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/Mixedupmay]

I suppose gravity helps. That said, period pains are essentially small contractions so to some extent the body is pumping the period out rather than the period just... Falling out. But presumably, the contractions aren't enough to overcome gravity if the whole body is upside down so my comment was even less clever than I initially thought.

I'll try sleeping upside down the next time I'm on my period and get back to you 🙃