From: adpeters@sunflower.bio.indiana.edu (Andy Peters)
Subject: Sex & Individual Selection (was Re: Atheistic creationism)
Organization: Program in Evolution, Ecology, and Behavior, Indiana University
Date: Tue, 13 Oct 1992 04:04:39 GMT

In article <1242@tdat.teradata.COM> swf@tdat.teradata.com (Stanley Friesen) writes:
>In article <Bvw2pA.3np@well.sf.ca.us> keithd@well.sf.ca.us (Keith Doyle) writes:
>|---------------------------------------------------------------------
>|As the microbiologist W.F. Bodmer has succinctly put it, sex
>|"facilitates the accumulation in a single individual of advantageous
>|mutations which arose separately in different individuals."
>|
>|In terms of the individual, sex appears paradoxical because it would seem
>|an inefficient way to propagate his genes, each child has only 50 percent
>|of his genes, the other 50 percent supplied by the sexual partner.
>|Sexual reproduction apparently has more group level advantages than
>|individual level advantages.  Efficiency from the whole individuals
>|point of view is then seen to be irrelevant.

I seemed to have missed Keith's original post; if someone could email it
to me, I'd appreciate it.

I would also be curious to see a reference for the Bodmer quote.  This is
by no means a front-runner among the explanations for the maintenance of
sexual reproduction.

Those explanations which _are_ front-runners most definitely _do_ work
in terms of individual selection.  They _also_ work in terms of a very
non-standard type of group selection, and are often discussed in those 
terms because it is easier to see both the costs and the proposed benefits
within such a framework:  a parthenogenetic female will produce twice
as many grandchildren, 4x as many great-grandchildren, 8x as many great^2-
grandchildren, etc, as a sexual female producing 50% males(the cost of males); 
or, she will be two times more related to her offspring than will a sexual
counterpart (the cost of meiosis).  This has been termed (by some) "group
selection" because it is essentially the competition between the sexual
"group" and the asexual "group" which is leading to the selection; the
observed phenomenon is not a rare allele increasing in a population, but
one population replacing another. Under individual selection, the cost of 
males has been shown to apply under some conditions, the cost of meiosis 
under others; they never both apply at the same time [1].

As for the current front-runner mechanisms:  the Red Queen hypothesis
postulates an advantage to the individual of producing rare offspring (which
are more likely to escape parasitism); Muller's Ratchet (which is enjoying
a modest comeback as a front-runner) postulates an advantage to the
indivdual of producing variable offspring (some of which will have few
nearly-neutral deleterious alleles); the recombinational repair hypothesis
postulates an advantage to the individual of recombination itself (through 
its repair of double-stranded breaks in the DNA) and outcrossing (through
the masking of deleterious recessive mutations).  All three models are
formulated in terms of individual fitness.  As for the "accumulation of
advantageous mutations" hypothesis, that isn't a front-runner precisely
because it involves the standard idea of group selection, and because
advantageous mutations are so much more infrequent than deleterious
mutations.

>Another aspect of this is brought out in the Scientific American article on
>"Genetic Algorithms".  It seems that sexual recombination increases the
>*parallelism* of selection (as an algorithm) and thus *its* efficiency.
>[That is selection is more effective at selecting a near optimal variant
>in a sexual population than in an asexual one].

I'm not sure I understand what you're saying here.

>sarima@teradata.com			(formerly tdatirv!sarima)
>  or
>Stanley.Friesen@ElSegundoCA.ncr.com

Reference:
[1] Lively, C. M., and D. Lloyd.  1990.  The cost of sex under individual
    selection.  Am Nat ?, pp. ??-?? (Sorry, don't have the ref with me)

Also of interest:
Bell, G.  1982.  The Masterpiece of Nature:  The Evolution and Genetics of
    Sexuality.  University of California Press, L. A.
and millions of others

Also, Heredity (I think) will be publishing a special issue sometime in the
next few months (maybe even 2 issues), devoted to the papers presented
at last July's Evolution of Sex symposium.  

-- 
* Andy Peters                     * "Slugs are small and portable    *From
* Program in Evolution,           * Just stuff 'em up your nose      *"Slugs,"
*      Ecology, and Behavior      * They'll fit beneath your armpits *by David
* Indiana University, Bloomington * Or right between your toes"      *Greenberg
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