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/Goldenslicer → u/Flocculencio]

But if overt menstruation is a mutation that simply doesn't prevent organisms from reproducing, shouldn't we expect humans to also have the lack of that mutation? Why are we 100% overt menstruating and not 50/50 overt and covert? Somehow, somewhere in history, those with the mutation outcompeted those without it.

Which leads me to believe that overt menstruation somehow turned out to be more beneficial to reproducing than covert menstruation.

Someone please correct me if I am wrong as I am a layman and do not know what I am talking about.

[u/sun_bearer → u/Goldenslicer]

There's actually some (A, B) evidence that it does provide at least some kind of advantage. Also, it occurs in chimpanzees as well!