, Volume 138, Issue 1, pp 5-18

First online:

Evolution of genitalia: theories, evidence, and new directions

  • William G. EberhardAffiliated withSmithsonian Tropical Research Institute, and Escuela de Biología, Universidad de Costa Rica, Ciudad Universitaria Email author 

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Many hypotheses have been proposed to explain why male intromittent genitalia consistently tend to diverge more rapidly than other body traits of the same individuals in a wide range of animal taxa. Currently the two most popular involve sexual selection: sexually antagonistic coevolution (SAC) and cryptic female choice (CFC). A review of the most extensive attempts to discriminate between these two hypotheses indicates that SAC is not likely to have played a major role in explaining this pattern of genital evolution. Promising lines for future, more direct tests of CFC include experimental modification of male genital form and female sensory abilities, analysis of possible male–female dialogues during copulation, and direct observations of genital behavior.


Sexual conflict Sexual selection Sexually antagonistic coevolution Cryptic female choice