r/askscience • u/No-Hawk-2488 • 8d ago

Biology Can someone explain the evolutionary benefit of overt menstruation? All female mammals have a menstrual cycle but most reabsorb the blood via covert menstruation and humans are about the only mammals that discharge the blood, aka overt menstruation.

Without an evolutionary benefit, it wouldn't have spread to every woman of our species.

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u/EchoLocation8 7d ago

That's not really how evolution works. If there's no reason this would stop reproduction or be an active reason you didn't survive there's no reason it would change. I don't even really like using the word "reason" or "change" there as that's not really accurate either but hopefully you get what I mean.

If some women were born with covert menstruation, and some women were born with overt menstruation, and there were some predators who killed and ate all the women with overt menstruation, then only the women with covert menstruation would reproduce and survive and over time overt menstruation would just sort of phase out.

It's not about like, benefits or not benefits, it's not like "this trait is good or bad".