Re: limit of selection???

From: Anon. (bob.ohara_at_SOD.OFF.Spammers.helsinki.fi)
Date: 08/31/04 

Date: Tue, 31 Aug 2004 15:53:48 +0000 (UTC)

A.C.H. wrote:
> William Morse <wdmorse@twcny.rr.com> wrote in message news:<cgvefb$2sgo$1@darwin.ediacara.org>...
>
<snip>
>>I do agree with the general nature of your argument - that there will be
>>no continuing evolution by natural selection (OK Larry, drift may still
>>play its part) in the absence of continuing selection pressure.
>
>
> The argument i was trying to make was more specific then that. I was
> trying to argue that the selection pressure DECREASES when a
> population gets more adapted.

This will be true if the fitness function is concave near the maximum,
which I think is what most evolutionary biologists would assume.

> And because natural selection decreases (though it doesn't stop), a
> state of perfect adaptation (ALL individuals survive a certain
> selection pressure) can not be reached.
>
This will be true if drift and mutation (and immigration) are also
affecting the population. The extent to which these are important will
depend on the sizes of their effects relative to the width of the
fitness curve.

In practice, deciding if you're right is an empirical exercise, and will
give different answers for different traits. many (some?) genes
involved in respiration are probably optimal, because they are so
important, and a small change will have a big effect. Traits like skin
colour are probably under much milder selection, so more variation is seen.

Bob 

-- 
Bob O'Hara
Dept. of Mathematics and Statistics
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