Menstruation (mammal)
Most female mammals have an estrous cycle, yet only ten primates species, four bats species, the elephant shrew, and the spiny mouse have a menstrual cycle. The relatedness of these groups suggests that four distinct evolutionary events have caused menstruation to arise.
The Evolution of Human Sexuality
According to Symons, while orgasm in the human female has been proposed to be an adaptation resulting from selective forces, the available evidence, which shows that the female orgasm is far from being a universal result of heterosexual intercourse and that its frequency varies greatly between cultures and between individuals, does not support that conclusion. Symons suggested that the female orgasm may be possible for female mammals because it is adaptive for males. He notes that in most mammalian species the only known function of the clitoris is to generate sensation during copulation, but saw no evidence that "the female genitals of any mammalian species have been designed by natural selection for efficiency in orgasm production." He criticizes Elizabeth Sherfey's view that the female orgasm is an adaptation, writing that her arguments are not supported by ethnographic or biological evidence. Symons proposes that male human ancestors lost the ability to detect ovulation in females by smell because females gained a reproductive advantage by concealing ovulation, and that estrus ceased to exist in humans at the same time. Observing that estrous female chimpanzees are more successful than nonestrous females in obtaining meat from males, Symons suggests that when hunting became a dominant male economic activity during human evolution, the benefits to females of receiving meat may have outweighed the costs to them of constant sexual activity, leading to women making sexual overtures to men in order to obtain meat.