From: Walter Hicks (wallyshoes@mindspring.com)
Date: Thu Oct 16 2003 - 22:35:13 EDT
I forward this post by David Campbell. I had not
intended for it to be off list.
-------- Original Message --------
Subject: Re: Predictions
Date: Thu, 16 Oct 2003 18:44:12 -0400
From: "bivalve"
<bivalve@mail.davidson.alumlink.com>
Reply-To: <bivalve@mail.davidson.alumlink.com>
To: Walter Hicks <wallyshoes@mindspring.com>
>Would you have any simple examples of the computer simulations such as might run on a home PC?<
I think I sent to you a copy of a DOS program that
models genetic drift about two years ago. I think
I included in the program a variable for selective
pressure on the alleles. I do not personally have
anything else handy, but the basic parameters are
simple enough so that I think there would be a lot
of programs available.
>Also what do you think of genetic algorithms which attempt to mimic evolution in various optimization tasks of physical objects?<
I think they give a good illustration of the basic
principles of evolution. Obviously, the
parameters of the algorithm would determine
whether it is a very realistic model of the actual
course of evolution in a particular case.
>I was reading some (simplified) discussions of genetic drift. It sounded like it was unclear as to whether that is more important than natural selection. If it is, would that not modify what you say here?<
To some degree, the relative importance is moot.
No fatal mutation will get anywhere with genetic
drift, because the selective pressure against it
is so high, and strongly positive or negative
selective factors will push genetic drift pretty
effectively. However, even a very positive or
very negative trait has some chance of
establishment through genetic drift. Thus, I'm
not sure how well they can be separated to single
out one as the most important for all of
evolution. On the other hand, in particular cases
one or the other may be identifiable as playing
the greater role.
I don't think it changes the overall picture of
evolution as the net result of a complex set of
forces. It does present a challenge to the
extreme adaptionist picture, because it shows that
features may be established largely by random
factors if there is no strong selective pressure
either way. Studies of molecular evolution
largely take drift into account by analyses that
look for bias in the pattern of change (e.g., a
high rate of change that affects the gene product
suggests selection is playing a big role; change
that emphasizes the DNA bases that have no effect
suggests that drift is dominant, with some
selective constraint imposed by the gene
function).
(I did not reply to the list because it looked as
though you replied directly to me; if you want
something discussed on the list, you can forward
it there.)
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487-0345 USA
bivalve@mail.davidson.alumlink.com
That is Uncle Joe, taken in the masonic regalia of
a Grand Exalted Periwinkle of the Mystic Order of
Whelks-P.G. Wodehouse, Romance at Droitgate Spa
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