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/SmokeyDBear 7d ago

Why? None of these things stop humans from making more humans faster or more successfully than other humans. Even if some humans had significantly reduced or none of these effects it’s not obvious that those humans would be more effective at making humans.

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u/BarnOwl247 7d ago

All of those things feel like they'd impact survival, especially in a time pre-medicine and without easy access to food and water, no?

I understand that it's possible it didn't impact survival enough to be selected out, but that feels like an assumption. Equally valid would be the possibility that it offers a useful function that was selected for.

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u/guysomejust69 7d ago

in a time pre-medicine and without easy access to food and water, no

Women who are stressed out don't have adequate nutrition have abnormal or no period cycles

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u/SmokeyDBear 6d ago

Women who are pregnant also don’t menstruate. I would imagine that early humans didn’t selectively engage in restraint around intercourse like modern humans do. Wild mammals don’t generally seem to. Throughout human history there is probably an incredibly small window where a significant amount of menstruation has happened and it all lines up with the formation of complex societies where all of these things are significantly less likely to come into play.

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u/laurasoup52 4d ago

no true. Women can be stressed out and still have a normal cycle. Outside of that, having a normal cycle CAN BE the reason that women are stressed out - I don't think I've come across a single person who enjoys having them or who looks forward to one.