InterJournal Complex Systems, 563
Status: Accepted
Manuscript Number: [563]
Submission Date: 20531
On the adaptive value of sex
Author(s): Klaus Jaffe

Subject(s): CX.19

Category: Brief Article


Using computer simulations I studied the conditions under which sex is evolutionary stable. The parameters that showed relevance to the stability of sex were: variable environments, mutation rates, ploidy, number of loci subject to evolution, mate selection strategy, reproductive system and number of gametes (spermatozoa). The simulations showed that mutants for sex and recombination are evolutionarily stable, displacing alleles for monosexuality when more than one of the following conditions were fulfilled simultaneously: selection pressure was variable, mate selection was not random, ploidy was two, the reproductive strategy was haplo-dipoid, diploid or hermaphroditic, the complexity of the genome was large (more than 4 loci suffered adaptation), and gamete selection occurred. The results suggest that at least four phenomena, related to sex, have convergent adaptive values: Diploidy, sexual reproduction (recombination), gamete selection and the segregation of sexes. The results suggest that the emergence of sex had to be preceded by the emergence of diploid monosexual organisms and provide an explanation for the emergence and maintenance of sex among diploids and for the scarcity of sex among haploid organisms. The divergence of the evolutionary adaptation of the sexes should be a derived consequence of the emergence of sex. I postulate that for a harmonious evolution of complex genomes, optimal levels of genetic variation are required. Sex with random mating provides genetic variation but in excess, and thus has to be modulated by mate and gamete selection mechanisms. Generalizing, the dynamic advantages of sexual reproduction are that it allows evolving organisms to modulate the genetic variance (assortative mating), it opens the way for new levels of selection (mate and gamete selection), and it allows for divergent adaptations of the sexes. (female and male)

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