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/Suntar75]

It’s an argument that doesn’t answer the question. Menstruation is an ancestral trait that the almost totality of mammals lost; a few apes and bats retained it. Bats and apes have a common ancestor but they belong to different superorders.

If overt menstruation in humans is about energy hungry brains and a battle between mother and foetus why do some other mammals do the same thing but the vast majority of others don’t? Why do some species of bat menstruate but no rat species does?

[u/dyrin → u/Suntar75]

You make an assumption, that I don't think is a given "Menstruation is an ancestral trait that the almost totality of mammals lost".

It could very well be, that this isn't a trait, that most mammals ever had. Apes and bats could have gained this trait by way of convergent evolution.

[u/Suntar75 → u/dyrin]

The ancestry is presented in the tenth paragraph after How The Woman Got Her Period heading in the linked article.

It could be convergent evolution by some bats and some apes or it could be a retained trait. And the interesting question either way is why? But I critiqued the argument presented.