What's the evolutionary advantage of very long hair on human heads?
10h 32m ago by mander.xyz/u/Mothra in nostupidquestions
Most mammals seem fine with shorter hair (usually denser though). The only other case that comes to mind of very long hair restricted to a specific body area is that of horses manes, which to be fair I'm also not totally sure what purpose it serves. Many equines seem fine with shorter manes and tails that don't have such long hair, like zebras. They swish flies away all the same.
Some animals have long hair but it covers most of their bodies (like llamas or yaks maybe), it's not restricted to a small area. Other animals have denser or longer hair in some areas, like lions, but this serves a purpose (protection of the neck and head) and even then the length ratio between these longer hairs and the rest of the fur isn't as skewed as that of humans.
So, why? I get that hair on the head helps protect it from the elements and sun, but why so long? Some humans can grow hair longer than their own body length, which is remarkable, and without doing any fact check I'd say we are probably among the top 5 species with longest hairs ever. Is it just a showoff feature like a peacock's tail feathers, an indicator of overall health? Or does it serve another function as well?
I didn't mean to type this wall of text..., thanks for coming to my TED talk
Evolution doesn't produce perfect adaptations, just "good enough".
Humans lost their body hair and got more on their head when they developed walking upright in Africa.
Lets sweat cool the body down and protects the head from the sun.
At some point, something lead to a mutation that turned curly hair into straight hair, and that seems to have been selected for in populations living in colder climates.
But that doesn't mean it increased chances of survival. Maybe it was just preferred by sexual partners for some reason, which may even have been cultural at that point.
At some point, something lead to a mutation that turned curly hair into straight hair, and that seems to have been selected for in populations living in colder climates. But that doesn’t mean it increased chances of survival. Maybe it was just preferred by sexual partners for some reason, which may even have been cultural at that point.
Perhaps the hair change was the result of some other gene expression that was beneficial while the hair change itself was neutral-ish.
This reminds me of something I've been wondering about for a while now - burning hair has a distinct and very strong smell. That makes sense - if your hair is on fire, you want to know ASAP. My question is whether our hair evolved to have something in it that produces this smell, or if we just evolved to be particularly receptive to the smell of burning keratin.
That is of course ignoring the boring answers: "A little bit of both" and "It just worked out like that randomly", as well as the best answer "Wait, that's what that smell is?! Oh shit, you're right, I'm burning! AAAAAAAA!!!!"
You had it: people whose hair didn't smell when burning probably died more often, skewing the chances of survival towards smelly-when-on-fire hair.
How often were people catching on fire and not noticing that this would cause any kind of selection criteria?
People catch on fire a lot actually. I’ve caught my hair on fire dozens of times. It didn’t cover my whole head on fire because I noticed and put it out. Having long hair and cooking over a fire …. You’re occasionally going to catch on fire.
Does the subject's awareness of the selection matter?
The premise here was that they noticed in time to not die... So, yes?
Ah I misread it.
I reckon it's not so much about noticing in absolute terms (to notice vs not to notice), but rather about the smallest difference that smelly hair would make. Amplify that over millions of years and smelly hair has a good chance of being everywhere eventually.
I dunno. I'm just having trouble conceptualizing any kind of scenario that could happen with enough frequency to cause this trait to be selected for.
I think it's more likely that the chemicals in hair just happen to smell bad when burnt. Those chemicals may have been filtered for other reasons.
Yea that could also very well be, that it was pre-existing and had no impact during evolution. I could see there being an evolutionary advantage to hair smelling bad. That's as far as my confidence and knowledge reaches on the matter. Very interesting nonetheless! :)
Not what I was wondering about, but thanks.
At some point, something lead to a mutation that turned curly hair into straight hair, and that seems to have been selected for in populations living in colder climates
It feels cool to have curly hair despite being from a long line of cold climaters.
Way I figure, the common traits for any given part of the world where as much influenced by the isolation of groups as environmental factors. Back in primitive times it could take months wandering before you happened across another group, and even then there may be 'untrusted tribe' type conflicts.
It still shows up today in how rural isolated communities tend to foster more prejudiced attitudes towards people different from them. But now we can move all over quickly and communicate instantly, so there's a less concentrated effect by location. Plus the whole advent of ordered society and the host of factors that brings into play.
Something doesn't have to be an evolutionary advantage to persist in a population. If long hair doesn't impact fitness then it won't get selected against.
Long hair could also just be a sign of fitness in the same way colorful feathers are for some birds.
I think many see evolution as a smart process moving towards something or as improvement. That's correlation, it looks that way from the outside, but evolution is merely what survived long enough to reproduce most, and traits best for that and/or selected by a partner, are what get passed on.
I think you are looking at this from the wrong perspective, I think you are discounting sexual selection as a basis of why humans have long hair. I suspect the advantage is less this helps me to survive, and more this helps me to find a mate.
Another response pointed out the advantages of having dense curly hair and how and why we evolved with that, I think our ancestors used that starting point as a means of signaling health, youth, and vitality. And from there different hair types evolved as an expression of sexual selection.
We evolved to have heads of long thick hair because our ancestors found it attractive. And to this day it continues to be used (subconsciously or consciously) as a means of determining the sexual health of a potential mate.
If you think about it, when we get old or sick the hair is one of the first things to falter, not having a head of long thick hair doesn't necessarily mean you are unhealthy, but it is also difficult to maintain a head of full shiny head of hair without having a level of health and vitality.
Tldr: I think to this day hair is used as an indicator of sexual health from a potential mate, having long, thick hair can signal that health from a distance, and would be a distinct advantage in spreading those genes.
This is essentially my take. A large part of human morphology is driven by sexual selection.
If you (ie, your genetic code) are looking for a partner to reproduce with, health is likely the biggest factor to consider. You don't just want someone who is healthy, but someone who has a long history of health. Having long hair allows your potential mates to check health history. So as other humans hair gets longer, if yours stays short, you are essentially saying "I don't wanna talk about my health history", which is a turn off.
I'm not sure it's the primary reason long hair evolved in humans and I'm not a scientist, but I do know that you can use it kind of like handlebars/reins when you're hitting it from behind. Only with their full, notarized consent, obviously.
Just more evidence of the Grand Design!
Checkmate, atheists!
Well... More to my point... That means it's a liability, right ?because that's all fine and dandy when consensual but over the course of history more people have died as a consequence of getting caught by the hair than the offspring such long hair ever facilitated. I mean most military forces cut their hair for a reason. But I'm neither a scientist or a soldier so, I could be wrong too.
Wouldn't deaths from battlegrounds be too small (before world wars) to impact a group's genetics?
Depends on how common fights are. I heard that in very dangerous populations/times left-handedness is a lot more common, since attacking with the other arm than most people is a distinct advantage.
You’re misreading the process of evolution.
Not everything that is retained has an evolutionary advantage. It might simply come down to preferential choices resulting in the spread of the gene (say, horses’ mane - a female horse may prefer the look of a longer mane, resulting in that gene spreading and becoming ubiquitous, and a species-defining trait).
Humans evolved with dense curly hair, which protects you from the heat https://www.psu.edu/news/research/story/life-air-conditioning-curly-hair-kept-early-humans-cool
Oh yeah, and if you have really curly hair, it is effectively shorter
Yes, that's very interesting, and I also read about similar studies which explain pubic hair texture as having moisture isolating capabilities. However this doesn't address my question, which is about the apparently excessive length of head hair regardless of texture.
It does. Curling up makes the hair effectively shorter. And keeps it closer to the head.
A built in sun hat.
Demonstrates health history and general safety over the last potentially many years, which is good for status and attracting mates. The capacity to shear hair once stood as a statement of technological capacity and combat effectiveness: "I have a sharp knife."
Alright, that's true with the history since long hairs stay for years, good point. I'm not sure I follow with shearing and technological capacity, mind explaining that a little bit more please?
If you have a shaved face or cropped hair, it means you have access to and are possibly carrying a sharp blade. For a million years, that was high tech. It indicates that not only are you dangerous to fuck with, but you also probably have other advanced technology and culture.
I'm not claiming this is an evolutionary reason, I just think it's interesting.
That's an interesting take, agreed. But it doesn't explain why the length... You can still shave hair that doesn't grow too long. And look dangerous to fuck with
Yes, that is not an evolutionary pressure. Long manes serve the same function in humans as a peacock's tail or a baboon's bright red ass.
This is the answer
I read/heard something recently that they found evidence that it has to do with bipedalism and keeping the sun off of you. Don’t need fur all over to do that if you stand up straight and grow hair from the top. Still, adaptation and trait selection is incredibly complicated and you probably can’t boil this one down into a nice answer.
So why am I bald. Worse, I'm the whitest person in whatever city I'm in (when I was in Stockholm it was a tie), and as such burn easially if the sun hits my head.
Because all your testosterone receptors are on the top of your head, and when those receptors are doing their job the chemical that’s released has the side effect of inhibiting hair growth.
There are two different things coming into play here.
First of all, hair length evolved before long hair did.
Modern humans originally evolved tightly curled hair. Basically like we still see in many African populations. It's thought that this was an adaptation to protect against the heat of the sun. Basically like an insulated sun hat. The longer this curly hair grew, the more protection our natural hat provided.
As homo-sapiens populations moved further North, this protection was no longer needed - in fact there was the opposite problem, it was cold and rainy.
Greasy straight hair offers an advantage over curly hair in this kind of environment. It acts like a waterproof blanket, preventing the skin beneath getting wet, and it dries more quickly. Heat is lost through wet skin significantly faster than dry skin, and in situations where energy sources might be hard to come by in winter months, this can be a disadvantage.
We already had hair length sorted, so it was simply a matter of reacquiring the straight hair shape.
Europeans got a leg-up in this regard - Neanderthals appear to have had straight hair, and interbreeding definitely occurred. At this point it's worth remembering that by the time anatomically modern humans evolved in Africa, earlier hominids were already living all over Africa, Europe and Asia. Neanderthals were very similar to modern humans and shared an extremely close common ancestor.
And this is how, and why, some homo sapiens populations have long straight hair.
We do lose most of our heat from the head, so the original purpose might have been insulation
The notion that we lose most of the heat from our heads comes from a study where people wore warm clothes and no hats...
oh, interesting! Can I have a source please? I love learning new things!!
Why do we get an advantage from hairs longer than 60cm? 20cm already does the job, it even covers your neck.
Gutsick Gibbon has a pretty good video on this topic!:
https://youtu.be/EgZAVIJHTiM
The short answer is that it protects our heads from the Sun's radiation.
By the by, here is a picture of a really cute 
There is the fun aquatic ape hypothesis. It's a fun one, along with the stoned ape hypothesis. But unfortunately there's not a lot of actual evidence for either of them.
Funny idea what if its a remnant from the early tool use era where hair was used to make all sorts of stuff and people that had more long hair could do more stuff which increased their survival chance? Pretty sure thats nonsense but it would be funny imo
TLDR I, specifically, look more fabulous
mate selection, almost entirely. it's sensitive to body condition to the extent that if a woman sees the same hairdresser consistently enough they can somewhat reliably tell if she's gotten pregnant. it's also an easy indicator of social class and stability ie: do they have the time and resources to take care of it?