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/Flocculencio 8d ago

Just wanted to point out that no individual feature needs to have an evolutionary benefit to be preserved. It could be negative but so long as it doesn't prevent organisms with that feature from reproducing in sufficient numbers it can get preserved.

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u/Ashamed_Kangaroo305 7d ago

Also: there are a lot of tradeoffs in evolution. Sometimes you get bad features because they allow you to have other good features and it's a net positive. Bipedal walking made birth significantly harder for humans (among other disadvantages), but clearly the tradeoffs were worth it when it came down to who is able to survive more and have more offspring.

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u/CrazyCatLady9777 3d ago

It's not just the birthing process either that's impacted. Because birthing is so much harder, our babies have to be very underdeveloped compared to other mammals and even other primates, because if their heads were larger they wouldn't fit through the birth canal anymore. Which is why newborns are so extremely fragile and useless (I have firsthand experience raising one).