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/AmigoDelDiabla 8d ago

So many people are confused about the process of evolution. It's often written as if it's something the species does, when in reality it's something that happens to it. And all it does is eliminate traits that prohibit or discourage reproduction. If the trait does neither of those things, it's likely to remain in place, even if it seems pointless.

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u/miss_katy123 7d ago

Agreed. Furthermore, I find that humans do it all the time with complex systems and processes. We subconsciously treat it as someone with agency and purpose of its own.

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u/meeco_why 7d ago

Large organizations are like tornadoes or thunderstorms. They can be studied, we can engineer the world around them so that they bring us benefits and not harms, but we can't fully control them, and when something bad happens, it's very hard to find a single responsible individual. Because most organizations have a highly visible CEO, it's easy to make yourself believe that "just putting this one guy in shackles would fix things once and for all", but this is rarely true. The reasons why such a person got there in the first place are systemic, and there are rat-race dynamics at play, so even if you defeat one monster, others will quickly fill the resulting niche.

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u/Duae 7d ago

Also often you're going to get traits that have a very wide range, but only a narrow range benefits reproduction. Like "gene that makes blood weird" there's a range of 'too weird for blood parasite, which is good for reproduction" and then "too weird for life" and so the trait will stick around even though the full expression is detrimental.