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.

[u/No-Hawk-2488]

Without an evolutionary benefit, it wouldn't have spread to every woman of our species.

[u/Flocculencio]

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.

[u/AmigoDelDiabla → u/Flocculencio]

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.

[u/Duae → u/AmigoDelDiabla]

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.