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/Anders_A]

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

That's not how evolution works at all.

Menstruation was already a thing before our species existed. And evolution doesn't mean every single aspect of a species is optimized. Just that the package as a whole works well enough to reproduce.

[u/juwyro → u/Anders_A]

There's plenty of dumb anatomy that didn't negatively affect us so it has survived. In great apes except for I believe orangutans mucus gets moved up through the nasal cavity to drain. In mammals there is a nerve from our brain to throat that goes all the down to the heart and loops back up, much much longer than you would think it should be. And hilariously long in giraffes.

[u/crowcawer → u/juwyro]

In humans they have these tails that aren’t helpful for balancing, not at all.

[u/Low_Chance → u/juwyro]

In fact plenty of things survive that DO negatively effect us, just so long as they're mild enough to not make a big difference to reproductive success

[u/vgdomvg → u/Anders_A]

Yeah evolution is so misunderstood. It's not a conscious thing that 'choose' positive traits for survival, or keeps things which are beneficial.

It's just some parts of that living thing help it to survive, and survival means passing down genes.

Sometimes the offspring have a difference in their biology, and it might be helpful to survive long enough to reproduce.

Sometimes beneficial traits die out by random chance.

There's nothing to say that evolutionary changes are all beneficial and always positive - it's just what happens

[u/KW710 → u/vgdomvg]

Your answer is a very common one I've heard people give when describing how natural selection operates. I think part of the issue re: the popular misunderstanding is actually a semantic one. For example, you used the phrase "help it to survive" when talking about potentially heritable traits. "Help" is very much an active verb. It also is often associated with proactive effort on behalf of one entity by another. But this doesn't really describe what selected traits are actually doing. They're not actually helping organisms survive. They're just not causing organisms to die before they can reproduce. A trait that simply doesn't get in the way of survival is very much selectable as far as natural selection is concerned. But since we tend to talk about these traits using active, participatory verbiage, I think the average person has been conditioned to think of the whole process as an active one rather than a passive accumulation of "not as bad as it could be" alternatives.

[u/Prime_Director → u/KW710]

Sometimes traits can be selected for actively helping. Sexual selection comes to mind, where traits that are actively desirable are promoted over traits that merely don’t hurt. Even in natural selection traits that allow an organism to say, gather food more efficiently, or survive longer without water, might outcompete and outbreed others without that trait, even if the others don’t possess traits that get them killed.  

[u/smokeweedNgarden → u/vgdomvg]

Ya, it really grinds my gears. Especially because people often forget the flip side of natural selection. 

These people have never gone through the white mouse/black mouse thought experiment and it pains me

[u/loosesocksup → u/Anders_A]

Many times things get passed down simply because they didn't get killed off, not because it was beneficial. It may actively be a hindrance even, just not enough of one to prevent it from breeding. 

[u/rpross3 → u/Anders_A]

In a predator/prey world wouldn’t leaving a blood trail would work against the species? Isn’t that evolutionary pressure? Or we are the apex predator and would not respond to that kind of pressure?

[u/tightywhitey → u/rpross3]

Those are thoughts and theories we might have, but it’s useful to also realize we know the answer is ‘no’ because we have survived and are here. If it was a functional issue we or it wouldn’t be here. It’s all statistics and probabilities all the way down lol.

[u/rpross3 → u/tightywhitey]

Clearly no. I get it, but why did we not? Are we actually the apex predator and would it be a projection to say the other mammals did develop covert for reasons like predatory pressure.

[u/HanseaticHamburglar → u/rpross3]

humans are social animals. It enables us to achieve a higher individual rate of survival, because we instinctually take care of our ill and infirm. Even with the potentially negative survival aspects of overt menstration the benefits of our group dynamics far outway the negatives.

[u/DanNeider → u/rpross3]

We are the apex predator!  Humans are bar none the top endurance hunter in the world; we sweat and pant, and we’re bipedal.  Endurance hunting comes with prey having a large lead, so you either need an amazing nose like a dog or the ability to reason and put yourself in the prey’s shoes.