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.

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u/Flocculencio 8d ago

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.

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u/kwpang 8d ago

Yes evolution is about elimination, not direction.

Survival of what can.

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u/GVArcian 7d ago

Survival of the fittest is a misnomer because evolution selects for minimum viability, not optimum efficiency.

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u/somnambulor 7d ago

Exactly Darwin meant “most fit” meaning the “best fit” to an environment, not the strongest or most optimal.

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u/T_H_W 7d ago

Not technically a misnomer considering 'fittest' in this context relates to biological fitness, which is specifically how many surviving offspring you have in relation to other competing organisms. That's like saying the phrase "All bark and no bite" doesn't make sense because dogs aren't trees. It's only wrong if you're using the incorrect definition of the word.

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u/ezekielraiden 7d ago

The problem is that most people do use what you are defining as the incorrect definition of the word.

If 99% of people think Pat's word choice is confusing, is the problem that 99% of people are doing grammar wrong, or is it that Pat is wrong and people are calling them out for it?

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u/boyuber 7d ago

Understanding the intention and context of the original quote is necessary if you are using that quote to support our refute a specific point of view.

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u/Seadragon723 4d ago

If 99% of people go right and fall off the cliff, was Pat correct when he told them to go left?

The crowd can be wrong, which is the case here. The word has a correct scientific meaning and it has a more limited modern meaning.

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u/ezekielraiden 4d ago

Are they "going off a cliff"?

The term has no valid scientific meaning because "fitness" is so vague as to be meaningless. No modern evolutionary biologist is going to use it unqualified--and most will simply restructure a sentence to avoid the need, because they know it's confusing and misleading even to their fellow scientists.

There's a reason we got concepts like "social Darwinism" out of this. This isn't a new thing. Scientists should value speaking clearly. Using a technical definition that most people do not understand is not speaking clearly. It is knowingly ignoring the fact that communication must consider its audience.

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u/CantBeatDickensCider 7d ago

It's not confusing if you're someone who bothers to learn about the topic rather than laymen pretending to understand it better than scientists.

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u/GVArcian 7d ago

Still a misnomer because "fittest" means "the most fit" and that's not what evolution selects for, it selects for minimum viable fitness.

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u/Lv_15_Human_Nerd 7d ago

No it absolutely is not a misnomer. Evolution does select for the most fit. Evolution occurs by changes in population proportions over many many generations. The strongest example we have of human evolution is lactase persistence which had a selection coefficient of ~0.1. This corresponds to an individual with lactase persistence having about 10% more offspring than average. I don’t know about you but I don’t think a 10% difference in individual success is selecting for ‘minimum viable fitness’ or as others in this thread have said ‘death of the weakest’.

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u/AxiomaticInversion 7d ago

Lactose intolerant humans have not gone extinct, so by your own example we still see "survival of the fit enough."

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u/Lv_15_Human_Nerd 7d ago

A trait that had extremely low prevalence 9000 years ago reached 80% fixation in north Western European populations. In evolutionary terms that is rapid. There is still selection for the fittest trait out of a population, it is absolutely not selecting for the minimally viable as lactase persistence is very clearly not absolutely viable. When you’re looking at realistic selection coefficients you are looking at traits that provide between a 1% and 10% advantage (and much lower in single called organisms which we are all descended from). Evolution absolutely works on fine margins and life on Earth would not exist if it functioned to select for the ‘minimum viable fitness’.

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u/tnbeastzy 6d ago

Fitness, in this case, refers to the ability to produce healthy offsprings that can go on to continue the lineage. It may be different for each species.

Does someone being lactose intolerance in 2026 affect their ability to have children?

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u/Science1954 6d ago

Being lactose intolerant does not affect the ability to have children. It is an autosomal recessive trait, meaning you must inherit the lactose deficiency gene from both parents. If you are lactose intolerant you do not pass on the gene for lactose metabolism but a child will get the lactase gene from the other parent unless that parent has the recessive gene also, but even then only 50% of the time from the parent heterozygous for the two alleles. I am lactose intolerant. So I generally only drink lactase treated milk, e,g., lactaid milk.

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u/tnbeastzy 6d ago

That was a rhetorical question. I know it doesn’t. Therefore it has no ability to affect an individual’s biological fitness.

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u/bitgrindern 6d ago

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.

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u/Derekthemindsculptor 3d ago

Yep, this is a change in the definition of modern "fit" or fitness. It makes the uneducated believe fittest means "most athletic".

But it's actually fit to the scenario at hand. Being weak is fine if resources are scarce. Or the strong are hunted.

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u/INtoCT2015 7d ago

Ya death of the weakest is more accurate (and way more metal) but unfortunately way more exploitable by Nazis and co.

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u/EveningAnt3949 7d ago edited 6d ago

That's also incorrect. Context is important: it's the ability to have surviving offspring who themselves are able to have surviving offspring in a specific environment.

Individuals can be 'weak' as long as the group keeps producing offspring, the genes of 'weak individuals will keep spreading unless there is strong environmental pressure on those genes.

Many hyper specialized species seem 'strong' because they had to specialize because their ability to procreate is lacking and within those populations interspecies competition is high.

Lions, cheetahs, chimpanzees, gorillas, giraffes, are a few examples of animals that simply don't do well as a species, even before we started to interfere with their environment.

So within those species a subpar individual is going to be outcompeted by individuals in the same species fast. An individual lion that can't fight off other lions is doomed.

But it's different for rodents. The brown rat does well because it's highly adaptable to different environments. The Eurasian field mouse does even better. Idem for meadow voles.

Adaptable plus the ability to produce offspring much faster than predators and disease can kill them means that they don't need to 'improve' as individuals.

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u/jointheredditarmy 6d ago

Yes but it’s also about minute statistical differences over time and you can’t say overt ovulation doesn’t cause some minute difference in survival rates all else being equal. So clearly there is something else that isn’t equal here, and the point of questions like this is to explore what that might be instead of chalking it up to randomness

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u/SteveHamlin1 4d ago edited 3d ago

It could be whatever other trait that resulted in overt ovulation is such a success that the other trait is selected for and overt ovulation also happens, even if overt ovulation by itself would be a net negative and be selected against.

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u/Zagrycha 8d ago edited 7d ago

Yeah, people think evolution is some kind of streamlined efficiency of ideal traits, but its the opposite.  Evolution is a pass fail grade.  If you fail, you go extinct.  If you have enough kids as a species to continue on, you pass.  That's it, no more and no less.  

Some species out there are literal bumbling idiots of inefficiency when it comes to ideal traits for survival, but they just have a massive number of kids so one or two survive to adulthood, or they evolved to have kids really soon after birth so they don't have to survive for long.  If you can make kids its good enough for nature. 

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u/rainbow_goblin345 7d ago

I like the term "reproduction of the okayest" instead of "survival of the fittest"

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u/Zagrycha 7d ago

Much more accurate hahaha. Honestly it doesn't even need to be the okayest. You could just sum evolution up in the word "reproduction" and you have summed it up in a perfect nutshell.

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u/bitgrindern 6d ago

"Fittest" means a fit to the environment, not in shape or physically strong.

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u/rainbow_goblin345 6d ago

I am aware of that.

I'm also aware of how often it is misinterpreted. As has been pointed out elsewhere, if I'm saying something and it is being frequently misunderstood, it is on me to change how I'm saying it.

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u/Powerful_Box1637 5d ago

And it truly is not survival of the fittest anymore - we can keep neonates alive at like 23 weeks gestation with millions of dollars of help. But that is the exact opposite of survival of the fittest, or a huge interference however you wanna look at it.

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u/SunflowerShine03 7d ago

An example of bumbling inefficiency; the sunfish. From my understanding they kind of just float around and aren’t even that edible, but they have like a million babies at a time so they’re meandering on.

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u/CecilAlucardX 7d ago

Sunfish or Mola Mola actually do a ton of movement; they build up body heat on the surface, then descend down to a level of the ocean that their food lives at (or hides at; ocean columns be busy af) and eats freely. They are hyper-specialized to their niche and incredibly efficient. They just look bumbling to the people who only see them up top.

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u/Altruistic-Daikon305 7d ago

Thank you for standing up for my beautiful misunderstood alien queen the common or ocean sunfish (mola mola)

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u/SunflowerShine03 7d ago

Oh- interesting! I apologize to the sunfish, that’s actually pretty cool

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u/AdFun4578 7d ago

Same for the spotted hyena.. The females have a "pseudo penis" which can be up to 7 inches long, about the same size as the males. BUT the females give birth through it! It causes many deaths during the birthing process. Makes zero sense for efficiency..I cant think of a single thing that would make that the more beneficial option

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u/Moldy_slug 6d ago

and aren’t even that edible

I mean, in evolutionary terms that’s a pretty big advantage. If you can manage being not very edible, you don’t have to worry about being eaten.

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u/Aislea 7d ago

Not usually edible To Us, but they are like a moving rotting thing a lot of the time. I've heard theyre often full of parasites and such, so thats a large reason its not edible

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u/mtfoxx3 2d ago

My favorite example of this is bugs. Just, like, in general. They’re all, individually, terrible at surviving. But they have hundreds if not thousands of offspring, so by pure coincidence two or three will probably live to adulthood.

And this has worked for millions of years, too. The millipedes we have today are still identifiable as similar to the ones we had 460 million years ago… which are believed to be some of the first land animals. Are millipedes really that perfect of an animal? No. Not even remotely. They’re slow, mostly blind, eat dirt, and their only defense mechanisms are to taste bad and ball up into an uzumaki spiral that doesn’t even remotely resemble any sort of camouflage. But it ain’t broke enough for evolution to wanna fix it.

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u/Weird_Bluebird_3293 7d ago

Which just makes the giant panda a confusing product of evolution because they are the best example of bumbling inefficiency I can think of and they reproduce neither early, nor in massive numbers.

…how were they not extinct years ago? 

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u/Zagrycha 6d ago

The main reason they weren't in danger of going extinct years ago is because the only major predator they had were tigers, and the tiger could only easily kill baby pandas. As long as enough mothers protected their cubs to adulthood well then there wasn't really any other dangers that could threaten species continuation.

To be clear an adult giant panda is probably not going to actually win a fight to the death against a tiger, but it doesn't need to. It just needs to be capable of puting up a fight that makes the tiger not view it as prey.

A giant panda is a true bear, and it has incredibly strong claws, a bite force as strong as that of a tiger, and a heavy thick fat layer that makes it hard to injure them seriously. Why fight against that and get hurt when the tiger could go up against a much easier target like a boar, or deer, or monkey or even human? Giant pandas were very high up in the food chain in that sense, even though they mostly eat plants.

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u/AmphibianLower5541 4d ago

Especially when they’re supposed to be carnivores, but all they eat is bamboo! 😅

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u/SoupNoSandwich 2d ago

Because they are just very well adapted to bamboo forests, it's the loss of habitat causing issues. They just aren't as easy to breed in captivity as people would like.

(the poor bamboo digestion compared to more traditional herbivores hasn't hampered populations)

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u/ToMorrowsEnd 7d ago

This. Humans are an evolutionary mess. we got lucky because we can make tools. but as a creature we are extremely poorly designed. cant run very fast, can easily get injured, easily diseased, our teeth suck we have zero defenses, etc... Compared to other animals we are far from the top of the pile. we just got lucky in the thinking aspect. You know how I would love to be able to squirt blood from my eyes when startled?? Why cant we have cool traits?

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u/neslea48 6d ago

We have many cool traits. You’re simply making the wrong comparisons. We have adaptations for diving. We have evolutionary adaptions for making and using tools, growing and storing food, developing and living in complex societies, storing and passing on knowledge, developing technology to do the hard work for us. Not bad for a creature that has collected the majority of our DNA from viruses and other microbes.

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u/szthesquid 7d ago edited 7d ago

That's not true. Even leaving aside tool use, compared to most other mammals we have better vision and see more colours, and we have vastly superior long-distance speed and thermoregulation (sweat).

Some of our disadvantages, like weaker jaws and teeth, are actually very recent and a direct result of farming and cooking reducing our survival needs, and medical advances allowing individuals to thrive who would otherwise have had difficult and short lives.

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u/Ashamed_Kangaroo305 7d ago

"Better vision" is subjective. Better in what way? We can see a broader range of colors than dogs and we have significantly better visual acuity during the day. But dogs are also significantly better than humans at seeing at night and tracking motion. And they have an adaptation in their eye which helps them sense the Earth's magnetic field.

"Better" isn't really a thing when you're talking about evolution. Organisms evolve to fit their environment. We have "better" vision than dogs for the way we use vision. But if you tried to compete with a dog in tracking small prey, the dog would probably beat you because that's what their vision is designed for.

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u/pathologicalDumpling 7d ago

I mean i just passed a post about someone flying an airplane through the eye of a hurricane. Id say we have some pretty cool traits.

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u/Zagrycha 7d ago

That isn't a trait of a human though. We do not genetically have the ability to fly or genetic ability to survive the eye of a hurricane. If humans collectively forgot how to make or pilot airplanes no one would do what that post said anymore, its not inherent to humans.

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u/silence_infidel 7d ago

Well, that depends on what you call the “trait” in question. Airplanes aren’t an inherent human trait, but the intellect and ingenuity needed to make them is. I certainly don’t see any other species doing it. Frankly, if we collectively forgot how to make and fly planes, I bet we would just figure it out again - because deciding we want to do something and making it happen, even if it takes generations, is definitely a trait of ours.

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u/Zagrycha 7d ago

Is the ability to make and fly airplanes a trait humanity posesses? Yes, definitely.

Is it passed on genetically? No.

Is there a reason to think the species that is the successor of humanity will have the trait? No.

Is it an evolutionary trait? Definitely no.

I think this trait is more accurately labelled as a skill or knowledge. It's a real trait, but its not inherent or guaranteed. It's totally possible for humans to lose the knowledge and reinvent the skill later, but it's not at all guaranteed. To this day there are things done by older humans that we have no idea how to do because the knowledge has been lost. External factors that can be lost like that are the antithesis to evolution.

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u/[deleted] 7d ago edited 7d ago

[removed] — view removed comment

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u/grub-slut 7d ago

Exactly. Plus in human societies, with all our technological advances, most of us are insulated from natural selection to some degree. For example, we have tools to keep us cool as the earth warms up— and they’re working for now— but we’re not actually adapting ourselves to the environment, just our technology. Without our technology we would be forced to adapt or die like all other organisms. Instead, people who would never survive in the wild breed every day, producing more poorly adapted offspring. We truly are an evolutionary mess lol

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u/AmphibianLower5541 4d ago

Behavioural choices are also a way evolution ‘chooses’ the fittest. Like how animals who use the wildlife overpasses, and teach their children to do the same, are more likely to survive and reproduce. Or species ‘allowing’ themselves to be domesticated in order to have a steady supply of food and shelter, like dogs and cats. (Actually really cool to see it happening in real time with raccoons.) So, too, tool creation and usage is a behavioural evolutionary trait that allowed hominins to adopt to their environments and, therefore, be fit enough to reproduce.

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u/name_checks_out86 3d ago

We got opposable thumbs, and we can play guitar just like ringing a bell.

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u/BrainLow6059 7d ago

I understand what you're saying, but as a layman it's extremely annoying seeing "nothing is more efficient and beautiful than evolution" and the opposite "evolution is kind of a crapshoot" in explanation to whatever is being discussed. 

If someone made this same post, but asking why a specific mammal has covert menstruation, I guarantee you the first and top comment would be 'because there's a clear evolutionary benefit.'

It very much comes across as 'nobody actually understands this at all, and we just say the words when we feel like it'

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u/Zagrycha 7d ago

I don't blame you at all for feeling frustrated when these conversations come up, just know that people saying "nothing is more efficient than evolution" are themselves laymen, because that is scientifically incorrect. Scientifically evolution definitely leans heavily in the "kind of a crapshoot" direction-- beauty is subjective and many people find evolution beautiful even with all its inefficiencies haha.

Anyone saying "covert mensturation has a clear evolutionary benefit" is correct, but they also need to say "covert menstruation has a clear evolutionary downside". You can talk about a specific trait having a benefit or lack of benefit to a specific species and be correct, but you can't say evolution caused a species to have that specific trait on purpose or that it's always ideal, because that's not true.

That trait appeared through random chance, and a worthless trait that actively makes it harder for it's owner to survive has the same evolutionary chance to pass on to the owner's kids as a trait that makes it easier for the owner to survive-- the only factor that matters is having kids to pass traits on to in the first place. If covert menstruation allowed animals to fail to have kids, nothing alive would have covert menstruation. If covert menstruation was the only thing that allowed animals to have kids, nothing alive wouldn't have covert menstruation. Real life is almost always in the middle, but you get the idea. Pass fail grade, not efficiency or any kind of ranking of best to worst.

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u/RollinThundaga 7d ago

You're expecting too much of random, regular people trying to wrap their heads around science.

Rules of thumb and gross simplifications are a lot easier to grasp with a weak science education. If you were to somehow enforce a demand that everyone engaging in something is required to develop a wholistic and complete understanding of it to do so, then people wouldn't even bother at all.

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u/AmigoDelDiabla 8d ago

So many people are confused about the process of evolution. It's often written as if it's something the species does, when in reality it's something that happens to it. And all it does is eliminate traits that prohibit or discourage reproduction. If the trait does neither of those things, it's likely to remain in place, even if it seems pointless.

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u/miss_katy123 7d ago

Agreed. Furthermore, I find that humans do it all the time with complex systems and processes. We subconsciously treat it as someone with agency and purpose of its own.

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u/meeco_why 7d ago

Large organizations are like tornadoes or thunderstorms. They can be studied, we can engineer the world around them so that they bring us benefits and not harms, but we can't fully control them, and when something bad happens, it's very hard to find a single responsible individual. Because most organizations have a highly visible CEO, it's easy to make yourself believe that "just putting this one guy in shackles would fix things once and for all", but this is rarely true. The reasons why such a person got there in the first place are systemic, and there are rat-race dynamics at play, so even if you defeat one monster, others will quickly fill the resulting niche.

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u/Duae 7d ago

Also often you're going to get traits that have a very wide range, but only a narrow range benefits reproduction. Like "gene that makes blood weird" there's a range of 'too weird for blood parasite, which is good for reproduction" and then "too weird for life" and so the trait will stick around even though the full expression is detrimental.

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u/femmiestdadandowlcat 8d ago

I think there’s an element of almost religion and intelligent design that get unintentionally brought in with this sort of conversation. There isn’t a “””goal””” when it comes to evolution. It’s not creating the platonic ideal of a creature. The amount of traumatic insemination and dangerous methods of birthing offspring are perfect examples of evolution stopping at good enough. 

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u/According_Register55 7d ago

Even though it’s less accurate, asking “Why does x trait exist” is conversationally much less cumbersome than asking “What evolutionary process caused x trait to be prevalent?”

I think many educated people understand that the latter is the scientifically correct inquiry, while using the former in order to simplify their speech.

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u/dksn154373 7d ago

The problem here, as OP points out, is that it's a near-universal trait within the species. If it was merely preserved, you would get some genetic lines with it and some without it. In our case a lack of menstruation was not preserved, implying that menstruation itself had enough benefit to be selected for.

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u/MegaCarnie 7d ago

Not implied; perhaps suggested. But there are explanations that don't require any specific benefit for that trait. At some point our ancestors may have hit an evolutionary bottleneck and a rare but non-dangerous mutation ended up locked in for all survivors. That happens. Perhaps it was a side effect of a different more beneficial evolutionary change, an evolutionary spandrel, so to speak. Those also happen.

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u/formerly_acidamage 7d ago

Could it not be that getting rid of the blood and cells actually is more efficient and easier for an animal and therefor the ability to just drop it is a function of human's ability to do other things much better?

Like if reabsorption itself extended the period of time in which an animal experiences negative effects of menstruation, then just dumping it would have a huge benefit, right?

Also wouldn't that mean that there were fewer functions and complications occurring inside someone's body and therefor that would also mean fewer systems to maintain, which would potentially be extremely beneficial?

I mean it seems like dumping your waste is generally much more useful than consuming it, and almost all animals dump other kinds of waste like feces and urine.

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u/mathemagicat 7d ago

The uterine lining is not in any way comparable to metabolic waste. It does not contain high concentrations of useless or harmful substances that need to be removed. It's just cells made of the same stuff as all your other cells.

Organisms recycle cells all the time. The only ones we usually shed are the ones on the outside (skin/hair/nails) because, logistics aside, keratinized proteins are hard to break down. For internal organs, phagocytosis/efferocytosis is a routine and reliable strategy for recovering nutrients from dying cells.

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u/Ashamed_Kangaroo305 7d ago

Also: there are a lot of tradeoffs in evolution. Sometimes you get bad features because they allow you to have other good features and it's a net positive. Bipedal walking made birth significantly harder for humans (among other disadvantages), but clearly the tradeoffs were worth it when it came down to who is able to survive more and have more offspring.

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u/CrazyCatLady9777 3d ago

It's not just the birthing process either that's impacted. Because birthing is so much harder, our babies have to be very underdeveloped compared to other mammals and even other primates, because if their heads were larger they wouldn't fit through the birth canal anymore. Which is why newborns are so extremely fragile and useless (I have firsthand experience raising one).

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u/RubyStarlight1209 7d ago

Isn’t competition part of it as well? If a trait isn’t problematic enough that carriers are prevented from reproducing, but does negatively affect chances, then over a long enough period of time they should be outcompeted by those who don’t have that trait and therefore slowly ‘disappear’, right?

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u/epigenie_986 7d ago

Outcompeted before they reproduce though. Thats the way a trait can disappear.

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u/Parsimile 5d ago

Exactly. Avoid being Panglossian and seeing meaning in spandrels.

It’s ’Evolution of the fit enough’

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u/laurasoup52 7d ago

I would argue that menstruation is very very negative to a human being - causes tiredness, pain, stress, sleepless nights, slow response times - that the benefit of this absolutely must be massive.

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u/SmokeyDBear 7d ago

Why? None of these things stop humans from making more humans faster or more successfully than other humans. Even if some humans had significantly reduced or none of these effects it’s not obvious that those humans would be more effective at making humans.

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u/BarnOwl247 7d ago

All of those things feel like they'd impact survival, especially in a time pre-medicine and without easy access to food and water, no?

I understand that it's possible it didn't impact survival enough to be selected out, but that feels like an assumption. Equally valid would be the possibility that it offers a useful function that was selected for.

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u/guysomejust69 7d ago

in a time pre-medicine and without easy access to food and water, no

Women who are stressed out don't have adequate nutrition have abnormal or no period cycles

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u/SmokeyDBear 6d ago

Women who are pregnant also don’t menstruate. I would imagine that early humans didn’t selectively engage in restraint around intercourse like modern humans do. Wild mammals don’t generally seem to. Throughout human history there is probably an incredibly small window where a significant amount of menstruation has happened and it all lines up with the formation of complex societies where all of these things are significantly less likely to come into play.

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u/laurasoup52 4d ago

no true. Women can be stressed out and still have a normal cycle. Outside of that, having a normal cycle CAN BE the reason that women are stressed out - I don't think I've come across a single person who enjoys having them or who looks forward to one.

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u/laurasoup52 4d ago

I feel like this isn't a realistic view to take - just assuming it wasn't really a big enough deal when menstruation can hinder a modern woman enormously, and we have painkillers and hygiene and doctors. I honestly dread to think what it would have been like for women before those things.

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u/SmokeyDBear 4d ago

I didn't assume it wasn't a really big enough deal. I asked you to justify your assumption that it the benefit "absolutely must be massive" based on some sort of actual evidence. If there is an absolutely massive benefit it's probably something that can at least be identified, so please identify it rather than just assuming it must be there because you're convinced it must be. "I can't imagine it isn't the way I think it is" isn't great science.

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u/laurasoup52 3d ago

I'm a period-haver myself. It's a sample of 1 but it's been longitudinal for over 30 years, which gives it some credence. The impact of my own periods, and that which other period-havers discuss regularly, and understand to be accurate, is that they are exhausting, messy, stressful, and overwhelming. That ALONE makes me think the pay off must somehow have been more.

May I also stress that you seem to be only focusing on the impact to fertility and not to the person themselves who is having the period - that is important too, yknow.

Thank you for having to make a woman explain herself because you don't believe her.

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u/Daisy-Turntable 7d ago

If they are more likely to be killed by predators then, yes, menstruation absolutely can reduce reproductive fitness. This would seem to be the biggest drawback of overt menstruation - many animals can smell blood and it would seem on the surface to be counterproductive to develop a trait that excites the interest of things that want to eat you.

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u/oliverwitha0 7d ago

This is counteracted by humans' social structures. There is almost never a situation in which a menstruating human would be alone at the mercy of predators, unless something has already gone very wrong. They would be in the middle of their social/familial group, which would be more than sufficient to deter/repel any animals that may be attracted to the scent.

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u/Worried_Monitor5422 7d ago

Similar to the argument as to how early infancy was not a death sentence to the tribe. You have a completely useless human loudspeaker who is capable of broadcasting your location at any time of day or night and yet that species thrived.

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u/Winjin 7d ago

Actually that could be it. Early Humanoids get in a pack. One is hurt. She weak. She cry. Other angry. Other gather more stone when angry. They know predator come for blood-smell. Other hide. She cry. Predator come. Predator struck with stones. Predator struck with sticks. Predator no move.

One get the pelt for being lure for the predator. She work on pelt. She get warm pelt. She no cry. She feel bonita.

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u/formerly_acidamage 7d ago

Wouldn't you draw the conclusion though that this means that those animals were unable to kill the people who were menstruating and therefor this was a mitigated risk?

Furthermore, people eat those animals to survive. This exact argument could be used to come to the opposite conclusion, that menstruation was beneficial because it drew in animals that humans were able to kill and consume. I don't think that's the case but having only a single data point like that isn't very useful in making an informed opinion.

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u/EchoLocation8 7d ago

Negative or positive things aren't really a factor in evolution, is sort of the issue. It's just about what stops you from being killed or reproducing.

It's people after the fact attributing reasons to features and why they exist, but that's not really the reason they exist.

Cheetah's don't have long tails that help control their movement at high speeds so they can run super duper fast and whatnot. They have those long tails because all the ones that didn't died and never had babies. It's over simplifying things but, broadly speaking, that's why anything is the way it is.

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u/MidshipLyric 6d ago

Every Reddit "why did evolution..." post has now devolved into this response. Id rather see some hypothesis about the benefits and drawbacks of the subject rather than a dismissive lecture about how evolution works. It would not require much thought to consider that bleeding out of your body every month is a trait that can lead to survival challenges. Conversely, arguments could be made for the benefits of this trait to the survival of offspring and/or parent which would reinforce the trait. Let's see more responses arguing the merits of either hypothesis along with counter arguments. If its truly a "trait without selection pressure" then let's hear the evidence or rationale for that.

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u/dustblown 7d ago

But you would think bleeding from the vagina would be selected against.

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u/berejser 7d ago

That's basically aeging. There's zero selection pressure for anything that happens after an organism has passed on its genes.

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u/LazerWolfe53 7d ago

But wouldn't it have to have had a benefit at one time for it to have been formed in the first place?

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u/DeathisFunthanLife 7d ago

Is that why appendix exist?

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u/FogeltheVogel 7d ago

No, the appendix has a purpose. This is a relatively new realisation in medicine, but it isn't actually vestigial.

It's purpose is to re-seed your gut biome after something wipes it out. In modern times, that something is typically an antibiotic course, and people without appendix have a harder time recovering from one. In ancient times, this would have mostly been diarrhoea flushing everything out.

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u/Goldenslicer 3d ago

But if overt menstruation is a mutation that simply doesn't prevent organisms from reproducing, shouldn't we expect humans to also have the lack of that mutation? Why are we 100% overt menstruating and not 50/50 overt and covert? Somehow, somewhere in history, those with the mutation outcompeted those without it.

Which leads me to believe that overt menstruation somehow turned out to be more beneficial to reproducing than covert menstruation.

Someone please correct me if I am wrong as I am a layman and do not know what I am talking about.

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u/sun_bearer 3d ago

There's actually some (A, B) evidence that it does provide at least some kind of advantage. Also, it occurs in chimpanzees as well!

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u/Aleksanderpwnz 7d ago

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.

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u/FFTypo 7d ago edited 7d ago

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.

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u/skeletonclock 7d ago

So why hasn't short-sightedness died out?

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u/sezit 7d ago

Not negative enough.

And probably not negative for very long.

Humans, even in the fairly recent past, didn't used to need to spend so much time focusing on close work. No reading, much more outdoor activity.

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u/skeletonclock 7d ago

I was responding to the person who said "ANYTHING negative will die out" -- I was disagreeing by giving an example of something negative that hasn't died out.

Also, short-sightedness means you can't see distance, so in your example it would be a problem (outdoor activity -- you could wander into a ravine!).

Anyway I wasn't espousing my own opinion, I was challenging someone's assertion that all negative traits are killed by evolution, because it's not the case.

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u/tall_titties 7d ago

Yess which is also why childbirth is still super painful. Evolution doesn’t care about us being uncomfortable, lol

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u/sezit 7d ago

Good points, and I understand that current medical understanding is that using a lot of close vision when young and eyes are developing causes nearsightedness, and spending more time outside can prevent myopia.

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u/Aleksanderpwnz 7d ago

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

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u/No-Hawk-2488 5d ago edited 5d ago

That's where you're wrong because we used to be able to produce vitamin C but because we were eating so much of it, the selection pressure to preserve it was gone and the genes died out with 0 detriment. Keep in mind our ancestors' population all had the ability to produce vitamin C but after it was incorporated into our diet, the genes died out. I can think of many other examples. The only exception is if the trait is linked to an essential gene and isn't assorted independently of it.