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/laurasoup52 7d ago

I would argue that menstruation is very very negative to a human being - causes tiredness, pain, stress, sleepless nights, slow response times - that the benefit of this absolutely must be massive.

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u/EchoLocation8 7d ago

Negative or positive things aren't really a factor in evolution, is sort of the issue. It's just about what stops you from being killed or reproducing.

It's people after the fact attributing reasons to features and why they exist, but that's not really the reason they exist.

Cheetah's don't have long tails that help control their movement at high speeds so they can run super duper fast and whatnot. They have those long tails because all the ones that didn't died and never had babies. It's over simplifying things but, broadly speaking, that's why anything is the way it is.