Path: utzoo!utgpu!watserv1!watmath!uunet!bionet!GENETICS.WASHINGTON.EDU!joe
From: joe@GENETICS.WASHINGTON.EDU (Joe Felsenstein)
Newsgroups: bionet.population-bio
Subject: Re: Average Fitness, Evolution of Sex and Others
Message-ID: <9010162206.AA06209@evolution.genetics.washington.edu>
Date: 16 Oct 90 22:06:49 GMT
References: <9010151827.AA00877@genbank.bio.net>
Sender: daemon@genbank.bio.net
Lines: 44



In comment on Xia's posting on:

>           Average of Fitness, Evolution of Sex and Others
>           ===============================================
> 

In the example of two alleles with fitnesses  (X+s):X in one
generation and (X-s):X in the next, the assumption is implicit that
both alleles have the same arithmetic mean fitness.  But if
they don't, then it is not obvious which one will win out without
computing the geometric means.  For example, if one generation
the alleles have fitnesses   X(1+2s) : X  and in the other
X/(1+s) : X, then the MORE variable one wins since  (1+2s)/(1+s) > 1.

> (BTW, the above simple formulation is the foundation of the so-called
> bet-hedgeing in life-history theory.)

> A corollary of the theorem is that any gene that reduces fitness
> variability of its carier will be favoured by natural selection.

So it is not just a matter of bet-hedging: if there is a cost of
bet-hedging then it can be selected against.

> The gene for sexual reproduction is such a gene, it reduces the 
> fitness variation of its carrier 1.414 (=square root of 2) times.

If the square root of two is based (as I suspect) on the fact that
there is a two-fold cost of sexual reproduction, then this won't work
as the reduction of mean is too great to make the reduction of variance
worhtwhile.

> (Please let me know if my writing is interesting so that I won't
> keep posting things that you do not read.)
>  

Do keep it up.

----
Joe Felsenstein, Dept. of Genetics, Univ. of Washington, Seattle, WA 98195
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