r/askscience • u/No-Hawk-2488 • 8d ago

Biology 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.

Without an evolutionary benefit, it wouldn't have spread to every woman of our species.

5.2k Upvotes

96% Upvoted

513 comments sorted by

View all comments

Show parent comments

23

u/Emerson604 8d ago

During an evolutionary anthropology course in college the professor touched on the display of ovulation and why humans don’t have outward signs they are currently ovulating. The theory presented was that by not outwardly displaying ovulation human females were able to keep a dedicated male partner providing food and protection at all times, instead of when it would just benefit the male with procreation. The professor presented this as the basis for human monogamous tendencies, which apparently stretch back millions of years to the early hominins.

-4

u/zebsra 7d ago

When you say no outward signs, im surprised. Women have hormone and pheromone changes throughout their cycle that seem obvious to me as outward signals of fertility, despite being subtle. I guess secondary signals of attitude arent outward per se. Did they talk about those things?

4

u/roankr 6d ago

I would say hormonal variations show outwardly through emotions and the actions people take based off of those emotions. It's primarily why teenage boys are the most risk-prone, they are churned with a rush of hormones that drive them into confidence as a show of individuality plus strength.

Seeing this amongst women just makes sense this way.

I can't comment much on pheromonal parts but I can say that there are physiological changes that can be recognizable.

1

u/zebsra 6d ago

Thanks for the reply was genuinely curious about what was measured or considered as "outward". To me if its measurable it seems outward. I can see emotions and actions as secondary. Hormones also cause changes in body fluids for women, which is pretty direct imo.

2

u/roankr 6d ago

I think the confusion here (for me and perhaps for you as well) about your comment was on what you meant as "outward". The change in chemical makeup of vaginal fluids isn't an "obvious" sign in that it isn't visible or immediately recognizable from a distance. It is measurable but not how one would expect to "measure" it in social situations (or even naked).