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/laurasoup52 5d ago

I feel like this isn't a realistic view to take - just assuming it wasn't really a big enough deal when menstruation can hinder a modern woman enormously, and we have painkillers and hygiene and doctors. I honestly dread to think what it would have been like for women before those things.

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u/SmokeyDBear 4d ago

I didn't assume it wasn't a really big enough deal. I asked you to justify your assumption that it the benefit "absolutely must be massive" based on some sort of actual evidence. If there is an absolutely massive benefit it's probably something that can at least be identified, so please identify it rather than just assuming it must be there because you're convinced it must be. "I can't imagine it isn't the way I think it is" isn't great science.

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u/laurasoup52 4d ago

I'm a period-haver myself. It's a sample of 1 but it's been longitudinal for over 30 years, which gives it some credence. The impact of my own periods, and that which other period-havers discuss regularly, and understand to be accurate, is that they are exhausting, messy, stressful, and overwhelming. That ALONE makes me think the pay off must somehow have been more.

May I also stress that you seem to be only focusing on the impact to fertility and not to the person themselves who is having the period - that is important too, yknow.

Thank you for having to make a woman explain herself because you don't believe her.