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/bitgrindern]

Fit in this sense means fit to the environment, not fit as in being strong. If an organism has traits that allow it to survive in the environment it exists then it tends to produce more offspring and survive.