Why have sex? The population genetics of sex and recombination

S. P. Otto, A. C. Gerstein

Research output: Contribution to journalReview articlepeer-review

70 Scopus citations


One of the greatest puzzles in evolutionary biology is the high frequency of sexual reproduction and recombination. Given that individuals surviving to reproductive age have genomes that function in their current environment, why should they risk shuffling their genes with those of another individual? Mathematical models are especially important in developing predictions about when sex and recombination can evolve, because it is difficult to intuit the outcome of evolution with several interacting genes. Interestingly, theoretical analyses have shown that it is often quite difficult to identify conditions that favour the evolution of high rates of sex and recombination. For example, fitness interactions among genes (epistasis) can favour sex and recombination but only if such interactions are negative, relatively weak and not highly variable. One reason why an answer to the paradox of sex has been so elusive is that our models have focused unduly on populations that are infinite in size, unstructured and isolated from other species. Yet most verbal theories for sex and recombination consider a finite number of genotypes evolving in a biologically and/or physically complex world. Here, we review various hypotheses for why sex and recombination are so prevalent and discuss theoretical results indicating which of these hypotheses is most promising.

Original languageEnglish (US)
Pages (from-to)519-522
Number of pages4
JournalBiochemical Society transactions
Issue number4
StatePublished - Aug 2006


  • Drift
  • Epistasis
  • Evolution of sex
  • Modifier theory
  • Recombination
  • Red Queen hypothesis


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