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From: whipp@roborough.gpsemi.com (David Whipp)
Subject: Re: Lamarckian Evolution
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Organization: GEC Plessey Semiconductors
References:  <1995Jan18.165850.75699@ucl.ac.uk>
Date: Mon, 23 Jan 1995 18:28:42 GMT
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In article <1995Jan18.165850.75699@ucl.ac.uk>, Chris Harris <charris@cs.ucl.ac.uk> writes:
|> If Lamarckian evolution is a possibility (and I might as well add here
|> that I don't consider it so) then how do its exponents explain the
|> amazing changes it must make to our genomes. If an organism picks up,
|> during its lifetime, a number of useful traits, which it somehow
|> genetically encodes, where does it put them? Does it just add these
|> sequences on to the end (i.e. new genetic material) or does it
|> replace ones that are already there so that the genome length is
|> preserved? If the latter, then how does it do that, and how does it 
|> decide which ones to 'get rid of'. If the former were the case then 
|> our genome would be getting longer and longer...

I do not think that either 'pure' neo-darwinism or 'pure' direct
Lamarckism can completely describe the processes of evolution.

I do not know of any direct lamarckian mechanisms (i.e. ones that
determine specific changes to be made to the genes) (except humans
and their genetic engineering).  However, I can postulate about
indirect ones - i.e those where specific actions by an individual
(that are made under free will) will determine the priority of
different traits.

The most obvious example is the selection of mates. Selection
will be based on selecting a mate that meets certain critera.
The reasons for selection will originate in features that have
positive survival benifit (for the offspring and therefore the
species), for example: size, but later these aspects will be
selected for no good evolutionary reason - from a starting point
of size being better you will eventually get to a point where
the offspring can no longer support their own weight.

Such overshoots in evolution cannot be explained purely in terms
of Darwinian selection.

However, it is possible to think of more direct ways in which
behaviour could modify the offsping.

Consider the fact that our bodies a regulated by hormones. These
turn genes on/off as required. A simple example is the way in
which the soles of one's feet thicken if you do a lot of walking.
An internal mechanism says "hey! make those feet thicker" - so
a gene is turned on to do this.

Some organisms completely change their physical bodies in response
to hormones (admittedly such changes are involuntary). For example:
a caterpillar changes into a butterfly and a tadpole changes into
a frog.

I do not think that it is totally implausable to suggest that hormones
from the parent could also effect the child (hormones do affect the
production of the sperm and the egg). If a catterpillar and a butterfly
both have the same genes then there is no reason to change the genes in
the child in order to change the physical (or mental) characteristics.

Darwinism is a neccessary component of a theory of evolution. However,
I do no beleive that it is a complete description by itself.
Unfortunately, I don't know what needs to be added to it - I can
only cast around in the dark and hope to find some evidence for
any other the multitude of additional theories (some of which will
be wrong).

-- 
                    David P. Whipp.            <whipp@roborough.gpsemi.com>
Not speaking for:   -------------------------------------------------------
 G.E.C. Plessey     Due to transcription and transmission errors, the views
 Semiconductors     expressed here may not reflect even  my  own  opinions!
