Much less is known about mechanisms of cryptic female choice in mammals than is the case for sperm competition. However, the limited evidence presented in this chapter is consistent with the conclusions reached in Chapter 3 concerning sperm competition and the origins of human sexual behaviour. Thus, there is little credible evidence that orgasm in women or in females of non-human primate species plays any role in sperm transport or fertility. Likewise, the evolution of human penile morphology and copulatory patterns is not connected to any requirement to induce female orgasm, in order to increase the likelihood of fertilizing ova. Rather, it appears that female orgasm, which occurs in a number of anthropoids besides Homo sapiens, represents a functionless homologue of responses which accompany ejaculation in the male. Func-tionless homologues of female structures (such as the nipples and uterus masculinus) also occur in men and in males of other mammals.

Recent work on the evolution of oviductal length in mammals is reviewed here. The extramural portion of the oviduct is significantly longer in those mammals in which females mate with multiple partners during the fertile period. Interestingly, relative testes sizes, sperm midpiece volumes, and relative oviductal lengths are positively correlated in mammals. Given that the oviduct is a final and critical arena for sperm competition, it is possible that longer and more convoluted oviducts serve to 'test' gametes, and represent a mechanism of cryptic female choice. In this regard it is significant that the human oviduct is relatively short by comparison with the oviducts of many other mammals. There is no evidence that cryptic female choice has affected the evolution of human oviductal morphology.

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