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Re: Holloway/Morgan
Guy Hoelzer (hoelzer@unr.edu)
Wed, 26 Jul 1995 09:24:03 -0800
In article <89823693wnr@desco.demon.co.uk>, Elaine Morgan
<Elaine@desco.demon.co.uk> wrote:
> Natural selection cannot initiate any change. All it can do is monitor
> it. Edit it. So someone, I am told, has worked out that genetic drift
> can account for brain growth. Big deal. That does not absolve us from
> enquiring why it was allowed to. Brain growth was on balance, most
> people would agree, conducive to inclusive fitness. If it had decreased
> inclusive fitness natural selection would have vetoed that drift and
> it would not have occurred. Okay, regulatory genes by means of
> e.g.heterochrony can produce a lot of change in a short time, but they
> are neither more nor less subject to editing by natural selection than
> other genes. [This has been cut from a much longer post]
I have been following this interesting thread and thought it might be
helpful to put in my two cents at this point. I teach and do a bit of work
in the area of population genetics, so I would like to clarify a
misunderstanding present in the paragraph above. Natural selection is not
an ever-present editor that can weed out all maladaptive mutations. It
works fine in very large, panmictic populations, but it becomes less
effective in smaller, subdivided populations. Migration from other
genetically distinct subpopulations can further interfere with the efficacy
of selection. Consequently, evolution is not constrained to adaptive or
neutral directions and it does not make sense to say that we must explain
"why (selection) has allowed" a particular evolutionary path. It is clear
from both population genetics theory and from empirical observations that
deleterious mutations can drift to fixation under certain circumstances,
which are not unrealistic or extraordinary.
--
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Guy Hoelzer
hoelzer@unr.edu
Dept. of Biology
University of Nevada Reno
Reno, NV 89557
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