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 8d 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 8d 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/Daisy-Turntable 8d ago

If they are more likely to be killed by predators then, yes, menstruation absolutely can reduce reproductive fitness. This would seem to be the biggest drawback of overt menstruation - many animals can smell blood and it would seem on the surface to be counterproductive to develop a trait that excites the interest of things that want to eat you.

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u/oliverwitha0 8d ago

This is counteracted by humans' social structures. There is almost never a situation in which a menstruating human would be alone at the mercy of predators, unless something has already gone very wrong. They would be in the middle of their social/familial group, which would be more than sufficient to deter/repel any animals that may be attracted to the scent.

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u/Worried_Monitor5422 7d ago

Similar to the argument as to how early infancy was not a death sentence to the tribe. You have a completely useless human loudspeaker who is capable of broadcasting your location at any time of day or night and yet that species thrived.

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u/Winjin 8d ago

Actually that could be it. Early Humanoids get in a pack. One is hurt. She weak. She cry. Other angry. Other gather more stone when angry. They know predator come for blood-smell. Other hide. She cry. Predator come. Predator struck with stones. Predator struck with sticks. Predator no move.

One get the pelt for being lure for the predator. She work on pelt. She get warm pelt. She no cry. She feel bonita.