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Roughgarden's evolution of sex paper in Am Nat

Chris Colby colby at bu-bio.bu.edu
Sat Apr 11 18:04:07 EST 1992

	I was wondering if anyone would like to comment on Rough-
garden's recent paper in Am. Nat. regarding the evolution of sex? (*)

	The standard reason given for the evolution of sex is that
it allows groups to evolve faster. Beneficial mutations occuring
in separate organisms could be shuffled onto the same chromosome
via recombination (whereas sequential mutations would have to occur in
an asexual population). Thus, the benefit of sex (to a group) was tied
to the ability to recombine; this is especially useful when
the environment is unstable. Sex is assumed not to be adaptive to

	Roughgraden attempts to decouple sex from recombination and
develops a one-locus model of why sex may be adaptive to groups of
organisms. He shows that in a sexual population, the distribution of
genotypes stays more stable with time (because random mating brings
about genotype frequencies in Hardy-Weinberg eq.) than in an asexual
population when the fitnesses of the different genotypes fluctuate.
So, when the fitnesses of the genotypes change, there are always more
representatives of the most favored genotype in a sexual population
than in an asexual one. The benefit of sex increases (in his model)
with the magnitude of environmental fluctuation.

	(His model is one-locus, two allele. The asexual population
is diploid and hermaphroditic. The sexual population is (of course)
diploid and randomly mated. I hope I have not butchered it in my
description above.)

	I have posted this to bionet.population-biology and
bionet.molbio.evolution because I think it may be relevant to
both groups. But, to prevent wasting bandwidth, I've set the
follow-up to the pop-bio board.

	Are there any criticisms of his model? It seems valid to
me (but I'm just a lowly grad-student -- what the hell do I know 8-)
(*) Roughgarden, 1991, The evolution of sex, American Naturalist 138:
934- 953

Chris Colby 	---	 email: colby at bu-bio.bu.edu	---
"'My boy,' he said, 'you are descended from a long line of determined,
resourceful, microscopic tadpoles--champions every one.'"
 	--Kurt Vonnegut from "Galapagos"

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