the great
importance of individual differences  and this led me fully to discuss the
results of unconscious selection by man  which depends on the preservation
of all the more or less valuable individuals  and on the destruction of the
worst   I saw  also  that the preservation in a state of nature of any
occasional deviation of structure  such as a monstrosity  would be a rare
event  and that  if at first preserved  it would generally be lost by
subsequent intercrossing with ordinary individuals   Nevertheless  until
reading an able and valuable article in the  North British Review   1867  
I did not appreciate how rarely single variations  whether slight or
strongly marked  could be perpetuated   The author takes the case of a pair
of animals  producing during their lifetime two hundred offspring  of
which  from various causes of destruction  only two on an average survive
to pro create their kind   This is rather an extreme estimate for most of
the higher animals  but by no means so for many of the lower organisms   He
then shows that if a single individual were born  which varied in some
manner  giving it twice as good a chance of life as that of the other
individuals  yet the chances would be strongly against its survival  
Supposing it to survive and to breed  and that half its young inherited the
favourable variation  still  as the Reviewer goes onto show  the young
would have only a slightly better chance of surviving and breeding  and
this chance would go on decreasing in the succeeding generations   The
justice of these remarks cannot  I think  be disputed   If  for instance  a
bird of some kind could procure its food more easily by having its beak
curved  and if one were born with its beak strongly curved  and which
consequently flourished  nevertheless there would be a very poor chance of
this one individual perpetuating its kind to the exclusion of the common
form  but there can hardly be a doubt  judging by what we see taking place
under domestication  that this result would follow from the preservation
during many generations of a large number of individuals with more or less
strongly curved beaks  and from the destruction of a still larger number
with the straightest beaks 

It should not  however  be overlooked that certain rather strongly marked
variations  which no one would rank as mere individual differences 
frequently recur owing to a similar organisation being similarly acted on  
of which fact numerous instances could be given with our domestic
productions   In such cases  if the varying individual did not actually
transmit to its offspring its newly acquired character  it would
undoubtedly transmit to them  as long as the existing conditions remained
the same  a still stronger tendency to vary in the same manner   There can
also be little doubt that the tendency to vary in the same manner has often
been so strong that all the individuals of the same species have been
similarly modified without the aid of any form of selection   Or only a
third  fifth  or tenth part of the individuals may have been thus affected 
of which fact several instances could be given   Thus Graba estimates that
about one fifth of the guillemots in the Faroe Islands consist of a variety
so well marked  that it was formerly ranked as a distinct species under the
name of Uria lacrymans   In cases of this kind  if the variation were of a
beneficial nature  the original form would soon be supplanted by the
modified form  through the survival of the fittest 

To the effects of intercrossing in eliminating variations of all kinds  I
shall have to recur  but it may be here remarked that most animals and
plants keep to their proper homes  and do not needlessly wander about  we
see this even with migratory birds  which almost always return to the same
spot   Consequently each newly formed variety would generally be at first
local  as seems to be the common rule with varieties in a state of nature 
so that similarly modified individuals would soon exist in a small body
together  and would often breed together   If the new variety were
successful in its battle for life  it would slowly spread from a central
district  competing with and conquering the unchanged individuals on the
margins of an ever increasing circle 

It may be worth while to give another and more complex illustration of the
action of natural selection   Certain plants excrete sweet juice 
apparently for the sake of eliminating something injurious from the sap  
this is effected  for instance  by glands at the base of the stipules in
some Leguminosae  and at the backs of the leaves of the common laurel  
This juice  though small in quantity  is greedily sought by insects  but
their visits do not in any way benefit the plant   Now  let us suppose that
the juice or nectar was excreted from the inside of the flowers of a
certain number of plants of any species   Insects in seeking the nectar
would get dusted with pollen  and would often transport it from one flower
to another   The flowers of two distinct individuals of the same species
would thus get crossed  and the act of crossing  as can be fully proved 
gives rise to vigorous seedlings  which consequently would have the best
chance of flourishing and surviving   The plants which produced flowers
with the largest glands or nectaries  excreting most nectar  would oftenest
be visited by insects  and would oftenest be crossed  and so in the
long run would gain the upper hand and form a local variety   The flowers 
also  which had their stamens and pistils placed  in relation to the size
and habits of the particular insect which visited them  so as to favour in
any degree the transportal of the pollen  would likewise be favoured   We
might have taken the case of insects visiting flowers for the sake of
collecting pollen instead of nectar  and as pollen is formed for the sole
purpose of fertilisation  its destruction appears to be a simple loss to
the plant  yet if a little pollen were carried  at first occasionally and
then habitually  by the pollen devouring insects from flower to flower  and
a cross thus effected  although nine tenths of the pollen were destroyed it
might still be a great gain to the plant to be thus robbed  and the
individuals which produced more and more pollen  and had larger anthers 
would be selected 

When our plant  by the above process long continued  had been rendered
highly attractive to insects  they would  unintentionally on their part 
regularly carry pollen from flower to flower  and that they do this
effectually I could easily show by many striking facts   I will give only
one  as likewise illustrating one step in the separation of the sexes of
plants   Some holly trees bear only male flowers  which have four stamens
producing a rather small quantity of pollen  and a rudimentary pistil 
other holly trees bear only female flowers  these have a full sized pistil 
and four stamens with shrivelled anthers  in which not a grain of pollen
can be detected   Having found a female tree exactly sixty yards from a
male tree  I put the stigmas of twenty flowers  taken from different
branches  under the microscope  and on all  without exception  there were a
few pollen grains  and on some a profusion   As the wind had set for
several days from the female to the male tree  the pollen could not thus
have been carried   The weather had been cold and boisterous and therefore
not favourable to bees  nevertheless every female flower which I examined
had been effectually fertilised by the bees  which had flown from tree to
tree in search of nectar   But to return to our imaginary case  as soon as
the plant had been rendered so highly attractive to insects that pollen was
regularly carried from flower to flower  another process might commence  
No naturalist doubts the advantage of what has been called the
 physiological division of labour   hence we may believe that it would be
advantageous to a plant to produce stamens alone in one flower or on one
whole plant  and pistils alone in another flower or on another plant   In
plants under culture and placed under new conditions of life  sometimes the
male organs and sometimes the female organs become more or less impotent 
now if we suppose this to occur in ever so slight a degree under nature 
then  as pollen is already carried regularly from flower to flower  and as
a more complete separation of the sexes of our plant would be advantageous
on the principle of the division of labour  individuals with this tendency
more and more increased  would be continually favoured or selected  until
at last a complete separation of the sexes might be effected   It would
take up too much space to show the various steps  through dimorphism and
other means  by which the separation of the sexes in plants of various
kinds is apparently now in progress  but I may add that some of the species
of holly in North America are  according to Asa Gray  in an exactly
intermediate condition  or  as he expresses it  are more or less
dioeciously polygamous 

Let us now turn to the nectar feeding insects  we may suppose the plant of
which we have been slowly increasing the nectar by continued selection  to
be a common plant  and that certain insects depended in main part on its
nectar for food   I could give many facts showing how anxious bees are to
save time   for instance  their habit of cutting holes and sucking the
nectar at the bases of certain flowers  which with a very little more
trouble they can enter by the mouth   Bearing such facts in mind  it may be
believed that under certain circumstances individual differences in the
curvature or length of the proboscis  etc   too slight to be appreciated by
us  might profit a bee or other insect  so that certain individuals would
be able to obtain their food more quickly than others  and thus the
communities to which they belonged would flourish and throw off many swarms
inheriting the same peculiarities   The tubes of the corolla of the common
red or incarnate clovers  Trifolium pratense and incarnatum  do not on a
hasty glance appear to differ in length  yet the hive bee can easily suck
the nectar out of the incarnate clover  but not out of the common red
clover  which is visited by humble bees alone  so that whole fields of the
red clover offer in vain an abundant supply of precious nectar to the
hive bee   That this nectar is much liked by the hive bee is certain  for I
have repeatedly seen  but only in the autumn  many hive bees sucking the
flowers through holes bitten in the base of the tube by humble bees   The
difference in the length of the corolla in the two kinds of clover  which
determines the visits of the hive bee  must be very trifling  for I have
been assured that when red clover has been mown  the flowers of the second
crop are somewhat smaller  and that these are visited by many hive bees   I
do not know whether this statement is accurate  nor whether another
published statement can be trusted  namely  that the Ligurian bee  which is
generally considered a mere variety of the common hive bee  and which
freely crosses with it  is able to reach and suck the nectar of the red
clover   Thus  in a country where this kind of clover abounded  it might be
a great advantage to the hive bee to have a slightly longer or differently
constructed proboscis   On the other hand  as the fertility of this clover
absolutely depends on bees visiting the flowers  if humble bees were to
become rare in any country  it might be a great advantage to the plant to
have a shorter or more deeply divided corolla  so that the hive bees should
be enabled to suck its flowers   Thus I can understand how a flower and a
bee might slowly become  either simultaneously or one after the other 
modified and adapted to each other in the most perfect manner  by the
continued preservation of all the individuals which presented slight
deviations of structure mutually favourable to each other 

I am well aware that this doctrine of natural selection  exemplified in the
above imaginary instances  is open to the same objections which were first
urged against Sir Charles Lyell s noble views on  the modern changes of the
earth  as illustrative of geology   but we now seldom hear the agencies
which we see still at work  spoken of as trifling and insignificant  when
used in explaining the excavation of the deepest valleys or the formation
of long lines of inland cliffs   Natural selection acts only by the
preservation and accumulation of small inherited modifications  each
profitable to the preserved being  and as modern geology has almost
banished such views as the excavation of a great valley by a single
diluvial wave  so will natural selection banish the belief of the continued
creation of new organic beings  or of any great and sudden modification in
their structure 

ON THE INTERCROSSING OF INDIVIDUALS 

I must here introduce a short digression   In the case of animals and
plants with separated sexes  it is of course obvious that two individuals
must always  with the exception of the curious and not well understood
cases of parthenogenesis  unite for each birth  but in the case of
hermaphrodites this is far from obvious   Nevertheless there is reason to
believe that with all hermaphrodites two individuals  either occasionally
or habitually  concur for the reproduction of their kind   This view was
long ago doubtfully suggested by Sprengel  Knight and Kolreuter   We shall
presently see its importance  but I must here treat the subject with
extreme brevity  though I have the materials prepared for an ample
discussion   All vertebrate animals  all insects and some other large
groups of animals  pair for each birth   Modern research has much
diminished the number of supposed hermaphrodites and of real hermaphrodites
a large number pair  that is  two individuals regularly unite for
reproduction  which is all that concerns us   But still there are many
hermaphrodite animals which certainly do not habitually pair  and a vast
majority of plants are hermaphrodites   What reason  it may be asked  is
there for supposing in these cases that two individuals ever concur in
reproduction   As it is impossible here to enter on details  I must trust
to some general considerations alone 

In the first place  I have collected so large a body of facts  and made so
many experiments  showing  in accordance with the almost universal belief
of breeders  that with animals and plants a cross between different
varieties  or between individuals of the same variety but of another
strain  gives vigour and fertility to the offspring  and on the other hand 
that CLOSE interbreeding diminishes vigour and fertility  that these facts
alone incline me to believe that it is a general law of nature that no
organic being fertilises itself for a perpetuity of generations  but that a
cross with another individual is occasionally  perhaps at long intervals of
time  indispensable 

On the belief that this is a law of nature  we can  I think  understand
several large classes of facts  such as the following  which on any other
view are inexplicable   Every hybridizer knows how unfavourable exposure to
wet is to the fertilisation of a flower  yet what a multitude of flowers
have their anthers and stigmas fully exposed to the weather   If an
occasional cross be indispensable  notwithstanding that the plant s own
anthers and pistil stand so near each other as almost to ensure self 
fertilisation  the fullest freedom for the entrance of pollen from another
individual will explain the above state of exposure of the organs   Many
flowers  on the other hand  have their organs of fructification closely
enclosed  as in the great papilionaceous or pea family  but these almost
invariably present beautiful and curious adaptations in relation to the
visits of insects   So necessary are the visits of bees to many
papilionaceous flowers  that their fertility is greatly diminished if these
visits be prevented   Now  it is scarcely possible for insects to fly from
flower to flower  and not to carry pollen from one to the other  to the
great good of the plant   Insects act like a camel hair pencil  and it is
sufficient  to ensure fertilisation  just to touch with the same brush the
anthers of one flower and then the stigma of another  but it must not be
supposed that bees would thus produce a multitude of hybrids between
distinct species  for if a plant s own pollen and that from another species
are placed on the same stigma  the former is so prepotent that it
invariably and completely destroys  as has been shown by Gartner  the
influence of the foreign pollen 

When the stamens of a flower suddenly spring towards the pistil  or slowly
move one after the other towards it  the contrivance seems adapted solely
to ensure self fertilisation  and no doubt it is useful for this end   but
the agency of insects is often required to cause the stamens to spring
forward  as Kolreuter has shown to be the case with the barberry  and in
this very genus  which seems to have a special contrivance for
self fertilisation  it is well known that  if closely allied forms or
varieties are planted near each other  it is hardly possible to raise pure
seedlings  so largely do they naturally cross   In numerous other cases 
far from self fertilisation being favoured  there are special contrivances
which effectually prevent the stigma receiving pollen from its own flower 
as I could show from the works of Sprengel and others  as well as from my
own observations   for instance  in Lobelia fulgens  there is a really
beautiful and elaborate contrivance by which all the infinitely numerous
pollen granules are swept out of the conjoined anthers of each flower 
before the stigma of that individual flower is ready to receive them  and
as this flower is never visited  at least in my garden  by insects  it
never sets a seed  though by placing pollen from one flower on the stigma
of another  I raise plenty of seedlings   Another species of Lobelia  which
is visited by bees  seeds freely in my garden   In very many other cases 
though there is no special mechanical contrivance to prevent the stigma
receiving pollen from the same flower  yet  as Sprengel  and more recently
Hildebrand and others have shown  and as I can confirm  either the anthers
burst before the stigma is ready for fertilisation  or the stigma is ready
before the pollen of that flower is ready  so that these so named
dichogamous plants have in fact separated sexes  and must habitually be
crossed   So it is with the reciprocally dimorphic and trimorphic plants
previously alluded to   How strange are these facts   How strange that the
pollen and stigmatic surface of the same flower  though placed so close
together  as if for the very purpose of self fertilisation  should be in so
many cases mutually useless to each other   How simply are these facts
explained on the view of an occasional cross with a distinct individual
being advantageous or indispensable 

If several varieties of the cabbage  radish  onion  and of some other
plants  be allowed to seed near each other  a large majority of the
seedlings thus raised turn out  as I found  mongrels   for instance  I
raised 233 seedling cabbages from some plants of different varieties
growing near each other  and of these only 78 were true to their kind  and
some even of these were not perfectly true   Yet the pistil of each
cabbage flower is surrounded not only by its own six stamens but by those
of the many other flowers on the same plant  and the pollen of each flower
readily gets on its stigma without insect agency  for I have found that
plants carefully protected from insects produce the full number of pods  
How  then  comes it that such a vast number of the seedlings are
mongrelized   It must arise from the pollen of a distinct VARIETY having a
prepotent effect over the flower s own pollen  and that this is part of the
general law of good being derived from the intercrossing of distinct
individuals of the same species   When distinct SPECIES are crossed the
case is reversed  for a plant s own pollen is always prepotent over foreign
pollen  but to this subject we shall return in a future chapter 

In the case of a large tree covered with innumerable flowers  it may be
objected that pollen could seldom be carried from tree to tree  and at most
only from flower to flower on the same tree  and flowers on the same tree
can be considered as distinct individuals only in a limited sense   I
believe this objection to be valid  but that nature has largely provided
against it by giving to trees a strong tendency to bear flowers with
separated sexes   When the sexes are separated  although the male and
female flowers may be produced on the same tree  pollen must be regularly
carried from flower to flower  and this will give a better chance of pollen
being occasionally carried from tree to tree   That trees belonging to all
orders have their sexes more often separated than other plants  I find to
be the case in this country  and at my request Dr  Hooker tabulated the
trees of New Zealand  and Dr  Asa Gray those of the United States  and the
result was as I anticipated   On the other hand  Dr  Hooker informs me that
the rule does not hold good in Australia   but if most of the Australian
trees are dichogamous  the same result would follow as if they bore flowers
with separated sexes   I have made these few remarks on trees simply to
call attention to the subject 

Turning for a brief space to animals   various terrestrial species are
hermaphrodites  such as the land mollusca and earth worms  but these all
pair   As yet I have not found a single terrestrial animal which can
fertilise itself   This remarkable fact  which offers so strong a contrast
with terrestrial plants  is intelligible on the view of an occasional cross
being indispensable  for owing to the nature of the fertilising element
there are no means  analogous to the action of insects and of the wind with
plants  by which an occasional cross could be effected with terrestrial
animals without the concurrence of two individuals   Of aquatic animals 
there are many self fertilising hermaphrodites  but here the currents of
water offer an obvious means for an occasional cross   As in the case of
flowers  I have as yet failed  after consultation with one of the highest
authorities  namely  Professor Huxley  to discover a single hermaphrodite
animal with the organs of reproduction so perfectly enclosed that access
from without  and the occasional influence of a distinct individual  can be
shown to be physically impossible   Cirripedes long appeared to me to
present  under this point of view  a case of great difficulty  but I have
been enabled  by a fortunate chance  to prove that two individuals  though
both are self fertilising hermaphrodites  do sometimes cross 

It must have struck most naturalists as a strange anomaly that  both with
animals and plants  some species of the same family and even of the same
genus  though agreeing closely with each other in their whole organisation 
are hermaphrodites  and some unisexual   But if  in fact  all
hermaphrodites do occasionally intercross  the difference between them and
unisexual species is  as far as function is concerned  very small 

 From these several considerations and from the many special facts which I
have collected  but which I am unable here to give  it appears that with
animals and plants an occasional intercross between distinct individuals is
a very general  if not universal  law of nature  

CIRCUMSTANCES FAVOURABLE FOR THE PRODUCTION OF NEW FORMS THROUGH NATURAL
SELECTION 

This is an extremely intricate subject   A great amount of variability 
under which term individual differences are always included  will evidently
be favourable   A large number of individuals  by giving a better chance
within any given period for the appearance of profitable variations  will
compensate for a lesser amount of variability in each individual  and is  I
believe  a highly important element of success   Though nature grants long
periods of time for the work of natural selection  she does not grant an
indefinite period  for as all organic beings are striving to seize on each
place in the economy of nature  if any one species does not become modified
and improved in a corresponding degree with its competitors it will be
exterminated   Unless favourable variations be inherited by some at least
of the offspring  nothing can be effected by natural selection   The
tendency to reversion may often check or prevent the work  but as this
tendency has not prevented man from forming by selection numerous domestic
races  why should it prevail against natural selection 

In the case of methodical selection  a breeder selects for some definite
object  and if the individuals be allowed freely to intercross  his work
will completely fail   But when many men  without intending to alter the
breed  have a nearly common standard of perfection  and all try to procure
and breed from the best animals  improvement surely but slowly follows from
this unconscious process of selection  notwithstanding that there is no
separation of selected individuals   Thus it will be under nature  for
within a confined area  with some place in the natural polity not perfectly
occupied   all the individuals varying in the right direction  though in
different degrees  will tend to be preserved   But if the area be large 
its several districts will almost certainly present different conditions of
life  and then  if the same species undergoes modification in different
districts  the newly formed varieties will intercross on the confines of
each   But we shall see in the sixth chapter that intermediate varieties 
inhabiting intermediate districts  will in the long run generally be
supplanted by one of the adjoining varieties   Intercrossing will chiefly
affect those animals which unite for each birth and wander much  and which
do not breed at a very quick rate   Hence with animals of this nature  for
instance birds  varieties will generally be confined to separated
countries  and this I find to be the case   With hermaphrodite organisms
which cross only occasionally  and likewise with animals which unite for
each birth  but which wander little and can increase at a rapid rate  a new
and improved variety might be quickly formed on any one spot  and might
there maintain itself in a body and afterward spread  so that the
individuals of the new variety would chiefly cross together   On this
principle nurserymen always prefer saving seed from a large body of plants 
as the chance of intercrossing is thus lessened 

Even with animals which unite for each birth  and which do not propagate
rapidly  we must not assume that free intercrossing would always eliminate
the effects of natural selection  for I can bring forward a considerable
body of facts showing that within the same area two varieties of the same
animal may long remain distinct  from haunting different stations  from
breeding at slightly different seasons  or from the individuals of each
variety preferring to pair together 

Intercrossing plays a very important part in nature by keeping the
individuals of the same species  or of the same variety  true and uniform
in character   It will obviously thus act far more efficiently with those
animals which unite for each birth  but  as already stated  we have reason
to believe that occasional intercrosses take place with all animals and
plants   Even if these take place only at long intervals of time  the young
thus produced will gain so much in vigour and fertility over the offspring
from long continued self fertilisation  that they will have a better chance
of surviving and propagating their kind  and thus in the long run the
influence of crosses  even at rare intervals  will be great   With respect
to organic beings extremely low in the scale  which do not propagate
sexually  nor conjugate  and which cannot possibly intercross  uniformity
of character can be retained by them under the same conditions of life 
only through the principle of inheritance  and through natural selection
which will destroy any individuals departing from the proper type   If the
conditions of life change and the form undergoes modification  uniformity
of character can be given to the modified offspring  solely by natural
selection preserving similar favourable variations 

Isolation also is an important element in the modification of species
through natural selection   In a confined or isolated area  if not very
large  the organic and inorganic conditions of life will generally be
almost uniform  so that natural selection will tend to modify all the
varying individuals of the same species in the same manner   Intercrossing
with the inhabitants of the surrounding districts  will also be thus
prevented   Moritz Wagner has lately published an interesting essay on this
subject  and has shown that the service rendered by isolation in preventing
crosses between newly formed varieties is probably greater even than I
supposed   But from reasons already assigned I can by no means agree with
this naturalist  that migration and isolation are necessary elements for
the formation of new species   The importance of isolation is likewise
great in preventing  after any physical change in the conditions  such as
of climate  elevation of the land  etc   the immigration of better adapted
organisms  and thus new places in the natural economy of the district will
be left open to be filled up by the modification of the old inhabitants   
Lastly  isolation will give time for a new variety to be improved at a slow
rate  and this may sometimes be of much importance   If  however  an
isolated area be very small  either from being surrounded by barriers  or
from having very peculiar physical conditions  the total number of the
inhabitants will be small  and this will retard the production of new
species through natural selection  by decreasing the chances of favourable
variations arising 

The mere lapse of time by itself does nothing  either for or against
natural selection   I state this because it has been erroneously asserted
that the element of time has been assumed by me to play an all important
part in modifying species  as if all the forms of life were necessarily
undergoing change through some innate law   Lapse of time is only so far
important  and its importance in this respect is great  that it gives a
better chance of beneficial variations arising and of their being selected 
accumulated  and fixed   It likewise tends to increase the direct action of
the physical conditions of life  in relation to the constitution of each
organism 

If we turn to nature to test the truth of these remarks  and look at any
small isolated area  such as an oceanic island  although the number of the
species inhabiting it is small  as we shall see in our chapter on
Geographical Distribution  yet of these species a very large proportion are
endemic   that is  have been produced there and nowhere else in the world  
Hence an oceanic island at first sight seems to have been highly favourable
for the production of new species   But we may thus deceive ourselves  for
to ascertain whether a small isolated area  or a large open area like a
continent  has been most favourable for the production of new organic
forms  we ought to make the comparison within equal times  and this we are
incapable of doing 

Although isolation is of great importance in the production of new species 
on the whole I am inclined to believe that largeness of area is still more
important  especially for the production of species which shall prove
capable of enduring for a long period  and of spreading widely   Throughout
a great and open area  not only will there be a better chance of favourable
variations  arising from the large number of individuals of the same
species there supported  but the conditions of life are much more complex
from the large number of already existing species  and if some of these
many species become modified and improved  others will have to be improved
in a corresponding degree  or they will be exterminated   Each new form 
also  as soon as it has been much improved  will be able to spread over the
open and continuous area  and will thus come into competition with many
other forms   Moreover  great areas  though now continuous  will often 
owing to former oscillations of level  have existed in a broken condition 
so that the good effects of isolation will generally  to a certain extent 
have concurred   Finally  I conclude that  although small isolated areas
have been in some respects highly favourable for the production of new
species  yet that the course of modification will generally have been more
rapid on large areas  and what is more important  that the new forms
produced on large areas  which already have been victorious over many
competitors  will be those that will spread most widely  and will give rise
to the greatest number of new varieties and species   They will thus play a
more important part in the changing history of the organic world 

In accordance with this view  we can  perhaps  understand some facts which
will be again alluded to in our chapter on Geographical Distribution  for
instance  the fact of the productions of the smaller continent of Australia
now yielding before those of the larger Europaeo Asiatic area   Thus  also 
it is that continental productions have everywhere become so largely
naturalised on islands   On a small island  the race for life will have
been less severe  and there will have been less modification and less
extermination   Hence  we can understand how it is that the flora of
Madeira  according to Oswald Heer  resembles to a certain extent the
extinct tertiary flora of Europe   All fresh water basins  taken together 
make a small area compared with that of the sea or of the land  
Consequently  the competition between fresh water productions will have
been less severe than elsewhere  new forms will have been more slowly
produced  and old forms more slowly exterminated   And it is in fresh water
basins that we find seven genera of Ganoid fishes  remnants of a once
preponderant order   and in fresh water we find some of the most anomalous
forms now known in the world  as the Ornithorhynchus and Lepidosiren 
which  like fossils  connect to a certain extent orders at present widely
separated in the natural scale   These anomalous forms may be called living
fossils  they have endured to the present day  from having inhabited a
confined area  and from having been exposed to less varied  and therefore
less severe  competition 

To sum up  as far as the extreme intricacy of the subject permits  the
circumstances favourable and unfavourable for the production of new species
through natural selection   I conclude that for terrestrial productions a
large continental area  which has undergone many oscillations of level 
will have been the most favourable for the production of many new forms of
life  fitted to endure for a long time and to spread widely   While the
area existed as a continent the inhabitants will have been numerous in
individuals and kinds  and will have been subjected to severe competition  
When converted by subsidence into large separate islands there will still
have existed many individuals of the same species on each island  
intercrossing on the confines of the range of each new species will have
been checked   after physical changes of any kind immigration will have
been prevented  so that new places in the polity of each island will have
had to be filled up by the modification of the old inhabitants  and time
will have been allowed for the varieties in each to become well modified
and perfected   When  by renewed elevation  the islands were reconverted
into a continental area  there will again have been very severe
competition  the most favoured or improved varieties will have been enabled
to spread  there will have been much extinction of the less improved forms 
and the relative proportional numbers of the various inhabitants of the
reunited continent will again have been changed  and again there will have
been a fair field for natural selection to improve still further the
inhabitants  and thus to produce new species 

That natural selection generally act with extreme slowness I fully admit  
It can act only when there are places in the natural polity of a district
which can be better occupied by the modification of some of its existing
inhabitants   The occurrence of such places will often depend on physical
changes  which generally take place very slowly  and on the immigration of
better adapted forms being prevented   As some few of the old inhabitants
become modified the mutual relations of others will often be disturbed  and
this will create new places  ready to be filled up by better adapted forms 
but all this will take place very slowly   Although all the individuals of
the same species differ in some slight degree from each other  it would
often be long before differences of the right nature in various parts of
the organisation might occur   The result would often be greatly retarded
by free intercrossing   Many will exclaim that these several causes are
amply sufficient to neutralise the power of natural selection   I do not
believe so   But I do believe that natural selection will generally act
very slowly  only at long intervals of time  and only on a few of the
inhabitants of the same region   I further believe that these slow 
intermittent results accord well with what geology tells us of the rate and
manner at which the inhabitants of the world have changed 

Slow though the process of selection may be  if feeble man can do much by
artificial selection  I can see no limit to the amount of change  to the
beauty and complexity of the coadaptations between all organic beings  one
with another and with their physical conditions of life  which may have
been effected in the long course of time through nature s power of
selection  that is by the survival of the fittest 

EXTINCTION CAUSED BY NATURAL SELECTION 

This subject will be more fully discussed in our chapter on Geology  but it
must here be alluded to from being intimately connected with natural
selection   Natural selection acts solely through the preservation of
variations in some way advantageous  which consequently endure   Owing to
the high geometrical rate of increase of all organic beings  each area is
already fully stocked with inhabitants  and it follows from this  that as
the favoured forms increase in number  so  generally  will the less
favoured decrease and become rare   Rarity  as geology tells us  is the
precursor to extinction   We can see that any form which is represented by
few individuals will run a good chance of utter extinction  during great
fluctuations in the nature or the seasons  or from a temporary increase in
the number of its enemies   But we may go further than this  for as new
forms are produced  unless we admit that specific forms can go on
indefinitely increasing in number  many old forms must become extinct  
That the number of specific forms has not indefinitely increased  geology
plainly tells us  and we shall presently attempt to show why it is that the
number of species throughout the world has not become immeasurably great 

We have seen that the species which are most numerous in individuals have
the best chance of producing favourable variations within any given period  
We have evidence of this  in the facts stated in the second chapter 
showing that it is the common and diffused or dominant species which offer
the greatest number of recorded varieties   Hence  rare species will be
less quickly modified or improved within any given period  they will
consequently be beaten in the race for life by the modified and improved
descendants of the commoner species 

 From these several considerations I think it inevitably follows  that as
new species in the course of time are formed through natural selection 
others will become rarer and rarer  and finally extinct   The forms which
stand in closest competition with those undergoing modification and
improvement  will naturally suffer most   And we have seen in the chapter
on the Struggle for Existence that it is the most closely allied
forms   varieties of the same species  and species of the same genus or
related genera   which  from having nearly the same structure  constitution
and habits  generally come into the severest competition with each other  
Consequently  each new variety or species  during the progress of its
formation  will generally press hardest on its nearest kindred  and tend to
exterminate them   We see the same process of extermination among our
domesticated productions  through the selection of improved forms by man  
Many curious instances could be given showing how quickly new breeds of
cattle  sheep and other animals  and varieties of flowers  take the place
of older and inferior kinds   In Yorkshire  it is historically known that
the ancient black cattle were displaced by the long horns  and that these
 were swept away by the short horns   I quote the words of an agricultural
writer   as if by some murderous pestilence  

DIVERGENCE OF CHARACTER 

The principle  which I have designated by this term  is of high importance 
and explains  as I believe  several important facts   In the first place 
varieties  even strongly marked ones  though having somewhat of the
character of species  as is shown by the hopeless doubts in many cases how
to rank them  yet certainly differ far less from each other than do good
and distinct species   Nevertheless according to my view  varieties are
species in the process of formation  or are  as I have called them 
incipient species   How  then  does the lesser difference between varieties
become augmented into the greater difference between species   That this
does habitually happen  we must infer from most of the innumerable species
throughout nature presenting well marked differences  whereas varieties 
the supposed prototypes and parents of future well marked species  present
slight and ill defined differences   Mere chance  as we may call it  might
cause one variety to differ in some character from its parents  and the
offspring of this variety again to differ from its parent in the very same
character and in a greater degree  but this alone would never account for
so habitual and large a degree of difference as that between the species of
the same genus 

As has always been my practice  I have sought light on this head from our
domestic productions   We shall here find something analogous   It will be
admitted that the production of races so different as short horn and
Hereford cattle  race and cart horses  the several breeds of pigeons  etc  
could never have been effected by the mere chance accumulation of similar
variations during many successive generations   In practice  a fancier is 
for instance  struck by a pigeon having a slightly shorter beak  another
fancier is struck by a pigeon having a rather longer beak  and on the
acknowledged principle that  fanciers do not and will not admire a medium
standard  but like extremes   they both go on  as has actually occurred
with the sub breeds of the tumbler pigeon  choosing and breeding from birds
with longer and longer beaks  or with shorter and shorter beaks   Again  we
may suppose that at an early period of history  the men of one nation or
district required swifter horses  while those of another required stronger
and bulkier horses   The early differences would be very slight  but  in
the course of time  from the continued selection of swifter horses in the
one case  and of stronger ones in the other  the differences would become
greater  and would be noted as forming two sub breeds   Ultimately after
the lapse of centuries  these sub breeds would become converted into two
well established and distinct breeds   As the differences became greater 
the inferior animals with intermediate characters  being neither very swift
nor very strong  would not have been used for breeding  and will thus have
tended to disappear   Here  then  we see in man s productions the action of
what may be called the principle of divergence  causing differences  at
first barely appreciable  steadily to increase  and the breeds to diverge
in character  both from each other and from their common parent 

But how  it may be asked  can any analogous principle apply in nature   I
believe it can and does apply most efficiently  though it was a long time
before I saw how   from the simple circumstance that the more diversified
the descendants from any one species become in structure  constitution  and
habits  by so much will they be better enabled to seize on many and widely
diversified places in the polity of nature  and so be enabled to increase
in numbers 

We can clearly discern this in the case of animals with simple habits  
Take the case of a carnivorous quadruped  of which the number that can be
supported in any country has long ago arrived at its full average   If its
natural power of increase be allowed to act  it can succeed in increasing
 the country not undergoing any change in conditions  only by its varying
descendants seizing on places at present occupied by other animals   some
of them  for instance  being enabled to feed on new kinds of prey  either
dead or alive  some inhabiting new stations  climbing trees  frequenting
water  and some perhaps becoming less carnivorous   The more diversified in
habits and structure the descendants of our carnivorous animals become  the
more places they will be enabled to occupy   What applies to one animal
will apply throughout all time to all animals  that is  if they vary  for
otherwise natural selection can effect nothing   So it will be with plants  
It has been experimentally proved  that if a plot of ground be sown with
one species of grass  and a similar plot be sown with several distinct
genera of grasses  a greater number of plants and a greater weight of dry
herbage can be raised in the latter than in the former case   The same has
been found to hold good when one variety and several mixed varieties of
wheat have been sown on equal spaces of ground   Hence  if any one species
of grass were to go on varying  and the varieties were continually selected
which differed from each other in the same manner  though in a very slight
degree  as do the distinct species and genera of grasses  a greater number
of individual plants of this species  including its modified descendants 
would succeed in living on the same piece of ground   And we know that each
species and each variety of grass is annually sowing almost countless
seeds  and is thus striving  as it may be said  to the utmost to increase
in number   Consequently  in the course of many thousand generations  the
most distinct varieties of any one species of grass would have the best
chance of succeeding and of increasing in numbers  and thus of supplanting
the less distinct varieties  and varieties  when rendered very distinct
from each other  take the rank of species 

The truth of the principle that the greatest amount of life can be
supported by great diversification of structure  is seen under many natural
circumstances   In an extremely small area  especially if freely open to
immigration  and where the contest between individual and individual must
be very severe  we always find great diversity in its inhabitants   For
instance  I found that a piece of turf  three feet by four in size  which
had been exposed for many years to exactly the same conditions  supported
twenty species of plants  and these belonged to eighteen genera and to
eight orders  which shows how much these plants differed from each other  
So it is with the plants and insects on small and uniform islets   also in
small ponds of fresh water   Farmers find that they can raise more food by
a rotation of plants belonging to the most different orders   nature
follows what may be called a simultaneous rotation   Most of the animals
and plants which live close round any small piece of ground  could live on
it  supposing its nature not to be in any way peculiar   and may be said to
be striving to the utmost to live there  but  it is seen  that where they
come into the closest competition  the advantages of diversification of
structure  with the accompanying differences of habit and constitution 
determine that the inhabitants  which thus jostle each other most closely 
shall  as a general rule  belong to what we call different genera and
orders 

The same principle is seen in the naturalisation of plants through man s
agency in foreign lands   It might have been expected that the plants which
would succeed in becoming naturalised in any land would generally have been
closely allied to the indigenes  for these are commonly looked at as
specially created and adapted for their own country   It might also 
perhaps  have been expected that naturalised plants would have belonged to
a few groups more especially adapted to certain stations in their new
homes   But the case is very different  and Alph  de Candolle has well
remarked  in his great and admirable work  that floras gain by
naturalisation  proportionally with the number of the native genera and
species  far more in new genera than in new species   To give a single
instance   in the last edition of Dr  Asa Gray s  Manual of the Flora of
the Northern United States   260 naturalised plants are enumerated  and
these belong to 162 genera   We thus see that these naturalised plants are
of a highly diversified nature   They differ  moreover  to a large extent 
from the indigenes  for out of the 162 naturalised genera  no less than 100
genera are not there indigenous  and thus a large proportional addition is
made to the genera now living in the United States 

By considering the nature of the plants or animals which have in any
country struggled successfully with the indigenes  and have there become
naturalised  we may gain some crude idea in what manner some of the natives
would have had to be modified in order to gain an advantage over their
compatriots  and we may at least infer that diversification of structure 
amounting to new generic differences  would be profitable to them 

The advantage of diversification of structure in the inhabitants of the
same region is  in fact  the same as that of the physiological division of
labour in the organs of the same individual body  a subject so well
elucidated by Milne Edwards   No physiologist doubts that a stomach by
being adapted to digest vegetable matter alone  or flesh alone  draws most
nutriment from these substances   So in the general economy of any land 
the more widely and perfectly the animals and plants are diversified for
different habits of life  so will a greater number of individuals be
capable of there supporting themselves   A set of animals  with their
organisation but little diversified  could hardly compete with a set more
perfectly diversified in structure   It may be doubted  for instance 
whether the Australian marsupials  which are divided into groups differing
but little from each other  and feebly representing  as Mr  Waterhouse and
others have remarked  our carnivorous  ruminant  and rodent mammals  could
successfully compete with these well developed orders   In the Australian
mammals  we see the process of diversification in an early and incomplete
stage of development 

THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION THROUGH DIVERGENCE
OF CHARACTER AND EXTINCTION  ON THE DESCENDANTS OF A COMMON ANCESTOR 

After the foregoing discussion  which has been much compressed  we may
assume that the modified descendants of any one species will succeed so
much the better as they become more diversified in structure  and are thus
enabled to encroach on places occupied by other beings   Now let us see how
this principle of benefit being derived from divergence of character 
combined with the principles of natural selection and of extinction  tends
to act 

The accompanying diagram will aid us in understanding this rather
perplexing subject   Let A to L represent the species of a genus large in
its own country  these species are supposed to resemble each other in
unequal degrees  as is so generally the case in nature  and as is
represented in the diagram by the letters standing at unequal distances   I
have said a large genus  because as we saw in the second chapter  on an
average more species vary in large genera than in small genera  and the
varying species of the large genera present a greater number of varieties  
We have  also  seen that the species  which are the commonest and most
widely diffused  vary more than do the rare and restricted species   Let
 A  be a common  widely diffused  and varying species  belonging to a genus
large in its own country   The branching and diverging dotted lines of
unequal lengths proceeding from  A   may represent its varying offspring  
The variations are supposed to be extremely slight  but of the most
diversified nature  they are not supposed all to appear simultaneously  but
often after long intervals of time  nor are they all supposed to endure for
equal periods   Only those variations which are in some way profitable will
be preserved or naturally selected   And here the importance of the
principle of benefit derived from divergence of character comes in  for
this will generally lead to the most different or divergent variations
 represented by the outer dotted lines  being preserved and accumulated by
natural selection   When a dotted line reaches one of the horizontal lines 
and is there marked by a small numbered letter  a sufficient amount of
variation is supposed to have been accumulated to form it into a fairly
well marked variety  such as would be thought worthy of record in a
systematic work 

The intervals between the horizontal lines in the diagram  may represent
each a thousand or more generations   After a thousand generations  species
 A  is supposed to have produced two fairly well marked varieties  namely
a1 and m1   These two varieties will generally still be exposed to the same
conditions which made their parents variable  and the tendency to
variability is in itself hereditary  consequently they will likewise tend
to vary  and commonly in nearly the same manner as did their parents  
Moreover  these two varieties  being only slightly modified forms  will
tend to inherit those advantages which made their parent  A  more numerous
than most of the other inhabitants of the same country  they will also
partake of those more general advantages which made the genus to which the
parent species belonged  a large genus in its own country   And all these
circumstances are favourable to the production of new varieties 

If  then  these two varieties be variable  the most divergent of their
variations will generally be preserved during the next thousand
generations   And after this interval  variety a1 is supposed in the
diagram to have produced variety a2  which will  owing to the principle of
divergence  differ more from  A  than did variety a1   Variety m1 is
supposed to have produced two varieties  namely m2 and s2  differing from
each other  and more considerably from their common parent  A    We may
continue the process by similar steps for any length of time  some of the
varieties  after each thousand generations  producing only a single
variety  but in a more and more modified condition  some producing two or
three varieties  and some failing to produce any   Thus the varieties or
modified descendants of the common parent  A   will generally go on
increasing in number and diverging in character   In the diagram the
process is represented up to the ten thousandth generation  and under a
condensed and simplified form up to the fourteen thousandth generation 

But I must here remark that I do not suppose that the process ever goes on
so regularly as is represented in the diagram  though in itself made
somewhat irregular  nor that it goes on continuously  it is far more
probable that each form remains for long periods unaltered  and then again
undergoes modification   Nor do I suppose that the most divergent varieties
are invariably preserved   a medium form may often long endure  and may or
may not produce more than one modified descendant  for natural selection
will always act according to the nature of the places which are either
unoccupied or not perfectly occupied by other beings  and this will depend
on infinitely complex relations   But as a general rule  the more
diversified in structure the descendants from any one species can be
rendered  the more places they will be enabled to seize on  and the more
their modified progeny will increase   In our diagram the line of
succession is broken at regular intervals by small numbered letters marking
the successive forms which have become sufficiently distinct to be recorded
as varieties   But these breaks are imaginary  and might have been inserted
anywhere  after intervals long enough to allow the accumulation of a
considerable amount of divergent variation 

As all the modified descendants from a common and widely diffused species 
belonging to a large genus  will tend to partake of the same advantages
which made their parent successful in life  they will generally go on
multiplying in number as well as diverging in character   this is
represented in the diagram by the several divergent branches proceeding
from  A    The modified offspring from the later and more highly improved
branches in the lines of descent  will  it is probable  often take the
place of  and so destroy  the earlier and less improved branches   this is
represented in the diagram by some of the lower branches not reaching to
the upper horizontal lines   In some cases no doubt the process of
modification will be confined to a single line of descent  and the number
of modified descendants will not be increased  although the amount of
divergent modification may have been augmented   This case would be
represented in the diagram  if all the lines proceeding from  A  were
removed  excepting that from a1 to a10   In the same way the English
racehorse and English pointer have apparently both gone on slowly diverging
in character from their original stocks  without either having given off
any fresh branches or races 

After ten thousand generations  species  A  is supposed to have produced
three forms  a10  f10  and m10  which  from having diverged in character
during the successive generations  will have come to differ largely  but
perhaps unequally  from each other and from their common parent   If we
suppose the amount of change between each horizontal line in our diagram to
be excessively small  these three forms may still be only well marked
varieties  but we have only to suppose the steps in the process of
modification to be more numerous or greater in amount  to convert these
three forms into doubtful or at least into well defined species   thus the
diagram illustrates the steps by which the small differences distinguishing
varieties are increased into the larger differences distinguishing species  
By continuing the same process for a greater number of generations  as
shown in the diagram in a condensed and simplified manner   we get eight
species  marked by the letters between a14 and m14  all descended from  A   
Thus  as I believe  species are multiplied and genera are formed 

In a large genus it is probable that more than one species would vary   In
the diagram I have assumed that a second species  I  has produced  by
analogous steps  after ten thousand generations  either two well marked
varieties  w10 and z10  or two species  according to the amount of change
supposed to be represented between the horizontal lines   After fourteen
thousand generations  six new species  marked by the letters n14 to z14 
are supposed to have been produced   In any genus  the species which are
already very different in character from each other  will generally tend to
produce the greatest number of modified descendants  for these will have
the best chance of seizing on new and widely different places in the polity
of nature   hence in the diagram I have chosen the extreme species  A   and
the nearly extreme species  I   as those which have largely varied  and
have given rise to new varieties and species   The other nine species
 marked by capital letters  of our original genus  may for long but unequal
periods continue to transmit unaltered descendants  and this is shown in
the diagram by the dotted lines unequally prolonged upwards 

But during the process of modification  represented in the diagram  another
of our principles  namely that of extinction  will have played an important
part   As in each fully stocked country natural selection necessarily acts
by the selected form having some advantage in the struggle for life over
other forms  there will be a constant tendency in the improved descendants
of any one species to supplant and exterminate in each stage of descent
their predecessors and their original progenitor   For it should be
remembered that the competition will generally be most severe between those
forms which are most nearly related to each other in habits  constitution
and structure   Hence all the intermediate forms between the earlier and
later states  that is between the less and more improved states of a the
same species  as well as the original parent species itself  will generally
tend to become extinct   So it probably will be with many whole collateral
lines of descent  which will be conquered by later and improved lines   If 
however  the modified offspring of a species get into some distinct
country  or become quickly adapted to some quite new station  in which
offspring and progenitor do not come into competition  both may continue to
exist 

If  then  our diagram be assumed to represent a considerable amount of
modification  species  A  and all the earlier varieties will have become
extinct  being replaced by eight new species  a14 to m14   and species  I 
will be replaced by six  n14 to z14  new species 

But we may go further than this   The original species of our genus were
supposed to resemble each other in unequal degrees  as is so generally the
case in nature  species  A  being more nearly related to B  C  and D than
to the other species  and species  I  more to G  H  K  L  than to the
others   These two species  A and I   were also supposed to be very common
and widely diffused species  so that they must originally have had some
advantage over most of the other species of the genus   Their modified
descendants  fourteen in number at the fourteen thousandth generation  will
probably have inherited some of the same advantages   they have also been
modified and improved in a diversified manner at each stage of descent  so
as to have become adapted to many related places in the natural economy of
their country   It seems  therefore  extremely probable that they will have
taken the places of  and thus exterminated  not only their parents  A  and
 I   but likewise some of the original species which were most nearly
related to their parents   Hence very few of the original species will have
transmitted offspring to the fourteen thousandth generation   We may
suppose that only one  F  of the two species  E and F  which were least
closely related to the other nine original species  has transmitted
descendants to this late stage of descent 

The new species in our diagram  descended from the original eleven species 
will now be fifteen in number   Owing to the divergent tendency of natural
selection  the extreme amount of difference in character between species
a14 and z14 will be much greater than that between the most distinct of the
original eleven species   The new species  moreover  will be allied to each
other in a widely different manner   Of the eight descendants from  A  the
three marked a14  q14  p14  will be nearly related from having recently
branched off from a10  b14 and f14  from having diverged at an earlier
period from a5  will be in some degree distinct from the three first named
species  and lastly  o14  e14  and m14  will be nearly related one to the
other  but  from having diverged at the first commencement of the process
of modification  will be widely different from the other five species  and
may constitute a sub genus or a distinct genus   

The six descendants from  I  will form two sub genera or genera   But as
the original species  I  differed largely from  A   standing nearly at the
extreme end of the original genus  the six descendants from  I  will  owing
to inheritance alone  differ considerably from the eight descendants from
 A   the two groups  moreover  are supposed to have gone on diverging in
different directions   The intermediate species  also  and this is a very
important consideration   which connected the original species  A  and  I  
have all become  except  F   extinct  and have left no descendants   Hence
the six new species descended from  I   and the eight descendants from  A  
will have to be ranked as very distinct genera  or even as distinct
sub families 

Thus it is  as I believe  that two or more genera are produced by descent
with modification  from two or more species of the same genus   And the two
or more parent species are supposed to be descended from some one species
of an earlier genus   In our diagram this is indicated by the broken lines
beneath the capital letters  converging in sub branches downwards towards a
single point  this point represents a species  the supposed progenitor of
our several new sub genera and genera 

It is worth while to reflect for a moment on the character of the new
species F14  which is supposed not to have diverged much in character  but
to have retained the form of  F   either unaltered or altered only in a
slight degree   In this case its affinities to the other fourteen new
species will be of a curious and circuitous nature   Being descended from a
form that stood between the parent species  A  and  I   now supposed to be
extinct and unknown  it will be in some degree intermediate in character
between the two groups descended from these two species   But as these two
groups have gone on diverging in character from the type of their parents 
the new species  F14  will not be directly intermediate between them  but
rather between types of the two groups  and every naturalist will be able
to call such cases before his mind 

In the diagram each horizontal line has hitherto been supposed to represent
a thousand generations  but each may represent a million or more
generations  it may also represent a section of the successive strata of
the earth s crust including extinct remains   We shall  when we come to our
chapter on geology  have to refer again to this subject  and I think we
shall then see that the diagram throws light on the affinities of extinct
beings  which  though generally belonging to the same orders  families  or
genera  with those now living  yet are often  in some degree  intermediate
in character between existing groups  and we can understand this fact  for
the extinct species lived at various remote epochs when the branching lines
of descent had diverged less 

I see no reason to limit the process of modification  as now explained  to
the formation of genera alone   If  in the diagram  we suppose the amount
of change represented by each successive group of diverging dotted lines to
be great  the forms marked a14 to p14  those marked b14 and f14  and those
marked o14 to m14  will form three very distinct genera   We shall also
have two very distinct genera descended from  I   differing widely from the
descendants of  A    These two groups of genera will thus form two distinct
families  or orders  according to the amount of divergent modification
supposed to be represented in the diagram   And the two new families  or
orders  are descended from two species of the original genus  and these are
supposed to be descended from some still more ancient and unknown form 

We have seen that in each country it is the species belonging to the larger
genera which oftenest present varieties or incipient species   This 
indeed  might have been expected  for as natural selection acts through one
form having some advantage over other forms in the struggle for existence 
it will chiefly act on those which already have some advantage  and the
largeness of any group shows that its species have inherited from a common
ancestor some advantage in common   Hence  the struggle for the production
of new and modified descendants will mainly lie between the larger groups 
which are all trying to increase in number   One large group will slowly
conquer another large group  reduce its number  and thus lessen its chance
of further variation and improvement   Within the same large group  the
later and more highly perfected sub groups  from branching out and seizing
on many new places in the polity of nature  will constantly tend to
supplant and destroy the earlier and less improved sub groups   Small and
broken groups and sub groups will finally disappear   Looking to the
future  we can predict that the groups of organic beings which are now
large and triumphant  and which are least broken up  that is  which have as
yet suffered least extinction  will  for a long period  continue to
increase   But which groups will ultimately prevail  no man can predict 
for we know that many groups  formerly most extensively developed  have now
become extinct   Looking still more remotely to the future  we may predict
that  owing to the continued and steady increase of the larger groups  a
multitude of smaller groups will become utterly extinct  and leave no
modified descendants  and consequently that  of the species living at any
one period  extremely few will transmit descendants to a remote futurity  
I shall have to return to this subject in the chapter on classification 
but I may add that as  according to this view  extremely few of the more
ancient species have transmitted descendants to the present day  and  as
all the descendants of the same species form a class  we can understand how
it is that there exist so few classes in each main division of the animal
and vegetable kingdoms   Although few of the most ancient species have left
modified descendants  yet  at remote geological periods  the earth may have
been almost as well peopled with species of many genera  families  orders
and classes  as at the present day 

ON THE DEGREE TO WHICH ORGANISATION TENDS TO ADVANCE 

Natural selection acts exclusively by the preservation and accumulation of
variations  which are beneficial under the organic and inorganic conditions
to which each creature is exposed at all periods of life   The ultimate
result is that each creature tends to become more and more improved in
relation to its conditions   This improvement inevitably leads to the
gradual advancement of the organisation of the greater number of living
beings throughout the world   But here we enter on a very intricate
subject  for naturalists have not defined to each other s satisfaction what
is meant by an advance in organisation   Among the vertebrata the degree of
intellect and an approach in structure to man clearly come into play   It
might be thought that the amount of change which the various parts and
organs pass through in their development from embryo to maturity would
suffice as a standard of comparison  but there are cases  as with certain
parasitic crustaceans  in which several parts of the structure become less
perfect  so that the mature animal cannot be called higher than its larva  
Von Baer s standard seems the most widely applicable and the best  namely 
the amount of differentiation of the parts of the same organic being  in
the adult state  as I should be inclined to add  and their specialisation
for different functions  or  as Milne Edwards would express it  the
completeness of the division of physiological labour   But we shall see how
obscure this subject is if we look  for instance  to fishes  among which
some naturalists rank those as highest which  like the sharks  approach
nearest to amphibians  while other naturalists rank the common bony or
teleostean fishes as the highest  inasmuch as they are most strictly fish 
like  and differ most from the other vertebrate classes   We see still more
plainly the obscurity of the subject by turning to plants  among which the
standard of intellect is of course quite excluded  and here some botanists
rank those plants as highest which have every organ  as sepals  petals 
stamens and pistils  fully developed in each flower  whereas other
botanists  probably with more truth  look at the plants which have their
several organs much modified and reduced in number as the highest 

If we take as the standard of high organisation  the amount of
differentiation and specialisation of the several organs in each being when
adult  and this will include the advancement of the brain for intellectual
purposes   natural selection clearly leads towards this standard   for all
physiologists admit that the specialisation of organs  inasmuch as in this
state they perform their functions better  is an advantage to each being 
and hence the accumulation of variations tending towards specialisation is
within the scope of natural selection   On the other hand  we can see 
bearing in mind that all organic beings are striving to increase at a high
ratio and to seize on every unoccupied or less well occupied place in the
economy of nature  that it is quite possible for natural selection
gradually to fit a being to a situation in which several organs would be
superfluous or useless   in such cases there would be retrogression in the
scale of organisation   Whether organisation on the whole has actually
advanced from the remotest geological periods to the present day will be
more conveniently discussed in our chapter on Geological Succession 

But it may be objected that if all organic beings thus tend to rise in the
scale  how is it that throughout the world a multitude of the lowest forms
still exist  and how is it that in each great class some forms are far more
highly developed than others   Why have not the more highly developed forms
every where supplanted and exterminated the lower   Lamarck  who believed
in an innate and inevitable tendency towards perfection in all organic
beings  seems to have felt this difficulty so strongly that he was led to
suppose that new and simple forms are continually being produced by
spontaneous generation   Science has not as yet proved the truth of this
belief  whatever the future may reveal   On our theory the continued
existence of lowly organisms offers no difficulty  for natural selection 
or the survival of the fittest  does not necessarily include progressive
development  it only takes advantage of such variations as arise and are
beneficial to each creature under its complex relations of life   And it
may be asked what advantage  as far as we can see  would it be to an
infusorian animalcule  to an intestinal worm  or even to an earth worm  to
be highly organised   If it were no advantage  these forms would be left 
by natural selection  unimproved or but little improved  and might remain
for indefinite ages in their present lowly condition   And geology tells us
that some of the lowest forms  as the infusoria and rhizopods  have
remained for an enormous period in nearly their present state   But to
suppose that most of the many now existing low forms have not in the least
advanced since the first dawn of life would be extremely rash  for every
naturalist who has dissected some of the beings now ranked as very low in
the scale  must have been struck with their really wondrous and beautiful
organisation 

Nearly the same remarks are applicable  if we look to the different grades
of organisation within the same great group  for instance  in the
vertebrata  to the co existence of mammals and fish  among mammalia  to the
co existence of man and the ornithorhynchus  among fishes  to the co 
existence of the shark and the lancelet  Amphioxus   which latter fish in
the extreme simplicity of its structure approaches the invertebrate
classes   But mammals and fish hardly come into competition with each
other  the advancement of the whole class of mammals  or of certain members
in this class  to the highest grade would not lead to their taking the
place of fishes   Physiologists believe that the brain must be bathed by
warm blood to be highly active  and this requires aerial respiration  so
that warm blooded mammals when inhabiting the water lie under a
disadvantage in having to come continually to the surface to breathe   With
fishes  members of the shark family would not tend to supplant the
lancelet  for the lancelet  as I hear from Fritz Muller  has as sole
companion and competitor on the barren sandy shore of South Brazil  an
anomalous annelid   The three lowest orders of mammals  namely  marsupials 
edentata  and rodents  co exist in South America in the same region with
numerous monkeys  and probably interfere little with each other   Although
organisation  on the whole  may have advanced and be still advancing
throughout the world  yet the scale will always present many degrees of
perfection  for the high advancement of certain whole classes  or of
certain members of each class  does not at all necessarily lead to the
extinction of those groups with which they do not enter into close
competition   In some cases  as we shall hereafter see  lowly organised
forms appear to have been preserved to the present day  from inhabiting
confined or peculiar stations  where they have been subjected to less
severe competition  and where their scanty numbers have retarded the chance
of favourable variations arising 

Finally  I believe that many lowly organised forms now exist throughout the
world  from various causes   In some cases variations or individual
differences of a favourable nature may never have arisen for natural
selection to act on and accumulate   In no case  probably  has time
sufficed for the utmost possible amount of development   In some few cases
there has been what we must call retrogression or organisation   But the
main cause lies in the fact that under very simple conditions of life a
high organisation would be of no service  possibly would be of actual
disservice  as being of a more delicate nature  and more liable to be put
out of order and injured 

Looking to the first dawn of life  when all organic beings  as we may
believe  presented the simplest structure  how  it has been asked  could
the first step in the advancement or differentiation of parts have arisen  
Mr  Herbert Spencer would probably answer that  as soon as simple
unicellular organisms came by growth or division to be compounded of
several cells  or became attached to any supporting surface  his law  that
homologous units of any order become differentiated in proportion as their
relations to incident forces become different  would come into action   But
as we have no facts to guide us  speculation on the subject is almost
useless   It is  however  an error to suppose that there would be no
struggle for existence  and  consequently  no natural selection  until many
forms had been produced   variations in a single species inhabiting an
isolated station might be beneficial  and thus the whole mass of
individuals might be modified  or two distinct forms might arise   But  as
I remarked towards the close of the introduction  no one ought to feel
surprise at much remaining as yet unexplained on the origin of species  if
we make due allowance for our profound ignorance on the mutual relations of
the inhabitants of the world at the present time  and still more so during
past ages 

CONVERGENCE OF CHARACTER 

Mr  H C  Watson thinks that I have overrated the importance of divergence
of character  in which  however  he apparently believes   and that
convergence  as it may be called  has likewise played a part   If two
species belonging to two distinct though allied genera  had both produced a
large number of new and divergent forms  it is conceivable that these might
approach each other so closely that they would have all to be classed under
the same genus  and thus the descendants of two distinct genera would
converge into one   But it would in most cases be extremely rash to
attribute to convergence a close and general similarity of structure in the
modified descendants of widely distinct forms   The shape of a crystal is
determined solely by the molecular forces  and it is not surprising that
dissimilar substances should sometimes assume the same form  but with
organic beings we should bear in mind that the form of each depends on an
infinitude of complex relations  namely on the variations which have
arisen  these being due to causes far too intricate to be followed out  on
the nature of the variations which have been preserved or selected  and
this depends on the surrounding physical conditions  and in a still higher
degree on the surrounding organisms with which each being has come into
competition  and lastly  on inheritance  in itself a fluctuating element 
from innumerable progenitors  all of which have had their forms determined
through equally complex relations   It is incredible that the descendants
of two organisms  which had originally differed in a marked manner  should
ever afterwards converge so closely as to lead to a near approach to
identity throughout their whole organisation   If this had occurred  we
should meet with the same form  independently of genetic connection 
recurring in widely separated geological formations  and the balance of
evidence is opposed to any such an admission 

Mr  Watson has also objected that the continued action of natural
selection  together with divergence of character  would tend to make an
indefinite number of specific forms   As far as mere inorganic conditions
are concerned  it seems probable that a sufficient number of species would
soon become adapted to all considerable diversities of heat  moisture 
etc   but I fully admit that the mutual relations of organic beings are
more important  and as the number of species in any country goes on
increasing  the organic conditions of life must become more and more
complex   Consequently there seems at first no limit to the amount of
profitable diversification of structure  and therefore no limit to the
number of species which might be produced   We do not know that even the
most prolific area is fully stocked with specific forms   at the Cape of
Good Hope and in Australia  which support such an astonishing number of
species  many European plants have become naturalised   But geology shows
us  that from an early part of the tertiary period the number of species of
shells  and that from the middle part of this same period  the number of
mammals has not greatly or at all increased   What then checks an
indefinite increase in the number of species   The amount of life  I do not
mean the number of specific forms  supported on an area must have a limit 
depending so largely as it does on physical conditions  therefore  if an
area be inhabited by very many species  each or nearly each species will be
represented by few individuals  and such species will be liable to
extermination from accidental fluctuations in the nature of the seasons or
in the number of their enemies   The process of extermination in such cases
would be rapid  whereas the production of new species must always be slow 
Imagine the extreme case of as many species as individuals in England  and
the first severe winter or very dry summer would exterminate thousands on
thousands of species   Rare species  and each species will become rare if
the number of species in any country becomes indefinitely increased  will 
on the principal often explained  present within a given period few
favourable variations  consequently  the process of giving birth to new
specific forms would thus be retarded   When any species becomes very rare 
close interbreeding will help to exterminate it  authors have thought that
this comes into play in accounting for the deterioration of the aurochs in
Lithuania  of red deer in Scotland and of bears in Norway  etc   Lastly 
and this I am inclined to think is the most important element  a dominant
species  which has already beaten many competitors in its own home  will
tend to spread and supplant many others   Alph  de Candolle has shown that
those species which spread widely tend generally to spread VERY widely 
consequently they will tend to supplant and exterminate several species in
several areas  and thus check the inordinate increase of specific forms
throughout the world   Dr  Hooker has recently shown that in the southeast
corner of Australia  where  apparently  there are many invaders from
different quarters of the globe  the endemic Australian species have been
greatly reduced in number   How much weight to attribute to these several
considerations I will not pretend to say  but conjointly they must limit in
each country the tendency to an indefinite augmentation of specific forms 

SUMMARY OF CHAPTER 

If under changing conditions of life organic beings present individual
differences in almost every part of their structure  and this cannot be
disputed  if there be  owing to their geometrical rate of increase  a
severe struggle for life at some age  season or year  and this certainly
cannot be disputed  then  considering the infinite complexity of the
relations of all organic beings to each other and to their conditions of
life  causing an infinite diversity in structure  constitution  and habits 
to be advantageous to them  it would be a most extraordinary fact if no
variations had ever occurred useful to each being s own welfare  in the
same manner as so many variations have occurred useful to man   But if
variations useful to any organic being ever do occur  assuredly individuals
thus characterised will have the best chance of being preserved in the
struggle for life  and from the strong principle of inheritance  these will
tend to produce offspring similarly characterised   This principle of
preservation  or the survival of the fittest  I have called natural
selection   It leads to the improvement of each creature in relation to its
organic and inorganic conditions of life  and consequently  in most cases 
to what must be regarded as an advance in organisation   Nevertheless  low
and simple forms will long endure if well fitted for their simple
conditions of life 

Natural selection  on the principle of qualities being inherited at
corresponding ages  can modify the egg  seed  or young as easily as the
adult   Among many animals sexual selection will have given its aid to
ordinary selection by assuring to the most vigorous and best adapted males
the greatest number of offspring   Sexual selection will also give
characters useful to the males alone in their struggles or rivalry with
other males  and these characters will be transmitted to one sex or to both
sexes  according to the form of inheritance which prevails 

Whether natural selection has really thus acted in adapting the various
forms of life to their several conditions and stations  must be judged by
the general tenour and balance of evidence given in the following chapters  
But we have already seen how it entails extinction  and how largely
extinction has acted in the world s history  geology plainly declares  
Natural selection  also  leads to divergence of character  for the more
organic beings diverge in structure  habits and constitution  by so much
the more can a large number be supported on the area  of which we see proof
by looking to the inhabitants of any small spot  and to the productions
naturalised in foreign lands   Therefore  during the modification of the
descendants of any one species  and during the incessant struggle of all
species to increase in numbers  the more diversified the descendants
become  the better will be their chance of success in the battle for life  
Thus the small differences distinguishing varieties of the same species 
steadily tend to increase  till they equal the greater differences between
species of the same genus  or even of distinct genera 

We have seen that it is the common  the widely diffused  and widely ranging
species  belonging to the larger genera within each class  which vary most 
and these tend to transmit to their modified offspring that superiority
which now makes them dominant in their own countries   Natural selection 
as has just been remarked  leads to divergence of character and to much
extinction of the less improved and intermediate forms of life   On these
principles  the nature of the affinities  and the generally well defined
distinctions between the innumerable organic beings in each class
throughout the world  may be explained   It is a truly wonderful fact  the
wonder of which we are apt to overlook from familiarity  that all animals
and all plants throughout all time and space should be related to each
other in groups  subordinate to groups  in the manner which we everywhere
behold  namely  varieties of the same species most closely related  species
of the same genus less closely and unequally related  forming sections and
sub genera  species of distinct genera much less closely related  and
genera related in different degrees  forming sub families  families 
orders  sub classes  and classes   The several subordinate groups in any
class cannot be ranked in a single file  but seem clustered round points 
and these round other points  and so on in almost endless cycles   If
species had been independently created  no explanation would have been
possible of this kind of classification  but it is explained through
inheritance and the complex action of natural selection  entailing
extinction and divergence of character  as we have seen illustrated in the
diagram 

The affinities of all the beings of the same class have sometimes been
represented by a great tree   I believe this simile largely speaks the
truth   The green and budding twigs may represent existing species  and
those produced during former years may represent the long succession of
extinct species   At each period of growth all the growing twigs have tried
to branch out on all sides  and to overtop and kill the surrounding twigs
and branches  in the same manner as species and groups of species have at
all times overmastered other species in the great battle for life   The
limbs divided into great branches  and these into lesser and lesser
branches  were themselves once  when the tree was young  budding twigs  and
this connexion of the former and present buds by ramifying branches may
well represent the classification of all extinct and living species in
groups subordinate to groups   Of the many twigs which flourished when the
tree was a mere bush  only two or three  now grown into great branches  yet
survive and bear the other branches  so with the species which lived during
long past geological periods  very few have left living and modified
descendants   From the first growth of the tree  many a limb and branch has
decayed and dropped off  and these fallen branches of various sizes may
represent those whole orders  families  and genera which have now no living
representatives  and which are known to us only in a fossil state   As we
here and there see a thin  straggling branch springing from a fork low down
in a tree  and which by some chance has been favoured and is still alive on
its summit  so we occasionally see an animal like the Ornithorhynchus or
Lepidosiren  which in some small degree connects by its affinities two
large branches of life  and which has apparently been saved from fatal
competition by having inhabited a protected station   As buds give rise by
growth to fresh buds  and these  if vigorous  branch out and overtop on all
sides many a feebler branch  so by generation I believe it has been with
the great Tree of Life  which fills with its dead and broken branches the
crust of the earth  and covers the surface with its ever branching and
beautiful ramifications 


CHAPTER V 
 
LAWS OF VARIATION 

Effects of changed conditions    Use and disuse  combined with natural
selection  organs of flight and of vision    Acclimatisation    Correlated
variation    Compensation and economy of growth    False correlations   
Multiple  rudimentary  and lowly organised structures variable    Parts
developed in an unusual manner are highly variable  specific characters
more variable than generic   secondary sexual characters variable   
Species of the same genus vary in an analogous manner    Reversions to
long lost characters    Summary 

I have hitherto sometimes spoken as if the variations  so common and
multiform with organic beings under domestication  and in a lesser degree
with those under nature  were due to chance   This  of course is a wholly
incorrect expression  but it serves to acknowledge plainly our ignorance of
the cause of each particular variation   Some authors believe it to be as
much the function of the reproductive system to produce individual
differences  or slight deviations of structure  as to make the child like
its parents   But the fact of variations and monstrosities occurring much
more frequently under domestication than under nature  and the greater
variability of species having wide ranges than of those with restricted
ranges  lead to the conclusion that variability is generally related to the
conditions of life to which each species has been exposed during several
successive generations   In the first chapter I attempted to show that
changed conditions act in two ways  directly on the whole organisation or
on certain parts alone  and indirectly through the reproductive system   In
all cases there are two factors  the nature of the organism  which is much
the most important of the two  and the nature of the conditions   The
direct action of changed conditions leads to definite or indefinite
results   In the latter case the organisation seems to become plastic  and
we have much fluctuating variability   In the former case the nature of the
organism is such that it yields readily  when subjected to certain
conditions  and all  or nearly all  the individuals become modified in the
same way 

It is very difficult to decide how far changed conditions  such as of
climate  food  etc   have acted in a definite manner   There is reason to
believe that in the course of time the effects have been greater than can
be proved by clear evidence   But we may safely conclude that the
innumerable complex co adaptations of structure  which we see throughout
nature between various organic beings  cannot be attributed simply to such
action   In the following cases the conditions seem to have produced some
slight definite effect   E  Forbes asserts that shells at their southern
limit  and when living in shallow water  are more brightly coloured than
those of the same species from further north or from a greater depth  but
this certainly does not always hold good   Mr  Gould believes that birds of
the same species are more brightly coloured under a clear atmosphere  than
when living near the coast or on islands  and Wollaston is convinced that
residence near the sea affects the colours of insects   Moquin Tandon gives
a list of plants which  when growing near the sea shore  have their leaves
in some degree fleshy  though not elsewhere fleshy   These slightly varying
organisms are interesting in as far as they present characters analogous to
those possessed by the species which are confined to similar conditions 

When a variation is of the slightest use to any being  we cannot tell how
much to attribute to the accumulative action of natural selection  and how
much to the definite action of the conditions of life   Thus  it is well
known to furriers that animals of the same species have thicker and better
fur the further north they live  but who can tell how much of this
difference may be due to the warmest clad individuals having been favoured
and preserved during many generations  and how much to the action of the
severe climate   For it would appear that climate has some direct action on
the hair of our domestic quadrupeds 

Instances could be given of similar varieties being produced from the same
species under external conditions of life as different as can well be
conceived  and  on the other hand  of dissimilar varieties being produced
under apparently the same external conditions   Again  innumerable
instances are known to every naturalist  of species keeping true  or not
varying at all  although living under the most opposite climates   Such
considerations as these incline me to lay less weight on the direct action
of the surrounding conditions  than on a tendency to vary  due to causes of
which we are quite ignorant 

In one sense the conditions of life may be said  not only to cause
variability  either directly or indirectly  but likewise to include natural
selection  for the conditions determine whether this or that variety shall
survive   But when man is the selecting agent  we clearly see that the two
elements of change are distinct  variability is in some manner excited  but
it is the will of man which accumulates the variations in certain
direction  and it is this latter agency which answers to the survival of
the fittest under nature 

EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS  AS CONTROLLED BY NATURAL
SELECTION 

 From the facts alluded to in the first chapter  I think there can be no
doubt that use in our domestic animals has strengthened and enlarged
certain parts  and disuse diminished them  and that such modifications are
inherited   Under free nature we have no standard of comparison by which to
judge of the effects of long continued use or disuse  for we know not the
parent forms  but many animals possess structures which can be best
explained by the effects of disuse   As Professor Owen has remarked  there
is no greater anomaly in nature than a bird that cannot fly  yet there are
several in this state   The logger headed duck of South America can only
flap along the surface of the water  and has its wings in nearly the same
condition as the domestic Aylesbury duck   it is a remarkable fact that the
young birds  according to Mr  Cunningham  can fly  while the adults have
lost this power   As the larger ground feeding birds seldom take flight
except to escape danger  it is probable that the nearly wingless condition
of several birds  now inhabiting or which lately inhabited several oceanic
islands  tenanted by no beasts of prey  has been caused by disuse   The
ostrich indeed inhabits continents  and is exposed to danger from which it
cannot escape by flight  but it can defend itself  by kicking its enemies 
as efficiently as many quadrupeds   We may believe that the progenitor of
the ostrich genus had habits like those of the bustard  and that  as the
size and weight of its body were increased during successive generations 
its legs were used more and its wings less  until they became incapable of
flight 

Kirby has remarked  and I have observed the same fact  that the anterior
tarsi  or feet  of many male dung feeding beetles are often broken off  he
examined seventeen specimens in his own collection  and not one had even a
relic left   In the Onites apelles the tarsi are so habitually lost that
the insect has been described as not having them   In some other genera
they are present  but in a rudimentary condition   In the Ateuchus or
sacred beetle of the Egyptians  they are totally deficient   The evidence
that accidental mutilations can be inherited is at present not decisive 
but the remarkable cases observed by Brown Sequard in guinea pigs  of the
inherited effects of operations  should make us cautious in denying this
tendency   Hence  it will perhaps be safest to look at the entire absence
of the anterior tarsi in Ateuchus  and their rudimentary condition in some
other genera  not as cases of inherited mutilations  but as due to the
effects of long continued disuse  for as many dung feeding beetles are
generally found with their tarsi lost  this must happen early in life 
therefore the tarsi cannot be of much importance or be much used by these
insects 

In some cases we might easily put down to disuse modifications of structure
which are wholly  or mainly due to natural selection   Mr  Wollaston has
discovered the remarkable fact that 200 beetles  out of the 550 species
 but more are now known  inhabiting Madeira  are so far deficient in wings
that they cannot fly  and that  of the twenty nine endemic genera  no less
than twenty three have all their species in this condition   Several facts 
namely  that beetles in many parts of the world are very frequently blown
to sea and perish  that the beetles in Madeira  as observed by Mr 
Wollaston  lie much concealed  until the wind lulls and the sun shines 
that the proportion of wingless beetles is larger on the exposed Desertas
than in Madeira itself  and especially the extraordinary fact  so strongly
insisted on by Mr  Wollaston  that certain large groups of beetles 
elsewhere excessively numerous  which absolutely require the use of their
wings  are here almost entirely absent   These several considerations make
me believe that the wingless condition of so many Madeira beetles is mainly
due to the action of natural selection  combined probably with disuse   For
during many successive generations each individual beetle which flew least 
either from its wings having been ever so little less perfectly developed
or from indolent habit  will have had the best chance of surviving from not
being blown out to sea  and  on the other hand  those beetles which most
readily took to flight would oftenest have been blown to sea  and thus
destroyed 

The insects in Madeira which are not ground feeders  and which  as certain
flower feeding coleoptera and lepidoptera  must habitually use their wings
to gain their subsistence  have  as Mr  Wollaston suspects  their wings not
at all reduced  but even enlarged   This is quite compatible with the
action of natural selection   For when a new insect first arrived on the
island  the tendency of natural selection to enlarge or to reduce the
wings  would depend on whether a greater number of individuals were saved
by successfully battling with the winds  or by giving up the attempt and
rarely or never flying   As with mariners shipwrecked near a coast  it
would have been better for the good swimmers if they had been able to swim
still further  whereas it would have been better for the bad swimmers if
they had not been able to swim at all and had stuck to the wreck 

The eyes of moles and of some burrowing rodents are rudimentary in size 
and in some cases are quite covered by skin and fur   This state of the
eyes is probably due to gradual reduction from disuse  but aided perhaps by
natural selection   In South America  a burrowing rodent  the tuco tuco  or
Ctenomys  is even more subterranean in its habits than the mole  and I was
assured by a Spaniard  who had often caught them  that they were frequently
blind   One which I kept alive was certainly in this condition  the cause 
as appeared on dissection  having been inflammation of the nictitating
membrane   As frequent inflammation of the eyes must be injurious to any
animal  and as eyes are certainly not necessary to animals having
subterranean habits  a reduction in their size  with the adhesion of the
eyelids and growth of fur over them  might in such case be an advantage 
and if so  natural selection would aid the effects of disuse 

It is well known that several animals  belonging to the most different
classes  which inhabit the caves of Carniola and Kentucky  are blind   In
some of the crabs the foot stalk for the eye remains  though the eye is
gone  the stand for the telescope is there  though the telescope with its
glasses has been lost   As it is difficult to imagine that eyes  though
useless  could be in any way injurious to animals living in darkness  their
loss may be attributed to disuse   In one of the blind animals  namely  the
cave rat  Neotoma   two of which were captured by Professor Silliman at
above half a mile distance from the mouth of the cave  and therefore not in
the profoundest depths  the eyes were lustrous and of large size  and these
animals  as I am informed by Professor Silliman  after having been exposed
for about a month to a graduated light  acquired a dim perception of
objects 

It is difficult to imagine conditions of life more similar than deep
limestone caverns under a nearly similar climate  so that  in accordance
with the old view of the blind animals having been separately created for
the American and European caverns  very close similarity in their
organisation and affinities might have been expected   This is certainly
not the case if we look at the two whole faunas  with respect to the
insects alone  Schiodte has remarked    We are accordingly prevented from
considering the entire phenomenon in any other light than something purely
local  and the similarity which is exhibited in a few forms between the
Mammoth Cave  in Kentucky  and the caves in Carniola  otherwise than as a
very plain expression of that analogy which subsists generally between the
fauna of Europe and of North America     On my view we must suppose that
American animals  having in most cases ordinary powers of vision  slowly
migrated by successive generations from the outer world into the deeper and
deeper recesses of the Kentucky caves  as did European animals into the
caves of Europe   We have some evidence of this gradation of habit  for  as
Schiodte remarks    We accordingly look upon the subterranean faunas as
small ramifications which have penetrated into the earth from the
geographically limited faunas of the adjacent tracts  and which  as they
extended themselves into darkness  have been accommodated to surrounding
circumstances   Animals not far remote from ordinary forms  prepare the
transition from light to darkness   Next follow those that are constructed
for twilight  and  last of all  those destined for total darkness  and
whose formation is quite peculiar    These remarks of Schiodte s it should
be understood  apply not to the same  but to distinct species   By the time
that an animal had reached  after numberless generations  the deepest
recesses  disuse will on this view have more or less perfectly obliterated
its eyes  and natural selection will often have effected other changes 
such as an increase in the length of the antennae or palpi  as a
compensation for blindness   Notwithstanding such modifications  we might
expect still to see in the cave animals of America  affinities to the other
inhabitants of that continent  and in those of Europe to the inhabitants of
the European continent   And this is the case with some of the American
cave animals  as I hear from Professor Dana  and some of the European
cave insects are very closely allied to those of the surrounding country  
It would be difficult to give any rational explanation of the affinities of
the blind cave animals to the other inhabitants of the two continents on
the ordinary view of their independent creation   That several of the
inhabitants of the caves of the Old and New Worlds should be closely
related  we might expect from the well known relationship of most of their
other productions   As a blind species of Bathyscia is found in abundance
on shady rocks far from caves  the loss of vision in the cave species of
this one genus has probably had no relation to its dark habitation  for it
is natural that an insect already deprived of vision should readily become
adapted to dark caverns   Another blind genus  Anophthalmus  offers this
remarkable peculiarity  that the species  as Mr  Murray observes  have not
as yet been found anywhere except in caves  yet those which inhabit the
several caves of Europe and America are distinct  but it is possible that
the progenitors of these several species  while they were furnished with
eyes  may formerly have ranged over both continents  and then have become
extinct  excepting in their present secluded abodes   Far from feeling
surprise that some of the cave animals should be very anomalous  as Agassiz
has remarked in regard to the blind fish  the Amblyopsis  and as is the
case with the blind Proteus  with reference to the reptiles of Europe  I am
only surprised that more wrecks of ancient life have not been preserved 
owing to the less severe competition to which the scanty inhabitants of
these dark abodes will have been exposed 

ACCLIMATISATION 

Habit is hereditary with plants  as in the period of flowering  in the time
of sleep  in the amount of rain requisite for seeds to germinate  etc   and
this leads me to say a few words on acclimatisation   As it is extremely
common for distinct species belonging to the same genus to inhabit hot and
cold countries  if it be true that all the species of the same genus are
descended from a single parent form  acclimatisation must be readily
effected during a long course of descent   It is notorious that each
species is adapted to the climate of its own home   species from an arctic
or even from a temperate region cannot endure a tropical climate  or
conversely   So again  many succulent plants cannot endure a damp climate  
But the degree of adaptation of species to the climates under which they
live is often overrated   We may infer this from our frequent inability to
predict whether or not an imported plant will endure our climate  and from
the number of plants and animals brought from different countries which are
here perfectly healthy   We have reason to believe that species in a state
of nature are closely limited in their ranges by the competition of other
organic beings quite as much as  or more than  by adaptation to particular
climates   But whether or not this adaptation is in most cases very close 
we have evidence with some few plants  of their becoming  to a certain
extent  naturally habituated to different temperatures  that is  they
become acclimatised   thus the pines and rhododendrons  raised from seed
collected by Dr  Hooker from the same species growing at different heights
on the Himalayas  were found to possess in this country different
constitutional powers of resisting cold   Mr  Thwaites informs me that he
has observed similar facts in Ceylon  analogous observations have been made
by Mr  H C  Watson on European species of plants brought from the Azores to
England  and I could give other cases   In regard to animals  several
authentic instances could be adduced of species having largely extended 
within historical times  their range from warmer to colder latitudes  and
conversely  but we do not positively know that these animals were strictly
adapted to their native climate  though in all ordinary cases we assume
such to be the case  nor do we know that they have subsequently become
specially acclimatised to their new homes  so as to be better fitted for
them than they were at first 

As we may infer that our domestic animals were originally chosen by
uncivilised man because they were useful  and because they bred readily
under confinement  and not because they were subsequently found capable of
far extended transportation  the common and extraordinary capacity in our
domestic animals of not only withstanding the most different climates  but
of being perfectly fertile  a far severer test  under them  may be used as
an argument that a large proportion of other animals now in a state of
nature could easily be brought to bear widely different climates   We must
not  however  push the foregoing argument too far  on account of the
probable origin of some of our domestic animals from several wild stocks  
the blood  for instance  of a tropical and arctic wolf may perhaps be
mingled in our domestic breeds   The rat and mouse cannot be considered as
domestic animals  but they have been transported by man to many parts of
the world  and now have a far wider range than any other rodent  for they
live under the cold climate of Faroe in the north and of the Falklands in
the south  and on many an island in the torrid zones   Hence adaptation to
any special climate may be looked at as a quality readily grafted on an
innate wide flexibility of constitution  common to most animals   On this
view  the capacity of enduring the most different climates by man himself
and by his domestic animals  and the fact of the extinct elephant and
rhinoceros having formerly endured a glacial climate  whereas the living
species are now all tropical or sub tropical in their habits  ought not to
be looked at as anomalies  but as examples of a very common flexibility of
constitution  brought  under peculiar circumstances  into action 

How much of the acclimatisation of species to any peculiar climate is due
to mere habit  and how much to the natural selection of varieties having
different innate constitutions  and how much to both means combined  is an
obscure question   That habit or custom has some influence  I must believe 
both from analogy and from the incessant advice given in agricultural
works  even in the ancient Encyclopaedias of China  to be very cautious in
transporting animals from one district to another   And as it is not likely
that man should have succeeded in selecting so many breeds and sub breeds
with constitutions specially fitted for their own districts  the result
must  I think  be due to habit   On the other hand  natural selection would
inevitably tend to preserve those individuals which were born with
constitutions best adapted to any country which they inhabited   In
treatises on many kinds of cultivated plants  certain varieties are said to
withstand certain climates better than others  this is strikingly shown in
works on fruit trees published in the United States  in which certain
varieties are habitually recommended for the northern and others for the
southern states  and as most of these varieties are of recent origin  they
cannot owe their constitutional differences to habit   The case of the
Jerusalem artichoke  which is never propagated in England by seed  and of
which  consequently  new varieties have not been produced  has even been
advanced  as proving that acclimatisation cannot be effected  for it is now
as tender as ever it was   The case  also  of the kidney bean has been
often cited for a similar purpose  and with much greater weight  but until
some one will sow  during a score of generations  his kidney beans so early
that a very large proportion are destroyed by frost  and then collect seed
from the few survivors  with care to prevent accidental crosses  and then
again get seed from these seedlings  with the same precautions  the
experiment cannot be said to have been even tried   Nor let it be supposed
that differences in the constitution of seedling kidney beans never appear 
for an account has been published how much more hardy some seedlings are
than others  and of this fact I have myself observed striking instances 

On the whole  we may conclude that habit  or use and disuse  have  in some
cases  played a considerable part in the modification of the constitution
and structure  but that the effects have often been largely combined with 
and sometimes overmastered by  the natural selection of innate variations 

CORRELATED VARIATION 

I mean by this expression that the whole organisation is so tied together 
during its growth and development  that when slight variations in any one
part occur and are accumulated through natural selection  other parts
become modified   This is a very important subject  most imperfectly
understood  and no doubt wholly different classes of facts may be here
easily confounded together   We shall presently see that simple inheritance
often gives the false appearance of correlation   One of the most obvious
real cases is  that variations of structure arising in the young or larvae
naturally tend to affect the structure of the mature animal   The several
parts which are homologous  and which  at an early embryonic period  are
identical in structure  and which are necessarily exposed to similar
conditions  seem eminently liable to vary in a like manner   we see this in
the right and left sides of the body varying in the same manner  in the
front and hind legs  and even in the jaws and limbs  varying together  for
the lower jaw is believed by some anatomists to be homologous with the
limbs   These tendencies  I do not doubt  may be mastered more or less
completely by natural selection   thus a family of stags once existed with
an antler only on one side  and if this had been of any great use to the
breed  it might probably have been rendered permanent by natural selection 

Homologous parts  as has been remarked by some authors  tend to cohere 
this is often seen in monstrous plants   and nothing is more common than
the union of homologous parts in normal structures  as in the union of the
petals into a tube   Hard parts seem to affect the form of adjoining soft
parts  it is believed by some authors that with birds the diversity in the
shape of the pelvis causes the remarkable diversity in the shape of the
kidneys   Others believe that the shape of the pelvis in the human mother
influences by pressure the shape of the head of the child   In snakes 
according to Schlegel  the shape of the body and the manner of swallowing
determine the position and form of several of the most important viscera 

The nature of the bond is frequently quite obscure   M  Is  Geoffroy St 
Hilaire has forcibly remarked that certain malconformations frequently  and
that others rarely  coexist without our being able to assign any reason  
What can be more singular than the relation in cats between complete
whiteness and blue eyes with deafness  or between the tortoise shell colour
and the female sex  or in pigeons  between their feathered feet and skin
betwixt the outer toes  or between the presence of more or less down on the
young pigeon when first hatched  with the future colour of its plumage  or 
again  the relation between the hair and the teeth in the naked Turkish
dog  though here no doubt homology comes into play   With respect to this
latter case of correlation  I think it can hardly be accidental that the
two orders of mammals which are most abnormal in their dermal covering 
viz   Cetacea  whales  and Edentata  armadilloes  scaly ant eaters  etc   
are likewise on the whole the most abnormal in their teeth  but there are
so many exceptions to this rule  as Mr  Mivart has remarked  that it has
little value 

I know of no case better adapted to show the importance of the laws of
correlation and variation  independently of utility  and therefore of
natural selection  than that of the difference between the outer and inner
flowers in some Compositous and Umbelliferous plants   Everyone is familiar
with the difference between the ray and central florets of  for instance 
the daisy  and this difference is often accompanied with the partial or
complete abortion of the reproductive organs   But in some of these plants
the seeds also differ in shape and sculpture   These differences have
sometimes been attributed to the pressure of the involucra on the florets 
or to their mutual pressure  and the shape of the seeds in the ray florets
of some Compositae countenances this idea  but with the Umbelliferae it is
by no means  as Dr  Hooker informs me  the species with the densest heads
which most frequently differ in their inner and outer flowers   It might
have been thought that the development of the ray petals  by drawing
nourishment from the reproductive organs causes their abortion  but this
can hardly be the sole case  for in some Compositae the seeds of the outer
and inner florets differ  without any difference in the corolla   Possibly
these several differences may be connected with the different flow of
nutriment towards the central and external flowers   We know  at least 
that with irregular flowers those nearest to the axis are most subject to
peloria  that is to become abnormally symmetrical   I may add  as an
instance of this fact  and as a striking case of correlation  that in many
pelargoniums the two upper petals in the central flower of the truss often
lose their patches of darker colour  and when this occurs  the adherent
nectary is quite aborted  the central flower thus becoming peloric or
regular   When the colour is absent from only one of the two upper petals 
the nectary is not quite aborted but is much shortened 

With respect to the development of the corolla  Sprengel s idea that the
ray florets serve to attract insects  whose agency is highly advantageous 
or necessary for the fertilisation of these plants  is highly probable  and
if so  natural selection may have come into play   But with respect to the
seeds  it seems impossible that their differences in shape  which are not
always correlated with any difference in the corolla  can be in any way
beneficial  yet in the Umbelliferae these differences are of such apparent
importance  the seeds being sometimes orthospermous in the exterior flowers
and coelospermous in the central flowers  that the elder De Candolle
founded his main divisions in the order on such characters   Hence
modifications of structure  viewed by systematists as of high value  may be
wholly due to the laws of variation and correlation  without being  as far
as we can judge  of the slightest service to the species 

We may often falsely attribute to correlated variation structures which are
common to whole groups of species  and which in truth are simply due to
inheritance  for an ancient progenitor may have acquired through natural
selection some one modification in structure  and  after thousands of
generations  some other and independent modification  and these two
modifications  having been transmitted to a whole group of descendants with
diverse habits  would naturally be thought to be in some necessary manner
correlated   Some other correlations are apparently due to the manner in
which natural selection can alone act   For instance  Alph  De Candolle has
remarked that winged seeds are never found in fruits which do not open  I
should explain this rule by the impossibility of seeds gradually becoming
winged through natural selection  unless the capsules were open  for in
this case alone could the seeds  which were a little better adapted to be
wafted by the wind  gain an advantage over others less well fitted for wide
dispersal 

COMPENSATION AND ECONOMY OF GROWTH 

The elder Geoffroy and Goethe propounded  at about the same time  their law
of compensation or balancement of growth  or  as Goethe expressed it   in
order to spend on one side  nature is forced to economise on the other
side    I think this holds true to a certain extent with our domestic
productions   if nourishment flows to one part or organ in excess  it
rarely flows  at least in excess  to another part  thus it is difficult to
get a cow to give much milk and to fatten readily   The same varieties of
the cabbage do not yield abundant and nutritious foliage and a copious
supply of oil bearing seeds   When the seeds in our fruits become
atrophied  the fruit itself gains largely in size and quality   In our
poultry  a large tuft of feathers on the head is generally accompanied by a
diminished comb  and a large beard by diminished wattles   With species in
a state of nature it can hardly be maintained that the law is of universal
application  but many good observers  more especially botanists  believe in
its truth   I will not  however  here give any instances  for I see hardly
any way of distinguishing between the effects  on the one hand  of a part
being largely developed through natural selection and another and adjoining
part being reduced by the same process or by disuse  and  on the other
hand  the actual withdrawal of nutriment from one part owing to the excess
of growth in another and adjoining part 

I suspect  also  that some of the cases of compensation which have been
advanced  and likewise some other facts  may be merged under a more general
principle  namely  that natural selection is continually trying to
economise in every part of the organisation   If under changed conditions
of life a structure  before useful  becomes less useful  its diminution
will be favoured  for it will profit the individual not to have its
nutriment wasted in building up a useless structure   I can thus only
understand a fact with which I was much struck when examining cirripedes 
and of which many other instances could be given   namely  that when a
cirripede is parasitic within another cirripede and is thus protected  it
loses more or less completely its own shell or carapace   This is the case
with the male Ibla  and in a truly extraordinary manner with the
Proteolepas   for the carapace in all other cirripedes consists of the
three highly important anterior segments of the head enormously developed 
and furnished with great nerves and muscles  but in the parasitic and
protected Proteolepas  the whole anterior part of the head is reduced to
the merest rudiment attached to the bases of the prehensile antennae   Now
the saving of a large and complex structure  when rendered superfluous 
would be a decided advantage to each successive individual of the species 
for in the struggle for life to which every animal is exposed  each would
have a better chance of supporting itself  by less nutriment being wasted 

Thus  as I believe  natural selection will tend in the long run to reduce
any part of the organisation  as soon as it becomes  through changed
habits  superfluous  without by any means causing some other part to be
largely developed in a corresponding degree   And conversely  that natural
selection may perfectly well succeed in largely developing an organ without
requiring as a necessary compensation the reduction of some adjoining part 

MULTIPLE  RUDIMENTARY  AND LOWLY ORGANISED STRUCTURES ARE VARIABLE 

It seems to be a rule  as remarked by Is  Geoffroy St  Hilaire  both with
varieties and species  that when any part or organ is repeated many times
in the same individual  as the vertebrae in snakes  and the stamens in
polyandrous flowers  the number is variable  whereas the number of the same
part or organ  when it occurs in lesser numbers  is constant   The same
author as well as some botanists  have further remarked that multiple parts
are extremely liable to vary in structure   As  vegetative repetition   to
use Professor Owen s expression  is a sign of low organisation  the
foregoing statements accord with the common opinion of naturalists  that
beings which stand low in the scale of nature are more variable than those
which are higher   I presume that lowness here means that the several parts
of the organisation have been but little specialised for particular
functions  and as long as the same part has to perform diversified work  we
can perhaps see why it should remain variable  that is  why natural
selection should not have preserved or rejected each little deviation of
form so carefully as when the part has to serve for some one special
purpose   In the same way that a knife which has to cut all sorts of things
may be of almost any shape  whilst a tool for some particular purpose must
be of some particular shape   Natural selection  it should never be
forgotten  can act solely through and for the advantage of each being 

Rudimentary parts  as is generally admitted  are apt to be highly variable  
We shall have to recur to this subject  and I will here only add that their
variability seems to result from their uselessness  and consequently from
natural selection having had no power to check deviations in their
structure 

A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY DEGREE OR MANNER  IN
COMPARISON WITH THE SAME PART IN ALLIED SPECIES  TENDS TO BE HIGHLY
VARIABLE 

Several years ago I was much struck by a remark to the above effect made by
Mr  Waterhouse   Professor Owen  also  seems to have come to a nearly
similar conclusion   It is hopeless to attempt to convince any one of the
truth of the above proposition without giving the long array of facts which
I have collected  and which cannot possibly be here introduced   I can only
state my conviction that it is a rule of high generality   I am aware of
several causes of error  but I hope that I have made due allowances for
them   It should be understood that the rule by no means applies to any
part  however unusually developed  unless it be unusually developed in one
species or in a few species in comparison with the same part in many
closely allied species   Thus  the wing of the bat is a most abnormal
structure in the class of mammals  but the rule would not apply here 
because the whole group of bats possesses wings  it would apply only if
some one species had wings developed in a remarkable manner in comparison
with the other species of the same genus   The rule applies very strongly
in the case of secondary sexual characters  when displayed in any unusual
manner   The term  secondary sexual characters  used by Hunter  relates to
characters which are attached to one sex  but are not directly connected
with the act of reproduction   The rule applies to males and females  but
more rarely to females  as they seldom offer remarkable secondary sexual
characters   The rule being so plainly applicable in the case of secondary
sexual characters  may be due to the great variability of these characters 
whether or not displayed in any unusual manner  of which fact I think there
can be little doubt   But that our rule is not confined to secondary sexual
characters is clearly shown in the case of hermaphrodite cirripedes  I
particularly attended to Mr  Waterhouse s remark  whilst investigating this
order  and I am fully convinced that the rule almost always holds good   I
shall  in a future work  give a list of all the more remarkable cases   I
will here give only one  as it illustrates the rule in its largest
application   The opercular valves of sessile cirripedes  rock barnacles 
are  in every sense of the word  very important structures  and they differ
extremely little even in distinct genera  but in the several species of one
genus  Pyrgoma  these valves present a marvellous amount of
diversification  the homologous valves in the different species being
sometimes wholly unlike in shape  and the amount of variation in the
individuals of the same species is so great that it is no exaggeration to
state that the varieties of the same species differ more from each other in
the characters derived from these important organs  than do the species
belonging to other distinct genera 

As with birds the individuals of the same species  inhabiting the same
country  vary extremely little  I have particularly attended to them  and
the rule certainly seems to hold good in this class   I cannot make out
that it applies to plants  and this would have seriously shaken my belief
in its truth  had not the great variability in plants made it particularly
difficult to compare their relative degrees of variability 

When we see any part or organ developed in a remarkable degree or manner in
a species  the fair presumption is that it is of high importance to that
species   nevertheless it is in this case eminently liable to variation  
Why should this be so   On the view that each species has been
independently created  with all its parts as we now see them  I can see no
explanation   But on the view that groups of species are descended from
some other species  and have been modified through natural selection  I
think we can obtain some light   First let me make some preliminary
remarks   If  in our domestic animals  any part or the whole animal be
neglected  and no selection be applied  that part  for instance  the comb
in the Dorking fowl  or the whole breed will cease to have a uniform
character   and the breed may be said to be degenerating   In rudimentary
organs  and in those which have been but little specialised for any
particular purpose  and perhaps in polymorphic groups  we see a nearly
parallel case  for in such cases natural selection either has not or cannot
come into full play  and thus the organisation is left in a fluctuating
condition   But what here more particularly concerns us is  that those
points in our domestic animals  which at the present time are undergoing
rapid change by continued selection  are also eminently liable to
variation   Look at the individuals of the same breed of the pigeon  and
see what a prodigious amount of difference there is in the beak of
tumblers  in the beak and wattle of carriers  in the carriage and tail of
fantails  etc   these being the points now mainly attended to by English
fanciers   Even in the same sub breed  as in that of the short faced
tumbler  it is notoriously difficult to breed nearly perfect birds  many
departing widely from the standard   There may truly be said to be a
constant struggle going on between  on the one hand  the tendency to
reversion to a less perfect state  as well as an innate tendency to new
variations  and  on the other hand  the power of steady selection to keep
the breed true   In the long run selection gains the day  and we do not
expect to fail so completely as to breed a bird as coarse as a common
tumbler pigeon from a good short faced strain   But as long as selection is
rapidly going on  much variability in the parts undergoing modification may
always be expected 

Now let us turn to nature   When a part has been developed in an
extraordinary manner in any one species  compared with the other species of
the same genus  we may conclude that this part has undergone an
extraordinary amount of modification since the period when the several
species branched off from the common progenitor of the genus   This period
will seldom be remote in any extreme degree  as species rarely endure for
more than one geological period   An extraordinary amount of modification
implies an unusually large and long continued amount of variability  which
has continually been accumulated by natural selection for the benefit of
the species   But as the variability of the extraordinarily developed part
or organ has been so great and long continued within a period not
excessively remote  we might  as a general rule  still expect to find more
variability in such parts than in other parts of the organisation which
have remained for a much longer period nearly constant   And this  I am
convinced  is the case   That the struggle between natural selection on the
one hand  and the tendency to reversion and variability on the other hand 
will in the course of time cease  and that the most abnormally developed
organs may be made constant  I see no reason to doubt   Hence  when an
organ  however abnormal it may be  has been transmitted in approximately
the same condition to many modified descendants  as in the case of the wing
of the bat  it must have existed  according to our theory  for an immense
period in nearly the same state  and thus it has come not to be more
variable than any other structure   It is only in those cases in which the
modification has been comparatively recent and extraordinarily great that
we ought to find the GENERATIVE VARIABILITY  as it may be called  still
present in a high degree   For in this case the variability will seldom as
yet have been fixed by the continued selection of the individuals varying
in the required manner and degree  and by the continued rejection of those
tending to revert to a former and less modified condition 

SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC CHARACTERS 

The principle discussed under the last heading may be applied to our
present subject   It is notorious that specific characters are more
variable than generic   To explain by a simple example what is meant   if
in a large genus of plants some species had blue flowers and some had red 
the colour would be only a specific character  and no one would be
surprised at one of the blue species varying into red  or conversely  but
if all the species had blue flowers  the colour would become a generic
character  and its variation would be a more unusual circumstance   I have
chosen this example because the explanation which most naturalists would
advance is not here applicable  namely  that specific characters are more
variable than generic  because they are taken from parts of less
physiological importance than those commonly used for classing genera   I
believe this explanation is partly  yet only indirectly  true  I shall 
however  have to return to this point in the chapter on Classification   It
would be almost superfluous to adduce evidence in support of the statement 
that ordinary specific characters are more variable than generic  but with
respect to important characters  I have repeatedly noticed in works on
natural history  that when an author remarks with surprise that some
important organ or part  which is generally very constant throughout a
large group of species  DIFFERS considerably in closely allied species  it
is often VARIABLE in the individuals of the same species   And this fact
shows that a character  which is generally of generic value  when it sinks
in value and becomes only of specific value  often becomes variable  though
its physiological importance may remain the same   Something of the same
kind applies to monstrosities   at least Is  Geoffroy St  Hilaire
apparently entertains no doubt  that the more an organ normally differs in
the different species of the same group  the more subject it is to
anomalies in the individuals 

On the ordinary view of each species having been independently created  why
should that part of the structure  which differs from the same part in
other independently created species of the same genus  be more variable
than those parts which are closely alike in the several species   I do not
see that any explanation can be given   But on the view that species are
only strongly marked and fixed varieties  we might expect often to find
them still continuing to vary in those parts of their structure which have
varied within a moderately recent period  and which have thus come to
differ   Or to state the case in another manner   the points in which all
the species of a genus resemble each other  and in which they differ from
allied genera  are called generic characters  and these characters may be
attributed to inheritance from a common progenitor  for it can rarely have
happened that natural selection will have modified several distinct
species  fitted to more or less widely different habits  in exactly the
same manner   and as these so called generic characters have been inherited
from before the period when the several species first branched off from
their common progenitor  and subsequently have not varied or come to differ
in any degree  or only in a slight degree  it is not probable that they
should vary at the present day   On the other hand  the points in which
species differ from other species of the same genus are called specific
characters  and as these specific characters have varied and come to differ
since the period when the species branched off from a common progenitor  it
is probable that they should still often be in some degree variable  at
least more variable than those parts of the organisation which have for a
very long period remained constant 

SECONDARY SEXUAL CHARACTERS VARIABLE 

I think it will be admitted by naturalists  without my entering on details 
that secondary sexual characters are highly variable   It will also be
admitted that species of the same group differ from each other more widely
in their secondary sexual characters  than in other parts of their
organisation  compare  for instance  the amount of difference between the
males of gallinaceous birds  in which secondary sexual characters are
strongly displayed  with the amount of difference between the females   The
cause of the original variability of these characters is not manifest  but
we can see why they should not have been rendered as constant and uniform
as others  for they are accumulated by sexual selection  which is less
rigid in its action than ordinary selection  as it does not entail death 
but only gives fewer offspring to the less favoured males   Whatever the
cause may be of the variability of secondary sexual characters  as they are
highly variable  sexual selection will have had a wide scope for action 
and may thus have succeeded in giving to the species of the same group a
greater amount of difference in these than in other respects 

It is a remarkable fact  that the secondary differences between the two
sexes of the same species are generally displayed in the very same parts of
the organisation in which the species of the same genus differ from each
other   Of this fact I will give in illustration the first two instances
which happen to stand on my list  and as the differences in these cases are
of a very unusual nature  the relation can hardly be accidental   The same
number of joints in the tarsi is a character common to very large groups of
beetles  but in the Engidae  as Westwood has remarked  the number varies
greatly and the number likewise differs in the two sexes of the same
species   Again in the fossorial hymenoptera  the neuration of the wings is
a character of the highest importance  because common to large groups  but
in certain genera the neuration differs in the different species  and
likewise in the two sexes of the same species   Sir J  Lubbock has recently
remarked  that several minute crustaceans offer excellent illustrations of
this law    In Pontella  for instance  the sexual characters are afforded
mainly by the anterior antennae and by the fifth pair of legs   the
specific differences also are principally given by these organs    This
relation has a clear meaning on my view   I look at all the species of the
same genus as having as certainly descended from the same progenitor  as
have the two sexes of any one species   Consequently  whatever part of the
structure of the common progenitor  or of its early descendants  became
variable  variations of this part would  it is highly probable  be taken
advantage of by natural and sexual selection  in order to fit the several
places in the economy of nature  and likewise to fit the two sexes of the
same species to each other  or to fit the males to struggle with other
males for the possession of the females 

Finally  then  I conclude that the greater variability of specific
characters  or those which distinguish species from species  than of
generic characters  or those which are possessed by all the species  that
the frequent extreme variability of any part which is developed in a
species in an extraordinary manner in comparison with the same part in its
congeners  and the slight degree of variability in a part  however
extraordinarily it may be developed  if it be common to a whole group of
species  that the great variability of secondary sexual characters and
their great difference in closely allied species  that secondary sexual and
ordinary specific differences are generally displayed in the same parts of
the organisation  are all principles closely connected together   All being
mainly due to the species of the same group being the descendants of a
common progenitor  from whom they have inherited much in common  to parts
which have recently and largely varied being more likely still to go on
varying than parts which have long been inherited and have not varied  to
natural selection having more or less completely  according to the lapse of
time  overmastered the tendency to reversion and to further variability  to
sexual selection being less rigid than ordinary selection  and to
variations in the same parts having been accumulated by natural and sexual
selection  and thus having been adapted for secondary sexual  and for
ordinary purposes 

DISTINCT SPECIES PRESENT ANALOGOUS VARIATIONS  SO THAT A VARIETY OF ONE
SPECIES OFTEN ASSUMES A CHARACTER PROPER TO AN ALLIED SPECIES  OR REVERTS
TO SOME OF THE CHARACTERS OF AN EARLY PROGENITOR 

These propositions will be most readily understood by looking to our
domestic races   The most distinct breeds of the pigeon  in countries
widely apart  present sub varieties with reversed feathers on the head  and
with feathers on the feet  characters not possessed by the aboriginal
rock pigeon  these then are analogous variations in two or more distinct
races   The frequent presence of fourteen or even sixteen tail feathers in
the pouter may be considered as a variation representing the normal
structure of another race  the fantail   I presume that no one will doubt
that all such analogous variations are due to the several races of the
pigeon having inherited from a common parent the same constitution and
tendency to variation  when acted on by similar unknown influences   In the
vegetable kingdom we have a case of analogous variation  in the enlarged
stems  or as commonly called roots  of the Swedish turnip and ruta baga 
plants which several botanists rank as varieties produced by cultivation
from a common parent   if this be not so  the case will then be one of
analogous variation in two so called distinct species  and to these a third
may be added  namely  the common turnip   According to the ordinary view of
each species having been independently created  we should have to attribute
this similarity in the enlarged stems of these three plants  not to the
vera causa of community of descent  and a consequent tendency to vary in a
like manner  but to three separate yet closely related acts of creation  
Many similar cases of analogous variation have been observed by Naudin in
the great gourd family  and by various authors in our cereals   Similar
cases occurring with insects under natural conditions have lately been
discussed with much ability by Mr  Walsh  who has grouped them under his
law of equable variability 

With pigeons  however  we have another case  namely  the occasional
appearance in all the breeds  of slaty blue birds with two black bars on
the wings  white loins  a bar at the end of the tail  with the outer
feathers externally edged near their bases with white   As all these marks
are characteristic of the parent rock pigeon  I presume that no one will
doubt that this is a case of reversion  and not of a new yet analogous
variation appearing in the several breeds   We may  I think  confidently
come to this conclusion  because  as we have seen  these coloured marks are
eminently liable to appear in the crossed offspring of two distinct and
differently coloured breeds  and in this case there is nothing in the
external conditions of life to cause the reappearance of the slaty blue 
with the several marks  beyond the influence of the mere act of crossing on
the laws of inheritance 

No doubt it is a very surprising fact that characters should reappear after
having been lost for many  probably for hundreds of generations   But when
a breed has been crossed only once by some other breed  the offspring
occasionally show for many generations a tendency to revert in character to
the foreign breed  some say  for a dozen or even a score of generations  
After twelve generations  the proportion of blood  to use a common
expression  from one ancestor  is only 1 in 2048  and yet  as we see  it is
generally believed that a tendency to reversion is retained by this remnant
of foreign blood   In a breed which has not been crossed  but in which BOTH
parents have lost some character which their progenitor possessed  the
tendency  whether strong or weak  to reproduce the lost character might  as
was formerly remarked  for all that we can see to the contrary  be
transmitted for almost any number of generations   When a character which
has been lost in a breed  reappears after a great number of generations 
the most probable hypothesis is  not that one individual suddenly takes
after an ancestor removed by some hundred generations  but that in each
successive generation the character in question has been lying latent  and
at last  under unknown favourable conditions  is developed   With the
barb pigeon  for instance  which very rarely produces a blue bird  it is
probable that there is a latent tendency in each generation to produce blue
plumage   The abstract improbability of such a tendency being transmitted
through a vast number of generations  is not greater than that of quite
useless or rudimentary organs being similarly transmitted   A mere tendency
to produce a rudiment is indeed sometimes thus inherited 

As all the species of the same genus are supposed to be descended from a
common progenitor  it might be expected that they would occasionally vary
in an analogous manner  so that the varieties of two or more species would
resemble each other  or that a variety of one species would resemble in
certain characters another and distinct species  this other species being 
according to our view  only a well marked and permanent variety   But
characters exclusively due to analogous variation would probably be of an
unimportant nature  for the preservation of all functionally important
characters will have been determined through natural selection  in
accordance with the different habits of the species   It might further be
expected that the species of the same genus would occasionally exhibit
reversions to long lost characters   As  however  we do not know the common
ancestor of any natural group  we cannot distinguish between reversionary
and analogous characters   If  for instance  we did not know that the
parent rock pigeon was not feather footed or turn crowned  we could not
have told  whether such characters in our domestic breeds were reversions
or only analogous variations  but we might have inferred that the blue
colour was a case of reversion from the number of the markings  which are
correlated with this tint  and which would not probably have all appeared
together from simple variation   More especially we might have inferred
this from the blue colour and the several marks so often appearing when
differently coloured breeds are crossed   Hence  although under nature it
must generally be left doubtful  what cases are reversions to formerly
existing characters  and what are new but analogous variations  yet we
ought  on our theory  sometimes to find the varying offspring of a species
assuming characters which are already present in other members of the same
group   And this undoubtedly is the case 

The difficulty in distinguishing variable species is largely due to the
varieties mocking  as it were  other species of the same genus   A
considerable catalogue  also  could be given of forms intermediate between
two other forms  which themselves can only doubtfully be ranked as species 
and this shows  unless all these closely allied forms be considered as
independently created species  that they have in varying assumed some of
the characters of the others   But the best evidence of analogous
variations is afforded by parts or organs which are generally constant in
character  but which occasionally vary so as to resemble  in some degree 
the same part or organ in an allied species   I have collected a long list
of such cases  but here  as before  I lie under the great disadvantage of
not being able to give them   I can only repeat that such cases certainly
occur  and seem to me very remarkable 

I will  however  give one curious and complex case  not indeed as affecting
any important character  but from occurring in several species of the same
genus  partly under domestication and partly under nature   It is a case
almost certainly of reversion   The ass sometimes has very distinct
transverse bars on its legs  like those on the legs of a zebra   It has
been asserted that these are plainest in the foal  and from inquiries which
I have made  I believe this to be true   The stripe on the shoulder is
sometimes double  and is very variable in length and outline   A white ass 
but NOT an albino  has been described without either spinal or shoulder
stripe  and these stripes are sometimes very obscure  or actually quite
lost  in dark coloured asses   The koulan of Pallas is said to have been
seen with a double shoulder stripe   Mr  Blyth has seen a specimen of the
hemionus with a distinct shoulder stripe  though it properly has none  and
I have been informed by Colonel Poole that foals of this species are
generally striped on the legs and faintly on the shoulder   The quagga 
though so plainly barred like a zebra over the body  is without bars on the
legs  but Dr  Gray has figured one specimen with very distinct zebra like
bars on the hocks 

With respect to the horse  I have collected cases in England of the spinal
stripe in horses of the most distinct breeds  and of ALL colours 
transverse bars on the legs are not rare in duns  mouse duns  and in one
instance in a chestnut  a faint shoulder stripe may sometimes be seen in
duns  and I have seen a trace in a bay horse   My son made a careful
examination and sketch for me of a dun Belgian cart horse with a double
stripe on each shoulder and with leg stripes   I have myself seen a dun
Devonshire pony  and a small dun Welsh pony has been carefully described to
me  both with THREE parallel stripes on each shoulder 

In the northwest part of India the Kattywar breed of horses is so generally
striped  that  as I hear from Colonel Poole  who examined this breed for
the Indian Government  a horse without stripes is not considered as purely
bred   The spine is always striped  the legs are generally barred  and the
shoulder stripe  which is sometimes double and sometimes treble  is common 
the side of the face  moreover  is sometimes striped   The stripes are
often plainest in the foal  and sometimes quite disappear in old horses  
Colonel Poole has seen both gray and bay Kattywar horses striped when first
foaled   I have also reason to suspect  from information given me by Mr 
W W  Edwards  that with the English race horse the spinal stripe is much
commoner in the foal than in the full grown animal   I have myself recently
bred a foal from a bay mare  offspring of a Turkoman horse and a Flemish
mare  by a bay English race horse   This foal  when a week old  was marked
on its hinder quarters and on its forehead with numerous very narrow  dark 
zebra like bars  and its legs were feebly striped   All the stripes soon
disappeared completely   Without here entering on further details I may
state that I have collected cases of leg and shoulder stripes in horses of
very different breeds in various countries from Britain to Eastern China 
and from Norway in the north to the Malay Archipelago in the south   In all
parts of the world these stripes occur far oftenest in duns and mouse duns 
by the term dun a large range of colour is included  from one between brown
and black to a close approach to cream colour 

I am aware that Colonel Hamilton Smith  who has written on this subject 
believes that the several breeds of the horse are descended from several
aboriginal species  one of which  the dun  was striped  and that the
above described appearances are all due to ancient crosses with the dun
stock   But this view may be safely rejected  for it is highly improbable
that the heavy Belgian cart horse  Welsh ponies  Norwegian cobs  the lanky
Kattywar race  etc   inhabiting the most distant parts of the world  should
have all have been crossed with one supposed aboriginal stock 

Now let us turn to the effects of crossing the several species of the horse
genus   Rollin asserts that the common mule from the ass and horse is
particularly apt to have bars on its legs  according to Mr  Gosse  in
certain parts of the United States  about nine out of ten mules have
striped legs   I once saw a mule with its legs so much striped that any one
might have thought that it was a hybrid zebra  and Mr  W C  Martin  in his
excellent treatise on the horse  has given a figure of a similar mule   In
four coloured drawings  which I have seen  of hybrids between the ass and
zebra  the legs were much more plainly barred than the rest of the body 
and in one of them there was a double shoulder stripe   In Lord Morton s
famous hybrid  from a chestnut mare and male quagga  the hybrid and even
the pure offspring subsequently produced from the same mare by a black
Arabian sire  were much more plainly barred across the legs than is even
the pure quagga   Lastly  and this is another most remarkable case  a
hybrid has been figured by Dr  Gray  and he informs me that he knows of a
second case  from the ass and the hemionus  and this hybrid  though the ass
only occasionally has stripes on his legs and the hemionus has none and has
not even a shoulder stripe  nevertheless had all four legs barred  and had
three short shoulder stripes  like those on the dun Devonshire and Welsh
ponies  and even had some zebra like stripes on the sides of its face  
With respect to this last fact  I was so convinced that not even a stripe
of colour appears from what is commonly called chance  that I was led
solely from the occurrence of the face stripes on this hybrid from the ass
and hemionus to ask Colonel Poole whether such face stripes ever occurred
in the eminently striped Kattywar breed of horses  and was  as we have
seen  answered in the affirmative 

What now are we to say to these several facts   We see several distinct
species of the horse genus becoming  by simple variation  striped on the
legs like a zebra  or striped on the shoulders like an ass   In the horse
we see this tendency strong whenever a dun tint appears  a tint which
approaches to that of the general colouring of the other species of the
genus   The appearance of the stripes is not accompanied by any change of
form  or by any other new character   We see this tendency to become
striped most strongly displayed in hybrids from between several of the most
distinct species   Now observe the case of the several breeds of pigeons  
they are descended from a pigeon  including two or three sub species or
geographical races  of a bluish colour  with certain bars and other marks 
and when any breed assumes by simple variation a bluish tint  these bars
and other marks invariably reappear  but without any other change of form
or character   When the oldest and truest breeds of various colours are
crossed  we see a strong tendency for the blue tint and bars and marks to
reappear in the mongrels   I have stated that the most probable hypothesis
to account for the reappearance of very ancient characters  is  that there
is a TENDENCY in the young of each successive generation to produce the
long lost character  and that this tendency  from unknown causes  sometimes
prevails   And we have just seen that in several species of the horse genus
the stripes are either plainer or appear more commonly in the young than in
the old   Call the breeds of pigeons  some of which have bred true for
centuries  species  and how exactly parallel is the case with that of the
species of the horse genus   For myself  I venture confidently to look back
thousands on thousands of generations  and I see an animal striped like a
zebra  but perhaps otherwise very differently constructed  the common
parent of our domestic horse  whether or not it be descended from one or
more wild stocks  of the ass  the hemionus  quagga  and zebra 

He who believes that each equine species was independently created  will  I
presume  assert that each species has been created with a tendency to vary 
both under nature and under domestication  in this particular manner  so as
often to become striped like the other species of the genus  and that each
has been created with a strong tendency  when crossed with species
inhabiting distant quarters of the world  to produce hybrids resembling in
their stripes  not their own parents  but other species of the genus   To
admit this view is  as it seems to me  to reject a real for an unreal  or
at least for an unknown cause   It makes the works of God a mere mockery
and deception  I would almost as soon believe with the old and ignorant
cosmogonists  that fossil shells had never lived  but had been created in
stone so as to mock the shells now living on the sea shore 

SUMMARY 

Our ignorance of the laws of variation is profound   Not in one case out of
a hundred can we pretend to assign any reason why this or that part has
varied   But whenever we have the means of instituting a comparison  the
same laws appear to have acted in producing the lesser differences between
varieties of the same species  and the greater differences between species
of the same genus   Changed conditions generally induce mere fluctuating
variability  but sometimes they cause direct and definite effects  and
these may become strongly marked in the course of time  though we have not
sufficient evidence on this head   Habit in producing constitutional
peculiarities  and use in strengthening  and disuse in weakening and
diminishing organs  appear in many cases to have been potent in their
effects   Homologous parts tend to vary in the same manner  and homologous
parts tend to cohere   Modifications in hard parts and in external parts
sometimes affect softer and internal parts   When one part is largely
developed  perhaps it tends to draw nourishment from the adjoining parts 
and every part of the structure which can be saved without detriment will
be saved   Changes of structure at an early age may affect parts
subsequently developed  and many cases of correlated variation  the nature
of which we are unable to understand  undoubtedly occur   Multiple parts
are variable in number and in structure  perhaps arising from such parts
not having been closely specialised for any particular function  so that
their modifications have not been closely checked by natural selection   It
follows probably from this same cause  that organic beings low in the scale
are more variable than those standing higher in the scale  and which have
their whole organisation more specialised   Rudimentary organs  from being
useless  are not regulated by natural selection  and hence are variable  
Specific characters  that is  the characters which have come to differ
since the several species of the same genus branched off from a common
parent  are more variable than generic characters  or those which have long
been inherited  and have not differed within this same period   In these
remarks we have referred to special parts or organs being still variable 
because they have recently varied and thus come to differ  but we have also
seen in the second chapter that the same principle applies to the whole
individual  for in a district where many species of a genus are found  that
is  where there has been much former variation and differentiation  or
where the manufactory of new specific forms has been actively at work  in
that district and among these species  we now find  on an average  most
varieties   Secondary sexual characters are highly variable  and such
characters differ much in the species of the same group   Variability in
the same parts of the organisation has generally been taken advantage of in
giving secondary sexual differences to the two sexes of the same species 
and specific differences to the several species of the same genus   Any
part or organ developed to an extraordinary size or in an extraordinary
manner  in comparison with the same part or organ in the allied species 
must have gone through an extraordinary amount of modification since the
genus arose  and thus we can understand why it should often still be
variable in a much higher degree than other parts  for variation is a
long continued and slow process  and natural selection will in such cases
not as yet have had time to overcome the tendency to further variability
and to reversion to a less modified state   But when a species with an
extraordinarily developed organ has become the parent of many modified
descendants  which on our view must be a very slow process  requiring a
long lapse of time  in this case  natural selection has succeeded in giving
a fixed character to the organ  in however extraordinary a manner it may
have been developed   Species inheriting nearly the same constitution from
a common parent  and exposed to similar influences  naturally tend to
present analogous variations  or these same species may occasionally revert
to some of the characters of their ancient progenitors   Although new and
important modifications may not arise from reversion and analogous
variation  such modifications will add to the beautiful and harmonious
diversity of nature 

Whatever the cause may be of each slight difference between the offspring
and their parents  and a cause for each must exist  we have reason to
believe that it is the steady accumulation of beneficial differences which
has given rise to all the more important modifications of structure in
relation to the habits of each species 
 

CHAPTER VI 

DIFFICULTIES OF THE THEORY 

Difficulties of the theory of descent with modification    Absence or
rarity of transitional varieties    Transitions in habits of life   
Diversified habits in the same species    Species with habits widely
different from those of their allies    Organs of extreme perfection   
Modes of transition    Cases of difficulty    Natura non facit saltum   
Organs of small importance    Organs not in all cases absolutely perfect   
The law of Unity of Type and of the Conditions of Existence embraced by the
theory of Natural Selection 

Long before the reader has arrived at this part of my work  a crowd of
difficulties will have occurred to him   Some of them are so serious that
to this day I can hardly reflect on them without being in some degree
staggered  but  to the best of my judgment  the greater number are only
apparent  and those that are real are not  I think  fatal to the theory 

These difficulties and objections may be classed under the following heads  
First  why  if species have descended from other species by fine
gradations  do we not everywhere see innumerable transitional forms   Why
is not all nature in confusion  instead of the species being  as we see
them  well defined 

Secondly  is it possible that an animal having  for instance  the structure
and habits of a bat  could have been formed by the modification of some
other animal with widely different habits and structure   Can we believe
that natural selection could produce  on the one hand  an organ of trifling
importance  such as the tail of a giraffe  which serves as a fly flapper 
and  on the other hand  an organ so wonderful as the eye 

Thirdly  can instincts be acquired and modified through natural selection  
What shall we say to the instinct which leads the bee to make cells  and
which has practically anticipated the discoveries of profound
mathematicians 

Fourthly  how can we account for species  when crossed  being sterile and
producing sterile offspring  whereas  when varieties are crossed  their
fertility is unimpaired 

The two first heads will be here discussed  some miscellaneous objections
in the following chapter  Instinct and Hybridism in the two succeeding
chapters 

ON THE ABSENCE OR RARITY OF TRANSITIONAL VARIETIES 

As natural selection acts solely by the preservation of profitable
modifications  each new form will tend in a fully stocked country to take
the place of  and finally to exterminate  its own less improved parent form
and other less favoured forms with which it comes into competition   Thus
extinction and natural selection go hand in hand   Hence  if we look at
each species as descended from some unknown form  both the parent and all
the transitional varieties will generally have been exterminated by the
very process of the formation and perfection of the new form 

But  as by this theory innumerable transitional forms must have existed 
why do we not find them embedded in countless numbers in the crust of the
earth   It will be more convenient to discuss this question in the chapter
on the imperfection of the geological record  and I will here only state
that I believe the answer mainly lies in the record being incomparably less
perfect than is generally supposed   The crust of the earth is a vast
museum  but the natural collections have been imperfectly made  and only at
long intervals of time 

But it may be urged that when several closely allied species inhabit the
same territory  we surely ought to find at the present time many
transitional forms   Let us take a simple case   in travelling from north
to south over a continent  we generally meet at successive intervals with
closely allied or representative species  evidently filling nearly the same
place in the natural economy of the land   These representative species
often meet and interlock  and as the one becomes rarer and rarer  the other
becomes more and more frequent  till the one replaces the other   But if we
compare these species where they intermingle  they are generally as
absolutely distinct from each other in every detail of structure as are
specimens taken from the metropolis inhabited by each   By my theory these
allied species are descended from a common parent  and during the process
of modification  each has become adapted to the conditions of life of its
own region  and has supplanted and exterminated its original parent form
and all the transitional varieties between its past and present states  
Hence we ought not to expect at the present time to meet with numerous
transitional varieties in each region  though they must have existed there 
and may be embedded there in a fossil condition   But in the intermediate
region  having intermediate conditions of life  why do we not now find
closely linking intermediate varieties   This difficulty for a long time
quite confounded me   But I think it can be in large part explained 

In the first place we should be extremely cautious in inferring  because an
area is now continuous  that it has been continuous during a long period  
Geology would lead us to believe that most continents have been broken up
into islands even during the later tertiary periods  and in such islands
distinct species might have been separately formed without the possibility
of intermediate varieties existing in the intermediate zones   By changes
in the form of the land and of climate  marine areas now continuous must
often have existed within recent times in a far less continuous and uniform
condition than at present   But I will pass over this way of escaping from
the difficulty  for I believe that many perfectly defined species have been
formed on strictly continuous areas  though I do not doubt that the
formerly broken condition of areas now continuous  has played an important
part in the formation of new species  more especially with freely crossing
and wandering animals 

In looking at species as they are now distributed over a wide area  we
generally find them tolerably numerous over a large territory  then
becoming somewhat abruptly rarer and rarer on the confines  and finally
disappearing   Hence the neutral territory between two representative
species is generally narrow in comparison with the territory proper to
each   We see the same fact in ascending mountains  and sometimes it is
quite remarkable how abruptly  as Alph  De Candolle has observed  a common
alpine species disappears   The same fact has been noticed by E  Forbes in
sounding the depths of the sea with the dredge   To those who look at
climate and the physical conditions of life as the all important elements
of distribution  these facts ought to cause surprise  as climate and height
or depth graduate away insensibly   But when we bear in mind that almost
every species  even in its metropolis  would increase immensely in numbers 
were it not for other competing species  that nearly all either prey on or
serve as prey for others  in short  that each organic being is either
directly or indirectly related in the most important manner to other
organic beings  we see that the range of the inhabitants of any country by
no means exclusively depends on insensibly changing physical conditions 
but in large part on the presence of other species  on which it lives  or
by which it is destroyed  or with which it comes into competition  and as
these species are already defined objects  not blending one into another by
insensible gradations  the range of any one species  depending as it does
on the range of others  will tend to be sharply defined   Moreover  each
species on the confines of its range  where it exists in lessened numbers 
will  during fluctuations in the number of its enemies or of its prey  or
in the nature of the seasons  be extremely liable to utter extermination 
and thus its geographical range will come to be still more sharply defined 

As allied or representative species  when inhabiting a continuous area  are
generally distributed in such a manner that each has a wide range  with a
comparatively narrow neutral territory between them  in which they become
rather suddenly rarer and rarer  then  as varieties do not essentially
differ from species  the same rule will probably apply to both  and if we
take a varying species inhabiting a very large area  we shall have to adapt
two varieties to two large areas  and a third variety to a narrow
intermediate zone   The intermediate variety  consequently  will exist in
lesser numbers from inhabiting a narrow and lesser area  and practically 
as far as I can make out  this rule holds good with varieties in a state of
nature   I have met with striking instances of the rule in the case of
varieties intermediate between well marked varieties in the genus Balanus  
And it would appear from information given me by Mr  Watson  Dr  Asa Gray 
and Mr  Wollaston  that generally  when varieties intermediate between two
other forms occur  they are much rarer numerically than the forms which
they connect   Now  if we may trust these facts and inferences  and
conclude that varieties linking two other varieties together generally have
existed in lesser numbers than the forms which they connect  then we can
understand why intermediate varieties should not endure for very long
periods   why  as a general rule  they should be exterminated and
disappear  sooner than the forms which they originally linked together 

For any form existing in lesser numbers would  as already remarked  run a
greater chance of being exterminated than one existing in large numbers 
and in this particular case the intermediate form would be eminently liable
to the inroads of closely allied forms existing on both sides of it   But
it is a far more important consideration  that during the process of
further modification  by which two varieties are supposed to be converted
and perfected into two distinct species  the two which exist in larger
numbers  from inhabiting larger areas  will have a great advantage over the
intermediate variety  which exists in smaller numbers in a narrow and
intermediate zone   For forms existing in larger numbers will have a better
chance  within any given period  of presenting further favourable
variations for natural selection to seize on  than will the rarer forms
which exist in lesser numbers   Hence  the more common forms  in the race
for life  will tend to beat and supplant the less common forms  for these
will be more slowly modified and improved   It is the same principle which 
as I believe  accounts for the common species in each country  as shown in
the second chapter  presenting on an average a greater number of
well marked varieties than do the rarer species   I may illustrate what I
mean by supposing three varieties of sheep to be kept  one adapted to an
extensive mountainous region  a second to a comparatively narrow  hilly
tract  and a third to the wide plains at the base  and that the inhabitants
are all trying with equal steadiness and skill to improve their stocks by
selection  the chances in this case will be strongly in favour of the great
holders on the mountains or on the plains improving their breeds more
quickly than the small holders on the intermediate narrow  hilly tract  and
consequently the improved mountain or plain breed will soon take the place
of the less improved hill breed  and thus the two breeds  which originally
existed in greater numbers  will come into close contact with each other 
without the interposition of the supplanted  intermediate hill variety 

To sum up  I believe that species come to be tolerably well defined
objects  and do not at any one period present an inextricable chaos of
varying and intermediate links   first  because new varieties are very
slowly formed  for variation is a slow process  and natural selection can
do nothing until favourable individual differences or variations occur  and
until a place in the natural polity of the country can be better filled by
some modification of some one or more of its inhabitants   And such new
places will depend on slow changes of climate  or on the occasional
immigration of new inhabitants  and  probably  in a still more important
degree  on some of the old inhabitants becoming slowly modified  with the
new forms thus produced and the old ones acting and reacting on each other  
So that  in any one region and at any one time  we ought to see only a few
species presenting slight modifications of structure in some degree
permanent  and this assuredly we do see 

Secondly  areas now continuous must often have existed within the recent
period as isolated portions  in which many forms  more especially among the
classes which unite for each birth and wander much  may have separately
been rendered sufficiently distinct to rank as representative species   In
this case  intermediate varieties between the several representative
species and their common parent  must formerly have existed within each
isolated portion of the land  but these links during the process of natural
selection will have been supplanted and exterminated  so that they will no
longer be found in a living state 

Thirdly  when two or more varieties have been formed in different portions
of a strictly continuous area  intermediate varieties will  it is probable 
at first have been formed in the intermediate zones  but they will
generally have had a short duration   For these intermediate varieties
will  from reasons already assigned  namely from what we know of the actual
distribution of closely allied or representative species  and likewise of
acknowledged varieties   exist in the intermediate zones in lesser numbers
than the varieties which they tend to connect   From this cause alone the
intermediate varieties will be liable to accidental extermination  and
during the process of further modification through natural selection  they
will almost certainly be beaten and supplanted by the forms which they
connect  for these  from existing in greater numbers will  in the
aggregate  present more varieties  and thus be further improved through
natural selection and gain further advantages 

Lastly  looking not to any one time  but at all time  if my theory be true 
numberless intermediate varieties  linking closely together all the species
of the same group  must assuredly have existed  but the very process of
natural selection constantly tends  as has been so often remarked  to
exterminate the parent forms and the intermediate links   Consequently
evidence of their former existence could be found only among fossil remains 
which are preserved  as we shall attempt to show in a future chapter  in an
extremely imperfect and intermittent record 

ON THE ORIGIN AND TRANSITION OF ORGANIC BEINGS WITH PECULIAR HABITS AND
STRUCTURE 

It has been asked by the opponents of such views as I hold  how  for
instance  could a land carnivorous animal have been converted into one with
aquatic habits  for how could the animal in its transitional state have
subsisted   It would be easy to show that there now exist carnivorous
animals presenting close intermediate grades from strictly terrestrial to
aquatic habits  and as each exists by a struggle for life  it is clear that
each must be well adapted to its place in nature   Look at the Mustela
vison of North America  which has webbed feet  and which resembles an otter
in its fur  short legs  and form of tail  during summer this animal dives
for and preys on fish  but during the long winter it leaves the frozen
waters  and preys  like other polecats on mice and land animals   If a
different case had been taken  and it had been asked how an insectivorous
quadruped could possibly have been converted into a flying bat  the
question would have been far more difficult to answer   Yet I think such
difficulties have little weight 

Here  as on other occasions  I lie under a heavy disadvantage  for  out of
the many striking cases which I have collected  I can give only one or two
instances of transitional habits and structures in allied species  and of
diversified habits  either constant or occasional  in the same species  
And it seems to me that nothing less than a long list of such cases is
sufficient to lessen the difficulty in any particular case like that of the
bat 

Look at the family of squirrels  here we have the finest gradation from
animals with their tails only slightly flattened  and from others  as Sir
J  Richardson has remarked  with the posterior part of their bodies rather
wide and with the skin on their flanks rather full  to the so called flying
squirrels  and flying squirrels have their limbs and even the base of the
tail united by a broad expanse of skin  which serves as a parachute and
allows them to glide through the air to an astonishing distance from tree
to tree   We cannot doubt that each structure is of use to each kind of
squirrel in its own country  by enabling it to escape birds or beasts of
prey  or to collect food more quickly  or  as there is reason to believe 
to lessen the danger from occasional falls   But it does not follow from
this fact that the structure of each squirrel is the best that it is
possible to conceive under all possible conditions   Let the climate and
vegetation change  let other competing rodents or new beasts of prey
immigrate  or old ones become modified  and all analogy would lead us to
believe that some  at least  of the squirrels would decrease in numbers or
become exterminated  unless they also become modified and improved in
structure in a corresponding manner   Therefore  I can see no difficulty 
more especially under changing conditions of life  in the continued
preservation of individuals with fuller and fuller flank membranes  each
modification being useful  each being propagated  until  by the accumulated
effects of this process of natural selection  a perfect so called flying
squirrel was produced 

Now look at the Galeopithecus or so called flying lemur  which was formerly
ranked among bats  but is now believed to belong to the Insectivora   An
extremely wide flank membrane stretches from the corners of the jaw to the
tail  and includes the limbs with the elongated fingers   This flank 
membrane is furnished with an extensor muscle   Although no graduated links
of structure  fitted for gliding through the air  now connect the
Galeopithecus with the other Insectivora  yet there is no difficulty in
supposing that such links formerly existed  and that each was developed in
the same manner as with the less perfectly gliding squirrels  each grade of
structure having been useful to its possessor   Nor can I see any
insuperable difficulty in further believing it possible that the
membrane connected fingers and fore arm of the Galeopithecus might have
been greatly lengthened by natural selection  and this  as far as the
organs of flight are concerned  would have converted the animal into a bat  
In certain bats in which the wing membrane extends from the top of the
shoulder to the tail and includes the hind legs  we perhaps see traces of
an apparatus originally fitted for gliding through the air rather than for
flight 

If about a dozen genera of birds were to become extinct  who would have
ventured to surmise that birds might have existed which used their wings
solely as flappers  like the logger headed duck  Micropterus of Eyton   as
fins in the water and as front legs on the land  like the penguin  as
sails  like the ostrich  and functionally for no purpose  like the apteryx  
Yet the structure of each of these birds is good for it  under the
conditions of life to which it is exposed  for each has to live by a
struggle   but it is not necessarily the best possible under all possible
conditions   It must not be inferred from these remarks that any of the
grades of wing structure here alluded to  which perhaps may all be the
result of disuse  indicate the steps by which birds actually acquired their
perfect power of flight  but they serve to show what diversified means of
transition are at least possible 

Seeing that a few members of such water breathing classes as the Crustacea
and Mollusca are adapted to live on the land  and seeing that we have
flying birds and mammals  flying insects of the most diversified types  and
formerly had flying reptiles  it is conceivable that flying fish  which now
glide far through the air  slightly rising and turning by the aid of their
fluttering fins  might have been modified into perfectly winged animals  
If this had been effected  who would have ever imagined that in an early
transitional state they had been inhabitants of the open ocean  and had
used their incipient organs of flight exclusively  so far as we know  to
escape being devoured by other fish 

When we see any structure highly perfected for any particular habit  as the
wings of a bird for flight  we should bear in mind that animals displaying
early transitional grades of the structure will seldom have survived to the
present day  for they will have been supplanted by their successors  which
were gradually rendered more perfect through natural selection  
Furthermore  we may conclude that transitional states between structures
fitted for very different habits of life will rarely have been developed at
an early period in great numbers and under many subordinate forms   Thus 
to return to our imaginary illustration of the flying fish  it does not
seem probable that fishes capable of true flight would have been developed
under many subordinate forms  for taking prey of many kinds in many ways 
on the land and in the water  until their organs of flight had come to a
high stage of perfection  so as to have given them a decided advantage over
other animals in the battle for life   Hence the chance of discovering
species with transitional grades of structure in a fossil condition will
always be less  from their having existed in lesser numbers  than in the
case of species with fully developed structures 

I will now give two or three instances  both of diversified and of changed
habits  in the individuals of the same species   In either case it would be
easy for natural selection to adapt the structure of the animal to its
changed habits  or exclusively to one of its several habits   It is 
however  difficult to decide and immaterial for us  whether habits
generally change first and structure afterwards  or whether slight
modifications of structure lead to changed habits  both probably often
occurring almost simultaneously   Of cases of changed habits it will
suffice merely to allude to that of the many British insects which now feed
on exotic plants  or exclusively on artificial substances   Of diversified
habits innumerable instances could be given   I have often watched a tyrant
flycatcher  Saurophagus sulphuratus  in South America  hovering over one
spot and then proceeding to another  like a kestrel  and at other times
standing stationary on the margin of water  and then dashing into it like a
kingfisher at a fish   In our own country the larger titmouse  Parus major 
may be seen climbing branches  almost like a creeper  it sometimes  like a
shrike  kills small birds by blows on the head  and I have many times seen
and heard it hammering the seeds of the yew on a branch  and thus breaking
them like a nuthatch   In North America the black bear was seen by Hearne
swimming for hours with widely open mouth  thus catching  almost like a
whale  insects in the water 

As we sometimes see individuals following habits different from those
proper to their species and to the other species of the same genus  we
might expect that such individuals would occasionally give rise to new
species  having anomalous habits  and with their structure either slightly
or considerably modified from that of their type   And such instances occur
in nature   Can a more striking instance of adaptation be given than that
of a woodpecker for climbing trees and seizing insects in the chinks of the
bark   Yet in North America there are woodpeckers which feed largely on
fruit  and others with elongated wings which chase insects on the wing   On
the plains of La Plata  where hardly a tree grows  there is a woodpecker
 Colaptes campestris  which has two toes before and two behind  a long 
pointed tongue  pointed tail feathers  sufficiently stiff to support the
bird in a vertical position on a post  but not so stiff as in the typical
wood peckers  and a straight  strong beak   The beak  however  is not so
straight or so strong as in the typical woodpeckers but it is strong enough
to bore into wood   Hence this Colaptes  in all the essential parts of its
structure  is a woodpecker   Even in such trifling characters as the
colouring  the harsh tone of the voice  and undulatory flight  its close
blood relationship to our common woodpecker is plainly declared  yet  as I
can assert  not only from my own observations  but from those of the
accurate Azara  in certain large districts it does not climb trees  and it
makes its nest in holes in banks   In certain other districts  however 
this same woodpecker  as Mr  Hudson states  frequents trees  and bores
holes in the trunk for its nest   I may mention as another illustration of
the varied habits of this genus  that a Mexican Colaptes has been described
by De Saussure as boring holes into hard wood in order to lay up a store of
acorns 

Petrels are the most aerial and oceanic of birds  but  in the quiet sounds
of Tierra del Fuego  the Puffinuria berardi  in its general habits  in its
astonishing power of diving  in its manner of swimming and of flying when
made to take flight  would be mistaken by any one for an auk or a grebe 
nevertheless  it is essentially a petrel  but with many parts of its
organisation profoundly modified in relation to its new habits of life 
whereas the woodpecker of La Plata has had its structure only slightly
modified   In the case of the water ouzel  the acutest observer  by
examining its dead body  would never have suspected its sub aquatic habits 
yet this bird  which is allied to the thrush family  subsists by
diving   using its wings under water and grasping stones with its feet  
All the members of the great order of Hymenopterous insects are
terrestrial  excepting the genus Proctotrupes  which Sir John Lubbock has
discovered to be aquatic in its habits  it often enters the water and dives
about by the use not of its legs but of its wings  and remains as long as
four hours beneath the surface  yet it exhibits no modification in
structure in accordance with its abnormal habits 

He who believes that each being has been created as we now see it  must
occasionally have felt surprise when he has met with an animal having
habits and structure not in agreement   What can be plainer than that the
webbed feet of ducks and geese are formed for swimming   Yet there are
upland geese with webbed feet which rarely go near the water  and no one
except Audubon  has seen the frigate bird  which has all its four toes
webbed  alight on the surface of the ocean   On the other hand  grebes and
coots are eminently aquatic  although their toes are only bordered by
membrane   What seems plainer than that the long toes  not furnished with
membrane  of the Grallatores  are formed for walking over swamps and
floating plants   The water hen and landrail are members of this order  yet
the first is nearly as aquatic as the coot  and the second is nearly as
terrestrial as the quail or partridge   In such cases  and many others
could be given  habits have changed without a corresponding change of
structure   The webbed feet of the upland goose may be said to have become
almost rudimentary in function  though not in structure   In the
frigate bird  the deeply scooped membrane between the toes shows that
structure has begun to change 

He who believes in separate and innumerable acts of creation may say  that
in these cases it has pleased the Creator to cause a being of one type to
take the place of one belonging to another type  but this seems to me only
restating the fact in dignified language   He who believes in the struggle
for existence and in the principle of natural selection  will acknowledge
that every organic being is constantly endeavouring to increase in numbers 
and that if any one being varies ever so little  either in habits or
structure  and thus gains an advantage over some other inhabitant of the
same country  it will seize on the place of that inhabitant  however
different that may be from its own place   Hence it will cause him no
surprise that there should be geese and frigate birds with webbed feet 
living on the dry land and rarely alighting on the water  that there should
be long toed corncrakes  living in meadows instead of in swamps  that there
should be woodpeckers where hardly a tree grows  that there should be
diving thrushes and diving Hymenoptera  and petrels with the habits of
auks 

ORGANS OF EXTREME PERFECTION AND COMPLICATION 

To suppose that the eye with all its inimitable contrivances for adjusting
the focus to different distances  for admitting different amounts of light 
and for the correction of spherical and chromatic aberration  could have
been formed by natural selection  seems  I freely confess  absurd in the
highest degree   When it was first said that the sun stood still and the
world turned round  the common sense of mankind declared the doctrine
false  but the old saying of Vox populi  vox Dei  as every philosopher
knows  cannot be trusted in science   Reason tells me  that if numerous
gradations from a simple and imperfect eye to one complex and perfect can
be shown to exist  each grade being useful to its possessor  as is
certainly the case  if further  the eye ever varies and the variations be
inherited  as is likewise certainly the case  and if such variations should
be useful to any animal under changing conditions of life  then the
difficulty of believing that a perfect and complex eye could be formed by
natural selection  though insuperable by our imagination  should not be
considered as subversive of the theory   How a nerve comes to be sensitive
to light  hardly concerns us more than how life itself originated  but I
may remark that  as some of the lowest organisms in which nerves cannot be
detected  are capable of perceiving light  it does not seem impossible that
certain sensitive elements in their sarcode should become aggregated and
developed into nerves  endowed with this special sensibility 

In searching for the gradations through which an organ in any species has
been perfected  we ought to look exclusively to its lineal progenitors  but
this is scarcely ever possible  and we are forced to look to other species
and genera of the same group  that is to the collateral descendants from
the same parent form  in order to see what gradations are possible  and for
the chance of some gradations having been transmitted in an unaltered or
little altered condition   But the state of the same organ in distinct
classes may incidentally throw light on the steps by which it has been
perfected 

The simplest organ which can be called an eye consists of an optic nerve 
surrounded by pigment cells and covered by translucent skin  but without
any lens or other refractive body   We may  however  according to M 
Jourdain  descend even a step lower and find aggregates of pigment cells 
apparently serving as organs of vision  without any nerves  and resting
merely on sarcodic tissue   Eyes of the above simple nature are not capable
of distinct vision  and serve only to distinguish light from darkness   In
certain star fishes  small depressions in the layer of pigment which
surrounds the nerve are filled  as described by the author just quoted 
with transparent gelatinous matter  projecting with a convex surface  like
the cornea in the higher animals   He suggests that this serves not to form
an image  but only to concentrate the luminous rays and render their
perception more easy   In this concentration of the rays we gain the first
and by far the most important step towards the formation of a true 
picture forming eye  for we have only to place the naked extremity of the
optic nerve  which in some of the lower animals lies deeply buried in the
body  and in some near the surface  at the right distance from the
concentrating apparatus  and an image will be formed on it 

In the great class of the Articulata  we may start from an optic nerve
simply coated with pigment  the latter sometimes forming a sort of pupil 
but destitute of lens or other optical contrivance   With insects it is now
known that the numerous facets on the cornea of their great compound eyes
form true lenses  and that the cones include curiously modified nervous
filaments   But these organs in the Articulata are so much diversified that
Muller formerly made three main classes with seven subdivisions  besides a
fourth main class of aggregated simple eyes 

When we reflect on these facts  here given much too briefly  with respect
to the wide  diversified  and graduated range of structure in the eyes of
the lower animals  and when we bear in mind how small the number of all
living forms must be in comparison with those which have become extinct 
the difficulty ceases to be very great in believing that natural selection
may have converted the simple apparatus of an optic nerve  coated with
pigment and invested by transparent membrane  into an optical instrument as
perfect as is possessed by any member of the Articulata class 

He who will go thus far  ought not to hesitate to go one step further  if
he finds on finishing this volume that large bodies of facts  otherwise
inexplicable  can be explained by the theory of modification through
natural selection  he ought to admit that a structure even as perfect as an
eagle s eye might thus be formed  although in this case he does not know
the transitional states   It has been objected that in order to modify the
eye and still preserve it as a perfect instrument  many changes would have
to be effected simultaneously  which  it is assumed  could not be done
through natural selection  but as I have attempted to show in my work on
the variation of domestic animals  it is not necessary to suppose that the
modifications were all simultaneous  if they were extremely slight and
gradual   Different kinds of modification would  also  serve for the same
general purpose   as Mr  Wallace has remarked   If a lens has too short or
too long a focus  it may be amended either by an alteration of curvature 
or an alteration of density  if the curvature be irregular  and the rays do
not converge to a point  then any increased regularity of curvature will be
an improvement   So the contraction of the iris and the muscular movements
of the eye are neither of them essential to vision  but only improvements
which might have been added and perfected at any stage of the construction
of the instrument    Within the highest division of the animal kingdom 
namely  the Vertebrata  we can start from an eye so simple  that it
consists  as in the lancelet  of a little sack of transparent skin 
furnished with a nerve and lined with pigment  but destitute of any other
apparatus   In fishes and reptiles  as Owen has remarked   The range of
gradation of dioptric structures is very great    It is a significant fact
that even in man  according to the high authority of Virchow  the beautiful
crystalline lens is formed in the embryo by an accumulation of epidermic
cells  lying in a sack like fold of the skin  and the vitreous body is
formed from embryonic subcutaneous tissue   To arrive  however  at a just
conclusion regarding the formation of the eye  with all its marvellous yet
not absolutely perfect characters  it is indispensable that the reason
should conquer the imagination  but I have felt the difficulty far to
keenly to be surprised at others hesitating to extend the principle of
natural selection to so startling a length 

It is scarcely possible to avoid comparing the eye with a telescope   We
know that this instrument has been perfected by the long continued efforts
of the highest human intellects  and we naturally infer that the eye has
been formed by a somewhat analogous process   But may not this inference be
presumptuous   Have we any right to assume that the Creator works by
intellectual powers like those of man   If we must compare the eye to an
optical instrument  we ought in imagination to take a thick layer of
transparent tissue  with spaces filled with fluid  and with a nerve
sensitive to light beneath  and then suppose every part of this layer to be
continually changing slowly in density  so as to separate into layers of
different densities and thicknesses  placed at different distances from
each other  and with the surfaces of each layer slowly changing in form  
Further we must suppose that there is a power  represented by natural
selection or the survival of the fittest  always intently watching each
slight alteration in the transparent layers  and carefully preserving each
which  under varied circumstances  in any way or degree  tends to produce a
distincter image   We must suppose each new state of the instrument to be
multiplied by the million  each to be preserved until a better is produced 
and then the old ones to be all destroyed   In living bodies  variation
will cause the slight alteration  generation will multiply them almost
infinitely  and natural selection will pick out with unerring skill each
improvement   Let this process go on for millions of years  and during each
year on millions of individuals of many kinds  and may we not believe that
a living optical instrument might thus be formed as superior to one of
glass  as the works of the Creator are to those of man 

MODES Of TRANSITION 

If it could be demonstrated that any complex organ existed  which could not
possibly have been formed by numerous  successive  slight modifications  my
theory would absolutely break down   But I can find out no such case   No
doubt many organs exist of which we do not know the transitional grades 
more especially if we look to much isolated species  around which 
according to the theory  there has been much extinction   Or again  if we
take an organ common to all the members of a class  for in this latter case
the organ must have been originally formed at a remote period  since which
all the many members of the class have been developed  and in order to
discover the early transitional grades through which the organ has passed 
we should have to look to very ancient ancestral forms  long since become
extinct 

We should be extremely cautious in concluding that an organ could not have
been formed by transitional gradations of some kind   Numerous cases could
be given among the lower animals of the same organ performing at the same
time wholly distinct functions  thus in the larva of the dragon fly and in
the fish Cobites the alimentary canal respires  digests  and excretes   In
the Hydra  the animal may be turned inside out  and the exterior surface
will then digest and the stomach respire   In such cases natural selection
might specialise  if any advantage were thus gained  the whole or part of
an organ  which had previously performed two functions  for one function
alone  and thus by insensible steps greatly change its nature   Many plants
are known which regularly produce at the same time differently constructed
flowers  and if such plants were to produce one kind alone  a great change
would be effected with comparative suddenness in the character of the
species   It is  however  probable that the two sorts of flowers borne by
the same plant were originally differentiated by finely graduated steps 
which may still be followed in some few cases 

Again  two distinct organs  or the same organ under two very different
forms  may simultaneously perform in the same individual the same function 
and this is an extremely important means of transition   to give one
instance  there are fish with gills or branchiae that breathe the air
dissolved in the water  at the same time that they breathe free air in
their swim bladders  this latter organ being divided by highly vascular
partitions and having a ductus pneumaticus for the supply of air   To give
another instance from the vegetable kingdom   plants climb by three
distinct means  by spirally twining  by clasping a support with their
sensitive tendrils  and by the emission of aerial rootlets  these three
means are usually found in distinct groups  but some few species exhibit
two of the means  or even all three  combined in the same individual   In
all such cases one of the two organs might readily be modified and
perfected so as to perform all the work  being aided during the progress of
modification by the other organ  and then this other organ might be
modified for some other and quite distinct purpose  or be wholly
obliterated 

The illustration of the swim bladder in fishes is a good one  because it
shows us clearly the highly important fact that an organ originally
constructed for one purpose  namely flotation  may be converted into one
for a widely different purpose  namely respiration   The swim bladder has 
also  been worked in as an accessory to the auditory organs of certain
fishes    All physiologists admit that the swim bladder is homologous  or
 ideally similar  in position and structure with the lungs of the higher
vertebrate animals   hence there is no reason to doubt that the swim 
bladder has actually been converted into lungs  or an organ used
exclusively for respiration 

According to this view it may be inferred that all vertebrate animals with
true lungs are descended by ordinary generation from an ancient and unknown
prototype which was furnished with a floating apparatus or swim bladder  
We can thus  as I infer from Professor Owen s interesting description of
these parts  understand the strange fact that every particle of food and
drink which we swallow has to pass over the orifice of the trachea  with
some risk of falling into the lungs  notwithstanding the beautiful
contrivance by which the glottis is closed   In the higher Vertebrata the
branchiae have wholly disappeared  but in the embryo the slits on the sides
of the neck and the loop like course of the arteries still mark their
former position   But it is conceivable that the now utterly lost branchiae
might have been gradually worked in by natural selection for some distinct
purpose   for instance  Landois has shown that the wings of insects are
developed from the trachea  it is therefore highly probable that in this
great class organs which once served for respiration have been actually
converted into organs for flight 

In considering transitions of organs  it is so important to bear in mind
the probability of conversion from one function to another  that I will
give another instance   Pedunculated cirripedes have two minute folds of
skin  called by me the ovigerous frena  which serve  through the means of a
sticky secretion  to retain the eggs until they are hatched within the
sack   These cirripedes have no branchiae  the whole surface of the body
and of the sack  together with the small frena  serving for respiration  
The Balanidae or sessile cirripedes  on the other hand  have no ovigerous
frena  the eggs lying loose at the bottom of the sack  within the
well enclosed shell  but they have  in the same relative position with the
frena  large  much folded membranes  which freely communicate with the
circulatory lacunae of the sack and body  and which have been considered by
all naturalists to act as branchiae   Now I think no one will dispute that
the ovigerous frena in the one family are strictly homologous with the
branchiae of the other family  indeed  they graduate into each other  
Therefore it need not be doubted that the two little folds of skin  which
originally served as ovigerous frena  but which  likewise  very slightly
aided in the act of respiration  have been gradually converted by natural
selection into branchiae  simply through an increase in their size and the
obliteration of their adhesive glands   If all pedunculated cirripedes had
become extinct  and they have suffered far more extinction than have
sessile cirripedes  who would ever have imagined that the branchiae in this
latter family had originally existed as organs for preventing the ova from
being washed out of the sack 

There is another possible mode of transition  namely  through the
acceleration or retardation of the period of reproduction   This has lately
been insisted on by Professor Cope and others in the United States   It is
now known that some animals are capable of reproduction at a very early
age  before they have acquired their perfect characters  and if this power
became thoroughly well developed in a species  it seems probable that the
adult stage of development would sooner or later be lost  and in this case 
especially if the larva differed much from the mature form  the character
of the species would be greatly changed and degraded   Again  not a few
animals  after arriving at maturity  go on changing in character during
nearly their whole lives   With mammals  for instance  the form of the
skull is often much altered with age  of which Dr  Murie has given some
striking instances with seals   Every one knows how the horns of stags
become more and more branched  and the plumes of some birds become more
finely developed  as they grow older   Professor Cope states that the teeth
of certain lizards change much in shape with advancing years   With
crustaceans not only many trivial  but some important parts assume a new
character  as recorded by Fritz Muller  after maturity   In all such cases 
 and many could be given  if the age for reproduction were retarded  the
character of the species  at least in its adult state  would be modified 
nor is it improbable that the previous and earlier stages of development
would in some cases be hurried through and finally lost   Whether species
have often or ever been modified through this comparatively sudden mode of
transition  I can form no opinion  but if this has occurred  it is probable
that the differences between the young and the mature  and between the
mature and the old  were primordially acquired by graduated steps 

SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION 

Although we must be extremely cautious in concluding that any organ could
not have been produced by successive  small  transitional gradations  yet
undoubtedly serious cases of difficulty occur 

One of the most serious is that of neuter insects  which are often
differently constructed from either the males or fertile females  but this
case will be treated of in the next chapter   The electric organs of fishes
offer another case of special difficulty  for it is impossible to conceive
by what steps these wondrous organs have been produced   But this is not
surprising  for we do not even know of what use they are   In the gymnotus
and torpedo they no doubt serve as powerful means of defence  and perhaps
for securing prey  yet in the ray  as observed by Matteucci  an analogous
organ in the tail manifests but little electricity  even when the animal is
greatly irritated  so little that it can hardly be of any use for the above
purposes   Moreover  in the ray  besides the organ just referred to  there
is  as Dr  R  McDonnell has shown  another organ near the head  not known
to be electrical  but which appears to be the real homologue of the
electric battery in the torpedo   It is generally admitted that there
exists between these organs and ordinary muscle a close analogy  in
intimate structure  in the distribution of the nerves  and in the manner in
which they are acted on by various reagents   It should  also  be
especially observed that muscular contraction is accompanied by an
electrical discharge  and  as Dr  Radcliffe insists   in the electrical
apparatus of the torpedo during rest  there would seem to be a charge in
every respect like that which is met with in muscle and nerve during the
rest  and the discharge of the torpedo  instead of being peculiar  may be
only another form of the discharge which attends upon the action of muscle
and motor nerve    Beyond this we cannot at present go in the way of
explanation  but as we know so little about the uses of these organs  and
as we know nothing about the habits and structure of the progenitors of the
existing electric fishes  it would be extremely bold to maintain that no
serviceable transitions are possible by which these organs might have been
gradually developed 

These organs appear at first to offer another and far more serious
difficulty  for they occur in about a dozen kinds of fish  of which several
are widely remote in their affinities   When the same organ is found in
several members of the same class  especially if in members having very
different habits of life  we may generally attribute its presence to
inheritance from a common ancestor  and its absence in some of the members
to loss through disuse or natural selection   So that  if the electric
organs had been inherited from some one ancient progenitor  we might have
expected that all electric fishes would have been specially related to each
other  but this is far from the case   Nor does geology at all lead to the
belief that most fishes formerly possessed electric organs  which their
modified descendants have now lost   But when we look at the subject more
closely  we find in the several fishes provided with electric organs  that
these are situated in different parts of the body  that they differ in
construction  as in the arrangement of the plates  and  according to
Pacini  in the process or means by which the electricity is excited  and
lastly  in being supplied with nerves proceeding from different sources 
and this is perhaps the most important of all the differences   Hence in
the several fishes furnished with electric organs  these cannot be
considered as homologous  but only as analogous in function   Consequently
there is no reason to suppose that they have been inherited from a common
progenitor  for had this been the case they would have closely resembled
each other in all respects   Thus the difficulty of an organ  apparently
the same  arising in several remotely allied species  disappears  leaving
only the lesser yet still great difficulty   namely  by what graduated
steps these organs have been developed in each separate group of fishes 

The luminous organs which occur in a few insects  belonging to widely
different families  and which are situated in different parts of the body 
offer  under our present state of ignorance  a difficulty almost exactly
parallel with that of the electric organs   Other similar cases could be
given  for instance in plants  the very curious contrivance of a mass of
pollen grains  borne on a foot stalk with an adhesive gland  is apparently
the same in Orchis and Asclepias  genera almost as remote as is possible
among flowering plants  but here again the parts are not homologous   In
all cases of beings  far removed from each other in the scale of
organisation  which are furnished with similar and peculiar organs  it will
be found that although the general appearance and function of the organs
may be the same  yet fundamental differences between them can always be
detected   For instance  the eyes of Cephalopods or cuttle fish and of
vertebrate animals appear wonderfully alike  and in such widely sundered
groups no part of this resemblance can be due to inheritance from a common
progenitor   Mr  Mivart has advanced this case as one of special
difficulty  but I am unable to see the force of his argument   An organ for
vision must be formed of transparent tissue  and must include some sort of
lens for throwing an image at the back of a darkened chamber   Beyond this
superficial resemblance  there is hardly any real similarity between the
eyes of cuttle fish and vertebrates  as may be seen by consulting Hensen s
admirable memoir on these organs in the Cephalopoda   It is impossible for
me here to enter on details  but I may specify a few of the points of
difference   The crystalline lens in the higher cuttle fish consists of two
parts  placed one behind the other like two lenses  both having a very
different structure and disposition to what occurs in the vertebrata   The
retina is wholly different  with an actual inversion of the elemental
parts  and with a large nervous ganglion included within the membranes of
the eye   The relations of the muscles are as different as it is possible
to conceive  and so in other points   Hence it is not a little difficult to
decide how far even the same terms ought to be employed in describing the
eyes of the Cephalopoda and Vertebrata   It is  of course  open to any one
to deny that the eye in either case could have been developed through the
natural selection of successive slight variations  but if this be admitted
in the one case it is clearly possible in the other  and fundamental
differences of structure in the visual organs of two groups might have been
anticipated  in accordance with this view of their manner of formation   As
two men have sometimes independently hit on the same invention  so in the
several foregoing cases it appears that natural selection  working for the
good of each being  and taking advantage of all favourable variations  has
produced similar organs  as far as function is concerned  in distinct
organic beings  which owe none of their structure in common to inheritance
from a common progenitor 

Fritz Muller  in order to test the conclusions arrived at in this volume 
has followed out with much care a nearly similar line of argument   Several
families of crustaceans include a few species  possessing an air breathing
apparatus and fitted to live out of the water   In two of these families 
which were more especially examined by Muller  and which are nearly related
to each other  the species agree most closely in all important characters  
namely in their sense organs  circulating systems  in the position of the
tufts of hair within their complex stomachs  and lastly in the whole
structure of the water breathing branchiae  even to the microscopical hooks
by which they are cleansed   Hence it might have been expected that in the
few species belonging to both families which live on the land  the equally
important air breathing apparatus would have been the same  for why should
this one apparatus  given for the same purpose  have been made to differ 
while all the other important organs were closely similar  or rather 
identical 

Fritz Muller argues that this close similarity in so many points of
structure must  in accordance with the views advanced by me  be accounted
for by inheritance from a common progenitor   But as the vast majority of
the species in the above two families  as well as most other crustaceans 
are aquatic in their habits  it is improbable in the highest degree that
their common progenitor should have been adapted for breathing air   Muller
was thus led carefully to examine the apparatus in the air breathing
species  and he found it to differ in each in several important points  as
in the position of the orifices  in the manner in which they are opened and
closed  and in some accessory details   Now such differences are
intelligible  and might even have been expected  on the supposition that
species belonging to distinct families had slowly become adapted to live
more and more out of water  and to breathe the air   For these species 
from belonging to distinct families  would have differed to a certain
extent  and in accordance with the principle that the nature of each
variation depends on two factors  viz   the nature of the organism and that
of the surrounding conditions  their variability assuredly would not have
been exactly the same   Consequently natural selection would have had
different materials or variations to work on  in order to arrive at the
same functional result  and the structures thus acquired would almost
necessarily have differed   On the hypothesis of separate acts of creation
the whole case remains unintelligible   This line of argument seems to have
had great weight in leading Fritz Muller to accept the views maintained by
me in this volume 

Another distinguished zoologist  the late Professor Claparede  has argued
in the same manner  and has arrived at the same result   He shows that
there are parasitic mites  Acaridae   belonging to distinct sub families
and families  which are furnished with hair claspers   These organs must
have been independently developed  as they could not have been inherited
from a common progenitor  and in the several groups they are formed by the
modification of the fore legs  of the hind legs  of the maxillae or lips 
and of appendages on the under side of the hind part of the body 

In the foregoing cases  we see the same end gained and the same function
performed  in beings not at all or only remotely allied  by organs in
appearance  though not in development  closely similar   On the other hand 
it is a common rule throughout nature that the same end should be gained 
even sometimes in the case of closely related beings  by the most
diversified means   How differently constructed is the feathered wing of a
bird and the membrane covered wing of a bat  and still more so the four
wings of a butterfly  the two wings of a fly  and the two wings with the
elytra of a beetle   Bivalve shells are made to open and shut  but on what
a number of patterns is the hinge constructed  from the long row of neatly
interlocking teeth in a Nucula to the simple ligament of a Mussel   Seeds
are disseminated by their minuteness  by their capsule being converted into
a light balloon like envelope  by being embedded in pulp or flesh  formed
of the most diverse parts  and rendered nutritious  as well as
conspicuously coloured  so as to attract and be devoured by birds  by
having hooks and grapnels of many kinds and serrated awns  so as to adhere
to the fur of quadrupeds  and by being furnished with wings and plumes  as
different in shape as they are elegant in structure  so as to be wafted by
every breeze   I will give one other instance   for this subject of the
same end being gained by the most diversified means well deserves
attention   Some authors maintain that organic beings have been formed in
many ways for the sake of mere variety  almost like toys in a shop  but
such a view of nature is incredible   With plants having separated sexes 
and with those in which  though hermaphrodites  the pollen does not
spontaneously fall on the stigma  some aid is necessary for their
fertilisation   With several kinds this is effected by the pollen grains 
which are light and incoherent  being blown by the wind through mere chance
on to the stigma  and this is the simplest plan which can well be
conceived   An almost equally simple  though very different plan occurs in
many plants in which a symmetrical flower secretes a few drops of nectar 
and is consequently visited by insects  and these carry the pollen from the
anthers to the stigma 

 From this simple stage we may pass through an inexhaustible number of
contrivances  all for the same purpose and effected in essentially the same
manner  but entailing changes in every part of the flower   The nectar may
be stored in variously shaped receptacles  with the stamens and pistils
modified in many ways  sometimes forming trap like contrivances  and
sometimes capable of neatly adapted movements through irritability or
elasticity   From such structures we may advance till we come to such a
case of extraordinary adaptation as that lately described by Dr  Cruger in
the Coryanthes   This orchid has part of its labellum or lower lip hollowed
out into a great bucket  into which drops of almost pure water continually
fall from two secreting horns which stand above it  and when the bucket is
half full  the water overflows by a spout on one side   The basal part of
the labellum stands over the bucket  and is itself hollowed out into a sort
of chamber with two lateral entrances  within this chamber there are
curious fleshy ridges   The most ingenious man  if he had not witnessed
what takes place  could never have imagined what purpose all these parts
serve   But Dr  Cruger saw crowds of large humble bees visiting the
gigantic flowers of this orchid  not in order to suck nectar  but to gnaw
off the ridges within the chamber above the bucket  in doing this they
frequently pushed each other into the bucket  and their wings being thus
wetted they could not fly away  but were compelled to crawl out through the
passage formed by the spout or overflow   Dr  Cruger saw a  continual
procession  of bees thus crawling out of their involuntary bath   The
passage is narrow  and is roofed over by the column  so that a bee  in
forcing its way out  first rubs its back against the viscid stigma and then
against the viscid glands of the pollen masses   The pollen masses are thus
glued to the back of the bee which first happens to crawl out through the
passage of a lately expanded flower  and are thus carried away   Dr  Cruger
sent me a flower in spirits of wine  with a bee which he had killed before
it had quite crawled out  with a pollen mass still fastened to its back  
When the bee  thus provided  flies to another flower  or to the same flower
a second time  and is pushed by its comrades into the bucket and then
crawls out by the passage  the pollen mass necessarily comes first into
contact with the viscid stigma  and adheres to it  and the flower is
fertilised   Now at last we see the full use of every part of the flower 
of the water secreting horns of the bucket half full of water  which
prevents the bees from flying away  and forces them to crawl out through
the spout  and rub against the properly placed viscid pollen masses and the
viscid stigma 

The construction of the flower in another closely allied orchid  namely 
the Catasetum  is widely different  though serving the same end  and is
equally curious   Bees visit these flowers  like those of the Coryanthes 
in order to gnaw the labellum  in doing this they inevitably touch a long 
tapering  sensitive projection  or  as I have called it  the antenna   This
antenna  when touched  transmits a sensation or vibration to a certain
membrane which is instantly ruptured  this sets free a spring by which the
pollen mass is shot forth  like an arrow  in the right direction  and
adheres by its viscid extremity to the back of the bee   The pollen mass of
the male plant  for the sexes are separate in this orchid  is thus carried
to the flower of the female plant  where it is brought into contact with
the stigma  which is viscid enough to break certain elastic threads  and
retain the pollen  thus effecting fertilisation 

How  it may be asked  in the foregoing and in innumerable other instances 
can we understand the graduated scale of complexity and the multifarious
means for gaining the same end   The answer no doubt is  as already
remarked  that when two forms vary  which already differ from each other in
some slight degree  the variability will not be of the same exact nature 
and consequently the results obtained through natural selection for the
same general purpose will not be the same   We should also bear in mind
that every highly developed organism has passed through many changes  and
that each modified structure tends to be inherited  so that each
modification will not readily be quite lost  but may be again and again
further altered   Hence  the structure of each part of each species  for
whatever purpose it may serve  is the sum of many inherited changes 
through which the species has passed during its successive adaptations to
changed habits and conditions of life 

Finally  then  although in many cases it is most difficult even to
conjecture by what transitions organs could have arrived at their present
state  yet  considering how small the proportion of living and known forms
is to the extinct and unknown  I have been astonished how rarely an organ
can be named  towards which no transitional grade is known to lead   It is
certainly true  that new organs appearing as if created for some special
purpose rarely or never appear in any being  as indeed is shown by that
old  but somewhat exaggerated  canon in natural history of  Natura non
facit saltum    We meet with this admission in the writings of almost every
experienced naturalist  or  as Milne Edwards has well expressed it   Nature
is prodigal in variety  but niggard in innovation    Why  on the theory of
Creation  should there be so much variety and so little real novelty   Why
should all the parts and organs of many independent beings  each supposed
to have been separately created for its own proper place in nature  be so
commonly linked together by graduated steps   Why should not Nature take a
sudden leap from structure to structure   On the theory of natural
selection  we can clearly understand why she should not  for natural
selection acts only by taking advantage of slight successive variations 
she can never take a great and sudden leap  but must advance by the short
and sure  though slow steps 

ORGANS OF LITTLE APPARENT IMPORTANCE  AS AFFECTED BY NATURAL SELECTION 

As natural selection acts by life and death  by the survival of the
fittest  and by the destruction of the less well fitted individuals  I have
sometimes felt great difficulty in understanding the origin or formation of
parts of little importance  almost as great  though of a very different
kind  as in the case of the most perfect and complex organs 

In the first place  we are much too ignorant in regard to the whole economy
of any one organic being to say what slight modifications would be of
importance or not   In a former chapter I have given instances of very
trifling characters  such as the down on fruit and the colour of its flesh 
the colour of the skin and hair of quadrupeds  which  from being correlated
with constitutional differences  or from determining the attacks of
insects  might assuredly be acted on by natural selection   The tail of the
giraffe looks like an artificially constructed fly flapper  and it seems at
first incredible that this could have been adapted for its present purpose
by successive slight modifications  each better and better fitted  for so
trifling an object as to drive away flies  yet we should pause before being
too positive even in this case  for we know that the distribution and
existence of cattle and other animals in South America absolutely depend on
their power of resisting the attacks of insects   so that individuals which
could by any means defend themselves from these small enemies  would be
able to range into new pastures and thus gain a great advantage   It is not
that the larger quadrupeds are actually destroyed  except in some rare
cases  by flies  but they are incessantly harassed and their strength
reduced  so that they are more subject to disease  or not so well enabled
in a coming dearth to search for food  or to escape from beasts of prey 

Organs now of trifling importance have probably in some cases been of high
importance to an early progenitor  and  after having been slowly perfected
at a former period  have been transmitted to existing species in nearly the
same state  although now of very slight use  but any actually injurious
deviations in their structure would of course have been checked by natural
selection   Seeing how important an organ of locomotion the tail is in most
aquatic animals  its general presence and use for many purposes in so many
land animals  which in their lungs or modified swim bladders betray their
aquatic origin  may perhaps be thus accounted for   A well developed tail
having been formed in an aquatic animal  it might subsequently come to be
worked in for all sorts of purposes  as a fly flapper  an organ of
prehension  or as an aid in turning  as in the case of the dog  though the
aid in this latter respect must be slight  for the hare  with hardly any
tail  can double still more quickly 

In the second place  we may easily err in attributing importance to
characters  and in believing that they have been developed through natural
selection   We must by no means overlook the effects of the definite action
of changed conditions of life  of so called spontaneous variations  which
seem to depend in a quite subordinate degree on the nature of the
conditions  of the tendency to reversion to long lost characters  of the
complex laws of growth  such as of correlation  comprehension  of the
pressure of one part on another  etc   and finally of sexual selection  by
which characters of use to one sex are often gained and then transmitted
more or less perfectly to the other sex  though of no use to the sex   But
structures thus indirectly gained  although at first of no advantage to a
species  may subsequently have been taken advantage of by its modified
descendants  under new conditions of life and newly acquired habits 

If green woodpeckers alone had existed  and we did not know that there were
many black and pied kinds  I dare say that we should have thought that the
green colour was a beautiful adaptation to conceal this tree frequenting
bird from its enemies  and consequently that it was a character of
importance  and had been acquired through natural selection  as it is  the
colour is probably in chief part due to sexual selection   A trailing palm
in the Malay Archipelago climbs the loftiest trees by the aid of
exquisitely constructed hooks clustered around the ends of the branches 
and this contrivance  no doubt  is of the highest service to the plant  but
as we see nearly similar hooks on many trees which are not climbers  and
which  as there is reason to believe from the distribution of the thorn 
bearing species in Africa and South America  serve as a defence against
browsing quadrupeds  so the spikes on the palm may at first have been
developed for this object  and subsequently have been improved and taken
advantage of by the plant  as it underwent further modification and became
a climber   The naked skin on the head of a vulture is generally considered
as a direct adaptation for wallowing in putridity  and so it may be  or it
may possibly be due to the direct action of putrid matter  but we should be
very cautious in drawing any such inference  when we see that the skin on
the head of the clean feeding male turkey is likewise naked   The sutures
in the skulls of young mammals have been advanced as a beautiful adaptation
for aiding parturition  and no doubt they facilitate  or may be
indispensable for this act  but as sutures occur in the skulls of young
birds and reptiles  which have only to escape from a broken egg  we may
infer that this structure has arisen from the laws of growth  and has been
taken advantage of in the parturition of the higher animals 

We are profoundly ignorant of the cause of each slight variation or
individual difference  and we are immediately made conscious of this by
reflecting on the differences between the breeds of our domesticated
animals in different countries  more especially in the less civilized
countries  where there has been but little methodical selection   Animals
kept by savages in different countries often have to struggle for their own
subsistence  and are exposed to a certain extent to natural selection  and
individuals with slightly different constitutions would succeed best under
different climates   With cattle susceptibility to the attacks of flies is
correlated with colour  as is the liability to be poisoned by certain
plants  so that even colour would be thus subjected to the action of
natural selection   Some observers are convinced that a damp climate
affects the growth of the hair  and that with the hair the horns are
correlated   Mountain breeds always differ from lowland breeds  and a
mountainous country would probably affect the hind limbs from exercising
them more  and possibly even the form of the pelvis  and then by the law of
homologous variation  the front limbs and the head would probably be
affected   The shape  also  of the pelvis might affect by pressure the
shape of certain parts of the young in the womb   The laborious breathing
necessary in high regions tends  as we have good reason to believe  to
increase the size of the chest  and again correlation would come into play  
The effects of lessened exercise  together with abundant food  on the whole
organisation is probably still more important  and this  as H  von
Nathusius has lately shown in his excellent Treatise  is apparently one
chief cause of the great modification which the breeds of swine have
undergone   But we are far too ignorant to speculate on the relative
importance of the several known and unknown causes of variation  and I have
made these remarks only to show that  if we are unable to account for the
characteristic differences of our several domestic breeds  which
nevertheless are generally admitted to have arisen through ordinary
generation from one or a few parent stocks  we ought not to lay too much
stress on our ignorance of the precise cause of the slight analogous
differences between true species 

UTILITARIAN DOCTRINE  HOW FAR TRUE   BEAUTY  HOW ACQUIRED 

The foregoing remarks lead me to say a few words on the protest lately made
by some naturalists against the utilitarian doctrine that every detail of
structure has been produced for the good of its possessor   They believe
that many structures have been created for the sake of beauty  to delight
man or the Creator  but this latter point is beyond the scope of scientific
discussion   or for the sake of mere variety  a view already discussed  
Such doctrines  if true  would be absolutely fatal to my theory   I fully
admit that many structures are now of no direct use to their possessors 
and may never have been of any use to their progenitors  but this does not
prove that they were formed solely for beauty or variety   No doubt the
definite action of changed conditions  and the various causes of
modifications  lately specified  have all produced an effect  probably a
great effect  independently of any advantage thus gained   But a still more
important consideration is that the chief part of the organisation of every
living creature is due to inheritance  and consequently  though each being
assuredly is well fitted for its place in nature  many structures have now
no very close and direct relation to present habits of life   Thus  we can
hardly believe that the webbed feet of the upland goose  or of the frigate 
bird  are of special use to these birds  we cannot believe that the similar
bones in the arm of the monkey  in the fore leg of the horse  in the wing
of the bat  and in the flipper of the seal  are of special use to these
animals   We may safely attribute these structures to inheritance  But
webbed feet no doubt were as useful to the progenitor of the upland goose
and of the frigate bird  as they now are to the most aquatic of living
birds   So we may believe that the progenitor of the seal did not possess a
flipper  but a foot with five toes fitted for walking or grasping  and we
may further venture to believe that the several bones in the limbs of the
monkey  horse and bat  were originally developed  on the principle of
utility  probably through the reduction of more numerous bones in the fin
of some ancient fish like progenitor of the whole class   It is scarcely
possible to decide how much allowance ought to be made for such causes of
change  as the definite action of external conditions  so called
spontaneous variations  and the complex laws of growth  but with these
important exceptions  we may conclude that the structure of every living
creature either now is  or was formerly  of some direct or indirect use to
its possessor 

With respect to the belief that organic beings have been created beautiful
for the delight of man  a belief which it has been pronounced is subversive
of my whole theory  I may first remark that the sense of beauty obviously
depends on the nature of the mind  irrespective of any real quality in the
admired object  and that the idea of what is beautiful  is not innate or
unalterable   We see this  for instance  in the men of different races
admiring an entirely different standard of beauty in their women   If
beautiful objects had been created solely for man s gratification  it ought
to be shown that before man appeared there was less beauty on the face of
the earth than since he came on the stage   Were the beautiful volute and
cone shells of the Eocene epoch  and the gracefully sculptured ammonites of
the Secondary period  created that man might ages afterwards admire them in
his cabinet   Few objects are more beautiful than the minute siliceous
cases of the diatomaceae   were these created that they might be examined
and admired under the higher powers of the microscope   The beauty in this
latter case  and in many others  is apparently wholly due to symmetry of
growth   Flowers rank among the most beautiful productions of nature  but
they have been rendered conspicuous in contrast with the green leaves  and
in consequence at the same time beautiful  so that they may be easily
observed by insects   I have come to this conclusion from finding it an
invariable rule that when a flower is fertilised by the wind it never has a
gaily coloured corolla   Several plants habitually produce two kinds of
flowers  one kind open and coloured so as to attract insects  the other
closed  not coloured  destitute of nectar  and never visited by insects  
Hence  we may conclude that  if insects had not been developed on the face
of the earth  our plants would not have been decked with beautiful flowers 
but would have produced only such poor flowers as we see on our fir  oak 
nut and ash trees  on grasses  spinach  docks and nettles  which are all
fertilised through the agency of the wind   A similar line of argument
holds good with fruits  that a ripe strawberry or cherry is as pleasing to
the eye as to the palate  that the gaily coloured fruit of the spindle wood
tree and the scarlet berries of the holly are beautiful objects  will be
admitted by everyone   But this beauty serves merely as a guide to birds
and beasts  in order that the fruit may be devoured and the matured seeds
disseminated   I infer that this is the case from having as yet found no
exception to the rule that seeds are always thus disseminated when embedded
within a fruit of any kind  that is within a fleshy or pulpy envelope   if
it be coloured of any brilliant tint  or rendered conspicuous by being
white or black 

On the other hand  I willingly admit that a great number of male animals 
as all our most gorgeous birds  some fishes  reptiles  and mammals  and a
host of magnificently coloured butterflies  have been rendered beautiful
for beauty s sake   But this has been effected through sexual selection 
that is  by the more beautiful males having been continually preferred by
the females  and not for the delight of man   So it is with the music of
birds   We may infer from all this that a nearly similar taste for
beautiful colours and for musical sounds runs through a large part of the
animal kingdom   When the female is as beautifully coloured as the male 
which is not rarely the case with birds and butterflies  the cause
apparently lies in the colours acquired through sexual selection having
been transmitted to both sexes  instead of to the males alone   How the
sense of beauty in its simplest form  that is  the reception of a peculiar
kind of pleasure from certain colours  forms and sounds  was first
developed in the mind of man and of the lower animals  is a very obscure
subject   The same sort of difficulty is presented if we enquire how it is
that certain flavours and odours give pleasure  and others displeasure  
Habit in all these cases appears to have come to a certain extent into
play  but there must be some fundamental cause in the constitution of the
nervous system in each species 

Natural selection cannot possibly produce any modification in a species
exclusively for the good of another species  though throughout nature one
species incessantly takes advantage of  and profits by the structures of
others   But natural selection can and does often produce structures for
the direct injury of other animals  as we see in the fang of the adder  and
in the ovipositor of the ichneumon  by which its eggs are deposited in the
living bodies of other insects   If it could be proved that any part of the
structure of any one species had been formed for the exclusive good of
another species  it would annihilate my theory  for such could not have
been produced through natural selection   Although many statements may be
found in works on natural history to this effect  I cannot find even one
which seems to me of any weight   It is admitted that the rattlesnake has a
poison fang for its own defence and for the destruction of its prey  but
some authors suppose that at the same time it is furnished with a rattle
for its own injury  namely  to warn its prey   I would almost as soon
believe that the cat curls the end of its tail when preparing to spring  in
order to warn the doomed mouse   It is a much more probable view that the
rattlesnake uses its rattle  the cobra expands its frill and the puff adder
swells while hissing so loudly and harshly  in order to alarm the many
birds and beasts which are known to attack even the most venomous species  
Snakes act on the same principle which makes the hen ruffle her feathers
and expand her wings when a dog approaches her chickens   But I have not
space here to enlarge on the many ways by which animals endeavour to
frighten away their enemies 

Natural selection will never produce in a being any structure more
injurious than beneficial to that being  for natural selection acts solely
by and for the good of each   No organ will be formed  as Paley has
remarked  for the purpose of causing pain or for doing an injury to its
possessor   If a fair balance be struck between the good and evil caused by
each part  each will be found on the whole advantageous   After the lapse
of time  under changing conditions of life  if any part comes to be
injurious  it will be modified  or if it be not so  the being will become
extinct  as myriads have become extinct 

Natural selection tends only to make each organic being as perfect as  or
slightly more perfect than the other inhabitants of the same country with
which it comes into competition   And we see that this is the standard of
perfection attained under nature   The endemic productions of New Zealand 
for instance  are perfect  one compared with another  but they are now
rapidly yielding before the advancing legions of plants and animals
introduced from Europe   Natural selection will not produce absolute
perfection  nor do we always meet  as far as we can judge  with this high
standard under nature   The correction for the aberration of light is said
by Muller not to be perfect even in that most perfect organ  the human eye  
Helmholtz  whose judgment no one will dispute  after describing in the
strongest terms the wonderful powers of the human eye  adds these
remarkable words    That which we have discovered in the way of inexactness
and imperfection in the optical machine and in the image on the retina  is
as nothing in comparison with the incongruities which we have just come
across in the domain of the sensations   One might say that nature has
taken delight in accumulating contradictions in order to remove all
foundation from the theory of a pre existing harmony between the external
and internal worlds    If our reason leads us to admire with enthusiasm a
multitude of inimitable contrivances in nature  this same reason tells us 
though we may easily err on both sides  that some other contrivances are
less perfect   Can we consider the sting of the bee as perfect  which  when
used against many kinds of enemies  cannot be withdrawn  owing to the
backward serratures  and thus inevitably causes the death of the insect by
tearing out its viscera 

If we look at the sting of the bee  as having existed in a remote
progenitor  as a boring and serrated instrument  like that in so many
members of the same great order  and that it has since been modified but
not perfected for its present purpose  with the poison originally adapted
for some other object  such as to produce galls  since intensified  we can
perhaps understand how it is that the use of the sting should so often
cause the insect s own death   for if on the whole the power of stinging be
useful to the social community  it will fulfil all the requirements of
natural selection  though it may cause the death of some few members   If
we admire the truly wonderful power of scent by which the males of many
insects find their females  can we admire the production for this single
purpose of thousands of drones  which are utterly useless to the community
for any other purpose  and which are ultimately slaughtered by their
industrious and sterile sisters   It may be difficult  but we ought to
admire the savage instinctive hatred of the queen bee  which urges her to
destroy the young queens  her daughters  as soon as they are born  or to
perish herself in the combat  for undoubtedly this is for the good of the
community  and maternal love or maternal hatred  though the latter
fortunately is most rare  is all the same to the inexorable principles of
natural selection   If we admire the several ingenious contrivances by
which orchids and many other plants are fertilised through insect agency 
can we consider as equally perfect the elaboration of dense clouds of
pollen by our fir trees  so that a few granules may be wafted by chance on
to the ovules 

SUMMARY   THE LAW OF UNITY OF TYPE AND OF THE CONDITIONS OF EXISTENCE
EMBRACED BY THE THEORY OF NATURAL SELECTION 

We have in this chapter discussed some of the difficulties and objections
which may be urged against the theory   Many of them are serious  but I
think that in the discussion light has been thrown on several facts  which
on the belief of independent acts of creation are utterly obscure   We have
seen that species at any one period are not indefinitely variable  and are
not linked together by a multitude of intermediate gradations  partly
because the process of natural selection is always very slow  and at any
one time acts only on a few forms  and partly because the very process of
natural selection implies the continual supplanting and extinction of
preceding and intermediate gradations   Closely allied species  now living
on a continuous area  must often have been formed when the area was not
continuous  and when the conditions of life did not insensibly graduate
away from one part to another   When two varieties are formed in two
districts of a continuous area  an intermediate variety will often be
formed  fitted for an intermediate zone  but from reasons assigned  the
intermediate variety will usually exist in lesser numbers than the two
forms which it connects  consequently the two latter  during the course of
further modification  from existing in greater numbers  will have a great
advantage over the less numerous intermediate variety  and will thus
generally succeed in supplanting and exterminating it 

We have seen in this chapter how cautious we should be in concluding that
the most different habits of life could not graduate into each other  that
a bat  for instance  could not have been formed by natural selection from
an animal which at first only glided through the air 

We have seen that a species under new conditions of life may change its
habits  or it may have diversified habits  with some very unlike those of
its nearest congeners   Hence we can understand  bearing in mind that each
organic being is trying to live wherever it can live  how it has arisen
that there are upland geese with webbed feet  ground woodpeckers  diving
thrushes  and petrels with the habits of auks 

Although the belief that an organ so perfect as the eye could have been
formed by natural selection  is enough to stagger any one  yet in the case
of any organ  if we know of a long series of gradations in complexity  each
good for its possessor  then under changing conditions of life  there is no
logical impossibility in the acquirement of any conceivable degree of
perfection through natural selection   In the cases in which we know of no
intermediate or transitional states  we should be extremely cautious in
concluding that none can have existed  for the metamorphoses of many organs
show what wonderful changes in function are at least possible   For
instance  a swim bladder has apparently been converted into an
air breathing lung   The same organ having performed simultaneously very
different functions  and then having been in part or in whole specialised
for one function  and two distinct organs having performed at the same time
the same function  the one having been perfected whilst aided by the other 
must often have largely facilitated transitions 

We have seen that in two beings widely remote from each other in the
natural scale  organs serving for the same purpose and in external
appearance closely similar may have been separately and independently
formed  but when such organs are closely examined  essential differences in
their structure can almost always be detected  and this naturally follows
from the principle of natural selection   On the other hand  the common
rule throughout nature is infinite diversity of structure for gaining the
same end  and this again naturally follows from the same great principle 

In many cases we are far too ignorant to be enabled to assert that a part
or organ is so unimportant for the welfare of a species  that modifications
in its structure could not have been slowly accumulated by means of natural
selection   In many other cases  modifications are probably the direct
result of the laws of variation or of growth  independently of any good
having been thus gained   But even such structures have often  as we may
feel assured  been subsequently taken advantage of  and still further
modified  for the good of species under new conditions of life   We may 
also  believe that a part formerly of high importance has frequently been
retained  as the tail of an aquatic animal by its terrestrial descendants  
though it has become of such small importance that it could not  in its
present state  have been acquired by means of  natural selection 

Natural selection can produce nothing in one species for the exclusive good
or injury of another  though it may well produce parts  organs  and
excretions highly useful or even indispensable  or highly injurious to
another species  but in all cases at the same time useful to the possessor 
In each well stocked country natural selection acts through the competition
of the inhabitants and consequently leads to success in the battle for
life  only in accordance with the standard of that particular country  
Hence the inhabitants of one country  generally the smaller one  often
yield to the inhabitants of another and generally the larger country   For
in the larger country there will have existed more individuals  and more
diversified forms  and the competition will have been severer  and thus the
standard of perfection will have been rendered higher   Natural selection
will not necessarily lead to absolute perfection  nor  as far as we can
judge by our limited faculties  can absolute perfection be everywhere
predicated 

On the theory of natural selection we can clearly understand the full
meaning of that old canon in natural history   Natura non facit saltum   
This canon  if we look to the present inhabitants alone of the world  is
not strictly correct  but if we include all those of past times  whether
known or unknown  it must on this theory be strictly true 

It is generally acknowledged that all organic beings have been formed on
two great laws  Unity of Type  and the Conditions of Existence   By unity
of type is meant that fundamental agreement in structure which we see in
organic beings of the same class  and which is quite independent of their
habits of life   On my theory  unity of type is explained by unity of
descent   The expression of conditions of existence  so often insisted on
by the illustrious Cuvier  is fully embraced by the principle of natural
selection   For natural selection acts by either now adapting the varying
parts of each being to its organic and inorganic conditions of life  or by
having adapted them during past periods of time   the adaptations being
aided in many cases by the increased use or disuse of parts  being affected
by the direct action of external conditions of life  and subjected in all
cases to the several laws of growth and variation   Hence  in fact  the law
of the Conditions of Existence is the higher law  as it includes  through
the inheritance of former variations and adaptations  that of Unity of
Type 


CHAPTER VII 

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION 

Longevity    Modifications not necessarily simultaneous    Modifications
apparently of no direct service    Progressive development    Characters of
small functional importance  the most constant    Supposed incompetence of
natural selection to account for the incipient stages of useful structures
   Causes which interfere with the acquisition through natural selection of
useful structures    Gradations of structure with changed functions   
Widely different organs in members of the same class  developed from one
and the same source    Reasons for disbelieving in great and abrupt
modifications 

I will devote this chapter to the consideration of various miscellaneous
objections which have been advanced against my views  as some of the
previous discussions may thus be made clearer  but it would be useless to
discuss all of them  as many have been made by writers who have not taken
the trouble to understand the subject   Thus a distinguished German
naturalist has asserted that the weakest part of my theory is  that I
consider all organic beings as imperfect   what I have really said is  that
all are not as perfect as they might have been in relation to their
conditions  and this is shown to be the case by so many native forms in
many quarters of the world having yielded their places to intruding
foreigners   Nor can organic beings  even if they were at any one time
perfectly adapted to their conditions of life  have remained so  when their
conditions changed  unless they themselves likewise changed  and no one
will dispute that the physical conditions of each country  as well as the
number and kinds of its inhabitants  have undergone many mutations 

A critic has lately insisted  with some parade of mathematical accuracy 
that longevity is a great advantage to all species  so that he who believes
in natural selection  must arrange his genealogical tree  in such a manner
that all the descendants have longer lives than their progenitors   Cannot
our critics conceive that a biennial plant or one of the lower animals
might range into a cold climate and perish there every winter  and yet 
owing to advantages gained through natural selection  survive from year to
year by means of its seeds or ova   Mr  E  Ray Lankester has recently
discussed this subject  and he concludes  as far as its extreme complexity
allows him to form a judgment  that longevity is generally related to the
standard of each species in the scale of organisation  as well as to the
amount of expenditure in reproduction and in general activity   And these
conditions have  it is probable  been largely determined through natural
selection 

It has been argued that  as none of the animals and plants of Egypt  of
which we know anything  have changed during the last three or four thousand
years  so probably have none in any part of the world   But  as Mr  G H 
Lewes has remarked  this line of argument proves too much  for the ancient
domestic races figured on the Egyptian monuments  or embalmed  are closely
similar or even identical with those now living  yet all naturalists admit
that such races have been produced through the modification of their
original types   The many animals which have remained unchanged since the
commencement of the glacial period  would have been an incomparably
stronger case  for these have been exposed to great changes of climate and
have migrated over great distances  whereas  in Egypt  during the last
several thousand years  the conditions of life  as far as we know  have
remained absolutely uniform   The fact of little or no modification having
been effected since the glacial period  would have been of some avail
against those who believe in an innate and necessary law of development 
but is powerless against the doctrine of natural selection or the survival
of the fittest  which implies that when variations or individual
differences of a beneficial nature happen to arise  these will be
preserved  but this will be effected only under certain favourable
circumstances 

The celebrated palaeontologist  Bronn  at the close of his German
translation of this work  asks how  on the principle of natural selection 
can a variety live side by side with the parent species   If both have
become fitted for slightly different habits of life or conditions  they
might live together  and if we lay on one side polymorphic species  in
which the variability seems to be of a peculiar nature  and all mere
temporary variations  such as size  albinism  etc   the more permanent
varieties are generally found  as far as I can discover  inhabiting
distinct stations  such as high land or low land  dry or moist districts  
Moreover  in the case of animals which wander much about and cross freely 
their varieties seem to be generally confined to distinct regions 

Bronn also insists that distinct species never differ from each other in
single characters  but in many parts  and he asks  how it always comes that
many parts of the organisation should have been modified at the same time
through variation and natural selection   But there is no necessity for
supposing that all the parts of any being have been simultaneously
modified   The most striking modifications  excellently adapted for some
purpose  might  as was formerly remarked  be acquired by successive
variations  if slight  first in one part and then in another  and as they
would be transmitted all together  they would appear to us as if they had
been simultaneously developed   The best answer  however  to the above
objection is afforded by those domestic races which have been modified 
chiefly through man s power of selection  for some special purpose   Look
at the race and dray horse  or at the greyhound and mastiff   Their whole
frames  and even their mental characteristics  have been modified  but if
we could trace each step in the history of their transformation  and the
latter steps can be traced  we should not see great and simultaneous
changes  but first one part and then another slightly modified and
improved   Even when selection has been applied by man to some one
character alone  of which our cultivated plants offer the best instances  
it will invariably be found that although this one part  whether it be the
flower  fruit  or leaves  has been greatly changed  almost all the other
parts have been slightly modified   This may be attributed partly to the
principle of correlated growth  and partly to so called spontaneous
variation 

A much more serious objection has been urged by Bronn  and recently by
Broca  namely  that many characters appear to be of no service whatever to
their possessors  and therefore cannot have been influenced through natural
selection   Bronn adduces the length of the ears and tails in the different
species of hares and mice  the complex folds of enamel in the teeth of many
animals  and a multitude of analogous cases   With respect to plants  this
subject has been discussed by Nageli in an admirable essay   He admits that
natural selection has effected much  but he insists that the families of
plants differ chiefly from each other in morphological characters  which
appear to be quite unimportant for the welfare of the species   He
consequently believes in an innate tendency towards progressive and more
perfect development   He specifies the arrangement of the cells in the
tissues  and of the leaves on the axis  as cases in which natural selection
could not have acted   To these may be added the numerical divisions in the
parts of the flower  the position of the ovules  the shape of the seed 
when not of any use for dissemination  etc 

There is much force in the above objection   Nevertheless  we ought  in the
first place  to be extremely cautious in pretending to decide what
structures now are  or have formerly been  of use to each species   In the
second place  it should always be borne in mind that when one part is
modified  so will be other parts  through certain dimly seen causes  such
as an increased or diminished flow of nutriment to a part  mutual pressure 
an early developed part affecting one subsequently developed  and so forth
  as well as through other causes which lead to the many mysterious cases
of correlation  which we do not in the least understand   These agencies
may be all grouped together  for the sake of brevity  under the expression
of the laws of growth   In the third place  we have to allow for the direct
and definite action of changed conditions of life  and for so called
spontaneous variations  in which the nature of the conditions apparently
plays a quite subordinate part   Bud variations  such as the appearance of
a moss rose on a common rose  or of a nectarine on a peach tree  offer good
instances of spontaneous variations  but even in these cases  if we bear in
mind the power of a minute drop of poison in producing complex galls  we
ought not to feel too sure that the above variations are not the effect of
some local change in the nature of the sap  due to some change in the
conditions   There must be some efficient cause for each slight individual
difference  as well as for more strongly marked variations which
occasionally arise  and if the unknown cause were to act persistently  it
is almost certain that all the individuals of the species would be
similarly modified 

In the earlier editions of this work I underrated  as it now seems
probable  the frequency and importance of modifications due to spontaneous
variability   But it is impossible to attribute to this cause the
innumerable structures which are so well adapted to the habits of life of
each species   I can no more believe in this than that the well adapted
form of a race horse or greyhound  which before the principle of selection
by man was well understood  excited so much surprise in the minds of the
older naturalists  can thus be explained 

It may be worth while to illustrate some of the foregoing remarks   With
respect to the assumed inutility of various parts and organs  it is hardly
necessary to observe that even in the higher and best known animals many
structures exist  which are so highly developed that no one doubts that
they are of importance  yet their use has not been  or has only recently
been  ascertained   As Bronn gives the length of the ears and tail in the
several species of mice as instances  though trifling ones  of differences
in structure which can be of no special use  I may mention that  according
to Dr  Schobl  the external ears of the common mouse are supplied in an
extraordinary manner with nerves  so that they no doubt serve as tactile
organs  hence the length of the ears can hardly be quite unimportant   We
shall  also  presently see that the tail is a highly useful prehensile
organ to some of the species  and its use would be much influence by its
length 

With respect to plants  to which on account of Nageli s essay I shall
confine myself in the following remarks  it will be admitted that the
flowers of the orchids present a multitude of curious structures  which a
few years ago would have been considered as mere morphological differences
without any special function  but they are now known to be of the highest
importance for the fertilisation of the species through the aid of insects 
and have probably been gained through natural selection   No one until
lately would have imagined that in dimorphic and trimorphic plants the
different lengths of the stamens and pistils  and their arrangement  could
have been of any service  but now we know this to be the case 

In certain whole groups of plants the ovules stand erect  and in others
they are suspended  and within the same ovarium of some few plants  one
ovule holds the former and a second ovule the latter position   These
positions seem at first purely morphological  or of no physiological
signification  but Dr  Hooker informs me that within the same ovarium the
upper ovules alone in some cases  and in others the lower ones alone are
fertilised  and he suggests that this probably depends on the direction in
which the pollen tubes enter the ovarium   If so  the position of the
ovules  even when one is erect and the other suspended within the same
ovarium  would follow the selection of any slight deviations in position
which favoured their fertilisation  and the production of seed 

Several plants belonging to distinct orders habitually produce flowers of
two kinds  the one open  of the ordinary structure  the other closed and
imperfect   These two kinds of flowers sometimes differ wonderfully in
structure  yet may be seen to graduate into each other on the same plant  
The ordinary and open flowers can be intercrossed  and the benefits which
certainly are derived from this process are thus secured   The closed and
imperfect flowers are  however  manifestly of high importance  as they
yield with the utmost safety a large stock of seed  with the expenditure of
wonderfully little pollen   The two kinds of flowers often differ much  as
just stated  in structure   The petals in the imperfect flowers almost
always consist of mere rudiments  and the pollen grains are reduced in
diameter   In Ononis columnae five of the alternate stamens are
rudimentary  and in some species of Viola three stamens are in this state 
two retaining their proper function  but being of very small size   In six
out of thirty of the closed flowers in an Indian violet  name unknown  for
the plants have never produced with me perfect flowers   the sepals are
reduced from the normal number of five to three   In one section of the
Malpighiaceae the closed flowers  according to A  de Jussieu  are still
further modified  for the five stamens which stand opposite to the sepals
are all aborted  a sixth stamen standing opposite to a petal being alone
developed  and this stamen is not present in the ordinary flowers of this
species  the style is aborted  and the ovaria are reduced from three to
two   Now although natural selection may well have had the power to prevent
some of the flowers from expanding  and to reduce the amount of pollen 
when rendered by the closure of the flowers superfluous  yet hardly any of
the above special modifications can have been thus determined  but must
have followed from the laws of growth  including the functional inactivity
of parts  during the progress of the reduction of the pollen and the
closure of the flowers 

It is so necessary to appreciate the important effects of the laws of
growth  that I will give some additional cases of another kind  namely of
differences in the same part or organ  due to differences in relative
position on the same plant   In the Spanish chestnut  and in certain fir 
trees  the angles of divergence of the leaves differ  according to Schacht 
in the nearly horizontal and in the upright branches   In the common rue
and some other plants  one flower  usually the central or terminal one 
opens first  and has five sepals and petals  and five divisions to the
ovarium  while all the other flowers on the plant are tetramerous   In the
British Adoxa the uppermost flower generally has two calyx lobes with the
other organs tetramerous  while the surrounding flowers generally have
three calyx lobes with the other organs pentamerous   In many Compositae
and Umbelliferae  and in some other plants  the circumferential flowers
have their corollas much more developed than those of the centre  and this
seems often connected with the abortion of the reproductive organs   It is
a more curious fact  previously referred to  that the achenes or seeds of
the circumference and centre sometimes differ greatly in form  colour and
other characters   In Carthamus and some other Compositae the central
achenes alone are furnished with a pappus  and in Hyoseris the same head
yields achenes of three different forms   In certain Umbelliferae the
exterior seeds  according to Tausch  are orthospermous  and the central one
coelospermous  and this is a character which was considered by De Candolle
to be in other species of the highest systematic importance   Professor
Braun mentions a Fumariaceous genus  in which the flowers in the lower part
of the spike bear oval  ribbed  one seeded nutlets  and in the upper part
of the spike  lanceolate  two valved and two seeded siliques   In these
several cases  with the exception of that of the well developed ray 
florets  which are of service in making the flowers conspicuous to insects 
natural selection cannot  as far as we can judge  have come into play  or
only in a quite subordinate manner   All these modifications follow from
the relative position and inter action of the parts  and it can hardly be
doubted that if all the flowers and leaves on the same plant had been
subjected to the same external and internal condition  as are the flowers
and leaves in certain positions  all would have been modified in the same
manner 

In numerous other cases we find modifications of structure  which are
considered by botanists to be generally of a highly important nature 
affecting only some of the flowers on the same plant  or occurring on
distinct plants  which grow close together under the same conditions   As
these variations seem of no special use to the plants  they cannot have
been influenced by natural selection   Of their cause we are quite
ignorant  we cannot even attribute them  as in the last class of cases  to
any proximate agency  such as relative position   I will give only a few
instances   It is so common to observe on the same plant  flowers
indifferently tetramerous  pentamerous  etc   that I need not give
examples  but as numerical variations are comparatively rare when the parts
are few  I may mention that  according to De Candolle  the flowers of
Papaver bracteatum offer either two sepals with four petals  which is the
common type with poppies   or three sepals with six petals   The manner in
which the petals are folded in the bud is in most groups a very constant
morphological character  but Professor Asa Gray states that with some
species of Mimulus  the aestivation is almost as frequently that of the
Rhinanthideae as of the Antirrhinideae  to which latter tribe the genus
belongs   Aug  St  Hilaire gives the following cases   the genus
Zanthoxylon belongs to a division of the Rutaceae with a single ovary  but
in some species flowers may be found on the same plant  and even in the
same panicle  with either one or two ovaries   In Helianthemum the capsule
has been described as unilocular or tri locular  and in H  mutabile   Une
lame PLUS OU MOINS LARGE  s etend entre le pericarpe et le placenta    In
the flowers of Saponaria officinalis Dr  Masters has observed instances of
both marginal and free central placentation   Lastly  St  Hilaire found
towards the southern extreme of the range of Gomphia oleaeformis two forms
which he did not at first doubt were distinct species  but he subsequently
saw them growing on the same bush  and he then adds   Voila donc dans un
meme individu des loges et un style qui se rattachent tantot a un axe
verticale et tantot a un gynobase  

We thus see that with plants many morphological changes may be attributed
to the laws of growth and the inter action of parts  independently of
natural selection   But with respect to Nageli s doctrine of an innate
tendency towards perfection or progressive development  can it be said in
the case of these strongly pronounced variations  that the plants have been
caught in the act of progressing towards a higher state of development   On
the contrary  I should infer from the mere fact of the parts in question
differing or varying greatly on the same plant  that such modifications
were of extremely small importance to the plants themselves  of whatever
importance they may generally be to us for our classifications   The
acquisition of a useless part can hardly be said to raise an organism in
the natural scale  and in the case of the imperfect  closed flowers  above
described  if any new principle has to be invoked  it must be one of
retrogression rather than of progression  and so it must be with many
parasitic and degraded animals   We are ignorant of the exciting cause of
the above specified modifications  but if the unknown cause were to act
almost uniformly for a length of time  we may infer that the result would
be almost uniform  and in this case all the individuals of the species
would be modified in the same manner 

 From the fact of the above characters being unimportant for the welfare of
the species  any slight variations which occurred in them would not have
been accumulated and augmented through natural selection   A structure
which has been developed through long continued selection  when it ceases
to be of service to a species  generally becomes variable  as we see with
rudimentary organs  for it will no longer be regulated by this same power
of selection   But when  from the nature of the organism and of the
conditions  modifications have been induced which are unimportant for the
welfare of the species  they may be  and apparently often have been 
transmitted in nearly the same state to numerous  otherwise modified 
descendants   It cannot have been of much importance to the greater number
of mammals  birds  or reptiles  whether they were clothed with hair 
feathers or scales  yet hair has been transmitted to almost all mammals 
feathers to all birds  and scales to all true reptiles   A structure 
whatever it may be  which is common to many allied forms  is ranked by us
as of high systematic importance  and consequently is often assumed to be
of high vital importance to the species   Thus  as I am inclined to
believe  morphological differences  which we consider as important  such as
the arrangement of the leaves  the divisions of the flower or of the
ovarium  the position of the ovules  etc   first appeared in many cases as
fluctuating variations  which sooner or later became constant through the
nature of the organism and of the surrounding conditions  as well as
through the intercrossing of distinct individuals  but not through natural
selection  for as these morphological characters do not affect the welfare
of the species  any slight deviations in them could not have been governed
or accumulated through this latter agency   It is a strange result which we
thus arrive at  namely  that characters of slight vital importance to the
species  are the most important to the systematist  but  as we shall
hereafter see when we treat of the genetic principle of classification 
this is by no means so paradoxical as it may at first appear 

Although we have no good evidence of the existence in organic beings of an
innate tendency towards progressive development  yet this necessarily
follows  as I have attempted to show in the fourth chapter  through the
continued action of natural selection   For the best definition which has
ever been given of a high standard of organisation  is the degree to which
the parts have been specialised or differentiated  and natural selection
tends towards this end  inasmuch as the parts are thus enabled to perform
their functions more efficiently 

A distinguished zoologist  Mr  St  George Mivart  has recently collected
all the objections which have ever been advanced by myself and others
against the theory of natural selection  as propounded by Mr  Wallace and
myself  and has illustrated them with admirable art and force   When thus
marshalled  they make a formidable array  and as it forms no part of Mr 
Mivart s plan to give the various facts and considerations opposed to his
conclusions  no slight effort of reason and memory is left to the reader 
who may wish to weigh the evidence on both sides   When discussing special
cases  Mr  Mivart passes over the effects of the increased use and disuse
of parts  which I have always maintained to be highly important  and have
treated in my  Variation under Domestication  at greater length than  as I
believe  any other writer   He likewise often assumes that I attribute
nothing to variation  independently of natural selection  whereas in the
work just referred to I have collected a greater number of well established
cases than can be found in any other work known to me   My judgment may not
be trustworthy  but after reading with care Mr  Mivart s book  and
comparing each section with what I have said on the same head  I never
before felt so strongly convinced of the general truth of the conclusions
here arrived at  subject  of course  in so intricate a subject  to much
partial error 

All Mr  Mivart s objections will be  or have been  considered in the
present volume   The one new point which appears to have struck many
readers is   That natural selection is incompetent to account for the
incipient stages of useful structures    This subject is intimately
connected with that of the gradation of the characters  often accompanied
by a change of function  for instance  the conversion of a swim bladder
into lungs  points which were discussed in the last chapter under two
headings   Nevertheless  I will here consider in some detail several of the
cases advanced by Mr  Mivart  selecting those which are the most
illustrative  as want of space prevents me from considering all 

The giraffe  by its lofty stature  much elongated neck  fore legs  head and
tongue  has its whole frame beautifully adapted for browsing on the higher
branches of trees   It can thus obtain food beyond the reach of the other
Ungulata or hoofed animals inhabiting the same country  and this must be a
great advantage to it during dearths   The Niata cattle in South America
show us how small a difference in structure may make  during such periods 
a great difference in preserving an animal s life   These cattle can browse
as well as others on grass  but from the projection of the lower jaw they
cannot  during the often recurrent droughts  browse on the twigs of trees 
reeds  etc   to which food the common cattle and horses are then driven  so
that at these times the Niatas perish  if not fed by their owners   Before
coming to Mr  Mivart s objections  it may be well to explain once again how
natural selection will act in all ordinary cases   Man has modified some of
his animals  without necessarily having attended to special points of
structure  by simply preserving and breeding from the fleetest individuals 
as with the race horse and greyhound  or as with the game cock  by breeding
from the victorious birds   So under nature with the nascent giraffe  the
individuals which were the highest browsers and were able during dearths to
reach even an inch or two above the others  will often have been preserved 
for they will have roamed over the whole country in search of food   That
the individuals of the same species often differ slightly in the relative
lengths of all their parts may be seen in many works of natural history  in
which careful measurements are given   These slight proportional
differences  due to the laws of growth and variation  are not of the
slightest use or importance to most species   But it will have been
otherwise with the nascent giraffe  considering its probable habits of
life  for those individuals which had some one part or several parts of
their bodies rather more elongated than usual  would generally have
survived   These will have intercrossed and left offspring  either
inheriting the same bodily peculiarities  or with a tendency to vary again
in the same manner  while the individuals less favoured in the same
respects will have been the most liable to perish 

We here see that there is no need to separate single pairs  as man does 
when he methodically improves a breed   natural selection will preserve and
thus separate all the superior individuals  allowing them freely to
intercross  and will destroy all the inferior individuals   By this process
long continued  which exactly corresponds with what I have called
unconscious selection by man  combined  no doubt  in a most important
manner with the inherited effects of the increased use of parts  it seems
to me almost certain that an ordinary hoofed quadruped might be converted
into a giraffe 

To this conclusion Mr  Mivart brings forward two objections   One is that
the increased size of the body would obviously require an increased supply
of food  and he considers it as  very problematical whether the
disadvantages thence arising would not  in times of scarcity  more than
counterbalance the advantages    But as the giraffe does actually exist in
large numbers in Africa  and as some of the largest antelopes in the world 
taller than an ox  abound there  why should we doubt that  as far as size
is concerned  intermediate gradations could formerly have existed there 
subjected as now to severe dearths   Assuredly the being able to reach  at
each stage of increased size  to a supply of food  left untouched by the
other hoofed quadrupeds of the country  would have been of some advantage
to the nascent giraffe   Nor must we overlook the fact  that increased bulk
would act as a protection against almost all beasts of prey excepting the
lion  and against this animal  its tall neck  and the taller the better  
would  as Mr  Chauncey Wright has remarked  serve as a watch tower   It is
from this cause  as Sir S  Baker remarks  that no animal is more difficult
to stalk than the giraffe   This animal also uses its long neck as a means
of offence or defence  by violently swinging its head armed with stump like
horns   The preservation of each species can rarely be determined by any
one advantage  but by the union of all  great and small 

Mr  Mivart then asks  and this is his second objection   if natural
selection be so potent  and if high browsing be so great an advantage  why
has not any other hoofed quadruped acquired a long neck and lofty stature 
besides the giraffe  and  in a lesser degree  the camel  guanaco and
macrauchenia   Or  again  why has not any member of the group acquired a
long proboscis   With respect to South Africa  which was formerly inhabited
by numerous herds of the giraffe  the answer is not difficult  and can best
be given by an illustration   In every meadow in England  in which trees
grow  we see the lower branches trimmed or planed to an exact level by the
browsing of the horses or cattle  and what advantage would it be  for
instance  to sheep  if kept there  to acquire slightly longer necks   In
every district some one kind of animal will almost certainly be able to
browse higher than the others  and it is almost equally certain that this
one kind alone could have its neck elongated for this purpose  through
natural selection and the effects of increased use   In South Africa the
competition for browsing on the higher branches of the acacias and other
trees must be between giraffe and giraffe  and not with the other ungulate
animals 

Why  in other quarters of the world  various animals belonging to this same
order have not acquired either an elongated neck or a proboscis  cannot be
distinctly answered  but it is as unreasonable to expect a distinct answer
to such a question as why some event in the history of mankind did not
occur in one country while it did in another   We are ignorant with respect
to the conditions which determine the numbers and range of each species 
and we cannot even conjecture what changes of structure would be favourable
to its increase in some new country   We can  however  see in a general
manner that various causes might have interfered with the development of a
long neck or proboscis   To reach the foliage at a considerable height
 without climbing  for which hoofed animals are singularly ill constructed 
implies greatly increased bulk of body  and we know that some areas support
singularly few large quadrupeds  for instance South America  though it is
so luxuriant  while South Africa abounds with them to an unparalleled
degree   Why this should be so we do not know  nor why the later tertiary
periods should have been much more favourable for their existence than the
present time   Whatever the causes may have been  we can see that certain
districts and times would have been much more favourable than others for
the development of so large a quadruped as the giraffe 

In order that an animal should acquire some structure specially and largely
developed  it is almost indispensable that several other parts should be
modified and coadapted   Although every part of the body varies slightly 
it does not follow that the necessary parts should always vary in the right
direction and to the right degree   With the different species of our
domesticated animals we know that the parts vary in a different manner and
degree  and that some species are much more variable than others   Even if
the fitting variations did arise  it does not follow that natural selection
would be able to act on them and produce a structure which apparently would
be beneficial to the species   For instance  if the number of individuals
existing in a country is determined chiefly through destruction by beasts
of prey  by external or internal parasites  etc   as seems often to be the
case  then natural selection will be able to do little  or will be greatly
retarded  in modifying any particular structure for obtaining food  
Lastly  natural selection is a slow process  and the same favourable
conditions must long endure in order that any marked effect should thus be
produced   Except by assigning such general and vague reasons  we cannot
explain why  in many quarters of the world  hoofed quadrupeds have not
acquired much elongated necks or other means for browsing on the higher
branches of trees 

Objections of the same nature as the foregoing have been advanced by many
writers   In each case various causes  besides the general ones just
indicated  have probably interfered with the acquisition through natural
selection of structures  which it is thought would be beneficial to certain
species   One writer asks  why has not the ostrich acquired the power of
flight   But a moment s reflection will show what an enormous supply of
food would be necessary to give to this bird of the desert force to move
its huge body through the air   Oceanic islands are inhabited by bats and
seals  but by no terrestrial mammals  yet as some of these bats are
peculiar species  they must have long inhabited their present homes  
Therefore Sir C  Lyell asks  and assigns certain reasons in answer  why
have not seals and bats given birth on such islands to forms fitted to live
on the land   But seals would necessarily be first converted into
terrestrial carnivorous animals of considerable size  and bats into
terrestrial insectivorous animals  for the former there would be no prey 
for the bats ground insects would serve as food  but these would already be
largely preyed on by the reptiles or birds  which first colonise and abound
on most oceanic islands   Gradations of structure  with each stage
beneficial to a changing species  will be favoured only under certain
peculiar conditions   A strictly terrestrial animal  by occasionally
hunting for food in shallow water  then in streams or lakes  might at last
be converted into an animal so thoroughly aquatic as to brave the open
ocean   But seals would not find on oceanic islands the conditions
favourable to their gradual reconversion into a terrestrial form   Bats  as
formerly shown  probably acquired their wings by at first gliding through
the air from tree to tree  like the so called flying squirrels  for the
sake of escaping from their enemies  or for avoiding falls  but when the
power of true flight had once been acquired  it would never be reconverted
back  at least for the above purposes  into the less efficient power of
gliding through the air   Bats  might  indeed  like many birds  have had
their wings greatly reduced in size  or completely lost  through disuse 
but in this case it would be necessary that they should first have acquired
the power of running quickly on the ground  by the aid of their hind legs
alone  so as to compete with birds or other ground animals  and for such a
change a bat seems singularly ill fitted   These conjectural remarks have
been made merely to show that a transition of structure  with each step
beneficial  is a highly complex affair  and that there is nothing strange
in a transition not having occurred in any particular case 

Lastly  more than one writer has asked why have some animals had their
mental powers more highly developed than others  as such development would
be advantageous to all   Why have not apes acquired the intellectual powers
of man   Various causes could be assigned  but as they are conjectural  and
their relative probability cannot be weighed  it would be useless to give
them   A definite answer to the latter question ought not to be expected 
seeing that no one can solve the simpler problem  why  of two races of
savages  one has risen higher in the scale of civilisation than the other 
and this apparently implies increased brain power 

We will return to Mr  Mivart s other objections   Insects often resemble
for the sake of protection various objects  such as green or decayed
leaves  dead twigs  bits of lichen  flowers  spines  excrement of birds 
and living insects  but to this latter point I shall hereafter recur   The
resemblance is often wonderfully close  and is not confined to colour  but
extends to form  and even to the manner in which the insects hold
themselves   The caterpillars which project motionless like dead twigs from
the bushes on which they feed  offer an excellent instance of a resemblance
of this kind   The cases of the imitation of such objects as the excrement
of birds  are rare and exceptional   On this head  Mr  Mivart remarks   As 
according to Mr  Darwin s theory  there is a constant tendency to
indefinite variation  and as the minute incipient variations will be in ALL
DIRECTIONS  they must tend to neutralize each other  and at first to form
such unstable modifications that it is difficult  if not impossible  to see
how such indefinite oscillations of infinitesimal beginnings can ever build
up a sufficiently appreciable resemblance to a leaf  bamboo  or other
object  for natural selection to seize upon and perpetuate  

But in all the foregoing cases the insects in their original state no doubt
presented some rude and accidental resemblance to an object commonly found
in the stations frequented by them   Nor is this at all improbable 
considering the almost infinite number of surrounding objects and the
diversity in form and colour of the hosts of insects which exist   As some
rude resemblance is necessary for the first start  we can understand how it
is that the larger and higher animals do not  with the exception  as far as
I know  of one fish  resemble for the sake of protection special objects 
but only the surface which commonly surrounds them  and this chiefly in
colour   Assuming that an insect originally happened to resemble in some
degree a dead twig or a decayed leaf  and that it varied slightly in many
ways  then all the variations which rendered the insect at all more like
any such object  and thus favoured its escape  would be preserved  while
other variations would be neglected and ultimately lost  or  if they
rendered the insect at all less like the imitated object  they would be
eliminated   There would indeed be force in Mr  Mivart s objection  if we
were to attempt to account for the above resemblances  independently of
natural selection  through mere fluctuating variability  but as the case
stands there is none 

Nor can I see any force in Mr  Mivart s difficulty with respect to  the
last touches of perfection in the mimicry   as in the case given by Mr 
Wallace  of a walking stick insect  Ceroxylus laceratus   which resembles
 a stick grown over by a creeping moss or jungermannia    So close was this
resemblance  that a native Dyak maintained that the foliaceous excrescences
were really moss   Insects are preyed on by birds and other enemies whose
sight is probably sharper than ours  and every grade in resemblance which
aided an insect to escape notice or detection  would tend towards its
preservation  and the more perfect the resemblance so much the better for
the insect   Considering the nature of the differences between the species
in the group which includes the above Ceroxylus  there is nothing
improbable in this insect having varied in the irregularities on its
surface  and in these having become more or less green coloured  for in
every group the characters which differ in the several species are the most
apt to vary  while the generic characters  or those common to all the
species  are the most constant 

The Greenland whale is one of the most wonderful animals in the world  and
the baleen  or whalebone  one of its greatest peculiarities   The baleen
consists of a row  on each side of the upper jaw  of about 300 plates or
laminae  which stand close together transversely to the longer axis of the
mouth   Within the main row there are some subsidiary rows   The
extremities and inner margins of all the plates are frayed into stiff
bristles  which clothe the whole gigantic palate  and serve to strain or
sift the water  and thus to secure the minute prey on which these great
animals subsist   The middle and longest lamina in the Greenland whale is
ten  twelve  or even fifteen feet in length  but in the different species
of Cetaceans there are gradations in length  the middle lamina being in one
species  according to Scoresby  four feet  in another three  in another
eighteen inches  and in the Balaenoptera rostrata only about nine inches in
length   The quality of the whalebone also differs in the different
species 

With respect to the baleen  Mr  Mivart remarks that if it  had once
attained such a size and development as to be at all useful  then its
preservation and augmentation within serviceable limits would be promoted
by natural selection alone   But how to obtain the beginning of such useful
development    In answer  it may be asked  why should not the early
progenitors of the whales with baleen have possessed a mouth constructed
something like the lamellated beak of a duck   Ducks  like whales  subsist
by sifting the mud and water  and the family has sometimes been called
Criblatores  or sifters   I hope that I may not be misconstrued into saying
that the progenitors of whales did actually possess mouths lamellated like
the beak of a duck   I wish only to show that this is not incredible  and
that the immense plates of baleen in the Greenland whale might have been
developed from such lamellae by finely graduated steps  each of service to
its possessor 

The beak of a shoveller duck  Spatula clypeata  is a more beautiful and
complex structure than the mouth of a whale   The upper mandible is
furnished on each side  in the specimen examined by me  with a row or comb
formed of 188 thin  elastic lamellae  obliquely bevelled so as to be
pointed  and placed transversely to the longer axis of the mouth   They
arise from the palate  and are attached by flexible membrane to the sides
of the mandible   Those standing towards the middle are the longest  being
about one third of an inch in length  and they project fourteen one 
hundredths of an inch beneath the edge   At their bases there is a short
subsidiary row of obliquely transverse lamellae   In these several respects
they resemble the plates of baleen in the mouth of a whale   But towards
the extremity of the beak they differ much  as they project inward  instead
of straight downward   The entire head of the shoveller  though
incomparably less bulky  is about one eighteenth of the length of the head
of a moderately large Balaenoptera rostrata  in which species the baleen is
only nine inches long  so that if we were to make the head of the shoveller
as long as that of the Balaenoptera  the lamellae would be six inches in
length  that is  two thirds of the length of the baleen in this species of
whale   The lower mandible of the shoveller duck is furnished with lamellae
of equal length with these above  but finer  and in being thus furnished it
differs conspicuously from the lower jaw of a whale  which is destitute of
baleen   On the other hand  the extremities of these lower lamellae are
frayed into fine bristly points  so that they thus curiously resemble the
plates of baleen   In the genus Prion  a member of the distinct family of
the Petrels  the upper mandible alone is furnished with lamellae  which are
well developed and project beneath the margin  so that the beak of this
bird resembles in this respect the mouth of a whale 

 From the highly developed structure of the shoveller s beak we may proceed
 as I have learned from information and specimens sent to me by Mr 
Salvin   without any great break  as far as fitness for sifting is
concerned  through the beak of the Merganetta armata  and in some respects
through that of the Aix sponsa  to the beak of the common duck   In this
latter species the lamellae are much coarser than in the shoveller  and are
firmly attached to the sides of the mandible  they are only about fifty in
number on each side  and do not project at all beneath the margin   They
are square topped  and are edged with translucent  hardish tissue  as if
for crushing food   The edges of the lower mandible are crossed by numerous
fine ridges  which project very little   Although the beak is thus very
inferior as a sifter to that of a shoveller  yet this bird  as every one
knows  constantly uses it for this purpose   There are other species  as I
hear from Mr  Salvin  in which the lamellae are considerably less developed
than in the common duck  but I do not know whether they use their beaks for
sifting the water 

Turning to another group of the same family   In the Egyptian goose
 Chenalopex  the beak closely resembles that of the common duck  but the
lamellae are not so numerous  nor so distinct from each other  nor do they
project so much inward  yet this goose  as I am informed by Mr  E 
Bartlett   uses its bill like a duck by throwing the water out at the
corners    Its chief food  however  is grass  which it crops like the
common goose   In this latter bird the lamellae of the upper mandible are
much coarser than in the common duck  almost confluent  about twenty seven
in number on each side  and terminating upward in teeth like knobs   The
palate is also covered with hard rounded knobs   The edges of the lower
mandible are serrated with teeth much more prominent  coarser and sharper
than in the duck   The common goose does not sift the water  but uses its
beak exclusively for tearing or cutting herbage  for which purpose it is so
well fitted that it can crop grass closer than almost any other animal  
There are other species of geese  as I hear from Mr  Bartlett  in which the
lamellae are less developed than in the common goose 

We thus see that a member of the duck family  with a beak constructed like
that of a common goose and adapted solely for grazing  or even a member
with a beak having less well developed lamellae  might be converted by
small changes into a species like the Egyptian goose  this into one like
the common duck  and  lastly  into one like the shoveller  provided with a
beak almost exclusively adapted for sifting the water  for this bird could
hardly use any part of its beak  except the hooked tip  for seizing or
tearing solid food   The beak of a goose  as I may add  might also be
converted by small changes into one provided with prominent  recurved
teeth  like those of the Merganser  a member of the same family   serving
for the widely different purpose of securing live fish 

Returning to the whales   The Hyperoodon bidens is destitute of true teeth
in an efficient condition  but its palate is roughened  according to
Lacepede  with small unequal  hard points of horn   There is  therefore 
nothing improbable in supposing that some early Cetacean form was provided
with similar points of horn on the palate  but rather more regularly
placed  and which  like the knobs on the beak of the goose  aided it in
seizing or tearing its food   If so  it will hardly be denied that the
points might have been converted through variation and natural selection
into lamellae as well developed as those of the Egyptian goose  in which
case they would have been used both for seizing objects and for sifting the
water  then into lamellae like those of the domestic duck  and so onward 
until they became as well constructed as those of the shoveller  in which
case they would have served exclusively as a sifting apparatus   From this
stage  in which the lamellae would be two thirds of the length of the
plates of baleen in the Balaenoptera rostrata  gradations  which may be
observed in still existing Cetaceans  lead us onward to the enormous plates
of baleen in the Greenland whale   Nor is there the least reason to doubt
that each step in this scale might have been as serviceable to certain
ancient Cetaceans  with the functions of the parts slowly changing during
the progress of development  as are the gradations in the beaks of the
different existing members of the duck family   We should bear in mind that
each species of duck is subjected to a severe struggle for existence  and
that the structure of every part of its frame must be well adapted to its
conditions of life 

The Pleuronectidae  or Flat fish  are remarkable for their asymmetrical
bodies   They rest on one side  in the greater number of species on the
left  but in some on the right side  and occasionally reversed adult
specimens occur   The lower  or resting surface  resembles at first sight
the ventral surface of an ordinary fish  it is of a white colour  less
developed in many ways than the upper side  with the lateral fins often of
smaller size  But the eyes offer the most remarkable peculiarity  for they
are both placed on the upper side of the head   During early youth 
however  they stand opposite to each other  and the whole body is then
symmetrical  with both sides equally coloured   Soon the eye proper to the
lower side begins to glide slowly round the head to the upper side  but
does not pass right through the skull  as was formerly thought to be the
case   It is obvious that unless the lower eye did thus travel round  it
could not be used by the fish while lying in its habitual position on one
side   The lower eye would  also  have been liable to be abraded by the
sandy bottom   That the Pleuronectidae are admirably adapted by their
flattened and asymmetrical structure for their habits of life  is manifest
from several species  such as soles  flounders  etc   being extremely
common   The chief advantages thus gained seem to be protection from their
enemies  and facility for feeding on the ground   The different members 
however  of the family present  as Schiodte remarks   a long series of
forms exhibiting a gradual transition from Hippoglossus pinguis  which does
not in any considerable degree alter the shape in which it leaves the ovum 
to the soles  which are entirely thrown to one side  

Mr  Mivart has taken up this case  and remarks that a sudden spontaneous
transformation in the position of the eyes is hardly conceivable  in which
I quite agree with him   He then adds    If the transit was gradual  then
how such transit of one eye a minute fraction of the journey towards the
other side of the head could benefit the individual is  indeed  far from
clear   It seems  even  that such an incipient transformation must rather
have been injurious    But he might have found an answer to this objection
in the excellent observations published in 1867 by Malm   The
Pleuronectidae  while very young and still symmetrical  with their eyes
standing on opposite sides of the head  cannot long retain a vertical
position  owing to the excessive depth of their bodies  the small size of
their lateral fins  and to their being destitute of a swim bladder   Hence 
soon growing tired  they fall to the bottom on one side   While thus at
rest they often twist  as Malm observed  the lower eye upward  to see above
them  and they do this so vigorously that the eye is pressed hard against
the upper part of the orbit   The forehead between the eyes consequently
becomes  as could be plainly seen  temporarily contracted in breadth   On
one occasion Malm saw a young fish raise and depress the lower eye through
an angular distance of about seventy degrees 

We should remember that the skull at this early age is cartilaginous and
flexible  so that it readily yields to muscular action   It is also known
with the higher animals  even after early youth  that the skull yields and
is altered in shape  if the skin or muscles be permanently contracted
through disease or some accident   With long eared rabbits  if one ear
flops forward and downward  its weight drags forward all the bones of the
skull on the same side  of which I have given a figure   Malm states that
the newly hatched young of perches  salmon  and several other symmetrical
fishes  have the habit of occasionally resting on one side at the bottom 
and he has observed that they often then strain their lower eyes so as to
look upward  and their skulls are thus rendered rather crooked   These
fishes  however  are soon able to hold themselves in a vertical position 
and no permanent effect is thus produced   With the Pleuronectidae  on the
other hand  the older they grow the more habitually they rest on one side 
owing to the increasing flatness of their bodies  and a permanent effect is
thus produced on the form of the head  and on the position of the eyes  
Judging from analogy  the tendency to distortion would no doubt be
increased through the principle of inheritance   Schiodte believes  in
opposition to some other naturalists  that the Pleuronectidae are not quite
symmetrical even in the embryo  and if this be so  we could understand how
it is that certain species  while young  habitually fall over and rest on
the left side  and other species on the right side   Malm adds  in
confirmation of the above view  that the adult Trachypterus arcticus  which
is not a member of the Pleuronectidae  rests on its left side at the
bottom  and swims diagonally through the water  and in this fish  the two
sides of the head are said to be somewhat dissimilar   Our great authority
on Fishes  Dr  Gunther  concludes his abstract of Malm s paper  by
remarking that  the author gives a very simple explanation of the abnormal
condition of the Pleuronectoids  

We thus see that the first stages of the transit of the eye from one side
of the head to the other  which Mr  Mivart considers would be injurious 
may be attributed to the habit  no doubt beneficial to the individual and
to the species  of endeavouring to look upward with both eyes  while
resting on one side at the bottom   We may also attribute to the inherited
effects of use the fact of the mouth in several kinds of flat fish being
bent towards the lower surface  with the jaw bones stronger and more
effective on this  the eyeless side of the head  than on the other  for the
sake  as Dr  Traquair supposes  of feeding with ease on the ground  
Disuse  on the other hand  will account for the less developed condition of
the whole inferior half of the body  including the lateral fins  though
Yarrel thinks that the reduced size of these fins is advantageous to the
fish  as  there is so much less room for their action than with the larger
fins above    Perhaps the lesser number of teeth in the proportion of four
to seven in the upper halves of the two jaws of the plaice  to twenty five
to thirty in the lower halves  may likewise be accounted for by disuse  
 From the colourless state of the ventral surface of most fishes and of many
other animals  we may reasonably suppose that the absence of colour in
flat fish on the side  whether it be the right or left  which is under 
most  is due to the exclusion of light   But it cannot be supposed that the
peculiar speckled appearance of the upper side of the sole  so like the
sandy bed of the sea  or the power in some species  as recently shown by
Pouchet  of changing their colour in accordance with the surrounding
surface  or the presence of bony tubercles on the upper side of the turbot 
are due to the action of the light   Here natural selection has probably
come into play  as well as in adapting the general shape of the body of
these fishes  and many other peculiarities  to their habits of life   We
should keep in mind  as I have before insisted  that the inherited effects
of the increased use of parts  and perhaps of their disuse  will be
strengthened by natural selection   For all spontaneous variations in the
right direction will thus be preserved  as will those individuals which
inherit in the highest degree the effects of the increased and beneficial
use of any part   How much to attribute in each particular case to the
effects of use  and how much to natural selection  it seems impossible to
decide 

I may give another instance of a structure which apparently owes its origin
exclusively to use or habit   The extremity of the tail in some American
monkeys has been converted into a wonderfully perfect prehensile organ  and
serves as a fifth hand   A reviewer  who agrees with Mr  Mivart in every
detail  remarks on this structure    It is impossible to believe that in
any number of ages the first slight incipient tendency to grasp could
preserve the lives of the individuals possessing it  or favour their chance
of having and of rearing offspring    But there is no necessity for any
such belief   Habit  and this almost implies that some benefit great or
small is thus derived  would in all probability suffice for the work  
Brehm saw the young of an African monkey  Cercopithecus  clinging to the
under surface of their mother by their hands  and at the same time they
hooked their little tails round that of their mother   Professor Henslow
kept in confinement some harvest mice  Mus messorius  which do not possess
a structurally prehensive tail  but he frequently observed that they curled
their tails round the branches of a bush placed in the cage  and thus aided
themselves in climbing   I have received an analogous account from Dr 
Gunther  who has seen a mouse thus suspend itself   If the harvest mouse
had been more strictly arboreal  it would perhaps have had its tail
rendered structurally prehensile  as is the case with some members of the
same order   Why Cercopithecus  considering its habits while young  has not
become thus provided  it would be difficult to say   It is  however 
possible that the long tail of this monkey may be of more service to it as
a balancing organ in making its prodigious leaps  than as a prehensile
organ 

The mammary glands are common to the whole class of mammals  and are
indispensable for their existence  they must  therefore  have been
developed at an extremely remote period  and we can know nothing positively
about their manner of development   Mr  Mivart asks    Is it conceivable
that the young of any animal was ever saved from destruction by
accidentally sucking a drop of scarcely nutritious fluid from an
accidentally hypertrophied cutaneous gland of its mother   And even if one
was so  what chance was there of the perpetuation of such a variation   
But the case is not here put fairly   It is admitted by most evolutionists
that mammals are descended from a marsupial form  and if so  the mammary
glands will have been at first developed within the marsupial sack   In the
case of the fish  Hippocampus  the eggs are hatched  and the young are
reared for a time  within a sack of this nature  and an American
naturalist  Mr  Lockwood  believes from what he has seen of the development
of the young  that they are nourished by a secretion from the cutaneous
glands of the sack   Now  with the early progenitors of mammals  almost
before they deserved to be thus designated  is it not at least possible
that the young might have been similarly nourished   And in this case  the
individuals which secreted a fluid  in some degree or manner the most
nutritious  so as to partake of the nature of milk  would in the long run
have reared a larger number of well nourished offspring  than would the
individuals which secreted a poorer fluid  and thus the cutaneous glands 
which are the homologues of the mammary glands  would have been improved or
rendered more effective   It accords with the widely extended principle of
specialisation  that the glands over a certain space of the sack should
have become more highly developed than the remainder  and they would then
have formed a breast  but at first without a nipple  as we see in the
Ornithorhyncus  at the base of the mammalian series   Through what agency
the glands over a certain space became more highly specialised than the
others  I will not pretend to decide  whether in part through compensation
of growth  the effects of use  or of natural selection 

The development of the mammary glands would have been of no service  and
could not have been affected through natural selection  unless the young at
the same time were able to partake of the secretion   There is no greater
difficulty in understanding how young mammals have instinctively learned to
suck the breast  than in understanding how unhatched chickens have learned
to break the egg shell by tapping against it with their specially adapted
beaks  or how a few hours after leaving the shell they have learned to pick
up grains of food   In such cases the most probable solution seems to be 
that the habit was at first acquired by practice at a more advanced age 
and afterwards transmitted to the offspring at an earlier age   But the
young kangaroo is said not to suck  only to cling to the nipple of its
mother  who has the power of injecting milk into the mouth of her helpless 
half formed offspring   On this head Mr  Mivart remarks    Did no special
provision exist  the young one must infallibly be choked by the intrusion
of the milk into the wind pipe   But there IS a special provision   The
larynx is so elongated that it rises up into the posterior end of the nasal
passage  and is thus enabled to give free entrance to the air for the
lungs  while the milk passes harmlessly on each side of this elongated
larynx  and so safely attains the gullet behind it    Mr  Mivart then asks
how did natural selection remove in the adult kangaroo  and in most other
mammals  on the assumption that they are descended from a marsupial form  
 this at least perfectly innocent and harmless structure    It may be
suggested in answer that the voice  which is certainly of high importance
to many animals  could hardly have been used with full force as long as the
larynx entered the nasal passage  and Professor Flower has suggested to me
that this structure would have greatly interfered with an animal swallowing
solid food 

We will now turn for a short space to the lower divisions of the animal
kingdom   The Echinodermata  star fishes  sea urchins  etc   are furnished
with remarkable organs  called pedicellariae  which consist  when well
developed  of a tridactyle forceps  that is  of one formed of three
serrated arms  neatly fitting together and placed on the summit of a
flexible stem  moved by muscles   These forceps can seize firmly hold of
any object  and Alexander Agassiz has seen an Echinus or sea urchin rapidly
passing particles of excrement from forceps to forceps down certain lines
of its body  in order that its shell should not be fouled   But there is no
doubt that besides removing dirt of all kinds  they subserve other
functions  and one of these apparently is defence 

With respect to these organs  Mr  Mivart  as on so many previous occasions 
asks    What would be the utility of the FIRST RUDIMENTARY BEGINNINGS of
such structures  and how could such insipient buddings have ever preserved
the life of a single Echinus    He adds   not even the SUDDEN development
of the snapping action would have been beneficial without the freely
movable stalk  nor could the latter have been efficient without the
snapping jaws  yet no minute  nearly indefinite variations could
simultaneously evolve these complex co ordinations of structure  to deny
this seems to do no less than to affirm a startling paradox    Paradoxical
as this may appear to Mr  Mivart  tridactyle forcepses  immovably fixed at
the base  but capable of a snapping action  certainly exist on some star 
fishes  and this is intelligible if they serve  at least in part  as a
means of defence   Mr  Agassiz  to whose great kindness I am indebted for
much information on the subject  informs me that there are other star 
fishes  in which one of the three arms of the forceps is reduced to a
support for the other two  and again  other genera in which the third arm
is completely lost   In Echinoneus  the shell is described by M  Perrier as
bearing two kinds of pedicellariae  one resembling those of Echinus  and
the other those of Spatangus  and such cases are always interesting as
affording the means of apparently sudden transitions  through the abortion
of one of the two states of an organ 

With respect to the steps by which these curious organs have been evolved 
Mr  Agassiz infers from his own researches and those of Mr  Muller  that
both in star fishes and sea urchins the pedicellariae must undoubtedly be
looked at as modified spines   This may be inferred from their manner of
development in the individual  as well as from a long and perfect series of
gradations in different species and genera  from simple granules to
ordinary spines  to perfect tridactyle pedicellariae   The gradation
extends even to the manner in which ordinary spines and the pedicellariae 
with their supporting calcareous rods  are articulated to the shell   In
certain genera of star fishes   the very combinations needed to show that
the pedicellariae are only modified branching spines  may be found   Thus
we have fixed spines  with three equi distant  serrated  movable branches 
articulated to near their bases  and higher up  on the same spine  three
other movable branches   Now when the latter arise from the summit of a
spine they form  in fact  a rude tridactyle pedicellariae  and such may be
seen on the same spine together with the three lower branches   In this
case the identity in nature between the arms of the pedicellariae and the
movable branches of a spine  is unmistakable   It is generally admitted
that the ordinary spines serve as a protection  and if so  there can be no
reason to doubt that those furnished with serrated and movable branches
likewise serve for the same purpose  and they would thus serve still more
effectively as soon as by meeting together they acted as a prehensile or
snapping apparatus   Thus every gradation  from an ordinary fixed spine to
a fixed pedicellariae  would be of service 

In certain genera of star fishes these organs  instead of being fixed or
borne on an immovable support  are placed on the summit of a flexible and
muscular  though short  stem  and in this case they probably subserve some
additional function besides defence   In the sea urchins the steps can be
followed by which a fixed spine becomes articulated to the shell  and is
thus rendered movable   I wish I had space here to give a fuller abstract
of Mr  Agassiz s interesting observations on the development of the
pedicellariae   All possible gradations  as he adds  may likewise be found
between the pedicellariae of the star fishes and the hooks of the
Ophiurians  another group of the Echinodermata  and again between the
pedicellariae of sea urchins and the anchors of the Holothuriae  also
belonging to the same great class 

Certain compound animals  or zoophytes  as they have been termed  namely
the Polyzoa  are provided with curious organs called avicularia   These
differ much in structure in the different species   In their most perfect
condition they curiously resemble the head and beak of a vulture in
miniature  seated on a neck and capable of movement  as is likewise the
lower jaw or mandible   In one species observed by me  all the avicularia
on the same branch often moved simultaneously backwards and forwards  with
the lower jaw widely open  through an angle of about 90 degrees  in the
course of five seconds  and their movement caused the whole polyzoary to
tremble   When the jaws are touched with a needle they seize it so firmly
that the branch can thus be shaken 

Mr  Mivart adduces this case  chiefly on account of the supposed difficulty
of organs  namely the avicularia of the Polyzoa and the pedicellariae of
the Echinodermata  which he considers as  essentially similar   having been
developed through natural selection in widely distinct divisions of the
animal kingdom   But  as far as structure is concerned  I can see no
similarity between tridactyle pedicellariae and avicularia   The latter
resembles somewhat more closely the chelae or pincers of Crustaceans  and
Mr  Mivart might have adduced with equal appropriateness this resemblance
as a special difficulty  or even their resemblance to the head and beak of
a bird   The avicularia are believed by Mr  Busk  Dr  Smitt and Dr 
Nitsche  naturalists who have carefully studied this group  to be
homologous with the zooids and their cells which compose the zoophyte  the
movable lip or lid of the cell corresponding with the lower and movable
mandible of the avicularium   Mr  Busk  however  does not know of any
gradations now existing between a zooid and an avicularium   It is
therefore impossible to conjecture by what serviceable gradations the one
could have been converted into the other  but it by no means follows from
this that such gradations have not existed 

As the chelae of Crustaceans resemble in some degree the avicularia of
Polyzoa  both serving as pincers  it may be worth while to show that with
the former a long series of serviceable gradations still exists   In the
first and simplest stage  the terminal segment of a limb shuts down either
on the square summit of the broad penultimate segment  or against one whole
side  and is thus enabled to catch hold of an object  but the limb still
serves as an organ of locomotion   We next find one corner of the broad
penultimate segment slightly prominent  sometimes furnished with irregular
teeth  and against these the terminal segment shuts down   By an increase
in the size of this projection  with its shape  as well as that of the
terminal segment  slightly modified and improved  the pincers are rendered
more and more perfect  until we have at last an instrument as efficient as
the chelae of a lobster   And all these gradations can be actually traced 

Besides the avicularia  the polyzoa possess curious organs called
vibracula   These generally consist of long bristles  capable of movement
and easily excited   In one species examined by me the vibracula were
slightly curved and serrated along the outer margin  and all of them on the
same polyzoary often moved simultaneously  so that  acting like long oars 
they swept a branch rapidly across the object glass of my microscope   When
a branch was placed on its face  the vibracula became entangled  and they
made violent efforts to free themselves   They are supposed to serve as a
defence  and may be seen  as Mr  Busk remarks   to sweep slowly and
carefully over the surface of the polyzoary  removing what might be noxious
to the delicate inhabitants of the cells when their tentacula are
protruded    The avicularia  like the vibracula  probably serve for
defence  but they also catch and kill small living animals  which  it is
believed  are afterwards swept by the currents within reach of the
tentacula of the zooids   Some species are provided with avicularia and
vibracula  some with avicularia alone and a few with vibracula alone 

It is not easy to imagine two objects more widely different in appearance
than a bristle or vibraculum  and an avicularium like the head of a bird 
yet they are almost certainly homologous and have been developed from the
same common source  namely a zooid with its cell   Hence  we can understand
how it is that these organs graduate in some cases  as I am informed by Mr 
Busk  into each other   Thus  with the avicularia of several species of
Lepralia  the movable mandible is so much produced and is so like a bristle
that the presence of the upper or fixed beak alone serves to determine its
avicularian nature   The vibracula may have been directly developed from
the lips of the cells  without having passed through the avicularian stage 
but it seems more probable that they have passed through this stage  as
during the early stages of the transformation  the other parts of the cell 
with the included zooid  could hardly have disappeared at once   In many
cases the vibracula have a grooved support at the base  which seems to
represent the fixed beak  though this support in some species is quite
absent   This view of the development of the vibracula  if trustworthy  is
interesting  for supposing that all the species provided with avicularia
had become extinct  no one with the most vivid imagination would ever have
thought that the vibracula had originally existed as part of an organ 
resembling a bird s head  or an irregular box or hood   It is interesting
to see two such widely different organs developed from a common origin  and
as the movable lip of the cell serves as a protection to the zooid  there
is no difficulty in believing that all the gradations  by which the lip
became converted first into the lower mandible of an avicularium  and then
into an elongated bristle  likewise served as a protection in different
ways and under different circumstances 

In the vegetable kingdom Mr  Mivart only alludes to two cases  namely the
structure of the flowers of orchids  and the movements of climbing plants  
With respect to the former  he says    The explanation of their ORIGIN is
deemed thoroughly unsatisfactory  utterly insufficient to explain the
incipient  infinitesimal beginnings of structures which are of utility only
when they are considerably developed    As I have fully treated this
subject in another work  I will here give only a few details on one alone
of the most striking peculiarities of the flowers of orchids  namely  their
pollinia   A pollinium  when highly developed  consists of a mass of
pollen grains  affixed to an elastic foot stalk or caudicle  and this to a
little mass of extremely viscid matter   The pollinia are by this means
transported by insects from one flower to the stigma of another   In some
orchids there is no caudicle to the pollen masses  and the grains are
merely tied together by fine threads  but as these are not confined to
orchids  they need not here be considered  yet I may mention that at the
base of the orchidaceous series  in Cypripedium  we can see how the threads
were probably first developed   In other orchids the threads cohere at one
end of the pollen masses  and this forms the first or nascent trace of a
caudicle   That this is the origin of the caudicle  even when of
considerable length and highly developed  we have good evidence in the
aborted pollen grains which can sometimes be detected embedded within the
central and solid parts 

With respect to the second chief peculiarity  namely  the little mass of
viscid matter attached to the end of the caudicle  a long series of
gradations can be specified  each of plain service to the plant   In most
flowers belonging to other orders the stigma secretes a little viscid
matter   Now  in certain orchids similar viscid matter is secreted  but in
much larger quantities by one alone of the three stigmas  and this stigma 
perhaps in consequence of the copious secretion  is rendered sterile   When
an insect visits a flower of this kind  it rubs off some of the viscid
matter  and thus at the same time drags away some of the pollen grains  
 From this simple condition  which differs but little from that of a
multitude of common flowers  there are endless gradations  to species in
which the pollen mass terminates in a very short  free caudicle  to others
in which the caudicle becomes firmly attached to the viscid matter  with
the sterile stigma itself much modified   In this latter case we have a
pollinium in its most highly developed and perfect condition   He who will
carefully examine the flowers of orchids for himself will not deny the
existence of the above series of gradations  from a mass of pollen grains
merely tied together by threads  with the stigma differing but little from
that of the ordinary flowers  to a highly complex pollinium  admirably
adapted for transportal by insects  nor will he deny that all the
gradations in the several species are admirably adapted in relation to the
general structure of each flower for its fertilisation by different
insects   In this  and in almost every other case  the enquiry may be
pushed further backwards  and it may be asked how did the stigma of an
ordinary flower become viscid  but as we do not know the full history of
any one group of beings  it is as useless to ask  as it is hopeless to
attempt answering  such questions 

We will now turn to climbing plants   These can be arranged in a long
series  from those which simply twine round a support  to those which I
have called leaf climbers  and to those provided with tendrils   In these
two latter classes the stems have generally  but not always  lost the power
of twining  though they retain the power of revolving  which the tendrils
likewise possess   The gradations from leaf climbers to tendril bearers are
wonderfully close  and certain plants may be differently placed in either
class   But in ascending the series from simple twiners to leaf climbers 
an important quality is added  namely sensitiveness to a touch  by which
means the foot stalks of the leaves or flowers  or these modified and
converted into tendrils  are excited to bend round and clasp the touching
object   He who will read my memoir on these plants will  I think  admit
that all the many gradations in function and structure between simple
twiners and tendril bearers are in each case beneficial in a high degree to
the species   For instance  it is clearly a great advantage to a twining
plant to become a leaf climber  and it is probable that every twiner which
possessed leaves with long foot stalks would have been developed into a
leaf climber  if the foot stalks had possessed in any slight degree the
requisite sensitiveness to a touch 

As twining is the simplest means of ascending a support  and forms the
basis of our series  it may naturally be asked how did plants acquire this
power in an incipient degree  afterwards to be improved and increased
through natural selection   The power of twining depends  firstly  on the
stems while young being extremely flexible  but this is a character common
to many plants which are not climbers   and  secondly  on their continually
bending to all points of the compass  one after the other in succession  in
the same order   By this movement the stems are inclined to all sides  and
are made to move round and round   As soon as the lower part of a stem
strikes against any object and is stopped  the upper part still goes on
bending and revolving  and thus necessarily twines round and up the
support   The revolving movement ceases after the early growth of each
shoot   As in many widely separated families of plants  single species and
single genera possess the power of revolving  and have thus become twiners 
they must have independently acquired it  and cannot have inherited it from
a common progenitor   Hence  I was led to predict that some slight tendency
to a movement of this kind would be found to be far from uncommon with
plants which did not climb  and that this had afforded the basis for
natural selection to work on and improve   When I made this prediction  I
knew of only one imperfect case  namely  of the young flower peduncles of a
Maurandia which revolved slightly and irregularly  like the stems of
twining plants  but without making any use of this habit   Soon afterwards
Fritz Muller discovered that the young stems of an Alisma and of a Linum  
plants which do not climb and are widely separated in the natural system  
revolved plainly  though irregularly  and he states that he has reason to
suspect that this occurs with some other plants   These slight movements
appear to be of no service to the plants in question  anyhow  they are not
of the least use in the way of climbing  which is the point that concerns
us   Nevertheless we can see that if the stems of these plants had been
flexible  and if under the conditions to which they are exposed it had
profited them to ascend to a height  then the habit of slightly and
irregularly revolving might have been increased and utilised through
natural selection  until they had become converted into well developed
twining species 

With respect to the sensitiveness of the foot stalks of the leaves and
flowers  and of tendrils  nearly the same remarks are applicable as in the
case of the revolving movements of twining plants   As a vast number of
species  belonging to widely distinct groups  are endowed with this kind of
sensitiveness  it ought to be found in a nascent condition in many plants
which have not become climbers   This is the case   I observed that the
young flower peduncles of the above Maurandia curved themselves a little
towards the side which was touched   Morren found in several species of
Oxalis that the leaves and their foot stalks moved  especially after
exposure to a hot sun  when they were gently and repeatedly touched  or
when the plant was shaken   I repeated these observations on some other
species of Oxalis with the same result  in some of them the movement was
distinct  but was best seen in the young leaves  in others it was extremely
slight   It is a more important fact that according to the high authority
of Hofmeister  the young shoots and leaves of all plants move after being
shaken  and with climbing plants it is  as we know  only during the early
stages of growth that the foot stalks and tendrils are sensitive 

It is scarcely possible that the above slight movements  due to a touch or
shake  in the young and growing organs of plants  can be of any functional
importance to them   But plants possess  in obedience to various stimuli 
powers of movement  which are of manifest importance to them  for instance 
towards and more rarely from the light  in opposition to  and more rarely
in the direction of  the attraction of gravity   When the nerves and
muscles of an animal are excited by galvanism or by the absorption of
strychnine  the consequent movements may be called an incidental result 
for the nerves and muscles have not been rendered specially sensitive to
these stimuli   So with plants it appears that  from having the power of
movement in obedience to certain stimuli  they are excited in an incidental
manner by a touch  or by being shaken   Hence there is no great difficulty
in admitting that in the case of leaf climbers and tendril bearers  it is
this tendency which has been taken advantage of and increased through
natural selection   It is  however  probable  from reasons which I have
assigned in my memoir  that this will have occurred only with plants which
had already acquired the power of revolving  and had thus become twiners 

I have already endeavoured to explain how plants became twiners  namely  by
the increase of a tendency to slight and irregular revolving movements 
which were at first of no use to them  this movement  as well as that due
to a touch or shake  being the incidental result of the power of moving 
gained for other and beneficial purposes   Whether  during the gradual
development of climbing plants  natural selection has been aided by the
inherited effects of use  I will not pretend to decide  but we know that
certain periodical movements  for instance the so called sleep of plants 
are governed by habit 

I have now considered enough  perhaps more than enough  of the cases 
selected with care by a skilful naturalist  to prove that natural selection
is incompetent to account for the incipient stages of useful structures 
and I have shown  as I hope  that there is no great difficulty on this
head   A good opportunity has thus been afforded for enlarging a little on
gradations of structure  often associated with strange functions  an
important subject  which was not treated at sufficient length in the former
editions of this work   I will now briefly recapitulate the foregoing
cases 

With the giraffe  the continued preservation of the individuals of some
extinct high reaching ruminant  which had the longest necks  legs  etc  
and could browse a little above the average height  and the continued
destruction of those which could not browse so high  would have sufficed
for the production of this remarkable quadruped  but the prolonged use of
all the parts  together with inheritance  will have aided in an important
manner in their co ordination   With the many insects which imitate various
objects  there is no improbability in the belief that an accidental
resemblance to some common object was in each case the foundation for the
work of natural selection  since perfected through the occasional 
preservation of slight variations which made the resemblance at all closer 
and this will have been carried on as long as the insect continued to vary 
and as long as a more and more perfect resemblance led to its escape from
sharp sighted enemies   In certain species of whales there is a tendency to
the formation of irregular little points of horn on the palate  and it
seems to be quite within the scope of natural selection to preserve all
favourable variations  until the points were converted  first into
lamellated knobs or teeth  like those on the beak of a goose  then into
short lamellae  like those of the domestic ducks  and then into lamellae 
as perfect as those of the shoveller duck  and finally into the gigantic
plates of baleen  as in the mouth of the Greenland whale   In the family of
the ducks  the lamellae are first used as teeth  then partly as teeth and
partly as a sifting apparatus  and at last almost exclusively for this
latter purpose 

With such structures as the above lamellae of horn or whalebone  habit or
use can have done little or nothing  as far as we can judge  towards their
development   On the other hand  the transportal of the lower eye of a
flat fish to the upper side of the head  and the formation of a prehensile
tail  may be attributed almost wholly to continued use  together with
inheritance   With respect to the mammae of the higher animals  the most
probable conjecture is that primordially the cutaneous glands over the
whole surface of a marsupial sack secreted a nutritious fluid  and that
these glands were improved in function through natural selection  and
concentrated into a confined area  in which case they would have formed a
mamma   There is no more difficulty in understanding how the branched
spines of some ancient Echinoderm  which served as a defence  became
developed through natural selection into tridactyle pedicellariae  than in
understanding the development of the pincers of crustaceans  through
slight  serviceable modifications in the ultimate and penultimate segments
of a limb  which was at first used solely for locomotion   In the
avicularia and vibracula of the Polyzoa we have organs widely different in
appearance developed from the same source  and with the vibracula we can
understand how the successive gradations might have been of service   With
the pollinia of orchids  the threads which originally served to tie
together the pollen grains  can be traced cohering into caudicles  and the
steps can likewise be followed by which viscid matter  such as that
secreted by the stigmas of ordinary flowers  and still subserving nearly
but not quite the same purpose  became attached to the free ends of the
caudicles  all these gradations being of manifest benefit to the plants in
question   With respect to climbing plants  I need not repeat what has been
so lately said 

It has often been asked  if natural selection be so potent  why has not
this or that structure been gained by certain species  to which it would
apparently have been advantageous   But it is unreasonable to expect a
precise answer to such questions  considering our ignorance of the past
history of each species  and of the conditions which at the present day
determine its numbers and range   In most cases only general reasons  but
in some few cases special reasons  can be assigned   Thus to adapt a
species to new habits of life  many co ordinated modifications are almost
indispensable  and it may often have happened that the requisite parts did
not vary in the right manner or to the right degree   Many species must
have been prevented from increasing in numbers through destructive
agencies  which stood in no relation to certain structures  which we
imagine would have been gained through natural selection from appearing to
us advantageous to the species   In this case  as the struggle for life did
not depend on such structures  they could not have been acquired through
natural selection   In many cases complex and long enduring conditions 
often of a peculiar nature  are necessary for the development of a
structure  and the requisite conditions may seldom have concurred   The
belief that any given structure  which we think  often erroneously  would
have been beneficial to a species  would have been gained under all
circumstances through natural selection  is opposed to what we can
understand of its manner of action   Mr  Mivart does not deny that natural
selection has effected something  but he considers it as  demonstrably
insufficient  to account for the phenomena which I explain by its agency  
His chief arguments have now been considered  and the others will hereafter
be considered   They seem to me to partake little of the character of
demonstration  and to have little weight in comparison with those in favour
of the power of natural selection  aided by the other agencies often
specified   I am bound to add  that some of the facts and arguments here
used by me  have been advanced for the same purpose in an able article
lately published in the  Medico Chirurgical Review  

At the present day almost all naturalists admit evolution under some form 
Mr  Mivart believes that species change through  an internal force or
tendency   about which it is not pretended that anything is known   That
species have a capacity for change will be admitted by all evolutionists 
but there is no need  as it seems to me  to invoke any internal force
beyond the tendency to ordinary variability  which through the aid of
selection  by man has given rise to many well adapted domestic races  and
which  through the aid of natural selection  would equally well give rise
by graduated steps to natural races or species   The final result will
generally have been  as already explained  an advance  but in some few
cases a retrogression  in organisation 

Mr  Mivart is further inclined to believe  and some naturalists agree with
him  that new species manifest themselves  with suddenness and by
modifications appearing at once    For instance  he supposes that the
differences between the extinct three toed Hipparion and the horse arose
suddenly   He thinks it difficult to believe that the wing of a bird  was
developed in any other way than by a comparatively sudden modification of a
marked and important kind   and apparently he would extend the same view to
the wings of bats and pterodactyles   This conclusion  which implies great
breaks or discontinuity in the series  appears to me improbable in the
highest degree 

Everyone who believes in slow and gradual evolution  will of course admit
that specific changes may have been as abrupt and as great as any single
variation which we meet with under nature  or even under domestication  
But as species are more variable when domesticated or cultivated than under
their natural conditions  it is not probable that such great and abrupt
variations have often occurred under nature  as are known occasionally to
arise under domestication   Of these latter variations several may be
attributed to reversion  and the characters which thus reappear were  it is
probable  in many cases at first gained in a gradual manner   A still
greater number must be called monstrosities  such as six fingered men 
porcupine men  Ancon sheep  Niata cattle  etc   and as they are widely
different in character from natural species  they throw very little light
on our subject   Excluding such cases of abrupt variations  the few which
remain would at best constitute  if found in a state of nature  doubtful
species  closely related to their parental types 

My reasons for doubting whether natural species have changed as abruptly as
have occasionally domestic races  and for entirely disbelieving that they
have changed in the wonderful manner indicated by Mr  Mivart  are as
follows   According to our experience  abrupt and strongly marked
variations occur in our domesticated productions  singly and at rather long
intervals of time   If such occurred under nature  they would be liable  as
formerly explained  to be lost by accidental causes of destruction and by
subsequent intercrossing  and so it is known to be under domestication 
unless abrupt variations of this kind are specially preserved and separated
by the care of man   Hence  in order that a new species should suddenly
appear in the manner supposed by Mr  Mivart  it is almost necessary to
believe  in opposition to all analogy  that several wonderfully changed
individuals appeared simultaneously within the same district   This
difficulty  as in the case of unconscious selection by man  is avoided on
the theory of gradual evolution  through the preservation of a large number
of individuals  which varied more or less in any favourable direction  and
of the destruction of a large number which varied in an opposite manner 

That many species have been evolved in an extremely gradual manner  there
can hardly be a doubt   The species and even the genera of many large
natural families are so closely allied together that it is difficult to
distinguish not a few of them   On every continent  in proceeding from
north to south  from lowland to upland  etc   we meet with a host of
closely related or representative species  as we likewise do on certain
distinct continents  which we have reason to believe were formerly
connected   But in making these and the following remarks  I am compelled
to allude to subjects hereafter to be discussed   Look at the many outlying
islands round a continent  and see how many of their inhabitants can be
raised only to the rank of doubtful species   So it is if we look to past
times  and compare the species which have just passed away with those still
living within the same areas  or if we compare the fossil species embedded
in the sub stages of the same geological formation   It is indeed manifest
that multitudes of species are related in the closest manner to other
species that still exist  or have lately existed  and it will hardly be
maintained that such species have been developed in an abrupt or sudden
manner   Nor should it be forgotten  when we look to the special parts of
allied species  instead of to distinct species  that numerous and
wonderfully fine gradations can be traced  connecting together widely
different structures 

Many large groups of facts are intelligible only on the principle that
species have been evolved by very small steps   For instance  the fact that
the species included in the larger genera are more closely related to each
other  and present a greater number of varieties than do the species in the
smaller genera   The former are also grouped in little clusters  like
varieties round species  and they present other analogies with varieties 
as was shown in our second chapter   On this same principle we can
understand how it is that specific characters are more variable than
generic characters  and how the parts which are developed in an
extraordinary degree or manner are more variable than other parts of the
same species   Many analogous facts  all pointing in the same direction 
could be added 

Although very many species have almost certainly been produced by steps not
greater than those separating fine varieties  yet it may be maintained that
some have been developed in a different and abrupt manner   Such an
admission  however  ought not to be made without strong evidence being
assigned   The vague and in some respects false analogies  as they have
been shown to be by Mr  Chauncey Wright  which have been advanced in favour
of this view  such as the sudden crystallisation of inorganic substances 
or the falling of a facetted spheroid from one facet to another  hardly
deserve consideration   One class of facts  however  namely  the sudden
appearance of new and distinct forms of life in our geological formations
supports at first sight the belief in abrupt development   But the value of
this evidence depends entirely on the perfection of the geological record 
in relation to periods remote in the history of the world   If the record
is as fragmentary as many geologists strenuously assert  there is nothing
strange in new forms appearing as if suddenly developed 

Unless we admit transformations as prodigious as those advocated by Mr 
Mivart  such as the sudden development of the wings of birds or bats  or
the sudden conversion of a Hipparion into a horse  hardly any light is
thrown by the belief in abrupt modifications on the deficiency of
connecting links in our geological formations   But against the belief in
such abrupt changes  embryology enters a strong protest   It is notorious
that the wings of birds and bats  and the legs of horses or other
quadrupeds  are undistinguishable at an early embryonic period  and that
they become differentiated by insensibly fine steps   Embryological
resemblances of all kinds can be accounted for  as we shall hereafter see 
by the progenitors of our existing species having varied after early youth 
and having transmitted their newly acquired characters to their offspring 
at a corresponding age   The embryo is thus left almost unaffected  and
serves as a record of the past condition of the species   Hence it is that
existing species during the early stages of their development so often
resemble ancient and extinct forms belonging to the same class   On this
view of the meaning of embryological resemblances  and indeed on any view 
it is incredible that an animal should have undergone such momentous and
abrupt transformations as those above indicated  and yet should not bear
even a trace in its embryonic condition of any sudden modification  every
detail in its structure being developed by insensibly fine steps 

He who believes that some ancient form was transformed suddenly through an
internal force or tendency into  for instance  one furnished with wings 
will be almost compelled to assume  in opposition to all analogy  that many
individuals varied simultaneously   It cannot be denied that such abrupt
and great changes of structure are widely different from those which most
species apparently have undergone   He will further be compelled to believe
that many structures beautifully adapted to all the other parts of the same
creature and to the surrounding conditions  have been suddenly produced 
and of such complex and wonderful co adaptations  he will not be able to
assign a shadow of an explanation   He will be forced to admit that these
great and sudden transformations have left no trace of their action on the
embryo   To admit all this is  as it seems to me  to enter into the realms
of miracle  and to leave those of science 


CHAPTER VIII 

INSTINCT 

Instincts comparable with habits  but different in their origin   
Instincts graduated    Aphides and ants    Instincts variable    Domestic
instincts  their origin    Natural instincts of the cuckoo  molothrus 
ostrich  and parasitic bees    Slave making ants    Hive bee  its
cell making instinct    Changes of instinct and structure not necessarily
simultaneous    Difficulties of the theory of the Natural Selection of
instincts    Neuter or sterile insects    Summary 

Many instincts are so wonderful that their development will probably appear
to the reader a difficulty sufficient to overthrow my whole theory   I may
here premise  that I have nothing to do with the origin of the mental
powers  any more than I have with that of life itself   We are concerned
only with the diversities of instinct and of the other mental faculties in
animals of the same class 

I will not attempt any definition of instinct   It would be easy to show
that several distinct mental actions are commonly embraced by this term 
but every one understands what is meant  when it is said that instinct
impels the cuckoo to migrate and to lay her eggs in other birds  nests   An
action  which we ourselves require experience to enable us to perform  when
performed by an animal  more especially by a very young one  without
experience  and when performed by many individuals in the same way  without
their knowing for what purpose it is performed  is usually said to be
instinctive   But I could show that none of these characters are universal  
A little dose of judgment or reason  as Pierre Huber expresses it  often
comes into play  even with animals low in the scale of nature 

Frederick Cuvier and several of the older metaphysicians have compared
instinct with habit   This comparison gives  I think  an accurate notion of
the frame of mind under which an instinctive action is performed  but not
necessarily of its origin   How unconsciously many habitual actions are
performed  indeed not rarely in direct opposition to our conscious will 
yet they may be modified by the will or reason   Habits easily become
associated with other habits  with certain periods of time and states of
the body   When once acquired  they often remain constant throughout life  
Several other points of resemblance between instincts and habits could be
pointed out   As in repeating a well known song  so in instincts  one
action follows another by a sort of rhythm  if a person be interrupted in a
song  or in repeating anything by rote  he is generally forced to go back
to recover the habitual train of thought   so P  Huber found it was with a
caterpillar  which makes a very complicated hammock  for if he took a
caterpillar which had completed its hammock up to  say  the sixth stage of
construction  and put it into a hammock completed up only to the third
stage  the caterpillar simply re performed the fourth  fifth  and sixth
stages of construction   If  however  a caterpillar were taken out of a
hammock made up  for instance  to the third stage  and were put into one
finished up to the sixth stage  so that much of its work was already done
for it  far from deriving any benefit from this  it was much embarrassed 
and  in order to complete its hammock  seemed forced to start from the
third stage  where it had left off  and thus tried to complete the already
finished work 

If we suppose any habitual action to become inherited  and it can be shown
that this does sometimes happen  then the resemblance between what
originally was a habit and an instinct becomes so close as not to be
distinguished   If Mozart  instead of playing the pianoforte at three years
old with wonderfully little practice  had played a tune with no practice at
all  be might truly be said to have done so instinctively   But it would be
a serious error to suppose that the greater number of instincts have been
acquired by habit in one generation  and then transmitted by inheritance to
succeeding generations   It can be clearly shown that the most wonderful
instincts with which we are acquainted  namely  those of the hive bee and
of many ants  could not possibly have been acquired by habit 

It will be universally admitted that instincts are as important as
corporeal structures for the welfare of each species  under its present
conditions of life   Under changed conditions of life  it is at least
possible that slight modifications of instinct might be profitable to a
species  and if it can be shown that instincts do vary ever so little  then
I can see no difficulty in natural selection preserving and continually
accumulating variations of instinct to any extent that was profitable   It
is thus  as I believe  that all the most complex and wonderful instincts
have originated   As modifications of corporeal structure arise from  and
are increased by  use or habit  and are diminished or lost by disuse  so I
do not doubt it has been with instincts   But I believe that the effects of
habit are in many cases of subordinate importance to the effects of the
natural selection of what may be called spontaneous variations of
instincts   that is of variations produced by the same unknown causes which
produce slight deviations of bodily structure 

No complex instinct can possibly be produced through natural selection 
except by the slow and gradual accumulation of numerous  slight  yet
profitable  variations   Hence  as in the case of corporeal structures  we
ought to find in nature  not the actual transitional gradations by which
each complex instinct has been acquired  for these could be found only in
the lineal ancestors of each species  but we ought to find in the
collateral lines of descent some evidence of such gradations  or we ought
at least to be able to show that gradations of some kind are possible  and
this we certainly can do   I have been surprised to find  making allowance
for the instincts of animals having been but little observed  except in
Europe and North America  and for no instinct being known among extinct
species  how very generally gradations  leading to the most complex
instincts  can be discovered   Changes of instinct may sometimes be
facilitated by the same species having different instincts at different
periods of life  or at different seasons of the year  or when placed under
different circumstances  etc   in which case either the one or the other
instinct might be preserved by natural selection   And such instances of
diversity of instinct in the same species can be shown to occur in nature 

Again  as in the case of corporeal structure  and conformably to my theory 
the instinct of each species is good for itself  but has never  as far as
we can judge  been produced for the exclusive good of others   One of the
strongest instances of an animal apparently performing an action for the
sole good of another  with which I am acquainted  is that of aphides
voluntarily yielding  as was first observed by Huber  their sweet excretion
to ants   that they do so voluntarily  the following facts show   I removed
all the ants from a group of about a dozen aphides on a dock plant  and
prevented their attendance during several hours   After this interval  I
felt sure that the aphides would want to excrete   I watched them for some
time through a lens  but not one excreted  I then tickled and stroked them
with a hair in the same manner  as well as I could  as the ants do with
their antennae  but not one excreted   Afterwards  I allowed an ant to
visit them  and it immediately seemed  by its eager way of running about to
be well aware what a rich flock it had discovered  it then began to play
with its antennae on the abdomen first of one aphis and then of another 
and each  as soon as it felt the antennae  immediately lifted up its
abdomen and excreted a limpid drop of sweet juice  which was eagerly
devoured by the ant   Even the quite young aphides behaved in this manner 
showing that the action was instinctive  and not the result of experience  
It is certain  from the observations of Huber  that the aphides show no
dislike to the ants   if the latter be not present they are at last
compelled to eject their excretion   But as the excretion is extremely
viscid  it is no doubt a convenience to the aphides to have it removed 
therefore probably they do not excrete solely for the good of the ants  
Although there is no evidence that any animal performs an action for the
exclusive good of another species  yet each tries to take advantage of the
instincts of others  as each takes advantage of the weaker bodily structure
of other species   So again certain instincts cannot be considered as
absolutely perfect  but as details on this and other such points are not
indispensable  they may be here passed over 

As some degree of variation in instincts under a state of nature  and the
inheritance of such variations  are indispensable for the action of natural
selection  as many instances as possible ought to be given  but want of
space prevents me   I can only assert that instincts certainly do vary  for
instance  the migratory instinct  both in extent and direction  and in its
total loss   So it is with the nests of birds  which vary partly in
dependence on the situations chosen  and on the nature and temperature of
the country inhabited  but often from causes wholly unknown to us   Audubon
has given several remarkable cases of differences in the nests of the same
species in the northern and southern United States   Why  it has been
asked  if instinct be variable  has it not granted to the bee  the ability
to use some other material when wax was deficient    But what other natural
material could bees use   They will work  as I have seen  with wax hardened
with vermilion or softened with lard   Andrew Knight observed that his
bees  instead of laboriously collecting propolis  used a cement of wax and
turpentine  with which he had covered decorticated trees   It has lately
been shown that bees  instead of searching for pollen  will gladly use a
very different substance  namely  oatmeal   Fear of any particular enemy is
certainly an instinctive quality  as may be seen in nestling birds  though
it is strengthened by experience  and by the sight of fear of the same
enemy in other animals   The fear of man is slowly acquired  as I have
elsewhere shown  by the various animals which inhabit desert islands  and
we see an instance of this  even in England  in the greater wildness of all
our large birds in comparison with our small birds  for the large birds
have been most persecuted by man   We may safely attribute the greater
wildness of our large birds to this cause  for in uninhabited islands large
birds are not more fearful than small  and the magpie  so wary in England 
is tame in Norway  as is the hooded crow in Egypt 

That the mental qualities of animals of the same kind  born in a state of
nature  vary much  could be shown by many facts   Several cases could also
be adduced of occasional and strange habits in wild animals  which  if
advantageous to the species  might have given rise  through natural
selection  to new instincts   But I am well aware that these general
statements  without the facts in detail  can produce but a feeble effect on
the reader s mind   I can only repeat my assurance  that I do not speak
without good evidence 

INHERITED CHANGES OF HABIT OR INSTINCT IN DOMESTICATED ANIMALS 

The possibility  or even probability  of inherited variations of instinct
in a state of nature will be strengthened by briefly considering a few
cases under domestication   We shall thus be enabled to see the part which
habit and the selection of so called spontaneous variations have played in
modifying the mental qualities of our domestic animals   It is notorious
how much domestic animals vary in their mental qualities   With cats  for
instance  one naturally takes to catching rats  and another mice  and these
tendencies are known to be inherited   One cat  according to Mr  St  John 
always brought home game birds  another hares or rabbits  and another
hunted on marshy ground and almost nightly caught woodcocks or snipes   A
number of curious and authentic instances could be given of various shades
of disposition and taste  and likewise of the oddest tricks  associated
with certain frames of mind or periods of time   But let us look to the
familiar case of the breeds of dogs   it cannot be doubted that young
pointers  I have myself seen striking instances  will sometimes point and
even back other dogs the very first time that they are taken out 
retrieving is certainly in some degree inherited by retrievers  and a
tendency to run round  instead of at  a flock of sheep  by shepherd dogs  
I cannot see that these actions  performed without experience by the young 
and in nearly the same manner by each individual  performed with eager
delight by each breed  and without the end being known  for the young
pointer can no more know that he points to aid his master  than the white
butterfly knows why she lays her eggs on the leaf of the cabbage  I cannot
see that these actions differ essentially from true instincts   If we were
to behold one kind of wolf  when young and without any training  as soon as
it scented its prey  stand motionless like a statue  and then slowly crawl
forward with a peculiar gait  and another kind of wolf rushing round 
instead of at  a herd of deer  and driving them to a distant point  we
should assuredly call these actions instinctive   Domestic instincts  as
they may be called  are certainly far less fixed than natural instincts 
but they have been acted on by far less rigorous selection  and have been
transmitted for an incomparably shorter period  under less fixed conditions
of life 

How strongly these domestic instincts  habits  and dispositions are
inherited  and how curiously they become mingled  is well shown when
different breeds of dogs are crossed   Thus it is known that a cross with a
bull dog has affected for many generations the courage and obstinacy of
greyhounds  and a cross with a greyhound has given to a whole family of
shepherd dogs a tendency to hunt hares   These domestic instincts  when
thus tested by crossing  resemble natural instincts  which in a like manner
become curiously blended together  and for a long period exhibit traces of
the instincts of either parent   for example  Le Roy describes a dog  whose
great grandfather was a wolf  and this dog showed a trace of its wild
parentage only in one way  by not coming in a straight line to his master 
when called 

Domestic instincts are sometimes spoken of as actions which have become
inherited solely from long continued and compulsory habit  but this is not
true   No one would ever have thought of teaching  or probably could have
taught  the tumbler pigeon to tumble  an action which  as I have witnessed 
is performed by young birds  that have never seen a pigeon tumble   We may
believe that some one pigeon showed a slight tendency to this strange
habit  and that the long continued selection of the best individuals in
successive generations made tumblers what they now are  and near Glasgow
there are house tumblers  as I hear from Mr  Brent  which cannot fly
eighteen inches high without going head over heels   It may be doubted
whether any one would have thought of training a dog to point  had not some
one dog naturally shown a tendency in this line  and this is known
occasionally to happen  as I once saw  in a pure terrier   the act of
pointing is probably  as many have thought  only the exaggerated pause of
an animal preparing to spring on its prey   When the first tendency to
point was once displayed  methodical selection and the inherited effects of
compulsory training in each successive generation would soon complete the
work  and unconscious selection is still in progress  as each man tries to
procure  without intending to improve the breed  dogs which stand and hunt
best   On the other hand  habit alone in some cases has sufficed  hardly
any animal is more difficult to tame than the young of the wild rabbit 
scarcely any animal is tamer than the young of the tame rabbit  but I can
hardly suppose that domestic rabbits have often been selected for tameness
alone  so that we must attribute at least the greater part of the inherited
change from extreme wildness to extreme tameness  to habit and
long continued close confinement 

Natural instincts are lost under domestication   a remarkable instance of
this is seen in those breeds of fowls which very rarely or never become
 broody   that is  never wish to sit on their eggs   Familiarity alone
prevents our seeing how largely and how permanently the minds of our
domestic animals have been modified   It is scarcely possible to doubt that
the love of man has become instinctive in the dog   All wolves  foxes 
jackals and species of the cat genus  when kept tame  are most eager to
attack poultry  sheep and pigs  and this tendency has been found incurable
in dogs which have been brought home as puppies from countries such as
Tierra del Fuego and Australia  where the savages do not keep these
domestic animals   How rarely  on the other hand  do our civilised dogs 
even when quite young  require to be taught not to attack poultry  sheep 
and pigs   No doubt they occasionally do make an attack  and are then
beaten  and if not cured  they are destroyed  so that habit and some degree
of selection have probably concurred in civilising by inheritance our dogs  
On the other hand  young chickens have lost wholly by habit  that fear of
the dog and cat which no doubt was originally instinctive in them  for I am
informed by Captain Hutton that the young chickens of the parent stock  the
Gallus bankiva  when reared in India under a hen  are at first excessively
wild   So it is with young pheasants reared in England under a hen   It is
not that chickens have lost all fear  but fear only of dogs and cats  for
if the hen gives the danger chuckle they will run  more especially young
turkeys  from under her and conceal themselves in the surrounding grass or
thickets  and this is evidently done for the instinctive purpose of
allowing  as we see in wild ground birds  their mother to fly away   But
this instinct retained by our chickens has become useless under
domestication  for the mother hen has almost lost by disuse the power of
flight 

Hence  we may conclude that under domestication instincts have been
acquired and natural instincts have been lost  partly by habit and partly
by man selecting and accumulating  during successive generations  peculiar
mental habits and actions  which at first appeared from what we must in our
ignorance call an accident   In some cases compulsory habit alone has
sufficed to produce inherited mental changes  in other cases compulsory
habit has done nothing  and all has been the result of selection  pursued
both methodically and unconsciously  but in most cases habit and selection
have probably concurred 

SPECIAL INSTINCTS 

We shall  perhaps  best understand how instincts in a state of nature have
become modified by selection by considering a few cases   I will select
only three  namely  the instinct which leads the cuckoo to lay her eggs in
other birds  nests  the slave making instinct of certain ants  and the
cell making power of the hive bee   these two latter instincts have
generally and justly been ranked by naturalists as the most wonderful of
all known instincts 

INSTINCTS OF THE CUCKOO 

It is supposed by some naturalists that the more immediate cause of the
instinct of the cuckoo is that she lays her eggs  not daily  but at
intervals of two or three days  so that  if she were to make her own nest
and sit on her own eggs  those first laid would have to be left for some
time unincubated or there would be eggs and young birds of different ages
in the same nest   If this were the case the process of laying and hatching
might be inconveniently long  more especially as she migrates at a very
early period  and the first hatched young would probably have to be fed by
the male alone   But the American cuckoo is in this predicament  for she
makes her own nest and has eggs and young successively hatched  all at the
same time   It has been both asserted and denied that the American cuckoo
occasionally lays her eggs in other birds  nests  but I have lately heard
from Dr  Merrill  of Iowa  that he once found in Illinois a young cuckoo 
together with a young jay in the nest of a blue jay  Garrulus cristatus  
and as both were nearly full feathered  there could be no mistake in their
identification   I could also give several instances of various birds which
have been known occasionally to lay their eggs in other birds  nests   Now
let us suppose that the ancient progenitor of our European cuckoo had the
habits of the American cuckoo  and that she occasionally laid an egg in
another bird s nest   If the old bird profited by this occasional habit
through being enabled to emigrate earlier or through any other cause  or if
the young were made more vigorous by advantage being taken of the mistaken
instinct of another species than when reared by their own mother 
encumbered as she could hardly fail to be by having eggs and young of
different ages at the same time  then the old birds or the fostered young
would gain an advantage   And analogy would lead us to believe that the
young thus reared would be apt to follow by inheritance the occasional and
aberrant habit of their mother  and in their turn would be apt to lay their
eggs in other birds  nests  and thus be more successful in rearing their
young   By a continued process of this nature  I believe that the strange
instinct of our cuckoo has been generated   It has  also recently been
ascertained on sufficient evidence  by Adolf Muller  that the cuckoo
occasionally lays her eggs on the bare ground  sits on them and feeds her
young   This rare event is probably a case of reversion to the long lost 
aboriginal instinct of nidification 

It has been objected that I have not noticed other related instincts and
adaptations of structure in the cuckoo  which are spoken of as necessarily
co ordinated   But in all cases  speculation on an instinct known to us
only in a single species  is useless  for we have hitherto had no facts to
guide us   Until recently the instincts of the European and of the non 
parasitic American cuckoo alone were known  now  owing to Mr  Ramsay s
observations  we have learned something about three Australian species 
which lay their eggs in other birds  nests   The chief points to be
referred to are three   first  that the common cuckoo  with rare
exceptions  lays only one egg in a nest  so that the large and voracious
young bird receives ample food   Secondly  that the eggs are remarkably
small  not exceeding those of the skylark  a bird about one fourth as large
as the cuckoo   That the small size of the egg is a real case of adaptation
we may infer from the fact of the mon parasitic American cuckoo laying
full sized eggs   Thirdly  that the young cuckoo  soon after birth  has the
instinct  the strength and a properly shaped back for ejecting its foster 
brothers  which then perish from cold and hunger   This has been boldly
called a beneficent arrangement  in order that the young cuckoo may get
sufficient food  and that its foster brothers may perish before they had
acquired much feeling 

Turning now to the Australian species   though these birds generally lay
only one egg in a nest  it is not rare to find two and even three eggs in
the same nest   In the bronze cuckoo the eggs vary greatly in size  from
eight to ten lines in length   Now  if it had been of an advantage to this
species to have laid eggs even smaller than those now laid  so as to have
deceived certain foster parents  or  as is more probable  to have been
hatched within a shorter period  for it is asserted that there is a
relation between the size of eggs and the period of their incubation   then
there is no difficulty in believing that a race or species might have been
formed which would have laid smaller and smaller eggs  for these would have
been more safely hatched and reared   Mr  Ramsay remarks that two of the
Australian cuckoos  when they lay their eggs in an open nest  manifest a
decided preference for nests containing eggs similar in colour to their
own   The European species apparently manifests some tendency towards a
similar instinct  but not rarely departs from it  as is shown by her laying
her dull and pale coloured eggs in the nest of the hedge warbler with
bright greenish blue eggs   Had our cuckoo invariably displayed the above
instinct  it would assuredly have been added to those which it is assumed
must all have been acquired together   The eggs of the Australian bronze
cuckoo vary  according to Mr  Ramsay  to an extraordinary degree in colour 
so that in this respect  as well as in size  natural selection might have
secured and fixed any advantageous variation 

In the case of the European cuckoo  the offspring of the foster parents are
commonly ejected from the nest within three days after the cuckoo is
hatched  and as the latter at this age is in a most helpless condition  Mr 
Gould was formerly inclined to believe that the act of ejection was
performed by the foster parents themselves   But he has now received a
trustworthy account of a young cuckoo which was actually seen  while still
blind and not able even to hold up its own head  in the act of ejecting its
foster brothers   One of these was replaced in the nest by the observer 
and was again thrown out   With respect to the means by which this strange
and odious instinct was acquired  if it were of great importance for the
young cuckoo  as is probably the case  to receive as much food as possible
soon after birth  I can see no special difficulty in its having gradually
acquired  during successive generations  the blind desire  the strength 
and structure necessary for the work of ejection  for those cuckoos which
had such habits and structure best developed would be the most securely
reared   The first step towards the acquisition of the proper instinct
might have been mere unintentional restlessness on the part of the young
bird  when somewhat advanced in age and strength  the habit having been
afterwards improved  and transmitted to an earlier age   I can see no more
difficulty in this than in the unhatched young of other birds acquiring the
instinct to break through their own shells  or than in young snakes
acquiring in their upper jaws  as Owen has remarked  a transitory sharp
tooth for cutting through the tough egg shell   For if each part is liable
to individual variations at all ages  and the variations tend to be
inherited at a corresponding or earlier age  propositions which cannot be
disputed  then the instincts and structure of the young could be slowly
modified as surely as those of the adult  and both cases must stand or fall
together with the whole theory of natural selection 

Some species of Molothrus  a widely distinct genus of American birds 
allied to our starlings  have parasitic habits like those of the cuckoo 
and the species present an interesting gradation in the perfection of their
instincts   The sexes of Molothrus badius are stated by an excellent
observer  Mr  Hudson  sometimes to live promiscuously together in flocks 
and sometimes to pair   They either build a nest of their own or seize on
one belonging to some other bird  occasionally throwing out the nestlings
of the stranger   They either lay their eggs in the nest thus appropriated 
or oddly enough build one for themselves on the top of it   They usually
sit on their own eggs and rear their own young  but Mr  Hudson says it is
probable that they are occasionally parasitic  for he has seen the young of
this species following old birds of a distinct kind and clamouring to be
fed by them   The parasitic habits of another species of Molothrus  the M 
bonariensis  are much more highly developed than those of the last  but are
still far from perfect   This bird  as far as it is known  invariably lays
its eggs in the nests of strangers  but it is remarkable that several
together sometimes commence to build an irregular untidy nest of their own 
placed in singular ill adapted situations  as on the leaves of a large
thistle   They never  however  as far as Mr  Hudson has ascertained 
complete a nest for themselves   They often lay so many eggs  from fifteen
to twenty  in the same foster nest  that few or none can possibly be
hatched   They have  moreover  the extraordinary habit of pecking holes in
the eggs  whether of their own species or of their foster parents  which
they find in the appropriated nests   They drop also many eggs on the bare
ground  which are thus wasted   A third species  the M  pecoris of North
America  has acquired instincts as perfect as those of the cuckoo  for it
never lays more than one egg in a foster nest  so that the young bird is
securely reared   Mr  Hudson is a strong disbeliever in evolution  but he
appears to have been so much struck by the imperfect instincts of the
Molothrus bonariensis that he quotes my words  and asks   Must we consider
these habits  not as especially endowed or created instincts  but as small
consequences of one general law  namely  transition  

Various birds  as has already been remarked  occasionally lay their eggs in
the nests of other birds   This habit is not very uncommon with the
Gallinaceae  and throws some light on the singular instinct of the ostrich 
In this family several hen birds unite and lay first a few eggs in one nest
and then in another  and these are hatched by the males   This instinct may
probably be accounted for by the fact of the hens laying a large number of
eggs  but  as with the cuckoo  at intervals of two or three days   The
instinct  however  of the American ostrich  as in the case of the Molothrus
bonariensis  has not as yet been perfected  for a surprising number of eggs
lie strewed over the plains  so that in one day s hunting I picked up no
less than twenty lost and wasted eggs 

Many bees are parasitic  and regularly lay their eggs in the nests of other
kinds of bees   This case is more remarkable than that of the cuckoo  for
these bees have not only had their instincts but their structure modified
in accordance with their parasitic habits  for they do not possess the
pollen collecting apparatus which would have been indispensable if they had
stored up food for their own young   Some species of Sphegidae  wasp like
insects  are likewise parasitic  and M  Fabre has lately shown good reason
for believing that  although the Tachytes nigra generally makes its own
burrow and stores it with paralysed prey for its own larvae  yet that  when
this insect finds a burrow already made and stored by another sphex  it
takes advantage of the prize  and becomes for the occasion parasitic   In
this case  as with that of the Molothrus or cuckoo  I can see no difficulty
in natural selection making an occasional habit permanent  if of advantage
to the species  and if the insect whose nest and stored food are
feloniously appropriated  be not thus exterminated 

SLAVE MAKING INSTINCT 

This remarkable instinct was first discovered in the Formica  Polyerges 
rufescens by Pierre Huber  a better observer even than his celebrated
father   This ant is absolutely dependent on its slaves  without their aid 
the species would certainly become extinct in a single year   The males and
fertile females do no work of any kind  and the workers or sterile females 
though most energetic and courageous in capturing slaves  do no other work  
They are incapable of making their own nests  or of feeding their own
larvae   When the old nest is found inconvenient  and they have to migrate 
it is the slaves which determine the migration  and actually carry their
masters in their jaws   So utterly helpless are the masters  that when
Huber shut up thirty of them without a slave  but with plenty of the food
which they like best  and with their larvae and pupae to stimulate them to
work  they did nothing  they could not even feed themselves  and many
perished of hunger   Huber then introduced a single slave  F  fusca   and
she instantly set to work  fed and saved the survivors  made some cells and
tended the larvae  and put all to rights   What can be more extraordinary
than these well ascertained facts   If we had not known of any other
slave making ant  it would have been hopeless to speculate how so wonderful
an instinct could have been perfected 

Another species  Formica sanguinea  was likewise first discovered by P 
Huber to be a slave making ant   This species is found in the southern
parts of England  and its habits have been attended to by Mr  F  Smith  of
the British Museum  to whom I am much indebted for information on this and
other subjects   Although fully trusting to the statements of Huber and Mr 
Smith  I tried to approach the subject in a sceptical frame of mind  as any
one may well be excused for doubting the existence of so extraordinary an
instinct as that of making slaves   Hence  I will give the observations
which I made in some little detail   I opened fourteen nests of F 
sanguinea  and found a few slaves in all   Males and fertile females of the
slave species  F  fusca  are found only in their own proper communities 
and have never been observed in the nests of F  sanguinea   The slaves are
black and not above half the size of their red masters  so that the
contrast in their appearance is great   When the nest is slightly
disturbed  the slaves occasionally come out  and like their masters are
much agitated and defend the nest   when the nest is much disturbed  and
the larvae and pupae are exposed  the slaves work energetically together
with their masters in carrying them away to a place of safety   Hence  it
is clear that the slaves feel quite at home   During the months of June and
July  on three successive years  I watched for many hours several nests in
Surrey and Sussex  and never saw a slave either leave or enter a nest   As 
during these months  the slaves are very few in number  I thought that they
might behave differently when more numerous  but Mr  Smith informs me that
he has watched the nests at various hours during May  June and August  both
in Surrey and Hampshire  and has never seen the slaves  though present in
large numbers in August  either leave or enter the nest   Hence  he
considers them as strictly household slaves   The masters  on the other
hand  may be constantly seen bringing in materials for the nest  and food
of all kinds   During the year 1860  however  in the month of July  I came
across a community with an unusually large stock of slaves  and I observed
a few slaves mingled with their masters leaving the nest  and marching
along the same road to a tall Scotch fir tree  twenty five yards distant 
which they ascended together  probably in search of aphides or cocci  
According to Huber  who had ample opportunities for observation  the slaves
in Switzerland habitually work with their masters in making the nest  and
they alone open and close the doors in the morning and evening  and  as
Huber expressly states  their principal office is to search for aphides  
This difference in the usual habits of the masters and slaves in the two
countries  probably depends merely on the slaves being captured in greater
numbers in Switzerland than in England 

One day I fortunately witnessed a migration of F  sanguinea from one nest
to another  and it was a most interesting spectacle to behold the masters
carefully carrying their slaves in their jaws instead of being carried by
them  as in the case of F  rufescens   Another day my attention was struck
by about a score of the slave makers haunting the same spot  and evidently
not in search of food  they approached and were vigorously repulsed by an
independent community of the slave species  F  fusca   sometimes as many as
three of these ants clinging to the legs of the slave making F  sanguinea  
The latter ruthlessly killed their small opponents and carried their dead
bodies as food to their nest  twenty nine yards distant  but they were
prevented from getting any pupae to rear as slaves   I then dug up a small
parcel of the pupae of F  fusca from another nest  and put them down on a
bare spot near the place of combat  they were eagerly seized and carried
off by the tyrants  who perhaps fancied that  after all  they had been
victorious in their late combat 

At the same time I laid on the same place a small parcel of the pupae of
another species  F  flava  with a few of these little yellow ants still
clinging to the fragments of their nest   This species is sometimes  though
rarely  made into slaves  as has been described by Mr  Smith   Although so
small a species  it is very courageous  and I have seen it ferociously
attack other ants   In one instance I found to my surprise an independent
community of F  flava under a stone beneath a nest of the slave making F 
sanguinea  and when I had accidentally disturbed both nests  the little
ants attacked their big neighbours with surprising courage   Now I was
curious to ascertain whether F  sanguinea could distinguish the pupae of F 
fusca  which they habitually make into slaves  from those of the little and
furious F  flava  which they rarely capture  and it was evident that they
did at once distinguish them  for we have seen that they eagerly and
instantly seized the pupae of F  fusca  whereas they were much terrified
when they came across the pupae  or even the earth from the nest  of F 
flava  and quickly ran away  but in about a quarter of an hour  shortly
after all the little yellow ants had crawled away  they took heart and
carried off the pupae 

One evening I visited another community of F  sanguinea  and found a number
of these ants returning home and entering their nests  carrying the dead
bodies of F  fusca  showing that it was not a migration  and numerous
pupae   I traced a long file of ants burdened with booty  for about forty
yards back  to a very thick clump of heath  whence I saw the last
individual of F  sanguinea emerge  carrying a pupa  but I was not able to
find the desolated nest in the thick heath   The nest  however  must have
been close at hand  for two or three individuals of F  fusca were rushing
about in the greatest agitation  and one was perched motionless with its
own pupa in its mouth on the top of a spray of heath  an image of despair
over its ravaged home 

Such are the facts  though they did not need confirmation by me  in regard
to the wonderful instinct of making slaves   Let it be observed what a
contrast the instinctive habits of F  sanguinea present with those of the
continental F  rufescens   The latter does not build its own nest  does not
determine its own migrations  does not collect food for itself or its
young  and cannot even feed itself   it is absolutely dependent on its
numerous slaves   Formica sanguinea  on the other hand  possesses much
fewer slaves  and in the early part of the summer extremely few   The
masters determine when and where a new nest shall be formed  and when they
migrate  the masters carry the slaves   Both in Switzerland and England the
slaves seem to have the exclusive care of the larvae  and the masters alone
go on slave making expeditions   In Switzerland the slaves and masters work
together  making and bringing materials for the nest   both  but chiefly
the slaves  tend and milk as it may be called  their aphides  and thus both
collect food for the community   In England the masters alone usually leave
the nest to collect building materials and food for themselves  their
slaves and larvae   So that the masters in this country receive much less
service from their slaves than they do in Switzerland 

By what steps the instinct of F  sanguinea originated I will not pretend to
conjecture   But as ants which are not slave makers  will  as I have seen 
carry off pupae of other species  if scattered near their nests  it is
possible that such pupae originally stored as food might become developed 
and the foreign ants thus unintentionally reared would then follow their
proper instincts  and do what work they could   If their presence proved
useful to the species which had seized them  if it were more advantageous
to this species  to capture workers than to procreate them  the habit of
collecting pupae  originally for food  might by natural selection be
strengthened and rendered permanent for the very different purpose of
raising slaves   When the instinct was once acquired  if carried out to a
much less extent even than in our British F  sanguinea  which  as we have
seen  is less aided by its slaves than the same species in Switzerland 
natural selection might increase and modify the instinct  always supposing
each modification to be of use to the species  until an ant was formed as
abjectly dependent on its slaves as is the Formica rufescens 

CELL MAKING INSTINCT OF THE HIVE BEE 

I will not here enter on minute details on this subject  but will merely
give an outline of the conclusions at which I have arrived   He must be a
dull man who can examine the exquisite structure of a comb  so beautifully
adapted to its end  without enthusiastic admiration   We hear from
mathematicians that bees have practically solved a recondite problem  and
have made their cells of the proper shape to hold the greatest possible
amount of honey  with the least possible consumption of precious wax in
their construction   It has been remarked that a skilful workman  with
fitting tools and measures  would find it very difficult to make cells of
wax of the true form  though this is effected by a crowd of bees working in
a dark hive   Granting whatever instincts you please  it seems at first
quite inconceivable how they can make all the necessary angles and planes 
or even perceive when they are correctly made   But the difficulty is not
nearly so great as at first appears   all this beautiful work can be shown 
I think  to follow from a few simple instincts 

I was led to investigate this subject by Mr  Waterhouse  who has shown that
the form of the cell stands in close relation to the presence of adjoining
cells  and the following view may  perhaps  be considered only as a
modification of his theory   Let us look to the great principle of
gradation  and see whether Nature does not reveal to us her method of work  
At one end of a short series we have humble bees  which use their old
cocoons to hold honey  sometimes adding to them short tubes of wax  and
likewise making separate and very irregular rounded cells of wax   At the
other end of the series we have the cells of the hive bee  placed in a
double layer   each cell  as is well known  is an hexagonal prism  with the
basal edges of its six sides bevelled so as to join an inverted pyramid  of
three rhombs   These rhombs have certain angles  and the three which form
the pyramidal base of a single cell on one side of the comb  enter into the
composition of the bases of three adjoining cells on the opposite side   In
the series between the extreme perfection of the cells of the hive bee and
the simplicity of those of the humble bee  we have the cells of the Mexican
Melipona domestica  carefully described and figured by Pierre Huber   The
Melipona itself is intermediate in structure between the hive and humble
bee  but more nearly related to the latter   it forms a nearly regular
waxen comb of cylindrical cells  in which the young are hatched  and  in
addition  some large cells of wax for holding honey   These latter cells
are nearly spherical and of nearly equal sizes  and are aggregated into an
irregular mass   But the important point to notice is  that these cells are
always made at that degree of nearness to each other that they would have
intersected or broken into each other if the spheres had been completed 
but this is never permitted  the bees building perfectly flat walls of wax
between the spheres which thus tend to intersect   Hence  each cell
consists of an outer spherical portion  and of two  three  or more flat
surfaces  according as the cell adjoins two  three or more other cells  
When one cell rests on three other cells  which  from the spheres being
nearly of the same size  is very frequently and necessarily the case  the
three flat surfaces are united into a pyramid  and this pyramid  as Huber
has remarked  is manifestly a gross imitation of the three sided pyramidal
base of the cell of the hive bee   As in the cells of the hive bee  so
here  the three plane surfaces in any one cell necessarily enter into the
construction of three adjoining cells   It is obvious that the Melipona
saves wax  and what is more important  labour  by this manner of building 
for the flat walls between the adjoining cells are not double  but are of
the same thickness as the outer spherical portions  and yet each flat
portion forms a part of two cells 

Reflecting on this case  it occurred to me that if the Melipona had made
its spheres at some given distance from each other  and had made them of
equal sizes and had arranged them symmetrically in a double layer  the
resulting structure would have been as perfect as the comb of the hive bee  
Accordingly I wrote to Professor Miller  of Cambridge  and this geometer
has kindly read over the following statement  drawn up from his
information  and tells me that it is strictly correct  

If a number of equal spheres be described with their centres placed in two
parallel layers  with the centre of each sphere at the distance of radius x
sqrt 2  or radius x 1 41421  or at some lesser distance   from the centres
of the six surrounding spheres in the same layer  and at the same distance
from the centres of the adjoining spheres in the other and parallel layer 
then  if planes of intersection between the several spheres in both layers
be formed  there will result a double layer of hexagonal prisms united
together by pyramidal bases formed of three rhombs  and the rhombs and the
sides of the hexagonal prisms will have every angle identically the same
with the best measurements which have been made of the cells of the
hive bee   But I hear from Professor Wyman  who has made numerous careful
measurements  that the accuracy of the workmanship of the bee has been
greatly exaggerated  so much so  that whatever the typical form of the cell
may be  it is rarely  if ever  realised 

Hence we may safely conclude that  if we could slightly modify the
instincts already possessed by the Melipona  and in themselves not very
wonderful  this bee would make a structure as wonderfully perfect as that
of the hive bee   We must suppose the Melipona to have the power of forming
her cells truly spherical  and of equal sizes  and this would not be very
surprising  seeing that she already does so to a certain extent  and seeing
what perfectly cylindrical burrows many insects make in wood  apparently by
turning round on a fixed point   We must suppose the Melipona to arrange
her cells in level layers  as she already does her cylindrical cells  and
we must further suppose  and this is the greatest difficulty  that she can
somehow judge accurately at what distance to stand from her
fellow labourers when several are making their spheres  but she is already
so far enabled to judge of distance  that she always describes her spheres
so as to intersect to a certain extent  and then she unites the points of
intersection by perfectly flat surfaces   By such modifications of
instincts which in themselves are not very wonderful  hardly more wonderful
than those which guide a bird to make its nest  I believe that the hive bee
has acquired  through natural selection  her inimitable architectural
powers 

But this theory can be tested by experiment   Following the example of Mr 
Tegetmeier  I separated two combs  and put between them a long  thick 
rectangular strip of wax   the bees instantly began to excavate minute
circular pits in it  and as they deepened these little pits  they made them
wider and wider until they were converted into shallow basins  appearing to
the eye perfectly true or parts of a sphere  and of about the diameter of a
cell   It was most interesting to observe that  wherever several bees had
begun to excavate these basins near together  they had begun their work at
such a distance from each other that by the time the basins had acquired
the above stated width  i e  about the width of an ordinary cell   and were
in depth about one sixth of the diameter of the sphere of which they formed
a part  the rims of the basins intersected or broke into each other   As
soon as this occurred  the bees ceased to excavate  and began to build up
flat walls of wax on the lines of intersection between the basins  so that
each hexagonal prism was built upon the scalloped edge of a smooth basin 
instead of on the straight edges of a three sided pyramid as in the case of
ordinary cells 

I then put into the hive  instead of a thick  rectangular piece of wax  a
thin and narrow  knife edged ridge  coloured with vermilion   The bees
instantly began on both sides to excavate little basins near to each other 
in the same way as before  but the ridge of wax was so thin  that the
bottoms of the basins  if they had been excavated to the same depth as in
the former experiment  would have broken into each other from the opposite
sides   The bees  however  did not suffer this to happen  and they stopped
their excavations in due time  so that the basins  as soon as they had been
a little deepened  came to have flat bases  and these flat bases  formed by
thin little plates of the vermilion wax left ungnawed  were situated  as
far as the eye could judge  exactly along the planes of imaginary
intersection between the basins on the opposite side of the ridge of wax  
In some parts  only small portions  in other parts  large portions of a
rhombic plate were thus left between the opposed basins  but the work  from
the unnatural state of things  had not been neatly performed   The bees
must have worked at very nearly the same rate in circularly gnawing away
and deepening the basins on both sides of the ridge of vermilion wax  in
order to have thus succeeded in leaving flat plates between the basins  by
stopping work at the planes of intersection 

Considering how flexible thin wax is  I do not see that there is any
difficulty in the bees  whilst at work on the two sides of a strip of wax 
perceiving when they have gnawed the wax away to the proper thinness  and
then stopping their work   In ordinary combs it has appeared to me that the
bees do not always succeed in working at exactly the same rate from the
opposite sides  for I have noticed half completed rhombs at the base of a
just commenced cell  which were slightly concave on one side  where I
suppose that the bees had excavated too quickly  and convex on the opposed
side where the bees had worked less quickly   In one well marked instance 
I put the comb back into the hive  and allowed the bees to go on working
for a short time  and again examined the cell  and I found that the rhombic
plate had been completed  and had become PERFECTLY FLAT   it was absolutely
impossible  from the extreme thinness of the little plate  that they could
have effected this by gnawing away the convex side  and I suspect that the
bees in such cases stand in the opposed cells and push and bend the ductile
and warm wax  which as I have tried is easily done  into its proper
intermediate plane  and thus flatten it 

 From the experiment of the ridge of vermilion wax we can see that  if the
bees were to build for themselves a thin wall of wax  they could make their
cells of the proper shape  by standing at the proper distance from each
other  by excavating at the same rate  and by endeavouring to make equal
spherical hollows  but never allowing the spheres to break into each other  
Now bees  as may be clearly seen by examining the edge of a growing comb 
do make a rough  circumferential wall or rim all round the comb  and they
gnaw this away from the opposite sides  always working circularly as they
deepen each cell   They do not make the whole three sided pyramidal base of
any one cell at the same time  but only that one rhombic plate which stands
on the extreme growing margin  or the two plates  as the case may be  and
they never complete the upper edges of the rhombic plates  until the
hexagonal walls are commenced   Some of these statements differ from those
made by the justly celebrated elder Huber  but I am convinced of their
accuracy  and if I had space  I could show that they are conformable with
my theory 

Huber s statement  that the very first cell is excavated out of a little
parallel sided wall of wax  is not  as far as I have seen  strictly
correct  the first commencement having always been a little hood of wax 
but I will not here enter on details   We see how important a part
excavation plays in the construction of the cells  but it would be a great
error to suppose that the bees cannot build up a rough wall of wax in the
proper position  that is  along the plane of intersection between two
adjoining spheres   I have several specimens showing clearly that they can
do this   Even in the rude circumferential rim or wall of wax round a
growing comb  flexures may sometimes be observed  corresponding in position
to the planes of the rhombic basal plates of future cells   But the rough
wall of wax has in every case to be finished off  by being largely gnawed
away on both sides   The manner in which the bees build is curious  they
always make the first rough wall from ten to twenty times thicker than the
excessively thin finished wall of the cell  which will ultimately be left  
We shall understand how they work  by supposing masons first to pile up a
broad ridge of cement  and then to begin cutting it away equally on both
sides near the ground  till a smooth  very thin wall is left in the middle 
the masons always piling up the cut away cement  and adding fresh cement on
the summit of the ridge   We shall thus have a thin wall steadily growing
upward but always crowned by a gigantic coping   From all the cells  both
those just commenced and those completed  being thus crowned by a strong
coping of wax  the bees can cluster and crawl over the comb without
injuring the delicate hexagonal walls   These walls  as Professor Miller
has kindly ascertained for me  vary greatly in thickness  being  on an
average of twelve measurements made near the border of the comb  1 352 of
an inch in thickness  whereas the basal rhomboidal plates are thicker 
nearly in the proportion of three to two  having a mean thickness  from
twenty one measurements  of 1 229 of an inch   By the above singular manner
of building  strength is continually given to the comb  with the utmost
ultimate economy of wax 

It seems at first to add to the difficulty of understanding how the cells
are made  that a multitude of bees all work together  one bee after working
a short time at one cell going to another  so that  as Huber has stated  a
score of individuals work even at the commencement of the first cell   I
was able practically to show this fact  by covering the edges of the
hexagonal walls of a single cell  or the extreme margin of the
circumferential rim of a growing comb  with an extremely thin layer of
melted vermilion wax  and I invariably found that the colour was most
delicately diffused by the bees  as delicately as a painter could have done
it with his brush  by atoms of the coloured wax having been taken from the
spot on which it had been placed  and worked into the growing edges of the
cells all round   The work of construction seems to be a sort of balance
struck between many bees  all instinctively standing at the same relative
distance from each other  all trying to sweep equal spheres  and then
building up  or leaving ungnawed  the planes of intersection between these
spheres   It was really curious to note in cases of difficulty  as when two
pieces of comb met at an angle  how often the bees would pull down and
rebuild in different ways the same cell  sometimes recurring to a shape
which they had at first rejected 

When bees have a place on which they can stand in their proper positions
for working  for instance  on a slip of wood  placed directly under the
middle of a comb growing downwards  so that the comb has to be built over
one face of the slip  in this case the bees can lay the foundations of one
wall of a new hexagon  in its strictly proper place  projecting beyond the
other completed cells   It suffices that the bees should be enabled to
stand at their proper relative distances from each other and from the walls
of the last completed cells  and then  by striking imaginary spheres  they
can build up a wall intermediate between two adjoining spheres  but  as far
as I have seen  they never gnaw away and finish off the angles of a cell
till a large part both of that cell and of the adjoining cells has been
built   This capacity in bees of laying down under certain circumstances a
rough wall in its proper place between two just commenced cells  is
important  as it bears on a fact  which seems at first subversive of the
foregoing theory  namely  that the cells on the extreme margin of
wasp combs are sometimes strictly hexagonal  but I have not space here to
enter on this subject   Nor does there seem to me any great difficulty in a
single insect  as in the case of a queen wasp  making hexagonal cells  if
she were to work alternately on the inside and outside of two or three
cells commenced at the same time  always standing at the proper relative
distance from the parts of the cells just begun  sweeping spheres or
cylinders  and building up intermediate planes 

As natural selection acts only by the accumulation of slight modifications
of structure or instinct  each profitable to the individual under its
conditions of life  it may reasonably be asked  how a long and graduated
succession of modified architectural instincts  all tending towards the
present perfect plan of construction  could have profited the progenitors
of the hive bee   I think the answer is not difficult   cells constructed
like those of the bee or the wasp gain in strength  and save much in labour
and space  and in the materials of which they are constructed   With
respect to the formation of wax  it is known that bees are often hard
pressed to get sufficient nectar  and I am informed by Mr  Tegetmeier that
it has been experimentally proved that from twelve to fifteen pounds of dry
sugar are consumed by a hive of bees for the secretion of a pound of wax 
so that a prodigious quantity of fluid nectar must be collected and
consumed by the bees in a hive for the secretion of the wax necessary for
the construction of their combs   Moreover  many bees have to remain idle
for many days during the process of secretion   A large store of honey is
indispensable to support a large stock of bees during the winter  and the
security of the hive is known mainly to depend on a large number of bees
being supported   Hence the saving of wax by largely saving honey  and the
time consumed in collecting the honey  must be an important element of
success any family of bees   Of course the success of the species may be
dependent on the number of its enemies  or parasites  or on quite distinct
causes  and so be altogether independent of the quantity of honey which the
bees can collect   But let us suppose that this latter circumstance
determined  as it probably often has determined  whether a bee allied to
our humble bees could exist in large numbers in any country  and let us
further suppose that the community lived through the winter  and
consequently required a store of honey   there can in this case be no doubt
that it would be an advantage to our imaginary humble bee if a slight
modification of her instincts led her to make her waxen cells near
together  so as to intersect a little  for a wall in common even to two
adjoining cells would save some little labour and wax   Hence  it would
continually be more and more advantageous to our humble bees  if they were
to make their cells more and more regular  nearer together  and aggregated
into a mass  like the cells of the Melipona  for in this case a large part
of the bounding surface of each cell would serve to bound the adjoining
cells  and much labour and wax would be saved   Again  from the same cause 
it would be advantageous to the Melipona  if she were to make her cells
closer together  and more regular in every way than at present  for then 
as we have seen  the spherical surfaces would wholly disappear and be
replaced by plane surfaces  and the Melipona would make a comb as perfect
as that of the hive bee   Beyond this stage of perfection in architecture 
natural selection could not lead  for the comb of the hive bee  as far as
we can see  is absolutely perfect in economising labour and wax 

Thus  as I believe  the most wonderful of all known instincts  that of the
hive bee  can be explained by natural selection having taken advantage of
numerous  successive  slight modifications of simpler instincts  natural
selection having  by slow degrees  more and more perfectly led the bees to
sweep equal spheres at a given distance from each other in a double layer 
and to build up and excavate the wax along the planes of intersection   The
bees  of course  no more knowing that they swept their spheres at one
particular distance from each other  than they know what are the several
angles of the hexagonal prisms and of the basal rhombic plates  the motive
power of the process of natural selection having been the construction of
cells of due strength and of the proper size and shape for the larvae  this
being effected with the greatest possible economy of labour and wax  that
individual swarm which thus made the best cells with least labour  and
least waste of honey in the secretion of wax  having succeeded best  and
having transmitted their newly acquired economical instincts to new swarms 
which in their turn will have had the best chance of succeeding in the
struggle for existence 

OBJECTIONS TO THE THEORY OF NATURAL SELECTION AS APPLIED TO INSTINCTS  
NEUTER AND STERILE INSECTS 

It has been objected to the foregoing view of the origin of instincts that
 the variations of structure and of instinct must have been simultaneous
and accurately adjusted to each other  as a modification in the one without
an immediate corresponding change in the other would have been fatal    The
force of this objection rests entirely on the assumption that the changes
in the instincts and structure are abrupt   To take as an illustration the
case of the larger titmouse   Parus major  alluded to in a previous
chapter  this bird often holds the seeds of the yew between its feet on a
branch  and hammers with its beak till it gets at the kernel   Now what
special difficulty would there be in natural selection preserving all the
slight individual variations in the shape of the beak  which were better
and better adapted to break open the seeds  until a beak was formed  as
well constructed for this purpose as that of the nuthatch  at the same time
that habit  or compulsion  or spontaneous variations of taste  led the bird
to become more and more of a seed eater   In this case the beak is supposed
to be slowly modified by natural selection  subsequently to  but in
accordance with  slowly changing habits or taste  but let the feet of the
titmouse vary and grow larger from correlation with the beak  or from any
other unknown cause  and it is not improbable that such larger feet would
lead the bird to climb more and more until it acquired the remarkable
climbing instinct and power of the nuthatch   In this case a gradual change
of structure is supposed to lead to changed instinctive habits   To take
one more case   few instincts are more remarkable than that which leads the
swift of the Eastern Islands to make its nest wholly of inspissated saliva 
Some birds build their nests of mud  believed to be moistened with saliva 
and one of the swifts of North America makes its nest  as I have seen  of
sticks agglutinated with saliva  and even with flakes of this substance  
Is it then very improbable that the natural selection of individual swifts 
which secreted more and more saliva  should at last produce a species with
instincts leading it to neglect other materials and to make its nest
exclusively of inspissated saliva   And so in other cases   It must 
however  be admitted that in many instances we cannot conjecture whether it
was instinct or structure which first varied 

No doubt many instincts of very difficult explanation could be opposed to
the theory of natural selection  cases  in which we cannot see how an
instinct could have originated  cases  in which no intermediate gradations
are known to exist  cases of instincts of such trifling importance  that
they could hardly have been acted on by natural selection  cases of
instincts almost identically the same in animals so remote in the scale of
nature that we cannot account for their similarity by inheritance from a
common progenitor  and consequently must believe that they were
independently acquired through natural selection   I will not here enter on
these several cases  but will confine myself to one special difficulty 
which at first appeared to me insuperable  and actually fatal to the whole
theory   I allude to the neuters or sterile females in insect communities  
for these neuters often differ widely in instinct and in structure from
both the males and fertile females  and yet  from being sterile  they
cannot propagate their kind 

The subject well deserves to be discussed at great length  but I will here
take only a single case  that of working or sterile ants   How the workers
have been rendered sterile is a difficulty  but not much greater than that
of any other striking modification of structure  for it can be shown that
some insects and other articulate animals in a state of nature occasionally
become sterile  and if such insects had been social  and it had been
profitable to the community that a number should have been annually born
capable of work  but incapable of procreation  I can see no especial
difficulty in this having been effected through natural selection   But I
must pass over this preliminary difficulty   The great difficulty lies in
the working ants differing widely from both the males and the fertile
females in structure  as in the shape of the thorax  and in being destitute
of wings and sometimes of eyes  and in instinct   As far as instinct alone
is concerned  the wonderful difference in this respect between the workers
and the perfect females would have been better exemplified by the hive bee  
If a working ant or other neuter insect had been an ordinary animal  I
should have unhesitatingly assumed that all its characters had been slowly
acquired through natural selection  namely  by individuals having been born
with slight profitable modifications  which were inherited by the
offspring  and that these again varied and again were selected  and so
onwards   But with the working ant we have an insect differing greatly from
its parents  yet absolutely sterile  so that it could never have
transmitted successively acquired modifications of structure or instinct to
its progeny   It may well be asked how it is possible to reconcile this
case with the theory of natural selection 

First  let it be remembered that we have innumerable instances  both in our
domestic productions and in those in a state of nature  of all sorts of
differences of inherited structure which are correlated with certain ages
and with either sex   We have differences correlated not only with one sex 
but with that short period when the reproductive system is active  as in
the nuptial plumage of many birds  and in the hooked jaws of the male
salmon   We have even slight differences in the horns of different breeds
of cattle in relation to an artificially imperfect state of the male sex 
for oxen of certain breeds have longer horns than the oxen of other breeds 
relatively to the length of the horns in both the bulls and cows of these
same breeds   Hence  I can see no great difficulty in any character
becoming correlated with the sterile condition of certain members of insect
communities  the difficulty lies in understanding how such correlated
modifications of structure could have been slowly accumulated by natural
selection 

This difficulty  though appearing insuperable  is lessened  or  as I
believe  disappears  when it is remembered that selection may be applied to
the family  as well as to the individual  and may thus gain the desired
end   Breeders of cattle wish the flesh and fat to be well marbled
together   An animal thus characterized has been slaughtered  but the
breeder has gone with confidence to the same stock and has succeeded   Such
faith may be placed in the power of selection that a breed of cattle 
always yielding oxen with extraordinarily long horns  could  it is
probable  be formed by carefully watching which individual bulls and cows 
when matched  produced oxen with the longest horns  and yet no one ox would
ever have propagated its kind   Here is a better and real illustration  
According to M  Verlot  some varieties of the double annual stock  from
having been long and carefully selected to the right degree  always produce
a large proportion of seedlings bearing double and quite sterile flowers 
but they likewise yield some single and fertile plants   These latter  by
which alone the variety can be propagated  may be compared with the fertile
male and female ants  and the double sterile plants with the neuters of the
same community   As with the varieties of the stock  so with social
insects  selection has been applied to the family  and not to the
individual  for the sake of gaining a serviceable end   Hence  we may
conclude that slight modifications of structure or of instinct  correlated
with the sterile condition of certain members of the community  have proved
advantageous  consequently the fertile males and females have flourished 
and transmitted to their fertile offspring a tendency to produce sterile
members with the same modifications   This process must have been repeated
many times  until that prodigious amount of difference between the fertile
and sterile females of the same species has been produced which we see in
many social insects 

But we have not as yet touched on the acme of the difficulty  namely  the
fact that the neuters of several ants differ  not only from the fertile
females and males  but from each other  sometimes to an almost incredible
degree  and are thus divided into two or even three castes   The castes 
moreover  do not generally graduate into each other  but are perfectly well
defined  being as distinct from each other as are any two species of the
same genus  or rather as any two genera of the same family   Thus  in
Eciton  there are working and soldier neuters  with jaws and instincts
extraordinarily different   in Cryptocerus  the workers of one caste alone
carry a wonderful sort of shield on their heads  the use of which is quite
unknown   in the Mexican Myrmecocystus  the workers of one caste never
leave the nest  they are fed by the workers of another caste  and they have
an enormously developed abdomen which secretes a sort of honey  supplying
the place of that excreted by the aphides  or the domestic cattle as they
may be called  which our European ants guard and imprison 

It will indeed be thought that I have an overweening confidence in the
principle of natural selection  when I do not admit that such wonderful and
well established facts at once annihilate the theory   In the simpler case
of neuter insects all of one caste  which  as I believe  have been rendered
different from the fertile males and females through natural selection  we
may conclude from the analogy of ordinary variations  that the successive 
slight  profitable modifications did not first arise in all the neuters in
the same nest  but in some few alone  and that by the survival of the
communities with females which produced most neuters having the
advantageous modification  all the neuters ultimately came to be thus
characterized   According to this view we ought occasionally to find in the
same nest neuter insects  presenting gradations of structure  and this we
do find  even not rarely  considering how few neuter insects out of Europe
have been carefully examined   Mr  F  Smith has shown that the neuters of
several British ants differ surprisingly from each other in size and
sometimes in colour  and that the extreme forms can be linked together by
individuals taken out of the same nest   I have myself compared perfect
gradations of this kind   It sometimes happens that the larger or the
smaller sized workers are the most numerous  or that both large and small
are numerous  while those of an intermediate size are scanty in numbers  
Formica flava has larger and smaller workers  with some few of intermediate
size  and  in this species  as Mr  F  Smith has observed  the larger
workers have simple eyes  ocelli   which  though small  can be plainly
distinguished  whereas the smaller workers have their ocelli rudimentary  
Having carefully dissected several specimens of these workers  I can affirm
that the eyes are far more rudimentary in the smaller workers than can be
accounted for merely by their proportionately lesser size  and I fully
believe  though I dare not assert so positively  that the workers of
intermediate size have their ocelli in an exactly intermediate condition  
So that here we have two bodies of sterile workers in the same nest 
differing not only in size  but in their organs of vision  yet connected by
some few members in an intermediate condition   I may digress by adding 
that if the smaller workers had been the most useful to the community  and
those males and females had been continually selected  which produced more
and more of the smaller workers  until all the workers were in this
condition  we should then have had a species of ant with neuters in nearly
the same condition as those of Myrmica   For the workers of Myrmica have
not even rudiments of ocelli  though the male and female ants of this genus
have well developed ocelli 

I may give one other case   so confidently did I expect occasionally to
find gradations of important structures between the different castes of
neuters in the same species  that I gladly availed myself of Mr  F  Smith s
offer of numerous specimens from the same nest of the driver ant  Anomma 
of West Africa   The reader will perhaps best appreciate the amount of
difference in these workers by my giving  not the actual measurements  but
a strictly accurate illustration   the difference was the same as if we
were to see a set of workmen building a house  of whom many were five feet
four inches high  and many sixteen feet high  but we must in addition
suppose that the larger workmen had heads four instead of three times as
big as those of the smaller men  and jaws nearly five times as big   The
jaws  moreover  of the working ants of the several sizes differed
wonderfully in shape  and in the form and number of the teeth   But the
important fact for us is that  though the workers can be grouped into
castes of different sizes  yet they graduate insensibly into each other  as
does the widely different structure of their jaws   I speak confidently on
this latter point  as Sir J  Lubbock made drawings for me  with the camera
lucida  of the jaws which I dissected from the workers of the several
sizes   Mr  Bates  in his interesting  Naturalist on the Amazons   has
described analogous cases 

With these facts before me  I believe that natural selection  by acting on
the fertile ants or parents  could form a species which should regularly
produce neuters  all of large size with one form of jaw  or all of small
size with widely different jaws  or lastly  and this is the greatest
difficulty  one set of workers of one size and structure  and
simultaneously another set of workers of a different size and structure  a
graduated series having first been formed  as in the case of the driver
ant  and then the extreme forms having been produced in greater and greater
numbers  through the survival of the parents which generated them  until
none with an intermediate structure were produced 

An analogous explanation has been given by Mr  Wallace  of the equally
complex case  of certain Malayan butterflies regularly appearing under two
or even three distinct female forms  and by Fritz Muller  of certain
Brazilian crustaceans likewise appearing under two widely distinct male
forms   But this subject need not here be discussed 

I have now explained how  I believe  the wonderful fact of two distinctly
defined castes of sterile workers existing in the same nest  both widely
different from each other and from their parents  has originated   We can
see how useful their production may have been to a social community of
ants  on the same principle that the division of labour is useful to
civilised man   Ants  however  work by inherited instincts and by inherited
organs or tools  while man works by acquired knowledge and manufactured
instruments   But I must confess  that  with all my faith in natural
selection  I should never have anticipated that this principle could have
been efficient in so high a degree  had not the case of these neuter
insects led me to this conclusion   I have  therefore  discussed this case 
at some little but wholly insufficient length  in order to show the power
of natural selection  and likewise because this is by far the most serious
special difficulty which my theory has encountered   The case  also  is
very interesting  as it proves that with animals  as with plants  any
amount of modification may be effected by the accumulation of numerous 
slight  spontaneous variations  which are in any way profitable  without
exercise or habit having been brought into play   For peculiar habits 
confined to the workers of sterile females  however long they might be
followed  could not possibly affect the males and fertile females  which
alone leave descendants   I am surprised that no one has advanced this
demonstrative case of neuter insects  against the well known doctrine of
inherited habit  as advanced by Lamarck 

SUMMARY 

I have endeavoured in this chapter briefly to show that the mental
qualities of our domestic animals vary  and that the variations are
inherited   Still more briefly I have attempted to show that instincts vary
slightly in a state of nature   No one will dispute that instincts are of
the highest importance to each animal   Therefore  there is no real
difficulty  under changing conditions of life  in natural selection
accumulating to any extent slight modifications of instinct which are in
any way useful   In many cases habit or use and disuse have probably come
into play   I do not pretend that the facts given in this chapter
strengthen in any great degree my theory  but none of the cases of
difficulty  to the best of my judgment  annihilate it   On the other hand 
the fact that instincts are not always absolutely perfect and are liable to
mistakes  that no instinct can be shown to have been produced for the good
of other animals  though animals take advantage of the instincts of others 
that the canon in natural history  of  Natura non facit saltum   is
applicable to instincts as well as to corporeal structure  and is plainly
explicable on the foregoing views  but is otherwise inexplicable  all tend
to corroborate the theory of natural selection 

This theory is also strengthened by some few other facts in regard to
instincts  as by that common case of closely allied  but distinct  species 
when inhabiting distant parts of the world and living under considerably
different conditions of life  yet often retaining nearly the same
instincts   For instance  we can understand  on the principle of
inheritance  how it is that the thrush of tropical South America lines its
nest with mud  in the same peculiar manner as does our British thrush  how
it is that the Hornbills of Africa and India have the same extraordinary
instinct of plastering up and imprisoning the females in a hole in a tree 
with only a small hole left in the plaster through which the males feed
them and their young when hatched  how it is that the male wrens
 Troglodytes  of North America  build  cock nests   to roost in  like the
males of our Kitty wrens   a habit wholly unlike that of any other known
bird   Finally  it may not be a logical deduction  but to my imagination it
is far more satisfactory to look at such instincts as the young cuckoo
ejecting its foster brothers  ants making slaves  the larvae of
ichneumonidae feeding within the live bodies of caterpillars  not as
specially endowed or created instincts  but as small consequences of one
general law leading to the advancement of all organic beings  namely 
multiply  vary  let the strongest live and the weakest die 

 
CHAPTER IX 

HYBRIDISM 

Distinction between the sterility of first crosses and of hybrids   
Sterility various in degree  not universal  affected by close
interbreeding  removed by domestication    Laws governing the sterility of
hybrids    Sterility not a special endowment  but incidental on other
differences  not accumulated by natural selection    Causes of the
sterility of first crosses and of hybrids    Parallelism between the
effects of changed conditions of life and of crossing    Dimorphism and
trimorphism    Fertility of varieties when crossed and of their mongrel
offspring not universal    Hybrids and mongrels compared independently of
their fertility    Summary 

The view commonly entertained by naturalists is that species  when
intercrossed  have been specially endowed with sterility  in order to
prevent their confusion   This view certainly seems at first highly
probable  for species living together could hardly have been kept distinct
had they been capable of freely crossing   The subject is in many ways
important for us  more especially as the sterility of species when first
crossed  and that of their hybrid offspring  cannot have been acquired  as
I shall show  by the preservation of successive profitable degrees of
sterility   It is an incidental result of differences in the reproductive
systems of the parent species 

In treating this subject  two classes of facts  to a large extent
fundamentally different  have generally been confounded  namely  the
sterility of species when first crossed  and the sterility of the hybrids
produced from them 

Pure species have of course their organs of reproduction in a perfect
condition  yet when intercrossed they produce either few or no offspring  
Hybrids  on the other hand  have their reproductive organs functionally
impotent  as may be clearly seen in the state of the male element in both
plants and animals  though the formative organs themselves are perfect in
structure  as far as the microscope reveals   In the first case the two
sexual elements which go to form the embryo are perfect  in the second case
they are either not at all developed  or are imperfectly developed   This
distinction is important  when the cause of the sterility  which is common
to the two cases  has to be considered   The distinction probably has been
slurred over  owing to the sterility in both cases being looked on as a
special endowment  beyond the province of our reasoning powers 

The fertility of varieties  that is of the forms known or believed to be
descended from common parents  when crossed  and likewise the fertility of
their mongrel offspring  is  with reference to my theory  of equal
importance with the sterility of species  for it seems to make a broad and
clear distinction between varieties and species 

DEGREES OF STERILITY 

First  for the sterility of species when crossed and of their hybrid
offspring   It is impossible to study the several memoirs and works of
those two conscientious and admirable observers  Kolreuter and Gartner  who
almost devoted their lives to this subject  without being deeply impressed
with the high generality of some degree of sterility   Kolreuter makes the
rule universal  but then he cuts the knot  for in ten cases in which he
found two forms  considered by most authors as distinct species  quite
fertile together  he unhesitatingly ranks them as varieties   Gartner 
also  makes the rule equally universal  and he disputes the entire
fertility of Kolreuter s ten cases   But in these and in many other cases 
Gartner is obliged carefully to count the seeds  in order to show that
there is any degree of sterility   He always compares the maximum number of
seeds produced by two species when first crossed  and the maximum produced
by their hybrid offspring  with the average number produced by both pure
parent species in a state of nature   But causes of serious error here
intervene   a plant  to be hybridised  must be castrated  and  what is
often more important  must be secluded in order to prevent pollen being
brought to it by insects from other plants   Nearly all the plants
experimented on by Gartner were potted  and were kept in a chamber in his
house   That these processes are often injurious to the fertility of a
plant cannot be doubted  for Gartner gives in his table about a score of
cases of plants which he castrated  and artificially fertilised with their
own pollen  and  excluding all cases such as the Leguminosae  in which
there is an acknowledged difficulty in the manipulation  half of these
twenty plants had their fertility in some degree impaired   Moreover  as
Gartner repeatedly crossed some forms  such as the common red and blue
pimpernels  Anagallis arvensis and coerulea   which the best botanists rank
as varieties  and found them absolutely sterile  we may doubt whether many
species are really so sterile  when intercrossed  as he believed 

It is certain  on the one hand  that the sterility of various species when
crossed is so different in degree and graduates away so insensibly  and  on
the other hand  that the fertility of pure species is so easily affected by
various circumstances  that for all practical purposes it is most difficult
to say where perfect fertility ends and sterility begins   I think no
better evidence of this can be required than that the two most experienced
observers who have ever lived  namely Kolreuter and Gartner  arrived at
diametrically opposite conclusions in regard to some of the very same
forms   It is also most instructive to compare  but I have not space here
to enter on details  the evidence advanced by our best botanists on the
question whether certain doubtful forms should be ranked as species or
varieties  with the evidence from fertility adduced by different
hybridisers  or by the same observer from experiments made during different
years   It can thus be shown that neither sterility nor fertility affords
any certain distinction between species and varieties   The evidence from
this source graduates away  and is doubtful in the same degree as is the
evidence derived from other constitutional and structural differences 

In regard to the sterility of hybrids in successive generations  though
Gartner was enabled to rear some hybrids  carefully guarding them from a
cross with either pure parent  for six or seven  and in one case for ten
generations  yet he asserts positively that their fertility never
increases  but generally decreases greatly and suddenly   With respect to
this decrease  it may first be noticed that when any deviation in structure
or constitution is common to both parents  this is often transmitted in an
augmented degree to the offspring  and both sexual elements in hybrid
plants are already affected in some degree   But I believe that their
fertility has been diminished in nearly all these cases by an independent
cause  namely  by too close interbreeding   I have made so many experiments
and collected so many facts  showing on the one hand that an occasional
cross with a distinct individual or variety increases the vigour and
fertility of the offspring  and on the other hand that very close
interbreeding lessens their vigour and fertility  that I cannot doubt the
correctness of this conclusion   Hybrids are seldom raised by
experimentalists in great numbers  and as the parent species  or other
allied hybrids  generally grow in the same garden  the visits of insects
must be carefully prevented during the flowering season   hence hybrids  if
left to themselves  will generally be fertilised during each generation by
pollen from the same flower  and this would probably be injurious to their
fertility  already lessened by their hybrid origin   I am strengthened in
this conviction by a remarkable statement repeatedly made by Gartner 
namely  that if even the less fertile hybrids be artificially fertilised
with hybrid pollen of the same kind  their fertility  notwithstanding the
frequent ill effects from manipulation  sometimes decidedly increases  and
goes on increasing   Now  in the process of artificial fertilisation 
pollen is as often taken by chance  as I know from my own experience  from
the anthers of another flower  as from the anthers of the flower itself
which is to be fertilised  so that a cross between two flowers  though
probably often on the same plant  would be thus effected   Moreover 
whenever complicated experiments are in progress  so careful an observer as
Gartner would have castrated his hybrids  and this would have insured in
each generation a cross with pollen from a distinct flower  either from the
same plant or from another plant of the same hybrid nature   And thus  the
strange fact of an increase of fertility in the successive generations of
ARTIFICIALLY FERTILISED hybrids  in contrast with those spontaneously self 
fertilised  may  as I believe  be accounted for by too close interbreeding
having been avoided 

Now let us turn to the results arrived at by a third most experienced
hybridiser  namely  the Hon  and Rev  W  Herbert   He is as emphatic in his
conclusion that some hybrids are perfectly fertile  as fertile as the pure
parent species  as are Kolreuter and Gartner that some degree of sterility
between distinct species is a universal law of nature   He experimented on
some of the very same species as did Gartner   The difference in their
results may  I think  be in part accounted for by Herbert s great
horticultural skill  and by his having hot houses at his command   Of his
many important statements I will here give only a single one as an example 
namely  that  every ovule in a pod of Crinum capense fertilised by C 
revolutum produced a plant  which I never saw to occur in a case of its
natural fecundation    So that here we have perfect  or even more than
commonly perfect fertility  in a first cross between two distinct species 

This case of the Crinum leads me to refer to a singular fact  namely  that
individual plants of certain species of Lobelia  Verbascum and Passiflora 
can easily be fertilised by the pollen from a distinct species  but not by
pollen from the same plant  though this pollen can be proved to be
perfectly sound by fertilising other plants or species   In the genus
Hippeastrum  in Corydalis as shown by Professor Hildebrand  in various
orchids as shown by Mr  Scott and Fritz Muller  all the individuals are in
this peculiar condition   So that with some species  certain abnormal
individuals  and in other species all the individuals  can actually be
hybridised much more readily than they can be fertilised by pollen from the
same individual plant   To give one instance  a bulb of Hippeastrum aulicum
produced four flowers  three were fertilised by Herbert with their own
pollen  and the fourth was subsequently fertilised by the pollen of a
compound hybrid descended from three distinct species   the result was that
 the ovaries of the three first flowers soon ceased to grow  and after a
few days perished entirely  whereas the pod impregnated by the pollen of
the hybrid made vigorous growth and rapid progress to maturity  and bore
good seed  which vegetated freely    Mr  Herbert tried similar experiments
during many years  and always with the same result   These cases serve to
show on what slight and mysterious causes the lesser or greater fertility
of a species sometimes depends 

The practical experiments of horticulturists  though not made with
scientific precision  deserve some notice   It is notorious in how
complicated a manner the species of Pelargonium  Fuchsia  Calceolaria 
Petunia  Rhododendron  etc   have been crossed  yet many of these hybrids
seed freely   For instance  Herbert asserts that a hybrid from Calceolaria
integrifolia and plantaginea  species most widely dissimilar in general
habit   reproduces itself as perfectly as if it had been a natural species
from the mountains of Chile    I have taken some pains to ascertain the
degree of fertility of some of the complex crosses of Rhododendrons  and I
am assured that many of them are perfectly fertile   Mr  C  Noble  for
instance  informs me that he raises stocks for grafting from a hybrid
between Rhod  ponticum and catawbiense  and that this hybrid  seeds as
freely as it is possible to imagine    Had hybrids  when fairly treated 
always gone on decreasing in fertility in each successive generation  as
Gartner believed to be the case  the fact would have been notorious to
nurserymen   Horticulturists raise large beds of the same hybrid  and such
alone are fairly treated  for by insect agency the several individuals are
allowed to cross freely with each other  and the injurious influence of
close interbreeding is thus prevented   Any one may readily convince
himself of the efficiency of insect agency by examining the flowers of the
more sterile kinds of hybrid Rhododendrons  which produce no pollen  for he
will find on their stigmas plenty of pollen brought from other flowers 

In regard to animals  much fewer experiments have been carefully tried than
with plants   If our systematic arrangements can be trusted  that is  if
the genera of animals are as distinct from each other as are the genera of
plants  then we may infer that animals more widely distinct in the scale of
nature can be crossed more easily than in the case of plants  but the
hybrids themselves are  I think  more sterile   It should  however  be
borne in mind that  owing to few animals breeding freely under confinement 
few experiments have been fairly tried   for instance  the canary bird has
been crossed with nine distinct species of finches  but  as not one of
these breeds freely in confinement  we have no right to expect that the
first crosses between them and the canary  or that their hybrids  should be
perfectly fertile   Again  with respect to the fertility in successive
generations of the more fertile hybrid animals  I hardly know of an
instance in which two families of the same hybrid have been raised at the
same time from different parents  so as to avoid the ill effects of close
interbreeding   On the contrary  brothers and sisters have usually been
crossed in each successive generation  in opposition to the constantly
repeated admonition of every breeder   And in this case  it is not at all
surprising that the inherent sterility in the hybrids should have gone on
increasing 

Although I know of hardly any thoroughly well authenticated cases of
perfectly fertile hybrid animals  I have reason to believe that the hybrids
from Cervulus vaginalis and Reevesii  and from Phasianus colchicus with P 
torquatus  are perfectly fertile   M  Quatrefages states that the hybrids
from two moths  Bombyx cynthia and arrindia  were proved in Paris to be
fertile inter se for eight generations   It has lately been asserted that
two such distinct species as the hare and rabbit  when they can be got to
breed together  produce offspring  which are highly fertile when crossed
with one of the parent species   The hybrids from the common and Chinese
geese  A  cygnoides   species which are so different that they are
generally ranked in distinct genera  have often bred in this country with
either pure parent  and in one single instance they have bred inter se  
This was effected by Mr  Eyton  who raised two hybrids from the same
parents  but from different hatches  and from these two birds he raised no
less than eight hybrids  grandchildren of the pure geese  from one nest  
In India  however  these cross bred geese must be far more fertile  for I
am assured by two eminently capable judges  namely Mr  Blyth and Captain
Hutton  that whole flocks of these crossed geese are kept in various parts
of the country  and as they are kept for profit  where neither pure
parent species exists  they must certainly be highly or perfectly fertile 

With our domesticated animals  the various races when crossed together are
quite fertile  yet in many cases they are descended from two or more wild
species   From this fact we must conclude either that the aboriginal
parent species at first produced perfectly fertile hybrids  or that the
hybrids subsequently reared under domestication became quite fertile   This
latter alternative  which was first propounded by Pallas  seems by far the
most probable  and can  indeed  hardly be doubted   It is  for instance 
almost certain that our dogs are descended from several wild stocks  yet 
with perhaps the exception of certain indigenous domestic dogs of South
America  all are quite fertile together  but analogy makes me greatly
doubt  whether the several aboriginal species would at first have freely
bred together and have produced quite fertile hybrids   So again I have
lately acquired decisive evidence that the crossed offspring from the
Indian humped and common cattle are inter se perfectly fertile  and from
the observations by Rutimeyer on their important osteological differences 
as well as from those by Mr  Blyth on their differences in habits  voice 
constitution  etc   these two forms must be regarded as good and distinct
species   The same remarks may be extended to the two chief races of the
pig   We must  therefore  either give up the belief of the universal
sterility of species when crossed  or we must look at this sterility in
animals  not as an indelible characteristic  but as one capable of being
removed by domestication 

Finally  considering all the ascertained facts on the intercrossing of
plants and animals  it may be concluded that some degree of sterility  both
in first crosses and in hybrids  is an extremely general result  but that
it cannot  under our present state of knowledge  be considered as
absolutely universal 

LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND OF HYBRIDS 

We will now consider a little more in detail the laws governing the
sterility of first crosses and of hybrids   Our chief object will be to see
whether or not these laws indicate that species have been specially endowed
with this quality  in order to prevent their crossing and blending together
in utter confusion   The following conclusions are drawn up chiefly from
Gartner s admirable work on the hybridisation of plants   I have taken much
pains to ascertain how far they apply to animals  and  considering how
scanty our knowledge is in regard to hybrid animals  I have been surprised
to find how generally the same rules apply to both kingdoms 

It has been already remarked  that the degree of fertility  both of first
crosses and of hybrids  graduates from zero to perfect fertility   It is
surprising in how many curious ways this gradation can be shown  but only
the barest outline of the facts can here be given   When pollen from a
plant of one family is placed on the stigma of a plant of a distinct
family  it exerts no more influence than so much inorganic dust   From this
absolute zero of fertility  the pollen of different species applied to the
stigma of some one species of the same genus  yields a perfect gradation in
the number of seeds produced  up to nearly complete or even quite complete
fertility  and  as we have seen  in certain abnormal cases  even to an
excess of fertility  beyond that which the plant s own pollen produces   So
in hybrids themselves  there are some which never have produced  and
probably never would produce  even with the pollen of the pure parents  a
single fertile seed   but in some of these cases a first trace of fertility
may be detected  by the pollen of one of the pure parent species causing
the flower of the hybrid to wither earlier than it otherwise would have
done  and the early withering of the flower is well known to be a sign of
incipient fertilisation   From this extreme degree of sterility we have
self fertilised hybrids producing a greater and greater number of seeds up
to perfect fertility 

The hybrids raised from two species which are very difficult to cross  and
which rarely produce any offspring  are generally very sterile  but the
parallelism between the difficulty of making a first cross  and the
sterility of the hybrids thus produced  two classes of facts which are
generally confounded together  is by no means strict   There are many
cases  in which two pure species  as in the genus Verbascum  can be united
with unusual facility  and produce numerous hybrid offspring  yet these
hybrids are remarkably sterile   On the other hand  there are species which
can be crossed very rarely  or with extreme difficulty  but the hybrids 
when at last produced  are very fertile   Even within the limits of the
same genus  for instance in Dianthus  these two opposite cases occur 

The fertility  both of first crosses and of hybrids  is more easily
affected by unfavourable conditions  than is that of pure species   But the
fertility of first crosses is likewise innately variable  for it is not
always the same in degree when the same two species are crossed under the
same circumstances  it depends in part upon the constitution of the
individuals which happen to have been chosen for the experiment   So it is
with hybrids  for their degree of fertility is often found to differ
greatly in the several individuals raised from seed out of the same capsule
and exposed to the same conditions 

By the term systematic affinity is meant  the general resemblance between
species in structure and constitution   Now the fertility of first crosses 
and of the hybrids produced from them  is largely governed by their
systematic affinity   This is clearly shown by hybrids never having been
raised between species ranked by systematists in distinct families  and on
the other hand  by very closely allied species generally uniting with
facility   But the correspondence between systematic affinity and the
facility of crossing is by no means strict   A multitude of cases could be
given of very closely allied species which will not unite  or only with
extreme difficulty  and on the other hand of very distinct species which
unite with the utmost facility   In the same family there may be a genus 
as Dianthus  in which very many species can most readily be crossed  and
another genus  as Silene  in which the most persevering efforts have failed
to produce between extremely close species a single hybrid   Even within
the limits of the same genus  we meet with this same difference  for
instance  the many species of Nicotiana have been more largely crossed than
the species of almost any other genus  but Gartner found that N  acuminata 
which is not a particularly distinct species  obstinately failed to
fertilise  or to be fertilised  by no less than eight other species of
Nicotiana   Many analogous facts could be given 

No one has been able to point out what kind or what amount of difference 
in any recognisable character  is sufficient to prevent two species
crossing   It can be shown that plants most widely different in habit and
general appearance  and having strongly marked differences in every part of
the flower  even in the pollen  in the fruit  and in the cotyledons  can be
crossed   Annual and perennial plants  deciduous and evergreen trees 
plants inhabiting different stations and fitted for extremely different
climates  can often be crossed with ease 

By a reciprocal cross between two species  I mean the case  for instance 
of a female ass being first crossed by a stallion  and then a mare by a
male ass   these two species may then be said to have been reciprocally
crossed   There is often the widest possible difference in the facility of
making reciprocal crosses   Such cases are highly important  for they prove
that the capacity in any two species to cross is often completely
independent of their systematic affinity  that is of any difference in
their structure or constitution  excepting in their reproductive systems  
The diversity of the result in reciprocal crosses between the same two
species was long ago observed by Kolreuter   To give an instance  
Mirabilis jalapa can easily be fertilised by the pollen of M  longiflora 
and the hybrids thus produced are sufficiently fertile  but Kolreuter tried
more than two hundred times  during eight following years  to fertilise
reciprocally M  longiflora with the pollen of M  jalapa  and utterly
failed   Several other equally striking cases could be given   Thuret has
observed the same fact with certain sea weeds or Fuci   Gartner  moreover 
found that this difference of facility in making reciprocal crosses is
extremely common in a lesser degree   He has observed it even between
closely related forms  as Matthiola annua and glabra  which many botanists
rank only as varieties   It is also a remarkable fact that hybrids raised
from reciprocal crosses  though of course compounded of the very same two
species  the one species having first been used as the father and then as
the mother  though they rarely differ in external characters  yet generally
differ in fertility in a small  and occasionally in a high degree 

Several other singular rules could be given from Gartner   for instance 
some species have a remarkable power of crossing with other species  other
species of the same genus have a remarkable power of impressing their
likeness on their hybrid offspring  but these two powers do not at all
necessarily go together   There are certain hybrids which  instead of
having  as is usual  an intermediate character between their two parents 
always closely resemble one of them  and such hybrids  though externally so
like one of their pure parent species  are with rare exceptions extremely
sterile   So again among hybrids which are usually intermediate in
structure between their parents  exceptional and abnormal individuals
sometimes are born  which closely resemble one of their pure parents  and
these hybrids are almost always utterly sterile  even when the other
hybrids raised from seed from the same capsule have a considerable degree
of fertility   These facts show how completely the fertility of a hybrid
may be independent of its external resemblance to either pure parent 

Considering the several rules now given  which govern the fertility of
first crosses and of hybrids  we see that when forms  which must be
considered as good and distinct species  are united  their fertility
graduates from zero to perfect fertility  or even to fertility under
certain conditions in excess  that their fertility  besides being eminently
susceptible to favourable and unfavourable conditions  is innately
variable  that it is by no means always the same in degree in the first
cross and in the hybrids produced from this cross  that the fertility of
hybrids is not related to the degree in which they resemble in external
appearance either parent  and lastly  that the facility of making a first
cross between any two species is not always governed by their systematic
affinity or degree of resemblance to each other   This latter statement is
clearly proved by the difference in the result of reciprocal crosses
between the same two species  for  according as the one species or the
other is used as the father or the mother  there is generally some
difference  and occasionally the widest possible difference  in the
facility of effecting an union   The hybrids  moreover  produced from
reciprocal crosses often differ in fertility 

Now do these complex and singular rules indicate that species have been
endowed with sterility simply to prevent their becoming confounded in
nature   I think not   For why should the sterility be so extremely
different in degree  when various species are crossed  all of which we must
suppose it would be equally important to keep from blending together   Why
should the degree of sterility be innately variable in the individuals of
the same species   Why should some species cross with facility and yet
produce very sterile hybrids  and other species cross with extreme
difficulty  and yet produce fairly fertile hybrids   Why should there often
be so great a difference in the result of a reciprocal cross between the
same two species   Why  it may even be asked  has the production of hybrids
been permitted   To grant to species the special power of producing
hybrids  and then to stop their further propagation by different degrees of
sterility  not strictly related to the facility of the first union between
their parents  seems a strange arrangement 

The foregoing rules and facts  on the other hand  appear to me clearly to
indicate that the sterility  both of first crosses and of hybrids  is
simply incidental or dependent on unknown differences in their reproductive
systems  the differences being of so peculiar and limited a nature  that 
in reciprocal crosses between the same two species  the male sexual element
of the one will often freely act on the female sexual element of the other 
but not in a reversed direction   It will be advisable to explain a little
more fully  by an example  what I mean by sterility being incidental on
other differences  and not a specially endowed quality   As the capacity of
one plant to be grafted or budded on another is unimportant for their
welfare in a state of nature  I presume that no one will suppose that this
capacity is a SPECIALLY endowed quality  but will admit that it is
incidental on differences in the laws of growth of the two plants   We can
sometimes see the reason why one tree will not take on another from
differences in their rate of growth  in the hardness of their wood  in the
period of the flow or nature of their sap  etc   but in a multitude of
cases we can assign no reason whatever   Great diversity in the size of two
plants  one being woody and the other herbaceous  one being evergreen and
the other deciduous  and adaptation to widely different climates  does not
always prevent the two grafting together   As in hybridisation  so with
grafting  the capacity is limited by systematic affinity  for no one has
been able to graft together trees belonging to quite distinct families 
and  on the other hand  closely allied species and varieties of the same
species  can usually  but not invariably  be grafted with ease   But this
capacity  as in hybridisation  is by no means absolutely governed by
systematic affinity   Although many distinct genera within the same family
have been grafted together  in other cases species of the same genus will
not take on each other   The pear can be grafted far more readily on the
quince  which is ranked as a distinct genus  than on the apple  which is a
member of the same genus   Even different varieties of the pear take with
different degrees of facility on the quince  so do different varieties of
the apricot and peach on certain varieties of the plum 

As Gartner found that there was sometimes an innate difference in different
INDIVIDUALS of the same two species in crossing  so Sagaret believes this
to be the case with different individuals of the same two species in being
grafted together   As in reciprocal crosses  the facility of effecting an
union is often very far from equal  so it sometimes is in grafting   The
common gooseberry  for instance  cannot be grafted on the currant  whereas
the currant will take  though with difficulty  on the gooseberry 

We have seen that the sterility of hybrids which have their reproductive
organs in an imperfect condition  is a different case from the difficulty
of uniting two pure species  which have their reproductive organs perfect 
yet these two distinct classes of cases run to a large extent parallel  
Something analogous occurs in grafting  for Thouin found that three species
of Robinia  which seeded freely on their own roots  and which could be
grafted with no great difficulty on a fourth species  when thus grafted
were rendered barren   On the other hand  certain species of Sorbus  when
grafted on other species  yielded twice as much fruit as when on their own
roots   We are reminded by this latter fact of the extraordinary cases of
Hippeastrum  Passiflora  etc   which seed much more freely when fertilised
with the pollen of a distinct species than when fertilised with pollen from
the same plant 

We thus see that  although there is a clear and great difference between
the mere adhesion of grafted stocks and the union of the male and female
elements in the act of reproduction  yet that there is a rude degree of
parallelism in the results of grafting and of crossing distinct species  
And as we must look at the curious and complex laws governing the facility
with which trees can be grafted on each other as incidental on unknown
differences in their vegetative systems  so I believe that the still more
complex laws governing the facility of first crosses are incidental on
unknown differences in their reproductive systems   These differences in
both cases follow  to a certain extent  as might have been expected 
systematic affinity  by which term every kind of resemblance and
dissimilarity between organic beings is attempted to be expressed   The
facts by no means seem to indicate that the greater or lesser difficulty of
either grafting or crossing various species has been a special endowment 
although in the case of crossing  the difficulty is as important for the
endurance and stability of specific forms as in the case of grafting it is
unimportant for their welfare 

ORIGIN AND CAUSES OF THE STERILITY OF FIRST CROSSES AND OF HYBRIDS 

At one time it appeared to me probable  as it has to others  that the
sterility of first crosses and of hybrids might have been slowly acquired
through the natural selection of slightly lessened degrees of fertility 
which  like any other variation  spontaneously appeared in certain
individuals of one variety when crossed with those of another variety   For
it would clearly be advantageous to two varieties or incipient species if
they could be kept from blending  on the same principle that  when man is
selecting at the same time two varieties  it is necessary that he should
keep them separate   In the first place  it may be remarked that species
inhabiting distinct regions are often sterile when crossed  now it could
clearly have been of no advantage to such separated species to have been
rendered mutually sterile  and consequently this could not have been
effected through natural selection  but it may perhaps be argued  that  if
a species was rendered sterile with some one compatriot  sterility with
other species would follow as a necessary contingency   In the second
place  it is almost as much opposed to the theory of natural selection as
to that of special creation  that in reciprocal crosses the male element of
one form should have been rendered utterly impotent on a second form  while
at the same time the male element of this second form is enabled freely to
fertilise the first form  for this peculiar state of the reproductive
system could hardly have been advantageous to either species 

In considering the probability of natural selection having come into
action  in rendering species mutually sterile  the greatest difficulty will
be found to lie in the existence of many graduated steps  from slightly
lessened fertility to absolute sterility   It may be admitted that it would
profit an incipient species  if it were rendered in some slight degree
sterile when crossed with its parent form or with some other variety  for
thus fewer bastardised and deteriorated offspring would be produced to
commingle their blood with the new species in process of formation   But he
who will take the trouble to reflect on the steps by which this first
degree of sterility could be increased through natural selection to that
high degree which is common with so many species  and which is universal
with species which have been differentiated to a generic or family rank 
will find the subject extraordinarily complex   After mature reflection  it
seems to me that this could not have been effected through natural
selection   Take the case of any two species which  when crossed  produced
few and sterile offspring  now  what is there which could favour the
survival of those individuals which happened to be endowed in a slightly
higher degree with mutual infertility  and which thus approached by one
small step towards absolute sterility   Yet an advance of this kind  if the
theory of natural selection be brought to bear  must have incessantly
occurred with many species  for a multitude are mutually quite barren  
With sterile neuter insects we have reason to believe that modifications in
their structure and fertility have been slowly accumulated by natural
selection  from an advantage having been thus indirectly given to the
community to which they belonged over other communities of the same
species  but an individual animal not belonging to a social community  if
rendered slightly sterile when crossed with some other variety  would not
thus itself gain any advantage or indirectly give any advantage to the
other individuals of the same variety  thus leading to their preservation 

But it would be superfluous to discuss this question in detail   for with
plants we have conclusive evidence that the sterility of crossed species
must be due to some principle  quite independent of natural selection  
Both Gartner and Kolreuter have proved that in genera including numerous
species  a series can be formed from species which when crossed yield fewer
and fewer seeds  to species which never produce a single seed  but yet are
affected by the pollen of certain other species  for the germen swells   It
is here manifestly impossible to select the more sterile individuals  which
have already ceased to yield seeds  so that this acme of sterility  when
the germen alone is effected  cannot have been gained through selection 
and from the laws governing the various grades of sterility being so
uniform throughout the animal and vegetable kingdoms  we may infer that the
cause  whatever it may be  is the same or nearly the same in all cases 

We will now look a little closer at the probable nature of the differences
between species which induce sterility in first crosses and in hybrids   In
the case of first crosses  the greater or less difficulty in effecting a
union and in obtaining offspring apparently depends on several distinct
causes   There must sometimes be a physical impossibility in the male
element reaching the ovule  as would be the case with a plant having a
pistil too long for the pollen tubes to reach the ovarium   It has also
been observed that when the pollen of one species is placed on the stigma
of a distantly allied species  though the pollen tubes protrude  they do
not penetrate the stigmatic surface   Again  the male element may reach the
female element  but be incapable of causing an embryo to be developed  as
seems to have been the case with some of Thuret s experiments on Fuci   No
explanation can be given of these facts  any more than why certain trees
cannot be grafted on others   Lastly  an embryo may be developed  and then
perish at an early period   This latter alternative has not been
sufficiently attended to  but I believe  from observations communicated to
me by Mr  Hewitt  who has had great experience in hybridising pheasants and
fowls  that the early death of the embryo is a very frequent cause of
sterility in first crosses   Mr  Salter has recently given the results of
an examination of about 500 eggs produced from various crosses between
three species of Gallus and their hybrids  the majority of these eggs had
been fertilised  and in the majority of the fertilised eggs  the embryos
had either been partially developed and had then perished  or had become
nearly mature  but the young chickens had been unable to break through the
shell   Of the chickens which were born  more than four fifths died within
the first few days  or at latest weeks   without any obvious cause 
apparently from mere inability to live   so that from the 500 eggs only
twelve chickens were reared   With plants  hybridized embryos probably
often perish in a like manner  at least it is known that hybrids raised
from very distinct species are sometimes weak and dwarfed  and perish at an
early age  of which fact Max Wichura has recently given some striking cases
with hybrid willows   It may be here worth noticing that in some cases of
parthenogenesis  the embryos within the eggs of silk moths which had not
been fertilised  pass through their early stages of development and then
perish like the embryos produced by a cross between distinct species  
Until becoming acquainted with these facts  I was unwilling to believe in
the frequent early death of hybrid embryos  for hybrids  when once born 
are generally healthy and long lived  as we see in the case of the common
mule   Hybrids  however  are differently circumstanced before and after
birth   when born and living in a country where their two parents live 
they are generally placed under suitable conditions of life   But a hybrid
partakes of only half of the nature and constitution of its mother  it may
therefore  before birth  as long as it is nourished within its mother s
womb  or within the egg or seed produced by the mother  be exposed to
conditions in some degree unsuitable  and consequently be liable to perish
at an early period  more especially as all very young beings are eminently
sensitive to injurious or unnatural conditions of life   But after all  the
cause more probably lies in some imperfection in the original act of
impregnation  causing the embryo to be imperfectly developed  rather than
in the conditions to which it is subsequently exposed 

In regard to the sterility of hybrids  in which the sexual elements are
imperfectly developed  the case is somewhat different   I have more than
once alluded to a large body of facts showing that  when animals and plants
are removed from their natural conditions  they are extremely liable to
have their reproductive systems seriously affected   This  in fact  is the
great bar to the domestication of animals   Between the sterility thus
superinduced and that of hybrids  there are many points of similarity   In
both cases the sterility is independent of general health  and is often
accompanied by excess of size or great luxuriance   In both cases the
sterility occurs in various degrees  in both  the male element is the most
liable to be affected  but sometimes the female more than the male   In
both  the tendency goes to a certain extent with systematic affinity  for
whole groups of animals and plants are rendered impotent by the same
unnatural conditions  and whole groups of species tend to produce sterile
hybrids   On the other hand  one species in a group will sometimes resist
great changes of conditions with unimpaired fertility  and certain species
in a group will produce unusually fertile hybrids   No one can tell till he
tries  whether any particular animal will breed under confinement  or any
exotic plant seed freely under culture  nor can he tell till he tries 
whether any two species of a genus will produce more or less sterile
hybrids   Lastly  when organic beings are placed during several generations
under conditions not natural to them  they are extremely liable to vary 
which seems to be partly due to their reproductive systems having been
specially affected  though in a lesser degree than when sterility ensues  
So it is with hybrids  for their offspring in successive generations are
eminently liable to vary  as every experimentalist has observed 

Thus we see that when organic beings are placed under new and unnatural
conditions  and when hybrids are produced by the unnatural crossing of two
species  the reproductive system  independently of the general state of
health  is affected in a very similar manner   In the one case  the
conditions of life have been disturbed  though often in so slight a degree
as to be inappreciable by us  in the other case  or that of hybrids  the
external conditions have remained the same  but the organisation has been
disturbed by two distinct structures and constitutions  including of course
the reproductive systems  having been blended into one   For it is scarcely
possible that two organisations should be compounded into one  without some
disturbance occurring in the development  or periodical action  or mutual
relations of the different parts and organs one to another or to the
conditions of life   When hybrids are able to breed inter se  they transmit
to their offspring from generation to generation the same compounded
organisation  and hence we need not be surprised that their sterility 
though in some degree variable  does not diminish  it is even apt to
increase  this being generally the result  as before explained  of too
close interbreeding   The above view of the sterility of hybrids being
caused by two constitutions being compounded into one has been strongly
maintained by Max Wichura 

It must  however  be owned that we cannot understand  on the above or any
other view  several facts with respect to the sterility of hybrids  for
instance  the unequal fertility of hybrids produced from reciprocal
crosses  or the increased sterility in those hybrids which occasionally and
exceptionally resemble closely either pure parent   Nor do I pretend that
the foregoing remarks go to the root of the matter   no explanation is
offered why an organism  when placed under unnatural conditions  is
rendered sterile   All that I have attempted to show is  that in two cases 
in some respects allied  sterility is the common result  in the one case
from the conditions of life having been disturbed  in the other case from
the organisation having been disturbed by two organisations being
compounded into one 

A similar parallelism holds good with an allied yet very different class of
facts   It is an old and almost universal belief  founded on a considerable
body of evidence  which I have elsewhere given  that slight changes in the
conditions of life are beneficial to all living things   We see this acted
on by farmers and gardeners in their frequent exchanges of seed  tubers 
etc   from one soil or climate to another  and back again   During the
convalescence of animals  great benefit is derived from almost any change
in their habits of life   Again  both with plants and animals  there is the
clearest evidence that a cross between individuals of the same species 
which differ to a certain extent  gives vigour and fertility to the
offspring  and that close interbreeding continued during several
generations between the nearest relations  if these be kept under the same
conditions of life  almost always leads to decreased size  weakness  or
sterility 

Hence it seems that  on the one hand  slight changes in the conditions of
life benefit all organic beings  and on the other hand  that slight
crosses  that is  crosses between the males and females of the same
species  which have been subjected to slightly different conditions  or
which have slightly varied  give vigour and fertility to the offspring  
But  as we have seen  organic beings long habituated to certain uniform
conditions under a state of nature  when subjected  as under confinement 
to a considerable change in their conditions  very frequently are rendered
more or less sterile  and we know that a cross between two forms that have
become widely or specifically different  produce hybrids which are almost
always in some degree sterile   I am fully persuaded that this double
parallelism is by no means an accident or an illusion   He who is able to
explain why the elephant  and a multitude of other animals  are incapable
of breeding when kept under only partial confinement in their native
country  will be able to explain the primary cause of hybrids being so
generally sterile   He will at the same time be able to explain how it is
that the races of some of our domesticated animals  which have often been
subjected to new and not uniform conditions  are quite fertile together 
although they are descended from distinct species  which would probably
have been sterile if aboriginally crossed   The above two parallel series
of facts seem to be connected together by some common but unknown bond 
which is essentially related to the principle of life  this principle 
according to Mr  Herbert Spencer  being that life depends on  or consists
in  the incessant action and reaction of various forces  which  as
throughout nature  are always tending towards an equilibrium  and when this
tendency is slightly disturbed by any change  the vital forces gain in
power 

RECIPROCAL DIMORPHISM AND TRIMORPHISM 

This subject may be here briefly discussed  and will be found to throw some
light on hybridism   Several plants belonging to distinct orders present
two forms  which exist in about equal numbers and which differ in no
respect except in their reproductive organs  one form having a long pistil
with short stamens  the other a short pistil with long stamens  the two
having differently sized pollen grains   With trimorphic plants there are
three forms likewise differing in the lengths of their pistils and stamens 
in the size and colour of the pollen grains  and in some other respects 
and as in each of the three forms there are two sets of stamens  the three
forms possess altogether six sets of stamens and three kinds of pistils  
These organs are so proportioned in length to each other that half the
stamens in two of the forms stand on a level with the stigma of the third
form   Now I have shown  and the result has been confirmed by other
observers  that in order to obtain full fertility with these plants  it is
necessary that the stigma of the one form should be fertilised by pollen
taken from the stamens of corresponding height in another form   So that
with dimorphic species two unions  which may be called legitimate  are
fully fertile  and two  which may be called illegitimate  are more or less
infertile   With trimorphic species six unions are legitimate  or fully
fertile  and twelve are illegitimate  or more or less infertile 

The infertility which may be observed in various dimorphic and trimorphic
plants  when they are illegitimately fertilised  that is by pollen taken
from stamens not corresponding in height with the pistil  differs much in
degree  up to absolute and utter sterility  just in the same manner as
occurs in crossing distinct species   As the degree of sterility in the
latter case depends in an eminent degree on the conditions of life being
more or less favourable  so I have found it with illegitimate unions   It
is well known that if pollen of a distinct species be placed on the stigma
of a flower  and its own pollen be afterwards  even after a considerable
interval of time  placed on the same stigma  its action is so strongly
prepotent that it generally annihilates the effect of the foreign pollen 
so it is with the pollen of the several forms of the same species  for
legitimate pollen is strongly prepotent over illegitimate pollen  when both
are placed on the same stigma   I ascertained this by fertilising several
flowers  first illegitimately  and twenty four hours afterwards
legitimately  with pollen taken from a peculiarly coloured variety  and all
the seedlings were similarly coloured  this shows that the legitimate
pollen  though applied twenty four hours subsequently  had wholly destroyed
or prevented the action of the previously applied illegitimate pollen  
Again  as in making reciprocal crosses between the same two species  there
is occasionally a great difference in the result  so the same thing occurs
with trimorphic plants  for instance  the mid styled form of Lythrum
salicaria was illegitimately fertilised with the greatest ease by pollen
from the longer stamens of the short styled form  and yielded many seeds 
but the latter form did not yield a single seed when fertilised by the
longer stamens of the mid styled form 

In all these respects  and in others which might be added  the forms of the
same undoubted species  when illegitimately united  behave in exactly the
same manner as do two distinct species when crossed   This led me carefully
to observe during four years many seedlings  raised from several
illegitimate unions   The chief result is that these illegitimate plants 
as they may be called  are not fully fertile   It is possible to raise from
dimorphic species  both long styled and short styled illegitimate plants 
and from trimorphic plants all three illegitimate forms   These can then be
properly united in a legitimate manner   When this is done  there is no
apparent reason why they should not yield as many seeds as did their
parents when legitimately fertilised   But such is not the case   They are
all infertile  in various degrees  some being so utterly and incurably
sterile that they did not yield during four seasons a single seed or even
seed capsule   The sterility of these illegitimate plants  when united with
each other in a legitimate manner  may be strictly compared with that of
hybrids when crossed inter se   If  on the other hand  a hybrid is crossed
with either pure parent species  the sterility is usually much lessened  
and so it is when an illegitimate plant is fertilised by a legitimate
plant   In the same manner as the sterility of hybrids does not always run
parallel with the difficulty of making the first cross between the two
parent species  so that sterility of certain illegitimate plants was
unusually great  while the sterility of the union from which they were
derived was by no means great   With hybrids raised from the same seed 
capsule the degree of sterility is innately variable  so it is in a marked
manner with illegitimate plants   Lastly  many hybrids are profuse and
persistent flowerers  while other and more sterile hybrids produce few
flowers  and are weak  miserable dwarfs  exactly similar cases occur with
the illegitimate offspring of various dimorphic and trimorphic plants 

Altogether there is the closest identity in character and behaviour between
illegitimate plants and hybrids   It is hardly an exaggeration to maintain
that illegitimate plants are hybrids  produced within the limits of the
same species by the improper union of certain forms  while ordinary hybrids
are produced from an improper union between so called distinct species   We
have also already seen that there is the closest similarity in all respects
between first illegitimate unions and first crosses between distinct
species   This will perhaps be made more fully apparent by an illustration 
we may suppose that a botanist found two well marked varieties  and such
occur  of the long styled form of the trimorphic Lythrum salicaria  and
that he determined to try by crossing whether they were specifically
distinct   He would find that they yielded only about one fifth of the
proper number of seed  and that they behaved in all the other above
specified respects as if they had been two distinct species   But to make
the case sure  he would raise plants from his supposed hybridised seed  and
he would find that the seedlings were miserably dwarfed and utterly
sterile  and that they behaved in all other respects like ordinary hybrids  
He might then maintain that he had actually proved  in accordance with the
common view  that his two varieties were as good and as distinct species as
any in the world  but he would be completely mistaken 

The facts now given on dimorphic and trimorphic plants are important 
because they show us  first  that the physiological test of lessened
fertility  both in first crosses and in hybrids  is no safe criterion of
specific distinction  secondly  because we may conclude that there is some
unknown bond which connects the infertility of illegitimate unions with
that of their illegitimate offspring  and we are led to extend the same
view to first crosses and hybrids  thirdly  because we find  and this seems
to me of especial importance  that two or three forms of the same species
may exist and may differ in no respect whatever  either in structure or in
constitution  relatively to external conditions  and yet be sterile when
united in certain ways   For we must remember that it is the union of the
sexual elements of individuals of the same form  for instance  of two long 
styled forms  which results in sterility  while it is the union of the
sexual elements proper to two distinct forms which is fertile   Hence the
case appears at first sight exactly the reverse of what occurs  in the
ordinary unions of the individuals of the same species and with crosses
between distinct species   It is  however  doubtful whether this is really
so  but I will not enlarge on this obscure subject 

We may  however  infer as probable from the consideration of dimorphic and
trimorphic plants  that the sterility of distinct species when crossed and
of their hybrid progeny  depends exclusively on the nature of their sexual
elements  and not on any difference in their structure or general
constitution   We are also led to this same conclusion by considering
reciprocal crosses  in which the male of one species cannot be united  or
can be united with great difficulty  with the female of a second species 
while the converse cross can be effected with perfect facility   That
excellent observer  Gartner  likewise concluded that species when crossed
are sterile owing to differences confined to their reproductive systems 

FERTILITY OF VARIETIES WHEN CROSSED  AND OF THEIR MONGREL OFFSPRING  NOT
UNIVERSAL 

It may be urged as an overwhelming argument that there must be some
essential distinction between species and varieties inasmuch as the latter 
however much they may differ from each other in external appearance  cross
with perfect facility  and yield perfectly fertile offspring   With some
exceptions  presently to be given  I fully admit that this is the rule  
But the subject is surrounded by difficulties  for  looking to varieties
produced under nature  if two forms hitherto reputed to be varieties be
found in any degree sterile together  they are at once ranked by most
naturalists as species   For instance  the blue and red pimpernel  which
are considered by most botanists as varieties  are said by Gartner to be
quite sterile when crossed  and he consequently ranks them as undoubted
species   If we thus argue in a circle  the fertility of all varieties
produced under nature will assuredly have to be granted 

If we turn to varieties  produced  or supposed to have been produced  under
domestication  we are still involved in some doubt   For when it is stated 
for instance  that certain South American indigenous domestic dogs do not
readily unite with European dogs  the explanation which will occur to
everyone  and probably the true one  is that they are descended from
aboriginally distinct species   Nevertheless the perfect fertility of so
many domestic races  differing widely from each other in appearance  for
instance  those of the pigeon  or of the cabbage  is a remarkable fact 
more especially when we reflect how many species there are  which  though
resembling each other most closely  are utterly sterile when intercrossed  
Several considerations  however  render the fertility of domestic varieties
less remarkable   In the first place  it may be observed that the amount of
external difference between two species is no sure guide to their degree of
mutual sterility  so that similar differences in the case of varieties
would be no sure guide   It is certain that with species the cause lies
exclusively in differences in their sexual constitution   Now the varying
conditions to which domesticated animals and cultivated plants have been
subjected  have had so little tendency towards modifying the reproductive
system in a manner leading to mutual sterility  that we have good grounds
for admitting the directly opposite doctrine of Pallas  namely  that such
conditions generally eliminate this tendency  so that the domesticated
descendants of species  which in their natural state probably would have
been in some degree sterile when crossed  become perfectly fertile
together   With plants  so far is cultivation from giving a tendency
towards sterility between distinct species  that in several well 
authenticated cases already alluded to  certain plants have been affected
in an opposite manner  for they have become self impotent  while still
retaining the capacity of fertilising  and being fertilised by  other
species   If the Pallasian doctrine of the elimination of sterility through
long continued domestication be admitted  and it can hardly be rejected  it
becomes in the highest degree improbable that similar conditions long 
continued should likewise induce this tendency  though in certain cases 
with species having a peculiar constitution  sterility might occasionally
be thus caused   Thus  as I believe  we can understand why  with
domesticated animals  varieties have not been produced which are mutually
sterile  and why with plants only a few such cases  immediately to be
given  have been observed 

The real difficulty in our present subject is not  as it appears to me  why
domestic varieties have not become mutually infertile when crossed  but why
this has so generally occurred with natural varieties  as soon as they have
been permanently modified in a sufficient degree to take rank as species  
We are far from precisely knowing the cause  nor is this surprising  seeing
how profoundly ignorant we are in regard to the normal and abnormal action
of the reproductive system   But we can see that species  owing to their
struggle for existence with numerous competitors  will have been exposed
during long periods of time to more uniform conditions  than have domestic
varieties  and this may well make a wide difference in the result   For we
know how commonly wild animals and plants  when taken from their natural
conditions and subjected to captivity  are rendered sterile  and the
reproductive functions of organic beings which have always lived under
natural conditions would probably in like manner be eminently sensitive to
the influence of an unnatural cross   Domesticated productions  on the
other hand  which  as shown by the mere fact of their domestication  were
not originally highly sensitive to changes in their conditions of life  and
which can now generally resist with undiminished fertility repeated changes
of conditions  might be expected to produce varieties  which would be
little liable to have their reproductive powers injuriously affected by the
act of crossing with other varieties which had originated in a like manner 

I have as yet spoken as if the varieties of the same species were
invariably fertile when intercrossed   But it is impossible to resist the
evidence of the existence of a certain amount of sterility in the few
following cases  which I will briefly abstract   The evidence is at least
as good as that from which we believe in the sterility of a multitude of
species   The evidence is also derived from hostile witnesses  who in all
other cases consider fertility and sterility as safe criterions of specific
distinction   Gartner kept  during several years  a dwarf kind of maize
with yellow seeds  and a tall variety with red seeds growing near each
other in his garden  and although these plants have separated sexes  they
never naturally crossed   He then fertilised thirteen flowers of the one
kind with pollen of the other  but only a single head produced any seed 
and this one head produced only five grains   Manipulation in this case
could not have been injurious  as the plants have separated sexes   No one 
I believe  has suspected that these varieties of maize are distinct
species  and it is important to notice that the hybrid plants thus raised
were themselves PERFECTLY fertile  so that even Gartner did not venture to
consider the two varieties as specifically distinct 

Girou de Buzareingues crossed three varieties of gourd  which like the
maize has separated sexes  and he asserts that their mutual fertilisation
is by so much the less easy as their differences are greater   How far
these experiments may be trusted  I know not  but the forms experimented on
are ranked by Sagaret  who mainly founds his classification by the test of
infertility  as varieties  and Naudin has come to the same conclusion 

The following case is far more remarkable  and seems at first incredible 
but it is the result of an astonishing number of experiments made during
many years on nine species of Verbascum  by so good an observer and so
hostile a witness as Gartner   namely  that the yellow and white varieties
when crossed produce less seed than the similarly coloured varieties of the
same species   Moreover  he asserts that  when yellow and white varieties
of one species are crossed with yellow and white varieties of a DISTINCT
species  more seed is produced by the crosses between the similarly
coloured flowers  than between those which are differently coloured   Mr 
Scott also has experimented on the species and varieties of Verbascum  and
although unable to confirm Gartner s results on the crossing of the
distinct species  he finds that the dissimilarly coloured varieties of the
same species yield fewer seeds  in the proportion of eighty six to 100 
than the similarly coloured varieties   Yet these varieties differ in no
respect  except in the colour of their flowers  and one variety can
sometimes be raised from the seed of another 

Kolreuter  whose accuracy has been confirmed by every subsequent observer 
has proved the remarkable fact that one particular variety of the common
tobacco was more fertile than the other varieties  when crossed with a
widely distinct species   He experimented on five forms which are commonly
reputed to be varieties  and which he tested by the severest trial  namely 
by reciprocal crosses  and he found their mongrel offspring perfectly
fertile   But one of these five varieties  when used either as the father
or mother  and crossed with the Nicotiana glutinosa  always yielded hybrids
not so sterile as those which were produced from the four other varieties
when crossed with N  glutinosa   Hence the reproductive system of this one
variety must have been in some manner and in some degree modified 

 From these facts it can no longer be maintained that varieties when crossed
are invariably quite fertile   From the great difficulty of ascertaining
the infertility of varieties in a state of nature  for a supposed variety 
if proved to be infertile in any degree  would almost universally be ranked
as a species  from man attending only to external characters in his
domestic varieties  and from such varieties not having been exposed for
very long periods to uniform conditions of life  from these several
considerations we may conclude that fertility does not constitute a
fundamental distinction between varieties and species when crossed   The
general sterility of crossed species may safely be looked at  not as a
special acquirement or endowment  but as incidental on changes of an
unknown nature in their sexual elements 

HYBRIDS AND MONGRELS COMPARED  INDEPENDENTLY OF THEIR FERTILITY 

Independently of the question of fertility  the offspring of species and of
varieties when crossed may be compared in several other respects   Gartner 
whose strong wish it was to draw a distinct line between species and
varieties  could find very few  and  as it seems to me  quite unimportant
differences between the so called hybrid offspring of species  and the
so called mongrel offspring of varieties   And  on the other hand  they
agree most closely in many important respects 

I shall here discuss this subject with extreme brevity   The most important
distinction is  that in the first generation mongrels are more variable
than hybrids  but Gartner admits that hybrids from species which have long
been cultivated are often variable in the first generation  and I have
myself seen striking instances of this fact   Gartner further admits that
hybrids between very closely allied species are more variable than those
from very distinct species  and this shows that the difference in the
degree of variability graduates away   When mongrels and the more fertile
hybrids are propagated for several generations  an extreme amount of
variability in the offspring in both cases is notorious  but some few
instances of both hybrids and mongrels long retaining a uniform character
could be given   The variability  however  in the successive generations of
mongrels is  perhaps  greater than in hybrids 

This greater variability in mongrels than in hybrids does not seem at all
surprising   For the parents of mongrels are varieties  and mostly domestic
varieties  very few experiments having been tried on natural varieties  
and this implies that there has been recent variability  which would often
continue and would augment that arising from the act of crossing   The
slight variability of hybrids in the first generation  in contrast with
that in the succeeding generations  is a curious fact and deserves
attention   For it bears on the view which I have taken of one of the
causes of ordinary variability  namely  that the reproductive system  from
being eminently sensitive to changed conditions of life  fails under these
circumstances to perform its proper function of producing offspring closely
similar in all respects to the parent form   Now  hybrids in the first
generation are descended from species  excluding those long cultivated 
which have not had their reproductive systems in any way affected  and they
are not variable  but hybrids themselves have their reproductive systems
seriously affected  and their descendants are highly variable 

But to return to our comparison of mongrels and hybrids   Gartner states
that mongrels are more liable than hybrids to revert to either parent form 
but this  if it be true  is certainly only a difference in degree  
Moreover  Gartner expressly states that the hybrids from long cultivated
plants are more subject to reversion than hybrids from species in their
natural state  and this probably explains the singular difference in the
results arrived at by different observers   Thus Max Wichura doubts whether
hybrids ever revert to their parent forms  and he experimented on
uncultivated species of willows  while Naudin  on the other hand  insists
in the strongest terms on the almost universal tendency to reversion in
hybrids  and he experimented chiefly on cultivated plants   Gartner further
states that when any two species  although most closely allied to each
other  are crossed with a third species  the hybrids are widely different
from each other  whereas if two very distinct varieties of one species are
crossed with another species  the hybrids do not differ much   But this
conclusion  as far as I can make out  is founded on a single experiment 
and seems directly opposed to the results of several experiments made by
Kolreuter 

Such alone are the unimportant differences which Gartner is able to point
out between hybrid and mongrel plants   On the other hand  the degrees and
kinds of resemblance in mongrels and in hybrids to their respective
parents  more especially in hybrids produced from nearly related species 
follow  according to Gartner the same laws   When two species are crossed 
one has sometimes a prepotent power of impressing its likeness on the
hybrid   So I believe it to be with varieties of plants  and with animals 
one variety certainly often has this prepotent power over another variety  
Hybrid plants produced from a reciprocal cross generally resemble each
other closely  and so it is with mongrel plants from a reciprocal cross  
Both hybrids and mongrels can be reduced to either pure parent form  by
repeated crosses in successive generations with either parent 

These several remarks are apparently applicable to animals  but the subject
is here much complicated  partly owing to the existence of secondary sexual
characters  but more especially owing to prepotency in transmitting
likeness running more strongly in one sex than in the other  both when one
species is crossed with another and when one variety is crossed with
another variety   For instance  I think those authors are right who
maintain that the ass has a prepotent power over the horse  so that both
the mule and the hinny resemble more closely the ass than the horse  but
that the prepotency runs more strongly in the male than in the female ass 
so that the mule  which is an offspring of the male ass and mare  is more
like an ass than is the hinny  which is the offspring of the female ass and
stallion 

Much stress has been laid by some authors on the supposed fact  that it is
only with mongrels that the offspring are not intermediate in character 
but closely resemble one of their parents  but this does sometimes occur
with hybrids  yet I grant much less frequently than with mongrels   Looking
to the cases which I have collected of cross bred animals closely
resembling one parent  the resemblances seem chiefly confined to characters
almost monstrous in their nature  and which have suddenly appeared  such as
albinism  melanism  deficiency of tail or horns  or additional fingers and
toes  and do not relate to characters which have been slowly acquired
through selection   A tendency to sudden reversions to the perfect
character of either parent would  also  be much more likely to occur with
mongrels  which are descended from varieties often suddenly produced and
semi monstrous in character  than with hybrids  which are descended from
species slowly and naturally produced   On the whole  I entirely agree with
Dr  Prosper Lucas  who  after arranging an enormous body of facts with
respect to animals  comes to the conclusion that the laws of resemblance of
the child to its parents are the same  whether the two parents differ
little or much from each other  namely  in the union of individuals of the
same variety  or of different varieties  or of distinct species 

Independently of the question of fertility and sterility  in all other
respects there seems to be a general and close similarity in the offspring
of crossed species  and of crossed varieties   If we look at species as
having been specially created  and at varieties as having been produced by
secondary laws  this similarity would be an astonishing fact   But it
harmonises perfectly with the view that there is no essential distinction
between species and varieties 

SUMMARY OF CHAPTER 

First crosses between forms  sufficiently distinct to be ranked as species 
and their hybrids  are very generally  but not universally  sterile   The
sterility is of all degrees  and is often so slight that the most careful
experimentalists have arrived at diametrically opposite conclusions in
ranking forms by this test   The sterility is innately variable in
individuals of the same species  and is eminently susceptible to action of
favourable and unfavourable conditions   The degree of sterility does not
strictly follow systematic affinity  but is governed by several curious and
complex laws   It is generally different  and sometimes widely different in
reciprocal crosses between the same two species   It is not always equal in
degree in a first cross and in the hybrids produced from this cross 

In the same manner as in grafting trees  the capacity in one species or
variety to take on another  is incidental on differences  generally of an
unknown nature  in their vegetative systems  so in crossing  the greater or
less facility of one species to unite with another is incidental on unknown
differences in their reproductive systems   There is no more reason to
think that species have been specially endowed with various degrees of
sterility to prevent their crossing and blending in nature  than to think
that trees have been specially endowed with various and somewhat analogous
degrees of difficulty in being grafted together in order to prevent their
inarching in our forests 

The sterility of first crosses and of their hybrid progeny has not been
acquired through natural selection   In the case of first crosses it seems
to depend on several circumstances  in some instances in chief part on the
early death of the embryo   In the case of hybrids  it apparently depends
on their whole organisation having been disturbed by being compounded from
two distinct forms  the sterility being closely allied to that which so
frequently affects pure species  when exposed to new and unnatural
conditions of life   He who will explain these latter cases will be able to
explain the sterility of hybrids   This view is strongly supported by a
parallelism of another kind   namely  that  firstly  slight changes in the
conditions of life add to the vigour and fertility of all organic beings 
and secondly  that the crossing of forms  which have been exposed to
slightly different conditions of life  or which have varied  favours the
size  vigour and fertility of their offspring   The facts given on the
sterility of the illegitimate unions of dimorphic and trimorphic plants and
of their illegitimate progeny  perhaps render it probable that some unknown
bond in all cases connects the degree of fertility of first unions with
that of their offspring   The consideration of these facts on dimorphism 
as well as of the results of reciprocal crosses  clearly leads to the
conclusion that the primary cause of the sterility of crossed species is
confined to differences in their sexual elements   But why  in the case of
distinct species  the sexual elements should so generally have become more
or less modified  leading to their mutual infertility  we do not know  but
it seems to stand in some close relation to species having been exposed for
long periods of time to nearly uniform conditions of life 

It is not surprising that the difficulty in crossing any two species  and
the sterility of their hybrid offspring  should in most cases correspond 
even if due to distinct causes   for both depend on the amount of
difference between the species which are crossed   Nor is it surprising
that the facility of effecting a first cross  and the fertility of the
hybrids thus produced  and the capacity of being grafted together  though
this latter capacity evidently depends on widely different
circumstances  should all run  to a certain extent  parallel with the
systematic affinity of the forms subjected to experiment  for systematic
affinity includes resemblances of all kinds 

First crosses between forms known to be varieties  or sufficiently alike to
be considered as varieties  and their mongrel offspring  are very
generally  but not  as is so often stated  invariably fertile   Nor is this
almost universal and perfect fertility surprising  when it is remembered
how liable we are to argue in a circle with respect to varieties in a state
of nature  and when we remember that the greater number of varieties have
been produced under domestication by the selection of mere external
differences  and that they have not been long exposed to uniform conditions
of life   It should also be especially kept in mind  that long continued
domestication tends to eliminate sterility  and is therefore little likely
to induce this same quality   Independently of the question of fertility 
in all other respects there is the closest general resemblance between
hybrids and mongrels  in their variability  in their power of absorbing
each other by repeated crosses  and in their inheritance of characters from
both parent forms   Finally  then  although we are as ignorant of the
precise cause of the sterility of first crosses and of hybrids as we are
why animals and plants removed from their natural conditions become
sterile  yet the facts given in this chapter do not seem to me opposed to
the belief that species aboriginally existed as varieties 

 
CHAPTER X 

ON THE IMPERFECTION OF THE GEOLOGICAL RECORD 

On the absence of intermediate varieties at the present day    On the
nature of extinct intermediate varieties  on their number    On the lapse
of time  as inferred from the rate of denudation and of deposition number
   On the lapse of time as estimated by years    On the poorness of our
palaeontological collections    On the intermittence of geological
formations    On the denudation of granitic areas    On the absence of
intermediate varieties in any one formation    On the sudden appearance of
groups of species    On their sudden appearance in the lowest known
fossiliferous strata    Antiquity of the habitable earth 

In the sixth chapter I enumerated the chief objections which might be
justly urged against the views maintained in this volume   Most of them
have now been discussed   One  namely  the distinctness of specific forms
and their not being blended together by innumerable transitional links  is
a very obvious difficulty   I assigned reasons why such links do not
commonly occur at the present day under the circumstances apparently most
favourable for their presence  namely  on an extensive and continuous area
with graduated physical conditions   I endeavoured to show  that the life
of each species depends in a more important manner on the presence of other
already defined organic forms  than on climate  and  therefore  that the
really governing conditions of life do not graduate away quite insensibly
like heat or moisture   I endeavoured  also  to show that intermediate
varieties  from existing in lesser numbers than the forms which they
connect  will generally be beaten out and exterminated during the course of
further modification and improvement   The main cause  however  of
innumerable intermediate links not now occurring everywhere throughout
nature depends  on the very process of natural selection  through which new
varieties continually take the places of and supplant their parent forms  
But just in proportion as this process of extermination has acted on an
enormous scale  so must the number of intermediate varieties  which have
formerly existed  be truly enormous   Why then is not every geological
formation and every stratum full of such intermediate links   Geology
assuredly does not reveal any such finely graduated organic chain  and
this  perhaps  is the most obvious and serious objection which can be urged
against my theory   The explanation lies  as I believe  in the extreme
imperfection of the geological record 

In the first place  it should always be borne in mind what sort of
intermediate forms must  on the theory  have formerly existed   I have
found it difficult  when looking at any two species  to avoid picturing to
myself forms DIRECTLY intermediate between them   But this is a wholly
false view  we should always look for forms intermediate between each
species and a common but unknown progenitor  and the progenitor will
generally have differed in some respects from all its modified descendants  
To give a simple illustration   the fantail and pouter pigeons are both
descended from the rock pigeon  if we possessed all the intermediate
varieties which have ever existed  we should have an extremely close series
between both and the rock pigeon  but we should have no varieties directly
intermediate between the fantail and pouter  none  for instance  combining
a tail somewhat expanded with a crop somewhat enlarged  the characteristic
features of these two breeds   These two breeds  moreover  have become so
much modified  that  if we had no historical or indirect evidence regarding
their origin  it would not have been possible to have determined from a
mere comparison of their structure with that of the rock pigeon  C  livia 
whether they had descended from this species or from some other allied
species  such as C  oenas 

So with natural species  if we look to forms very distinct  for instance to
the horse and tapir  we have no reason to suppose that links directly
intermediate between them ever existed  but between each and an unknown
common parent   The common parent will have had in its whole organisation
much general resemblance to the tapir and to the horse  but in some points
of structure may have differed considerably from both  even perhaps more
than they differ from each other   Hence  in all such cases  we should be
unable to recognise the parent form of any two or more species  even if we
closely compared the structure of the parent with that of its modified
descendants  unless at the same time we had a nearly perfect chain of the
intermediate links 

It is just possible  by the theory  that one of two living forms might have
descended from the other  for instance  a horse from a tapir  and in this
case DIRECT intermediate links will have existed between them   But such a
case would imply that one form had remained for a very long period
unaltered  whilst its descendants had undergone a vast amount of change 
and the principle of competition between organism and organism  between
child and parent  will render this a very rare event  for in all cases the
new and improved forms of life tend to supplant the old and unimproved
forms 

By the theory of natural selection all living species have been connected
with the parent species of each genus  by differences not greater than we
see between the natural and domestic varieties of the same species at the
present day  and these parent species  now generally extinct  have in their
turn been similarly connected with more ancient forms  and so on backwards 
always converging to the common ancestor of each great class   So that the
number of intermediate and transitional links  between all living and
extinct species  must have been inconceivably great   But assuredly  if
this theory be true  such have lived upon the earth 

ON THE LAPSE OF TIME  AS INFERRED FROM THE RATE OF DEPOSITION AND EXTENT OF
DENUDATION 

Independently of our not finding fossil remains of such infinitely numerous
connecting links  it may be objected that time cannot have sufficed for so
great an amount of organic change  all changes having been effected slowly  
It is hardly possible for me to recall to the reader who is not a practical
geologist  the facts leading the mind feebly to comprehend the lapse of
time   He who can read Sir Charles Lyell s grand work on the Principles of
Geology  which the future historian will recognise as having produced a
revolution in natural science  and yet does not admit how vast have been
the past periods of time  may at once close this volume   Not that it
suffices to study the Principles of Geology  or to read special treatises
by different observers on separate formations  and to mark how each author
attempts to give an inadequate idea of the duration of each formation  or
even of each stratum   We can best gain some idea of past time by knowing
the agencies at work  and learning how deeply the surface of the land has
been denuded  and how much sediment has been deposited   As Lyell has well
remarked  the extent and thickness of our sedimentary formations are the
result and the measure of the denudation which the earth s crust has
elsewhere undergone   Therefore a man should examine for himself the great
piles of superimposed strata  and watch the rivulets bringing down mud  and
the waves wearing away the sea cliffs  in order to comprehend something
about the duration of past time  the monuments of which we see all around
us 

It is good to wander along the coast  when formed of moderately hard rocks 
and mark the process of degradation   The tides in most cases reach the
cliffs only for a short time twice a day  and the waves eat into them only
when they are charged with sand or pebbles  for there is good evidence that
pure water effects nothing in wearing away rock   At last the base of the
cliff is undermined  huge fragments fall down  and these remaining fixed 
have to be worn away atom by atom  until after being reduced in size they
can be rolled about by the waves  and then they are more quickly ground
into pebbles  sand  or mud   But how often do we see along the bases of
retreating cliffs rounded boulders  all thickly clothed by marine
productions  showing how little they are abraded and how seldom they are
rolled about   Moreover  if we follow for a few miles any line of rocky
cliff  which is undergoing degradation  we find that it is only here and
there  along a short length or round a promontory  that the cliffs are at
the present time suffering   The appearance of the surface and the
vegetation show that elsewhere years have elapsed since the waters washed
their base 

We have  however  recently learned from the observations of Ramsay  in the
van of many excellent observers  of Jukes  Geikie  Croll and others  that
subaerial degradation is a much more important agency than coast action  or
the power of the waves   The whole surface of the land is exposed to the
chemical action of the air and of the rainwater  with its dissolved
carbonic acid  and in colder countries to frost  the disintegrated matter
is carried down even gentle slopes during heavy rain  and to a greater
extent than might be supposed  especially in arid districts  by the wind 
it is then transported by the streams and rivers  which  when rapid deepen
their channels  and triturate the fragments   On a rainy day  even in a
gently undulating country  we see the effects of subaerial degradation in
the muddy rills which flow down every slope   Messrs  Ramsay and Whitaker
have shown  and the observation is a most striking one  that the great
lines of escarpment in the Wealden district and those ranging across
England  which formerly were looked at as ancient sea coasts  cannot have
been thus formed  for each line is composed of one and the same formation 
while our sea cliffs are everywhere formed by the intersection of various
formations   This being the case  we are compelled to admit that the
escarpments owe their origin in chief part to the rocks of which they are
composed  having resisted subaerial denudation better than the surrounding
surface  this surface consequently has been gradually lowered  with the
lines of harder rock left projecting   Nothing impresses the mind with the
vast duration of time  according to our ideas of time  more forcibly than
the conviction thus gained that subaerial agencies  which apparently have
so little power  and which seem to work so slowly  have produced great
results 

When thus impressed with the slow rate at which the land is worn away
through subaerial and littoral action  it is good  in order to appreciate
the past duration of time  to consider  on the one hand  the masses of rock
which have been removed over many extensive areas  and on the other hand
the thickness of our sedimentary formations   I remember having been much
struck when viewing volcanic islands  which have been worn by the waves and
pared all round into perpendicular cliffs of one or two thousand feet in
height  for the gentle slope of the lava streams  due to their formerly
liquid state  showed at a glance how far the hard  rocky beds had once
extended into the open ocean   The same story is told still more plainly by
faults  those great cracks along which the strata have been upheaved on one
side  or thrown down on the other  to the height or depth of thousands of
feet  for since the crust cracked  and it makes no great difference whether
the upheaval was sudden  or  as most geologists now believe  was slow and
effected by many starts  the surface of the land has been so completely
planed down that no trace of these vast dislocations is externally visible 
The Craven fault  for instance  extends for upward of thirty miles  and
along this line the vertical displacement of the strata varies from 600 to
3 000 feet   Professor Ramsay has published an account of a downthrow in
Anglesea of 2 300 feet  and he informs me that he fully believes that there
is one in Merionethshire of 12 000 feet  yet in these cases there is
nothing on the surface of the land to show such prodigious movements  the
pile of rocks on either side of the crack having been smoothly swept away 

On the other hand  in all parts of the world the piles of sedimentary
strata are of wonderful thickness   In the Cordillera  I estimated one mass
of conglomerate at ten thousand feet  and although conglomerates have
probably been accumulated at a quicker rate than finer sediments  yet from
being formed of worn and rounded pebbles  each of which bears the stamp of
time  they are good to show how slowly the mass must have been heaped
together   Professor Ramsay has given me the maximum thickness  from actual
measurement in most cases  of the successive formations in DIFFERENT parts
of Great Britain  and this is the result 
                                                 Feet
Palaeozoic strata  not including igneous beds   57 154
Secondary strata                                13 190
Tertiary strata                                  2 240

  making altogether 72 584 feet  that is  very nearly thirteen and
three quarters British miles   Some of these formations  which are
represented in England by thin beds  are thousands of feet in thickness on
the Continent   Moreover  between each successive formation we have  in the
opinion of most geologists  blank periods of enormous length   So that the
lofty pile of sedimentary rocks in Britain gives but an inadequate idea of
the time which has elapsed during their accumulation   The consideration of
these various facts impresses the mind almost in the same manner as does
the vain endeavour to grapple with the idea of eternity 

Nevertheless this impression is partly false   Mr  Croll  in an interesting
paper  remarks that we do not err  in forming too great a conception of the
length of geological periods   but in estimating them by years   When
geologists look at large and complicated phenomena  and then at the figures
representing several million years  the two produce a totally different
effect on the mind  and the figures are at once pronounced too small   In
regard to subaerial denudation  Mr  Croll shows  by calculating the known
amount of sediment annually brought down by certain rivers  relatively to
their areas of drainage  that 1 000 feet of solid rock  as it became
gradually disintegrated  would thus be removed from the mean level of the
whole area in the course of six million years   This seems an astonishing
result  and some considerations lead to the suspicion that it may be too
large  but if halved or quartered it is still very surprising   Few of us 
however  know what a million really means   Mr  Croll gives the following
illustration   Take a narrow strip of paper  eighty three feet four inches
in length  and stretch it along the wall of a large hall  then mark off at
one end the tenth of an inch   This tenth of an inch will represent one
hundred years  and the entire strip a million years   But let it be borne
in mind  in relation to the subject of this work  what a hundred years
implies  represented as it is by a measure utterly insignificant in a hall
of the above dimensions   Several eminent breeders  during a single
lifetime  have so largely modified some of the higher animals  which
propagate their kind much more slowly than most of the lower animals  that
they have formed what well deserves to be called a new sub breed   Few men
have attended with due care to any one strain for more than half a century 
so that a hundred years represents the work of two breeders in succession  
It is not to be supposed that species in a state of nature ever change so
quickly as domestic animals under the guidance of methodical selection  
The comparison would be in every way fairer with the effects which follow
from unconscious selection  that is  the preservation of the most useful or
beautiful animals  with no intention of modifying the breed  but by this
process of unconscious selection  various breeds have been sensibly changed
in the course of two or three centuries 

Species  however  probably change much more slowly  and within the same
country only a few change at the same time   This slowness follows from all
the inhabitants of the same country being already so well adapted to each
other  that new places in the polity of nature do not occur until after
long intervals  due to the occurrence of physical changes of some kind  or
through the immigration of new forms   Moreover  variations or individual
differences of the right nature  by which some of the inhabitants might be
better fitted to their new places under the altered circumstance  would not
always occur at once   Unfortunately we have no means of determining 
according to the standard of years  how long a period it takes to modify a
species  but to the subject of time we must return 

ON THE POORNESS OF PALAEONTOLOGICAL COLLECTIONS 

Now let us turn to our richest museums  and what a paltry display we
behold    That our collections are imperfect is admitted by every one   The
remark of that admirable palaeontologist  Edward Forbes  should never be
forgotten  namely  that very many fossil species are known and named from
single and often broken specimens  or from a few specimens collected on
some one spot   Only a small portion of the surface of the earth has been
geologically explored  and no part with sufficient care  as the important
discoveries made every year in Europe prove   No organism wholly soft can
be preserved   Shells and bones decay and disappear when left on the bottom
of the sea  where sediment is not accumulating   We probably take a quite
erroneous view  when we assume that sediment is being deposited over nearly
the whole bed of the sea  at a rate sufficiently quick to embed and
preserve fossil remains   Throughout an enormously large proportion of the
ocean  the bright blue tint of the water bespeaks its purity   The many
cases on record of a formation conformably covered  after an immense
interval of time  by another and later formation  without the underlying
bed having suffered in the interval any wear and tear  seem explicable only
on the view of the bottom of the sea not rarely lying for ages in an
unaltered condition   The remains which do become embedded  if in sand or
gravel  will  when the beds are upraised  generally be dissolved by the
percolation of rain water charged with carbonic acid   Some of the many
kinds of animals which live on the beach between high and low water mark
seem to be rarely preserved   For instance  the several species of the
Chthamalinae  a sub family of sessile cirripedes  coat the rocks all over
the world in infinite numbers   they are all strictly littoral  with the
exception of a single Mediterranean species  which inhabits deep water and
this has been found fossil in Sicily  whereas not one other species has
hitherto been found in any tertiary formation   yet it is known that the
genus Chthamalus existed during the Chalk period   Lastly  many great
deposits  requiring a vast length of time for their accumulation  are
entirely destitute of organic remains  without our being able to assign any
reason   one of the most striking instances is that of the Flysch
formation  which consists of shale and sandstone  several thousand 
occasionally even six thousand feet in thickness  and extending for at
least 300 miles from Vienna to Switzerland  and although this great mass
has been most carefully searched  no fossils  except a few vegetable
remains  have been found 

With respect to the terrestrial productions which lived during the
Secondary and Palaeozoic periods  it is superfluous to state that our
evidence is fragmentary in an extreme degree   For instance  until recently
not a land shell was known belonging to either of these vast periods  with
the exception of one species discovered by Sir C  Lyell and Dr  Dawson in
the carboniferous strata of North America  but now land shells have been
found in the lias   In regard to mammiferous remains  a glance at the
historical table published in Lyell s Manual  will bring home the truth 
how accidental and rare is their preservation  far better than pages of
detail   Nor is their rarity surprising  when we remember how large a
proportion of the bones of tertiary mammals have been discovered either in
caves or in lacustrine deposits  and that not a cave or true lacustrine bed
is known belonging to the age of our secondary or palaeozoic formations 

But the imperfection in the geological record largely results from another
and more important cause than any of the foregoing  namely  from the
several formations being separated from each other by wide intervals of
time   This doctrine has been emphatically admitted by many geologists and
palaeontologists  who  like E  Forbes  entirely disbelieve in the change of
species   When we see the formations tabulated in written works  or when we
follow them in nature  it is difficult to avoid believing that they are
closely consecutive   But we know  for instance  from Sir R  Murchison s
great work on Russia  what wide gaps there are in that country between the
superimposed formations  so it is in North America  and in many other parts
of the world   The most skilful geologist  if his attention had been
confined exclusively to these large territories  would never have suspected
that during the periods which were blank and barren in his own country 
great piles of sediment  charged with new and peculiar forms of life  had
elsewhere been accumulated   And if  in every separate territory  hardly
any idea can be formed of the length of time which has elapsed between the
consecutive formations  we may infer that this could nowhere be
ascertained   The frequent and great changes in the mineralogical
composition of consecutive formations  generally implying great changes in
the geography of the surrounding lands  whence the sediment was derived 
accord with the belief of vast intervals of time having elapsed between
each formation 

We can  I think  see why the geological formations of each region are
almost invariably intermittent  that is  have not followed each other in
close sequence   Scarcely any fact struck me more when examining many
hundred miles of the South American coasts  which have been upraised
several hundred feet within the recent period  than the absence of any
recent deposits sufficiently extensive to last for even a short geological
period   Along the whole west coast  which is inhabited by a peculiar
marine fauna  tertiary beds are so poorly developed that no record of
several successive and peculiar marine faunas will probably be preserved to
a distant age   A little reflection will explain why  along the rising
coast of the western side of South America  no extensive formations with
recent or tertiary remains can anywhere be found  though the supply of
sediment must for ages have been great  from the enormous degradation of
the coast rocks and from the muddy streams entering the sea   The
explanation  no doubt  is that the littoral and sub littoral deposits are
continually worn away  as soon as they are brought up by the slow and
gradual rising of the land within the grinding action of the coast waves 

We may  I think  conclude that sediment must be accumulated in extremely
thick  solid  or extensive masses  in order to withstand the incessant
action of the waves  when first upraised and during subsequent oscillations
of level  as well as the subsequent subaerial degradation   Such thick and
extensive accumulations of sediment may be formed in two ways  either in
profound depths of the sea  in which case the bottom will not be inhabited
by so many and such varied forms of life as the more shallow seas  and the
mass when upraised will give an imperfect record of the organisms which
existed in the neighbourhood during the period of its accumulation   Or
sediment may be deposited to any thickness and extent over a shallow
bottom  if it continue slowly to subside   In this latter case  as long as
the rate of subsidence and supply of sediment nearly balance each other 
the sea will remain shallow and favourable for many and varied forms  and
thus a rich fossiliferous formation  thick enough  when upraised  to resist
a large amount of denudation  may be formed 

I am convinced that nearly all our ancient formations  which are throughout
the greater part of their thickness RICH IN FOSSILS  have thus been formed
during subsidence   Since publishing my views on this subject in 1845  I
have watched the progress of geology  and have been surprised to note how
author after author  in treating of this or that great formation  has come
to the conclusion that it was accumulated during subsidence   I may add 
that the only ancient tertiary formation on the west coast of South
America  which has been bulky enough to resist such degradation as it has
as yet suffered  but which will hardly last to a distant geological age 
was deposited during a downward oscillation of level  and thus gained
considerable thickness 

All geological facts tell us plainly that each area has undergone numerous
slow oscillations of level  and apparently these oscillations have affected
wide spaces   Consequently  formations rich in fossils and sufficiently
thick and extensive to resist subsequent degradation  will have been formed
over wide spaces during periods of subsidence  but only where the supply of
sediment was sufficient to keep the sea shallow and to embed and preserve
the remains before they had time to decay   On the other hand  as long as
the bed of the sea remained stationary  THICK deposits cannot have been
accumulated in the shallow parts  which are the most favourable to life  
Still less can this have happened during the alternate periods of
elevation  or  to speak more accurately  the beds which were then
accumulated will generally have been destroyed by being upraised and
brought within the limits of the coast action 

These remarks apply chiefly to littoral and sublittoral deposits   In the
case of an extensive and shallow sea  such as that within a large part of
the Malay Archipelago  where the depth varies from thirty or forty to sixty
fathoms  a widely extended formation might be formed during a period of
elevation  and yet not suffer excessively from denudation during its slow
upheaval  but the thickness of the formation could not be great  for owing
to the elevatory movement it would be less than the depth in which it was
formed  nor would the deposit be much consolidated  nor be capped by
overlying formations  so that it would run a good chance of being worn away
by atmospheric degradation and by the action of the sea during subsequent
oscillations of level   It has  however  been suggested by Mr  Hopkins 
that if one part of the area  after rising and before being denuded 
subsided  the deposit formed during the rising movement  though not thick 
might afterwards become protected by fresh accumulations  and thus be
preserved for a long period 

Mr  Hopkins also expresses his belief that sedimentary beds of considerable
horizontal extent have rarely been completely destroyed   But all
geologists  excepting the few who believe that our present metamorphic
schists and plutonic rocks once formed the primordial nucleus of the globe 
will admit that these latter rocks have been stripped of their covering to
an enormous extent   For it is scarcely possible that such rocks could have
been solidified and crystallised while uncovered  but if the metamorphic
action occurred at profound depths of the ocean  the former protecting
mantle of rock may not have been very thick   Admitting then that gneiss 
mica schist  granite  diorite  etc   were once necessarily covered up  how
can we account for the naked and extensive areas of such rocks in many
parts of the world  except on the belief that they have subsequently been
completely denuded of all overlying strata   That such extensive areas do
exist cannot be doubted   the granitic region of Parime is described by
Humboldt as being at least nineteen times as large as Switzerland   South
of the Amazon  Boue colours an area composed of rocks of this nature as
equal to that of Spain  France  Italy  part of Germany  and the British
Islands  all conjoined   This region has not been carefully explored  but
from the concurrent testimony of travellers  the granitic area is very
large   thus Von Eschwege gives a detailed section of these rocks 
stretching from Rio de Janeiro for 260 geographical miles inland in a
straight line  and I travelled for 150 miles in another direction  and saw
nothing but granitic rocks   Numerous specimens  collected along the whole
coast  from near Rio de Janeiro to the mouth of the Plata  a distance of
1 100 geographical miles  were examined by me  and they all belonged to
this class   Inland  along the whole northern bank of the Plata  I saw 
besides modern tertiary beds  only one small patch of slightly
metamorphosed rock  which alone could have formed a part of the original
capping of the granitic series   Turning to a well known region  namely  to
the United States and Canada  as shown in Professor H D  Rogers  beautiful
map  I have estimated the areas by cutting out and weighing the paper  and
I find that the metamorphic  excluding the  semi metamorphic   and granite
rocks exceed  in the proportion of 19 to 12 5  the whole of the newer
Palaeozoic formations   In many regions the metamorphic and granite rocks
would be found much more widely extended than they appear to be  if all the
sedimentary beds were removed which rest unconformably on them  and which
could not have formed part of the original mantle under which they were
crystallised   Hence  it is probable that in some parts of the world whole
formations have been completely denuded  with not a wreck left behind 


One remark is here worth a passing notice   During periods of elevation the
area of the land and of the adjoining shoal parts of the sea will be
increased and new stations will often be formed  all circumstances
favourable  as previously explained  for the formation of new varieties and
species  but during such periods there will generally be a blank in the
geological record   On the other hand  during subsidence  the inhabited
area and number of inhabitants will decrease  excepting on the shores of a
continent when first broken up into an archipelago   and consequently
during subsidence  though there will be much extinction  few new varieties
or species will be formed  and it is during these very periods of
subsidence that the deposits which are richest in fossils have been
accumulated 

ON THE ABSENCE OF NUMEROUS INTERMEDIATE VARIETIES IN ANY SINGLE FORMATION 

 From these several considerations it cannot be doubted that the geological
record  viewed as a whole  is extremely imperfect  but if we confine our
attention to any one formation  it becomes much more difficult to
understand why we do not therein find closely graduated varieties between
the allied species which lived at its commencement and at its close  
Several cases are on record of the same species presenting varieties in the
upper and lower parts of the same formation   Thus Trautschold gives a
number of instances with Ammonites  and Hilgendorf has described a most
curious case of ten graduated forms of Planorbis multiformis in the
successive beds of a fresh water formation in Switzerland   Although each
formation has indisputably required a vast number of years for its
deposition  several reasons can be given why each should not commonly
include a graduated series of links between the species which lived at its
commencement and close  but I cannot assign due proportional weight to the
following considerations 

Although each formation may mark a very long lapse of years  each probably
is short compared with the period requisite to change one species into
another   I am aware that two palaeontologists  whose opinions are worthy
of much deference  namely Bronn and Woodward  have concluded that the
average duration of each formation is twice or thrice as long as the
average duration of specific forms   But insuperable difficulties  as it
seems to me  prevent us from coming to any just conclusion on this head  
When we see a species first appearing in the middle of any formation  it
would be rash in the extreme to infer that it had not elsewhere previously
existed   So again  when we find a species disappearing before the last
layers have been deposited  it would be equally rash to suppose that it
then became extinct   We forget how small the area of Europe is compared
with the rest of the world  nor have the several stages of the same
formation throughout Europe been correlated with perfect accuracy 

We may safely infer that with marine animals of all kinds there has been a
large amount of migration due to climatal and other changes  and when we
see a species first appearing in any formation  the probability is that it
only then first immigrated into that area   It is well known  for instance 
that several species appear somewhat earlier in the palaeozoic beds of
North America than in those of Europe  time having apparently been required
for their migration from the American to the European seas   In examining
the latest deposits  in various quarters of the world  it has everywhere
been noted  that some few still existing species are common in the deposit 
but have become extinct in the immediately surrounding sea  or  conversely 
that some are now abundant in the neighbouring sea  but are rare or absent
in this particular deposit   It is an excellent lesson to reflect on the
ascertained amount of migration of the inhabitants of Europe during the
glacial epoch  which forms only a part of one whole geological period  and
likewise to reflect on the changes of level  on the extreme change of
climate  and on the great lapse of time  all included within this same
glacial period   Yet it may be doubted whether  in any quarter of the
world  sedimentary deposits  INCLUDING FOSSIL REMAINS  have gone on
accumulating within the same area during the whole of this period   It is
not  for instance  probable that sediment was deposited during the whole of
the glacial period near the mouth of the Mississippi  within that limit of
depth at which marine animals can best flourish   for we know that great
geographical changes occurred in other parts of America during this space
of time   When such beds as were deposited in shallow water near the mouth
of the Mississippi during some part of the glacial period shall have been
upraised  organic remains will probably first appear and disappear at
different levels  owing to the migrations of species and to geographical
changes   And in the distant future  a geologist  examining these beds 
would be tempted to conclude that the average duration of life of the
embedded fossils had been less than that of the glacial period  instead of
having been really far greater  that is  extending from before the glacial
epoch to the present day 

In order to get a perfect gradation between two forms in the upper and
lower parts of the same formation  the deposit must have gone on
continuously accumulating during a long period  sufficient for the slow
process of modification  hence  the deposit must be a very thick one  and
the species undergoing change must have lived in the same district
throughout the whole time   But we have seen that a thick formation 
fossiliferous throughout its entire thickness  can accumulate only during a
period of subsidence  and to keep the depth approximately the same  which
is necessary that the same marine species may live on the same space  the
supply of sediment must nearly counterbalance the amount of subsidence  
But this same movement of subsidence will tend to submerge the area whence
the sediment is derived  and thus diminish the supply  whilst the downward
movement continues   In fact  this nearly exact balancing between the
supply of sediment and the amount of subsidence is probably a rare
contingency  for it has been observed by more than one palaeontologist that
very thick deposits are usually barren of organic remains  except near
their upper or lower limits 

It would seem that each separate formation  like the whole pile of
formations in any country  has generally been intermittent in its
accumulation   When we see  as is so often the case  a formation composed
of beds of widely different mineralogical composition  we may reasonably
suspect that the process of deposition has been more or less interrupted 
Nor will the closest inspection of a formation give us any idea of the
length of time which its deposition may have consumed   Many instances
could be given of beds  only a few feet in thickness  representing
formations which are elsewhere thousands of feet in thickness  and which
must have required an enormous period for their accumulation  yet no one
ignorant of this fact would have even suspected the vast lapse of time
represented by the thinner formation   Many cases could be given of the
lower beds of a formation having been upraised  denuded  submerged  and
then re covered by the upper beds of the same formation  facts  showing
what wide  yet easily overlooked  intervals have occurred in its
accumulation   In other cases we have the plainest evidence in great
fossilised trees  still standing upright as they grew  of many long
intervals of time and changes of level during the process of deposition 
which would not have been suspected  had not the trees been preserved  
thus Sir C  Lyell and Dr  Dawson found carboniferous beds 1 400 feet thick
in Nova Scotia  with ancient root bearing strata  one above the other  at
no less than sixty eight different levels   Hence  when the same species
occurs at the bottom  middle  and top of a formation  the probability is
that it has not lived on the same spot during the whole period of
deposition  but has disappeared and reappeared  perhaps many times  during
the same geological period   Consequently if it were to undergo a
considerable amount of modification during the deposition of any one
geological formation  a section would not include all the fine intermediate
gradations which must on our theory have existed  but abrupt  though
perhaps slight  changes of form 

It is all important to remember that naturalists have no golden rule by
which to distinguish species and varieties  they grant some little
variability to each species  but when they meet with a somewhat greater
amount of difference between any two forms  they rank both as species 
unless they are enabled to connect them together by the closest
intermediate gradations  and this  from the reasons just assigned  we can
seldom hope to effect in any one geological section   Supposing B and C to
be two species  and a third  A  to be found in an older and underlying bed 
even if A were strictly intermediate between B and C  it would simply be
ranked as a third and distinct species  unless at the same time it could be
closely connected by intermediate varieties with either one or both forms  
Nor should it be forgotten  as before explained  that A might be the actual
progenitor of B and C  and yet would not necessarily be strictly
intermediate between them in all respects   So that we might obtain the
parent species and its several modified descendants from the lower and
upper beds of the same formation  and unless we obtained numerous
transitional gradations  we should not recognise their blood relationship 
and should consequently rank them as distinct species 

It is notorious on what excessively slight differences many
palaeontologists have founded their species  and they do this the more
readily if the specimens come from different sub stages of the same
formation   Some experienced conchologists are now sinking many of the very
fine species of D Orbigny and others into the rank of varieties  and on
this view we do find the kind of evidence of change which on the theory we
ought to find   Look again at the later tertiary deposits  which include
many shells believed by the majority of naturalists to be identical with
existing species  but some excellent naturalists  as Agassiz and Pictet 
maintain that all these tertiary species are specifically distinct  though
the distinction is admitted to be very slight  so that here  unless we
believe that these eminent naturalists have been misled by their
imaginations  and that these late tertiary species really present no
difference whatever from their living representatives  or unless we admit 
in opposition to the judgment of most naturalists  that these tertiary
species are all truly distinct from the recent  we have evidence of the
frequent occurrence of slight modifications of the kind required   If we
look to rather wider intervals of time  namely  to distinct but consecutive
stages of the same great formation  we find that the embedded fossils 
though universally ranked as specifically different  yet are far more
closely related to each other than are the species found in more widely
separated formations  so that here again we have undoubted evidence of
change in the direction required by the theory  but to this latter subject
I shall return in the following chapter 

With animals and plants that propagate rapidly and do not wander much 
there is reason to suspect  as we have formerly seen  that their varieties
are generally at first local  and that such local varieties do not spread
widely and supplant their parent form until they have been modified and
perfected in some considerable degree   According to this view  the chance
of discovering in a formation in any one country all the early stages of
transition between any two forms  is small  for the successive changes are
supposed to have been local or confined to some one spot   Most marine
animals have a wide range  and we have seen that with plants it is those
which have the widest range  that oftenest present varieties  so that  with
shells and other marine animals  it is probable that those which had the
widest range  far exceeding the limits of the known geological formations
in Europe  have oftenest given rise  first to local varieties and
ultimately to new species  and this again would greatly lessen the chance
of our being able to trace the stages of transition in any one geological
formation 

It is a more important consideration  leading to the same result  as lately
insisted on by Dr  Falconer  namely  that the period during which each
species underwent modification  though long as measured by years  was
probably short in comparison with that during which it remained without
undergoing any change 

It should not be forgotten  that at the present day  with perfect specimens
for examination  two forms can seldom be connected by intermediate
varieties  and thus proved to be the same species  until many specimens are
collected from many places  and with fossil species this can rarely be
done   We shall  perhaps  best perceive the improbability of our being
enabled to connect species by numerous  fine  intermediate  fossil links 
by asking ourselves whether  for instance  geologists at some future period
will be able to prove that our different breeds of cattle  sheep  horses 
and dogs are descended from a single stock or from several aboriginal
stocks  or  again  whether certain sea shells inhabiting the shores of
North America  which are ranked by some conchologists as distinct species
from their European representatives  and by other conchologists as only
varieties  are really varieties  or are  as it is called  specifically
distinct   This could be effected by the future geologist only by his
discovering in a fossil state numerous intermediate gradations  and such
success is improbable in the highest degree 

It has been asserted over and over again  by writers who believe in the
immutability of species  that geology yields no linking forms   This
assertion  as we shall see in the next chapter  is certainly erroneous   As
Sir J  Lubbock has remarked   Every species is a link between other allied
forms    If we take a genus having a score of species  recent and extinct 
and destroy four fifths of them  no one doubts that the remainder will
stand much more distinct from each other   If the extreme forms in the
genus happen to have been thus destroyed  the genus itself will stand more
distinct from other allied genera   What geological research has not
revealed  is the former existence of infinitely numerous gradations  as
fine as existing varieties  connecting together nearly all existing and
extinct species   But this ought not to be expected  yet this has been
repeatedly advanced as a most serious objection against my views 

It may be worth while to sum up the foregoing remarks on the causes of the
imperfection of the geological record under an imaginary illustration   The
Malay Archipelago is about the size of Europe from the North Cape to the
Mediterranean  and from Britain to Russia  and therefore equals all the
geological formations which have been examined with any accuracy  excepting
those of the United States of America   I fully agree with Mr  Godwin 
Austen  that the present condition of the Malay Archipelago  with its
numerous large islands separated by wide and shallow seas  probably
represents the former state of Europe  while most of our formations were
accumulating   The Malay Archipelago is one of the richest regions in
organic beings  yet if all the species were to be collected which have ever
lived there  how imperfectly would they represent the natural history of
the world 

But we have every reason to believe that the terrestrial productions of the
archipelago would be preserved in an extremely imperfect manner in the
formations which we suppose to be there accumulating   Not many of the
strictly littoral animals  or of those which lived on naked submarine
rocks  would be embedded  and those embedded in gravel or sand would not
endure to a distant epoch   Wherever sediment did not accumulate on the bed
of the sea  or where it did not accumulate at a sufficient rate to protect
organic bodies from decay  no remains could be preserved 

Formations rich in fossils of many kinds  and of thickness sufficient to
last to an age as distant in futurity as the secondary formations lie in
the past  would generally be formed in the archipelago only during periods
of subsidence   These periods of subsidence would be separated from each
other by immense intervals of time  during which the area would be either
stationary or rising  whilst rising  the fossiliferous formations on the
steeper shores would be destroyed  almost as soon as accumulated  by the
incessant coast action  as we now see on the shores of South America   Even
throughout the extensive and shallow seas within the archipelago 
sedimentary beds could hardly be accumulated of great thickness during the
periods of elevation  or become capped and protected by subsequent
deposits  so as to have a good chance of enduring to a very distant future  
During the periods of subsidence  there would probably be much extinction
of life  during the periods of elevation  there would be much variation 
but the geological record would then be less perfect 

It may be doubted whether the duration of any one great period of
subsidence over the whole or part of the archipelago  together with a
contemporaneous accumulation of sediment  would EXCEED the average duration
of the same specific forms  and these contingencies are indispensable for
the preservation of all the transitional gradations between any two or more
species   If such gradations were not all fully preserved  transitional
varieties would merely appear as so many new  though closely allied
species   It is also probable that each great period of subsidence would be
interrupted by oscillations of level  and that slight climatical changes
would intervene during such lengthy periods  and in these cases the
inhabitants of the archipelago would migrate  and no closely consecutive
record of their modifications could be preserved in any one formation 

Very many of the marine inhabitants of the archipelago now range thousands
of miles beyond its confines  and analogy plainly leads to the belief that
it would be chiefly these far ranging species  though only some of them 
which would oftenest produce new varieties  and the varieties would at
first be local or confined to one place  but if possessed of any decided
advantage  or when further modified and improved  they would slowly spread
and supplant their parent forms   When such varieties returned to their
ancient homes  as they would differ from their former state in a nearly
uniform  though perhaps extremely slight degree  and as they would be found
embedded in slightly different sub stages of the same formation  they
would  according to the principles followed by many palaeontologists  be
ranked as new and distinct species 

If then there be some degree of truth in these remarks  we have no right to
expect to find  in our geological formations  an infinite number of those
fine transitional forms  which  on our theory  have connected all the past
and present species of the same group into one long and branching chain of
life   We ought only to look for a few links   and such assuredly we do
find  some more distantly  some more closely  related to each other  and
these links  let them be ever so close  if found in different stages of the
same formation  would  by many palaeontologists  be ranked as distinct
species   But I do not pretend that I should ever have suspected how poor
was the record in the best preserved geological sections  had not the
absence of innumerable transitional links between the species which lived
at the commencement and close of each formation  pressed so hardly on my
theory 

ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF ALLIED SPECIES 

The abrupt manner in which whole groups of species suddenly appear in
certain formations  has been urged by several palaeontologists  for
instance  by Agassiz  Pictet  and Sedgwick  as a fatal objection to the
belief in the transmutation of species   If numerous species  belonging to
the same genera or families  have really started into life at once  the
fact would be fatal to the theory of evolution through natural selection  
For the development by this means of a group of forms  all of which are
descended from some one progenitor  must have been an extremely slow
process  and the progenitors must have lived long before their modified
descendants   But we continually overrate the perfection of the geological
record  and falsely infer  because certain genera or families have not been
found beneath a certain stage  that they did not exist before that stage  
In all cases positive palaeontological evidence may be implicitly trusted 
negative evidence is worthless  as experience has so often shown   We
continually forget how large the world is  compared with the area over
which our geological formations have been carefully examined  we forget
that groups of species may elsewhere have long existed  and have slowly
multiplied  before they invaded the ancient archipelagoes of Europe and the
United States   We do not make due allowance for the enormous intervals of
time which have elapsed between our consecutive formations  longer perhaps
in many cases than the time required for the accumulation of each
formation   These intervals will have given time for the multiplication of
species from some one parent form   and in the succeeding formation  such
groups or species will appear as if suddenly created 

I may here recall a remark formerly made  namely  that it might require a
long succession of ages to adapt an organism to some new and peculiar line
of life  for instance  to fly through the air  and consequently that the
transitional forms would often long remain confined to some one region  but
that  when this adaptation had once been effected  and a few species had
thus acquired a great advantage over other organisms  a comparatively short
time would be necessary to produce many divergent forms  which would spread
rapidly and widely throughout the world   Professor Pictet  in his
excellent Review of this work  in commenting on early transitional forms 
and taking birds as an illustration  cannot see how the successive
modifications of the anterior limbs of a supposed prototype could possibly
have been of any advantage   But look at the penguins of the Southern
Ocean  have not these birds their front limbs in this precise intermediate
state of  neither true arms nor true wings    Yet these birds hold their
place victoriously in the battle for life  for they exist in infinite
numbers and of many kinds   I do not suppose that we here see the real
transitional grades through which the wings of birds have passed  but what
special difficulty is there in believing that it might profit the modified
descendants of the penguin  first to become enabled to flap along the
surface of the sea like the logger headed duck  and ultimately to rise from
its surface and glide through the air 

I will now give a few examples to illustrate the foregoing remarks  and to
show how liable we are to error in supposing that whole groups of species
have suddenly been produced   Even in so short an interval as that between
the first and second editions of Pictet s great work on Palaeontology 
published in 1844 46 and in 1853 57  the conclusions on the first
appearance and disappearance of several groups of animals have been
considerably modified  and a third edition would require still further
changes   I may recall the well known fact that in geological treatises 
published not many years ago  mammals were always spoken of as having
abruptly come in at the commencement of the tertiary series   And now one
of the richest known accumulations of fossil mammals belongs to the middle
of the secondary series  and true mammals have been discovered in the new
red sandstone at nearly the commencement of this great series   Cuvier used
to urge that no monkey occurred in any tertiary stratum  but now extinct
species have been discovered in India  South America and in Europe  as far
back as the miocene stage   Had it not been for the rare accident of the
preservation of footsteps in the new red sandstone of the United States 
who would have ventured to suppose that no less than at least thirty
different bird like animals  some of gigantic size  existed during that
period   Not a fragment of bone has been discovered in these beds   Not
long ago  palaeontologists maintained that the whole class of birds came
suddenly into existence during the eocene period  but now we know  on the
authority of Professor Owen  that a bird certainly lived during the
deposition of the upper greensand  and still more recently  that strange
bird  the Archeopteryx  with a long lizard like tail  bearing a pair of
feathers on each joint  and with its wings furnished with two free claws 
has been discovered in the oolitic slates of Solenhofen   Hardly any recent
discovery shows more forcibly than this how little we as yet know of the
former inhabitants of the world 

I may give another instance  which  from having passed under my own eyes
has much struck me   In a memoir on Fossil Sessile Cirripedes  I stated
that  from the large number of existing and extinct tertiary species  from
the extraordinary abundance of the individuals of many species all over the
world  from the Arctic regions to the equator  inhabiting various zones of
depths  from the upper tidal limits to fifty fathoms  from the perfect
manner in which specimens are preserved in the oldest tertiary beds  from
the ease with which even a fragment of a valve can be recognised  from all
these circumstances  I inferred that  had sessile cirripedes existed during
the secondary periods  they would certainly have been preserved and
discovered  and as not one species had then been discovered in beds of this
age  I concluded that this great group had been suddenly developed at the
commencement of the tertiary series   This was a sore trouble to me 
adding  as I then thought  one more instance of the abrupt appearance of a
great group of species   But my work had hardly been published  when a
skilful palaeontologist  M  Bosquet  sent me a drawing of a perfect
specimen of an unmistakable sessile cirripede  which he had himself
extracted from the chalk of Belgium   And  as if to make the case as
striking as possible  this cirripede was a Chthamalus  a very common 
large  and ubiquitous genus  of which not one species has as yet been found
even in any tertiary stratum   Still more recently  a Pyrgoma  a member of
a distinct subfamily of sessile cirripedes  has been discovered by Mr 
Woodward in the upper chalk  so that we now have abundant evidence of the
existence of this group of animals during the secondary period 

The case most frequently insisted on by palaeontologists of the apparently
sudden appearance of a whole group of species  is that of the teleostean
fishes  low down  according to Agassiz  in the Chalk period   This group
includes the large majority of existing species   But certain Jurassic and
Triassic forms are now commonly admitted to be teleostean  and even some
palaeozoic forms have thus been classed by one high authority  If the
teleosteans had really appeared suddenly in the northern hemisphere at the
commencement of the chalk formation  the fact would have been highly
remarkable  but it would not have formed an insuperable difficulty  unless
it could likewise have been shown that at the same period the species were
suddenly and simultaneously developed in other quarters of the world   It
is almost superfluous to remark that hardly any fossil fish are known from
south of the equator  and by running through Pictet s Palaeontology it will
be seen that very few species are known from several formations in Europe  
Some few families of fish now have a confined range  the teleostean fishes
might formerly have had a similarly confined range  and after having been
largely developed in some one sea  have spread widely   Nor have we any
right to suppose that the seas of the world have always been so freely open
from south to north as they are at present   Even at this day  if the Malay
Archipelago were converted into land  the tropical parts of the Indian
Ocean would form a large and perfectly enclosed basin  in which any great
group of marine animals might be multiplied  and here they would remain
confined  until some of the species became adapted to a cooler climate  and
were enabled to double the southern capes of Africa or Australia  and thus
reach other and distant seas 

 From these considerations  from our ignorance of the geology of other
countries beyond the confines of Europe and the United States  and from the
revolution in our palaeontological knowledge effected by the discoveries of
the last dozen years  it seems to me to be about as rash to dogmatize on
the succession of organic forms throughout the world  as it would be for a
naturalist to land for five minutes on a barren point in Australia  and
then to discuss the number and range of its productions 

ON THE SUDDEN APPEARANCE OF GROUPS OF ALLIED SPECIES IN THE LOWEST KNOWN
FOSSILIFEROUS STRATA 

There is another and allied difficulty  which is much more serious   I
allude to the manner in which species belonging to several of the main
divisions of the animal kingdom suddenly appear in the lowest known
fossiliferous rocks   Most of the arguments which have convinced me that
all the existing species of the same group are descended from a single
progenitor  apply with equal force to the earliest known species   For
instance  it cannot be doubted that all the Cambrian and Silurian
trilobites are descended from some one crustacean  which must have lived
long before the Cambrian age  and which probably differed greatly from any
known animal   Some of the most ancient animals  as the Nautilus  Lingula 
etc   do not differ much from living species  and it cannot on our theory
be supposed  that these old species were the progenitors of all the species
belonging to the same groups which have subsequently appeared  for they are
not in any degree intermediate in character 

Consequently  if the theory be true  it is indisputable that before the
lowest Cambrian stratum was deposited long periods elapsed  as long as  or
probably far longer than  the whole interval from the Cambrian age to the
present day  and that during these vast periods the world swarmed with
living creatures   Here we encounter a formidable objection  for it seems
doubtful whether the earth  in a fit state for the habitation of living
creatures  has lasted long enough   Sir W  Thompson concludes that the
consolidation of the crust can hardly have occurred less than twenty or
more than four hundred million years ago  but probably not less than
ninety eight or more than two hundred million years   These very wide
limits show how doubtful the data are  and other elements may have
hereafter to be introduced into the problem   Mr  Croll estimates that
about sixty million years have elapsed since the Cambrian period  but this 
judging from the small amount of organic change since the commencement of
the Glacial epoch  appears a very short time for the many and great
mutations of life  which have certainly occurred since the Cambrian
formation  and the previous one hundred and forty million years can hardly
be considered as sufficient for the development of the varied forms of life
which already existed during the Cambrian period   It is  however 
probable  as Sir William Thompson insists  that the world at a very early
period was subjected to more rapid and violent changes in its physical
conditions than those now occurring  and such changes would have tended to
induce changes at a corresponding rate in the organisms which then existed 

To the question why we do not find rich fossiliferous deposits belonging to
these assumed earliest periods prior to the Cambrian system  I can give no
satisfactory answer   Several eminent geologists  with Sir R  Murchison at
their head  were until recently convinced that we beheld in the organic
remains of the lowest Silurian stratum the first dawn of life   Other
highly competent judges  as Lyell and E  Forbes  have disputed this
conclusion   We should not forget that only a small portion of the world is
known with accuracy   Not very long ago M  Barrande added another and lower
stage  abounding with new and peculiar species  beneath the then known
Silurian system  and now  still lower down in the Lower Cambrian formation 
Mr Hicks has found South Wales beds rich in trilobites  and containing
various molluscs and annelids   The presence of phosphatic nodules and
bituminous matter  even in some of the lowest azotic rocks  probably
indicates life at these periods  and the existence of the Eozoon in the
Laurentian formation of Canada is generally admitted   There are three
great series of strata beneath the Silurian system in Canada  in the lowest
of which the Eozoon is found   Sir W  Logan states that their  united
thickness may possibly far surpass that of all the succeeding rocks  from
the base of the palaeozoic series to the present time   We are thus carried
back to a period so remote  that the appearance of the so called primordial
fauna  of Barrande  may by some be considered as a comparatively modern
event    The Eozoon belongs to the most lowly organised of all classes of
animals  but is highly organised for its class  it existed in countless
numbers  and  as Dr  Dawson has remarked  certainly preyed on other minute
organic beings  which must have lived in great numbers   Thus the words 
which I wrote in 1859  about the existence of living beings long before the
Cambrian period  and which are almost the same with those since used by Sir
W  Logan  have proved true   Nevertheless  the difficulty of assigning any
good reason for the absence of vast piles of strata rich in fossils beneath
the Cambrian system is very great   It does not seem probable that the most
ancient beds have been quite worn away by denudation  or that their fossils
have been wholly obliterated by metamorphic action  for if this had been
the case we should have found only small remnants of the formations next
succeeding them in age  and these would always have existed in a partially
metamorphosed condition   But the descriptions which we possess of the
Silurian deposits over immense territories in Russia and in North America 
do not support the view that the older a formation is the more invariably
it has suffered extreme denudation and metamorphism 

The case at present must remain inexplicable  and may be truly urged as a
valid argument against the views here entertained   To show that it may
hereafter receive some explanation  I will give the following hypothesis  
 From the nature of the organic remains which do not appear to have
inhabited profound depths  in the several formations of Europe and of the
United States  and from the amount of sediment  miles in thickness  of
which the formations are composed  we may infer that from first to last
large islands or tracts of land  whence the sediment was derived  occurred
in the neighbourhood of the now existing continents of Europe and North
America   This same view has since been maintained by Agassiz and others  
But we do not know what was the state of things in the intervals between
the several successive formations  whether Europe and the United States
during these intervals existed as dry land  or as a submarine surface near
land  on which sediment was not deposited  or as the bed of an open and
unfathomable sea 

Looking to the existing oceans  which are thrice as extensive as the land 
we see them studded with many islands  but hardly one truly oceanic island
 with the exception of New Zealand  if this can be called a truly oceanic
island  is as yet known to afford even a remnant of any palaeozoic or
secondary formation   Hence  we may perhaps infer  that during the
palaeozoic and secondary periods  neither continents nor continental
islands existed where our oceans now extend  for had they existed 
palaeozoic and secondary formations would in all probability have been
accumulated from sediment derived from their wear and tear  and would have
been at least partially upheaved by the oscillations of level  which must
have intervened during these enormously long periods   If  then  we may
infer anything from these facts  we may infer that  where our oceans now
extend  oceans have extended from the remotest period of which we have any
record  and on the other hand  that where continents now exist  large
tracts of land have existed  subjected  no doubt  to great oscillations of
level  since the Cambrian period   The coloured map appended to my volume
on Coral Reefs  led me to conclude that the great oceans are still mainly
areas of subsidence  the great archipelagoes still areas of oscillations of
level  and the continents areas of elevation   But we have no reason to
assume that things have thus remained from the beginning of the world   Our
continents seem to have been formed by a preponderance  during many
oscillations of level  of the force of elevation   But may not the areas of
preponderant movement have changed in the lapse of ages   At a period long
antecedent to the Cambrian epoch  continents may have existed where oceans
are now spread out  and clear and open oceans may have existed where our
continents now stand   Nor should we be justified in assuming that if  for
instance  the bed of the Pacific Ocean were now converted into a continent
we should there find sedimentary formations  in recognisable condition 
older than the Cambrian strata  supposing such to have been formerly
deposited  for it might well happen that strata which had subsided some
miles nearer to the centre of the earth  and which had been pressed on by
an enormous weight of superincumbent water  might have undergone far more
metamorphic action than strata which have always remained nearer to the
surface   The immense areas in some parts of the world  for instance in
South America  of naked metamorphic rocks  which must have been heated
under great pressure  have always seemed to me to require some special
explanation  and we may perhaps believe that we see in these large areas
the many formations long anterior to the Cambrian epoch in a completely
metamorphosed and denuded condition 

The several difficulties here discussed  namely  that  though we find in
our geological formations many links between the species which now exist
and which formerly existed  we do not find infinitely numerous fine
transitional forms closely joining them all together   The sudden manner in
which several groups of species first appear in our European formations 
the almost entire absence  as at present known  of formations rich in
fossils beneath the Cambrian strata  are all undoubtedly of the most
serious nature   We see this in the fact that the most eminent
palaeontologists  namely  Cuvier  Agassiz  Barrande  Pictet  Falconer  E 
Forbes  etc   and all our greatest geologists  as Lyell  Murchison 
Sedgwick  etc   have unanimously  often vehemently  maintained the
immutability of species   But Sir Charles Lyell now gives the support of
his high authority to the opposite side  and most geologists and
palaeontologists are much shaken in their former belief   Those who believe
that the geological record is in any degree perfect  will undoubtedly at
once reject my theory   For my part  following out Lyell s metaphor  I look
at the geological record as a history of the world imperfectly kept and
written in a changing dialect   Of this history we possess the last volume
alone  relating only to two or three countries   Of this volume  only here
and there a short chapter has been preserved  and of each page  only here
and there a few lines   Each word of the slowly changing language  more or
less different in the successive chapters  may represent the forms of life 
which are entombed in our consecutive formations  and which falsely appear
to have been abruptly introduced   On this view the difficulties above
discussed are greatly diminished or even disappear 


CHAPTER XI 

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS 

On the slow and successive appearance of new species    On their different
rates of change    Species once lost do not reappear    Groups of species
follow the same general rules in their appearance and disappearance as do
single species    On extinction    On simultaneous changes in the forms of
life throughout the world    On the affinities of extinct species to each
other and to living species    On the state of development of ancient forms
   On the succession of the same types within the same areas    Summary of
preceding and present chapters 

Let us now see whether the several facts and laws relating to the
geological succession of organic beings accord best with the common view of
the immutability of species  or with that of their slow and gradual
modification  through variation and natural selection 

New species have appeared very slowly  one after another  both on the land
and in the waters   Lyell has shown that it is hardly possible to resist
the evidence on this head in the case of the several tertiary stages  and
every year tends to fill up the blanks between the stages  and to make the
proportion between the lost and existing forms more gradual   In some of
the most recent beds  though undoubtedly of high antiquity if measured by
years  only one or two species are extinct  and only one or two are new 
having appeared there for the first time  either locally  or  as far as we
know  on the face of the earth   The secondary formations are more broken 
but  as Bronn has remarked  neither the appearance nor disappearance of the
many species embedded in each formation has been simultaneous 

Species belonging to different genera and classes have not changed at the
same rate  or in the same degree   In the older tertiary beds a few living
shells may still be found in the midst of a multitude of extinct forms  
Falconer has given a striking instance of a similar fact  for an existing
crocodile is associated with many lost mammals and reptiles in the
sub Himalayan deposits   The Silurian Lingula differs but little from the
living species of this genus  whereas most of the other Silurian Molluscs
and all the Crustaceans have changed greatly   The productions of the land
seem to have changed at a quicker rate than those of the sea  of which a
striking instance has been observed in Switzerland   There is some reason
to believe that organisms high in the scale  change more quickly than those
that are low   though there are exceptions to this rule   The amount of
organic change  as Pictet has remarked  is not the same in each successive
so called formation   Yet if we compare any but the most closely related
formations  all the species will be found to have undergone some change  
When a species has once disappeared from the face of the earth  we have no
reason to believe that the same identical form ever reappears   The
strongest apparent exception to this latter rule is that of the so called
 colonies  of M  Barrande  which intrude for a period in the midst of an
older formation  and then allow the pre existing fauna to reappear  but
Lyell s explanation  namely  that it is a case of temporary migration from
a distinct geographical province  seems satisfactory 

These several facts accord well with our theory  which includes no fixed
law of development  causing all the inhabitants of an area to change
abruptly  or simultaneously  or to an equal degree   The process of
modification must be slow  and will generally affect only a few species at
the same time  for the variability of each species is independent of that
of all others   Whether such variations or individual differences as may
arise will be accumulated through natural selection in a greater or less
degree  thus causing a greater or less amount of permanent modification  
will depend on many complex contingencies  on the variations being of a
beneficial nature  on the freedom of intercrossing  on the slowly changing
physical conditions of the country  on the immigration of new colonists 
and on the nature of the other inhabitants with which the varying species
come into competition   Hence it is by no means surprising that one species
should retain the same identical form much longer than others  or  if
changing  should change in a less degree   We find similar relations
between the existing inhabitants of distinct countries  for instance  the
land shells and coleopterous insects of Madeira have come to differ
considerably from their nearest allies on the continent of Europe  whereas
the marine shells and birds have remained unaltered   We can perhaps
understand the apparently quicker rate of change in terrestrial and in more
highly organised productions compared with marine and lower productions  by
the more complex relations of the higher beings to their organic and
inorganic conditions of life  as explained in a former chapter   When many
of the inhabitants of any area have become modified and improved  we can
understand  on the principle of competition  and from the all important
relations of organism to organism in the struggle for life  that any form
which did not become in some degree modified and improved  would be liable
to extermination   Hence  we see why all the species in the same region do
at last  if we look to long enough intervals of time  become modified  for
otherwise they would become extinct 

In members of the same class the average amount of change  during long and
equal periods of time  may  perhaps  be nearly the same  but as the
accumulation of enduring formations  rich in fossils  depends on great
masses of sediment being deposited on subsiding areas  our formations have
been almost necessarily accumulated at wide and irregularly intermittent
intervals of time  consequently the amount of organic change exhibited by
the fossils embedded in consecutive formations is not equal   Each
formation  on this view  does not mark a new and complete act of creation 
but only an occasional scene  taken almost at hazard  in an ever slowly
changing drama 

We can clearly understand why a species when once lost should never
reappear  even if the very same conditions of life  organic and inorganic 
should recur   For though the offspring of one species might be adapted
 and no doubt this has occurred in innumerable instances  to fill the place
of another species in the economy of nature  and thus supplant it  yet the
two forms  the old and the new  would not be identically the same  for both
would almost certainly inherit different characters from their distinct
progenitors  and organisms already differing would vary in a different
manner   For instance  it is possible  if all our fantail pigeons were
destroyed  that fanciers might make a new breed hardly distinguishable from
the present breed  but if the parent rock pigeon were likewise destroyed 
and under nature we have every reason to believe that parent forms are
generally supplanted and exterminated by their improved offspring  it is
incredible that a fantail  identical with the existing breed  could be
raised from any other species of pigeon  or even from any other well
established race of the domestic pigeon  for the successive variations
would almost certainly be in some degree different  and the newly formed
variety would probably inherit from its progenitor some characteristic
differences 

Groups of species  that is  genera and families  follow the same general
rules in their appearance and disappearance as do single species  changing
more or less quickly  and in a greater or lesser degree   A group  when it
has once disappeared  never reappears  that is  its existence  as long as
it lasts  is continuous   I am aware that there are some apparent
exceptions to this rule  but the exceptions are surprisingly few  so few
that E  Forbes  Pictet  and Woodward  though all strongly opposed to such
views as I maintain  admit its truth  and the rule strictly accords with
the theory   For all the species of the same group  however long it may
have lasted  are the modified descendants one from the other  and all from
a common progenitor   In the genus Lingula  for instance  the species which
have successively appeared at all ages must have been connected by an
unbroken series of generations  from the lowest Silurian stratum to the
present day 

We have seen in the last chapter that whole groups of species sometimes
falsely appear to have been abruptly developed  and I have attempted to
give an explanation of this fact  which if true would be fatal to my views  
But such cases are certainly exceptional  the general rule being a gradual
increase in number  until the group reaches its maximum  and then  sooner
or later  a gradual decrease   If the number of the species included within
a genus  or the number of the genera within a family  be represented by a
vertical line of varying thickness  ascending through the successive
geological formations  in which the species are found  the line will
sometimes falsely appear to begin at its lower end  not in a sharp point 
but abruptly  it then gradually thickens upwards  often keeping of equal
thickness for a space  and ultimately thins out in the upper beds  marking
the decrease and final extinction of the species   This gradual increase in
number of the species of a group is strictly conformable with the theory 
for the species of the same genus  and the genera of the same family  can
increase only slowly and progressively  the process of modification and the
production of a number of allied forms necessarily being a slow and gradual
process  one species first giving rise to two or three varieties  these
being slowly converted into species  which in their turn produce by equally
slow steps other varieties and species  and so on  like the branching of a
great tree from a single stem  till the group becomes large 

ON EXTINCTION 

We have as yet only spokesn incidentally of the disappearance of species
and of groups of species   On the theory of natural selection  the
extinction of old forms and the production of new and improved forms are
intimately connected together   The old notion of all the inhabitants of
the earth having been swept away by catastrophes at successive periods is
very generally given up  even by those geologists  as Elie de Beaumont 
Murchison  Barrande  etc   whose general views would naturally lead them to
this conclusion   On the contrary  we have every reason to believe  from
the study of the tertiary formations  that species and groups of species
gradually disappear  one after another  first from one spot  then from
another  and finally from the world   In some few cases  however  as by the
breaking of an isthmus and the consequent irruption of a multitude of new
inhabitants into an adjoining sea  or by the final subsidence of an island 
the process of extinction may have been rapid   Both single species and
whole groups of species last for very unequal periods  some groups  as we
have seen  have endured from the earliest known dawn of life to the present
day  some have disappeared before the close of the palaeozoic period   No
fixed law seems to determine the length of time during which any single
species or any single genus endures   There is reason to believe that the
extinction of a whole group of species is generally a slower process than
their production   if their appearance and disappearance be represented  as
before  by a vertical line of varying thickness the line is found to taper
more gradually at its upper end  which marks the progress of extermination 
than at its lower end  which marks the first appearance and the early
increase in number of the species   In some cases  however  the
extermination of whole groups  as of ammonites  towards the close of the
secondary period  has been wonderfully sudden 

The extinction of species has been involved in the most gratuitous mystery  
Some authors have even supposed that  as the individual has a definite
length of life  so have species a definite duration   No one can have
marvelled more than I have done at the extinction of species   When I found
in La Plata the tooth of a horse embedded with the remains of Mastodon 
Megatherium  Toxodon and other extinct monsters  which all co existed with
still living shells at a very late geological period  I was filled with
astonishment  for  seeing that the horse  since its introduction by the
Spaniards into South America  has run wild over the whole country and has
increased in numbers at an unparalleled rate  I asked myself what could so
recently have exterminated the former horse under conditions of life
apparently so favourable   But my astonishment was groundless   Professor
Owen soon perceived that the tooth  though so like that of the existing
horse  belonged to an extinct species   Had this horse been still living 
but in some degree rare  no naturalist would have felt the least surprise
at its rarity  for rarity is the attribute of a vast number of species of
all classes  in all countries   If we ask ourselves why this or that
species is rare  we answer that something is unfavourable in its conditions
of life  but what that something is  we can hardly ever tell   On the
supposition of the fossil horse still existing as a rare species  we might
have felt certain  from the analogy of all other mammals  even of the
slow breeding elephant  and from the history of the naturalisation of the
domestic horse in South America  that under more favourable conditions it
would in a very few years have stocked the whole continent   But we could
not have told what the unfavourable conditions were which checked its
increase  whether some one or several contingencies  and at what period of
the horse s life  and in what degree they severally acted   If the
conditions had gone on  however slowly  becoming less and less favourable 
we assuredly should not have perceived the fact  yet the fossil horse would
certainly have become rarer and rarer  and finally extinct  its place being
seized on by some more successful competitor 

It is most difficult always to remember that the increase of every living
creature is constantly being checked by unperceived hostile agencies  and
that these same unperceived agencies are amply sufficient to cause rarity 
and finally extinction   So little is this subject understood  that I have
heard surprise repeatedly expressed at such great monsters as the Mastodon
and the more ancient Dinosaurians having become extinct  as if mere bodily
strength gave victory in the battle of life   Mere size  on the contrary 
would in some cases determine  as has been remarked by Owen  quicker
extermination  from the greater amount of requisite food   Before man
inhabited India or Africa  some cause must have checked the continued
increase of the existing elephant   A highly capable judge  Dr  Falconer 
believes that it is chiefly insects which  from incessantly harassing and
weakening the elephant in India  check its increase  and this was Bruce s
conclusion with respect to the African elephant in Abyssinia   It is
certain that insects and blood sucking bats determine the existence of the
larger naturalised quadrupeds in several parts of South America 

We see in many cases in the more recent tertiary formations that rarity
precedes extinction  and we know that this has been the progress of events
with those animals which have been exterminated  either locally or wholly 
through man s agency   I may repeat what I published in 1845  namely  that
to admit that species generally become rare before they become extinct  to
feel no surprise at the rarity of a species  and yet to marvel greatly when
the species ceases to exist  is much the same as to admit that sickness in
the individual is the forerunner of death  to feel no surprise at sickness 
but  when the sick man dies  to wonder and to suspect that he died by some
deed of violence 

The theory of natural selection is grounded on the belief that each new
variety and ultimately each new species  is produced and maintained by
having some advantage over those with which it comes into competition  and
the consequent extinction of less favoured forms almost inevitably follows  
It is the same with our domestic productions   when a new and slightly
improved variety has been raised  it at first supplants the less improved
varieties in the same neighbourhood  when much improved it is transported
far and near  like our short horn cattle  and takes the place of other
breeds in other countries   Thus the appearance of new forms and the
disappearance of old forms  both those naturally and artificially produced 
are bound together   In flourishing groups  the number of new specific
forms which have been produced within a given time has at some periods
probably been greater than the number of the old specific forms which have
been exterminated  but we know that species have not gone on indefinitely
increasing  at least during the later geological epochs  so that  looking
to later times  we may believe that the production of new forms has caused
the extinction of about the same number of old forms 

The competition will generally be most severe  as formerly explained and
illustrated by examples  between the forms which are most like each other
in all respects   Hence the improved and modified descendants of a species
will generally cause the extermination of the parent species  and if many
new forms have been developed from any one species  the nearest allies of
that species  i e  the species of the same genus  will be the most liable
to extermination   Thus  as I believe  a number of new species descended
from one species  that is a new genus  comes to supplant an old genus 
belonging to the same family   But it must often have happened that a new
species belonging to some one group has seized on the place occupied by a
species belonging to a distinct group  and thus have caused its
extermination   If many allied forms be developed from the successful
intruder  many will have to yield their places  and it will generally be
the allied forms  which will suffer from some inherited inferiority in
common   But whether it be species belonging to the same or to a distinct
class  which have yielded their places to other modified and improved
species  a few of the sufferers may often be preserved for a long time 
from being fitted to some peculiar line of life  or from inhabiting some
distant and isolated station  where they will have escaped severe
competition   For instance  some species of Trigonia  a great genus of
shells in the secondary formations  survive in the Australian seas  and a
few members of the great and almost extinct group of Ganoid fishes still
inhabit our fresh waters   Therefore  the utter extinction of a group is
generally  as we have seen  a slower process than its production 

With respect to the apparently sudden extermination of whole families or
orders  as of Trilobites at the close of the palaeozoic period  and of
Ammonites at the close of the secondary period  we must remember what has
been already said on the probable wide intervals of time between our
consecutive formations  and in these intervals there may have been much
slow extermination   Moreover  when  by sudden immigration or by unusually
rapid development  many species of a new group have taken possession of an
area   many of the older species will have been exterminated in a
correspondingly rapid manner  and the forms which thus yield their places
will commonly be allied  for they will partake of the same inferiority in
common 

Thus  as it seems to me  the manner in which single species and whole
groups of species become extinct accords well with the theory of natural
selection   We need not marvel at extinction  if we must marvel  let it be
at our presumption in imagining for a moment that we understand the many
complex contingencies on which the existence of each species depends   If
we forget for an instant that each species tends to increase inordinately 
and that some check is always in action  yet seldom perceived by us  the
whole economy of nature will be utterly obscured   Whenever we can
precisely say why this species is more abundant in individuals than that 
why this species and not another can be naturalised in a given country 
then  and not until then  we may justly feel surprise why we cannot account
for the extinction of any particular species or group of species 

ON THE FORMS OF LIFE CHANGING ALMOST SIMULTANEOUSLY THROUGHOUT THE WORLD 

Scarcely any palaeontological discovery is more striking than the fact that
the forms of life change almost simultaneously throughout the world   Thus
our European Chalk formation can be recognised in many distant regions 
under the most different climates  where not a fragment of the mineral
chalk itself can be found  namely  in North America  in equatorial South
America  in Tierra del Fuego  at the Cape of Good Hope  and in the
peninsula of India   For at these distant points  the organic remains in
certain beds present an unmistakable resemblance to those of the Chalk   It
is not that the same species are met with  for in some cases not one
species is identically the same  but they belong to the same families 
genera  and sections of genera  and sometimes are similarly characterised
in such trifling points as mere superficial sculpture   Moreover  other
forms  which are not found in the Chalk of Europe  but which occur in the
formations either above or below  occur in the same order at these distant
points of the world   In the several successive palaeozoic formations of
Russia  Western Europe and North America  a similar parallelism in the
forms of life has been observed by several authors  so it is  according to
Lyell  with the European and North American tertiary deposits   Even if the
few fossil species which are common to the Old and New Worlds were kept
wholly out of view  the general parallelism in the successive forms of
life  in the palaeozoic and tertiary stages  would still be manifest  and
the several formations could be easily correlated 

These observations  however  relate to the marine inhabitants of the world  
we have not sufficient data to judge whether the productions of the land
and of fresh water at distant points change in the same parallel manner  
We may doubt whether they have thus changed   if the Megatherium  Mylodon 
Macrauchenia  and Toxodon had been brought to Europe from La Plata  without
any information in regard to their geological position  no one would have
suspected that they had co existed with sea shells all still living  but as
these anomalous monsters co existed with the Mastodon and Horse  it might
at least have been inferred that they had lived during one of the later
tertiary stages 

When the marine forms of life are spoken of as having changed
simultaneously throughout the world  it must not be supposed that this
expression relates to the same year  or even to the same century  or even
that it has a very strict geological sense  for if all the marine animals
now living in Europe  and all those that lived in Europe during the
pleistocene period  a very remote period as measured by years  including
the whole glacial epoch  were compared with those now existing in South
America or in Australia  the most skilful naturalist would hardly be able
to say whether the present or the pleistocene inhabitants of Europe
resembled most closely those of the southern hemisphere   So  again 
several highly competent observers maintain that the existing productions
of the United States are more closely related to those which lived in
Europe during certain late tertiary stages  than to the present inhabitants
of Europe  and if this be so  it is evident that fossiliferous beds now
deposited on the shores of North America would hereafter be liable to be
classed with somewhat older European beds   Nevertheless  looking to a
remotely future epoch  there can be little doubt that all the more modern
MARINE formations  namely  the upper pliocene  the pleistocene and strictly
modern beds of Europe  North and South America  and Australia  from
containing fossil remains in some degree allied  and from not including
those forms which are found only in the older underlying deposits  would be
correctly ranked as simultaneous in a geological sense 

The fact of the forms of life changing simultaneously in the above large
sense  at distant parts of the world  has greatly struck those admirable
observers  MM  de Verneuil and d Archiac   After referring to the
parallelism of the palaeozoic forms of life in various parts of Europe 
they add   If struck by this strange sequence  we turn our attention to
North America  and there discover a series of analogous phenomena  it will
appear certain that all these modifications of species  their extinction 
and the introduction of new ones  cannot be owing to mere changes in marine
currents or other causes more or less local and temporary  but depend on
general laws which govern the whole animal kingdom    M  Barrande has made
forcible remarks to precisely the same effect   It is  indeed  quite futile
to look to changes of currents  climate  or other physical conditions  as
the cause of these great mutations in the forms of life throughout the
world  under the most different climates   We must  as Barrande has
remarked  look to some special law   We shall see this more clearly when we
treat of the present distribution of organic beings  and find how slight is
the relation between the physical conditions of various countries and the
nature of their inhabitants 

This great fact of the parallel succession of the forms of life throughout
the world  is explicable on the theory of natural selection   New species
are formed by having some advantage over older forms  and the forms  which
are already dominant  or have some advantage over the other forms in their
own country  give birth to the greatest number of new varieties or
incipient species   We have distinct evidence on this head  in the plants
which are dominant  that is  which are commonest and most widely diffused 
producing the greatest number of new varieties   It is also natural that
the dominant  varying and far spreading species  which have already
invaded  to a certain extent  the territories of other species  should be
those which would have the best chance of spreading still further  and of
giving rise in new countries to other new varieties and species   The
process of diffusion would often be very slow  depending on climatal and
geographical changes  on strange accidents  and on the gradual
acclimatization of new species to the various climates through which they
might have to pass  but in the course of time the dominant forms would
generally succeed in spreading and would ultimately prevail   The diffusion
would  it is probable  be slower with the terrestrial inhabitants of
distinct continents than with the marine inhabitants of the continuous sea  
We might therefore expect to find  as we do find  a less strict degree of
parallelism in the succession of the productions of the land than with
those of the sea 

Thus  as it seems to me  the parallel  and  taken in a large sense 
simultaneous  succession of the same forms of life throughout the world 
accords well with the principle of new species having been formed by
dominant species spreading widely and varying  the new species thus
produced being themselves dominant  owing to their having had some
advantage over their already dominant parents  as well as over other
species  and again spreading  varying  and producing new forms   The old
forms which are beaten and which yield their places to the new and
victorious forms  will generally be allied in groups  from inheriting some
inferiority in common  and  therefore  as new and improved groups spread
throughout the world  old groups disappear from the world  and the
succession of forms everywhere tends to correspond both in their first
appearance and final disappearance 

There is one other remark connected with this subject worth making   I have
given my reasons for believing that most of our great formations  rich in
fossils  were deposited during periods of subsidence  and that blank
intervals of vast duration  as far as fossils are concerned  occurred
during the periods when the bed of the sea was either stationary or rising 
and likewise when sediment was not thrown down quickly enough to embed and
preserve organic remains   During these long and blank intervals I suppose
that the inhabitants of each region underwent a considerable amount of
modification and extinction  and that there was much migration from other
parts of the world   As we have reason to believe that large areas are
affected by the same movement  it is probable that strictly contemporaneous
formations have often been accumulated over very wide spaces in the same
quarter of the world  but we are very far from having any right to conclude
that this has invariably been the case  and that large areas have
invariably been affected by the same movements   When two formations have
been deposited in two regions during nearly  but not exactly  the same
period  we should find in both  from the causes explained in the foregoing
paragraphs  the same general succession in the forms of life  but the
species would not exactly correspond  for there will have been a little
more time in the one region than in the other for modification  extinction 
and immigration 

I suspect that cases of this nature occur in Europe   Mr  Prestwich  in his
admirable Memoirs on the eocene deposits of England and France  is able to
draw a close general parallelism between the successive stages in the two
countries  but when he compares certain stages in England with those in
France  although he finds in both a curious accordance in the numbers of
the species belonging to the same genera  yet the species themselves differ
in a manner very difficult to account for considering the proximity of the
two areas  unless  indeed  it be assumed that an isthmus separated two seas
inhabited by distinct  but contemporaneous faunas   Lyell has made similar
observations on some of the later tertiary formations   Barrande  also 
shows that there is a striking general parallelism in the successive
Silurian deposits of Bohemia and Scandinavia  nevertheless he finds a
surprising amount of difference in the species   If the several formations
in these regions have not been deposited during the same exact periods  a
formation in one region often corresponding with a blank interval in the
other  and if in both regions the species have gone on slowly changing
during the accumulation of the several formations and during the long
intervals of time between them  in this case the several formations in the
two regions could be arranged in the same order  in accordance with the
general succession of the forms of life  and the order would falsely appear
to be strictly parallel  nevertheless the species would not all be the same
in the apparently corresponding stages in the two regions 

ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER  AND TO LIVING FORMS 

Let us now look to the mutual affinities of extinct and living species  
All fall into a few grand classes  and this fact is at once explained on
the principle of descent   The more ancient any form is  the more  as a
general rule  it differs from living forms   But  as Buckland long ago
remarked  extinct species can all be classed either in still existing
groups  or between them   That the extinct forms of life help to fill up
the intervals between existing genera  families  and orders  is certainly
true  but as this statement has often been ignored or even denied  it may
be well to make some remarks on this subject  and to give some instances  
If we confine our attention either to the living or to the extinct species
of the same class  the series is far less perfect than if we combine both
into one general system   In the writings of Professor Owen we continually
meet with the expression of generalised forms  as applied to extinct
animals  and in the writings of Agassiz  of prophetic or synthetic types 
and these terms imply that such forms are  in fact  intermediate or
connecting links   Another distinguished palaeontologist  M  Gaudry  has
shown in the most striking manner that many of the fossil mammals
discovered by him in Attica serve to break down the intervals between
existing genera   Cuvier ranked the Ruminants and Pachyderms as two of the
most distinct orders of mammals  but so many fossil links have been
disentombed that Owen has had to alter the whole classification  and has
placed certain Pachyderms in the same sub order with ruminants  for
example  he dissolves by gradations the apparently wide interval between
the pig and the camel   The Ungulata or hoofed quadrupeds are now divided
into the even toed or odd toed divisions  but the Macrauchenia of South
America connects to a certain extent these two grand divisions   No one
will deny that the Hipparion is intermediate between the existing horse and
certain other ungulate forms   What a wonderful connecting link in the
chain of mammals is the Typotherium from South America  as the name given
to it by Professor Gervais expresses  and which cannot be placed in any
existing order   The Sirenia form a very distinct group of the mammals  and
one of the most remarkable peculiarities in existing dugong and lamentin is
the entire absence of hind limbs  without even a rudiment being left  but
the extinct Halitherium had  according to Professor Flower  an ossified
thigh bone  articulated to a well defined acetabulum in the pelvis   and it
thus makes some approach to ordinary hoofed quadrupeds  to which the
Sirenia are in other respects allied   The cetaceans or whales are widely
different from all other mammals  but the tertiary Zeuglodon and Squalodon 
which have been placed by some naturalists in an order by themselves  are
considered by Professor Huxley to be undoubtedly cetaceans   and to
constitute connecting links with the aquatic carnivora  

Even the wide interval between birds and reptiles has been shown by the
naturalist just quoted to be partially bridged over in the most unexpected
manner  on the one hand  by the ostrich and extinct Archeopteryx  and on
the other hand by the Compsognathus  one of the Dinosaurians  that group
which includes the most gigantic of all terrestrial reptiles   Turning to
the Invertebrata  Barrande asserts  a higher authority could not be named 
that he is every day taught that  although palaeozoic animals can certainly
be classed under existing groups  yet that at this ancient period the
groups were not so distinctly separated from each other as they now are 

Some writers have objected to any extinct species  or group of species 
being considered as intermediate between any two living species  or groups
of species   If by this term it is meant that an extinct form is directly
intermediate in all its characters between two living forms or groups  the
objection is probably valid   But in a natural classification many fossil
species certainly stand between living species  and some extinct genera
between living genera  even between genera belonging to distinct families  
The most common case  especially with respect to very distinct groups  such
as fish and reptiles  seems to be that  supposing them to be distinguished
at the present day by a score of characters  the ancient members are
separated by a somewhat lesser number of characters  so that the two groups
formerly made a somewhat nearer approach to each other than they now do 

It is a common belief that the more ancient a form is  by so much the more
it tends to connect by some of its characters groups now widely separated
from each other   This remark no doubt must be restricted to those groups
which have undergone much change in the course of geological ages  and it
would be difficult to prove the truth of the proposition  for every now and
then even a living animal  as the Lepidosiren  is discovered having
affinities directed towards very distinct groups   Yet if we compare the
older Reptiles and Batrachians  the older Fish  the older Cephalopods  and
the eocene Mammals  with the recent members of the same classes  we must
admit that there is truth in the remark 

Let us see how far these several facts and inferences accord with the
theory of descent with modification   As the subject is somewhat complex  I
must request the reader to turn to the diagram in the fourth chapter   We
may suppose that the numbered letters in italics represent genera  and the
dotted lines diverging from them the species in each genus   The diagram is
much too simple  too few genera and too few species being given  but this
is unimportant for us   The horizontal lines may represent successive
geological formations  and all the forms beneath the uppermost line may be
considered as extinct   The three existing genera  a14  q14  p14  will form
a small family  b14 and f14  a closely allied family or subfamily  and o14 
i14  m14  a third family   These three families  together with the many
extinct genera on the several lines of descent diverging from the parent
form  A  will form an order  for all will have inherited something in
common from their ancient progenitor   On the principle of the continued
tendency to divergence of character  which was formerly illustrated by this
diagram  the more recent any form is the more it will generally differ from
its ancient progenitor   Hence  we can understand the rule that the most
ancient fossils differ most from existing forms   We must not  however 
assume that divergence of character is a necessary contingency  it depends
solely on the descendants from a species being thus enabled to seize on
many and different places in the economy of nature   Therefore it is quite
possible  as we have seen in the case of some Silurian forms  that a
species might go on being slightly modified in relation to its slightly
altered conditions of life  and yet retain throughout a vast period the
same general characteristics   This is represented in the diagram by the
letter F14 

All the many forms  extinct and recent  descended from  A   make  as before
remarked  one order  and this order  from the continued effects of
extinction and divergence of character  has become divided into several
sub families and families  some of which are supposed to have perished at
different periods  and some to have endured to the present day 

By looking at the diagram we can see that if many of the extinct forms
supposed to be embedded in the successive formations  were discovered at
several points low down in the series  the three existing families on the
uppermost line would be rendered less distinct from each other   If  for
instance  the genera a1  a5  a10  f8  m3  m6  m9  were disinterred  these
three families would be so closely linked together that they probably would
have to be united into one great family  in nearly the same manner as has
occurred with ruminants and certain pachyderms   Yet he who objected to
consider as intermediate the extinct genera  which thus link together the
living genera of three families  would be partly justified  for they are
intermediate  not directly  but only by a long and circuitous course
through many widely different forms   If many extinct forms were to be
discovered above one of the middle horizontal lines or geological
formations  for instance  above No  VI   but none from beneath this line 
then only two of the families  those on the left hand a14  etc   and b14 
etc   would have to be united into one  and there would remain two families
which would be less distinct from each other than they were before the
discovery of the fossils   So again  if the three families formed of eight
genera  a14 to m14   on the uppermost line  be supposed to differ from each
other by half a dozen important characters  then the families which existed
at a period marked VI would certainly have differed from each other by a
less number of characters  for they would at this early stage of descent
have diverged in a less degree from their common progenitor   Thus it comes
that ancient and extinct genera are often in a greater or less degree
intermediate in character between their modified descendants  or between
their collateral relations 

Under nature the process will be far more complicated than is represented
in the diagram  for the groups will have been more numerous  they will have
endured for extremely unequal lengths of time  and will have been modified
in various degrees   As we possess only the last volume of the geological
record  and that in a very broken condition  we have no right to expect 
except in rare cases  to fill up the wide intervals in the natural system 
and thus to unite distinct families or orders   All that we have a right to
expect is  that those groups which have  within known geological periods 
undergone much modification  should in the older formations make some
slight approach to each other  so that the older members should differ less
from each other in some of their characters than do the existing members of
the same groups  and this by the concurrent evidence of our best
palaeontologists is frequently the case 

Thus  on the theory of descent with modification  the main facts with
respect to the mutual affinities of the extinct forms of life to each other
and to living forms  are explained in a satisfactory manner   And they are
wholly inexplicable on any other view 

On this same theory  it is evident that the fauna during any one great
period in the earth s history will be intermediate in general character
between that which preceded and that which succeeded it   Thus the species
which lived at the sixth great stage of descent in the diagram are the
modified offspring of those which lived at the fifth stage  and are the
parents of those which became still more modified at the seventh stage 
hence they could hardly fail to be nearly intermediate in character between
the forms of life above and below   We must  however  allow for the entire
extinction of some preceding forms  and in any one region for the
immigration of new forms from other regions  and for a large amount of
modification during the long and blank intervals between the successive
formations   Subject to these allowances  the fauna of each geological
period undoubtedly is intermediate in character  between the preceding and
succeeding faunas   I need give only one instance  namely  the manner in
which the fossils of the Devonian system  when this system was first
discovered  were at once recognised by palaeontologists as intermediate in
character between those of the overlying carboniferous and underlying
Silurian systems   But each fauna is not necessarily exactly intermediate 
as unequal intervals of time have elapsed between consecutive formations 

It is no real objection to the truth of the statement that the fauna of
each period as a whole is nearly intermediate in character between the
preceding and succeeding faunas  that certain genera offer exceptions to
the rule   For instance  the species of mastodons and elephants  when
arranged by Dr  Falconer in two series  in the first place according to
their mutual affinities  and in the second place according to their periods
of existence  do not accord in arrangement   The species extreme in
character are not the oldest or the most recent  nor are those which are
intermediate in character  intermediate in age   But supposing for an
instant  in this and other such cases  that the record of the first
appearance and disappearance of the species was complete  which is far from
the case  we have no reason to believe that forms successively produced
necessarily endure for corresponding lengths of time   A very ancient form
may occasionally have lasted much longer than a form elsewhere subsequently
produced  especially in the case of terrestrial productions inhabiting
separated districts   To compare small things with great  if the principal
living and extinct races of the domestic pigeon were arranged in serial
affinity  this arrangement would not closely accord with the order in time
of their production  and even less with the order of their disappearance 
for the parent rock pigeon still lives  and many varieties between the
rock pigeon and the carrier have become extinct  and carriers which are
extreme in the important character of length of beak originated earlier
than short beaked tumblers  which are at the opposite end of the series in
this respect 

Closely connected with the statement  that the organic remains from an
intermediate formation are in some degree intermediate in character  is the
fact  insisted on by all palaeontologists  that fossils from two
consecutive formations are far more closely related to each other  than are
the fossils from two remote formations   Pictet gives as a well known
instance  the general resemblance of the organic remains from the several
stages of the Chalk formation  though the species are distinct in each
stage   This fact alone  from its generality  seems to have shaken
Professor Pictet in his belief in the immutability of species   He who is
acquainted with the distribution of existing species over the globe  will
not attempt to account for the close resemblance of distinct species in
closely consecutive formations  by the physical conditions of the ancient
areas having remained nearly the same   Let it be remembered that the forms
of life  at least those inhabiting the sea  have changed almost
simultaneously throughout the world  and therefore under the most different
climates and conditions   Consider the prodigious vicissitudes of climate
during the pleistocene period  which includes the whole glacial epoch  and
note how little the specific forms of the inhabitants of the sea have been
affected 

On the theory of descent  the full meaning of the fossil remains from
closely consecutive formations  being closely related  though ranked as
distinct species  is obvious   As the accumulation of each formation has
often been interrupted  and as long blank intervals have intervened between
successive formations  we ought not to expect to find  as I attempted to
show in the last chapter  in any one or in any two formations  all the
intermediate varieties between the species which appeared at the
commencement and close of these periods   but we ought to find after
intervals  very long as measured by years  but only moderately long as
measured geologically  closely allied forms  or  as they have been called
by some authors  representative species  and these assuredly we do find  
We find  in short  such evidence of the slow and scarcely sensible
mutations of specific forms  as we have the right to expect 

ON THE STATE OF DEVELOPMENT OF ANCIENT COMPARED WITH LIVING FORMS 

We have seen in the fourth chapter that the degree of differentiation and
specialisation of the parts in organic beings  when arrived at maturity  is
the best standard  as yet suggested  of their degree of perfection or
highness   We have also seen that  as the specialisation of parts is an
advantage to each being  so natural selection will tend to render the
organisation of each being more specialised and perfect  and in this sense
higher  not but that it may leave many creatures with simple and unimproved
structures fitted for simple conditions of life  and in some cases will
even degrade or simplify the organisation  yet leaving such degraded beings
better fitted for their new walks of life   In another and more general
manner  new species become superior to their predecessors  for they have to
beat in the struggle for life all the older forms  with which they come
into close competition   We may therefore conclude that if under a nearly
similar climate the eocene inhabitants of the world could be put into
competition with the existing inhabitants  the former would be beaten and
exterminated by the latter  as would the secondary by the eocene  and the
palaeozoic by the secondary forms   So that by this fundamental test of
victory in the battle for life  as well as by the standard of the
specialisation of organs  modern forms ought  on the theory of natural
selection  to stand higher than ancient forms   Is this the case   A large
majority of palaeontologists would answer in the affirmative  and it seems
that this answer must be admitted as true  though difficult of proof 

It is no valid objection to this conclusion  that certain Brachiopods have
been but slightly modified from an extremely remote geological epoch  and
that certain land and fresh water shells have remained nearly the same 
from the time when  as far as is known  they first appeared   It is not an
insuperable difficulty that Foraminifera have not  as insisted on by Dr 
Carpenter  progressed in organisation since even the Laurentian epoch  for
some organisms would have to remain fitted for simple conditions of life 
and what could be better fitted for this end than these lowly organised
Protozoa   Such objections as the above would be fatal to my view  if it
included advance in organisation as a necessary contingent   They would
likewise be fatal  if the above Foraminifera  for instance  could be proved
to have first come into existence during the Laurentian epoch  or the above
Brachiopods during the Cambrian formation  for in this case  there would
not have been time sufficient for the development of these organisms up to
the standard which they had then reached   When advanced up to any given
point  there is no necessity  on the theory of natural selection  for their
further continued process  though they will  during each successive age 
have to be slightly modified  so as to hold their places in relation to
slight changes in their conditions   The foregoing objections hinge on the
question whether we really know how old the world is  and at what period
the various forms of life first appeared  and this may well be disputed 

The problem whether organisation on the whole has advanced is in many ways
excessively intricate   The geological record  at all times imperfect  does
not extend far enough back to show with unmistakable clearness that within
the known history of the world organisation has largely advanced   Even at
the present day  looking to members of the same class  naturalists are not
unanimous which forms ought to be ranked as highest   thus  some look at
the selaceans or sharks  from their approach in some important points of
structure to reptiles  as the highest fish  others look at the teleosteans
as the highest   The ganoids stand intermediate between the selaceans and
teleosteans  the latter at the present day are largely preponderant in
number  but formerly selaceans and ganoids alone existed  and in this case 
according to the standard of highness chosen  so will it be said that
fishes have advanced or retrograded in organisation   To attempt to compare
members of distinct types in the scale of highness seems hopeless  who will
decide whether a cuttle fish be higher than a bee  that insect which the
great Von Baer believed to be  in fact more highly organised than a fish 
although upon another type    In the complex struggle for life it is quite
credible that crustaceans  not very high in their own class  might beat
cephalopods  the highest molluscs  and such crustaceans  though not highly
developed  would stand very high in the scale of invertebrate animals  if
judged by the most decisive of all trials  the law of battle   Beside these
inherent difficulties in deciding which forms are the most advanced in
organisation  we ought not solely to compare the highest members of a class
at any two periods  though undoubtedly this is one and perhaps the most
important element in striking a balance  but we ought to compare all the
members  high and low  at two periods   At an ancient epoch the highest and
lowest molluscoidal animals  namely  cephalopods and brachiopods  swarmed
in numbers  at the present time both groups are greatly reduced  while
others  intermediate in organisation  have largely increased  consequently
some naturalists maintain that molluscs were formerly more highly developed
than at present  but a stronger case can be made out on the opposite side 
by considering the vast reduction of brachiopods  and the fact that our
existing cephalopods  though few in number  are more highly organised than
their ancient representatives   We ought also to compare the relative
proportional numbers  at any two periods  of the high and low classes
throughout the world   if  for instance  at the present day fifty thousand
kinds of vertebrate animals exist  and if we knew that at some former
period only ten thousand kinds existed  we ought to look at this increase
in number in the highest class  which implies a great displacement of lower
forms  as a decided advance in the organisation of the world   We thus see
how hopelessly difficult it is to compare with perfect fairness  under such
extremely complex relations  the standard of organisation of the
imperfectly known faunas of successive periods 

We shall appreciate this difficulty more clearly by looking to certain
existing faunas and floras   From the extraordinary manner in which
European productions have recently spread over New Zealand  and have seized
on places which must have been previously occupied by the indigenes  we
must believe  that if all the animals and plants of Great Britain were set
free in New Zealand  a multitude of British forms would in the course of
time become thoroughly naturalized there  and would exterminate many of the
natives   On the other hand  from the fact that hardly a single inhabitant
of the southern hemisphere has become wild in any part of Europe  we may
well doubt whether  if all the productions of New Zealand were set free in
Great Britain  any considerable number would be enabled to seize on places
now occupied by our native plants and animals   Under this point of view 
the productions of Great Britain stand much higher in the scale than those
of New Zealand   Yet the most skilful naturalist  from an examination of
the species of the two countries  could not have foreseen this result 

Agassiz and several other highly competent judges insist that ancient
animals resemble to a certain extent the embryos of recent animals
belonging to the same classes  and that the geological succession of
extinct forms is nearly parallel with the embryological development of
existing forms   This view accords admirably well with our theory   In a
future chapter I shall attempt to show that the adult differs from its
embryo  owing to variations having supervened at a not early age  and
having been inherited at a corresponding age   This process  whilst it
leaves the embryo almost unaltered  continually adds  in the course of
successive generations  more and more difference to the adult   Thus the
embryo comes to be left as a sort of picture  preserved by nature  of the
former and less modified condition of the species   This view may be true 
and yet may never be capable of proof   Seeing  for instance  that the
oldest known mammals  reptiles  and fishes strictly belong to their proper
classes  though some of these old forms are in a slight degree less
distinct from each other than are the typical members of the same groups at
the present day  it would be vain to look for animals having the common
embryological character of the Vertebrata  until beds rich in fossils are
discovered far beneath the lowest Cambrian strata  a discovery of which the
chance is small 

ON THE SUCCESSION OF THE SAME TYPES WITHIN THE SAME AREAS  DURING THE LATER
TERTIARY PERIODS 

Mr  Clift many years ago showed that the fossil mammals from the Australian
caves were closely allied to the living marsupials of that continent   In
South America  a similar relationship is manifest  even to an uneducated
eye  in the gigantic pieces of armour  like those of the armadillo  found
in several parts of La Plata  and Professor Owen has shown in the most
striking manner that most of the fossil mammals  buried there in such
numbers  are related to South American types   This relationship is even
more clearly seen in the wonderful collection of fossil bones made by MM 
Lund and Clausen in the caves of Brazil   I was so much impressed with
these facts that I strongly insisted  in 1839 and 1845  on this  law of the
succession of types    on  this wonderful relationship in the same
continent between the dead and the living    Professor Owen has
subsequently extended the same generalisation to the mammals of the Old
World   We see the same law in this author s restorations of the extinct
and gigantic birds of New Zealand   We see it also in the birds of the
caves of Brazil   Mr  Woodward has shown that the same law holds good with
sea shells  but  from the wide distribution of most molluscs  it is not
well displayed by them   Other cases could be added  as the relation
between the extinct and living land shells of Madeira  and between the
extinct and living brackish water shells of the Aralo Caspian Sea 

Now  what does this remarkable law of the succession of the same types
within the same areas mean   He would be a bold man who  after comparing
the present climate of Australia and of parts of South America  under the
same latitude  would attempt to account  on the one hand through dissimilar
physical conditions  for the dissimilarity of the inhabitants of these two
continents  and  on the other hand through similarity of conditions  for
the uniformity of the same types in each continent during the later
tertiary periods   Nor can it be pretended that it is an immutable law that
marsupials should have been chiefly or solely produced in Australia  or
that Edentata and other American types should have been solely produced in
South America   For we know that Europe in ancient times was peopled by
numerous marsupials  and I have shown in the publications above alluded to 
that in America the law of distribution of terrestrial mammals was formerly
different from what it now is   North America formerly partook strongly of
the present character of the southern half of the continent  and the
southern half was formerly more closely allied  than it is at present  to
the northern half   In a similar manner we know  from Falconer and
Cautley s discoveries  that Northern India was formerly more closely
related in its mammals to Africa than it is at the present time   Analogous
facts could be given in relation to the distribution of marine animals 

On the theory of descent with modification  the great law of the long
enduring  but not immutable  succession of the same types within the same
areas  is at once explained  for the inhabitants of each quarter of the
world will obviously tend to leave in that quarter  during the next
succeeding period of time  closely allied though in some degree modified
descendants   If the inhabitants of one continent formerly differed greatly
from those of another continent  so will their modified descendants still
differ in nearly the same manner and degree   But after very long intervals
of time  and after great geographical changes  permitting much
intermigration  the feebler will yield to the more dominant forms  and
there will be nothing immutable in the distribution of organic beings 

It may be asked in ridicule whether I suppose that the megatherium and
other allied huge monsters  which formerly lived in South America  have
left behind them the sloth  armadillo  and anteater  as their degenerate
descendants   This cannot for an instant be admitted   These huge animals
have become wholly extinct  and have left no progeny   But in the caves of
Brazil there are many extinct species which are closely allied in size and
in all other characters to the species still living in South America  and
some of these fossils may have been the actual progenitors of the living
species   It must not be forgotten that  on our theory  all the species of
the same genus are the descendants of some one species  so that  if six
genera  each having eight species  be found in one geological formation 
and in a succeeding formation there be six other allied or representative
genera  each with the same number of species  then we may conclude that
generally only one species of each of the older genera has left modified
descendants  which constitute the new genera containing the several
species  the other seven species of each old genus having died out and left
no progeny   Or  and this will be a far commoner case  two or three species
in two or three alone of the six older genera will be the parents of the
new genera   the other species and the other old genera having become
utterly extinct   In failing orders  with the genera and species decreasing
in numbers as is the case with the Edentata of South America  still fewer
genera and species will leave modified blood descendants 

SUMMARY OF THE PRECEDING AND PRESENT CHAPTERS 

I have attempted to show that the geological record is extremely imperfect 
that only a small portion of the globe has been geologically explored with
care  that only certain classes of organic beings have been largely
preserved in a fossil state  that the number both of specimens and of
species  preserved in our museums  is absolutely as nothing compared with
the number of generations which must have passed away even during a single
formation  that  owing to subsidence being almost necessary for the
accumulation of deposits rich in fossil species of many kinds  and thick
enough to outlast future degradation  great intervals of time must have
elapsed between most of our successive formations  that there has probably
been more extinction during the periods of subsidence  and more variation
during the periods of elevation  and during the latter the record will have
been least perfectly kept  that each single formation has not been
continuously deposited  that the duration of each formation is probably
short compared with the average duration of specific forms  that migration
has played an important part in the first appearance of new forms in any
one area and formation  that widely ranging species are those which have
varied most frequently  and have oftenest given rise to new species  that
varieties have at first been local  and lastly  although each species must
have passed through numerous transitional stages  it is probable that the
periods  during which each underwent modification  though many and long as
measured by years  have been short in comparison with the periods during
which each remained in an unchanged condition   These causes  taken
conjointly  will to a large extent explain why  though we do find many
links  we do not find interminable varieties  connecting together all
extinct and existing forms by the finest graduated steps   It should also
be constantly borne in mind that any linking variety between two forms 
which might be found  would be ranked  unless the whole chain could be
perfectly restored  as a new and distinct species  for it is not pretended
that we have any sure criterion by which species and varieties can be
discriminated 

He who rejects this view of the imperfection of the geological record  will
rightly reject the whole theory   For he may ask in vain where are the
numberless transitional links which must formerly have connected the
closely allied or representative species  found in the successive stages of
the same great formation   He may disbelieve in the immense intervals of
time which must have elapsed between our consecutive formations  he may
overlook how important a part migration has played  when the formations of
any one great region  as those of Europe  are considered  he may urge the
apparent  but often falsely apparent  sudden coming in of whole groups of
species   He may ask where are the remains of those infinitely numerous
organisms which must have existed long before the Cambrian system was
deposited   We now know that at least one animal did then exist  but I can
answer this last question only by supposing that where our oceans now
extend they have extended for an enormous period  and where our oscillating
continents now stand they have stood since the commencement of the Cambrian
system  but that  long before that epoch  the world presented a widely
different aspect  and that the older continents  formed of formations older
than any known to us  exist now only as remnants in a metamorphosed
condition  or lie still buried under the ocean 

Passing from these difficulties  the other great leading facts in
palaeontology agree admirably with the theory of descent with modification
through variation and natural selection   We can thus understand how it is
that new species come in slowly and successively  how species of different
classes do not necessarily change together  or at the same rate  or in the
same degree  yet in the long run that all undergo modification to some
extent   The extinction of old forms is the almost inevitable consequence
of the production of new forms   We can understand why  when a species has
once disappeared  it never reappears   Groups of species increase in
numbers slowly  and endure for unequal periods of time  for the process of
modification is necessarily slow  and depends on many complex
contingencies   The dominant species belonging to large and dominant groups
tend to leave many modified descendants  which form new sub groups and
groups   As these are formed  the species of the less vigorous groups  from
their inferiority inherited from a common progenitor  tend to become
extinct together  and to leave no modified offspring on the face of the
earth   But the utter extinction of a whole group of species has sometimes
been a slow process  from the survival of a few descendants  lingering in
protected and isolated situations   When a group has once wholly
disappeared  it does not reappear  for the link of generation has been
broken 

We can understand how it is that dominant forms which spread widely and
yield the greatest number of varieties tend to people the world with
allied  but modified  descendants  and these will generally succeed in
displacing the groups which are their inferiors in the struggle for
existence   Hence  after long intervals of time  the productions of the
world appear to have changed simultaneously 

We can understand how it is that all the forms of life  ancient and recent 
make together a few grand classes   We can understand  from the continued
tendency to divergence of character  why the more ancient a form is  the
more it generally differs from those now living   Why ancient and extinct
forms often tend to fill up gaps between existing forms  sometimes blending
two groups  previously classed as distinct into one  but more commonly
bringing them only a little closer together   The more ancient a form is 
the more often it stands in some degree intermediate between groups now
distinct  for the more ancient a form is  the more nearly it will be
related to  and consequently resemble  the common progenitor of groups 
since become widely divergent   Extinct forms are seldom directly
intermediate between existing forms  but are intermediate only by a long
and circuitous course through other extinct and different forms   We can
clearly see why the organic remains of closely consecutive formations are
closely allied  for they are closely linked together by generation   We can
clearly see why the remains of an intermediate formation are intermediate
in character 

The inhabitants of the world at each successive period in its history have
beaten their predecessors in the race for life  and are  in so far  higher
in the scale  and their structure has generally become more specialised  
and this may account for the common belief held by so many
palaeontologists  that organisation on the whole has progressed   Extinct
and ancient animals resemble to a certain extent the embryos of the more
recent animals belonging to the same classes  and this wonderful fact
receives a simple explanation according to our views   The succession of
the same types of structure within the same areas during the later
geological periods ceases to be mysterious  and is intelligible on the
principle of inheritance 

If  then  the geological record be as imperfect as many believe  and it may
at least be asserted that the record cannot be proved to be much more
perfect  the main objections to the theory of natural selection are greatly
diminished or disappear   On the other hand  all the chief laws of
palaeontology plainly proclaim  as it seems to me  that species have been
produced by ordinary generation   old forms having been supplanted by new
and improved forms of life  the products of variation and the survival of
the fittest 


CHAPTER XII 

GEOGRAPHICAL DISTRIBUTION 

Present distribution cannot be accounted for by differences in physical
conditions    Importance of barriers    Affinity of the productions of the
same continent    Centres of creation    Means of dispersal by changes of
climate and of the level of the land  and by occasional means    Dispersal
during the Glacial period    Alternate Glacial periods in the North and
South 

In considering the distribution of organic beings over the face of the
globe  the first great fact which strikes us is  that neither the
similarity nor the dissimilarity of the inhabitants of various regions can
be wholly accounted for by climatal and other physical conditions   Of
late  almost every author who has studied the subject has come to this
conclusion   The case of America alone would almost suffice to prove its
truth  for if we exclude the arctic and northern temperate parts  all
authors agree that one of the most fundamental divisions in geographical
distribution is that between the New and Old Worlds  yet if we travel over
the vast American continent  from the central parts of the United States to
its extreme southern point  we meet with the most diversified conditions 
humid districts  arid deserts  lofty mountains  grassy plains  forests 
marshes  lakes and great rivers  under almost every temperature   There is
hardly a climate or condition in the Old World which cannot be paralleled
in the New  at least so closely as the same species generally require   No
doubt small areas can be pointed out in the Old World hotter than any in
the New World  but these are not inhabited by a fauna different from that
of the surrounding districts  for it is rare to find a group of organisms
confined to a small area  of which the conditions are peculiar in only a
slight degree   Notwithstanding this general parallelism in the conditions
of Old and New Worlds  how widely different are their living productions 

In the southern hemisphere  if we compare large tracts of land in
Australia  South Africa  and western South America  between latitudes 25
and 35 degrees  we shall find parts extremely similar in all their
conditions  yet it would not be possible to point out three faunas and
floras more utterly dissimilar   Or  again  we may compare the productions
of South America south of latitude 35 degrees with those north of 25
degrees  which consequently are separated by a space of ten degrees of
latitude  and are exposed to considerably different conditions  yet they
are incomparably more closely related to each other than they are to the
productions of Australia or Africa under nearly the same climate  
Analogous facts could be given with respect to the inhabitants of the sea 

A second great fact which strikes us in our general review is  that
barriers of any kind  or obstacles to free migration  are related in a
close and important manner to the differences between the productions of
various regions   We see this in the great difference in nearly all the
terrestrial productions of the New and Old Worlds  excepting in the
northern parts  where the land almost joins  and where  under a slightly
different climate  there might have been free migration for the northern
temperate forms  as there now is for the strictly arctic productions   We
see the same fact in the great difference between the inhabitants of
Australia  Africa  and South America under the same latitude  for these
countries are almost as much isolated from each other as is possible   On
each continent  also  we see the same fact  for on the opposite sides of
lofty and continuous mountain ranges  and of great deserts and even of
large rivers  we find different productions  though as mountain chains 
deserts  etc   are not as impassable  or likely to have endured so long  as
the oceans separating continents  the differences are very inferior in
degree to those characteristic of distinct continents 

Turning to the sea  we find the same law   The marine inhabitants of the
eastern and western shores of South America are very distinct  with
extremely few shells  crustacea  or echinodermata in common  but Dr 
Gunther has recently shown that about thirty per cent of the fishes are the
same on the opposite sides of the isthmus of Panama  and this fact has led
naturalists to believe that the isthmus was formerly open   Westward of the
shores of America  a wide space of open ocean extends  with not an island
as a halting place for emigrants  here we have a barrier of another kind 
and as soon as this is passed we meet in the eastern islands of the Pacific
with another and totally distinct fauna   So that three marine faunas range
northward and southward in parallel lines not far from each other  under
corresponding climate  but from being separated from each other by
impassable barriers  either of land or open sea  they are almost wholly
distinct   On the other hand  proceeding still further westward from the
eastern islands of the tropical parts of the Pacific  we encounter no
impassable barriers  and we have innumerable islands as halting places  or
continuous coasts  until  after travelling over a hemisphere  we come to
the shores of Africa  and over this vast space we meet with no well defined
and distinct marine faunas   Although so few marine animals are common to
the above named three approximate faunas of Eastern and Western America and
the eastern Pacific islands  yet many fishes range from the Pacific into
the Indian Ocean  and many shells are common to the eastern islands of the
Pacific and the eastern shores of Africa on almost exactly opposite
meridians of longitude 

A third great fact  partly included in the foregoing statement  is the
affinity of the productions of the same continent or of the same sea 
though the species themselves are distinct at different points and
stations   It is a law of the widest generality  and every continent offers
innumerable instances   Nevertheless  the naturalist  in travelling  for
instance  from north to south  never fails to be struck by the manner in
which successive groups of beings  specifically distinct  though nearly
related  replace each other   He hears from closely allied  yet distinct
kinds of birds  notes nearly similar  and sees their nests similarly
constructed  but not quite alike  with eggs coloured in nearly the same
manner   The plains near the Straits of Magellan are inhabited by one
species of Rhea  American ostrich   and northward the plains of La Plata by
another species of the same genus  and not by a true ostrich or emu  like
those inhabiting Africa and Australia under the same latitude   On these
same plains of La Plata we see the agouti and bizcacha  animals having
nearly the same habits as our hares and rabbits  and belonging to the same
order of Rodents  but they plainly display an American type of structure  
We ascend the lofty peaks of the Cordillera  and we find an alpine species
of bizcacha  we look to the waters  and we do not find the beaver or
muskrat  but the coypu and capybara  rodents of the South American type  
Innumerable other instances could be given   If we look to the islands off
the American shore  however much they may differ in geological structure 
the inhabitants are essentially American  though they may be all peculiar
species   We may look back to past ages  as shown in the last chapter  and
we find American types then prevailing on the American continent and in the
American seas   We see in these facts some deep organic bond  throughout
space and time  over the same areas of land and water  independently of
physical conditions   The naturalist must be dull who is not led to inquire
what this bond is 

The bond is simply inheritance  that cause which alone  as far as we
positively know  produces organisms quite like each other  or  as we see in
the case of varieties  nearly alike   The dissimilarity of the inhabitants
of different regions may be attributed to modification through variation
and natural selection  and probably in a subordinate degree to the definite
influence of different physical conditions   The degrees of dissimilarity
will depend on the migration of the more dominant forms of life from one
region into another having been more or less effectually prevented  at
periods more or less remote  on the nature and number of the former
immigrants  and on the action of the inhabitants on each other in leading
to the preservation of different modifications  the relation of organism to
organism in the struggle for life being  as I have already often remarked 
the most important of all relations   Thus the high importance of barriers
comes into play by checking migration  as does time for the slow process of
modification through natural selection   Widely ranging species  abounding
in individuals  which have already triumphed over many competitors in their
own widely extended homes  will have the best chance of seizing on new
places  when they spread out into new countries   In their new homes they
will be exposed to new conditions  and will frequently undergo further
modification and improvement  and thus they will become still further
victorious  and will produce groups of modified descendants   On this
principle of inheritance with modification we can understand how it is that
sections of genera  whole genera  and even families  are confined to the
same areas  as is so commonly and notoriously the case 

There is no evidence  as was remarked in the last chapter  of the existence
of any law of necessary development   As the variability of each species is
an independent property  and will be taken advantage of by natural
selection  only so far as it profits each individual in its complex
struggle for life  so the amount of modification in different species will
be no uniform quantity   If a number of species  after having long competed
with each other in their old home  were to migrate in a body into a new and
afterwards isolated country  they would be little liable to modification 
for neither migration nor isolation in themselves effect anything   These
principles come into play only by bringing organisms into new relations
with each other and in a lesser degree with the surrounding physical
conditions   As we have seen in the last chapter that some forms have
retained nearly the same character from an enormously remote geological
period  so certain species have migrated over vast spaces  and have not
become greatly or at all modified 

According to these views  it is obvious that the several species of the
same genus  though inhabiting the most distant quarters of the world  must
originally have proceeded from the same source  as they are descended from
the same progenitor   In the case of those species which have undergone 
during whole geological periods  little modification  there is not much
difficulty in believing that they have migrated from the same region  for
during the vast geographical and climatical changes which have supervened
since ancient times  almost any amount of migration is possible   But in
many other cases  in which we have reason to believe that the species of a
genus have been produced within comparatively recent times  there is great
difficulty on this head   It is also obvious that the individuals of the
same species  though now inhabiting distant and isolated regions  must have
proceeded from one spot  where their parents were first produced   for  as
has been explained  it is incredible that individuals identically the same
should have been produced from parents specifically distinct 

SINGLE CENTRES OF SUPPOSED CREATION 

We are thus brought to the question which has been largely discussed by
naturalists  namely  whether species have been created at one or more
points of the earth s surface   Undoubtedly there are many cases of extreme
difficulty in understanding how the same species could possibly have
migrated from some one point to the several distant and isolated points 
where now found   Nevertheless the simplicity of the view that each species
was first produced within a single region captivates the mind   He who
rejects it  rejects the vera causa of ordinary generation with subsequent
migration  and calls in the agency of a miracle   It is universally
admitted  that in most cases the area inhabited by a species is continuous 
and that when a plant or animal inhabits two points so distant from each
other  or with an interval of such a nature  that the space could not have
been easily passed over by migration  the fact is given as something
remarkable and exceptional   The incapacity of migrating across a wide sea
is more clear in the case of terrestrial mammals than perhaps with any
other organic beings  and  accordingly  we find no inexplicable instances
of the same mammals inhabiting distant points of the world   No geologist
feels any difficulty in Great Britain possessing the same quadrupeds with
the rest of Europe  for they were no doubt once united   But if the same
species can be produced at two separate points  why do we not find a single
mammal common to Europe and Australia or South America   The conditions of
life are nearly the same  so that a multitude of European animals and
plants have become naturalised in America and Australia  and some of the
aboriginal plants are identically the same at these distant points of the
northern and southern hemispheres   The answer  as I believe  is  that
mammals have not been able to migrate  whereas some plants  from their
varied means of dispersal  have migrated across the wide and broken
interspaces   The great and striking influence of barriers of all kinds  is
intelligible only on the view that the great majority of species have been
produced on one side  and have not been able to migrate to the opposite
side   Some few families  many subfamilies  very many genera  a still
greater number of sections of genera  are confined to a single region  and
it has been observed by several naturalists that the most natural genera 
or those genera in which the species are most closely related to each
other  are generally confined to the same country  or if they have a wide
range that their range is continuous   What a strange anomaly it would be
if a directly opposite rule were to prevail when we go down one step lower
in the series  namely to the individuals of the same species  and these had
not been  at least at first  confined to some one region 

Hence  it seems to me  as it has to many other naturalists  that the view
of each species having been produced in one area alone  and having
subsequently migrated from that area as far as its powers of migration and
subsistence under past and present conditions permitted  is the most
probable   Undoubtedly many cases occur in which we cannot explain how the
same species could have passed from one point to the other   But the
geographical and climatical changes which have certainly occurred within
recent geological times  must have rendered discontinuous the formerly
continuous range of many species   So that we are reduced to consider
whether the exceptions to continuity of range are so numerous  and of so
grave a nature  that we ought to give up the belief  rendered probable by
general considerations  that each species has been produced within one
area  and has migrated thence as far as it could   It would be hopelessly
tedious to discuss all the exceptional cases of the same species  now
living at distant and separated points  nor do I for a moment pretend that
any explanation could be offered of many instances   But  after some
preliminary remarks  I will discuss a few of the most striking classes of
facts  namely  the existence of the same species on the summits of distant
mountain ranges  and at distant points in the Arctic and Antarctic regions 
and secondly  in the following chapter   the wide distribution of fresh
water productions  and thirdly  the occurrence of the same terrestrial
species on islands and on the nearest mainland  though separated by
hundreds of miles of open sea   If the existence of the same species at
distant and isolated points of the earth s surface can in many instances be
explained on the view of each species having migrated from a single
birthplace  then  considering our ignorance with respect to former
climatical and geographical changes  and to the various occasional means of
transport  the belief that a single birthplace is the law seems to me
incomparably the safest 

In discussing this subject we shall be enabled at the same time to consider
a point equally important for us  namely  whether the several species of a
genus which must on our theory all be descended from a common progenitor 
can have migrated  undergoing modification during their migration from some
one area   If  when most of the species inhabiting one region are different
from those of another region  though closely allied to them  it can be
shown that migration from the one region to the other has probably occurred
at some former period  our general view will be much strengthened  for the
explanation is obvious on the principle of descent with modification   A
volcanic island  for instance  upheaved and formed at the distance of a few
hundreds of miles from a continent  would probably receive from it in the
course of time a few colonists  and their descendants  though modified 
would still be related by inheritance to the inhabitants of that continent  
Cases of this nature are common  and are  as we shall hereafter see 
inexplicable on the theory of independent creation   This view of the
relation of the species of one region to those of another  does not differ
much from that advanced by Mr  Wallace  who concludes that  every species
has come into existence coincident both in space and time with a
pre existing closely allied species    And it is now well known that he
attributes this coincidence to descent with modification 

The question of single or multiple centres of creation differs from another
though allied question  namely  whether all the individuals of the same
species are descended from a single pair  or single hermaphrodite  or
whether  as some authors suppose  from many individuals simultaneously
created   With organic beings which never intercross  if such exist  each
species  must be descended from a succession of modified varieties  that
have supplanted each other  but have never blended with other individuals
or varieties of the same species  so that  at each successive stage of
modification  all the individuals of the same form will be descended from a
single parent   But in the great majority of cases  namely  with all
organisms which habitually unite for each birth  or which occasionally
intercross  the individuals of the same species inhabiting the same area
will be kept nearly uniform by intercrossing  so that many individuals will
go on simultaneously changing  and the whole amount of modification at each
stage will not be due to descent from a single parent   To illustrate what
I mean   our English race horses differ from the horses of every other
breed  but they do not owe their difference and superiority to descent from
any single pair  but to continued care in the selecting and training of
many individuals during each generation 

Before discussing the three classes of facts  which I have selected as
presenting the greatest amount of difficulty on the theory of  single
centres of creation   I must say a few words on the means of dispersal 

MEANS OF DISPERSAL 

Sir C  Lyell and other authors have ably treated this subject   I can give
here only the briefest abstract of the more important facts   Change of
climate must have had a powerful influence on migration   A region now
impassable to certain organisms from the nature of its climate  might have
been a high road for migration  when the climate was different   I shall 
however  presently have to discuss this branch of the subject in some
detail   Changes of level in the land must also have been highly
influential   a narrow isthmus now separates two marine faunas  submerge
it  or let it formerly have been submerged  and the two faunas will now
blend together  or may formerly have blended   Where the sea now extends 
land may at a former period have connected islands or possibly even
continents together  and thus have allowed terrestrial productions to pass
from one to the other   No geologist disputes that great mutations of level
have occurred within the period of existing organisms   Edward Forbes
insisted that all the islands in the Atlantic must have been recently
connected with Europe or Africa  and Europe likewise with America   Other
authors have thus hypothetically bridged over every ocean  and united
almost every island with some mainland   If  indeed  the arguments used by
Forbes are to be trusted  it must be admitted that scarcely a single island
exists which has not recently been united to some continent   This view
cuts the Gordian knot of the dispersal of the same species to the most
distant points  and removes many a difficulty  but to the best of my
judgment we are not authorized in admitting such enormous geographical
changes within the period of existing species   It seems to me that we have
abundant evidence of great oscillations in the level of the land or sea 
but not of such vast changes in the position and extension of our
continents  as to have united them within the recent period to each other
and to the several intervening oceanic islands   I freely admit the former
existence of many islands  now buried beneath the sea  which may have
served as halting places for plants and for many animals during their
migration   In the coral producing oceans such sunken islands are now
marked by rings of coral or atolls standing over them   Whenever it is
fully admitted  as it will some day be  that each species has proceeded
from a single birthplace  and when in the course of time we know something
definite about the means of distribution  we shall be enabled to speculate
with security on the former extension of the land   But I do not believe
that it will ever be proved that within the recent period most of our
continents which now stand quite separate  have been continuously  or
almost continuously united with each other  and with the many existing
oceanic islands   Several facts in distribution  such as the great
difference in the marine faunas on the opposite sides of almost every
continent  the close relation of the tertiary inhabitants of several lands
and even seas to their present inhabitants  the degree of affinity between
the mammals inhabiting islands with those of the nearest continent  being
in part determined  as we shall hereafter see  by the depth of the
intervening ocean  these and other such facts are opposed to the admission
of such prodigious geographical revolutions within the recent period  as
are necessary on the view advanced by Forbes and admitted by his followers  
The nature and relative proportions of the inhabitants of oceanic islands
are likewise opposed to the belief of their former continuity of
continents   Nor does the almost universally volcanic composition of such
islands favour the admission that they are the wrecks of sunken continents 
if they had originally existed as continental mountain ranges  some at
least of the islands would have been formed  like other mountain summits 
of granite  metamorphic schists  old fossiliferous and other rocks  instead
of consisting of mere piles of volcanic matter 

I must now say a few words on what are called accidental means  but which
more properly should be called occasional means of distribution   I shall
here confine myself to plants   In botanical works  this or that plant is
often stated to be ill adapted for wide dissemination  but the greater or
less facilities for transport across the sea may be said to be almost
wholly unknown   Until I tried  with Mr  Berkeley s aid  a few experiments 
it was not even known how far seeds could resist the injurious action of
sea water   To my surprise I found that out of eighty seven kinds  sixty 
four germinated after an immersion of twenty eight days  and a few survived
an immersion of 137 days   It deserves notice that certain orders were far
more injured than others   nine Leguminosae were tried  and  with one
exception  they resisted the salt water badly  seven species of the allied
orders  Hydrophyllaceae and Polemoniaceae  were all killed by a month s
immersion   For convenience sake I chiefly tried small seeds without the
capsules or fruit  and as all of these sank in a few days  they could not
have been floated across wide spaces of the sea  whether or not they were
injured by salt water   Afterwards I tried some larger fruits  capsules 
etc   and some of these floated for a long time   It is well known what a
difference there is in the buoyancy of green and seasoned timber  and it
occurred to me that floods would often wash into the sea dried plants or
branches with seed capsules or fruit attached to them   Hence I was led to
dry the stems and branches of ninety four plants with ripe fruit  and to
place them on sea water   The majority sank quickly  but some which  whilst
green  floated for a very short time  when dried floated much longer  for
instance  ripe hazel nuts sank immediately  but when dried they floated for
ninety days  and afterwards when planted germinated  an asparagus plant
with ripe berries floated for twenty three days  when dried it floated for
eighty five days  and the seeds afterwards germinated   the ripe seeds of
Helosciadium sank in two days  when dried they floated for above ninety
days  and afterwards germinated   Altogether  out of the ninety four dried
plants  eighteen floated for above twenty eight days  and some of the
eighteen floated for a very much longer period   So that as 64 87 kinds of
seeds germinated after an immersion of twenty eight days  and as 18 94
distinct species with ripe fruit  but not all the same species as in the
foregoing experiment  floated  after being dried  for above twenty eight
days  we may conclude  as far as anything can be inferred from these scanty
facts  that the seeds of 14 100 kinds of plants of any country might be
floated by sea currents during twenty eight days  and would retain their
power of germination   In Johnston s Physical Atlas  the average rate of
the several Atlantic currents is thirty three miles per diem  some currents
running at the rate of sixty miles per diem   on this average  the seeds of
14 100 plants belonging to one country might be floated across 924 miles of
sea to another country  and when stranded  if blown by an inland gale to a
favourable spot  would germinate 

Subsequently to my experiments  M  Martens tried similar ones  but in a
much better manner  for he placed the seeds in a box in the actual sea  so
that they were alternately wet and exposed to the air like really floating
plants   He tried ninety eight seeds  mostly different from mine  but he
chose many large fruits  and likewise seeds  from plants which live near
the sea  and this would have favoured both the average length of their
flotation and their resistance to the injurious action of the salt water  
On the other hand  he did not previously dry the plants or branches with
the fruit  and this  as we have seen  would have caused some of them to
have floated much longer   The result was that 18 98 of his seeds of
different kinds floated for forty two days  and were then capable of
germination   But I do not doubt that plants exposed to the waves would
float for a less time than those protected from violent movement as in our
experiments   Therefore  it would perhaps be safer to assume that the seeds
of about 10 100 plants of a flora  after having been dried  could be
floated across a space of sea 900 miles in width  and would then germinate  
The fact of the larger fruits often floating longer than the small  is
interesting  as plants with large seeds or fruit which  as Alph  de
Candolle has shown  generally have restricted ranges  could hardly be
transported by any other means 

Seeds may be occasionally transported in another manner   Drift timber is
thrown up on most islands  even on those in the midst of the widest oceans 
and the natives of the coral islands in the Pacific procure stones for
their tools  solely from the roots of drifted trees  these stones being a
valuable royal tax   I find that when irregularly shaped stones are
embedded in the roots of trees  small parcels of earth are very frequently
enclosed in their interstices and behind them  so perfectly that not a
particle could be washed away during the longest transport   out of one
small portion of earth thus COMPLETELY enclosed by the roots of an oak
about fifty years old  three dicotyledonous plants germinated   I am
certain of the accuracy of this observation   Again  I can show that the
carcasses of birds  when floating on the sea  sometimes escape being
immediately devoured  and many kinds of seeds in the crops of floating
birds long retain their vitality   peas and vetches  for instance  are
killed by even a few days  immersion in sea water  but some taken out of
the crop of a pigeon  which had floated on artificial sea water for thirty
days  to my surprise nearly all germinated 

Living birds can hardly fail to be highly effective agents in the
transportation of seeds   I could give many facts showing how frequently
birds of many kinds are blown by gales to vast distances across the ocean  
We may safely assume that under such circumstances their rate of flight
would often be thirty five miles an hour  and some authors have given a far
higher estimate   I have never seen an instance of nutritious seeds passing
through the intestines of a bird  but hard seeds of fruit pass uninjured
through even the digestive organs of a turkey   In the course of two
months  I picked up in my garden twelve kinds of seeds  out of the
excrement of small birds  and these seemed perfect  and some of them  which
were tried  germinated   But the following fact is more important   the
crops of birds do not secrete gastric juice  and do not  as I know by
trial  injure in the least the germination of seeds  now  after a bird has
found and devoured a large supply of food  it is positively asserted that
all the grains do not pass into the gizzard for twelve or even eighteen
hours   A bird in this interval might easily be blown to the distance of
five hundred miles  and hawks are known to look out for tired birds  and
the contents of their torn crops might thus readily get scattered   Some
hawks and owls bolt their prey whole  and after an interval of from twelve
to twenty hours  disgorge pellets  which  as I know from experiments made
in the Zoological Gardens  include seeds capable of germination   Some
seeds of the oat  wheat  millet  canary  hemp  clover  and beet germinated
after having been from twelve to twenty one hours in the stomachs of
different birds of prey  and two seeds of beet grew after having been thus
retained for two days and fourteen hours   Fresh water fish  I find  eat
seeds of many land and water plants  fish are frequently devoured by birds 
and thus the seeds might be transported from place to place   I forced many
kinds of seeds into the stomachs of dead fish  and then gave their bodies
to fishing eagles  storks  and pelicans  these birds  after an interval of
many hours  either rejected the seeds in pellets or passed them in their
excrement  and several of these seeds retained the power of germination  
Certain seeds  however  were always killed by this process 

Locusts are sometimes blown to great distances from the land   I myself
caught one 370 miles from the coast of Africa  and have heard of others
caught at greater distances   The Rev  R T  Lowe informed Sir C  Lyell that
in November  1844  swarms of locusts visited the island of Madeira   They
were in countless numbers  as thick as the flakes of snow in the heaviest
snowstorm  and extended upward as far as could be seen with a telescope  
During two or three days they slowly careered round and round in an immense
ellipse  at least five or six miles in diameter  and at night alighted on
the taller trees  which were completely coated with them   They then
disappeared over the sea  as suddenly as they had appeared  and have not
since visited the island   Now  in parts of Natal it is believed by some
farmers  though on insufficient evidence  that injurious seeds are
introduced into their grass land in the dung left by the great flights of
locusts which often visit that country   In consequence of this belief Mr 
Weale sent me in a letter a small packet of the dried pellets  out of which
I extracted under the microscope several seeds  and raised from them seven
grass plants  belonging to two species  of two genera   Hence a swarm of
locusts  such as that which visited Madeira  might readily be the means of
introducing several kinds of plants into an island lying far from the
mainland 

Although the beaks and feet of birds are generally clean  earth sometimes
adheres to them   in one case I removed sixty one grains  and in another
case twenty two grains of dry argillaceous earth from the foot of a
partridge  and in the earth there was a pebble as large as the seed of a
vetch   Here is a better case   the leg of a woodcock was sent to me by a
friend  with a little cake of dry earth attached to the shank  weighing
only nine grains  and this contained a seed of the toad rush  Juncus
bufonius  which germinated and flowered   Mr  Swaysland  of Brighton  who
during the last forty years has paid close attention to our migratory
birds  informs me that he has often shot wagtails  Motacillae   wheatears 
and whinchats  Saxicolae   on their first arrival on our shores  before
they had alighted  and he has several times noticed little cakes of earth
attached to their feet   Many facts could be given showing how generally
soil is charged with seeds   For instance  Professor Newton sent me the leg
of a red legged partridge  Caccabis rufa  which had been wounded and could
not fly  with a ball of hard earth adhering to it  and weighing six and a
half ounces   The earth had been kept for three years  but when broken 
watered and placed under a bell glass  no less than eighty two plants
sprung from it   these consisted of twelve monocotyledons  including the
common oat  and at least one kind of grass  and of seventy dicotyledons 
which consisted  judging from the young leaves  of at least three distinct
species   With such facts before us  can we doubt that the many birds which
are annually blown by gales across great spaces of ocean  and which
annually migrate  for instance  the millions of quails across the
Mediterranean  must occasionally transport a few seeds embedded in dirt
adhering to their feet or beaks   But I shall have to recur to this
subject 

As icebergs are known to be sometimes loaded with earth and stones  and
have even carried brushwood  bones  and the nest of a land bird  it can
hardly be doubted that they must occasionally  as suggested by Lyell  have
transported seeds from one part to another of the arctic and antarctic
regions  and during the Glacial period from one part of the now temperate
regions to another   In the Azores  from the large number of plants common
to Europe  in comparison with the species on the other islands of the
Atlantic  which stand nearer to the mainland  and  as remarked by Mr  H C 
Watson  from their somewhat northern character  in comparison with the
latitude  I suspected that these islands had been partly stocked by
ice borne seeds during the Glacial epoch   At my request Sir C  Lyell wrote
to M  Hartung to inquire whether he had observed erratic boulders on these
islands  and he answered that he had found large fragments of granite and
other rocks  which do not occur in the archipelago   Hence we may safely
infer that icebergs formerly landed their rocky burdens on the shores of
these mid ocean islands  and it is at least possible that they may have
brought thither the seeds of northern plants 

Considering that these several means of transport  and that other means 
which without doubt remain to be discovered  have been in action year after
year for tens of thousands of years  it would  I think  be a marvellous
fact if many plants had not thus become widely transported   These means of
transport are sometimes called accidental  but this is not strictly
correct   the currents of the sea are not accidental  nor is the direction
of prevalent gales of wind   It should be observed that scarcely any means
of transport would carry seeds for very great distances  for seeds do not
retain their vitality when exposed for a great length of time to the action
of sea water  nor could they be long carried in the crops or intestines of
birds   These means  however  would suffice for occasional transport across
tracts of sea some hundred miles in breadth  or from island to island  or
from a continent to a neighbouring island  but not from one distant
continent to another   The floras of distant continents would not by such
means become mingled  but would remain as distinct as they now are   The
currents  from their course  would never bring seeds from North America to
Britain  though they might and do bring seeds from the West Indies to our
western shores  where  if not killed by their very long immersion in salt
water  they could not endure our climate   Almost every year  one or two
land birds are blown across the whole Atlantic Ocean  from North America to
the western shores of Ireland and England  but seeds could be transported
by these rare wanderers only by one means  namely  by dirt adhering to
their feet or beaks  which is in itself a rare accident   Even in this
case  how small would be the chance of a seed falling on favourable soil 
and coming to maturity   But it would be a great error to argue that
because a well stocked island  like Great Britain  has not  as far as is
known  and it would be very difficult to prove this   received within the
last few centuries  through occasional means of transport  immigrants from
Europe or any other continent  that a poorly stocked island  though
standing more remote from the mainland  would not receive colonists by
similar means   Out of a hundred kinds of seeds or animals transported to
an island  even if far less well stocked than Britain  perhaps not more
than one would be so well fitted to its new home  as to become naturalised  
But this is no valid argument against what would be effected by occasional
means of transport  during the long lapse of geological time  whilst the
island was being upheaved  and before it had become fully stocked with
inhabitants   On almost bare land  with few or no destructive insects or
birds living there  nearly every seed which chanced to arrive  if fitted
for the climate  would germinate and survive 

DISPERSAL DURING THE GLACIAL PERIOD 

The identity of many plants and animals  on mountain summits  separated
from each other by hundreds of miles of lowlands  where Alpine species
could not possibly exist  is one of the most striking cases known of the
same species living at distant points  without the apparent possibility of
their having migrated from one point to the other   It is indeed a
remarkable fact to see so many plants of the same species living on the
snowy regions of the Alps or Pyrenees  and in the extreme northern parts of
Europe  but it is far more remarkable  that the plants on the White
Mountains  in the United States of America  are all the same with those of
Labrador  and nearly all the same  as we hear from Asa Gray  with those on
the loftiest mountains of Europe   Even as long ago as 1747  such facts led
Gmelin to conclude that the same species must have been independently
created at many distinct points  and we might have remained in this same
belief  had not Agassiz and others called vivid attention to the Glacial
period  which  as we shall immediately see  affords a simple explanation of
these facts   We have evidence of almost every conceivable kind  organic
and inorganic  that  within a very recent geological period  central Europe
and North America suffered under an Arctic climate   The ruins of a house
burnt by fire do not tell their tale more plainly than do the mountains of
Scotland and Wales  with their scored flanks  polished surfaces  and
perched boulders  of the icy streams with which their valleys were lately
filled   So greatly has the climate of Europe changed  that in Northern
Italy  gigantic moraines  left by old glaciers  are now clothed by the vine
and maize   Throughout a large part of the United States  erratic boulders
and scored rocks plainly reveal a former cold period 

The former influence of the glacial climate on the distribution of the
inhabitants of Europe  as explained by Edward Forbes  is substantially as
follows   But we shall follow the changes more readily  by supposing a new
glacial period slowly to come on  and then pass away  as formerly occurred  
As the cold came on  and as each more southern zone became fitted for the
inhabitants of the north  these would take the places of the former
inhabitants of the temperate regions   The latter  at the same time would
travel further and further southward  unless they were stopped by barriers 
in which case they would perish   The mountains would become covered with
snow and ice  and their former Alpine inhabitants would descend to the
plains   By the time that the cold had reached its maximum  we should have
an arctic fauna and flora  covering the central parts of Europe  as far
south as the Alps and Pyrenees  and even stretching into Spain   The now
temperate regions of the United States would likewise be covered by arctic
plants and animals and these would be nearly the same with those of Europe 
for the present circumpolar inhabitants  which we suppose to have
everywhere travelled southward  are remarkably uniform round the world 

As the warmth returned  the arctic forms would retreat northward  closely
followed up in their retreat by the productions of the more temperate
regions   And as the snow melted from the bases of the mountains  the
arctic forms would seize on the cleared and thawed ground  always
ascending  as the warmth increased and the snow still further disappeared 
higher and higher  whilst their brethren were pursuing their northern
journey   Hence  when the warmth had fully returned  the same species 
which had lately lived together on the European and North American 
lowlands  would again be found in the arctic regions of the Old and New
Worlds  and on many isolated mountain summits far distant from each other 

Thus we can understand the identity of many plants at points so immensely
remote as the mountains of the United States and those of Europe   We can
thus also understand the fact that the Alpine plants of each mountain range
are more especially related to the arctic forms living due north or nearly
due north of them   for the first migration when the cold came on  and the
re migration on the returning warmth  would generally have been due south
and north   The Alpine plants  for example  of Scotland  as remarked by Mr 
H C  Watson  and those of the Pyrenees  as remarked by Ramond  are more
especially allied to the plants of northern Scandinavia  those of the
United States to Labrador  those of the mountains of Siberia to the arctic
regions of that country   These views  grounded as they are on the
perfectly well ascertained occurrence of a former Glacial period  seem to
me to explain in so satisfactory a manner the present distribution of the
Alpine and Arctic productions of Europe and America  that when in other
regions we find the same species on distant mountain summits  we may almost
conclude  without other evidence  that a colder climate formerly permitted
their migration across the intervening lowlands  now become too warm for
their existence 

As the arctic forms moved first southward and afterwards backward to the
north  in unison with the changing climate  they will not have been exposed
during their long migrations to any great diversity of temperature  and as
they all migrated in a body together  their mutual relations will not have
been much disturbed   Hence  in accordance with the principles inculcated
in this volume  these forms will not have been liable to much modification  
But with the Alpine productions  left isolated from the moment of the
returning warmth  first at the bases and ultimately on the summits of the
mountains  the case will have been somewhat different  for it is not likely
that all the same arctic species will have been left on mountain ranges far
distant from each other  and have survived there ever since  they will
also  in all probability  have become mingled with ancient Alpine species 
which must have existed on the mountains before the commencement of the
Glacial epoch  and which during the coldest period will have been
temporarily driven down to the plains  they will  also  have been
subsequently exposed to somewhat different climatical influences   Their
mutual relations will thus have been in some degree disturbed  consequently
they will have been liable to modification  and they have been modified 
for if we compare the present Alpine plants and animals of the several
great European mountain ranges  one with another  though many of the
species remain identically the same  some exist as varieties  some as
doubtful forms or sub species and some as distinct yet closely allied
species representing each other on the several ranges 

In the foregoing illustration  I have assumed that at the commencement of
our imaginary Glacial period  the arctic productions were as uniform round
the polar regions as they are at the present day   But it is also necessary
to assume that many sub arctic and some few temperate forms were the same
round the world  for some of the species which now exist on the lower
mountain slopes and on the plains of North America and Europe are the same 
and it may be asked how I account for this degree of uniformity of the
sub arctic and temperate forms round the world  at the commencement of the
real Glacial period   At the present day  the sub arctic and northern
temperate productions of the Old and New Worlds are separated from each
other by the whole Atlantic Ocean and by the northern part of the Pacific  
During the Glacial period  when the inhabitants of the Old and New Worlds
lived further southwards than they do at present  they must have been still
more completely separated from each other by wider spaces of ocean  so that
it may well be asked how the same species could then or previously have
entered the two continents   The explanation  I believe  lies in the nature
of the climate before the commencement of the Glacial period   At this  the
newer Pliocene period  the majority of the inhabitants of the world were
specifically the same as now  and we have good reason to believe that the
climate was warmer than at the present day   Hence  we may suppose that the
organisms which now live under latitude 60 degrees  lived during the
Pliocene period further north  under the Polar Circle  in latitude 66 67
degrees  and that the present arctic productions then lived on the broken
land still nearer to the pole   Now  if we look at a terrestrial globe  we
see under the Polar Circle that there is almost continuous land from
western Europe through Siberia  to eastern America   And this continuity of
the circumpolar land  with the consequent freedom under a more favourable
climate for intermigration  will account for the supposed uniformity of the
sub arctic and temperate productions of the Old and New Worlds  at a period
anterior to the Glacial epoch 

Believing  from reasons before alluded to  that our continents have long
remained in nearly the same relative position  though subjected to great
oscillations of level  I am strongly inclined to extend the above view  and
to infer that during some earlier and still warmer period  such as the
older Pliocene period  a large number of the same plants and animals
inhabited the almost continuous circumpolar land  and that these plants and
animals  both in the Old and New Worlds  began slowly to migrate southwards
as the climate became less warm  long before the commencement of the
Glacial period   We now see  as I believe  their descendants  mostly in a
modified condition  in the central parts of Europe and the United States  
On this view we can understand the relationship with very little identity 
between the productions of North America and Europe  a relationship which
is highly remarkable  considering the distance of the two areas  and their
separation by the whole Atlantic Ocean   We can further understand the
singular fact remarked on by several observers that the productions of
Europe and America during the later tertiary stages were more closely
related to each other than they are at the present time  for during these
warmer periods the northern parts of the Old and New Worlds will have been
almost continuously united by land  serving as a bridge  since rendered
impassable by cold  for the intermigration of their inhabitants 

During the slowly decreasing warmth of the Pliocene period  as soon as the
species in common  which inhabited the New and Old Worlds  migrated south
of the Polar Circle  they will have been completely cut off from each
other   This separation  as far as the more temperate productions are
concerned  must have taken place long ages ago   As the plants and animals
migrated southward  they will have become mingled in the one great region
with the native American productions  and would have had to compete with
them  and in the other great region  with those of the Old World  
Consequently we have here everything favourable for much modification  for
far more modification than with the Alpine productions  left isolated 
within a much more recent period  on the several mountain ranges and on the
arctic lands of Europe and North America   Hence  it has come  that when we
compare the now living productions of the temperate regions of the New and
Old Worlds  we find very few identical species  though Asa Gray has lately
shown that more plants are identical than was formerly supposed   but we
find in every great class many forms  which some naturalists rank as
geographical races  and others as distinct species  and a host of closely
allied or representative forms which are ranked by all naturalists as
specifically distinct 

As on the land  so in the waters of the sea  a slow southern migration of a
marine fauna  which  during the Pliocene or even a somewhat earlier period 
was nearly uniform along the continuous shores of the Polar Circle  will
account  on the theory of modification  for many closely allied forms now
living in marine areas completely sundered   Thus  I think  we can
understand the presence of some closely allied  still existing and extinct
tertiary forms  on the eastern and western shores of temperate North
America  and the still more striking fact of many closely allied
crustaceans  as described in Dana s admirable work   some fish and other
marine animals  inhabiting the Mediterranean and the seas of Japan  these
two areas being now completely separated by the breadth of a whole
continent and by wide spaces of ocean 

These cases of close relationship in species either now or formerly
inhabiting the seas on the eastern and western shores of North America  the
Mediterranean and Japan  and the temperate lands of North America and
Europe  are inexplicable on the theory of creation   We cannot maintain
that such species have been created alike  in correspondence with the
nearly similar physical conditions of the areas  for if we compare  for
instance  certain parts of South America with parts of South Africa or
Australia  we see countries closely similar in all their physical
conditions  with their inhabitants utterly dissimilar 

ALTERNATE GLACIAL PERIODS IN THE NORTH AND SOUTH 

But we must return to our more immediate subject   I am convinced that
Forbes s view may be largely extended   In Europe we meet with the plainest
evidence of the Glacial period  from the western shores of Britain to the
Ural range  and southward to the Pyrenees   We may infer from the frozen
mammals and nature of the mountain vegetation  that Siberia was similarly
affected   In the Lebanon  according to Dr  Hooker  perpetual snow formerly
covered the central axis  and fed glaciers which rolled 4 000 feet down the
valleys   The same observer has recently found great moraines at a low
level on the Atlas range in North Africa   Along the Himalaya  at points
900 miles apart  glaciers have left the marks of their former low descent 
and in Sikkim  Dr  Hooker saw maize growing on ancient and gigantic
moraines   Southward of the Asiatic continent  on the opposite side of the
equator  we know  from the excellent researches of Dr  J  Haast and Dr 
Hector  that in New Zealand immense glaciers formerly descended to a low
level  and the same plants  found by Dr  Hooker on widely separated
mountains in this island tell the same story of a former cold period   From
facts communicated to me by the Rev  W B  Clarke  it appears also that
there are traces of former glacial action on the mountains of the south 
eastern corner of Australia 

Looking to America   in the northern half  ice borne fragments of rock have
been observed on the eastern side of the continent  as far south as
latitude 36 and 37 degrees  and on the shores of the Pacific  where the
climate is now so different  as far south as latitude 46 degrees   Erratic
boulders have  also  been noticed on the Rocky Mountains   In the
Cordillera of South America  nearly under the equator  glaciers once
extended far below their present level   In central Chile I examined a vast
mound of detritus with great boulders  crossing the Portillo valley  which 
there can hardly be a doubt  once formed a huge moraine  and Mr  D  Forbes
informs me that he found in various parts of the Cordillera  from latitude
13 to 30 degrees south  at about the height of 12 000 feet  deeply furrowed
rocks  resembling those with which he was familiar in Norway  and likewise
great masses of detritus  including grooved pebbles   Along this whole
space of the Cordillera true glaciers do not now exist even at much more
considerable heights   Further south  on both sides of the continent  from
latitude 41 degrees to the southernmost extremity  we have the clearest
evidence of former glacial action  in numerous immense boulders transported
far from their parent source 

 From these several facts  namely  from the glacial action having extended
all round the northern and southern hemispheres  from the period having
been in a geological sense recent in both hemispheres  from its having
lasted in both during a great length of time  as may be inferred from the
amount of work effected  and lastly  from glaciers having recently
descended to a low level along the whole line of the Cordillera  it at one
time appeared to me that we could not avoid the conclusion that the
temperature of the whole world had been simultaneously lowered during the
Glacial period   But now  Mr  Croll  in a series of admirable memoirs  has
attempted to show that a glacial condition of climate is the result of
various physical causes  brought into operation by an increase in the
eccentricity of the earth s orbit   All these causes tend towards the same
end  but the most powerful appears to be the indirect influence of the
eccentricity of the orbit upon oceanic currents   According to Mr  Croll 
cold periods regularly recur every ten or fifteen thousand years  and these
at long intervals are extremely severe  owing to certain contingencies  of
which the most important  as Sir C  Lyell has shown  is the relative
position of the land and water   Mr  Croll believes that the last great
glacial period occurred about 240 000 years ago  and endured  with slight
alterations of climate  for about 160 000 years   With respect to more
ancient glacial periods  several geologists are convinced  from direct
evidence  that such occurred during the miocene and eocene formations  not
to mention still more ancient formations   But the most important result
for us  arrived at by Mr  Croll  is that whenever the northern hemisphere
passes through a cold period the temperature of the southern hemisphere is
actually raised  with the winters rendered much milder  chiefly through
changes in the direction of the ocean currents   So conversely it will be
with the northern hemisphere  while the southern passes through a glacial
period   This conclusion throws so much light on geographical distribution
that I am strongly inclined to trust in it  but I will first give the facts
which demand an explanation 

In South America  Dr  Hooker has shown that besides many closely allied
species  between forty and fifty of the flowering plants of Tierra del
Fuego  forming no inconsiderable part of its scanty flora  are common to
North America and Europe  enormously remote as these areas in opposite
hemispheres are from each other   On the lofty mountains of equatorial
America a host of peculiar species belonging to European genera occur   On
the Organ Mountains of Brazil some few temperate European  some Antarctic
and some Andean genera were found by Gardner which do not exist in the low
intervening hot countries   On the Silla of Caraccas the illustrious
Humboldt long ago found species belonging to genera characteristic of the
Cordillera 

In Africa  several forms characteristic of Europe  and some few
representatives of the flora of the Cape of Good Hope  occur on the
mountains of Abyssinia   At the Cape of Good Hope a very few European
species  believed not to have been introduced by man  and on the mountains
several representative European forms are found which have not been
discovered in the intertropical parts of Africa   Dr  Hooker has also
lately shown that several of the plants living on the upper parts of the
lofty island of Fernando Po  and on the neighbouring Cameroon Mountains  in
the Gulf of Guinea  are closely related to those on the mountains of
Abyssinia  and likewise to those of temperate Europe   It now also appears 
as I hear from Dr  Hooker  that some of these same temperate plants have
been discovered by the Rev  R T  Lowe on the mountains of the Cape Verde
Islands   This extension of the same temperate forms  almost under the
equator  across the whole continent of Africa and to the mountains of the
Cape Verde archipelago  is one of the most astonishing facts ever recorded
in the distribution of plants 

On the Himalaya  and on the isolated mountain ranges of the peninsula of
India  on the heights of Ceylon  and on the volcanic cones of Java  many
plants occur either identically the same or representing each other  and at
the same time representing plants of Europe not found in the intervening
hot lowlands   A list of the genera of plants collected on the loftier
peaks of Java  raises a picture of a collection made on a hillock in
Europe   Still more striking is the fact that peculiar Australian forms are
represented by certain plants growing on the summits of the mountains of
Borneo   Some of these Australian forms  as I hear from Dr  Hooker  extend
along the heights of the peninsula of Malacca  and are thinly scattered on
the one hand over India  and on the other hand as far north as Japan 

On the southern mountains of Australia  Dr  F  Muller has discovered
several European species  other species  not introduced by man  occur on
the lowlands  and a long list can be given  as I am informed by Dr  Hooker 
of European genera  found in Australia  but not in the intermediate torrid
regions   In the admirable  Introduction to the Flora of New Zealand   by
Dr  Hooker  analogous and striking facts are given in regard to the plants
of that large island   Hence  we see that certain plants growing on the
more lofty mountains of the tropics in all parts of the world  and on the
temperate plains of the north and south  are either the same species or
varieties of the same species   It should  however  be observed that these
plants are not strictly arctic forms  for  as Mr  H C  Watson has remarked 
 in receding from polar toward equatorial latitudes  the Alpine or mountain
flora really become less and less Arctic    Besides these identical and
closely allied forms  many species inhabiting the same widely sundered
areas  belong to genera not now found in the intermediate tropical
lowlands 

These brief remarks apply to plants alone  but some few analogous facts
could be given in regard to terrestrial animals   In marine productions 
similar cases likewise occur  as an example  I may quote a statement by the
highest authority  Prof  Dana  that  it is certainly a wonderful fact that
New Zealand should have a closer resemblance in its crustacea to Great
Britain  its antipode  than to any other part of the world    Sir J 
Richardson  also  speaks of the reappearance on the shores of New Zealand 
Tasmania  etc   of northern forms of fish   Dr  Hooker informs me that
twenty five species of Algae are common to New Zealand and to Europe  but
have not been found in the intermediate tropical seas 

 From the foregoing facts  namely  the presence of temperate forms on the
highlands across the whole of equatorial Africa  and along the Peninsula of
India  to Ceylon and the Malay Archipelago  and in a less well marked
manner across the wide expanse of tropical South America  it appears almost
certain that at some former period  no doubt during the most severe part of
a Glacial period  the lowlands of these great continents were everywhere
tenanted under the equator by a considerable number of temperate forms   At
this period the equatorial climate at the level of the sea was probably
about the same with that now experienced at the height of from five to six
thousand feet under the same latitude  or perhaps even rather cooler  
During this  the coldest period  the lowlands under the equator must have
been clothed with a mingled tropical and temperate vegetation  like that
described by Hooker as growing luxuriantly at the height of from four to
five thousand feet on the lower slopes of the Himalaya  but with perhaps a
still greater preponderance of temperate forms   So again in the
mountainous island of Fernando Po  in the Gulf of Guinea  Mr  Mann found
temperate European forms beginning to appear at the height of about five
thousand feet   On the mountains of Panama  at the height of only two
thousand feet  Dr  Seemann found the vegetation like that of Mexico   with
forms of the torrid zone harmoniously blended with those of the temperate  

Now let us see whether Mr  Croll s conclusion that when the northern
hemisphere suffered from the extreme cold of the great Glacial period  the
southern hemisphere was actually warmer  throws any clear light on the
present apparently inexplicable distribution of various organisms in the
temperate parts of both hemispheres  and on the mountains of the tropics 
The Glacial period  as measured by years  must have been very long  and
when we remember over what vast spaces some naturalised plants and animals
have spread within a few centuries  this period will have been ample for
any amount of migration   As the cold became more and more intense  we know
that Arctic forms invaded the temperate regions  and from the facts just
given  there can hardly be a doubt that some of the more vigorous  dominant
and widest spreading temperate forms invaded the equatorial lowlands   The
inhabitants of these hot lowlands would at the same time have migrated to
the tropical and subtropical regions of the south  for the southern
hemisphere was at this period warmer   On the decline of the Glacial
period  as both hemispheres gradually recovered their former temperature 
the northern temperate forms living on the lowlands under the equator 
would have been driven to their former homes or have been destroyed  being
replaced by the equatorial forms returning from the south   Some  however 
of the northern temperate forms would almost certainly have ascended any
adjoining high land  where  if sufficiently lofty  they would have long
survived like the Arctic forms on the mountains of Europe   They might have
survived  even if the climate was not perfectly fitted for them  for the
change of temperature must have been very slow  and plants undoubtedly
possess a certain capacity for acclimatisation  as shown by their
transmitting to their offspring different constitutional powers of
resisting heat and cold 

In the regular course of events the southern hemisphere would in its turn
be subjected to a severe Glacial period  with the northern hemisphere
rendered warmer  and then the southern temperate forms would invade the
equatorial lowlands   The northern forms which had before been left on the
mountains would now descend and mingle with the southern forms   These
latter  when the warmth returned  would return to their former homes 
leaving some few species on the mountains  and carrying southward with them
some of the northern temperate forms which had descended from their
mountain fastnesses   Thus  we should have some few species identically the
same in the northern and southern temperate zones and on the mountains of
the intermediate tropical regions   But the species left during a long time
on these mountains  or in opposite hemispheres  would have to compete with
many new forms and would be exposed to somewhat different physical
conditions  hence  they would be eminently liable to modification  and
would generally now exist as varieties or as representative species  and
this is the case   We must  also  bear in mind the occurrence in both
hemispheres of former Glacial periods  for these will account  in
accordance with the same principles  for the many quite distinct species
inhabiting the same widely separated areas  and belonging to genera not now
found in the intermediate torrid zones 

It is a remarkable fact  strongly insisted on by Hooker in regard to
America  and by Alph  de Candolle in regard to Australia  that many more
identical or slightly modified species have migrated from the north to the
south  than in a reversed direction   We see  however  a few southern forms
on the mountains of Borneo and Abyssinia   I suspect that this preponderant
migration from the north to the south is due to the greater extent of land
in the north  and to the northern forms having existed in their own homes
in greater numbers  and having consequently been advanced through natural
selection and competition to a higher stage of perfection  or dominating
power  than the southern forms   And thus  when the two sets became
commingled in the equatorial regions  during the alternations of the
Glacial periods  the northern forms were the more powerful and were able to
hold their places on the mountains  and afterwards migrate southward with
the southern forms  but not so the southern in regard to the northern
forms   In the same manner  at the present day  we see that very many
European productions cover the ground in La Plata  New Zealand  and to a
lesser degree in Australia  and have beaten the natives  whereas extremely
few southern forms have become naturalised in any part of the northern
hemisphere  though hides  wool  and other objects likely to carry seeds
have been largely imported into Europe during the last two or three
centuries from La Plata and during the last forty or fifty years from
Australia   The Neilgherrie Mountains in India  however  offer a partial
exception  for here  as I hear from Dr  Hooker  Australian forms are
rapidly sowing themselves and becoming naturalised   Before the last great
Glacial period  no doubt the intertropical mountains were stocked with
endemic Alpine forms  but these have almost everywhere yielded to the more
dominant forms generated in the larger areas and more efficient workshops
of the north   In many islands the native productions are nearly equalled 
or even outnumbered  by those which have become naturalised  and this is
the first stage towards their extinction   Mountains are islands on the
land  and their inhabitants have yielded to those produced within the
larger areas of the north  just in the same way as the inhabitants of real
islands have everywhere yielded and are still yielding to continental forms
naturalised through man s agency 

The same principles apply to the distribution of terrestrial animals and of
marine productions  in the northern and southern temperate zones  and on
the intertropical mountains   When  during the height of the Glacial
period  the ocean currents were widely different to what they now are  some
of the inhabitants of the temperate seas might have reached the equator  of
these a few would perhaps at once be able to migrate southwards  by keeping
to the cooler currents  while others might remain and survive in the colder
depths until the southern hemisphere was in its turn subjected to a glacial
climate and permitted their further progress  in nearly the same manner as 
according to Forbes  isolated spaces inhabited by Arctic productions exist
to the present day in the deeper parts of the northern temperate seas 

I am far from supposing that all the difficulties in regard to the
distribution and affinities of the identical and allied species  which now
live so widely separated in the north and south  and sometimes on the
intermediate mountain ranges  are removed on the views above given   The
exact lines of migration cannot be indicated   We cannot say why certain
species and not others have migrated  why certain species have been
modified and have given rise to new forms  while others have remained
unaltered   We cannot hope to explain such facts  until we can say why one
species and not another becomes naturalised by man s agency in a foreign
land  why one species ranges twice or thrice as far  and is twice or thrice
as common  as another species within their own homes 

Various special difficulties also remain to be solved  for instance  the
occurrence  as shown by Dr  Hooker  of the same plants at points so
enormously remote as Kerguelen Land  New Zealand  and Fuegia  but icebergs 
as suggested by Lyell  may have been concerned in their dispersal   The
existence at these and other distant points of the southern hemisphere  of
species  which  though distinct  belong to genera exclusively confined to
the south  is a more remarkable case   Some of these species are so
distinct  that we cannot suppose that there has been time since the
commencement of the last Glacial period for their migration and subsequent
modification to the necessary degree   The facts seem to indicate that
distinct species belonging to the same genera have migrated in radiating
lines from a common centre  and I am inclined to look in the southern  as
in the northern hemisphere  to a former and warmer period  before the
commencement of the last Glacial period  when the Antarctic lands  now
covered with ice  supported a highly peculiar and isolated flora   It may
be suspected that before this flora was exterminated during the last
Glacial epoch  a few forms had been already widely dispersed to various
points of the southern hemisphere by occasional means of transport  and by
the aid  as halting places  of now sunken islands   Thus the southern
shores of America  Australia  and New Zealand may have become slightly
tinted by the same peculiar forms of life 

Sir C  Lyell in a striking passage has speculated  in language almost
identical with mine  on the effects of great alternations of climate
throughout the world on geographical distribution   And we have now seen
that Mr  Croll s conclusion that successive Glacial periods in the one
hemisphere coincide with warmer periods in the opposite hemisphere 
together with the admission of the slow modification of species  explains a
multitude of facts in the distribution of the same and of the allied forms
of life in all parts of the globe   The living waters have flowed during
one period from the north and during another from the south  and in both
cases have reached the equator  but the stream of life has flowed with
greater force from the north than in the opposite direction  and has
consequently more freely inundated the south   As the tide leaves its drift
in horizontal lines  rising higher on the shores where the tide rises
highest  so have the living waters left their living drift on our mountain
summits  in a line gently rising from the Arctic lowlands to a great
latitude under the equator   The various beings thus left stranded may be
compared with savage races of man  driven up and surviving in the mountain
fastnesses of almost every land  which serves as a record  full of interest
to us  of the former inhabitants of the surrounding lowlands 


CHAPTER XIII 

GEOGRAPHICAL DISTRIBUTION  continued 

Distribution of fresh water productions    On the inhabitants of oceanic
islands    Absence of Batrachians and of terrestrial Mammals    On the
relation of the inhabitants of islands to those of the nearest mainland   
On colonisation from the nearest source with subsequent modification   
Summary of the last and present chapters 

FRESH WATER PRODUCTIONS 

As lakes and river systems are separated from each other by barriers of
land  it might have been thought that fresh water productions would not
have ranged widely within the same country  and as the sea is apparently a
still more formidable barrier  that they would never have extended to
distant countries   But the case is exactly the reverse   Not only have
many fresh water species  belonging to different classes  an enormous
range  but allied species prevail in a remarkable manner throughout the
world   When first collecting in the fresh waters of Brazil  I well
remember feeling much surprise at the similarity of the fresh water
insects  shells  etc   and at the dissimilarity of the surrounding
terrestrial beings  compared with those of Britain 

But the wide ranging power of fresh water productions can  I think  in most
cases be explained by their having become fitted  in a manner highly useful
to them  for short and frequent migrations from pond to pond  or from
stream to stream  within their own countries  and liability to wide
dispersal would follow from this capacity as an almost necessary
consequence   We can here consider only a few cases  of these  some of the
most difficult to explain are presented by fish   It was formerly believed
that the same fresh water species never existed on two continents distant
from each other   But Dr  Gunther has lately shown that the Galaxias
attenuatus inhabits Tasmania  New Zealand  the Falkland Islands and the
mainland of South America   This is a wonderful case  and probably
indicates dispersal from an Antarctic centre during a former warm period  
This case  however  is rendered in some degree less surprising by the
species of this genus having the power of crossing by some unknown means
considerable spaces of open ocean   thus there is one species common to New
Zealand and to the Auckland Islands  though separated by a distance of
about 230 miles   On the same continent fresh water fish often range
widely  and as if capriciously  for in two adjoining river systems some of
the species may be the same and some wholly different 

It is probable that they are occasionally transported by what may be called
accidental means   Thus fishes still alive are not very rarely dropped at
distant points by whirlwinds  and it is known that the ova retain their
vitality for a considerable time after removal from the water   Their
dispersal may  however  be mainly attributed to changes in the level of the
land within the recent period  causing rivers to flow into each other  
Instances  also  could be given of this having occurred during floods 
without any change of level   The wide differences of the fish on the
opposite sides of most mountain ranges  which are continuous and
consequently must  from an early period  have completely prevented the
inosculation of the river systems on the two sides  leads to the same
conclusion   Some fresh water fish belong to very ancient forms  and in
such cases there will have been ample time for great geographical changes 
and consequently time and means for much migration   Moreover  Dr  Gunther
has recently been led by several considerations to infer that with fishes
the same forms have a long endurance   Salt water fish can with care be
slowly accustomed to live in fresh water  and  according to Valenciennes 
there is hardly a single group of which all the members are confined to
fresh water  so that a marine species belonging to a fresh water group
might travel far along the shores of the sea  and could  it is probable 
become adapted without much difficulty to the fresh waters of a distant
land 

Some species of fresh water shells have very wide ranges  and allied
species which  on our theory  are descended from a common parent  and must
have proceeded from a single source  prevail throughout the world   Their
distribution at first perplexed me much  as their ova are not likely to be
transported by birds  and the ova  as well as the adults  are immediately
killed by sea water   I could not even understand how some naturalised
species have spread rapidly throughout the same country   But two facts 
which I have observed  and many others no doubt will be discovered  throw
some light on this subject   When ducks suddenly emerge from a pond covered
with duck weed  I have twice seen these little plants adhering to their
backs  and it has happened to me  in removing a little duck weed from one
aquarium to another  that I have unintentionally stocked the one with
fresh water shells from the other   But another agency is perhaps more
effectual   I suspended the feet of a duck in an aquarium  where many ova
of fresh water shells were hatching  and I found that numbers of the
extremely minute and just hatched shells crawled on the feet  and clung to
them so firmly that when taken out of the water they could not be jarred
off  though at a somewhat more advanced age they would voluntarily drop
off   These just hatched molluscs  though aquatic in their nature  survived
on the duck s feet  in damp air  from twelve to twenty hours  and in this
length of time a duck or heron might fly at least six or seven hundred
miles  and if blown across the sea to an oceanic island  or to any other
distant point  would be sure to alight on a pool or rivulet   Sir Charles
Lyell informs me that a Dyticus has been caught with an Ancylus  a
fresh water shell like a limpet  firmly adhering to it  and a water beetle
of the same family  a Colymbetes  once flew on board the  Beagle   when
forty five miles distant from the nearest land   how much farther it might
have been blown by a favouring gale no one can tell 

With respect to plants  it has long been known what enormous ranges many
fresh water  and even marsh species  have  both over continents and to the
most remote oceanic islands   This is strikingly illustrated  according to
Alph  de Candolle  in those large groups of terrestrial plants  which have
very few aquatic members  for the latter seem immediately to acquire  as if
in consequence  a wide range   I think favourable means of dispersal
explain this fact   I have before mentioned that earth occasionally adheres
in some quantity to the feet and beaks of birds   Wading birds  which
frequent the muddy edges of ponds  if suddenly flushed  would be the most
likely to have muddy feet   Birds of this order wander more than those of
any other  and are occasionally found on the most remote and barren islands
of the open ocean  they would not be likely to alight on the surface of the
sea  so that any dirt on their feet would not be washed off  and when
gaining the land  they would be sure to fly to their natural fresh water
haunts   I do not believe that botanists are aware how charged the mud of
ponds is with seeds   I have tried several little experiments  but will
here give only the most striking case   I took in February three
tablespoonfuls of mud from three different points  beneath water  on the
edge of a little pond  this mud when dry weighed only 6 and 3 4 ounces  I
kept it covered up in my study for six months  pulling up and counting each
plant as it grew  the plants were of many kinds  and were altogether 537 in
number  and yet the viscid mud was all contained in a breakfast cup  
Considering these facts  I think it would be an inexplicable circumstance
if water birds did not transport the seeds of fresh water plants to
unstocked ponds and streams  situated at very distant points   The same
agency may have come into play with the eggs of some of the smaller
fresh water animals 

Other and unknown agencies probably have also played a part   I have stated
that fresh water fish eat some kinds of seeds  though they reject many
other kinds after having swallowed them  even small fish swallow seeds of
moderate size  as of the yellow water lily and Potamogeton   Herons and
other birds  century after century  have gone on daily devouring fish  they
then take flight and go to other waters  or are blown across the sea  and
we have seen that seeds retain their power of germination  when rejected
many hours afterwards in pellets or in the excrement   When I saw the great
size of the seeds of that fine water lily  the Nelumbium  and remembered
Alph  de Candolle s remarks on the distribution of this plant  I thought
that the means of its dispersal must remain inexplicable  but Audubon
states that he found the seeds of the great southern water lily  probably
according to Dr  Hooker  the Nelumbium luteum  in a heron s stomach   Now
this bird must often have flown with its stomach thus well stocked to
distant ponds  and  then getting a hearty meal of fish  analogy makes me
believe that it would have rejected the seeds in the pellet in a fit state
for germination 

In considering these several means of distribution  it should be remembered
that when a pond or stream is first formed  for instance on a rising islet 
it will be unoccupied  and a single seed or egg will have a good chance of
succeeding   Although there will always be a struggle for life between the
inhabitants of the same pond  however few in kind  yet as the number even
in a well stocked pond is small in comparison with the number of species
inhabiting an equal area of land  the competition between them will
probably be less severe than between terrestrial species  consequently an
intruder from the waters of a foreign country would have a better chance of
seizing on a new place  than in the case of terrestrial colonists   We
should also remember that many fresh water productions are low in the scale
of nature  and we have reason to believe that such beings become modified
more slowly than the high  and this will give time for the migration of
aquatic species   We should not forget the probability of many fresh water
forms having formerly ranged continuously over immense areas  and then
having become extinct at intermediate points   But the wide distribution of
fresh water plants  and of the lower animals  whether retaining the same
identical form  or in some degree modified  apparently depends in main part
on the wide dispersal of their seeds and eggs by animals  more especially
by fresh water birds  which have great powers of flight  and naturally
travel from one piece of water to another 

ON THE INHABITANTS OF OCEANIC ISLANDS 

We now come to the last of the three classes of facts  which I have
selected as presenting the greatest amount of difficulty with respect to
distribution  on the view that not only all the individuals of the same
species have migrated from some one area  but that allied species  although
now inhabiting the most distant points  have proceeded from a single area 
the birthplace of their early progenitors   I have already given my reasons
for disbelieving in continental extensions within the period of existing
species on so enormous a scale that all the many islands of the several
oceans were thus stocked with their present terrestrial inhabitants   This
view removes many difficulties  but it does not accord with all the facts
in regard to the productions of islands   In the following remarks I shall
not confine myself to the mere question of dispersal  but shall consider
some other cases bearing on the truth of the two theories of independent
creation and of descent with modification 

The species of all kinds which inhabit oceanic islands are few in number
compared with those on equal continental areas   Alph  de Candolle admits
this for plants  and Wollaston for insects   New Zealand  for instance 
with its lofty mountains and diversified stations  extending over 780 miles
of latitude  together with the outlying islands of Auckland  Campbell and
Chatham  contain altogether only 960 kinds of flowering plants  if we
compare this moderate number with the species which swarm over equal areas
in Southwestern Australia or at the Cape of Good Hope  we must admit that
some cause  independently of different physical conditions  has given rise
to so great a difference in number   Even the uniform county of Cambridge
has 847 plants  and the little island of Anglesea 764  but a few ferns and
a few introduced plants are included in these numbers  and the comparison
in some other respects is not quite fair   We have evidence that the barren
island of Ascension aboriginally possessed less than half a dozen flowering
plants  yet many species have now become naturalised on it  as they have in
New Zealand and on every other oceanic island which can be named   In St 
Helena there is reason to believe that the naturalised plants and animals
have nearly or quite exterminated many native productions   He who admits
the doctrine of the creation of each separate species  will have to admit
that a sufficient number of the best adapted plants and animals were not
created for oceanic islands  for man has unintentionally stocked them far
more fully and perfectly than did nature 

Although in oceanic islands the species are few in number  the proportion
of endemic kinds  i e  those found nowhere else in the world  is often
extremely large   If we compare  for instance  the number of endemic
land shells in Madeira  or of endemic birds in the Galapagos Archipelago 
with the number found on any continent  and then compare the area of the
island with that of the continent  we shall see that this is true   This
fact might have been theoretically expected  for  as already explained 
species occasionally arriving  after long intervals of time in the new and
isolated district  and having to compete with new associates  would be
eminently liable to modification  and would often produce groups of
modified descendants   But it by no means follows that  because in an
island nearly all the species of one class are peculiar  those of another
class  or of another section of the same class  are peculiar  and this
difference seems to depend partly on the species which are not modified
having immigrated in a body  so that their mutual relations have not been
much disturbed  and partly on the frequent arrival of unmodified immigrants
from the mother country  with which the insular forms have intercrossed  
It should be borne in mind that the offspring of such crosses would
certainly gain in vigour  so that even an occasional cross would produce
more effect than might have been anticipated   I will give a few
illustrations of the foregoing remarks   in the Galapagos Islands there are
twenty six land birds  of these twenty one  or perhaps twenty three  are
peculiar  whereas of the eleven marine birds only two are peculiar  and it
is obvious that marine birds could arrive at these islands much more easily
and frequently than land birds   Bermuda  on the other hand  which lies at
about the same distance from North America as the Galapagos Islands do from
South America  and which has a very peculiar soil  does not possess a
single endemic land bird  and we know from Mr  J M  Jones s admirable
account of Bermuda  that very many North American birds occasionally or
even frequently visit this island   Almost every year  as I am informed by
Mr  E V  Harcourt  many European and African birds are blown to Madeira 
this island is inhabited by ninety nine kinds  of which one alone is
peculiar  though very closely related to a European form  and three or four
other species are confined to this island and to the Canaries   So that the
islands of Bermuda and Madeira have been stocked from the neighbouring
continents with birds  which for long ages have there struggled together 
and have become mutually co adapted   Hence  when settled in their new
homes  each kind will have been kept by the others to its proper place and
habits  and will consequently have been but little liable to modification  
Any tendency to modification will also have been checked by intercrossing
with the unmodified immigrants  often arriving from the mother country  
Madeira again is inhabited by a wonderful number of peculiar land shells 
whereas not one species of sea shell is peculiar to its shores   now 
though we do not know how sea shells are dispersed  yet we can see that
their eggs or larvae  perhaps attached to seaweed or floating timber  or to
the feet of wading birds  might be transported across three or four hundred
miles of open sea far more easily than land shells   The different orders
of insects inhabiting Madeira present nearly parallel cases 

Oceanic islands are sometimes deficient in animals of certain whole
classes  and their places are occupied by other classes  thus in the
Galapagos Islands reptiles  and in New Zealand gigantic wingless birds 
take  or recently took  the place of mammals   Although New Zealand is here
spoken of as an oceanic island  it is in some degree doubtful whether it
should be so ranked  it is of large size  and is not separated from
Australia by a profoundly deep sea  from its geological character and the
direction of its mountain ranges  the Rev  W B  Clarke has lately
maintained that this island  as well as New Caledonia  should be considered
as appurtenances of Australia   Turning to plants  Dr  Hooker has shown
that in the Galapagos Islands the proportional numbers of the different
orders are very different from what they are elsewhere   All such
differences in number  and the absence of certain whole groups of animals
and plants  are generally accounted for by supposed differences in the
physical conditions of the islands  but this explanation is not a little
doubtful   Facility of immigration seems to have been fully as important as
the nature of the conditions 

Many remarkable little facts could be given with respect to the inhabitants
of oceanic islands   For instance  in certain islands not tenanted by a
single mammal  some of the endemic plants have beautifully hooked seeds 
yet few relations are more manifest than that hooks serve for the
transportal of seeds in the wool or fur of quadrupeds   But a hooked seed
might be carried to an island by other means  and the plant then becoming
modified would form an endemic species  still retaining its hooks  which
would form a useless appendage  like the shrivelled wings under the
soldered wing covers of many insular beetles   Again  islands often possess
trees or bushes belonging to orders which elsewhere include only herbaceous
species  now trees  as Alph  de Candolle has shown  generally have 
whatever the cause may be  confined ranges   Hence trees would be little
likely to reach distant oceanic islands  and an herbaceous plant  which had
no chance of successfully competing with the many fully developed trees
growing on a continent  might  when established on an island  gain an
advantage over other herbaceous plants by growing taller and taller and
overtopping them   In this case  natural selection would tend to add to the
stature of the plant  to whatever order it belonged  and thus first convert
it into a bush and then into a tree 

ABSENCE OF BATRACHIANS AND TERRESTRIAL MAMMALS ON OCEANIC ISLANDS 

With respect to the absence of whole orders of animals on oceanic islands 
Bory St  Vincent long ago remarked that Batrachians  frogs  toads  newts 
are never found on any of the many islands with which the great oceans are
studded   I have taken pains to verify this assertion  and have found it
true  with the exception of New Zealand  New Caledonia  the Andaman
Islands  and perhaps the Solomon Islands and the Seychelles   But I have
already remarked that it is doubtful whether New Zealand and New Caledonia
ought to be classed as oceanic islands  and this is still more doubtful
with respect to the Andaman and Solomon groups and the Seychelles   This
general absence of frogs  toads and newts on so many true oceanic islands
cannot be accounted for by their physical conditions  indeed it seems that
islands are peculiarly fitted for these animals  for frogs have been
introduced into Madeira  the Azores  and Mauritius  and have multiplied so
as to become a nuisance   But as these animals and their spawn are
immediately killed  with the exception  as far as known  of one Indian
species  by sea water  there would be great difficulty in their transportal
across the sea  and therefore we can see why they do not exist on strictly
oceanic islands   But why  on the theory of creation  they should not have
been created there  it would be very difficult to explain 

Mammals offer another and similar case   I have carefully searched the
oldest voyages  and have not found a single instance  free from doubt  of a
terrestrial mammal  excluding domesticated animals kept by the natives 
inhabiting an island situated above 300 miles from a continent or great
continental island  and many islands situated at a much less distance are
equally barren   The Falkland Islands  which are inhabited by a wolf like
fox  come nearest to an exception  but this group cannot be considered as
oceanic  as it lies on a bank in connection with the mainland at a distance
of about 280 miles  moreover  icebergs formerly brought boulders to its
western shores  and they may have formerly transported foxes  as now
frequently happens in the arctic regions   Yet it cannot be said that small
islands will not support at least small mammals  for they occur in many
parts of the world on very small islands  when lying close to a continent 
and hardly an island can be named on which our smaller quadrupeds have not
become naturalised and greatly multiplied   It cannot be said  on the
ordinary view of creation  that there has not been time for the creation of
mammals  many volcanic islands are sufficiently ancient  as shown by the
stupendous degradation which they have suffered  and by their tertiary
strata   there has also been time for the production of endemic species
belonging to other classes  and on continents it is known that new species
of mammals appear and disappear at a quicker rate than other and lower
animals   Although terrestrial mammals do not occur on oceanic islands 
aerial mammals do occur on almost every island   New Zealand possesses two
bats found nowhere else in the world   Norfolk Island  the Viti
Archipelago  the Bonin Islands  the Caroline and Marianne Archipelagoes 
and Mauritius  all possess their peculiar bats   Why  it may be asked  has
the supposed creative force produced bats and no other mammals on remote
islands   On my view this question can easily be answered  for no
terrestrial mammal can be transported across a wide space of sea  but bats
can fly across   Bats have been seen wandering by day far over the Atlantic
Ocean  and two North American species  either regularly or occasionally 
visit Bermuda  at the distance of 600 miles from the mainland   I hear from
Mr  Tomes  who has specially studied this family  that many species have
enormous ranges  and are found on continents and on far distant islands  
Hence  we have only to suppose that such wandering species have been
modified in their new homes in relation to their new position  and we can
understand the presence of endemic bats on oceanic islands  with the
absence of all other terrestrial mammals 

Another interesting relation exists  namely  between the depth of the sea
separating islands from each other  or from the nearest continent  and the
degree of affinity of their mammalian inhabitants   Mr  Windsor Earl has
made some striking observations on this head  since greatly extended by Mr 
Wallace s admirable researches  in regard to the great Malay Archipelago 
which is traversed near Celebes by a space of deep ocean  and this
separates two widely distinct mammalian faunas   On either side  the
islands stand on a moderately shallow submarine bank  and these islands are
inhabited by the same or by closely allied quadrupeds   I have not as yet
had time to follow up this subject in all quarters of the world  but as far
as I have gone  the relation holds good   For instance  Britain is
separated by a shallow channel from Europe  and the mammals are the same on
both sides  and so it is with all the islands near the shores of Australia  
The West Indian Islands  on the other hand  stand on a deeply submerged
bank  nearly one thousand fathoms in depth  and here we find American
forms  but the species and even the genera are quite distinct   As the
amount of modification which animals of all kinds undergo partly depends on
the lapse of time  and as the islands which are separated from each other 
or from the mainland  by shallow channels  are more likely to have been
continuously united within a recent period than the islands separated by
deeper channels  we can understand how it is that a relation exists between
the depth of the sea separating two mammalian faunas  and the degree of
their affinity  a relation which is quite inexplicable on the theory of
independent acts of creation 

The foregoing statements in regard to the inhabitants of oceanic islands 
namely  the fewness of the species  with a large proportion consisting of
endemic forms  the members of certain groups  but not those of other groups
in the same class  having been modified  the absence of certain whole
orders  as of batrachians and of terrestrial mammals  notwithstanding the
presence of aerial bats  the singular proportions of certain orders of
plants  herbaceous forms having been developed into trees  etc   seem to me
to accord better with the belief in the efficiency of occasional means of
transport  carried on during a long course of time  than with the belief in
the former connection of all oceanic islands with the nearest continent 
for on this latter view it is probable that the various classes would have
immigrated more uniformly  and from the species having entered in a body 
their mutual relations would not have been much disturbed  and
consequently  they would either have not been modified  or all the species
in a more equable manner 

I do not deny that there are many and serious difficulties in understanding
how many of the inhabitants of the more remote islands  whether still
retaining the same specific form or subsequently modified  have reached
their present homes   But the probability of other islands having once
existed as halting places  of which not a wreck now remains  must not be
overlooked   I will specify one difficult case   Almost all oceanic
islands  even the most isolated and smallest  are inhabited by land shells 
generally by endemic species  but sometimes by species found elsewhere
striking instances of which have been given by Dr  A A  Gould in relation
to the Pacific   Now it is notorious that land shells are easily killed by
sea water  their eggs  at least such as I have tried  sink in it and are
killed   Yet there must be some unknown  but occasionally efficient means
for their transportal   Would the just hatched young sometimes adhere to
the feet of birds roosting on the ground and thus get transported   It
occurred to me that land shells  when hybernating and having a membranous
diaphragm over the mouth of the shell  might be floated in chinks of
drifted timber across moderately wide arms of the sea   And I find that
several species in this state withstand uninjured an immersion in sea water
during seven days   One shell  the Helix pomatia  after having been thus
treated  and again hybernating  was put into sea water for twenty days and
perfectly recovered   During this length of time the shell might have been
carried by a marine country of average swiftness to a distance of 660
geographical miles   As this Helix has a thick calcareous operculum I
removed it  and when it had formed a new membranous one  I again immersed
it for fourteen days in sea water  and again it recovered and crawled away 
Baron Aucapitaine has since tried similar experiments   He placed 100 land 
shells  belonging to ten species  in a box pierced with holes  and immersed
it for a fortnight in the sea   Out of the hundred shells twenty seven
recovered   The presence of an operculum seems to have been of importance 
as out of twelve specimens of Cyclostoma elegans  which is thus furnished 
eleven revived   It is remarkable  seeing how well the Helix pomatia
resisted with me the salt water  that not one of fifty four specimens
belonging to four other species of Helix tried by Aucapitaine recovered  
It is  however  not at all probable that land shells have often been thus
transported  the feet of birds offer a more probable method 

ON THE RELATIONS OF THE INHABITANTS OF ISLANDS TO THOSE OF THE NEAREST
MAINLAND 

The most striking and important fact for us is the affinity of the species
which inhabit islands to those of the nearest mainland  without being
actually the same   Numerous instances could be given   The Galapagos
Archipelago  situated under the equator  lies at a distance of between 500
and 600 miles from the shores of South America   Here almost every product
of the land and of the water bears the unmistakable stamp of the American
continent   There are twenty six land birds   Of these twenty one  or
perhaps twenty three  are ranked as distinct species  and would commonly be
assumed to have been here created  yet the close affinity of most of these
birds to American species is manifest in every character in their habits 
gestures  and tones of voice   So it is with the other animals  and with a
large proportion of the plants  as shown by Dr  Hooker in his admirable
Flora of this archipelago   The naturalist  looking at the inhabitants of
these volcanic islands in the Pacific  distant several hundred miles from
the continent  feels that he is standing on American land   Why should this
be so   Why should the species which are supposed to have been created in
the Galapagos Archipelago  and nowhere else  bear so plainly the stamp of
affinity to those created in America   There is nothing in the conditions
of life  in the geological nature of the islands  in their height or
climate  or in the proportions in which the several classes are associated
together  which closely resembles the conditions of the South American
coast   In fact  there is a considerable dissimilarity in all these
respects   On the other hand  there is a considerable degree of resemblance
in the volcanic nature of the soil  in the climate  height  and size of the
islands  between the Galapagos and Cape Verde Archipelagos   but what an
entire and absolute difference in their inhabitants   The inhabitants of
the Cape Verde Islands are related to those of Africa  like those of the
Galapagos to America   Facts  such as these  admit of no sort of
explanation on the ordinary view of independent creation  whereas  on the
view here maintained  it is obvious that the Galapagos Islands would be
likely to receive colonists from America  whether by occasional means of
transport or  though I do not believe in this doctrine  by formerly
continuous land  and the Cape Verde Islands from Africa  such colonists
would be liable to modification  the principle of inheritance still
betraying their original birthplace 

Many analogous facts could be given   indeed it is an almost universal rule
that the endemic productions of islands are related to those of the nearest
continent  or of the nearest large island   The exceptions are few  and
most of them can be explained   Thus  although Kerguelen Land stands nearer
to Africa than to America  the plants are related  and that very closely 
as we know from Dr  Hooker s account  to those of America   but on the view
that this island has been mainly stocked by seeds brought with earth and
stones on icebergs  drifted by the prevailing currents  this anomaly
disappears   New Zealand in its endemic plants is much more closely related
to Australia  the nearest mainland  than to any other region   and this is
what might have been expected  but it is also plainly related to South
America  which  although the next nearest continent  is so enormously
remote  that the fact becomes an anomaly   But this difficulty partially
disappears on the view that New Zealand  South America  and the other
southern lands  have been stocked in part from a nearly intermediate though
distant point  namely  from the antarctic islands  when they were clothed
with vegetation  during a warmer tertiary period  before the commencement
of the last Glacial period   The affinity  which  though feeble  I am
assured by Dr  Hooker is real  between the flora of the south western
corner of Australia and of the Cape of Good Hope  is a far more remarkable
case  but this affinity is confined to the plants  and will  no doubt  some
day be explained 

The same law which has determined the relationship between the inhabitants
of islands and the nearest mainland  is sometimes displayed on a small
scale  but in a most interesting manner  within the limits of the same
archipelago   Thus each separate island of the Galapagos Archipelago is
tenanted  and the fact is a marvellous one  by many distinct species  but
these species are related to each other in a very much closer manner than
to the inhabitants of the American continent  or of any other quarter of
the world   This is what might have been expected  for islands situated so
near to each other would almost necessarily receive immigrants from the
same original source  and from each other   But how is it that many of the
immigrants have been differently modified  though only in a small degree 
in islands situated within sight of each other  having the same geological
nature  the same height  climate  etc   This long appeared to me a great
difficulty   but it arises in chief part from the deeply seated error of
considering the physical conditions of a country as the most important 
whereas it cannot be disputed that the nature of the other species with
which each has to compete  is at least as important  and generally a far
more important element of success   Now if we look to the species which
inhabit the Galapagos Archipelago  and are likewise found in other parts of
the world  we find that they differ considerably in the several islands  
This difference might indeed have been expected if the islands have been
stocked by occasional means of transport  a seed  for instance  of one
plant having been brought to one island  and that of another plant to
another island  though all proceeding from the same general source   Hence 
when in former times an immigrant first settled on one of the islands  or
when it subsequently spread from one to another  it would undoubtedly be
exposed to different conditions in the different islands  for it would have
to compete with a different set of organisms  a plant  for instance  would
find the ground best fitted for it occupied by somewhat different species
in the different islands  and would be exposed to the attacks of somewhat
different enemies   If  then  it varied  natural selection would probably
favour different varieties in the different islands   Some species 
however  might spread and yet retain the same character throughout the
group  just as we see some species spreading widely throughout a continent
and remaining the same 

The really surprising fact in this case of the Galapagos Archipelago  and
in a lesser degree in some analogous cases  is that each new species after
being formed in any one island  did not spread quickly to the other
islands   But the islands  though in sight of each other  are separated by
deep arms of the sea  in most cases wider than the British Channel  and
there is no reason to suppose that they have at any former period been
continuously united   The currents of the sea are rapid and deep between
the islands  and gales of wind are extraordinarily rare  so that the
islands are far more effectually separated from each other than they appear
on a map   Nevertheless  some of the species  both of those found in other
parts of the world and of those confined to the archipelago  are common to
the several islands  and we may infer from the present manner of
distribution that they have spread from one island to the others   But we
often take  I think  an erroneous view of the probability of closely allied
species invading each other s territory  when put into free
intercommunication   Undoubtedly  if one species has any advantage over
another  it will in a very brief time wholly or in part supplant it  but if
both are equally well fitted for their own places  both will probably hold
their separate places for almost any length of time   Being familiar with
the fact that many species  naturalised through man s agency  have spread
with astonishing rapidity over wide areas  we are apt to infer that most
species would thus spread  but we should remember that the species which
become naturalised in new countries are not generally closely allied to the
aboriginal inhabitants  but are very distinct forms  belonging in a large
proportion of cases  as shown by Alph  de Candolle  to distinct genera   In
the Galapagos Archipelago  many even of the birds  though so well adapted
for flying from island to island  differ on the different islands  thus
there are three closely allied species of mocking thrush  each confined to
its own island   Now let us suppose the mocking thrush of Chatham Island to
be blown to Charles Island  which has its own mocking thrush  why should it
succeed in establishing itself there   We may safely infer that Charles
Island is well stocked with its own species  for annually more eggs are
laid and young birds hatched than can possibly be reared  and we may infer
that the mocking thrush peculiar to Charles Island is at least as well
fitted for its home as is the species peculiar to Chatham Island   Sir C 
Lyell and Mr  Wollaston have communicated to me a remarkable fact bearing
on this subject  namely  that Madeira and the adjoining islet of Porto
Santo possess many distinct but representative species of land shells  some
of which live in crevices of stone  and although large quantities of stone
are annually transported from Porto Santo to Madeira  yet this latter
island has not become colonised by the Porto Santo species   nevertheless 
both islands have been colonised by some European land shells  which no
doubt had some advantage over the indigenous species   From these
considerations I think we need not greatly marvel at the endemic species
which inhabit the several islands of the Galapagos Archipelago not having
all spread from island to island   On the same continent  also 
pre occupation has probably played an important part in checking the
commingling of the species which inhabit different districts with nearly
the same physical conditions   Thus  the south east and south west corners
of Australia have nearly the same physical conditions  and are united by
continuous land  yet they are inhabited by a vast number of distinct
mammals  birds  and plants  so it is  according to Mr  Bates  with the
butterflies and other animals inhabiting the great  open  and continuous
valley of the Amazons 

The same principle which governs the general character of the inhabitants
of oceanic islands  namely  the relation to the source whence colonists
could have been most easily derived  together with their subsequent
modification  is of the widest application throughout nature   We see this
on every mountain summit  in every lake and marsh   For Alpine species 
excepting in as far as the same species have become widely spread during
the Glacial epoch  are related to those of the surrounding lowlands  thus
we have in South America  Alpine humming birds  Alpine rodents  Alpine
plants  etc   all strictly belonging to American forms  and it is obvious
that a mountain  as it became slowly upheaved  would be colonised from the
surrounding lowlands   So it is with the inhabitants of lakes and marshes 
excepting in so far as great facility of transport has allowed the same
forms to prevail throughout large portions of the world   We see the same
principle in the character of most of the blind animals inhabiting the
caves of America and of Europe   Other analogous facts could be given   It
will  I believe  be found universally true  that wherever in two regions 
let them be ever so distant  many closely allied or representative species
occur  there will likewise be found some identical species  and wherever
many closely allied species occur  there will be found many forms which
some naturalists rank as distinct species  and others as mere varieties 
these doubtful forms showing us the steps in the process of modification 

The relation between the power and extent of migration in certain species 
either at the present or at some former period  and the existence at remote
points of the world of closely allied species  is shown in another and more
general way   Mr  Gould remarked to me long ago  that in those genera of
birds which range over the world  many of the species have very wide
ranges   I can hardly doubt that this rule is generally true  though
difficult of proof   Among mammals  we see it strikingly displayed in Bats 
and in a lesser degree in the Felidae and Canidae   We see the same rule in
the distribution of butterflies and beetles   So it is with most of the
inhabitants of fresh water  for many of the genera in the most distinct
classes range over the world  and many of the species have enormous ranges  
It is not meant that all  but that some of the species have very wide
ranges in the genera which range very widely   Nor is it meant that the
species in such genera have  on an average  a very wide range  for this
will largely depend on how far the process of modification has gone  for
instance  two varieties of the same species inhabit America and Europe  and
thus the species has an immense range  but  if variation were to be carried
a little further  the two varieties would be ranked as distinct species 
and their range would be greatly reduced   Still less is it meant  that
species which have the capacity of crossing barriers and ranging widely  as
in the case of certain powerfully winged birds  will necessarily range
widely  for we should never forget that to range widely implies not only
the power of crossing barriers  but the more important power of being
victorious in distant lands in the struggle for life with foreign
associates   But according to the view that all the species of a genus 
though distributed to the most remote points of the world  are descended
from a single progenitor  we ought to find  and I believe as a general rule
we do find  that some at least of the species range very widely 

We should bear in mind that many genera in all classes are of ancient
origin  and the species in this case will have had ample time for dispersal
and subsequent modification   There is also reason to believe  from
geological evidence  that within each great class the lower organisms
change at a slower rate than the higher  consequently they will have had a
better chance of ranging widely and of still retaining the same specific
character   This fact  together with that of the seeds and eggs of most
lowly organised forms being very minute and better fitted for distant
transportal  probably accounts for a law which has long been observed  and
which has lately been discussed by Alph  de Candolle in regard to plants 
namely  that the lower any group of organisms stands the more widely it
ranges 

The relations just discussed  namely  lower organisms ranging more widely
than the higher  some of the species of widely ranging genera themselves
ranging widely  such facts  as alpine  lacustrine  and marsh productions
being generally related to those which live on the surrounding low lands
and dry lands  the striking relationship between the inhabitants of islands
and those of the nearest mainland  the still closer relationship of the
distinct inhabitants of the islands of the same archipelago  are
inexplicable on the ordinary view of the independent creation of each
species  but are explicable if we admit colonisation from the nearest or
readiest source  together with the subsequent adaptation of the colonists
to their new homes 

SUMMARY OF THE LAST AND PRESENT CHAPTERS 

In these chapters I have endeavoured to show that if we make due allowance
for our ignorance of the full effects of changes of climate and of the
level of the land  which have certainly occurred within the recent period 
and of other changes which have probably occurred  if we remember how
ignorant we are with respect to the many curious means of occasional
transport  if we bear in mind  and this is a very important consideration 
how often a species may have ranged continuously over a wide area  and then
have become extinct in the intermediate tracts  the difficulty is not
insuperable in believing that all the individuals of the same species 
wherever found  are descended from common parents   And we are led to this
conclusion  which has been arrived at by many naturalists under the
designation of single centres of creation  by various general
considerations  more especially from the importance of barriers of all
kinds  and from the analogical distribution of subgenera  genera  and
families 

With respect to distinct species belonging to the same genus  which on our
theory have spread from one parent source  if we make the same allowances
as before for our ignorance  and remember that some forms of life have
changed very slowly  enormous periods of time having been thus granted for
their migration  the difficulties are far from insuperable  though in this
case  as in that of the individuals of the same species  they are often
great 

As exemplifying the effects of climatical changes on distribution  I have
attempted to show how important a part the last Glacial period has played 
which affected even the equatorial regions  and which  during the
alternations of the cold in the north and the south  allowed the
productions of opposite hemispheres to mingle  and left some of them
stranded on the mountain summits in all parts of the world   As showing how
diversified are the means of occasional transport  I have discussed at some
little length the means of dispersal of fresh water productions 

If the difficulties be not insuperable in admitting that in the long course
of time all the individuals of the same species  and likewise of the
several species belonging to the same genus  have proceeded from some one
source  then all the grand leading facts of geographical distribution are
explicable on the theory of migration  together with subsequent
modification and the multiplication of new forms   We can thus understand
the high importance of barriers  whether of land or water  in not only
separating but in apparently forming the several zoological and botanical
provinces   We can thus understand the concentration of related species
within the same areas  and how it is that under different latitudes  for
instance  in South America  the inhabitants of the plains and mountains  of
the forests  marshes  and deserts  are linked together in so mysterious a
manner  and are likewise linked to the extinct beings which formerly
inhabited the same continent   Bearing in mind that the mutual relation of
organism to organism is of the highest importance  we can see why two
areas  having nearly the same physical conditions  should often be
inhabited by very different forms of life  for according to the length of
time which has elapsed since the colonists entered one of the regions  or
both  according to the nature of the communication which allowed certain
forms and not others to enter  either in greater or lesser numbers 
according or not as those which entered happened to come into more or less
direct competition with each other and with the aborigines  and according
as the immigrants were capable of varying more or less rapidly  there would
ensue in the to or more regions  independently of their physical
conditions  infinitely diversified conditions of life  there would be an
almost endless amount of organic action and reaction  and we should find
some groups of beings greatly  and some only slightly modified  some
developed in great force  some existing in scanty numbers  and this we do
find in the several great geographical provinces of the world 

On these same principles we can understand  as I have endeavoured to show 
why oceanic islands should have few inhabitants  but that of these  a large
proportion should be endemic or peculiar  and why  in relation to the means
of migration  one group of beings should have all its species peculiar  and
another group  even within the same class  should have all its species the
same with those in an adjoining quarter of the world   We can see why whole
groups of organisms  as batrachians and terrestrial mammals  should be
absent from oceanic islands  whilst the most isolated islands should
possess their own peculiar species of aerial mammals or bats   We can see
why  in islands  there should be some relation between the presence of
mammals  in a more or less modified condition  and the depth of the sea
between such islands and the mainland   We can clearly see why all the
inhabitants of an archipelago  though specifically distinct on the several
islets  should be closely related to each other  and should likewise be
related  but less closely  to those of the nearest continent  or other
source whence immigrants might have been derived   We can see why  if there
exist very closely allied or representative species in two areas  however
distant from each other  some identical species will almost always there be
found 

As the late Edward Forbes often insisted  there is a striking parallelism
in the laws of life throughout time and space  the laws governing the
succession of forms in past times being nearly the same with those
governing at the present time the differences in different areas   We see
this in many facts   The endurance of each species and group of species is
continuous in time  for the apparent exceptions to the rule are so few that
they may fairly be attributed to our not having as yet discovered in an
intermediate deposit certain forms which are absent in it  but which occur
above and below   so in space  it certainly is the general rule that the
area inhabited by a single species  or by a group of species  is
continuous  and the exceptions  which are not rare  may  as I have
attempted to show  be accounted for by former migrations under different
circumstances  or through occasional means of transport  or by the species
having become extinct in the intermediate tracts   Both in time and space
species and groups of species have their points of maximum development  
Groups of species  living during the same period of time  or living within
the same area  are often characterised by trifling features in common  as
of sculpture or colour   In looking to the long succession of past ages  as
in looking to distant provinces throughout the world  we find that species
in certain classes differ little from each other  whilst those in another
class  or only in a different section of the same order  differ greatly
from each other   In both time and space the lowly organised members of
each class generally change less than the highly organised  but there are
in both cases marked exceptions to the rule   According to our theory 
these several relations throughout time and space are intelligible  for
whether we look to the allied forms of life which have changed during
successive ages  or to those which have changed after having migrated into
distant quarters  in both cases they are connected by the same bond of
ordinary generation  in both cases the laws of variation have been the
same  and modifications have been accumulated by the same means of natural
selection 


CHAPTER XIV 

MUTUAL AFFINITIES OF ORGANIC BEINGS   MORPHOLOGY    EMBRYOLOGY    
RUDIMENTARY ORGANS 

Classification  groups subordinate to groups    Natural system    Rules and
difficulties in classification  explained on the theory of descent with
modification    Classification of varieties    Descent always used in
classification    Analogical or adaptive characters    Affinities  general 
complex and radiating    Extinction separates and defines groups   
Morphology  between members of the same class  between parts of the same
individual    Embryology  laws of  explained by variations not supervening
at an early age  and being inherited at a corresponding age    Rudimentary
organs  their origin explained    Summary 

CLASSIFICATION 

 From the most remote period in the history of the world organic beings have
been found to resemble each other in descending degrees  so that they can
be classed in groups under groups   This classification is not arbitrary
like the grouping of the stars in constellations   The existence of groups
would have been of simple significance  if one group had been exclusively
fitted to inhabit the land  and another the water  one to feed on flesh 
another on vegetable matter  and so on  but the case is widely different 
for it is notorious how commonly members of even the same subgroup have
different habits   In the second and fourth chapters  on Variation and on
Natural Selection  I have attempted to show that within each country it is
the widely ranging  the much diffused and common  that is the dominant
species  belonging to the larger genera in each class  which vary most  
The varieties  or incipient species  thus produced  ultimately become
converted into new and distinct species  and these  on the principle of
inheritance  tend to produce other new and dominant species   Consequently
the groups which are now large  and which generally include many dominant
species  tend to go on increasing in size   I further attempted to show
that from the varying descendants of each species trying to occupy as many
and as different places as possible in the economy of nature  they
constantly tend to diverge in character   This latter conclusion is
supported by observing the great diversity of forms  which  in any small
area  come into the closest competition  and by certain facts in
naturalisation 

I attempted also to show that there is a steady tendency in the forms which
are increasing in number and diverging in character  to supplant and
exterminate the preceding  less divergent and less improved forms   I
request the reader to turn to the diagram illustrating the action  as
formerly explained  of these several principles  and he will see that the
inevitable result is  that the modified descendants proceeding from one
progenitor become broken up into groups subordinate to groups   In the
diagram each letter on the uppermost line may represent a genus including
several species  and the whole of the genera along this upper line form
together one class  for all are descended from one ancient parent  and 
consequently  have inherited something in common   But the three genera on
the left hand have  on this same principle  much in common  and form a
subfamily  distinct from that containing the next two genera on the right
hand  which diverged from a common parent at the fifth stage of descent  
These five genera have also much in common  though less than when grouped
in subfamilies  and they form a family distinct from that containing the
three genera still further to the right hand  which diverged at an earlier
period   And all these genera  descended from  A   form an order distinct
from the genera descended from  I    So that we here have many species
descended from a single progenitor grouped into genera  and the genera into
subfamilies  families and orders  all under one great class   The grand
fact of the natural subordination of organic beings in groups under groups 
which  from its familiarity  does not always sufficiently strike us  is in
my judgment thus explained   No doubt organic beings  like all other
objects  can be classed in many ways  either artificially by single
characters  or more naturally by a number of characters   We know  for
instance  that minerals and the elemental substances can be thus arranged 
In this case there is of course no relation to genealogical succession  and
no cause can at present be assigned for their falling into groups   But
with organic beings the case is different  and the view above given accords
with their natural arrangement in group under group  and no other
explanation has ever been attempted 

Naturalists  as we have seen  try to arrange the species  genera and
families in each class  on what is called the Natural System   But what is
meant by this system   Some authors look at it merely as a scheme for
arranging together those living objects which are most alike  and for
separating those which are most unlike  or as an artificial method of
enunciating  as briefly as possible  general propositions  that is  by one
sentence to give the characters common  for instance  to all mammals  by
another those common to all carnivora  by another those common to the
dog genus  and then  by adding a single sentence  a full description is
given of each kind of dog   The ingenuity and utility of this system are
indisputable   But many naturalists think that something more is meant by
the Natural System  they believe that it reveals the plan of the Creator 
but unless it be specified whether order in time or space  or both  or what
else is meant by the plan of the Creator  it seems to me that nothing is
thus added to our knowledge   Expressions such as that famous one by
Linnaeus  which we often meet with in a more or less concealed form 
namely  that the characters do not make the genus  but that the genus gives
the characters  seem to imply that some deeper bond is included in our
classifications than mere resemblance   I believe that this is the case 
and that community of descent  the one known cause of close similarity in
organic beings  is the bond  which  though observed by various degrees of
modification  is partially revealed to us by our classifications 

Let us now consider the rules followed in classification  and the
difficulties which are encountered on the view that classification either
gives some unknown plan of creation  or is simply a scheme for enunciating
general propositions and of placing together the forms most like each
other   It might have been thought  and was in ancient times thought  that
those parts of the structure which determined the habits of life  and the
general place of each being in the economy of nature  would be of very high
importance in classification   Nothing can be more false   No one regards
the external similarity of a mouse to a shrew  of a dugong to a whale  of a
whale to a fish  as of any importance   These resemblances  though so
intimately connected with the whole life of the being  are ranked as merely
 adaptive or analogical characters   but to the consideration of these
resemblances we shall recur   It may even be given as a general rule  that
the less any part of the organisation is concerned with special habits  the
more important it becomes for classification   As an instance   Owen  in
speaking of the dugong  says   The generative organs  being those which are
most remotely related to the habits and food of an animal  I have always
regarded as affording very clear indications of its true affinities   We
are least likely in the modifications of these organs to mistake a merely
adaptive for an essential character    With plants how remarkable it is
that the organs of vegetation  on which their nutrition and life depend 
are of little signification  whereas the organs of reproduction  with their
product the seed and embryo  are of paramount importance   So again  in
formerly discussing certain morphological characters which are not
functionally important  we have seen that they are often of the highest
service in classification   This depends on their constancy throughout many
allied groups  and their constancy chiefly depends on any slight deviations
not having been preserved and accumulated by natural selection  which acts
only on serviceable characters 

That the mere physiological importance of an organ does not determine its
classificatory value  is almost proved by the fact  that in allied groups 
in which the same organ  as we have every reason to suppose  has nearly the
same physiological value  its classificatory value is widely different   No
naturalist can have worked at any group without being struck with this
fact  and it has been fully acknowledged in the writings of almost every
author   It will suffice to quote the highest authority  Robert Brown  who 
in speaking of certain organs in the Proteaceae  says their generic
importance   like that of all their parts  not only in this  but  as I
apprehend in every natural family  is very unequal  and in some cases seems
to be entirely lost    Again  in another work he says  the genera of the
Connaraceae  differ in having one or more ovaria  in the existence or
absence of albumen  in the imbricate or valvular aestivation   Any one of
these characters singly is frequently of more than generic importance 
though here even  when all taken together  they appear insufficient to
separate Cnestis from Connarus    To give an example among insects   in one
great division of the Hymenoptera  the antennae  as Westwood has remarked 
are most constant in structure  in another division they differ much  and
the differences are of quite subordinate value in classification  yet no
one will say that the antennae in these two divisions of the same order are
of unequal physiological importance   Any number of instances could be
given of the varying importance for classification of the same important
organ within the same group of beings 

Again  no one will say that rudimentary or atrophied organs are of high
physiological or vital importance  yet  undoubtedly  organs in this
condition are often of much value in classification   No one will dispute
that the rudimentary teeth in the upper jaws of young ruminants  and
certain rudimentary bones of the leg  are highly serviceable in exhibiting
the close affinity between Ruminants and Pachyderms   Robert Brown has
strongly insisted on the fact that the position of the rudimentary florets
is of the highest importance in the classification of the Grasses 

Numerous instances could be given of characters derived from parts which
must be considered of very trifling physiological importance  but which are
universally admitted as highly serviceable in the definition of whole
groups   For instance  whether or not there is an open passage from the
nostrils to the mouth  the only character  according to Owen  which
absolutely distinguishes fishes and reptiles  the inflection of the angle
of the lower jaw in Marsupials  the manner in which the wings of insects
are folded  mere colour in certain Algae  mere pubescence on parts of the
flower in grasses  the nature of the dermal covering  as hair or feathers 
in the Vertebrata   If the Ornithorhynchus had been covered with feathers
instead of hair  this external and trifling character would have been
considered by naturalists as an important aid in determining the degree of
affinity of this strange creature to birds 

The importance  for classification  of trifling characters  mainly depends
on their being correlated with many other characters of more or less
importance   The value indeed of an aggregate of characters is very evident
in natural history   Hence  as has often been remarked  a species may
depart from its allies in several characters  both of high physiological
importance  and of almost universal prevalence  and yet leave us in no
doubt where it should be ranked   Hence  also  it has been found that a
classification founded on any single character  however important that may
be  has always failed  for no part of the organisation is invariably
constant   The importance of an aggregate of characters  even when none are
important  alone explains the aphorism enunciated by Linnaeus  namely  that
the characters do not give the genus  but the genus gives the character 
for this seems founded on the appreciation of many trifling points of
resemblance  too slight to be defined   Certain plants  belonging to the
Malpighiaceae  bear perfect and degraded flowers  in the latter  as A  de
Jussieu has remarked   The greater number of the characters proper to the
species  to the genus  to the family  to the class  disappear  and thus
laugh at our classification    When Aspicarpa produced in France  during
several years  only these degraded flowers  departing so wonderfully in a
number of the most important points of structure from the proper type of
the order  yet M  Richard sagaciously saw  as Jussieu observes  that this
genus should still be retained among the Malpighiaceae   This case well
illustrates the spirit of our classifications 

Practically  when naturalists are at work  they do not trouble themselves
about the physiological value of the characters which they use in defining
a group or in allocating any particular species   If they find a character
nearly uniform  and common to a great number of forms  and not common to
others  they use it as one of high value  if common to some lesser number 
they use it as of subordinate value   This principle has been broadly
confessed by some naturalists to be the true one  and by none more clearly
than by that excellent botanist  Aug  St  Hilaire   If several trifling
characters are always found in combination  though no apparent bond of
connexion can be discovered between them  especial value is set on them  
As in most groups of animals  important organs  such as those for
propelling the blood  or for aerating it  or those for propagating the
race  are found nearly uniform  they are considered as highly serviceable
in classification  but in some groups all these  the most important vital
organs  are found to offer characters of quite subordinate value   Thus  as
Fritz Muller has lately remarked  in the same group of crustaceans 
Cypridina is furnished with a heart  while in two closely allied genera 
namely Cypris and Cytherea  there is no such organ  one species of
Cypridina has well developed branchiae  while another species is destitute
of them 

We can see why characters derived from the embryo should be of equal
importance with those derived from the adult  for a natural classification
of course includes all ages   But it is by no means obvious  on the
ordinary view  why the structure of the embryo should be more important for
this purpose than that of the adult  which alone plays its full part in the
economy of nature   Yet it has been strongly urged by those great
naturalists  Milne Edwards and Agassiz  that embryological characters are
the most important of all  and this doctrine has very generally been
admitted as true   Nevertheless  their importance has sometimes been
exaggerated  owing to the adaptive characters of larvae not having been
excluded  in order to show this  Fritz Muller arranged  by the aid of such
characters alone  the great class of crustaceans  and the arrangement did
not prove a natural one   But there can be no doubt that embryonic 
excluding larval characters  are of the highest value for classification 
not only with animals but with plants   Thus the main divisions of
flowering plants are founded on differences in the embryo  on the number
and position of the cotyledons  and on the mode of development of the
plumule and radicle   We shall immediately see why these characters possess
so high a value in classification  namely  from the natural system being
genealogical in its arrangement 

Our classifications are often plainly influenced by chains of affinities  
Nothing can be easier than to define a number of characters common to all
birds  but with crustaceans  any such definition has hitherto been found
impossible   There are crustaceans at the opposite ends of the series 
which have hardly a character in common  yet the species at both ends  from
being plainly allied to others  and these to others  and so onwards  can be
recognised as unequivocally belonging to this  and to no other class of the
Articulata 

Geographical distribution has often been used  though perhaps not quite
logically  in classification  more especially in very large groups of
closely allied forms   Temminck insists on the utility or even necessity of
this practice in certain groups of birds  and it has been followed by
several entomologists and botanists 

Finally  with respect to the comparative value of the various groups of
species  such as orders  suborders  families  subfamilies  and genera  they
seem to be  at least at present  almost arbitrary   Several of the best
botanists  such as Mr  Bentham and others  have strongly insisted on their
arbitrary value   Instances could be given among plants and insects  of a
group first ranked by practised naturalists as only a genus  and then
raised to the rank of a subfamily or family  and this has been done  not
because further research has detected important structural differences  at
first overlooked  but because numerous allied species  with slightly
different grades of difference  have been subsequently discovered 

All the foregoing rules and aids and difficulties in classification may be
explained  if I do not greatly deceive myself  on the view that the natural
system is founded on descent with modification  that the characters which
naturalists consider as showing true affinity between any two or more
species  are those which have been inherited from a common parent  all true
classification being genealogical  that community of descent is the hidden
bond which naturalists have been unconsciously seeking  and not some
unknown plan of creation  or the enunciation of general propositions  and
the mere putting together and separating objects more or less alike 

But I must explain my meaning more fully   I believe that the ARRANGEMENT
of the groups within each class  in due subordination and relation to each
other  must be strictly genealogical in order to be natural  but that the
AMOUNT of difference in the several branches or groups  though allied in
the same degree in blood to their common progenitor  may differ greatly 
being due to the different degrees of modification which they have
undergone  and this is expressed by the forms being ranked under different
genera  families  sections or orders   The reader will best understand what
is meant  if he will take the trouble to refer to the diagram in the fourth
chapter   We will suppose the letters A to L to represent allied genera
existing during the Silurian epoch  and descended from some still earlier
form   In three of these genera  A  F  and I  a species has transmitted
modified descendants to the present day  represented by the fifteen genera
 a14 to z14  on the uppermost horizontal line   Now  all these modified
descendants from a single species are related in blood or descent in the
same degree   They may metaphorically be called cousins to the same
millionth degree  yet they differ widely and in different degrees from each
other   The forms descended from A  now broken up into two or three
families  constitute a distinct order from those descended from I  also
broken up into two families   Nor can the existing species descended from A
be ranked in the same genus with the parent A  or those from I with parent
I   But the existing genus F14 may be supposed to have been but slightly
modified  and it will then rank with the parent genus F  just as some few
still living organisms belong to Silurian genera   So that the comparative
value of the differences between these organic beings  which are all
related to each other in the same degree in blood  has come to be widely
different   Nevertheless  their genealogical ARRANGEMENT remains strictly
true  not only at the present time  but at each successive period of
descent   All the modified descendants from A will have inherited something
in common from their common parent  as will all the descendants from I  so
will it be with each subordinate branch of descendants at each successive
stage   If  however  we suppose any descendant of A or of I to have become
so much modified as to have lost all traces of its parentage in this case 
its place in the natural system will be lost  as seems to have occurred
with some few existing organisms   All the descendants of the genus F 
along its whole line of descent  are supposed to have been but little
modified  and they form a single genus   But this genus  though much
isolated  will still occupy its proper intermediate position   The
representation of the groups as here given in the diagram on a flat
surface  is much too simple   The branches ought to have diverged in all
directions   If the names of the groups had been simply written down in a
linear series the representation would have been still less natural  and it
is notoriously not possible to represent in a series  on a flat surface 
the affinities which we discover in nature among the beings of the same
group   Thus  the natural system is genealogical in its arrangement  like a
pedigree   But the amount of modification which the different groups have
undergone has to be expressed by ranking them under different so called
genera  subfamilies  families  sections  orders  and classes 

It may be worth while to illustrate this view of classification  by taking
the case of languages   If we possessed a perfect pedigree of mankind  a
genealogical arrangement of the races of man would afford the best
classification of the various languages now spoken throughout the world 
and if all extinct languages  and all intermediate and slowly changing
dialects  were to be included  such an arrangement would be the only
possible one   Yet it might be that some ancient languages had altered very
little and had given rise to few new languages  whilst others had altered
much owing to the spreading  isolation and state of civilisation of the
several co descended races  and had thus given rise to many new dialects
and languages   The various degrees of difference between the languages of
the same stock would have to be expressed by groups subordinate to groups 
but the proper or even the only possible arrangement would still be
genealogical  and this would be strictly natural  as it would connect
together all languages  extinct and recent  by the closest affinities  and
would give the filiation and origin of each tongue 

In confirmation of this view  let us glance at the classification of
varieties  which are known or believed to be descended from a single
species   These are grouped under the species  with the subvarieties under
the varieties  and in some cases  as with the domestic pigeon  with several
other grades of difference   Nearly the same rules are followed as in
classifying species   Authors have insisted on the necessity of arranging
varieties on a natural instead of an artificial system  we are cautioned 
for instance  not to class two varieties of the pine apple together  merely
because their fruit  though the most important part  happens to be nearly
identical  no one puts the Swedish and common turnip together  though the
esculent and thickened stems are so similar   Whatever part is found to be
most constant  is used in classing varieties   thus the great agriculturist
Marshall says the horns are very useful for this purpose with cattle 
because they are less variable than the shape or colour of the body  etc  
whereas with sheep the horns are much less serviceable  because less
constant   In classing varieties  I apprehend that if we had a real
pedigree  a genealogical classification would be universally preferred  and
it has been attempted in some cases   For we might feel sure  whether there
had been more or less modification  that the principle of inheritance would
keep the forms together which were allied in the greatest number of points  
In tumbler pigeons  though some of the subvarieties differ in the important
character of the length of the beak  yet all are kept together from having
the common habit of tumbling  but the short faced breed has nearly or quite
lost this habit  nevertheless  without any thought on the subject  these
tumblers are kept in the same group  because allied in blood and alike in
some other respects 

With species in a state of nature  every naturalist has in fact brought
descent into his classification  for he includes in his lowest grade  that
of species  the two sexes  and how enormously these sometimes differ in the
most important characters is known to every naturalist   scarcely a single
fact can be predicated in common of the adult males and hermaphrodites of
certain cirripedes  and yet no one dreams of separating them   As soon as
the three Orchidean forms  Monachanthus  Myanthus  and Catasetum  which had
previously been ranked as three distinct genera  were known to be sometimes
produced on the same plant  they were immediately considered as varieties 
and now I have been able to show that they are the male  female  and
hermaphrodite forms of the same species   The naturalist includes as one
species the various larval stages of the same individual  however much they
may differ from each other and from the adult  as well as the so called
alternate generations of Steenstrup  which can only in a technical sense be
considered as the same individual   He includes monsters and varieties  not
from their partial resemblance to the parent form  but because they are
descended from it 

As descent has universally been used in classing together the individuals
of the same species  though the males and females and larvae are sometimes
extremely different  and as it has been used in classing varieties which
have undergone a certain  and sometimes a considerable amount of
modification  may not this same element of descent have been unconsciously
used in grouping species under genera  and genera under higher groups  all
under the so called natural system   I believe it has been unconsciously
used  and thus only can I understand the several rules and guides which
have been followed by our best systematists   As we have no written
pedigrees  we are forced to trace community of descent by resemblances of
any kind   Therefore  we choose those characters which are the least likely
to have been modified  in relation to the conditions of life to which each
species has been recently exposed   Rudimentary structures on this view are
as good as  or even sometimes better than other parts of the organisation  
We care not how trifling a character may be  let it be the mere inflection
of the angle of the jaw  the manner in which an insect s wing is folded 
whether the skin be covered by hair or feathers  if it prevail throughout
many and different species  especially those having very different habits
of life  it assumes high value  for we can account for its presence in so
many forms with such different habits  only by inheritance from a common
parent   We may err in this respect in regard to single points of
structure  but when several characters  let them be ever so trifling 
concur throughout a large group of beings having different habits  we may
feel almost sure  on the theory of descent  that these characters have been
inherited from a common ancestor  and we know that such aggregated
characters have especial value in classification 

We can understand why a species or a group of species may depart from its
allies  in several of its most important characteristics  and yet be safely
classed with them   This may be safely done  and is often done  as long as
a sufficient number of characters  let them be ever so unimportant  betrays
the hidden bond of community of descent   Let two forms have not a single
character in common  yet  if these extreme forms are connected together by
a chain of intermediate groups  we may at once infer their community of
descent  and we put them all into the same class   As we find organs of
high physiological importance  those which serve to preserve life under the
most diverse conditions of existence  are generally the most constant  we
attach especial value to them  but if these same organs  in another group
or section of a group  are found to differ much  we at once value them less
in our classification   We shall presently see why embryological characters
are of such high classificatory importance   Geographical distribution may
sometimes be brought usefully into play in classing large genera  because
all the species of the same genus  inhabiting any distinct and isolated
region  are in all probability descended from the same parents 

ANALOGICAL RESEMBLANCES 

We can understand  on the above views  the very important distinction
between real affinities and analogical or adaptive resemblances   Lamarck
first called attention to this subject  and he has been ably followed by
Macleay and others   The resemblance in the shape of the body and in the
fin like anterior limbs between dugongs and whales  and between these two
orders of mammals and fishes  are analogical   So is the resemblance
between a mouse and a shrew mouse  Sorex   which belong to different
orders  and the still closer resemblance  insisted on by Mr  Mivart 
between the mouse and a small marsupial animal  Antechinus  of Australia  
These latter resemblances may be accounted for  as it seems to me  by
adaptation for similarly active movements through thickets and herbage 
together with concealment from enemies 

Among insects there are innumerable instances  thus Linnaeus  misled by
external appearances  actually classed an homopterous insect as a moth   We
see something of the same kind even with our domestic varieties  as in the
strikingly similar shape of the body in the improved breeds of the Chinese
and common pig  which are descended from distinct species  and in the
similarly thickened stems of the common and specifically distinct Swedish
turnip   The resemblance between the greyhound and race horse is hardly
more fanciful than the analogies which have been drawn by some authors
between widely different animals 

On the view of characters being of real importance for classification  only
in so far as they reveal descent  we can clearly understand why analogical
or adaptive characters  although of the utmost importance to the welfare of
the being  are almost valueless to the systematist   For animals  belonging
to two most distinct lines of descent  may have become adapted to similar
conditions  and thus have assumed a close external resemblance  but such
resemblances will not reveal  will rather tend to conceal their
blood relationship   We can thus also understand the apparent paradox  that
the very same characters are analogical when one group is compared with
another  but give true affinities when the members of the same group are
compared together   thus the shape of the body and fin like limbs are only
analogical when whales are compared with fishes  being adaptations in both
classes for swimming through the water  but between the  the several
members of the whale family  the shape of the body and the fin like limbs
offer characters exhibiting true affinity  for as these parts are so nearly
similar throughout the whole family  we cannot doubt that they have been
inherited from a common ancestor   So it is with fishes 

Numerous cases could be given of striking resemblances in quite distinct
beings between single parts or organs  which have been adapted for the same
functions   A good instance is afforded by the close resemblance of the
jaws of the dog and Tasmanian wolf or Thylacinus  animals which are widely
sundered in the natural system   But this resemblance is confined to
general appearance  as in the prominence of the canines  and in the cutting
shape of the molar teeth   For the teeth really differ much   thus the dog
has on each side of the upper jaw four pre molars and only two molars 
while the Thylacinus has three pre molars and four molars   The molars also
differ much in the two animals in relative size and structure   The adult
dentition is preceded by a widely different milk dentition   Any one may 
of course  deny that the teeth in either case have been adapted for tearing
flesh  through the natural selection of successive variations  but if this
be admitted in the one case  it is unintelligible to me that it should be
denied in the other   I am glad to find that so high an authority as
Professor Flower has come to this same conclusion 

The extraordinary cases given in a former chapter  of widely different
fishes possessing electric organs  of widely different insects possessing
luminous organs  and of orchids and asclepiads having pollen masses with
viscid discs  come under this same head of analogical resemblances   But
these cases are so wonderful that they were introduced as difficulties or
objections to our theory   In all such cases some fundamental difference in
the growth or development of the parts  and generally in their matured
structure  can be detected   The end gained is the same  but the means 
though appearing superficially to be the same  are essentially different  
The principle formerly alluded to under the term of ANALOGICAL VARIATION
has probably in these cases often come into play  that is  the members of
the same class  although only distantly allied  have inherited so much in
common in their constitution  that they are apt to vary under similar
exciting causes in a similar manner  and this would obviously aid in the
acquirement through natural selection of parts or organs  strikingly like
each other  independently of their direct inheritance from a common
progenitor 

As species belonging to distinct classes have often been adapted by
successive slight modifications to live under nearly similar circumstances
  to inhabit  for instance  the three elements of land  air and water  we
can perhaps understand how it is that a numerical parallelism has sometimes
been observed between the subgroups of distinct classes   A naturalist 
struck with a parallelism of this nature  by arbitrarily raising or sinking
the value of the groups in several classes  and all our experience shows
that their valuation is as yet arbitrary   could easily extend the
parallelism over a wide range  and thus the septenary  quinary  quaternary
and ternary classifications have probably arisen 

There is another and curious class of cases in which close external
resemblance does not depend on adaptation to similar habits of life  but
has been gained for the sake of protection   I allude to the wonderful
manner in which certain butterflies imitate  as first described by Mr 
Bates  other and quite distinct species   This excellent observer has shown
that in some districts of South America  where  for instance  an Ithomia
abounds in gaudy swarms  another butterfly  namely  a Leptalis  is often
found mingled in the same flock  and the latter so closely resembles the
Ithomia in every shade and stripe of colour  and even in the shape of its
wings  that Mr  Bates  with his eyes sharpened by collecting during eleven
years  was  though always on his guard  continually deceived   When the
mockers and the mocked are caught and compared  they are found to be very
different in essential structure  and to belong not only to distinct
genera  but often to distinct families   Had this mimicry occurred in only
one or two instances  it might have been passed over as a strange
coincidence   But  if we proceed from a district where one Leptalis
imitates an Ithomia  another mocking and mocked species  belonging to the
same two genera  equally close in their resemblance  may be found  
Altogether no less than ten genera are enumerated  which include species
that imitate other butterflies   The mockers and mocked always inhabit the
same region  we never find an imitator living remote from the form which it
imitates   The mockers are almost invariably rare insects  the mocked in
almost every case abounds in swarms   In the same district in which a
species of Leptalis closely imitates an Ithomia  there are sometimes other
Lepidoptera mimicking the same Ithomia   so that in the same place  species
of three genera of butterflies and even a moth are found all closely
resembling a butterfly belonging to a fourth genus   It deserves especial
notice that many of the mimicking forms of the Leptalis  as well as of the
mimicked forms  can be shown by a graduated series to be merely varieties
of the same species  while others are undoubtedly distinct species   But
why  it may be asked  are certain forms treated as the mimicked and others
as the mimickers   Mr  Bates satisfactorily answers this question by
showing that the form which is imitated keeps the usual dress of the group
to which it belongs  while the counterfeiters have changed their dress and
do not resemble their nearest allies 

We are next led to enquire what reason can be assigned for certain
butterflies and moths so often assuming the dress of another and quite
distinct form  why  to the perplexity of naturalists  has nature
condescended to the tricks of the stage   Mr  Bates has  no doubt  hit on
the true explanation   The mocked forms  which always abound in numbers 
must habitually escape destruction to a large extent  otherwise they could
not exist in such swarms  and a large amount of evidence has now been
collected  showing that they are distasteful to birds and other insect 
devouring animals   The mocking forms  on the other hand  that inhabit the
same district  are comparatively rare  and belong to rare groups  hence 
they must suffer habitually from some danger  for otherwise  from the
number of eggs laid by all butterflies  they would in three or four
generations swarm over the whole country   Now if a member of one of these
persecuted and rare groups were to assume a dress so like that of a well 
protected species that it continually deceived the practised eyes of an
entomologist  it would often deceive predaceous birds and insects  and thus
often escape destruction   Mr  Bates may almost be said to have actually
witnessed the process by which the mimickers have come so closely to
resemble the mimicked  for he found that some of the forms of Leptalis
which mimic so many other butterflies  varied in an extreme degree   In one
district several varieties occurred  and of these one alone resembled  to a
certain extent  the common Ithomia of the same district   In another
district there were two or three varieties  one of which was much commoner
than the others  and this closely mocked another form of Ithomia   From
facts of this nature  Mr  Bates concludes that the Leptalis first varies 
and when a variety happens to resemble in some degree any common butterfly
inhabiting the same district  this variety  from its resemblance to a
flourishing and little persecuted kind  has a better chance of escaping
destruction from predaceous birds and insects  and is consequently oftener
preserved   the less perfect degrees of resemblance being generation after
generation eliminated  and only the others left to propagate their kind   
So that here we have an excellent illustration of natural selection 

Messrs  Wallace and Trimen have likewise described several equally striking
cases of imitation in the Lepidoptera of the Malay Archipelago and Africa 
and with some other insects   Mr  Wallace has also detected one such case
with birds  but we have none with the larger quadrupeds   The much greater
frequency of imitation with insects than with other animals  is probably
the consequence of their small size  insects cannot defend themselves 
excepting indeed the kinds furnished with a sting  and I have never heard
of an instance of such kinds mocking other insects  though they are mocked 
insects cannot easily escape by flight from the larger animals which prey
on them  therefore  speaking metaphorically  they are reduced  like most
weak creatures  to trickery and dissimulation 

It should be observed that the process of imitation probably never
commenced between forms widely dissimilar in colour   But  starting with
species already somewhat like each other  the closest resemblance  if
beneficial  could readily be gained by the above means  and if the imitated
form was subsequently and gradually modified through any agency  the
imitating form would be led along the same track  and thus be altered to
almost any extent  so that it might ultimately assume an appearance or
colouring wholly unlike that of the other members of the family to which it
belonged   There is  however  some difficulty on this head  for it is
necessary to suppose in some cases that ancient members belonging to
several distinct groups  before they had diverged to their present extent 
accidentally resembled a member of another and protected group in a
sufficient degree to afford some slight protection  this having given the
basis for the subsequent acquisition of the most perfect resemblance 

ON THE NATURE OF THE AFFINITIES CONNECTING ORGANIC BEINGS 

As the modified descendants of dominant species  belonging to the larger
genera  tend to inherit the advantages which made the groups to which they
belong large and their parents dominant  they are almost sure to spread
widely  and to seize on more and more places in the economy of nature   The
larger and more dominant groups within each class thus tend to go on
increasing in size  and they consequently supplant many smaller and feebler
groups   Thus  we can account for the fact that all organisms  recent and
extinct  are included under a few great orders and under still fewer
classes   As showing how few the higher groups are in number  and how
widely they are spread throughout the world  the fact is striking that the
discovery of Australia has not added an insect belonging to a new class 
and that in the vegetable kingdom  as I learn from Dr  Hooker  it has added
only two or three families of small size 

In the chapter on geological succession I attempted to show  on the
principle of each group having generally diverged much in character during
the long continued process of modification  how it is that the more ancient
forms of life often present characters in some degree intermediate between
existing groups   As some few of the old and intermediate forms having
transmitted to the present day descendants but little modified  these
constitute our so called osculant or aberrant groups   The more aberrant
any form is  the greater must be the number of connecting forms which have
been exterminated and utterly lost   And we have evidence of aberrant
groups having suffered severely from extinction  for they are almost always
represented by extremely few species  and such species as do occur are
generally very distinct from each other  which again implies extinction  
The genera Ornithorhynchus and Lepidosiren  for example  would not have
been less aberrant had each been represented by a dozen species  instead of
as at present by a single one  or by two or three   We can  I think 
account for this fact only by looking at aberrant groups as forms which
have been conquered by more successful competitors  with a few members
still preserved under unusually favourable conditions 

Mr  Waterhouse has remarked that when a member belonging to one group of
animals exhibits an affinity to a quite distinct group  this affinity in
most cases is general and not special   thus  according to Mr  Waterhouse 
of all Rodents  the bizcacha is most nearly related to Marsupials  but in
the points in which it approaches this order  its relations are general 
that is  not to any one Marsupial species more than to another   As these
points of affinity are believed to be real and not merely adaptive  they
must be due in accordance with our view to inheritance from a common
progenitor   Therefore  we must suppose either that all Rodents  including
the bizcacha  branched off from some ancient Marsupial  which will
naturally have been more or less intermediate in character with respect to
all existing Marsupials  or that both Rodents and Marsupials branched off
from a common progenitor  and that both groups have since undergone much
modification in divergent directions   On either view we must suppose that
the bizcacha has retained  by inheritance  more of the character of its
ancient progenitor than have other Rodents  and therefore it will not be
specially related to any one existing Marsupial  but indirectly to all or
nearly all Marsupials  from having partially retained the character of
their common progenitor  or of some early member of the group   On the
other hand  of all Marsupials  as Mr  Waterhouse has remarked  the
Phascolomys resembles most nearly  not any one species  but the general
order of Rodents   In this case  however  it may be strongly suspected that
the resemblance is only analogical  owing to the Phascolomys having become
adapted to habits like those of a Rodent   The elder De Candolle has made
nearly similar observations on the general nature of the affinities of
distinct families of plants 

On the principle of the multiplication and gradual divergence in character
of the species descended from a common progenitor  together with their
retention by inheritance of some characters in common  we can understand
the excessively complex and radiating affinities by which all the members
of the same family or higher group are connected together   For the common
progenitor of a whole family  now broken up by extinction into distinct
groups and subgroups  will have transmitted some of its characters 
modified in various ways and degrees  to all the species  and they will
consequently be related to each other by circuitous lines of affinity of
various lengths  as may be seen in the diagram so often referred to  
mounting up through many predecessors   As it is difficult to show the
blood relationship between the numerous kindred of any ancient and noble
family  even by the aid of a genealogical tree  and almost impossible to do
so without this aid  we can understand the extraordinary difficulty which
naturalists have experienced in describing  without the aid of a diagram 
the various affinities which they perceive between the many living and
extinct members of the same great natural class 

Extinction  as we have seen in the fourth chapter  has played an important
part in defining and widening the intervals between the several groups in
each class   We may thus account for the distinctness of whole classes from
each other  for instance  of birds from all other vertebrate animals  by
the belief that many ancient forms of life have been utterly lost  through
which the early progenitors of birds were formerly connected with the early
progenitors of the other and at that time less differentiated vertebrate
classes   There has been much less extinction of the forms of life which
once connected fishes with Batrachians   There has been still less within
some whole classes  for instance the Crustacea  for here the most
wonderfully diverse forms are still linked together by a long and only
partially broken chain of affinities   Extinction has only defined the
groups   it has by no means made them  for if every form which has ever
lived on this earth were suddenly to reappear  though it would be quite
impossible to give definitions by which each group could be distinguished 
still a natural classification  or at least a natural arrangement  would be
possible   We shall see this by turning to the diagram   the letters  A to
L  may represent eleven Silurian genera  some of which have produced large
groups of modified descendants  with every link in each branch and
sub branch still alive  and the links not greater than those between
existing varieties   In this case it would be quite impossible to give
definitions by which the several members of the several groups could be
distinguished from their more immediate parents and descendants   Yet the
arrangement in the diagram would still hold good and would be natural  for 
on the principle of inheritance  all the forms descended  for instance from
A  would have something in common   In a tree we can distinguish this or
that branch  though at the actual fork the two unite and blend together  
We could not  as I have said  define the several groups  but we could pick
out types  or forms  representing most of the characters of each group 
whether large or small  and thus give a general idea of the value of the
differences between them   This is what we should be driven to  if we were
ever to succeed in collecting all the forms in any one class which have
lived throughout all time and space   Assuredly we shall never succeed in
making so perfect a collection   nevertheless  in certain classes  we are
tending toward this end  and Milne Edwards has lately insisted  in an able
paper  on the high importance of looking to types  whether or not we can
separate and define the groups to which such types belong 

Finally  we have seen that natural selection  which follows from the
struggle for existence  and which almost inevitably leads to extinction and
divergence of character in the descendants from any one parent species 
explains that great and universal feature in the affinities of all organic
beings  namely  their subordination in group under group   We use the
element of descent in classing the individuals of both sexes and of all
ages under one species  although they may have but few characters in
common  we use descent in classing acknowledged varieties  however
different they may be from their parents  and I believe that this element
of descent is the hidden bond of connexion which naturalists have sought
under the term of the Natural System   On this idea of the natural system
being  in so far as it has been perfected  genealogical in its arrangement 
with the grades of difference expressed by the terms genera  families 
orders  etc   we can understand the rules which we are compelled to follow
in our classification   We can understand why we value certain resemblances
far more than others  why we use rudimentary and useless organs  or others
of trifling physiological importance  why  in finding the relations between
one group and another  we summarily reject analogical or adaptive
characters  and yet use these same characters within the limits of the same
group   We can clearly see how it is that all living and extinct forms can
be grouped together within a few great classes  and how the several members
of each class are connected together by the most complex and radiating
lines of affinities   We shall never  probably  disentangle the
inextricable web of the affinities between the members of any one class 
but when we have a distinct object in view  and do not look to some unknown
plan of creation  we may hope to make sure but slow progress 

Professor Haeckel in his  Generelle Morphologie  and in another works  has
recently brought his great knowledge and abilities to bear on what he calls
phylogeny  or the lines of descent of all organic beings   In drawing up
the several series he trusts chiefly to embryological characters  but
receives aid from homologous and rudimentary organs  as well as from the
successive periods at which the various forms of life are believed to have
first appeared in our geological formations   He has thus boldly made a
great beginning  and shows us how classification will in the future be
treated 

MORPHOLOGY 

We have seen that the members of the same class  independently of their
habits of life  resemble each other in the general plan of their
organisation   This resemblance is often expressed by the term  unity of
type   or by saying that the several parts and organs in the different
species of the class are homologous   The whole subject is included under
the general term of Morphology   This is one of the most interesting
departments of natural history  and may almost be said to be its very soul  
What can be more curious than that the hand of a man  formed for grasping 
that of a mole for digging  the leg of the horse  the paddle of the
porpoise  and the wing of the bat  should all be constructed on the same
pattern  and should include similar bones  in the same relative positions 
How curious it is  to give a subordinate though striking instance  that the
hind feet of the kangaroo  which are so well fitted for bounding over the
open plains  those of the climbing  leaf eating koala  equally well fitted
for grasping the branches of trees  those of the ground dwelling  insect or
root eating  bandicoots  and those of some other Australian marsupials  
should all be constructed on the same extraordinary type  namely with the
bones of the second and third digits extremely slender and enveloped within
the same skin  so that they appear like a single toe furnished with two
claws   Notwithstanding this similarity of pattern  it is obvious that the
hind feet of these several animals are used for as widely different
purposes as it is possible to conceive   The case is rendered all the more
striking by the American opossums  which follow nearly the same habits of
life as some of their Australian relatives  having feet constructed on the
ordinary plan   Professor Flower  from whom these statements are taken 
remarks in conclusion    We may call this conformity to type  without
getting much nearer to an explanation of the phenomenon   and he then adds
 but is it not powerfully suggestive of true relationship  of inheritance
from a common ancestor  

Geoffroy St  Hilaire has strongly insisted on the high importance of
relative position or connexion in homologous parts  they may differ to
almost any extent in form and size  and yet remain connected together in
the same invariable order   We never find  for instance  the bones of the
arm and forearm  or of the thigh and leg  transposed   Hence the same names
can be given to the homologous bones in widely different animals   We see
the same great law in the construction of the mouths of insects   what can
be more different than the immensely long spiral proboscis of a
sphinx moth  the curious folded one of a bee or bug  and the great jaws of
a beetle   Yet all these organs  serving for such widely different
purposes  are formed by infinitely numerous modifications of an upper lip 
mandibles  and two pairs of maxillae   The same law governs the
construction of the mouths and limbs of crustaceans   So it is with the
flowers of plants 

Nothing can be more hopeless than to attempt to explain this similarity of
pattern in members of the same class  by utility or by the doctrine of
final causes   The hopelessness of the attempt has been expressly admitted
by Owen in his most interesting work on the  Nature of Limbs    On the
ordinary view of the independent creation of each being  we can only say
that so it is  that it has pleased the Creator to construct all the animals
and plants in each great class on a uniform plan  but this is not a
scientific explanation 

The explanation is to a large extent simple  on the theory of the selection
of successive slight modifications  each being profitable in some way to
the modified form  but often affecting by correlation other parts of the
organisation   In changes of this nature  there will be little or no
tendency to alter the original pattern  or to transpose the parts   The
bones of a limb might be shortened and flattened to any extent  becoming at
the same time enveloped in thick membrane  so as to serve as a fin  or a
webbed hand might have all its bones  or certain bones  lengthened to any
extent  with the membrane connecting them increased  so as to serve as a
wing  yet all these modifications would not tend to alter the framework of
the bones or the relative connexion of the parts   If we suppose that an
early progenitor  the archetype  as it may be called  of all mammals  birds
and reptiles  had its limbs constructed on the existing general pattern 
for whatever purpose they served  we can at once perceive the plain
signification of the homologous construction of the limbs throughout the
class   So with the mouths of insects  we have only to suppose that their
common progenitor had an upper lip  mandibles  and two pairs of maxillae 
these parts being perhaps very simple in form  and then natural selection
will account for the infinite diversity in structure and function of the
mouths of insects   Nevertheless  it is conceivable that the general
pattern of an organ might become so much obscured as to be finally lost  by
the reduction and ultimately by the complete abortion of certain parts  by
the fusion of other parts  and by the doubling or multiplication of others 
variations which we know to be within the limits of possibility   In the
paddles of the gigantic extinct sea lizards  and in the mouths of certain
suctorial crustaceans  the general pattern seems thus to have become
partially obscured 

There is another and equally curious branch of our subject  namely  serial
homologies  or the comparison of the different parts or organs in the same
individual  and not of the same parts or organs in different members of the
same class   Most physiologists believe that the bones of the skull are
homologous  that is  correspond in number and in relative connexion  with
the elemental parts of a certain number of vertebrae   The anterior and
posterior limbs in all the higher vertebrate classes are plainly
homologous   So it is with the wonderfully complex jaws and legs of
crustaceans   It is familiar to almost every one  that in a flower the
relative position of the sepals  petals  stamens  and pistils  as well as
their intimate structure  are intelligible on the view that they consist of
metamorphosed leaves  arranged in a spire   In monstrous plants  we often
get direct evidence of the possibility of one organ being transformed into
another  and we can actually see  during the early or embryonic stages of
development in flowers  as well as in crustaceans and many other animals 
that organs  which when mature become extremely different are at first
exactly alike 

How inexplicable are the cases of serial homologies on the ordinary view of
creation   Why should the brain be enclosed in a box composed of such
numerous and such extraordinarily shaped pieces of bone apparently
representing vertebrae   As Owen has remarked  the benefit derived from the
yielding of the separate pieces in the act of parturition by mammals  will
by no means explain the same construction in the skulls of birds and
reptiles   Why should similar bones have been created to form the wing and
the leg of a bat  used as they are for such totally different purposes 
namely flying and walking   Why should one crustacean  which has an
extremely complex mouth formed of many parts  consequently always have
fewer legs  or conversely  those with many legs have simpler mouths   Why
should the sepals  petals  stamens  and pistils  in each flower  though
fitted for such distinct purposes  be all constructed on the same pattern 

On the theory of natural selection  we can  to a certain extent  answer
these questions   We need not here consider how the bodies of some animals
first became divided into a series of segments  or how they became divided
into right and left sides  with corresponding organs  for such questions
are almost beyond investigation   It is  however  probable that some serial
structures are the result of cells multiplying by division  entailing the
multiplication of the parts developed from such cells   It must suffice for
our purpose to bear in mind that an indefinite repetition of the same part
or organ is the common characteristic  as Owen has remarked  of all low or
little specialised forms  therefore the unknown progenitor of the
Vertebrata probably possessed many vertebrae  the unknown progenitor of the
Articulata  many segments  and the unknown progenitor of flowering plants 
many leaves arranged in one or more spires   We have also formerly seen
that parts many times repeated are eminently liable to vary  not only in
number  but in form   Consequently such parts  being already present in
considerable numbers  and being highly variable  would naturally afford the
materials for adaptation to the most different purposes  yet they would
generally retain  through the force of inheritance  plain traces of their
original or fundamental resemblance   They would retain this resemblance
all the more  as the variations  which afforded the basis for their
subsequent modification through natural selection  would tend from the
first to be similar  the parts being at an early stage of growth alike  and
being subjected to nearly the same conditions   Such parts  whether more or
less modified  unless their common origin became wholly obscured  would be
serially homologous 

In the great class of molluscs  though the parts in distinct species can be
shown to be homologous  only a few serial homologies  such as the valves of
Chitons  can be indicated  that is  we are seldom enabled to say that one
part is homologous with another part in the same individual   And we can
understand this fact  for in molluscs  even in the lowest members of the
class  we do not find nearly so much indefinite repetition of any one part
as we find in the other great classes of the animal and vegetable kingdoms 

But morphology is a much more complex subject than it at first appears  as
has lately been well shown in a remarkable paper by Mr  E  Ray Lankester 
who has drawn an important distinction between certain classes of cases
which have all been equally ranked by naturalists as homologous   He
proposes to call the structures which resemble each other in distinct
animals  owing to their descent from a common progenitor with subsequent
modification   homogenous   and the resemblances which cannot thus be
accounted for  he proposes to call  homoplastic    For instance  he
believes that the hearts of birds and mammals are as a whole homogenous  
that is  have been derived from a common progenitor  but that the four
cavities of the heart in the two classes are homoplastic  that is  have
been independently developed   Mr  Lankester also adduces the close
resemblance of the parts on the right and left sides of the body  and in
the successive segments of the same individual animal  and here we have
parts commonly called homologous which bear no relation to the descent of
distinct species from a common progenitor   Homoplastic structures are the
same with those which I have classed  though in a very imperfect manner  as
analogous modifications or resemblances   Their formation may be attributed
in part to distinct organisms  or to distinct parts of the same organism 
having varied in an analogous manner  and in part to similar modifications 
having been preserved for the same general purpose or function  of which
many instances have been given 

Naturalists frequently speak of the skull as formed of metamorphosed
vertebrae  the jaws of crabs as metamorphosed legs  the stamens and pistils
in flowers as metamorphosed leaves  but it would in most cases be more
correct  as Professor Huxley has remarked  to speak of both skull and
vertebrae  jaws and legs  etc   as having been metamorphosed  not one from
the other  as they now exist  but from some common and simpler element  
Most naturalists  however  use such language only in a metaphorical sense  
they are far from meaning that during a long course of descent  primordial
organs of any kind  vertebrae in the one case and legs in the other  have
actually been converted into skulls or jaws   Yet so strong is the
appearance of this having occurred that naturalists can hardly avoid
employing language having this plain signification   According to the views
here maintained  such language may be used literally  and the wonderful
fact of the jaws  for instance  of a crab retaining numerous characters 
which they probably would have retained through inheritance  if they had
really been metamorphosed from true though extremely simple legs  is in
part explained 

DEVELOPMENT AND EMBRYOLOGY 

This is one of the most important subjects in the whole round of natural
history   The metamorphoses of insects  with which every one is familiar 
are generally effected abruptly by a few stages  but the transformations
are in reality numerous and gradual  though concealed   A certain
ephemerous insect  Chloeon  during its development  moults  as shown by Sir
J  Lubbock  above twenty times  and each time undergoes a certain amount of
change  and in this case we see the act of metamorphosis performed in a
primary and gradual manner   Many insects  and especially certain
crustaceans  show us what wonderful changes of structure can be effected
during development   Such changes  however  reach their acme in the so 
called alternate generations of some of the lower animals   It is  for
instance  an astonishing fact that a delicate branching coralline  studded
with polypi  and attached to a submarine rock  should produce  first by
budding and then by transverse division  a host of huge floating jelly 
fishes  and that these should produce eggs  from which are hatched swimming
animalcules  which attach themselves to rocks and become developed into
branching corallines  and so on in an endless cycle   The belief in the
essential identity of the process of alternate generation and of ordinary
metamorphosis has been greatly strengthened by Wagner s discovery of the
larva or maggot of a fly  namely the Cecidomyia  producing asexually other
larvae  and these others  which finally are developed into mature males and
females  propagating their kind in the ordinary manner by eggs 

It may be worth notice that when Wagner s remarkable discovery was first
announced  I was asked how was it possible to account for the larvae of
this fly having acquired the power of a sexual reproduction   As long as
the case remained unique no answer could be given   But already Grimm has
shown that another fly  a Chironomus  reproduces itself in nearly the same
manner  and he believes that this occurs frequently in the order   It is
the pupa  and not the larva  of the Chironomus which has this power  and
Grimm further shows that this case  to a certain extent   unites that of
the Cecidomyia with the parthenogenesis of the Coccidae   the term
parthenogenesis implying that the mature females of the Coccidae are
capable of producing fertile eggs without the concourse of the male  
Certain animals belonging to several classes are now known to have the
power of ordinary reproduction at an unusually early age  and we have only
to accelerate parthenogenetic reproduction by gradual steps to an earlier
and earlier age  Chironomus showing us an almost exactly intermediate
stage  viz   that of the pupa  and we can perhaps account for the
marvellous case of the Cecidomyia 

It has already been stated that various parts in the same individual  which
are exactly alike during an early embryonic period  become widely different
and serve for widely different purposes in the adult state   So again it
has been shown that generally the embryos of the most distinct species
belonging to the same class are closely similar  but become  when fully
developed  widely dissimilar   A better proof of this latter fact cannot be
given than the statement by Von Baer that  the embryos of mammalia  of
birds  lizards and snakes  probably also of chelonia  are in the earliest
states exceedingly like one another  both as a whole and in the mode of
development of their parts  so much so  in fact  that we can often
distinguish the embryos only by their size   In my possession are two
little embryos in spirit  whose names I have omitted to attach  and at
present I am quite unable to say to what class they belong   They may be
lizards or small birds  or very young mammalia  so complete is the
similarity in the mode of formation of the head and trunk in these animals 
The extremities  however  are still absent in these embryos   But even if
they had existed in the earliest stage of their development we should learn
nothing  for the feet of lizards and mammals  the wings and feet of birds 
no less than the hands and feet of man  all arise from the same fundamental
form    The larvae of most crustaceans  at corresponding stages of
development  closely resemble each other  however different the adults may
become  and so it is with very many other animals   A trace of the law of
embryonic resemblance occasionally lasts till a rather late age   thus
birds of the same genus  and of allied genera  often resemble each other in
their immature plumage  as we see in the spotted feathers in the young of
the thrush group   In the cat tribe  most of the species when adult are
striped or spotted in lines  and stripes or spots can be plainly
distinguished in the whelp of the lion and the puma   We occasionally 
though rarely  see something of the same kind in plants  thus the first
leaves of the ulex or furze  and the first leaves of the phyllodineous
acacias  are pinnate or divided like the ordinary leaves of the
leguminosae 

The points of structure  in which the embryos of widely different animals
within the same class resemble each other  often have no direct relation to
their conditions of existence   We cannot  for instance  suppose that in
the embryos of the vertebrata the peculiar loop like courses of the
arteries near the branchial slits are related to similar conditions  in the
young mammal which is nourished in the womb of its mother  in the egg of
the bird which is hatched in a nest  and in the spawn of a frog under
water   We have no more reason to believe in such a relation than we have
to believe that the similar bones in the hand of a man  wing of a bat  and
fin of a porpoise  are related to similar conditions of life   No one
supposes that the stripes on the whelp of a lion  or the spots on the young
blackbird  are of any use to these animals 

The case  however  is different when an animal  during any part of its
embryonic career  is active  and has to provide for itself   The period of
activity may come on earlier or later in life  but whenever it comes on 
the adaptation of the larva to its conditions of life is just as perfect
and as beautiful as in the adult animal   In how important a manner this
has acted  has recently been well shown by Sir J  Lubbock in his remarks on
the close similarity of the larvae of some insects belonging to very
different orders  and on the dissimilarity of the larvae of other insects
within the same order  according to their habits of life   Owing to such
adaptations the similarity of the larvae of allied animals is sometimes
greatly obscured  especially when there is a division of labour during the
different stages of development  as when the same larva has during one
stage to search for food  and during another stage has to search for a
place of attachment   Cases can even be given of the larvae of allied
species  or groups of species  differing more from each other than do the
adults   In most cases  however  the larvae  though active  still obey 
more or less closely  the law of common embryonic resemblance   Cirripedes
afford a good instance of this   even the illustrious Cuvier did not
perceive that a barnacle was a crustacean   but a glance at the larva shows
this in an unmistakable manner   So again the two main divisions of
cirripedes  the pedunculated and sessile  though differing widely in
external appearance  have larvae in all their stages barely
distinguishable 

The embryo in the course of development generally rises in organisation   I
use this expression  though I am aware that it is hardly possible to define
clearly what is meant by organisation being higher or lower   But no one
probably will dispute that the butterfly is higher than the caterpillar  
In some cases  however  the mature animal must be considered as lower in
the scale than the larva  as with certain parasitic crustaceans   To refer
once again to cirripedes   the larvae in the first stage have three pairs
of locomotive organs  a simple single eye  and a probosciformed mouth  with
which they feed largely  for they increase much in size   In the second
stage  answering to the chrysalis stage of butterflies  they have six pairs
of beautifully constructed natatory legs  a pair of magnificent compound
eyes  and extremely complex antennae  but they have a closed and imperfect
mouth  and cannot feed   their function at this stage is  to search out by
their well developed organs of sense  and to reach by their active powers
of swimming  a proper place on which to become attached and to undergo
their final metamorphosis   When this is completed they are fixed for life  
their legs are now converted into prehensile organs  they again obtain a
well constructed mouth  but they have no antennae  and their two eyes are
now reconverted into a minute  single  simple eye spot   In this last and
complete state  cirripedes may be considered as either more highly or more
lowly organised than they were in the larval condition   But in some genera
the larvae become developed into hermaphrodites having the ordinary
structure  or into what I have called complemental males  and in the latter
the development has assuredly been retrograde  for the male is a mere sack 
which lives for a short time and is destitute of mouth  stomach  and every
other organ of importance  excepting those for reproduction 

We are so much accustomed to see a difference in structure between the
embryo and the adult  that we are tempted to look at this difference as in
some necessary manner contingent on growth   But there is no reason why 
for instance  the wing of a bat  or the fin of a porpoise  should not have
been sketched out with all their parts in proper proportion  as soon as any
part became visible   In some whole groups of animals and in certain
members of other groups this is the case  and the embryo does not at any
period differ widely from the adult   thus Owen has remarked in regard to
cuttle fish   there is no metamorphosis  the cephalopodic character is
manifested long before the parts of the embryo are completed    Land shells
and fresh water crustaceans are born having their proper forms  while the
marine members of the same two great classes pass through considerable and
often great changes during their development   Spiders  again  barely
undergo any metamorphosis   The larvae of most insects pass through a
worm like stage  whether they are active and adapted to diversified habits 
or are inactive from being placed in the midst of proper nutriment  or from
being fed by their parents  but in some few cases  as in that of Aphis  if
we look to the admirable drawings  of the development of this insect  by
Professor Huxley  we see hardly any trace of the vermiform stage 

Sometimes it is only the earlier developmental stages which fail   Thus 
Fritz Muller has made the remarkable discovery that certain shrimp like
crustaceans  allied to Penoeus  first appear under the simple nauplius 
form  and after passing through two or more zoea stages  and then through
the mysis stage  finally acquire their mature structure   now in the whole
great malacostracan order  to which these crustaceans belong  no other
member is as yet known to be first developed under the nauplius form 
though many appear as zoeas  nevertheless Muller assigns reasons for his
belief  that if there had been no suppression of development  all these
crustaceans would have appeared as nauplii 

How  then  can we explain these several facts in embryology  namely  the
very general  though not universal  difference in structure between the
embryo and the adult  the various parts in the same individual embryo 
which ultimately become very unlike  and serve for diverse purposes  being
at an early period of growth alike  the common  but not invariable 
resemblance between the embryos or larvae of the most distinct species in 
the same class  the embryo often retaining  while within the egg or womb 
structures which are of no service to it  either at that or at a later
period of life  on the other hand  larvae which have to provide for their
own wants  being perfectly adapted to the surrounding conditions  and
lastly  the fact of certain larvae standing higher in the scale of
organisation than the mature animal into which they are developed   I
believe that all these facts can be explained as follows 

It is commonly assumed  perhaps from monstrosities affecting the embryo at
a very early period  that slight variations or individual differences
necessarily appear at an equally early period   We have little evidence on
this head  but what we have certainly points the other way  for it is
notorious that breeders of cattle  horses and various fancy animals  cannot
positively tell  until some time after birth  what will be the merits and
demerits of their young animals   We see this plainly in our own children 
we cannot tell whether a child will be tall or short  or what its precise
features will be   The question is not  at what period of life any
variation may have been caused  but at what period the effects are
displayed   The cause may have acted  and I believe often has acted  on one
or both parents before the act of generation   It deserves notice that it
is of no importance to a very young animal  as long as it is nourished and
protected by its parent  whether most of its characters are acquired a
little earlier or later in life   It would not signify  for instance  to a
bird which obtained its food by having a much curved beak whether or not
while young it possessed a beak of this shape  as long as it was fed by its
parents 

I have stated in the first chapter  that at whatever age any variation
first appears in the parent  it tends to reappear at a corresponding age in
the offspring   Certain variations can only appear at corresponding ages 
for instance  peculiarities in the caterpillar  cocoon  or imago states of
the silk moth  or  again  in the full grown horns of cattle   But
variations which  for all that we can see might have appeared either
earlier or later in life  likewise tend to reappear at a corresponding age
in the offspring and parent   I am far from meaning that this is invariably
the case  and I could give several exceptional cases of variations  taking
the word in the largest sense  which have supervened at an earlier age in
the child than in the parent 

These two principles  namely  that slight variations generally appear at a
not very early period of life  and are inherited at a corresponding not
early period  explain  as I believe  all the above specified leading facts
in embryology   But first let us look to a few analogous cases in our
domestic varieties   Some authors who have written on Dogs maintain that
the greyhound and bull dog  though so different  are really closely allied
varieties  descended from the same wild stock  hence I was curious to see
how far their puppies differed from each other   I was told by breeders
that they differed just as much as their parents  and this  judging by the
eye  seemed almost to be the case  but on actually measuring the old dogs
and their six days old puppies  I found that the puppies had not acquired
nearly their full amount of proportional difference   So  again  I was told
that the foals of cart and race horses  breeds which have been almost
wholly formed by selection under domestication  differed as much as the
full grown animals  but having had careful measurements made of the dams
and of three days old colts of race and heavy cart horses  I find that this
is by no means the case 

As we have conclusive evidence that the breeds of the Pigeon are descended
from a single wild species  I compared the young pigeons within twelve
hours after being hatched   I carefully measured the proportions  but will
not here give the details  of the beak  width of mouth  length of nostril
and of eyelid  size of feet and length of leg  in the wild parent species 
in pouters  fantails  runts  barbs  dragons  carriers  and tumblers   Now 
some of these birds  when mature  differ in so extraordinary a manner in
the length and form of beak  and in other characters  that they would
certainly have been ranked as distinct genera if found in a state of
nature   But when the nestling birds of these several breeds were placed in
a row  though most of them could just be distinguished  the proportional
differences in the above specified points were incomparably less than in
the full grown birds   Some characteristic points of difference  for
instance  that of the width of mouth  could hardly be detected in the
young   But there was one remarkable exception to this rule  for the young
of the short faced tumbler differed from the young of the wild rock pigeon 
and of the other breeds  in almost exactly the same proportions as in the
adult stage 

These facts are explained by the above two principles   Fanciers select
their dogs  horses  pigeons  etc   for breeding  when nearly grown up  
They are indifferent whether the desired qualities are acquired earlier or
later in life  if the full grown animal possesses them   And the cases just
given  more especially that of the pigeons  show that the characteristic
differences which have been accumulated by man s selection  and which give
value to his breeds  do not generally appear at a very early period of
life  and are inherited at a corresponding not early period   But the case
of the short faced tumbler  which when twelve hours old possessed its
proper characters  proves that this is not the universal rule  for here the
characteristic differences must either have appeared at an earlier period
than usual  or  if not so  the differences must have been inherited  not at
a corresponding  but at an earlier age 

Now  let us apply these two principles to species in a state of nature  
Let us take a group of birds  descended from some ancient form and modified
through natural selection for different habits   Then  from the many slight
successive variations having supervened in the several species at a not
early age  and having been inherited at a corresponding age  the young will
have been but little modified  and they will still resemble each other much
more closely than do the adults  just as we have seen with the breeds of
the pigeon   We may extend this view to widely distinct structures and to
whole classes   The fore limbs  for instance  which once served as legs to
a remote progenitor  may have become  through a long course of
modification  adapted in one descendant to act as hands  in another as
paddles  in another as wings  but on the above two principles the
fore limbs will not have been much modified in the embryos of these several
forms  although in each form the fore limb will differ greatly in the adult
state   Whatever influence long continued use or disuse may have had in
modifying the limbs or other parts of any species  this will chiefly or
solely have affected it when nearly mature  when it was compelled to use
its full powers to gain its own living  and the effects thus produced will
have been transmitted to the offspring at a corresponding nearly mature
age   Thus the young will not be modified  or will be modified only in a
slight degree  through the effects of the increased use or disuse of parts 

With some animals the successive variations may have supervened at a very
early period of life  or the steps may have been inherited at an earlier
age than that at which they first occurred   In either of these cases the
young or embryo will closely resemble the mature parent form  as we have
seen with the short faced tumbler   And this is the rule of development in
certain whole groups  or in certain sub groups alone  as with cuttle fish 
land shells  fresh water crustaceans  spiders  and some members of the
great class of insects   With respect to the final cause of the young in
such groups not passing through any metamorphosis  we can see that this
would follow from the following contingencies   namely  from the young
having to provide at a very early age for their own wants  and from their
following the same habits of life with their parents  for in this case it
would be indispensable for their existence that they should be modified in
the same manner as their parents   Again  with respect to the singular fact
that many terrestrial and fresh water animals do not undergo any
metamorphosis  while marine members of the same groups pass through various
transformations  Fritz Muller has suggested that the process of slowly
modifying and adapting an animal to live on the land or in fresh water 
instead of in the sea  would be greatly simplified by its not passing
through any larval stage  for it is not probable that places well adapted
for both the larval and mature stages  under such new and greatly changed
habits of life  would commonly be found unoccupied or ill occupied by other
organisms   In this case the gradual acquirement at an earlier and earlier
age of the adult structure would be favoured by natural selection  and all
traces of former metamorphoses would finally be lost 

If  on the other hand  it profited the young of an animal to follow habits
of life slightly different from those of the parent form  and consequently
to be constructed on a slightly different plan  or if it profited a larva
already different from its parent to change still further  then  on the
principle of inheritance at corresponding ages  the young or the larvae
might be rendered by natural selection more and more different from their
parents to any conceivable extent   Differences in the larva might  also 
become correlated with successive stages of its development  so that the
larva  in the first stage  might come to differ greatly from the larva in
the second stage  as is the case with many animals   The adult might also
become fitted for sites or habits  in which organs of locomotion or of the
senses  etc   would be useless  and in this case the metamorphosis would be
retrograde 

 From the remarks just made we can see how by changes of structure in the
young  in conformity with changed habits of life  together with inheritance
at corresponding ages  animals might come to pass through stages of
development  perfectly distinct from the primordial condition of their
adult progenitors   Most of our best authorities are now convinced that the
various larval and pupal stages of insects have thus been acquired through
adaptation  and not through inheritance from some ancient form   The
curious case of Sitaris  a beetle which passes through certain unusual
stages of development  will illustrate how this might occur   The first
larval form is described by M  Fabre  as an active  minute insect 
furnished with six legs  two long antennae  and four eyes   These larvae
are hatched in the nests of bees  and when the male bees emerge from their
burrows  in the spring  which they do before the females  the larvae spring
on them  and afterwards crawl on to the females while paired with the
males   As soon as the female bee deposits her eggs on the surface of the
honey stored in the cells  the larvae of the Sitaris leap on the eggs and
devour them   Afterwards they undergo a complete change  their eyes
disappear  their legs and antennae become rudimentary  and they feed on
honey  so that they now more closely resemble the ordinary larvae of
insects  ultimately they undergo a further transformation  and finally
emerge as the perfect beetle   Now  if an insect  undergoing
transformations like those of the Sitaris  were to become the progenitor of
a whole new class of insects  the course of development of the new class
would be widely different from that of our existing insects  and the first
larval stage certainly would not represent the former condition of any
adult and ancient form 

On the other hand it is highly probable that with many animals the
embryonic or larval stages show us  more or less completely  the condition
of the progenitor of the whole group in its adult state   In the great
class of the Crustacea  forms wonderfully distinct from each other  namely 
suctorial parasites  cirripedes  entomostraca  and even the malacostraca 
appear at first as larvae under the nauplius form  and as these larvae live
and feed in the open sea  and are not adapted for any peculiar habits of
life  and from other reasons assigned by Fritz Muller  it is probable that
at some very remote period an independent adult animal  resembling the
Nauplius  existed  and subsequently produced  along several divergent lines
of descent  the above named great Crustacean groups   So again  it is
probable  from what we know of the embryos of mammals  birds  fishes and
reptiles  that these animals are the modified descendants of some ancient
progenitor  which was furnished in its adult state with branchiae  a swim 
bladder  four fin like limbs  and a long tail  all fitted for an aquatic
life 

As all the organic beings  extinct and recent  which have ever lived  can
be arranged within a few great classes  and as all within each class have 
according to our theory  been connected together by fine gradations  the
best  and  if our collections were nearly perfect  the only possible
arrangement  would be genealogical  descent being the hidden bond of
connexion which naturalists have been seeking under the term of the Natural
System   On this view we can understand how it is that  in the eyes of most
naturalists  the structure of the embryo is even more important for
classification than that of the adult   In two or more groups of animals 
however much they may differ from each other in structure and habits in
their adult condition  if they pass through closely similar embryonic
stages  we may feel assured that they are all descended from one parent 
form  and are therefore closely related   Thus  community in embryonic
structure reveals community of descent  but dissimilarity in embryonic
development does not prove discommunity of descent  for in one of two
groups the developmental stages may have been suppressed  or may have been
so greatly modified through adaptation to new habits of life as to be no
longer recognisable   Even in groups  in which the adults have been
modified to an extreme degree  community of origin is often revealed by the
structure of the larvae  we have seen  for instance  that cirripedes 
though externally so like shell fish  are at once known by their larvae to
belong to the great class of crustaceans   As the embryo often shows us
more or less plainly the structure of the less modified and ancient
progenitor of the group  we can see why ancient and extinct forms so often
resemble in their adult state the embryos of existing species of the same
class   Agassiz believes this to be a universal law of nature  and we may
hope hereafter to see the law proved true   It can  however  be proved true
only in those cases in which the ancient state of the progenitor of the
group has not been wholly obliterated  either by successive variations
having supervened at a very early period of growth  or by such variations
having been inherited at an earlier age than that at which they first
appeared   It should also be borne in mind  that the law may be true  but
yet  owing to the geological record not extending far enough back in time 
may remain for a long period  or for ever  incapable of demonstration   The
law will not strictly hold good in those cases in which an ancient form
became adapted in its larval state to some special line of life  and
transmitted the same larval state to a whole group of descendants  for such
larval state will not resemble any still more ancient form in its adult
state 

Thus  as it seems to me  the leading facts in embryology  which are second
to none in importance  are explained on the principle of variations in the
many descendants from some one ancient progenitor  having appeared at a not
very early period of life  and having been inherited at a corresponding
period   Embryology rises greatly in interest  when we look at the embryo
as a picture  more or less obscured  of the progenitor  either in its adult
or larval state  of all the members of the same great class 

RUDIMENTARY  ATROPHIED  AND ABORTED ORGANS 

Organs or parts in this strange condition  bearing the plain stamp of
inutility  are extremely common  or even general  throughout nature   It
would be impossible to name one of the higher animals in which some part or
other is not in a rudimentary condition   In the mammalia  for instance 
the males possess rudimentary mammae  in snakes one lobe of the lungs is
rudimentary  in birds the  bastard wing  may safely be considered as a
rudimentary digit  and in some species the whole wing is so far rudimentary
that it cannot be used for flight   What can be more curious than the
presence of teeth in foetal whales  which when grown up have not a tooth in
their heads  or the teeth  which never cut through the gums  in the upper
jaws of unborn calves 

Rudimentary organs plainly declare their origin and meaning in various
ways   There are beetles belonging to closely allied species  or even to
the same identical species  which have either full sized and perfect wings 
or mere rudiments of membrane  which not rarely lie under wing covers
firmly soldered together  and in these cases it is impossible to doubt 
that the rudiments represent wings   Rudimentary organs sometimes retain
their potentiality   this occasionally occurs with the mammae of male
mammals  which have been known to become well developed and to secrete
milk   So again in the udders of the genus Bos  there are normally four
developed and two rudimentary teats  but the latter in our domestic cows
sometimes become well developed and yield milk   In regard to plants  the
petals are sometimes rudimentary  and sometimes well developed in the
individuals of the same species   In certain plants having separated sexes
Kolreuter found that by crossing a species  in which the male flowers
included a rudiment of a pistil  with an hermaphrodite species  having of
course a well developed pistil  the rudiment in the hybrid offspring was
much increased in size  and this clearly shows that the rudimentary and
perfect pistils are essentially alike in nature   An animal may possess
various parts in a perfect state  and yet they may in one sense be
rudimentary  for they are useless   thus the tadpole of the common
salamander or water newt  as Mr  G H  Lewes remarks   has gills  and passes
its existence in the water  but the Salamandra atra  which lives high up
among the mountains  brings forth its young full formed   This animal never
lives in the water   Yet if we open a gravid female  we find tadpoles
inside her with exquisitely feathered gills  and when placed in water they
swim about like the tadpoles of the water newt   Obviously this aquatic
organisation has no reference to the future life of the animal  nor has it
any adaptation to its embryonic condition  it has solely reference to
ancestral adaptations  it repeats a phase in the development of its
progenitors  

An organ  serving for two purposes  may become rudimentary or utterly
aborted for one  even the more important purpose  and remain perfectly
efficient for the other   Thus  in plants  the office of the pistil is to
allow the pollen tubes to reach the ovules within the ovarium   The pistil
consists of a stigma supported on the style  but in some Compositae  the
male florets  which of course cannot be fecundated  have a rudimentary
pistil  for it is not crowned with a stigma  but the style remains well
developed and is clothed in the usual manner with hairs  which serve to
brush the pollen out of the surrounding and conjoined anthers   Again  an
organ may become rudimentary for its proper purpose  and be used for a
distinct one   in certain fishes the swim bladder seems to be rudimentary
for its proper function of giving buoyancy  but has become converted into a
nascent breathing organ or lung   Many similar instances could be given 

Useful organs  however little they may be developed  unless we have reason
to suppose that they were formerly more highly developed  ought not to be
considered as rudimentary   They may be in a nascent condition  and in
progress towards further development   Rudimentary organs  on the other
hand  are either quite useless  such as teeth which never cut through the
gums  or almost useless  such as the wings of an ostrich  which serve
merely as sails   As organs in this condition would formerly  when still
less developed  have been of even less use than at present  they cannot
formerly have been produced through variation and natural selection  which
acts solely by the preservation of useful modifications   They have been
partially retained by the power of inheritance  and relate to a former
state of things   It is  however  often difficult to distinguish between
rudimentary and nascent organs  for we can judge only by analogy whether a
part is capable of further development  in which case alone it deserves to
be called nascent   Organs in this condition will always be somewhat rare 
for beings thus provided will commonly have been supplanted by their
successors with the same organ in a more perfect state  and consequently
will have become long ago extinct   The wing of the penguin is of high
service  acting as a fin  it may  therefore  represent the nascent state of
the wing   not that I believe this to be the case  it is more probably a
reduced organ  modified for a new function   the wing of the Apteryx  on
the other hand  is quite useless  and is truly rudimentary   Owen considers
the simple filamentary limbs of the Lepidosiren as the  beginnings of
organs which attain full functional development in higher vertebrates  
but  according to the view lately advocated by Dr  Gunther  they are
probably remnants  consisting of the persistent axis of a fin  with the
lateral rays or branches aborted   The mammary glands of the
Ornithorhynchus may be considered  in comparison with the udders of a cow 
as in a nascent condition   The ovigerous frena of certain cirripedes 
which have ceased to give attachment to the ova and are feebly developed 
are nascent branchiae 

Rudimentary organs in the individuals of the same species are very liable
to vary in the degree of their development and in other respects   In
closely allied species  also  the extent to which the same organ has been
reduced occasionally differs much   This latter fact is well exemplified in
the state of the wings of female moths belonging to the same family  
Rudimentary organs may be utterly aborted  and this implies  that in
certain animals or plants  parts are entirely absent which analogy would
lead us to expect to find in them  and which are occasionally found in
monstrous individuals   Thus in most of the Scrophulariaceae the fifth
stamen is utterly aborted  yet we may conclude that a fifth stamen once
existed  for a rudiment of it is found in many species of the family  and
this rudiment occasionally becomes perfectly developed  as may sometimes be
seen in the common snap dragon   In tracing the homologies of any part in
different members of the same class  nothing is more common  or  in order
fully to understand the relations of the parts  more useful than the
discovery of rudiments   This is well shown in the drawings given by Owen
of the leg bones of the horse  ox  and rhinoceros 

It is an important fact that rudimentary organs  such as teeth in the upper
jaws of whales and ruminants  can often be detected in the embryo  but
afterwards wholly disappear   It is also  I believe  a universal rule  that
a rudimentary part is of greater size in the embryo relatively to the
adjoining parts  than in the adult  so that the organ at this early age is
less rudimentary  or even cannot be said to be in any degree rudimentary  
Hence rudimentary organs in the adult are often said to have retained their
embryonic condition 

I have now given the leading facts with respect to rudimentary organs   In
reflecting on them  every one must be struck with astonishment  for the
same reasoning power which tells us that most parts and organs are
exquisitely adapted for certain purposes  tells us with equal plainness
that these rudimentary or atrophied organs are imperfect and useless   In
works on natural history  rudimentary organs are generally said to have
been created  for the sake of symmetry   or in order  to complete the
scheme of nature    But this is not an explanation  merely a restatement of
the fact   Nor is it consistent with itself   thus the boa constrictor has
rudiments of hind limbs and of a pelvis  and if it be said that these bones
have been retained  to complete the scheme of nature   why  as Professor
Weismann asks  have they not been retained by other snakes  which do not
possess even a vestige of these same bones   What would be thought of an
astronomer who maintained that the satellites revolve in elliptic courses
round their planets  for the sake of symmetry   because the planets thus
revolve round the sun   An eminent physiologist accounts for the presence
of rudimentary organs  by supposing that they serve to excrete matter in
excess  or matter injurious to the system  but can we suppose that the
minute papilla  which often represents the pistil in male flowers  and
which is formed of mere cellular tissue  can thus act   Can we suppose that
rudimentary teeth  which are subsequently absorbed  are beneficial to the
rapidly growing embryonic calf by removing matter so precious as phosphate
of lime   When a man s fingers have been amputated  imperfect nails have
been known to appear on the stumps  and I could as soon believe that these
vestiges of nails are developed in order to excrete horny matter  as that
the rudimentary nails on the fin of the manatee have been developed for
this same purpose 

On the view of descent with modification  the origin of rudimentary organs
is comparatively simple  and we can understand to a large extent the laws
governing their imperfect development   We have plenty of cases of
rudimentary organs in our domestic productions  as the stump of a tail in
tailless breeds  the vestige of an ear in earless breeds of sheep  the
reappearance of minute dangling horns in hornless breeds of cattle  more
especially  according to Youatt  in young animals  and the state of the
whole flower in the cauliflower   We often see rudiments of various parts
in monsters  but I doubt whether any of these cases throw light on the
origin of rudimentary organs in a state of nature  further than by showing
that rudiments can be produced  for the balance of evidence clearly
indicates that species under nature do not undergo great and abrupt
changes   But we learn from the study of our domestic productions that the
disuse of parts leads to their reduced size  and that the result is
inherited  

It appears probable that disuse has been the main agent in rendering organs
rudimentary   It would at first lead by slow steps to the more and more
complete reduction of a part  until at last it became rudimentary  as in
the case of the eyes of animals inhabiting dark caverns  and of the wings
of birds inhabiting oceanic islands  which have seldom been forced by
beasts of prey to take flight  and have ultimately lost the power of
flying   Again  an organ  useful under certain conditions  might become
injurious under others  as with the wings of beetles living on small and
exposed islands  and in this case natural selection will have aided in
reducing the organ  until it was rendered harmless and rudimentary 

Any change in structure and function  which can be effected by small
stages  is within the power of natural selection  so that an organ
rendered  through changed habits of life  useless or injurious for one
purpose  might be modified and used for another purpose   An organ might 
also  be retained for one alone of its former functions   Organs 
originally formed by the aid of natural selection  when rendered useless
may well be variable  for their variations can no longer be checked by
natural selection   All this agrees well with what we see under nature  
Moreover  at whatever period of life either disuse or selection reduces an
organ  and this will generally be when the being has come to maturity and
to exert its full powers of action  the principle of inheritance at
corresponding ages will tend to reproduce the organ in its reduced state at
the same mature age  but will seldom affect it in the embryo   Thus we can
understand the greater size of rudimentary organs in the embryo relatively
to the adjoining parts  and their lesser relative size in the adult   If 
for instance  the digit of an adult animal was used less and less during
many generations  owing to some change of habits  or if an organ or gland
was less and less functionally exercised  we may infer that it would become
reduced in size in the adult descendants of this animal  but would retain
nearly its original standard of development in the embryo 

There remains  however  this difficulty   After an organ has ceased being
used  and has become in consequence much reduced  how can it be still
further reduced in size until the merest vestige is left  and how can it be
finally quite obliterated   It is scarcely possible that disuse can go on
producing any further effect after the organ has once been rendered
functionless   Some additional explanation is here requisite which I cannot
give   If  for instance  it could be proved that every part of the
organisation tends to vary in a greater degree towards diminution than
toward augmentation of size  then we should be able to understand how an
organ which has become useless would be rendered  independently of the
effects of disuse  rudimentary and would at last be wholly suppressed  for
the variations towards diminished size would no longer be checked by
natural selection   The principle of the economy of growth  explained in a
former chapter  by which the materials forming any part  if not useful to
the possessor  are saved as far as is possible  will perhaps come into play
in rendering a useless part rudimentary   But this principle will almost
necessarily be confined to the earlier stages of the process of reduction 
for we cannot suppose that a minute papilla  for instance  representing in
a male flower the pistil of the female flower  and formed merely of
cellular tissue  could be further reduced or absorbed for the sake of
economising nutriment 

Finally  as rudimentary organs  by whatever steps they may have been
degraded into their present useless condition  are the record of a former
state of things  and have been retained solely through the power of
inheritance  we can understand  on the genealogical view of classification 
how it is that systematists  in placing organisms in their proper places in
the natural system  have often found rudimentary parts as useful as  or
even sometimes more useful than  parts of high physiological importance  
Rudimentary organs may be compared with the letters in a word  still
retained in the spelling  but become useless in the pronunciation  but
which serve as a clue for its derivation   On the view of descent with
modification  we may conclude that the existence of organs in a
rudimentary  imperfect  and useless condition  or quite aborted  far from
presenting a strange difficulty  as they assuredly do on the old doctrine
of creation  might even have been anticipated in accordance with the views
here explained 

SUMMARY 

In this chapter I have attempted to show that the arrangement of all
organic beings throughout all time in groups under groups  that the nature
of the relationships by which all living and extinct organisms are united
by complex  radiating  and circuitous lines of affinities into a few grand
classes  the rules followed and the difficulties encountered by naturalists
in their classifications  the value set upon characters  if constant and
prevalent  whether of high or of the most trifling importance  or  as with
rudimentary organs of no importance  the wide opposition in value between
analogical or adaptive characters  and characters of true affinity  and
other such rules  all naturally follow if we admit the common parentage of
allied forms  together with their modification through variation and
natural selection  with the contingencies of extinction and divergence of
character   In considering this view of classification  it should be borne
in mind that the element of descent has been universally used in ranking
together the sexes  ages  dimorphic forms  and acknowledged varieties of
the same species  however much they may differ from each other in
structure   If we extend the use of this element of descent  the one
certainly known cause of similarity in organic beings  we shall understand
what is meant by the Natural System   it is genealogical in its attempted
arrangement  with the grades of acquired difference marked by the terms 
varieties  species  genera  families  orders  and classes 

On this same view of descent with modification  most of the great facts in
Morphology become intelligible  whether we look to the same pattern
displayed by the different species of the same class in their homologous
organs  to whatever purpose applied  or to the serial and lateral
homologies in each individual animal and plant 

On the principle of successive slight variations  not necessarily or
generally supervening at a very early period of life  and being inherited
at a corresponding period  we can understand the leading facts in
embryology  namely  the close resemblance in the individual embryo of the
parts which are homologous  and which when matured become widely different
in structure and function  and the resemblance of the homologous parts or
organs in allied though distinct species  though fitted in the adult state
for habits as different as is possible   Larvae are active embryos  which
have become specially modified in a greater or less degree in relation to
their habits of life  with their modifications inherited at a corresponding
early age   On these same principles  and bearing in mind that when organs
are reduced in size  either from disuse or through natural selection  it
will generally be at that period of life when the being has to provide for
its own wants  and bearing in mind how strong is the force of
inheritance  the occurrence of rudimentary organs might even have been
anticipated   The importance of embryological characters and of rudimentary
organs in classification is intelligible  on the view that a natural
arrangement must be genealogical 

Finally  the several classes of facts which have been considered in this
chapter  seem to me to proclaim so plainly  that the innumerable species 
genera and families  with which this world is peopled  are all descended 
each within its own class or group  from common parents  and have all been
modified in the course of descent  that I should without hesitation adopt
this view  even if it were unsupported by other facts or arguments 


CHAPTER XV 

RECAPITULATION AND CONCLUSION 

Recapitulation of the objections to the theory of Natural Selection   
Recapitulation of the general and special circumstances in its favour   
Causes of the general belief in the immutability of species    How far the
theory of Natural Selection may be extended    Effects of its adoption on
the study of Natural History    Concluding remarks 

As this whole volume is one long argument  it may be convenient to the
reader to have the leading facts and inferences briefly recapitulated 

That many and serious objections may be advanced against the theory of
descent with modification through variation and natural selection  I do not
deny   I have endeavoured to give to them their full force   Nothing at
first can appear more difficult to believe than that the more complex
organs and instincts have been perfected  not by means superior to  though
analogous with  human reason  but by the accumulation of innumerable slight
variations  each good for the individual possessor   Nevertheless  this
difficulty  though appearing to our imagination insuperably great  cannot
be considered real if we admit the following propositions  namely  that all
parts of the organisation and instincts offer  at least individual
differences  that there is a struggle for existence leading to the
preservation of profitable deviations of structure or instinct  and 
lastly  that gradations in the state of perfection of each organ may have
existed  each good of its kind   The truth of these propositions cannot  I
think  be disputed 

It is  no doubt  extremely difficult even to conjecture by what gradations
many structures have been perfected  more especially among broken and
failing groups of organic beings  which have suffered much extinction  but
we see so many strange gradations in nature  that we ought to be extremely
cautious in saying that any organ or instinct  or any whole structure 
could not have arrived at its present state by many graduated steps   There
are  it must be admitted  cases of special difficulty opposed to the theory
of natural selection  and one of the most curious of these is the existence 
in the same community of two or three defined castes of workers or sterile
female ants  but I have attempted to show how these difficulties can be
mastered 

With respect to the almost universal sterility of species when first
crossed  which forms so remarkable a contrast with the almost universal
fertility of varieties when crossed  I must refer the reader to the
recapitulation of the facts given at the end of the ninth chapter  which
seem to me conclusively to show that this sterility is no more a special
endowment than is the incapacity of two distinct kinds of trees to be
grafted together  but that it is incidental on differences confined to the
reproductive systems of the intercrossed species   We see the truth of this
conclusion in the vast difference in the results of crossing the same two
species reciprocally  that is  when one species is first used as the father
and then as the mother   Analogy from the consideration of dimorphic and
trimorphic plants clearly leads to the same conclusion  for when the forms
are illegitimately united  they yield few or no seed  and their offspring
are more or less sterile  and these forms belong to the same undoubted
species  and differ from each other in no respect except in their
reproductive organs and functions 

Although the fertility of varieties when intercrossed  and of their mongrel
offspring  has been asserted by so many authors to be universal  this
cannot be considered as quite correct after the facts given on the high
authority of Gartner and Kolreuter   Most of the varieties which have been
experimented on have been produced under domestication  and as
domestication  I do not mean mere confinement  almost certainly tends to
eliminate that sterility which  judging from analogy  would have affected
the parent species if intercrossed  we ought not to expect that
domestication would likewise induce sterility in their modified descendants
when crossed   This elimination of sterility apparently follows from the
same cause which allows our domestic animals to breed freely under
diversified circumstances  and this again apparently follows from their
having been gradually accustomed to frequent changes in their conditions of
life 

A double and parallel series of facts seems to throw much light on the
sterility of species  when first crossed  and of their hybrid offspring  
On the one side  there is good reason to believe that slight changes in the
conditions of life give vigour and fertility to all organic beings   We
know also that a cross between the distinct individuals of the same
variety  and between distinct varieties  increases the number of their
offspring  and certainly gives to them increased size and vigour   This is
chiefly owing to the forms which are crossed having been exposed to
somewhat different conditions of life  for I have ascertained by a
labourious series of experiments that if all the individuals of the same
variety be subjected during several generations to the same conditions  the
good derived from crossing is often much diminished or wholly disappears  
This is one side of the case   On the other side  we know that species
which have long been exposed to nearly uniform conditions  when they are
subjected under confinement to new and greatly changed conditions  either
perish  or if they survive  are rendered sterile  though retaining perfect
health   This does not occur  or only in a very slight degree  with our
domesticated productions  which have long been exposed to fluctuating
conditions   Hence when we find that hybrids produced by a cross between
two distinct species are few in number  owing to their perishing soon after
conception or at a very early age  or if surviving that they are rendered
more or less sterile  it seems highly probable that this result is due to
their having been in fact subjected to a great change in their conditions
of life  from being compounded of two distinct organisations   He who will
explain in a definite manner why  for instance  an elephant or a fox will
not breed under confinement in its native country  whilst the domestic pig
or dog will breed freely under the most diversified conditions  will at the
same time be able to give a definite answer to the question why two
distinct species  when crossed  as well as their hybrid offspring  are
generally rendered more or less sterile  while two domesticated varieties
when crossed and their mongrel offspring are perfectly fertile 

Turning to geographical distribution  the difficulties encountered on the
theory of descent with modification are serious enough   All the
individuals of the same species  and all the species of the same genus  or
even higher group  are descended from common parents  and therefore  in
however distant and isolated parts of the world they may now be found  they
must in the course of successive generations have travelled from some one
point to all the others   We are often wholly unable even to conjecture how
this could have been effected   Yet  as we have reason to believe that some
species have retained the same specific form for very long periods of time 
immensely long as measured by years  too much stress ought not to be laid
on the occasional wide diffusion of the same species  for during very long
periods there will always have been a good chance for wide migration by
many means   A broken or interrupted range may often be accounted for by
the extinction of the species in the intermediate regions   It cannot be
denied that we are as yet very ignorant as to the full extent of the
various climatical and geographical changes which have affected the earth
during modern periods  and such changes will often have facilitated
migration   As an example  I have attempted to show how potent has been the
influence of the Glacial period on the distribution of the same and of
allied species throughout the world   We are as yet profoundly ignorant of
the many occasional means of transport   With respect to distinct species
of the same genus  inhabiting distant and isolated regions  as the process
of modification has necessarily been slow  all the means of migration will
have been possible during a very long period  and consequently the
difficulty of the wide diffusion of the species of the same genus is in
some degree lessened 

As according to the theory of natural selection an interminable number of
intermediate forms must have existed  linking together all the species in
each group by gradations as fine as our existing varieties  it may be
asked  Why do we not see these linking forms all around us   Why are not
all organic beings blended together in an inextricable chaos   With respect
to existing forms  we should remember that we have no right to expect
 excepting in rare cases  to discover DIRECTLY connecting links between
them  but only between each and some extinct and supplanted form   Even on
a wide area  which has during a long period remained continuous  and of
which the climatic and other conditions of life change insensibly in
proceeding from a district occupied by one species into another district
occupied by a closely allied species  we have no just right to expect often
to find intermediate varieties in the intermediate zones   For we have
reason to believe that only a few species of a genus ever undergo change 
the other species becoming utterly extinct and leaving no modified progeny 
Of the species which do change  only a few within the same country change
at the same time  and all modifications are slowly effected   I have also
shown that the intermediate varieties which probably at first existed in
the intermediate zones  would be liable to be supplanted by the allied
forms on either hand  for the latter  from existing in greater numbers 
would generally be modified and improved at a quicker rate than the
intermediate varieties  which existed in lesser numbers  so that the
intermediate varieties would  in the long run  be supplanted and
exterminated 

On this doctrine of the extermination of an infinitude of connecting links 
between the living and extinct inhabitants of the world  and at each
successive period between the extinct and still older species  why is not
every geological formation charged with such links   Why does not every
collection of fossil remains afford plain evidence of the gradation and
mutation of the forms of life   Although geological research has
undoubtedly revealed the former existence of many links  bringing numerous
forms of life much closer together  it does not yield the infinitely many
fine gradations between past and present species required on the theory 
and this is the most obvious of the many objections which may be urged
against it   Why  again  do whole groups of allied species appear  though
this appearance is often false  to have come in suddenly on the successive
geological stages   Although we now know that organic beings appeared on
this globe  at a period incalculably remote  long before the lowest bed of
the Cambrian system was deposited  why do we not find beneath this system
great piles of strata stored with the remains of the progenitors of the
Cambrian fossils   For on the theory  such strata must somewhere have been
deposited at these ancient and utterly unknown epochs of the world s
history 

I can answer these questions and objections only on the supposition that
the geological record is far more imperfect than most geologists believe   
The number of specimens in all our museums is absolutely as nothing
compared with the countless generations of countless species which have
certainly existed   The parent form of any two or more species would not be
in all its characters directly intermediate between its modified offspring 
any more than the rock pigeon is directly intermediate in crop and tail
between its descendants  the pouter and fantail pigeons   We should not be
able to recognise a species as the parent of another and modified species 
if we were to examine the two ever so closely  unless we possessed most of
the intermediate links  and owing to the imperfection of the geological
record  we have no just right to expect to find so many links   If two or
three  or even more linking forms were discovered  they would simply be
ranked by many naturalists as so many new species  more especially if found
in different geological substages  let their differences be ever so slight  
Numerous existing doubtful forms could be named which are probably
varieties  but who will pretend that in future ages so many fossil links
will be discovered  that naturalists will be able to decide whether or not
these doubtful forms ought to be called varieties   Only a small portion of
the world has been geologically explored   Only organic beings of certain
classes can be preserved in a fossil condition  at least in any great
number   Many species when once formed never undergo any further change but
become extinct without leaving modified descendants  and the periods during
which species have undergone modification  though long as measured by
years  have probably been short in comparison with the periods during which
they retained the same form   It is the dominant and widely ranging species
which vary most frequently and vary most  and varieties are often at first
local  both causes rendering the discovery of intermediate links in any one
formation less likely   Local varieties will not spread into other and
distant regions until they are considerably modified and improved  and when
they have spread  and are discovered in a geological formation  they appear
as if suddenly created there  and will be simply classed as new species  
Most formations have been intermittent in their accumulation  and their
duration has probably been shorter than the average duration of specific
forms   Successive formations are in most cases separated from each other
by blank intervals of time of great length  for fossiliferous formations
thick enough to resist future degradation can  as a general rule  be
accumulated only where much sediment is deposited on the subsiding bed of
the sea   During the alternate periods of elevation and of stationary level
the record will generally be blank   During these latter periods there will
probably be more variability in the forms of life  during periods of
subsidence  more extinction 

With respect to the absence of strata rich in fossils beneath the Cambrian
formation  I can recur only to the hypothesis given in the tenth chapter 
namely  that though our continents and oceans have endured for an enormous
period in nearly their present relative positions  we have no reason to
assume that this has always been the case  consequently formations much
older than any now known may lie buried beneath the great oceans   With
respect to the lapse of time not having been sufficient since our planet
was consolidated for the assumed amount of organic change  and this
objection  as urged by Sir William Thompson  is probably one of the gravest
as yet advanced  I can only say  firstly  that we do not know at what rate
species change  as measured by years  and secondly  that many philosophers
are not as yet willing to admit that we know enough of the constitution of
the universe and of the interior of our globe to speculate with safety on
its past duration 

That the geological record is imperfect all will admit  but that it is
imperfect to the degree required by our theory  few will be inclined to
admit   If we look to long enough intervals of time  geology plainly
declares that species have all changed  and they have changed in the manner
required by the theory  for they have changed slowly and in a graduated
manner   We clearly see this in the fossil remains from consecutive
formations invariably being much more closely related to each other than
are the fossils from widely separated formations 

Such is the sum of the several chief objections and difficulties which may
justly be urged against the theory  and I have now briefly recapitulated
the answers and explanations which  as far as I can see  may be given   I
have felt these difficulties far too heavily during many years to doubt
their weight   But it deserves especial notice that the more important
objections relate to questions on which we are confessedly ignorant  nor do
we know how ignorant we are   We do not know all the possible transitional
gradations between the simplest and the most perfect organs  it cannot be
pretended that we know all the varied means of Distribution during the long
lapse of years  or that we know how imperfect is the Geological Record  
Serious as these several objections are  in my judgment they are by no
means sufficient to overthrow the theory of descent with subsequent
modification 

Now let us turn to the other side of the argument   Under domestication we
see much variability  caused  or at least excited  by changed conditions of
life  but often in so obscure a manner  that we are tempted to consider the
variations as spontaneous   Variability is governed by many complex laws 
by correlated growth  compensation  the increased use and disuse of parts 
and the definite action of the surrounding conditions   There is much
difficulty in ascertaining how largely our domestic productions have been
modified  but we may safely infer that the amount has been large  and that
modifications can be inherited for long periods   As long as the conditions
of life remain the same  we have reason to believe that a modification 
which has already been inherited for many generations  may continue to be
inherited for an almost infinite number of generations   On the other hand
we have evidence that variability  when it has once come into play  does
not cease under domestication for a very long period  nor do we know that
it ever ceases  for new varieties are still occasionally produced by our
oldest domesticated productions 

Variability is not actually caused by man  he only unintentionally exposes
organic beings to new conditions of life and then nature acts on the
organisation and causes it to vary   But man can and does select the
variations given to him by nature  and thus accumulates them in any desired
manner   He thus adapts animals and plants for his own benefit or pleasure  
He may do this methodically  or he may do it unconsciously by preserving
the individuals most useful or pleasing to him without any intention of
altering the breed   It is certain that he can largely influence the
character of a breed by selecting  in each successive generation 
individual differences so slight as to be inappreciable except by an
educated eye   This unconscious process of selection has been the great
agency in the formation of the most distinct and useful domestic breeds  
That many breeds produced by man have to a large extent the character of
natural species  is shown by the inextricable doubts whether many of them
are varieties or aboriginally distinct species 

There is no reason why the principles which have acted so efficiently under
domestication should not have acted under nature   In the survival of
favoured individuals and races  during the constantly recurrent Struggle
for Existence  we see a powerful and ever acting form of Selection   The
struggle for existence inevitably follows from the high geometrical ratio
of increase which is common to all organic beings   This high rate of
increase is proved by calculation  by the rapid increase of many animals
and plants during a succession of peculiar seasons  and when naturalised in
new countries   More individuals are born than can possibly survive   A
grain in the balance may determine which individuals shall live and which
shall die  which variety or species shall increase in number  and which
shall decrease  or finally become extinct   As the individuals of the same
species come in all respects into the closest competition with each other 
the struggle will generally be most severe between them  it will be almost
equally severe between the varieties of the same species  and next in
severity between the species of the same genus   On the other hand the
struggle will often be severe between beings remote in the scale of nature  
The slightest advantage in certain individuals  at any age or during any
season  over those with which they come into competition  or better
adaptation in however slight a degree to the surrounding physical
conditions  will  in the long run  turn the balance 

With animals having separated sexes  there will be in most cases a struggle
between the males for the possession of the females   The most vigorous
males  or those which have most successfully struggled with their
conditions of life  will generally leave most progeny   But success will
often depend on the males having special weapons or means of defence or
charms  and a slight advantage will lead to victory 

As geology plainly proclaims that each land has undergone great physical
changes  we might have expected to find that organic beings have varied
under nature  in the same way as they have varied under domestication   And
if there has been any variability under nature  it would be an
unaccountable fact if natural selection had not come into play   It has
often been asserted  but the assertion is incapable of proof  that the
amount of variation under nature is a strictly limited quantity   Man 
though acting on external characters alone and often capriciously  can
produce within a short period a great result by adding up mere individual
differences in his domestic productions  and every one admits that species
present individual differences   But  besides such differences  all
naturalists admit that natural varieties exist  which are considered
sufficiently distinct to be worthy of record in systematic works   No one
has drawn any clear distinction between individual differences and slight
varieties  or between more plainly marked varieties and subspecies and
species   On separate continents  and on different parts of the same
continent  when divided by barriers of any kind  and on outlying islands 
what a multitude of forms exist  which some experienced naturalists rank as
varieties  others as geographical races or sub species  and others as
distinct  though closely allied species 

If  then  animals and plants do vary  let it be ever so slightly or slowly 
why should not variations or individual differences  which are in any way
beneficial  be preserved and accumulated through natural selection  or the
survival of the fittest   If man can by patience select variations useful
to him  why  under changing and complex conditions of life  should not
variations useful to nature s living products often arise  and be preserved
or selected   What limit can be put to this power  acting during long ages
and rigidly scrutinising the whole constitution  structure  and habits of
each creature  favouring the good and rejecting the bad   I can see no
limit to this power  in slowly and beautifully adapting each form to the
most complex relations of life   The theory of natural selection  even if
we look no further than this  seems to be in the highest degree probable  
I have already recapitulated  as fairly as I could  the opposed
difficulties and objections   now let us turn to the special facts and
arguments in favour of the theory 

On the view that species are only strongly marked and permanent varieties 
and that each species first existed as a variety  we can see why it is that
no line of demarcation can be drawn between species  commonly supposed to
have been produced by special acts of creation  and varieties which are
acknowledged to have been produced by secondary laws   On this same view we
can understand how it is that in a region where many species of a genus
have been produced  and where they now flourish  these same species should
present many varieties  for where the manufactory of species has been
active  we might expect  as a general rule  to find it still in action  and
this is the case if varieties be incipient species   Moreover  the species
of the larger genera  which afford the greater number of varieties or
incipient species  retain to a certain degree the character of varieties 
for they differ from each other by a less amount of difference than do the
species of smaller genera   The closely allied species also of a larger
genera apparently have restricted ranges  and in their affinities they are
clustered in little groups round other species  in both respects resembling
varieties   These are strange relations on the view that each species was
independently created  but are intelligible if each existed first as a
variety 

As each species tends by its geometrical rate of reproduction to increase
inordinately in number  and as the modified descendants of each species
will be enabled to increase by as much as they become more diversified in
habits and structure  so as to be able to seize on many and widely
different places in the economy of nature  there will be a constant
tendency in natural selection to preserve the most divergent offspring of
any one species   Hence during a long continued course of modification  the
slight differences characteristic of varieties of the same species  tend to
be augmented into the greater differences characteristic of the species of
the same genus   New and improved varieties will inevitably supplant and
exterminate the older  less improved and intermediate varieties  and thus
species are rendered to a large extent defined and distinct objects  
Dominant species belonging to the larger groups within each class tend to
give birth to new and dominant forms  so that each large group tends to
become still larger  and at the same time more divergent in character   But
as all groups cannot thus go on increasing in size  for the world would not
hold them  the more dominant groups beat the less dominant   This tendency
in the large groups to go on increasing in size and diverging in character 
together with the inevitable contingency of much extinction  explains the
arrangement of all the forms of life in groups subordinate to groups  all
within a few great classes  which has prevailed throughout all time   This
grand fact of the grouping of all organic beings under what is called the
Natural System  is utterly inexplicable on the theory of creation 

As natural selection acts solely by accumulating slight  successive 
favourable variations  it can produce no great or sudden modifications  it
can act only by short and slow steps   Hence  the canon of  Natura non
facit saltum   which every fresh addition to our knowledge tends to
confirm  is on this theory intelligible   We can see why throughout nature
the same general end is gained by an almost infinite diversity of means 
for every peculiarity when once acquired is long inherited  and structures
already modified in many different ways have to be adapted for the same
general purpose   We can  in short  see why nature is prodigal in variety 
though niggard in innovation   But why this should be a law of nature if
each species has been independently created no man can explain 

Many other facts are  as it seems to me  explicable on this theory   How
strange it is that a bird  under the form of a woodpecker  should prey on
insects on the ground  that upland geese  which rarely or never swim  would
possess webbed feet  that a thrush like bird should dive and feed on
sub aquatic insects  and that a petrel should have the habits and structure
fitting it for the life of an auk  and so in endless other cases   But on
the view of each species constantly trying to increase in number  with
natural selection always ready to adapt the slowly varying descendants of
each to any unoccupied or ill occupied place in nature  these facts cease
to be strange  or might even have been anticipated 

We can to a certain extent understand how it is that there is so much
beauty throughout nature  for this may be largely attributed to the agency
of selection   That beauty  according to our sense of it  is not universal 
must be admitted by every one who will look at some venomous snakes  at
some fishes  and at certain hideous bats with a distorted resemblance to
the human face   Sexual selection has given the most brilliant colours 
elegant patterns  and other ornaments to the males  and sometimes to both
sexes of many birds  butterflies and other animals   With birds it has
often rendered the voice of the male musical to the female  as well as to
our ears   Flowers and fruit have been rendered conspicuous by brilliant
colours in contrast with the green foliage  in order that the flowers may
be easily seen  visited and fertilised by insects  and the seeds
disseminated by birds   How it comes that certain colours  sounds and forms
should give pleasure to man and the lower animals  that is  how the sense
of beauty in its simplest form was first acquired  we do not know any more
than how certain odours and flavours were first rendered agreeable 

As natural selection acts by competition  it adapts and improves the
inhabitants of each country only in relation to their co inhabitants  so
that we need feel no surprise at the species of any one country  although
on the ordinary view supposed to have been created and specially adapted
for that country  being beaten and supplanted by the naturalised
productions from another land   Nor ought we to marvel if all the
contrivances in nature be not  as far as we can judge  absolutely perfect 
as in the case even of the human eye  or if some of them be abhorrent to
our ideas of fitness   We need not marvel at the sting of the bee  when
used against the enemy  causing the bee s own death  at drones being
produced in such great numbers for one single act  and being then
slaughtered by their sterile sisters  at the astonishing waste of pollen by
our fir trees  at the instinctive hatred of the queen bee for her own
fertile daughters  at ichneumonidae feeding within the living bodies of
caterpillars  and at other such cases   The wonder  indeed  is  on the
theory of natural selection  that more cases of the want of absolute
perfection have not been detected 

The complex and little known laws governing the production of varieties are
the same  as far as we can judge  with the laws which have governed the
production of distinct species   In both cases physical conditions seem to
have produced some direct and definite effect  but how much we cannot say  
Thus  when varieties enter any new station  they occasionally assume some
of the characters proper to the species of that station   With both
varieties and species  use and disuse seem to have produced a considerable
effect  for it is impossible to resist this conclusion when we look  for
instance  at the logger headed duck  which has wings incapable of flight 
in nearly the same condition as in the domestic duck  or when we look at
the burrowing tucu tucu  which is occasionally blind  and then at certain
moles  which are habitually blind and have their eyes covered with skin  or
when we look at the blind animals inhabiting the dark caves of America and
Europe   With varieties and species  correlated variation seems to have
played an important part  so that when one part has been modified other
parts have been necessarily modified   With both varieties and species 
reversions to long lost characters occasionally occur   How inexplicable on
the theory of creation is the occasional appearance of stripes on the
shoulders and legs of the several species of the horse genus and of their
hybrids   How simply is this fact explained if we believe that these
species are all descended from a striped progenitor  in the same manner as
the several domestic breeds of the pigeon are descended from the blue and
barred rock pigeon 

On the ordinary view of each species having been independently created  why
should specific characters  or those by which the species of the same genus
differ from each other  be more variable than the generic characters in
which they all agree   Why  for instance  should the colour of a flower be
more likely to vary in any one species of a genus  if the other species
possess differently coloured flowers  than if all possessed the same
coloured flowers   If species are only well marked varieties  of which the
characters have become in a high degree permanent  we can understand this
fact  for they have already varied since they branched off from a common
progenitor in certain characters  by which they have come to be
specifically distinct from each other  therefore these same characters
would be more likely again to vary than the generic characters which have
been inherited without change for an immense period   It is inexplicable on
the theory of creation why a part developed in a very unusual manner in one
species alone of a genus  and therefore  as we may naturally infer  of
great importance to that species  should be eminently liable to variation 
but  on our view  this part has undergone  since the several species
branched off from a common progenitor  an unusual amount of variability and
modification  and therefore we might expect the part generally to be still
variable   But a part may be developed in the most unusual manner  like the
wing of a bat  and yet not be more variable than any other structure  if
the part be common to many subordinate forms  that is  if it has been
inherited for a very long period  for in this case it will have been
rendered constant by long continued natural selection 

Glancing at instincts  marvellous as some are  they offer no greater
difficulty than do corporeal structures on the theory of the natural
selection of successive  slight  but profitable modifications   We can thus
understand why nature moves by graduated steps in endowing different
animals of the same class with their several instincts   I have attempted
to show how much light the principle of gradation throws on the admirable
architectural powers of the hive bee   Habit no doubt often comes into play
in modifying instincts  but it certainly is not indispensable  as we see in
the case of neuter insects  which leave no progeny to inherit the effects
of long continued habit   On the view of all the species of the same genus
having descended from a common parent  and having inherited much in common 
we can understand how it is that allied species  when placed under widely
different conditions of life  yet follow nearly the same instincts  why the
thrushes of tropical and temperate South America  for instance  line their
nests with mud like our British species   On the view of instincts having
been slowly acquired through natural selection  we need not marvel at some
instincts being not perfect and liable to mistakes  and at many instincts
causing other animals to suffer 

If species be only well marked and permanent varieties  we can at once see
why their crossed offspring should follow the same complex laws in their
degrees and kinds of resemblance to their parents  in being absorbed into
each other by successive crosses  and in other such points  as do the
crossed offspring of acknowledged varieties   This similarity would be a
strange fact  if species had been independently created and varieties had
been produced through secondary laws 

If we admit that the geological record is imperfect to an extreme degree 
then the facts  which the record does give  strongly support the theory of
descent with modification   New species have come on the stage slowly and
at successive intervals  and the amount of change after equal intervals of
time  is widely different in different groups   The extinction of species
and of whole groups of species  which has played so conspicuous a part in
the history of the organic world  almost inevitably follows from the
principle of natural selection  for old forms are supplanted by new and
improved forms   Neither single species nor groups of species reappear when
the chain of ordinary generation is once broken   The gradual diffusion of
dominant forms  with the slow modification of their descendants  causes the
forms of life  after long intervals of time  to appear as if they had
changed simultaneously throughout the world   The fact of the fossil
remains of each formation being in some degree intermediate in character
between the fossils in the formations above and below  is simply explained
by their intermediate position in the chain of descent   The grand fact
that all extinct beings can be classed with all recent beings  naturally
follows from the living and the extinct being the offspring of common
parents   As species have generally diverged in character during their long
course of descent and modification  we can understand why it is that the
more ancient forms  or early progenitors of each group  so often occupy a
position in some degree intermediate between existing groups   Recent forms
are generally looked upon as being  on the whole  higher in the scale of
organisation than ancient forms  and they must be higher  in so far as the
later and more improved forms have conquered the older and less improved
forms in the struggle for life  they have also generally had their organs
more specialised for different functions   This fact is perfectly
compatible with numerous beings still retaining simple and but little
improved structures  fitted for simple conditions of life  it is likewise
compatible with some forms having retrograded in organisation  by having
become at each stage of descent better fitted for new and degraded habits
of life   Lastly  the wonderful law of the long endurance of allied forms
on the same continent  of marsupials in Australia  of edentata in America 
and other such cases  is intelligible  for within the same country the
existing and the extinct will be closely allied by descent 

Looking to geographical distribution  if we admit that there has been
during the long course of ages much migration from one part of the world to
another  owing to former climatical and geographical changes and to the
many occasional and unknown means of dispersal  then we can understand  on
the theory of descent with modification  most of the great leading facts in
Distribution   We can see why there should be so striking a parallelism in
the distribution of organic beings throughout space  and in their
geological succession throughout time  for in both cases the beings have
been connected by the bond of ordinary generation  and the means of
modification have been the same   We see the full meaning of the wonderful
fact  which has struck every traveller  namely  that on the same continent 
under the most diverse conditions  under heat and cold  on mountain and
lowland  on deserts and marshes  most of the inhabitants within each great
class are plainly related  for they are the descendants of the same
progenitors and early colonists   On this same principle of former
migration  combined in most cases with modification  we can understand  by
the aid of the Glacial period  the identity of some few plants  and the
close alliance of many others  on the most distant mountains  and in the
northern and southern temperate zones  and likewise the close alliance of
some of the inhabitants of the sea in the northern and southern temperate
latitudes  though separated by the whole intertropical ocean   Although two
countries may present physical conditions as closely similar as the same
species ever require  we need feel no surprise at their inhabitants being
widely different  if they have been for a long period completely sundered
from each other  for as the relation of organism to organism is the most
important of all relations  and as the two countries will have received
colonists at various periods and in different proportions  from some other
country or from each other  the course of modification in the two areas
will inevitably have been different 

On this view of migration  with subsequent modification  we see why oceanic
islands are inhabited by only few species  but of these  why many are
peculiar or endemic forms   We clearly see why species belonging to those
groups of animals which cannot cross wide spaces of the ocean  as frogs and
terrestrial mammals  do not inhabit oceanic islands  and why  on the other
hand  new and peculiar species of bats  animals which can traverse the
ocean  are often found on islands far distant from any continent   Such
cases as the presence of peculiar species of bats on oceanic islands and
the absence of all other terrestrial mammals  are facts utterly
inexplicable on the theory of independent acts of creation 

The existence of closely allied representative species in any two areas 
implies  on the theory of descent with modification  that the same parent 
forms formerly inhabited both areas  and we almost invariably find that
wherever many closely allied species inhabit two areas  some identical
species are still common to both   Wherever many closely allied yet
distinct species occur  doubtful forms and varieties belonging to the same
groups likewise occur   It is a rule of high generality that the
inhabitants of each area are related to the inhabitants of the nearest
source whence immigrants might have been derived   We see this in the
striking relation of nearly all the plants and animals of the Galapagos
Archipelago  of Juan Fernandez  and of the other American islands  to the
plants and animals of the neighbouring American mainland  and of those of
the Cape de Verde Archipelago  and of the other African islands to the
African mainland   It must be admitted that these facts receive no
explanation on the theory of creation 

The fact  as we have seen  that all past and present organic beings can be
arranged within a few great classes  in groups subordinate to groups  and
with the extinct groups often falling in between the recent groups  is
intelligible on the theory of natural selection with its contingencies of
extinction and divergence of character   On these same principles we see
how it is that the mutual affinities of the forms within each class are so
complex and circuitous   We see why certain characters are far more
serviceable than others for classification  why adaptive characters  though
of paramount importance to the beings  are of hardly any importance in
classification  why characters derived from rudimentary parts  though of no
service to the beings  are often of high classificatory value  and why
embryological characters are often the most valuable of all   The real
affinities of all organic beings  in contradistinction to their adaptive
resemblances  are due to inheritance or community of descent   The Natural
System is a genealogical arrangement  with the acquired grades of
difference  marked by the terms  varieties  species  genera  families 
etc   and we have to discover the lines of descent by the most permanent
characters  whatever they may be  and of however slight vital importance 

The similar framework of bones in the hand of a man  wing of a bat  fin of
the porpoise  and leg of the horse  the same number of vertebrae forming
the neck of the giraffe and of the elephant  and innumerable other such
facts  at once explain themselves on the theory of descent with slow and
slight successive modifications   The similarity of pattern in the wing and
in the leg of a bat  though used for such different purpose  in the jaws
and legs of a crab  in the petals  stamens  and pistils of a flower  is
likewise  to a large extent  intelligible on the view of the gradual
modification of parts or organs  which were aboriginally alike in an early
progenitor in each of these classes   On the principle of successive
variations not always supervening at an early age  and being inherited at a
corresponding not early period of life  we clearly see why the embryos of
mammals  birds  reptiles  and fishes should be so closely similar  and so
unlike the adult forms   We may cease marvelling at the embryo of an
air breathing mammal or bird having branchial slits and arteries running in
loops  like those of a fish which has to breathe the air dissolved in water
by the aid of well developed branchiae 

Disuse  aided sometimes by natural selection  will often have reduced
organs when rendered useless under changed habits or conditions of life 
and we can understand on this view the meaning of rudimentary organs   But
disuse and selection will generally act on each creature  when it has come
to maturity and has to play its full part in the struggle for existence 
and will thus have little power on an organ during early life  hence the
organ will not be reduced or rendered rudimentary at this early age   The
calf  for instance  has inherited teeth  which never cut through the gums
of the upper jaw  from an early progenitor having well developed teeth  and
we may believe  that the teeth in the mature animal were formerly reduced
by disuse owing to the tongue and palate  or lips  having become
excellently fitted through natural selection to browse without their aid 
whereas in the calf  the teeth have been left unaffected  and on the
principle of inheritance at corresponding ages have been inherited from a
remote period to the present day   On the view of each organism with all
its separate parts having been specially created  how utterly inexplicable
is it that organs bearing the plain stamp of inutility  such as the teeth
in the embryonic calf or the shrivelled wings under the soldered
wing covers of many beetles  should so frequently occur   Nature may be
said to have taken pains to reveal her scheme of modification  by means of
rudimentary organs  of embryological and homologous structures  but we are
too blind to understand her meaning 

I have now recapitulated the facts and considerations which have thoroughly
convinced me that species have been modified  during a long course of
descent   This has been effected chiefly through the natural selection of
numerous successive  slight  favourable variations  aided in an important
manner by the inherited effects of the use and disuse of parts  and in an
unimportant manner  that is  in relation to adaptive structures  whether
past or present  by the direct action of external conditions  and by
variations which seem to us in our ignorance to arise spontaneously   It
appears that I formerly underrated the frequency and value of these latter
forms of variation  as leading to permanent modifications of structure
independently of natural selection   But as my conclusions have lately been
much misrepresented  and it has been stated that I attribute the
modification of species exclusively to natural selection  I may be
permitted to remark that in the first edition of this work  and
subsequently  I placed in a most conspicuous position  namely  at the close
of the Introduction  the following words    I am convinced that natural
selection has been the main but not the exclusive means of modification   
This has been of no avail   Great is the power of steady misrepresentation 
but the history of science shows that fortunately this power does not long
endure 

It can hardly be supposed that a false theory would explain  in so
satisfactory a manner as does the theory of natural selection  the several
large classes of facts above specified   It has recently been objected that
this is an unsafe method of arguing  but it is a method used in judging of
the common events of life  and has often been used by the greatest natural
philosophers   The undulatory theory of light has thus been arrived at  and
the belief in the revolution of the earth on its own axis was until lately
supported by hardly any direct evidence   It is no valid objection that
science as yet throws no light on the far higher problem of the essence or
origin of life   Who can explain what is the essence of the attraction of
gravity   No one now objects to following out the results consequent on
this unknown element of attraction  notwithstanding that Leibnitz formerly
accused Newton of introducing  occult qualities and miracles into
philosophy  

I see no good reasons why the views given in this volume should shock the
religious feelings of any one   It is satisfactory  as showing how
transient such impressions are  to remember that the greatest discovery
ever made by man  namely  the law of the attraction of gravity  was also
attacked by Leibnitz   as subversive of natural  and inferentially of
revealed  religion    A celebrated author and divine has written to me that
 he has gradually learned to see that it is just as noble a conception of
the Deity to believe that He created a few original forms capable of self 
development into other and needful forms  as to believe that He required a
fresh act of creation to supply the voids caused by the action of His
laws  

Why  it may be asked  until recently did nearly all the most eminent living
naturalists and geologists disbelieve in the mutability of species   It
cannot be asserted that organic beings in a state of nature are subject to
no variation  it cannot be proved that the amount of variation in the
course of long ages is a limited quantity  no clear distinction has been 
or can be  drawn between species and well marked varieties   It cannot be
maintained that species when intercrossed are invariably sterile and
varieties invariably fertile  or that sterility is a special endowment and
sign of creation   The belief that species were immutable productions was
almost unavoidable as long as the history of the world was thought to be of
short duration  and now that we have acquired some idea of the lapse of
time  we are too apt to assume  without proof  that the geological record
is so perfect that it would have afforded us plain evidence of the mutation
of species  if they had undergone mutation 

But the chief cause of our natural unwillingness to admit that one species
has given birth to other and distinct species  is that we are always slow
in admitting any great changes of which we do not see the steps   The
difficulty is the same as that felt by so many geologists  when Lyell first
insisted that long lines of inland cliffs had been formed  and great
valleys excavated  by the agencies which we still see at work   The mind
cannot possibly grasp the full meaning of the term of even a million years 
it cannot add up and perceive the full effects of many slight variations 
accumulated during an almost infinite number of generations 

Although I am fully convinced of the truth of the views given in this
volume under the form of an abstract  I by no means expect to convince
experienced naturalists whose minds are stocked with a multitude of facts
all viewed  during a long course of years  from a point of view directly
opposite to mine   It is so easy to hide our ignorance under such
expressions as the  plan of creation    unity of design   etc   and to
think that we give an explanation when we only restate a fact   Any one
whose disposition leads him to attach more weight to unexplained
difficulties than to the explanation of a certain number of facts will
certainly reject the theory   A few naturalists  endowed with much
flexibility of mind  and who have already begun to doubt the immutability
of species  may be influenced by this volume  but I look with confidence to
the future  to young and rising naturalists  who will be able to view both
sides of the question with impartiality   Whoever is led to believe that
species are mutable will do good service by conscientiously expressing his
conviction  for thus only can the load of prejudice by which this subject
is overwhelmed be removed 

Several eminent naturalists have of late published their belief that a
multitude of reputed species in each genus are not real species  but that
other species are real  that is  have been independently created   This
seems to me a strange conclusion to arrive at   They admit that a multitude
of forms  which till lately they themselves thought were special creations 
and which are still thus looked at by the majority of naturalists  and
which consequently have all the external characteristic features of true
species  they admit that these have been produced by variation  but they
refuse to extend the same view to other and slightly different forms  
Nevertheless  they do not pretend that they can define  or even conjecture 
which are the created forms of life  and which are those produced by
secondary laws   They admit variation as a vera causa in one case  they
arbitrarily reject it in another  without assigning any distinction in the
two cases   The day will come when this will be given as a curious
illustration of the blindness of preconceived opinion   These authors seem
no more startled at a miraculous act of creation than at an ordinary birth  
But do they really believe that at innumerable periods in the earth s
history certain elemental atoms have been commanded suddenly to flash into
living tissues   Do they believe that at each supposed act of creation one
individual or many were produced   Were all the infinitely numerous kinds
of animals and plants created as eggs or seed  or as full grown  and in the
case of mammals  were they created bearing the false marks of nourishment
from the mother s womb   Undoubtedly some of these same questions cannot be
answered by those who believe in the appearance or creation of only a few
forms of life or of some one form alone   It has been maintained by several
authors that it is as easy to believe in the creation of a million beings
as of one  but Maupertuis  philosophical axiom  of least action  leads the
mind more willingly to admit the smaller number  and certainly we ought not
to believe that innumerable beings within each great class have been
created with plain  but deceptive  marks of descent from a single parent 

As a record of a former state of things  I have retained in the foregoing
paragraphs  and elsewhere  several sentences which imply that naturalists
believe in the separate creation of each species  and I have been much
censured for having thus expressed myself   But undoubtedly this was the
general belief when the first edition of the present work appeared   I
formerly spoke to very many naturalists on the subject of evolution  and
never once met with any sympathetic agreement   It is probable that some
did then believe in evolution  but they were either silent or expressed
themselves so ambiguously that it was not easy to understand their meaning  
Now  things are wholly changed  and almost every naturalist admits the
great principle of evolution   There are  however  some who still think
that species have suddenly given birth  through quite unexplained means  to
new and totally different forms   But  as I have attempted to show  weighty
evidence can be opposed to the admission of great and abrupt modifications  
Under a scientific point of view  and as leading to further investigation 
but little advantage is gained by believing that new forms are suddenly
developed in an inexplicable manner from old and widely different forms 
over the old belief in the creation of species from the dust of the earth 

It may be asked how far I extend the doctrine of the modification of
species   The question is difficult to answer  because the more distinct
the forms are which we consider  by so much the arguments in favour of
community of descent become fewer in number and less in force   But some
arguments of the greatest weight extend very far   All the members of whole
classes are connected together by a chain of affinities  and all can be
classed on the same principle  in groups subordinate to groups   Fossil
remains sometimes tend to fill up very wide intervals between existing
orders 

Organs in a rudimentary condition plainly show that an early progenitor had
the organ in a fully developed condition  and this in some cases implies an
enormous amount of modification in the descendants   Throughout whole
classes various structures are formed on the same pattern  and at a very
early age the embryos closely resemble each other   Therefore I cannot
doubt that the theory of descent with modification embraces all the members
of the same great class or kingdom   I believe that animals are descended
from at most only four or five progenitors  and plants from an equal or
lesser number 

Analogy would lead me one step further  namely  to the belief that all
animals and plants are descended from some one prototype   But analogy may
be a deceitful guide   Nevertheless all living things have much in common 
in their chemical composition  their cellular structure  their laws of
growth  and their liability to injurious influences   We see this even in
so trifling a fact as that the same poison often similarly affects plants
and animals  or that the poison secreted by the gall fly produces monstrous
growths on the wild rose or oak tree   With all organic beings  excepting
perhaps some of the very lowest  sexual reproduction seems to be
essentially similar   With all  as far as is at present known  the germinal
vesicle is the same  so that all organisms start from a common origin   If
we look even to the two main divisions  namely  to the animal and vegetable
kingdoms  certain low forms are so far intermediate in character that
naturalists have disputed to which kingdom they should be referred   As
Professor Asa Gray has remarked   the spores and other reproductive bodies
of many of the lower algae may claim to have first a characteristically
animal  and then an unequivocally vegetable existence    Therefore  on the
principle of natural selection with divergence of character  it does not
seem incredible that  from some such low and intermediate form  both
animals and plants may have been developed  and  if we admit this  we must
likewise admit that all the organic beings which have ever lived on this
earth may be descended from some one primordial form   But this inference
is chiefly grounded on analogy  and it is immaterial whether or not it be
accepted   No doubt it is possible  as Mr  G H  Lewes has urged  that at
the first commencement of life many different forms were evolved  but if
so  we may conclude that only a very few have left modified descendants  
For  as I have recently remarked in regard to the members of each great
kingdom  such as the Vertebrata  Articulata  etc   we have distinct
evidence in their embryological  homologous  and rudimentary structures 
that within each kingdom all the members are descended from a single
progenitor 

When the views advanced by me in this volume  and by Mr  Wallace or when
analogous views on the origin of species are generally admitted  we can
dimly foresee that there will be a considerable revolution in natural
history   Systematists will be able to pursue their labours as at present 
but they will not be incessantly haunted by the shadowy doubt whether this
or that form be a true species   This  I feel sure and I speak after
experience  will be no slight relief   The endless disputes whether or not
some fifty species of British brambles are good species will cease  
Systematists will have only to decide  not that this will be easy  whether
any form be sufficiently constant and distinct from other forms  to be
capable of definition  and if definable  whether the differences be
sufficiently important to deserve a specific name   This latter point will
become a far more essential consideration than it is at present  for
differences  however slight  between any two forms  if not blended by
intermediate gradations  are looked at by most naturalists as sufficient to
raise both forms to the rank of species 

Hereafter we shall be compelled to acknowledge that the only distinction
between species and well marked varieties is  that the latter are known  or
believed to be connected at the present day by intermediate gradations 
whereas species were formerly thus connected   Hence  without rejecting the
consideration of the present existence of intermediate gradations between
any two forms  we shall be led to weigh more carefully and to value higher
the actual amount of difference between them   It is quite possible that
forms now generally acknowledged to be merely varieties may hereafter be
thought worthy of specific names  and in this case scientific and common
language will come into accordance   In short  we shall have to treat
species in the same manner as those naturalists treat genera  who admit
that genera are merely artificial combinations made for convenience   This
may not be a cheering prospect  but we shall at least be freed from the
vain search for the undiscovered and undiscoverable essence of the term
species 

The other and more general departments of natural history will rise greatly
in interest   The terms used by naturalists  of affinity  relationship 
community of type  paternity  morphology  adaptive characters  rudimentary
and aborted organs  etc   will cease to be metaphorical and will have a
plain signification   When we no longer look at an organic being as a
savage looks at a ship  as something wholly beyond his comprehension  when
we regard every production of nature as one which has had a long history 
when we contemplate every complex structure and instinct as the summing up
of many contrivances  each useful to the possessor  in the same way as any
great mechanical invention is the summing up of the labour  the experience 
the reason  and even the blunders of numerous workmen  when we thus view
each organic being  how far more interesting  I speak from experience  does
the study of natural history become 

A grand and almost untrodden field of inquiry will be opened  on the causes
and laws of variation  on correlation  on the effects of use and disuse  on
the direct action of external conditions  and so forth   The study of
domestic productions will rise immensely in value   A new variety raised by
man will be a far more important and interesting subject for study than one
more species added to the infinitude of already recorded species   Our
classifications will come to be  as far as they can be so made 
genealogies  and will then truly give what may be called the plan of
creation   The rules for classifying will no doubt become simpler when we
have a definite object in view   We possess no pedigree or armorial
bearings  and we have to discover and trace the many diverging lines of
descent in our natural genealogies  by characters of any kind which have
long been inherited   Rudimentary organs will speak infallibly with respect
to the nature of long lost structures   Species and groups of species which
are called aberrant  and which may fancifully be called living fossils 
will aid us in forming a picture of the ancient forms of life   Embryology
will often reveal to us the structure  in some degree obscured  of the
prototypes of each great class 

When we can feel assured that all the individuals of the same species  and
all the closely allied species of most genera  have  within a not very
remote period descended from one parent  and have migrated from some one
birth place  and when we better know the many means of migration  then  by
the light which geology now throws  and will continue to throw  on former
changes of climate and of the level of the land  we shall surely be enabled
to trace in an admirable manner the former migrations of the inhabitants of
the whole world   Even at present  by comparing the differences between the
inhabitants of the sea on the opposite sides of a continent  and the nature
of the various inhabitants of that continent in relation to their apparent
means of immigration  some light can be thrown on ancient geography 

The noble science of geology loses glory from the extreme imperfection of
the record   The crust of the earth  with its embedded remains  must not be
looked at as a well filled museum  but as a poor collection made at hazard
and at rare intervals   The accumulation of each great fossiliferous
formation will be recognised as having depended on an unusual occurrence of
favourable circumstances  and the blank intervals between the successive
stages as having been of vast duration   But we shall be able to gauge with
some security the duration of these intervals by a comparison of the
preceding and succeeding organic forms   We must be cautious in attempting
to correlate as strictly contemporaneous two formations  which do not
include many identical species  by the general succession of the forms of
life   As species are produced and exterminated by slowly acting and still
existing causes  and not by miraculous acts of creation  and as the most
important of all causes of organic change is one which is almost
independent of altered and perhaps suddenly altered physical conditions 
namely  the mutual relation of organism to organism  the improvement of one
organism entailing the improvement or the extermination of others  it
follows  that the amount of organic change in the fossils of consecutive
formations probably serves as a fair measure of the relative  though not
actual lapse of time   A number of species  however  keeping in a body
might remain for a long period unchanged  whilst within the same period 
several of these species  by migrating into new countries and coming into
competition with foreign associates  might become modified  so that we must
not overrate the accuracy of organic change as a measure of time 

In the future I see open fields for far more important researches  
Psychology will be securely based on the foundation already well laid by
Mr  Herbert Spencer  that of the necessary acquirement of each mental power
and capacity by gradation   Much light will be thrown on the origin of man
and his history 

Authors of the highest eminence seem to be fully satisfied with the view
that each species has been independently created   To my mind it accords
better with what we know of the laws impressed on matter by the Creator 
that the production and extinction of the past and present inhabitants of
the world should have been due to secondary causes  like those determining
the birth and death of the individual   When I view all beings not as
special creations  but as the lineal descendants of some few beings which
lived long before the first bed of the Cambrian system was deposited  they
seem to me to become ennobled   Judging from the past  we may safely infer
that not one living species will transmit its unaltered likeness to a
distinct futurity   And of the species now living very few will transmit
progeny of any kind to a far distant futurity  for the manner in which all
organic beings are grouped  shows that the greater number of species in
each genus  and all the species in many genera  have left no descendants 
but have become utterly extinct   We can so far take a prophetic glance
into futurity as to foretell that it will be the common and widely spread
species  belonging to the larger and dominant groups within each class 
which will ultimately prevail and procreate new and dominant species   As
all the living forms of life are the lineal descendants of those which
lived long before the Cambrian epoch  we may feel certain that the ordinary
succession by generation has never once been broken  and that no cataclysm
has desolated the whole world   Hence  we may look with some confidence to
a secure future of great length   And as natural selection works solely by
and for the good of each being  all corporeal and mental endowments will
tend to progress towards perfection 

It is interesting to contemplate a tangled bank  clothed with many plants
of many kinds  with birds singing on the bushes  with various insects
flitting about  and with worms crawling through the damp earth  and to
reflect that these elaborately constructed forms  so different from each
other  and dependent upon each other in so complex a manner  have all been
produced by laws acting around us   These laws  taken in the largest sense 
being Growth with reproduction  Inheritance which is almost implied by
reproduction  Variability from the indirect and direct action of the
conditions of life  and from use and disuse  a Ratio of Increase so high as
to lead to a Struggle for Life  and as a consequence to Natural Selection 
entailing Divergence of Character and the Extinction of less improved
forms   Thus  from the war of nature  from famine and death  the most
exalted object which we are capable of conceiving  namely  the production
of the higher animals  directly follows   There is grandeur in this view of
life  with its several powers  having been originally breathed by the
Creator into a few forms or into one  and that  whilst this planet has gone
circling on according to the fixed law of gravity  from so simple a
beginning endless forms most beautiful and most wonderful have been  and
are being evolved 


GLOSSARY OF THE PRINCIPAL SCIENTIFIC TERMS USED IN THE PRESENT VOLUME 

 I am indebted to the kindness of Mr  W S  Dallas for this Glossary  which
has been given because several readers have complained to me that some of
the terms used were unintelligible to them   Mr  Dallas has endeavoured to
give the explanations of the terms in as popular a form as possible  

ABERRANT   Forms or groups of animals or plants which deviate in important
characters from their nearest allies  so as not to be easily included in
the same group with them  are said to be aberrant 

ABERRATION  in Optics    In the refraction of light by a convex lens the
rays passing through different parts of the lens are brought to a focus at
slightly different distances  this is called SPHERICAL ABERRATION  at the
same time the coloured rays are separated by the prismatic action of the
lens and likewise brought to a focus at different distances  this is
CHROMATIC ABERRATION 

ABNORMAL   Contrary to the general rule 

ABORTED   An organ is said to be aborted  when its development has been
arrested at a very early stage 

ALBINISM   Albinos are animals in which the usual colouring matters
characteristic of the species have not been produced in the skin and its
appendages   Albinism is the state of being an albino 

ALGAE   A class of plants including the ordinary sea weeds and the
filamentous fresh water weeds 

ALTERNATION OF GENERATIONS   This term is applied to a peculiar mode of
reproduction which prevails among many of the lower animals  in which the
egg produces a living form quite different from its parent  but from which
the parent form is reproduced by a process of budding  or by the division
of the substance of the first product of the egg 

AMMONITES   A group of fossil  spiral  chambered shells  allied to the
existing pearly Nautilus  but having the partitions between the chambers
waved in complicated patterns at their junction with the outer wall of the
shell 

ANALOGY   That resemblance of structures which depends upon similarity of
function  as in the wings of insects and birds   Such structures are said
to be ANALOGOUS  and to be ANALOGUES of each other 

ANIMALCULE   A minute animal   generally applied to those visible only by
the microscope 

ANNELIDS   A class of worms in which the surface of the body exhibits a
more or less distinct division into rings or segments  generally provided
with appendages for locomotion and with gills   It includes the ordinary
marine worms  the earth worms  and the leeches 

ANTENNAE   Jointed organs appended to the head in Insects  Crustacea and
Centipedes  and not belonging to the mouth 

ANTHERS   The summits of the stamens of flowers  in which the pollen or
fertilising dust is produced 

APLACENTALIA  APLACENTATA or APLACENTAL MAMMALS   See MAMMALIA 

ARCHETYPAL   Of or belonging to the Archetype  or ideal primitive form upon
which all the beings of a group seem to be organised 

ARTICULATA   A great division of the Animal Kingdom characterised generally
by having the surface of the body divided into rings called segments  a
greater or less number of which are furnished with jointed legs  such as
Insects  Crustaceans and Centipedes  

ASYMMETRICAL   Having the two sides unlike 

ATROPHIED   Arrested in development at a very early stage 

BALANUS   The genus including the common Acorn shells which live in
abundance on the rocks of the sea coast 

BATRACHIANS   A class of animals allied to the Reptiles  but undergoing a
peculiar metamorphosis  in which the young animal is generally aquatic and
breathes by gills    Examples  Frogs  Toads  and Newts  

BOULDERS   Large transported blocks of stone generally embedded in clays or
gravels 

BRACHIOPODA   A class of marine Mollusca  or soft bodied animals  furnished
with a bivalve shell  attached to submarine objects by a stalk which passes
through an aperture in one of the valves  and furnished with fringed arms 
by the action of which food is carried to the mouth 

BRANCHIAE   Gills or organs for respiration in water 

BRANCHIAL   Pertaining to gills or branchiae 

CAMBRIAN SYSTEM   A series of very ancient Palaeozoic rocks  between the
Laurentian and the Silurian   Until recently these were regarded as the
oldest fossiliferous rocks 

CANIDAE   The Dog family  including the Dog  Wolf  Fox  Jackal  etc 

CARAPACE   The shell enveloping the anterior part of the body in
Crustaceans generally  applied also to the hard shelly pieces of the
Cirripedes 

CARBONIFEROUS   This term is applied to the great formation which includes 
among other rocks  the coal measures   It belongs to the oldest  or
Palaeozoic  system of formations 

CAUDAL   Of or belonging to the tail 

CEPHALOPODS   The highest class of the Mollusca  or soft bodied animals 
characterised by having the mouth surrounded by a greater or less number of
fleshy arms or tentacles  which  in most living species  are furnished with
sucking cups    Examples  Cuttle fish  Nautilus  

CETACEA   An order of Mammalia  including the Whales  Dolphins  etc  
having the form of the body fish like  the skin naked  and only the fore
limbs developed 

CHELONIA   An order of Reptiles including the Turtles  Tortoises  etc 

CIRRIPEDES   An order of Crustaceans including the Barnacles and Acorn 
shells   Their young resemble those of many other Crustaceans in form  but
when mature they are always attached to other objects  either directly or
by means of a stalk  and their bodies are enclosed by a calcareous shell
composed of several pieces  two of which can open to give issue to a bunch
of curled  jointed tentacles  which represent the limbs 

COCCUS   The genus of Insects including the Cochineal   In these the male
is a minute  winged fly  and the female generally a motionless  berry like
mass 

COCOON   A case usually of silky material  in which insects are frequently
enveloped during the second or resting stage  pupa  of their existence  
The term  cocoon stage  is here used as equivalent to  pupa stage  

COELOSPERMOUS   A term applied to those fruits of the Umbelliferae which
have the seed hollowed on the inner face 

COLEOPTERA   Beetles  an order of Insects  having a biting mouth and the
first pair of wings more or less horny  forming sheaths for the second
pair  and usually meeting in a straight line down the middle of the back 

COLUMN   A peculiar organ in the flowers of Orchids  in which the stamens 
style and stigma  or the reproductive parts  are united 

COMPOSITAE or COMPOSITOUS PLANTS   Plants in which the inflorescence
consists of numerous small flowers  florets  brought together into a dense
head  the base of which is enclosed by a common envelope    Examples  the
Daisy  Dandelion  etc  

CONFERVAE   The filamentous weeds of fresh water 

CONGLOMERATE   A rock made up of fragments of rock or pebbles  cemented
together by some other material 

COROLLA   The second envelope of a flower usually composed of coloured 
leaf like organs  petals   which may be united by their edges either in the
basal part or throughout 

CORRELATION   The normal coincidence of one phenomenon  character  etc  
with another 

CORYMB   A bunch of flowers in which those springing from the lower part of
the flower stalks are supported on long stalks so as to be nearly on a
level with the upper ones 

COTYLEDONS   The first or seed leaves of plants 

CRUSTACEANS   A class of articulated animals  having the skin of the body
generally more or less hardened by the deposition of calcareous matter 
breathing by means of gills    Examples  Crab  Lobster  Shrimp  etc  

CURCULIO   The old generic term for the Beetles known as Weevils 
characterised by their four jointed feet  and by the head being produced
into a sort of beak  upon the sides of which the antennae are inserted 

CUTANEOUS   Of or belonging to the skin 

DEGRADATION   The wearing down of land by the action of the sea or of
meteoric agencies 

DENUDATION   The wearing away of the surface of the land by water 

DEVONIAN SYSTEM or FORMATION   A series of Palaeozoic rocks  including the
Old Red Sandstone 

DICOTYLEDONS  or DICOTYLEDONOUS PLANTS   A class of plants characterised by
having two seed leaves  by the formation of new wood between the bark and
the old wood  exogenous growth  and by the reticulation of the veins of the
leaves   The parts of the flowers are generally in multiples of five 

DIFFERENTATION   The separation or discrimination of parts or organs which
in simpler forms of life are more or less united 

DIMORPHIC   Having two distinct forms   DIMORPHISM is the condition of the
appearance of the same species under two dissimilar forms 

DIOECIOUS   Having the organs of the sexes upon distinct individuals 

DIORITE   A peculiar form of Greenstone 

DORSAL   Of or belonging to the back 

EDENTATA   A peculiar order of Quadrupeds  characterised by the absence of
at least the middle incisor  front  teeth in both jaws    Examples  the
Sloths and Armadillos  

ELYTRA   The hardened fore wings of Beetles  serving as sheaths for the
membranous hind wings  which constitute the true organs of flight 

EMBRYO   The young animal undergoing development within the egg or womb 

EMBRYOLOGY   The study of the development of the embryo 

ENDEMIC   Peculiar to a given locality 

ENTOMOSTRACA   A division of the class Crustacea  having all the segments
of the body usually distinct  gills attached to the feet or organs of the
mouth  and the feet fringed with fine hairs   They are generally of small
size 

EOCENE   The earliest of the three divisions of the Tertiary epoch of
geologists   Rocks of this age contain a small proportion of shells
identical with species now living 

EPHEMEROUS INSECTS   Insects allied to the May fly 

FAUNA   The totality of the animals naturally inhabiting a certain country
or region  or which have lived during a given geological period 

FELIDAE   The Cat family 

FERAL   Having become wild from a state of cultivation or domestication 

FLORA   The totality of the plants growing naturally in a country  or
during a given geological period 

FLORETS   Flowers imperfectly developed in some respects  and collected
into a dense spike or head  as in the Grasses  the Dandelion  etc 

FOETAL   Of or belonging to the foetus  or embryo in course of development 

FORAMINIFERA   A class of animals of very low organisation and generally of
small size  having a jelly like body  from the surface of which delicate
filaments can be given off and retracted for the prehension of external
objects  and having a calcareous or sandy shell  usually divided into
chambers and perforated with small apertures 

FOSSILIFEROUS   Containing fossils 

FOSSORIAL   Having a faculty of digging   The Fossorial Hymenoptera are a
group of Wasp like Insects  which burrow in sandy soil to make nests for
their young 

FRENUM  pl  FRENA    A small band or fold of skin 

FUNGI  sing  FUNGUS    A class of cellular plants  of which Mushrooms 
Toadstools  and Moulds  are familiar examples 

FURCULA   The forked bone formed by the union of the collar bones in many
birds  such as the common Fowl 

GALLINACEOUS BIRDS   An order of birds of which the common Fowl  Turkey 
and Pheasant  are well known examples 

GALLUS   The genus of birds which includes the common Fowl 

GANGLION   A swelling or knot from which nerves are given off as from a
centre 

GANOID FISHES   Fishes covered with peculiar enamelled bony scales   Most
of them are extinct 

GERMINAL VESICLE   A minute vesicle in the eggs of animals  from which the
development of the embryo proceeds 

GLACIAL PERIOD   A period of great cold and of enormous extension of ice
upon the surface of the earth   It is believed that glacial periods have
occurred repeatedly during the geological history of the earth  but the
term is generally applied to the close of the Tertiary epoch  when nearly
the whole of Europe was subjected to an arctic climate 

GLAND   An organ which secretes or separates some peculiar product from the
blood or sap of animals or plants 

GLOTTIS   The opening of the windpipe into the oesophagus or gullet 

GNEISS   A rock approaching granite in composition  but more or less
laminated  and really produced by the alteration of a sedimentary deposit
after its consolidation 

GRALLATORES   The so called wading birds  storks  cranes  snipes  etc   
which are generally furnished with long legs  bare of feathers above the
heel  and have no membranes between the toes 

GRANITE   A rock consisting essentially of crystals of felspar and mica in
a mass of quartz 

HABITAT   The locality in which a plant or animal naturally lives 

HEMIPTERA   An order or sub order of insects  characterised by the
possession of a jointed beak or rostrum  and by having the fore wings horny
in the basal portion and membranous at the extremity  where they cross each
other   This group includes the various species of bugs 

HERMAPHRODITE   Possessing the organs of both sexes 

HOMOLOGY   That relation between parts which results from their development
from corresponding embryonic parts  either in different animals  as in the
case of the arm of man  the fore leg of a quadruped  and the wing of a
bird  or in the same individual  as in the case of the fore and hind legs
in quadrupeds  and the segments or rings and their appendages of which the
body of a worm  a centipede  etc   is composed   The latter is called
serial homology   The parts which stand in such a relation to each other
are said to be homologous  and one such part or organ is called the
homologue of the other   In different plants the parts of the flower are
homologous  and in general these parts are regarded as homologous with
leaves 

HOMOPTERA   An order or sub order of insects having  like the Hemiptera  a
jointed beak  but in which the fore wings are either wholly membranous or
wholly leathery  The Cicadae  frog hoppers  and Aphides  are well known
examples 

HYBRID   The offspring of the union of two distinct species 

HYMENOPTERA   An order of insects possessing biting jaws and usually four
membranous wings in which there are a few veins   Bees and wasps are
familiar examples of this group 

HYPERTROPHIED   Excessively developed 

ICHNEUMONIDAE   A family of hymenopterous insects  the members of which lay
their eggs in the bodies or eggs of other insects 

IMAGO   The perfect  generally winged  reproductive state of an insect 

INDIGENES   The aboriginal animal or vegetable inhabitants of a country or
region 

INFLORESCENCE   The mode of arrangement of the flowers of plants 

INFUSORIA   A class of microscopic animalcules  so called from their having
originally been observed in infusions of vegetable matters   They consist
of a gelatinous material enclosed in a delicate membrane  the whole or part
of which is furnished with short vibrating hairs  called cilia   by means
of which the animalcules swim through the water or convey the minute
particles of their food to the orifice of the mouth 

INSECTIVOROUS   Feeding on insects 

INVERTEBRATA  or INVERTEBRATE ANIMALS   Those animals which do not possess
a backbone or spinal column 

LACUNAE   Spaces left among the tissues in some of the lower animals and
serving in place of vessels for the circulation of the fluids of the body 

LAMELLATED   Furnished with lamellae or little plates 

LARVA  pl  LARVAE    The first condition of an insect at its issuing from
the egg  when it is usually in the form of a grub  caterpillar  or maggot 

LARYNX   The upper part of the windpipe opening into the gullet 

LAURENTIAN   A group of greatly altered and very ancient rocks  which is
greatly developed along the course of the St  Laurence  whence the name  
It is in these that the earliest known traces of organic bodies have been
found 

LEGUMINOSAE   An order of plants represented by the common peas and beans 
having an irregular flower in which one petal stands up like a wing  and
the stamens and pistil are enclosed in a sheath formed by two other petals  
The fruit is a pod  or legume  

LEMURIDAE   A group of four handed animals  distinct from the monkeys and
approaching the insectivorous quadrupeds in some of their characters and
habits   Its members have the nostrils curved or twisted  and a claw
instead of a nail upon the first finger of the hind hands 

LEPIDOPTERA   An order of insects  characterised by the possession of a
spiral proboscis  and of four large more or less scaly wings   It includes
the well known butterflies and moths 

LITTORAL   Inhabiting the seashore 

LOESS   A marly deposit of recent  Post Tertiary  date  which occupies a
great part of the valley of the Rhine 

MALACOSTRACA   The higher division of the Crustacea  including the ordinary
crabs  lobsters  shrimps  etc   together with the woodlice and
sand hoppers 

MAMMALIA   The highest class of animals  including the ordinary hairy
quadrupeds  the whales and man  and characterised by the production of
living young which are nourished after birth by milk from the teats
 MAMMAE  MAMMARY GLANDS  of the mother   A striking difference in embryonic
development has led to the division of this class into two great groups  in
one of these  when the embryo has attained a certain stage  a vascular
connection  called the PLACENTA  is formed between the embryo and the
mother  in the other this is wanting  and the young are produced in a very
incomplete state   The former  including the greater part of the class  are
called PLACENTAL MAMMALS  the latter  or APLACENTAL MAMMALS  include the
Marsupials and Monotremes  ORNITHORHYNCHUS  

MAMMIFEROUS   Having mammae or teats  see MAMMALIA  

MANDIBLES   in insects  the first or uppermost pair of jaws  which are
generally solid  horny  biting organs   In birds the term is applied to
both jaws with their horny coverings   In quadrupeds the mandible is
properly the lower jaw 

MARSUPIALS   An order of Mammalia in which the young are born in a very
incomplete state of development  and carried by the mother  while sucking 
in a ventral pouch  marsupium   such as the kangaroos  opossums  etc   see
MAMMALIA  

MAXILLAE   in insects  the second or lower pair of jaws  which are composed
of several joints and  furnished with peculiar jointed appendages called
palpi  or feelers 

MELANISM   The opposite of albinism  an undue development of colouring
material in the skin and its appendages 

METAMORPHIC ROCKS   Sedimentary rocks which have undergone alteration 
generally by the action of heat  subsequently to their deposition and
consolidation 

MOLLUSCA   One of the great divisions of the animal kingdom  including
those animals which have a soft body  usually furnished with a shell  and
in which the nervous ganglia  or centres  present no definite general
arrangement   They are generally known under the denomination of
 shellfish   the cuttle fish  and the common snails  whelks  oysters 
mussels  and cockles  may serve as examples of them 

MONOCOTYLEDONS  or MONOCOTYLEDONOUS PLANTS   Plants in which the seed sends
up only a single seed leaf  or cotyledon   characterised by the absence of
consecutive layers of wood in the stem  endogenous growth   by the veins of
the leaves being generally straight  and by the parts of the flowers being
generally in multiples of three    Examples  grasses  lilies  orchids 
palms  etc  

MORAINES   The accumulations of fragments of rock brought down by glaciers 

MORPHOLOGY   The law of form or structure independent of function 

MYSIS STAGE   A stage in the development of certain crustaceans  prawns  
in which they closely resemble the adults of a genus  Mysis  belonging to a
slightly lower group 

NASCENT   Commencing development 

NATATORY   Adapted for the purpose of swimming 

NAUPLIUS FORM   The earliest stage in the development of many Crustacea 
especially belonging to the lower groups   In this stage the animal has a
short body  with indistinct indications of a division into segments  and
three pairs of fringed limbs   This form of the common fresh water CYCLOPS
was described as a distinct genus under the name of NAUPLIUS 

NEURATION   The arrangement of the veins or nervures in the wings of
insects 

NEUTERS   Imperfectly developed females of certain social insects  such as
ants and bees   which perform all the labours of the community   Hence 
they are also called WORKERS 

NICTITATING MEMBRANE   A semi transparent membrane  which can be drawn
across the eye in birds and reptiles  either to moderate the effects of a
strong light or to sweep particles of dust  etc   from the surface of the
eye 

OCELLI   The simple eyes or stemmata of insects  usually situated on the
crown of the head between the great compound eyes 

OESOPHAGUS   The gullet 

OOLITIC   A great series of secondary rocks  so called from the texture of
some of its members  which appear to be made up of a mass of small EGG LIKE
calcareous bodies 

OPERCULUM   A calcareous plate employed by many Molluscae to close the
aperture of their shell   The OPERCULAR VALVES of Cirripedes are those
which close the aperture of the shell 

ORBIT   The bony cavity for the reception of the eye 

ORGANISM   An organised being  whether plant or animal 

ORTHOSPERMOUS   A term applied to those fruits of the Umbelliferae which
have the seed straight 

OSCULANT   Forms or groups apparently intermediate between and connecting
other groups are said to be osculant 

OVA   Eggs 

OVARIUM or OVARY  in plants    The lower part of the pistil or female organ
of the flower  containing the ovules or incipient seeds  by growth after
the other organs of the flower have fallen  it usually becomes converted
into the fruit 

OVIGEROUS   Egg bearing 

OVULES  of plants    The seeds in the earliest condition 

PACHYDERMS   A group of Mammalia  so called from their thick skins  and
including the elephant  rhinoceros  hippopotamus  etc 

PALAEOZOIC   The oldest system of fossiliferous rocks 

PALPI   Jointed appendages to some of the organs of the mouth in insects
and Crustacea 

PAPILIONACEAE   An order of plants  see LEGUMINOSAE   The flowers of these
plants are called PAPILIONACEOUS  or butterfly like  from the fancied
resemblance of the expanded superior petals to the wings of a butterfly 

PARASITE   An animal or plant living upon or in  and at the expense of 
another organism 

PARTHENOGENESIS   The production of living organisms from unimpregnated
eggs or seeds 

PEDUNCULATED   Supported upon a stem or stalk   The pedunculated oak has
its acorns borne upon a footstool 

PELORIA or PELORISM   The appearance of regularity of structure in the
flowers of plants which normally bear irregular flowers 

PELVIS   The bony arch to which the hind limbs of vertebrate animals are
articulated 

PETALS   The leaves of the corolla  or second circle of organs in a flower  
They are usually of delicate texture and brightly coloured 

PHYLLODINEOUS   Having flattened  leaf like twigs or leafstalks instead of
true leaves 

PIGMENT   The colouring material produced generally in the superficial
parts of animals   The cells secreting it are called PIGMENT CELLS 

PINNATE   Bearing leaflets on each side of a central stalk 

PISTILS   The female organs of a flower  which occupy a position in the
centre of the other floral organs   The pistil is generally divisible into
the ovary or germen  the style and the stigma 

PLACENTALIA  PLACENTATA   or PLACENTAL MAMMALS  See MAMMALIA 

PLANTIGRADES   Quadrupeds which walk upon the whole sole of the foot  like
the bears 

PLASTIC   Readily capable of change 

PLEISTOCENE PERIOD   The latest portion of the Tertiary epoch 

PLUMULE  in plants    The minute bud between the seed leaves of
newly germinated plants 

PLUTONIC ROCKS   Rocks supposed to have been produced by igneous action in
the depths of the earth 

POLLEN   The male element in flowering plants  usually a fine dust produced
by the anthers  which  by contact with the stigma effects the fecundation
of the seeds   This impregnation is brought about by means of tubes
 POLLEN TUBES  which issue from the pollen grains adhering to the stigma 
and penetrate through the tissues until they reach the ovary 

POLYANDROUS  flowers    Flowers having many stamens 

POLYGAMOUS PLANTS   Plants in which some flowers are unisexual and others
hermaphrodite   The unisexual  male and female  flowers  may be on the same
or on different plants 

POLYMORPHIC   Presenting many forms 

POLYZOARY   The common structure formed by the cells of the Polyzoa  such
as the well known seamats 

PREHENSILE   Capable of grasping 

PREPOTENT   Having a superiority of power 

PRIMARIES   The feathers forming the tip of the wing of a bird  and
inserted upon that part which represents the hand of man 

PROCESSES   Projecting portions of bones  usually for the attachment of
muscles  ligaments  etc 

PROPOLIS   A resinous material collected by the hivebees from the opening
buds of various trees 

PROTEAN   Exceedingly variable 

PROTOZOA   The lowest great division of the animal kingdom   These animals
are composed of a gelatinous material  and show scarcely any trace of
distinct organs   The Infusoria  Foraminifera  and sponges  with some other
forms  belong to this division 

PUPA  pl  PUPAE    The second stage in the development of an insect  from
which it emerges in the perfect  winged  reproductive form   In most
insects the PUPAL STAGE is passed in perfect repose   The CHRYSALIS is the
pupal state of butterflies 

RADICLE   The minute root of an embryo plant 

RAMUS   One half of the lower jaw in the Mammalia   The portion which rises
to articulate with the skull is called the ASCENDING RAMUS 

RANGE   The extent of country over which a plant or animal is naturally
spread   RANGE IN TIME expresses the distribution of a species or group
through the fossiliferous beds of the earth s crust 

RETINA   The delicate inner coat of the eye  formed by nervous filaments
spreading from the optic nerve  and serving for the perception of the
impressions produced by light 

RETROGRESSION   Backward development   When an animal  as it approaches
maturity  becomes less perfectly organised than might be expected from its
early stages and known relationships  it is said to undergo a RETROGRADE
DEVELOPMENT or METAMORPHOSIS 

RHIZOPODS   A class of lowly organised animals  Protozoa   having a
gelatinous body  the surface of which can be protruded in the form of
root like processes or filaments  which serve for locomotion and the
prehension of food   The most important order is that of the Foraminifera 

RODENTS   The gnawing Mammalia  such as the rats  rabbits  and squirrels  
They are especially characterised by the possession of a single pair of
chisel like cutting teeth in each jaw  between which and the grinding teeth
there is a great gap 

RUBUS   The bramble genus 

RUDIMENTARY   Very imperfectly developed 

RUMINANTS   The group of quadrupeds which ruminate or chew the cud  such as
oxen  sheep  and deer   They have divided hoofs  and are destitute of front
teeth in the upper jaw 

SACRAL   Belonging to the sacrum  or the bone composed usually of two or
more united vertebrae to which the sides of the pelvis in vertebrate
animals are attached 

SARCODE   The gelatinous material of which the bodies of the lowest animals
 Protozoa  are composed 

SCUTELLAE   The horny plates with which the feet of birds are generally
more or less covered  especially in front 

SEDIMENTARY FORMATIONS   Rocks deposited as sediments from water 

SEGMENTS   The transverse rings of which the body of an articulate animal
or annelid is composed 

SEPALS   The leaves or segments of the calyx  or outermost envelope of an
ordinary flower   They are usually green  but sometimes brightly coloured 

SERRATURES   Teeth like those of a saw 

SESSILE   Not supported on a stem or footstalk 

SILURIAN SYSTEM   A very ancient system of fossiliferous rocks belonging to
the earlier part of the Palaeozoic series 

SPECIALISATION   The setting apart of a particular organ for the
performance of a particular function 

SPINAL CORD   The central portion of the nervous system in the Vertebrata 
which descends from the brain through the arches of the vertebrae  and
gives off nearly all the nerves to the various organs of the body 

STAMENS   The male organs of flowering plants  standing in a circle within
the petals   They usually consist of a filament and an anther  the anther
being the essential part in which the pollen  or fecundating dust  is
formed 

STERNUM   The breast bone 

STIGMA   The apical portion of the pistil in flowering plants 

STIPULES   Small leafy organs placed at the base of the footstalks of the
leaves in many plants 

STYLE   The middle portion of the perfect pistil  which rises like a column
from the ovary and supports the stigma at its summit 

SUBCUTANEOUS   Situated beneath the skin 

SUCTORIAL   Adapted for sucking 

SUTURES  in the skull    The lines of junction of the bones of which the
skull is composed 

TARSUS  pl  TARSI    The jointed feet of articulate animals  such as
insects 

TELEOSTEAN FISHES   Fishes of the kind familiar to us in the present day 
having the skeleton usually completely ossified and the scales horny 

TENTACULA or TENTACLES   Delicate fleshy organs of prehension or touch
possessed by many of the lower animals 

TERTIARY   The latest geological epoch  immediately preceding the
establishment of the present order of things 

TRACHEA   The windpipe or passage for the admission of air to the lungs 

TRIDACTYLE   Three fingered  or composed of three movable parts attached to
a common base 

TRILOBITES   A peculiar group of extinct crustaceans  somewhat resembling
the woodlice in external form  and  like some of them  capable of rolling
themselves up into a ball   Their remains are found only in the Palaeozoic
rocks  and most abundantly in those of Silurian age 

TRIMORPHIC   Presenting three distinct forms 

UMBELLIFERAE   An order of plants in which the flowers  which contain five
stamens and a pistil with two styles  are supported upon footstalks which
spring from the top of the flower stem and spread out like the wires of an
umbrella  so as to bring all the flowers in the same head  UMBEL  nearly to
the same level    Examples  parsley and carrot  

UNGULATA   Hoofed quadrupeds 

UNICELLULAR   Consisting of a single cell 

VASCULAR   Containing blood vessels 

VERMIFORM   Like a worm 

VERTEBRATA or VERTEBRATE ANIMALS   The highest division of the animal
kingdom  so called from the presence in most cases of a backbone composed
of numerous joints or VERTEBRAE  which constitutes the centre of the
skeleton and at the same time supports and protects the central parts of
the nervous system 

WHORLS   The circles or spiral lines in which the parts of plants are
arranged upon the axis of growth 

WORKERS   See neuters 

ZOEA STAGE   The earliest stage in the development of many of the higher
Crustacea  so called from the name of ZOEA applied to these young animals
when they were supposed to constitute a peculiar genus 

ZOOIDS   In many of the lower animals  such as the Corals  Medusae  etc  
reproduction takes place in two ways  namely  by means of eggs and by a
process of budding with or without separation from the parent of the
product of the latter  which is often very different from that of the egg  
The individuality of the species is represented by the whole of the form
produced between two sexual reproductions  and these forms  which are
apparently individual animals  have been called ZOOIDE 


INDEX 

Aberrant groups

Abyssinia  plants of

Acclimatisation

Adoxa

Affinities of extinct species
  of organic beings

Agassiz on Amblyopsis
  on groups of species suddenly appearing
  on prophetic forms
  on embryological succession
  on the Glacial period
  on embryological characters
  on the latest tertiary forms
  on parallelism of embryological development and geological succession
  Alex   on pedicellariae

Algae of New Zealand

Alligators  males  fighting

Alternate generations

Amblyopsis  blind fish

America  North  productions allied to those of Europe
  boulders and glaciers of
  South  no modern formations on west coast

Ammonites  sudden extinction of

Anagallis  sterility of

Analogy of variations

Andaman Islands inhabited by a toad

Ancylus

Animals  not domesticated from being variable
  domestic  descended from several stocks
  acclimatisation of

Animals of Australia
  with thicker fur in cold climates
  blind  in caves
  extinct  of Australia

Anomma

Antarctic islands  ancient flora of

Antechinus

Ants attending aphides
  slave making instinct
  neuters  structure of

Apes  not having acquired intellectual powers

Aphides attended by ants

Aphis  development of

Apteryx

Arab horses

Aralo Caspian Sea

Archeopteryx

Archiac  M  de  on the succession of species

Artichoke  Jerusalem

Ascension  plants of

Asclepias  pollen of

Asparagus

Aspicarpa

Asses  striped
  improved by selection

Ateuchus

Aucapitaine  on land shells

Audubon  on habits of frigate bird
  on variation in birds  nests
  on heron eating seeds

Australia  animals of
  dogs of
  extinct animals of
  European plants in
  glaciers of

Azara  on flies destroying cattle

Azores  flora of

Babington  Mr   on British plants

Baer  Von  standard of Highness
  comparison of bee and fish
  embryonic similarity of the Vertebrata

Baker  Sir S   on the giraffe

Balancement of growth

Baleen

Barberry  flowers of

Barrande  M   on Silurian colonies
  on the succession of species
  on parallelism of palaeozoic formations
  on affinities of ancient species

Barriers  importance of

Bates  Mr   on mimetic butterflies

Batrachians on islands

Bats  how structure acquired
  distribution of

Bear  catching water insects

Beauty  how acquired

Bee  sting of
  queen  killing rivals
  Australian  extermination of

Bees  fertilizing flowers
  hive  not sucking the red clover
  hive  cell making instinct
  Ligurian
  variation in habits 

Bees  parasitic
  humble  cells of

Beetles  wingless  in Madeira
  with deficient tarsi

Bentham  Mr   on British plants
  on classification

Berkeley  Mr   on seeds in salt water

Bermuda  birds of

Birds acquiring fear
  beauty of
  annually cross the Atlantic
  colour of  on continents
  footsteps  and remains of  in secondary rocks
  fossil  in caves of Brazil
  of Madeira  Bermuda  and Galapagos
  song of males
  transporting seeds
  waders
  wingless

Bizcacha  affinities of

Bladder for swimming  in fish

Blindness of cave animals

Blyth  Mr   on distinctness of Indian cattle
  on striped Hemionus
  on crossed geese

Borrow  Mr   on the Spanish pointer

Bory St  Vincent  on Batrachians

Bosquet  M   on fossil Chthamalus

Boulders  erratic  on the Azores

Branchiae
  of crustaceans

Braun  Prof   on the seeds of Fumariaceae

Brent  Mr   on house tumblers

Britain  mammals of

Broca  Prof   on Natural Selection

Bronn  Prof   on duration of specific forms
  various objections by

Brown  Robert  on classification

Brown Sequard  on inherited mutilations

Busk  Mr   on the Polyzoa

Butterflies  mimetic

Buzareingues  on sterility of varieties

Cabbage  varieties of  crossed

Calceolaria

Canary birds  sterility of hybrids

Cape de Verde Islands  productions of
  plants of  on mountains

Cape of Good Hope  plants of

Carpenter  Dr   on foraminifera

Carthemus

Catasetum

Cats  with blue eyes  deaf
  variation in habits of
  curling tail when going to spring

Cattle destroying fir trees
  destroyed by flies in Paraguay
  breeds of  locally extinct
  fertility of Indian and European breeds
  Indian

Cave  inhabitants of  blind

Cecidomyia

Celts  proving antiquity of man

Centres of creation

Cephalopodae  structures of eyes
  development of

Cercopithecus  tail of

Ceroxylus laceratus

Cervulus

Cetacea  teeth and hair
  development of the whalebone

Cetaceans

Ceylon  plants of

Chalk formation

Characters  divergence of
  sexual  variable
  adaptive or analogical

Charlock

Checks to increase
  mutual

Chelae of Crustaceans

Chickens  instinctive tameness of

Chironomus  its asexual reproduction

Chthamalinae

Chthamalus  cretacean species of

Circumstances favourable to selection of domestic products
  to natural selection

Cirripedes capable of crossing
  carapace aborted
  their ovigerous frena
  fossil
  larvae of

Claparede  Prof   on the hair claspers of the Acaridae

Clarke  Rev  W B   on old glaciers in Australia

Classification

Clift  Mr   on the succession of types

Climate  effects of  in checking increase of beings
  adaptation of  to organisms

Climbing plants
  development of

Clover visited by bees

Cobites  intestine of

Cockroach

Collections  palaeontological  poor

Colour  influenced by climate
  in relation to attacks by flies

Columba livia  parent of domestic pigeons

Colymbetes

Compensation of growth

Compositae  flowers and seeds of
  outer and inner florets of
  male flowers of

Conclusion  general

Conditions  slight changes in  favourable to fertility

Convergence of genera

Coot

Cope  Prof   on the acceleration or retardation of the period of
reproduction

Coral islands  seeds drifted to
  reefs  indicating movements of earth

Corn crake

Correlated variation in domestic productions

Coryanthes

Creation  single centres of

Crinum

Croll  Mr   on subaerial denudation
  on the age of our oldest formations
  on alternate Glacial periods in the North and South

Crosses  reciprocal

Crossing of domestic animals  importance in altering breeds
  advantages of
  unfavourable to selection

Cruger  Dr   on Coryanthes

Crustacea of New Zealand

Crustacean  blind
air breathers

Crustaceans  their chelae

Cryptocerus

Ctenomys  blind

Cuckoo  instinct of

Cunningham  Mr   on the flight of the logger headed duck

Currants  grafts of

Currents of sea  rate of

Cuvier on conditions of existence
  on fossil monkeys

Cuvier  Fred   on instinct

Cyclostoma  resisting salt water

Dana  Prof   on blind cave animals
  on relations of crustaceans of Japan
  on crustaceans of New Zealand

Dawson  Dr   on eozoon

De Candolle  Aug  Pyr   on struggle for existence
  on umbelliferae
  on general affinities

De Candolle  Alph   on the variability of oaks
  on low plants  widely dispersed
  on widely ranging plants being variable
  on naturalisation
  on winged seeds
  on Alpine species suddenly becoming rare
  on distribution of plants with large seeds
  on vegetation of Australia
  on fresh water plants
  on insular plants

Degradation of rocks

Denudation  rate of
  of oldest rocks
  of granite areas

Development of ancient forms

Devonian system

Dianthus  fertility of crosses

Dimorphism in plants

Dirt on feet of birds

Dispersal  means of
  during Glacial period

Distribution  geographical
  means of

Disuse  effect of  under nature 

Diversification of means for same general purpose

Division  physiological  of labour

Divergence of character

Dog  resemblance of jaw to that of the Thylacinus

Dogs  hairless  with imperfect teeth
  descended from several wild stocks
  domestic instincts of
  inherited civilisation of
  fertility of breeds together
  of crosses
  proportions of body in different breeds  when young

Domestication  variation under

Double flowers

Downing  Mr   on fruit trees in America

Dragon flies  intestines of

Drift timber

Driver ant

Drones killed by other bees

Duck  domestic  wings of  reduced
  beak of
  logger headed

Duckweed

Dugong  affinities of

Dung beetles with deficient tarsi

Dyticus

Earl  Mr   W   on the Malay Archipelago

Ears  drooping  in domestic animals
  rudimentary

Earth  seeds in roots of trees
  charged with seeds

Echinodermata  their pedicellariae

Eciton

Economy of organisation

Edentata  teeth and hair
  fossil species of

Edwards  Milne  on physiological division of labour
  on gradations of structure

Edwards  on embryological characters

Eggs  young birds escaping from

Egypt  productions of  not modified

Electric organs

Elephant  rate of increase
  of Glacial period

Embryology

Eozoon Canadense

Epilipsy inherited

Existence  struggle for
  condition of

Extinction  as bearing on natural selection
  of domestic varieties

Eye  structure of
  correction for aberration

Eyes  reduced  in moles

Fabre  M   on hymenoptera fighting
  on parasitic sphex
  on Sitaris

Falconer  Dr   on naturalisation of plants in India
  on elephants and mastodons
  and Cautley on mammals of sub Himalayan beds

Falkland Islands  wolf of

Faults

Faunas  marine

Fear  instinctive  in birds

Feet of birds  young molluscs adhering to

Fertilisation variously effected

Fertility of hybrids
  from slight changes in conditions
  of crossed varieties

Fir trees destroyed by cattle
  pollen of

Fish  flying
  teleostean  sudden appearance of
  eating seeds
  fresh water  distribution of

Fishes  ganoid  now confined to fresh water
  ganoid  living in fresh water
  electric organs of
  of southern hemisphere

Flight  powers of  how acquired

Flint tools  proving antiquity of man

Flower  Prof   on the larynx
  on Halitherium
  on the resemblance between the jaws of the dog and Thylacinus
  on the homology of the feet of certain marsupials

Flowers  structure of
  in relation to crossing
  of composite and umbelliferae
  beauty of
  double

Flysch formation  destitute of organic remains

Forbes  Mr  D   on glacial action in the Andes

Forbes  E   on colours of shells
  on abrupt range of shells in depth
  on poorness of palaeontological collections
  on continuous succession of genera
  on continental extensions
  on distribution during Glacial period
  on parallelism in time and space

Forests  changes in  in America

Formation  Devonian
  Cambrian
  intermittent
  thickness of  in Britain

Formica
  rufescens
  sanguinea
  flava  neuter of

Forms  lowly organised  long enduring

Frena  ovigerous  of cirripedes

Fresh water productions  dispersal of

Fries on species in large genera being closely allied to other species

Frigate bird

Frogs on islands

Fruit trees  gradual improvement of
  in United States
  varieties of  acclimatised in United States

Fuci  crossed

Fur  thicker in cold climates

Furze

Galapagos Archipelago  birds of
  productions of

Galaxias  its wide range

Galeopithecus

Game  increase of  checked by vermin

Gartner on sterility of hybrids
  on reciprocal crosses
  on crossed maize and verbascum
  on comparison of hybrids and mongrels

Gaudry  Prof   on intermediate genera of fossil mammals in Attica

Geese  fertility when crossed
  upland

Geikie  Mr   on subaerial denudation

Genealogy  important in classification

Generations  alternate

Geoffroy St  Hilaire  on balancement
  on homologous organs

Geoffroy St  Hilaire  Isidore  on variability of repeated parts
  on correlation  in monstrosities
  on correlation
  on variable parts being often monstrous

Geographical distribution

Geography  ancient

Geology  future progress of
  imperfection of the record

Gervais  Prof   on Typotherium

Giraffe  tail of
  structure of

Glacial period
  affecting the North and South

Glands  mammary

Gmelin  on distribution

Godwin Austin  Mr   on the Malay Archipelago

Goethe  on compensation of growth

Gomphia

Gooseberry  grafts of

Gould  Dr  Aug  A   on land shells

Gould  Mr   on colours of birds
  on instincts of cuckoo
  on distribution of genera of birds

Gourds  crossed

Graba  on the Uria lacrymans

Grafting  capacity of

Granite  areas of denuded

Grasses  varieties of

Gray  Dr  Asa  on the variability of oaks
  on man not causing variability
  on sexes of the holly
  on trees of the United States
  on naturalised plants in the United States
  on aestivation
  on rarity of intermediate varieties
  on Alpine plants

Gray  Dr  J E   on striped mule

Grebe

Grimm  on asexual reproduction

Groups  aberrant

Grouse  colours of
  red  a doubtful species

Growth  compensation of

Gunther  Dr   on flat fish
  on prehensile tails
  on the fishes of Panama
  on the range of fresh water fishes
  on the limbs of Lepidosiren

Haast  Dr   on glaciers of New Zealand

Habit  effect of  under domestication
  effect of  under nature
  diversified  of same species

Hackel  Prof   on classification and the lines of descent

Hair and teeth  correlated

Halitherium

Harcourt  Mr  E V   on the birds of Madeira

Hartung  M   on boulders in the Azores

Hazel nuts

Hearne  on habits of bears

Heath  changes in vegetation

Hector  Dr   on glaciers of New Zealand

Heer  Oswald  on ancient cultivated plants
  on plants of Madeira

Helianthemum

Helix pomatia  resisting salt water

Helmholtz  M   on the imperfection of the human eye

Helosciadium

Hemionus  striped

Hensen  Dr   on the eyes of Cephalopods

Herbert  W   on struggle for existence
  on sterility of hybrids

Hermaphrodites crossing

Heron eating seed

Heron  Sir R   on peacocks

Heusinger  on white animals poisoned by certain plants

Hewitt  Mr   on sterility of first crosses

Hildebrand  Prof   on the self sterility of Corydalis

Hilgendorf  on intermediate varieties

Himalaya  glaciers of
  plants of

Hippeastrum

Hippocampus

Hofmeister  Prof   on the movements of plants

Holly trees  sexes of

Hooker  Dr   on trees of New Zealand
  on acclimatisation of Himalayan trees
  on flowers of umbelliferae
  on the position of ovules
  on glaciers of Himalaya
  on algae of New Zealand
  on vegetation at the base of the Himalaya
  on plants of Tierra del Fuego
  on Australian plants
  on relations of flora of America
  on flora of the Antarctic lands
  on the plants of the Galapagos
  on glaciers of the Lebanon
  on man not causing variability
  on plants of mountains of Fernando Po

Hooks on palms
  on seeds  on islands

Hopkins  Mr   on denudation

Hornbill  remarkable instinct of

Horns  rudimentary

Horse  fossil in La Plata
  proportions of  when young

Horses destroyed by flies in Paraguay
  striped

Horticulturists  selection applied by

Huber on cells of bees

Huber  P   on reason blended with instinct
  on habitual nature of instincts
  on slave making ants
  on Melipona domestica

Hudson  Mr   on the Ground woodpecker of La Plata
  on the Molothrus

Humble bees  cells of

Hunter  J   on secondary sexual characters

Hutton  Captain  on crossed geese

Huxley  Prof   on structure of hermaphrodites
  on the affinities of the Sirenia
  on forms connecting birds and reptiles
  on homologous organs
  on the development of aphis

Hybrids and mongrels compared

Hybridism

Hydra  structure of

Hymenoptera  fighting

Hymenopterous insect  diving

Hyoseris

Ibla

Icebergs transporting seeds

Increase  rate of

Individuals  numbers favourable to selection
  many  whether simultaneously created

Inheritance  laws of
  at corresponding ages

Insects  colour of  fitted for their stations
  sea side  colours of
  blind  in caves
  luminous
  their resemblance to certain objects
  neuter

Instinct  not varying simultaneously with structure

Instincts  domestic

Intercrossing  advantages of

Islands  oceanic

Isolation favourable to selection

Japan  productions of

Java  plants of

Jones  Mr  J M   on the birds of Bermuda

Jordain  M   on the eye spots of star fishes

Jukes  Prof   on subaerial denudation

Jussieu on classification

Kentucky  caves of

Kerguelen land  flora of

Kidney bean  acclimatisation of

Kidneys of birds

Kirby  on tarsi deficient in beetles

Knight  Andrew  on cause of variation

Kolreuter  on intercrossing
  on the barberry
  on sterility of hybrids
  on reciprocal crosses
  on crossed varieties of nicotiana
  on crossing male and hermaphrodite flowers

Lamarck  on adaptive characters

Lancelet  eyes of

Landois  on the development of the wings of insects

Land shells  distribution of
  of Madeira  naturalised
  resisting salt water

Languages  classification of

Lankester  Mr  E  Ray  on longevity
  on homologies

Lapse  great  of time

Larvae

Laurel  nectar secreted by the leaves

Laurentian formation

Laws of variation

Leech  varieties of

Leguminosae  nectar secreted by glands

Leibnitz  attack on Newton

Lepidosiren  limbs in a nascent condition

Lewes  Mr  G H   on species not having changed in Egypt
  on the Salamandra atra
  on many forms of life having been at first evolved

Life  struggle for

Lingula  Silurian

Linnaeus  aphorism of

Lion  mane of
  young of  striped

Lobelia fulgens

Lobelia  sterility of crosses

Lockwood  Mr   on the ova of the Hippocampus

Locusts transporting seeds

Logan  Sir W   on Laurentian formation

Lowe  Rev  R T   on locusts visiting Madeira

Lowness  of structure connected with variability
  related to wide distribution

Lubbock  Sir J   on the nerves of coccus
  on secondary sexual characters
  on a diving hymenopterous insect
  on affinities
  on metamorphoses

Lucas  Dr  P   on inheritance
  on resemblance of child to parent

Lund and Clausen  on fossils of Brazil

Lyell  Sir C   on the struggle for existence
  on modern changes of the earth
  on terrestrial animals not having been developed on islands
  on a carboniferous land shell
  on strata beneath Silurian system
  on the imperfection of the geological record
  on the appearance of species
  on Barrande s colonies
  on tertiary formations of Europe and North America
  on parallelism of tertiary formations
  on transport of seeds by icebergs
  on great alternations of climate
  on the distribution of fresh water shells
  on land shells of Madeira

Lyell and Dawson  on fossilized trees in Nova Scotia

Lythrum salicaria  trimorphic

Macleay  on analogical characters

Macrauchenia

McDonnell  Dr   on electric organs

Madeira  plants of
  beetles of  wingless
  fossil land shells of
  birds of

Magpie tame in Norway

Males  fighting

Maize  crossed

Malay Archipelago  compared with Europe
  mammals of

Malm  on flat fish

Malpighiaceae  small imperfect flowers of

Mammae  their development
  rudimentary

Mammals  fossil  in secondary formation
  insular

Man  origin of

Manatee  rudimentary nails of

Marsupials  fossil species of

Marsupials of Australia  structure of their feet

Martens  M   experiment on seeds

Martin  Mr  W C   on striped mules

Masters  Dr   on Saponaria

Matteucci  on the electric organs of rays

Matthiola  reciprocal crosses of

Maurandia

Means of dispersal

Melipona domestica

Merrill  Dr   on the American cuckoo

Metamorphism of oldest rocks

Mice destroying bees
  acclimatisation of
  tails of

Miller  Prof   on the cells of bees

Mirabilis  crosses of

Missel thrush

Mistletoe  complex relations of

Mivart  Mr   on the relation of hair and teeth
  on the eyes of cephalopods
  various objections to Natural Selection
  on abrupt modifications
  on the resemblance of the mouse and antechinus

Mocking thrush of the Galapagos

Modification of species  not abrupt

Moles  blind

Molothrus  habits of

Mongrels  fertility and sterility of
  and hybrids compared

Monkeys  fossil

Monachanthus

Mons  Van  on the origin of fruit trees

Monstrosities

Moquin Tandon  on sea side plants

Morphology

Morren  on the leaves of Oxalis

Moths  hybrid

Mozart  musical powers of

Mud  seeds in

Mules  striped

Muller  Adolph  on the instincts of the cuckoo

Muller  Dr  Ferdinand  on Alpine Australian plants

Muller  Fritz  on dimorphic crustaceans
  on the lancelet
  on air breathing crustaceans
  on the self sterility of orchids
  on embryology in relation to classification
  on the metamorphoses of crustaceans
  on terrestrial and fresh water organisms not undergoing any metamorphosis
  on climbing plants

Multiplication of species not indefinite

Murchison  Sir  R   on the formations of Russia
  on azoic formations
  on extinction

Murie  Dr   on the modification of the skull in old age

Murray  Mr  A   on cave insects

Mustela vison

Myanthus

Myrmecocystus

Myrmica  eyes of

Nageli  on morphological characters

Nails  rudimentary

Nathusius  Von  on pigs

Natural history  future progress of
  selection
  system

Naturalisation of forms distinct from the indigenous species
  in New Zealand

Naudin  on analagous variations in gourds
  on hybrid gourds
  on reversion

Nautilus  Silurian

Nectar of plants

Nectaries  how formed

Nelumbium luteum

Nests  variation in

Neuter insects

New Zealand  productions of  not perfect
  naturalised products of
  fossil birds of
  glaciers of
  crustaceans of
  algae of
  number of plants of
  flora of

Newman  Col   on humble bees

Newton  Prof   on earth attached to a partridge s foot

Newton  Sir I   attacked for irreligion

Nicotiana  crossed varieties of
  certain species very sterile

Nitsche  Dr   on the Polyzoa

Noble  Mr   on fertility of Rhododendron

Nodules  phosphatic  in azoic rocks

Oak  varieties of

Onites apelles

Orchids  fertilisation of
  the development of their flowers
  forms of

Orchis  pollen of

Organisation  tendency to advance

Organs of extreme perfection
  electric  of fishes
  of little importance
  homologous
  rudiments of  and nascent

Ornithorhynchus  mammae of

Ostrich not capable of flight
  habit of laying eggs together
  American  two species of

Otter  habits of  how acquired

Ouzel  water

Owen  Prof   on birds not flying
  on vegetative repetition
  on variability of unusually developed parts
  on the eyes of fishes
  on the swim bladder of fishes
  on fossil horse of La Plata
  on generalised form
  on relation of ruminants and pachyderms
  on fossil birds of New Zealand
  on succession of types
  on affinities of the dugong
  on homologous organs
  on the metamorphosis of cephalopods

Pacific Ocean  faunas of

Pacini  on electric organs

Paley  on no organ formed to give pain

Pallas  on the fertility of the domesticated descendants of wild stocks 

Palm with hooks

Papaver bracteatum

Paraguay  cattle destroyed by flies

Parasites

Partridge  with ball of dirt attached to foot

Parts greatly developed  variable

Parus major

Passiflora

Peaches in United States

Pear  grafts of

Pedicellariae

Pelargonium  flowers of
  sterility of

Peloria

Pelvis of women

Period  glacial

Petrels  habits of

Phasianus  fertility of hybrids

Pheasant  young  wild

Pictet  Prof   on groups of species suddenly appearing
  on rate of organic change
  on continuous succession of genera
  on close alliance of fossils in consecutive formations
  on change in latest tertiary forms
  on early transitional links

Pierce  Mr   on varieties of wolves

Pigeons with feathered feet and skin between toes
  breeds described  and origin of
  breeds of  how produced
  tumbler  not being able to get out of egg
  reverting to blue colour
  instinct of tumbling
  young of

Pigs  black  not affected by the paint root
  modified by want of exercise

Pistil  rudimentary

Plants  poisonous  not affecting certain coloured animals
  selection  applied to
  gradual improvement of
  not improved in barbarous countries
  dimorphic
  destroyed by insects
  in midst of range  have to struggle with other plants
  nectar of
  fleshy  on sea shores
  climbing
  fresh water  distribution of
  low in scale  widely distributed

Pleuronectidae  their structure

Plumage  laws of change in sexes of birds

Plums in the United States

Pointer dog  origin of
  habits of

Poison not affecting certain coloured animals

Poison  similar effect of  on animals and plants

Pollen of fir trees
  transported by various means

Pollinia  their development

Polyzoa  their avicularia

Poole  Col   on striped hemionus

Potemogeton

Pouchet  on the colours of flat fish

Prestwich  Mr   on English and French eocene formations

Proctotrupes

Proteolepas

Proteus

Psychology  future progress of

Pyrgoma  found in the chalk

Quagga  striped

Quatrefages  M   on hybrid moths

Quercus  variability of

Quince  grafts of

Rabbits  disposition of young

Races  domestic  characters of

Race horses  Arab
  English

Radcliffe  Dr   the electrical organs of the torpedo

Ramond  on plants of Pyrenees

Ramsay  Prof   on subaerial denudation
  on thickness of the British formations
  on faults

Ramsay  Mr   on instincts of cuckoo

Ratio of increase

Rats  supplanting each other
  acclimatisation of
  blind  in cave

Rattle snake

Reason and instinct

Recapitulation  general

Reciprocity of crosses

Record  geological  imperfect

Rengger  on flies destroying cattle

Reproduction  rate of

Resemblance  protective  of insects
  to parents in mongrels and hybrids

Reversion  law of inheritance
  in pigeons  to blue colour

Rhododendron  sterility of

Richard  Prof   on Aspicarpa

Richardson  Sir J   on structure of squirrels
  on fishes of the southern hemisphere

Robinia  grafts of

Rodents  blind

Rogers  Prof   Map of N  America 

Rudimentary organs

Rudiments important for classification

Rutimeyer  on Indian cattle

Sageret  on grafts

Salamandra atra

Saliva used in nests

Salmons  males fighting  and hooked jaws of

Salt water  how far injurious to seeds
  not destructive to land shells

Salter  Mr   on early death of hybrid embryos

Salvin  Mr   on the beaks of ducks

Saurophagus sulphuratus

Schacht  Prof   on Phyllotaxy

Schiodte  on blind insects
  on flat fish

Schlegel  on snakes

Schobl  Dr   on the ears of mice

Scott  Mr  J   on the self sterility of orchids
  on the crossing of varieties of verbascum

Sea water  how far injurious to seeds
  not destructive to land shells

Sebright  Sir J   on crossed animals

Sedgwick  Prof   on groups of species suddenly appearing

Seedlings destroyed by insects

Seeds  nutriment in
  winged
  means of dissemination
  power of resisting salt water
  in crops and intestines of birds
  eaten by fish
  in mud
  hooked  on islands

Selection of domestic products
  principle not of recent origin
  unconscious
  natural
  sexual
  objections to term
  natural  has not induced sterility

Sexes  relations of

Sexual characters variable
  selection

Sheep  Merino  their selection
  two sub breeds  unintentionally produced
  mountain  varieties of

Shells  colours of  littoral
  hinges of
  seldom embedded

Shells  fresh water  long retain the same forms
  fresh water  dispersal of
  of Madeira
  land  distribution of
  land  resisting salt water

Shrew mouse

Silene  infertility of crosses

Silliman  Prof   on blind rat

Sirenia  their affinities

Sitaris  metamorphosis of

Skulls of young mammals

Slave making instinct

Smith  Col  Hamilton  on striped horses

Smith  Dr   on the Polyzoa

Smith  Mr  Fred   on slave making ants
  on neuter ants

Snake with tooth for cutting through egg shell

Somerville  Lord  on selection of sheep

Sorbus  grafts of

Sorex

Spaniel  King Charles  breed

Specialisation of organs

Species  polymorphic
  dominant
  common  variable
  in large genera variable
  groups of  suddenly appearing
  beneath Silurian formations
  successively appearing
  changing simultaneously throughout the world

Spencer  Lord  on increase in size of cattle

Spencer  Mr  Herbert  on the first steps in differentiation
  on the tendency to an equilibrium in all forces

Sphex  parasitic

Spiders  development of

Sports in plants

Sprengel  C C   on crossing
  on ray florets

Squalodon

Squirrels  gradations in structure

Staffordshire  heath  changes in

Stag beetles  fighting

Star fishes  eyes of
  their pedicellariae

Sterility from changed conditions of life
  of hybrids
  laws of
  causes of
  from unfavourable conditions
  not induced through natural selection

St  Helena  productions of

St  Hilaire  Aug   on variability of certain plants
  on classification

St  John  Mr   on habits of cats

Sting of bee

Stocks  aboriginal  of domestic animals

Strata  thickness of  in Britain

Stripes on horses

Structure  degrees of utility of

Struggle for existence

Succession  geological
  of types in same areas

Swallow  one species supplanting another

Swaysland  Mr   on earth adhering to the feet of migratory birds

Swifts  nests of

Swim bladder

Switzerland  lake inhabitants of

System  natural

Tail of giraffe
  of aquatic animals
  prehensile
  rudimentary

Tanais  dimorphic

Tarsi deficient

Tausch  Dr   on umbelliferae

Teeth and hair correlated
  rudimentary  in embryonic calf

Tegetmeier  Mr   on cells of bees

Temminck  on distribution aiding classification

Tendrils  their development

Thompson  Sir W   on the age of the habitable world
  on the consolidation of the crust of the earth

Thouin  on grafts

Thrush  aquatic species of
  mocking  of the Galapagos
  young of  spotted
  nest of

Thuret  M   on crossed fuci

Thwaites  Mr   on acclimatisation

Thylacinus

Tierra del Fuego  dogs of
  plants of

Timber drift

Time  lapse of
  by itself not causing modification

Titmouse

Toads on islands

Tobacco  crossed varieties of

Tomes  Mr   on the distribution of bats

Transitions in varieties rare

Traquair  Dr   on flat fish

Trautschold  on intermediate varieties

Trees on islands belong to peculiar orders
  with separated sexes

Trifolium pratense
  incarnatum

Trigonia

Trilobites
  sudden extinction of

Trimen  Mr   on imitating insects

Trimorphism in plants

Troglodytes

Tuco tuco  blind

Tumbler pigeons  habits of  hereditary
  young of

Turkey cock  tuft of hair on breast

Turkey  naked skin on head
  young of  instinctively wild

Turnip and cabbage  analogous variations of

Type  unity of

Types  succession of  in same areas

Typotherium

Udders enlarged by use
  rudimentary

Ulex  young leaves of

Umbelliferae  flowers and seeds of
  outer and inner florets of

Unity of type

Uria lacrymans

Use  effects of
  under domestication
  in a state of nature

Utility  how far important in the construction of each part

Valenciennes  on fresh water fish

Variability of mongrels and hybrids

Variation  under domestication
  caused by reproductive system being affected by conditions of life
  under nature
  laws of
  correlated

Variations appear at corresponding ages
  analogous in distinct species

Varieties  natural
  struggle between
  domestic  extinction of
  transitional  rarity of

Varieties  when crossed
  fertile
  sterile
  classification of

Verbascum  sterility of
  varieties of  crossed

Verlot  M   on double stocks

Verneuil  M  de  on the succession of species

Vibracula of the Polyzoa

Viola  small imperfect flowers of
  tricolor

Virchow  on the structure of the crystalline lens

Virginia  pigs of

Volcanic islands  denudation of

Vulture  naked skin on head

Wading birds

Wagner  Dr   on Cecidomyia

Wagner  Moritz  on the importance of isolation

Wallace  Mr   on origin of species
  on the limit of variation under domestication
  on dimorphic lepidoptera
  on races in the Malay Archipelago
  on the improvement of the eye
  on the walking stick insect
  on laws of geographical distribution
  on the Malay Archipelago
  on mimetic animals

Walsh  Mr  B D   on phytophagic forms
  on equal variability

Water  fresh  productions of

Water hen

Waterhouse  Mr   on Australian marsupials
  on greatly developed parts being variable
  on the cells of bees
  on general affinities

Water ouzel

Watson  Mr  H C   on range of varieties of British plants
  on acclimatisation
  on flora of Azores
  on rarity of intermediate varieties
  on Alpine plants
  on convergence
  on the indefinite multiplication of species

Weale  Mr   on locusts transporting seeds

Web of feet in water birds

Weismann  Prof   on the causes of variability
  on rudimentary organs

West Indian islands  mammals of

Westwood  on species in large genera being closely allied to others
  on the tarsi of Engidae
  on the antennae of hymenopterous insects

Whales

Wheat  varieties of

White Mountains  flora of

Whittaker  Mr   on lines of escarpment

Wichura  Max  on hybrids

Wings  reduction of size
  of insects homologous with branchiae
  rudimentary  in insects

Wolf crossed with dog
  of Falkland Isles

Wollaston  Mr   on varieties of insects
  on fossil varieties of shells in Madeira

Wollaston  Mr   on colours of insects on sea shore
  on wingless beetles
  on rarity of intermediate varieties
  on insular insects
  on land shells of Madeira naturalised

Wolves  varieties of

Woodcock with earth attached to leg

Woodpecker  habits of
  green colour of

Woodward  Mr   on the duration of specific forms
  on Pyrgoma
  on the continuous succession of genera
  on the succession of types

World  species changing simultaneously throughout

Wright  Mr  Chauncey  on the giraffe
  on abrupt modifications

Wrens  nest of

Wyman  Prof   on correlation of colour and effects of poison
  on the cells of the bee

Youatt  Mr   on selection
  on sub breeds of sheep
  on rudimentary horns in young cattle

Zanthoxylon

Zebra  stripes on

Zeuglodons


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