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From: peter@aisb.ed.ac.uk (Peter Ross)
Subject: Re: Evolution of Species
In-Reply-To: simon@ling.ed.ac.uk's message of 03 Oct 1995 11:57:32 GMT
Message-ID: <PETER.95Oct4131532@balder.aisb.ed.ac.uk>
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Organization: Dept. of AI, University of Edinburgh
References: <WHIPP.95Sep25150159@psupw22.roborough.gpsemi.COM>
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Date: Wed, 4 Oct 1995 12:15:32 GMT
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In article <SIMON.95Oct3125732@xbabel.ling.ed.ac.uk> simon@ling.ed.ac.uk (Simon Kirby) writes:

   In article <44p74q$k3c@sally.dma.org> jet@dma.org (Jeremy E. Thompson) writes:

      Along with all the mentions of finches, i recall an instance documented 
      from England during the Industrial Revolution where a black moth evolved 
      into a white moth due to all the white ash from industrial smokestacks 
      collecting on the bark of the surrounding forests.  These moths were 
      ....

   The case of the black/white moths is clearly one of a change in
   relative frequency of two genes in a population over time (both genes
   have a non-zero frequency throughout the documented process). Any
   biologists out there care to comment on whether this would be classed
   as "evolution" or not? (And if not, why not?)


Actually the peppered moth changed from whitish to black; tree bark
grew much darker because of pollution. It seems to be generally
accepted that this particular case is an instance of the spread of a
modifier gene; the moths might have genes for both white and black,
but a different modifier gene is responsible for the final choice of
which gets expressed. Sheppard (Natural Selection and Heredity,
Hutchinson, 1958) seems to have first proposed the variant of Fisher's
modifier theory that can account for the swift change in peppered moth
colouration. Although I'm not an expert on evolution, I doubt this
example would be classed as a particularly dramatic instance: the
genes involved were probably all present beforehand, just the
proportions present in the whole population changed - they didn't in
some sense acquire new genes.


Peter Ross
Dept of AI
Edinburgh
