Understanding the subject: Menstruation

[Miigwech]

Apart from humans and our close relatives, the only animals that menstruate are elephant shrews and certain bats. Why did it only evolve in these species?

Apart from humans, most of the other menstruating animals are primates, the group that includes monkeys and apes as well as humans. Most monkeys living in Africa and Asia, such as rhesus macaques, menstruate.

Great apes do it too. Menstrual bleeding is easily detectable in chimpanzees and gibbons. However, gorillas and orang-utans bleed less copiously, so menstruation is only visible on closer inspection. Other primates, such as tarsiers, may also menstruate, but there is little hard evidence.

Other than our close relatives, menstruation also evolved independently in two other groups: some bats and elephant shrews.

http://www.bbc.com/earth/story/20150420-why-do-women-have-periods