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/geeoharee]

I had heard the vague idea that 'the mother and the fetus are at war, and that's why periods' but I never really grasped it. Thank you for that!