Why Do Humans Menstruate When Most Mammals Don’t?

TL;DR

Humans menstruate because it's a byproduct of evolutionary adaptations involving the invasive human placenta. Menstruation allows the host to control resources and may help in identifying genetically abnormal embryos by terminating pregnancies early. This unique cycle contrasts with most mammals, which do not experience monthly menstruation.

Transcript

[♪ INTRO] Humans have been getting their periods since, well, forever. So you might think that’s just something that comes along with being a mammal. But… it’s not. Few mammals get periods every month, or at all. Like, that bleeding thing that female dogs do? It’s not menstruation. It comes from the vagina, not the uterus, and happens before ovulat... Read More

Key Insights

• ❓ Menstruation is a unique trait that is not commonly found in mammals.
• ❓ Menstruation has been poorly understood throughout history due to societal taboos and misconceptions.
• 🥺 The current hypothesis suggests that the invasive nature of the human placenta and the struggle between a fetus and its host have led to the evolution of menstruation.
• 👻 Spontaneous decidualization may serve as a way for the host to control resources and prevent the implantation of genetically abnormal embryos.

Questions & Answers

Q: Why do only a few mammalian species, including humans, experience menstruation?

Menstruation is rare in mammals because it is tied to the invasive nature of the placenta and the evolutionary struggle between a fetus and its host. Only species with hemochorial placentation, like humans, experience menstruation.

Q: What are some misconceptions and myths surrounding menstruation?

Throughout history, people believed that contact with menstrual blood could have negative effects, such as turning crops barren or killing bees. There were also misguided notions about the presence of toxins in menstrual fluids.

Q: What is the purpose of spontaneous decidualization?

Spontaneous decidualization is driven by the host's hormones and serves as a way for the host to maintain control over resources and prevent the fetus from exploiting its parent. It may also help detect genetic abnormalities in embryos and lead to early miscarriage.

Q: How does understanding menstruation and spontaneous decidualization benefit medical science?

Understanding menstruation and spontaneous decidualization can help doctors treat conditions related to the reproductive system, such as infertility and recurrent pregnancy loss. It provides insights into the functioning of the uterus and ovaries.

Summary & Key Takeaways

• Menstruation is a monthly cycle regulated by hormones, involving the shedding of the uterine lining and the release of a mature egg cell.

• The concept of menstruation has been poorly understood throughout history due to societal taboos and misconceptions.

• The current hypothesis suggests that menstruation evolved as a result of the invasive nature of the human placenta and to potentially prevent the implantation of genetically abnormal embryos.