Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Sexual swelling
To successfully ensure paternal confusion, Hrdy predicted that ovulation must be randomly distributed across the term where the sexual swelling is of maximum tumescence. This would ensure that males were unable to use the swelling as a signal of female fertility. One example of this stems from research into sooty mangabey ("Cercocebus atys"); the females of this species have been found to produce sexual swellings both when they are fertile and when they are with child. Additionally, sexual swellings are only observed during the most fertile period of a female’s menstrual cycle in 26-35 species of anthropoid primates, in contrast to Hrdy's prediction.