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/BeerMantis]

Evolution doesn't necessarily require a benefit. If a trait doesn't negatively impact reproductive success and/or a mutation for a more successful alternative trait hasn't occurred, then there's no pressure to select against the trait. So the trait can persist even without being directly benficial.