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.
Orgasm
The mechanics of male orgasm are similar in most male mammals. Females of some mammal and some non-mammal species, such as alligators, have clitorises. There has been ongoing research about the sexuality and orgasms of dolphins, a species which apparently engages in sexual intercourse for reasons other than procreation. The duration of orgasm varies considerably among different mammal species.