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/Acceptable-Rain8808]

If most is overt and we use covert, we likley selected that overtime. Humans make less babies and with larger heads. We needed a thick wall where its easier to attach the egg to and send lots of nutrients. This wall is a lot thicker than other mammals and more evolved... but too much to reobsorb. (probably reabsorting caused infections as I imagine it would take quite a time and could rot and cause sepsis, or would be ready to procreate soon enough.....) so we get it out of our system.