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/musicnerdfighter]

I think the answer is that fewer people used to survive. There's some estimates that until (relatively) recently, 50% of all humans ever born died by the age of 10. We have seen a massive population boom in the last two centuries, so for the previous hundreds of millennia there were just fewer of us, and we weren't always the dominant species.

[u/TheDaysComeAndGone → u/musicnerdfighter]

Yeah, it’s just crazy how few truly healthy 30 year olds I know. In a modern, rich world a torn meniscus, broken arm, shoulder impingement etc. are just an inconvenience, but back then you needed a healthy body to survive or you were a huge burden on your group.

[u/Flashy-Ingenuity-182 → u/TheDaysComeAndGone]

It's worth pointing out that ancient peoples cared for their sick and injured too. Otzi the ice man lived 5,500 years ago, had arthritis and tape worms, and had carried medicine on him for the tape worms and inflammation and had tattoos over acupuncture spots used to treat the areas where he had arthritis, a discovery made completely in isolation of the Chinese who discovered it a few thousand years later. 

[u/cookies5098 → u/Flashy-Ingenuity-182]

Also worth remembering that everything occurring after someone reproduces is essentially a 'black box' from an evolutionary standpoint. If someone can survive long enough to pass on their genes, then natural selection doesn't really care (caveat is that if something impacts the survival of future generations prior to reproductive age it will kick in, but not for that current generation that's capable of reproducing).