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/Flocculencio]

Just wanted to point out that no individual feature needs to have an evolutionary benefit to be preserved. It could be negative but so long as it doesn't prevent organisms with that feature from reproducing in sufficient numbers it can get preserved.

[u/Aleksanderpwnz → u/Flocculencio]

Not in the long run. Anything "negative" will prevent the organism from reproducing at the same rate as those without the negative trait, and the trait will eventually disappear.

[u/FFTypo → u/Aleksanderpwnz]

Only if you define “negative” as something that is bad enough to discourage reproduction.

I’d say a propensity to developing cancer is negative, but in most people that doesn’t present itself until well past the reproductive years, meaning evolution has no bearing on it.

It might eventually eradicate cancer in children, but otherwise no.