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Evolution of sex

The evolution of sex is a longstanding problem, and even after 50 years of intensive research "the twofold cost of sex" still makes it difficult to understand the origin and evolutionary stability of sexual reproduction. In his talk, Ilan Eshel pointed out that the wideheld belief that sex speeds up evolution is only justified in a fluctuating environment. He showed that in a constant environment sex will even slow down evolution (since recombination destroys favourable gene combinations faster than it can create them). In the second part of his talk, Ilan Eshel argued that the evolution of sex is a problem that is inseparably linked to the evolutionary theory of ageing. In fact, the decision whether to reproduce sexually or asexually is very much like the decision whether to invest in self-maintenance or to create new offspring. Steven Siller pointed out that the maintenance of sex is much easier to understand if one takes into account that sexual reproduction almost automatically leads to distinct sex roles and to sexual selection. In particular, sexual selection by mate choice can reduce the genetic load of a sexual lineage relative to the genetic load of an otherwise equivalent clonal lineage. If one sex (typically the male sex) does not provide parental care and hence does not contribute to the population growth rate, sexual selection on this sex can be highly efficient in purging the population of deleterious mutations without negative consequences at the population level. The details have still to be worked out, but the proposed synthesis between the 'evolution of sex' theory and sexual selection theory is highly promising.

Bob Kooi
Wed Jan 10 12:08:31 MET 2001