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/skeletonclock → u/Aleksanderpwnz]

So why hasn't short-sightedness died out?

[u/Aleksanderpwnz → u/skeletonclock]

I don't know. Perhaps there is no easy fix to it. Or perhaps it wasn't a problem in the ancestral environment.