Do Animals Get Periods?

Human body is quite complex and has its own unique characteristics. One of the most complex processes is menstruation, which is part of the reproductive cycle. The process begins prior to an egg being released from the ovaries. Due to hormones such as progesterone, the endometrium (lining of the uterus) thickens and fills up with blood vessels. This happens in anticipation of the egg being fertilized. The blood vessels will enable the fertilized egg to start growing.

When there is no fertilization, progesterone levels start to fall rapidly. It leads to rapid destruction of the endometrium. The subsequent release is what is referred to as menstruation. The discharge is a mix of various fluids including blood, cells of endometrium and vaginal fluid. Menstruation is largely an uncomfortable experience, but an unavoidable part of a sexually reproducing species.

Sometimes it makes us wonder if animals also have periods. To answer such question, here are some facts we need to know.

Limited to primates – Based on available evidence, it is considered that menstruation occurs largely among primates. This is quite surprising, as there must be thousands of sexually reproducing species of animals on the planet. Other animal species (non-primates) that are known to experience menstruation include spiny mouse species Acomys cahirinus, elephant shrew and bats.

Only a few bleed – Even rare is the process of overt menstruation, wherein bleeding occurs. Overt menstruation is found among mammals that are considered as close relatives of humans. For example, chimpanzees are known to experience overt menstruation.

Covert menstruation – Certain species that belong to placental mammal group experience a different type of menstruation known as estrous cycles. In this process, the endometrium is not shed like humans. Instead, it is fully reabsorbed inside the body in case there is no fertilization. In this process, there is no discharge of blood or other fluids.

What is evolutionary advantage of menstruation?

The fact that overt menstruation is so rare, makes us wonder if it has any evolutionary advantages. There must be some reasons why nature chose this for humans and other closely related primates. The research on this subject is ongoing. There are possibly multiple reasons, which are still to be identified.

One theory is that menstruation process can help identify abnormalities / genetic disorders in embryo in early stage. It is theorized that some cells in the uterus can detect abnormalities in the developing embryo. This can help reduce the risk of stillbirth or miscarriage.

Some experts also say that menstruation may not actually have any specific evolutionary advantages. It may just be a different way of doing things. Nothing conclusive has been derived as yet and such matters are being probed further.