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Old 10-21-2019, 07:12 AM
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Origin of Head Hair.


Why do humans typically have hair on their heads? Bald people obviously don't. But still.

Yes I know evolution has something to do with it. But how? And why?

Also I remember watching this news magazine on TV, oh, well over 30 years ago when I was still in HS. And they were speculating about humans in the future. And they said since we'd be living in sterile domed cities, we'd have no need for hair. I obviously have no cite. But what does that mean?

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Old 10-21-2019, 07:24 AM
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Anyone who has nursed small babies will know that you need to keep their heads covered or they lose heat fast. Sometime back in evolutionary history, more babies with head hair survived than those without... That's my WAG
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Old 10-21-2019, 08:00 AM
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Originally Posted by bob++ View Post
. Sometime back in evolutionary history, more babies with head hair survived than those without... That's my WAG

Not sure this is true. When my baby was born (we are of Indian origin), she had lot of head hair . When I visited the nursery at the hospital though, there were babies who were totally bald and babies who looked like wearing a toupee

Our baby lost her baby hair fairly quickly too - so I doubt it’s a evolutionary thing.

But you could be right and I may have observed some outliers.
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Old 10-21-2019, 08:06 AM
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Anyone who has nursed small babies will know that you need to keep their heads covered or they lose heat fast. .....
You maybe right on this point though for adults. Our brains consume about 20 % of our daily calories, so it may do well with some insulation :

https://www.scientificamerican.com/a...hard-calories/
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Old 10-21-2019, 08:48 AM
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We have hair on our heads because we evolved from animals that had hair on their heads and we haven't lost it.

Why we haven't (totally) lost the hair on our heads may be an interesting question.
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Old 10-21-2019, 09:02 AM
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When the question is "why did it evolve" the most likely answer is "to do what it does currently". That is, functions of evolved traits don't usually change. Sometimes they do, like in vestigial traits, but you'll need evidence to determine that they have done so.

From my cursory understanding, human head hair is for cutting and styling into personalized shapes so as to assert certain roles in society and to attract mates. Pubic hair and what other body hair we have retained has a similar function.

Sun blocking and warming functions might be a small part of why we have hair, but I imagine hats were invented at the same time as other clothes (before or around the time we lost our ape-like body hair?), and we'd have hair on a lot more of our bodies than our head if its main function was blocking the sun or maintaining body temperature in cold climates.
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Old 10-21-2019, 09:25 AM
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Also to point out that head hair has a cost to humans in terms of parasites like lice and dandruff (maybe not so much to modern man but definitely to our ancestors)
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Old 10-21-2019, 09:29 AM
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All of the above might be true, but what I have read suggests that when Homo adopted a cursorial (running down game) life style on open grassland we lost most of our body hair to help with cooling, but the hair on the head protects from the sun and was not lost. As for pubic and underarm hair, I cannot even speculate. Also why women lost facial hair and men didn't seems mysterious too.

A slightly related question. Do transwomen go bald like men or mostly don't like women? And what about transmen? Data only please.
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Old 10-21-2019, 09:33 AM
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Originally Posted by Jim B. View Post
Why do humans typically have hair on their heads? Bald people obviously don't. But still.

Yes I know evolution has something to do with it. But how? And why?

Also I remember watching this news magazine on TV, oh, well over 30 years ago when I was still in HS. And they were speculating about humans in the future. And they said since we'd be living in sterile domed cities, we'd have no need for hair. I obviously have no cite. But what does that mean?

No one knows "why" these things happen, but having hair on your head has obvious advantages; it protects you from the elements to an extent hair on other parts of your body would not. That is the likely reason why humans were selected for head hair by the forces of natural selection.

It is also possible, albeit less obvious, that head hair helps in attracting mates. Healthy-looking hair is a signal that the owner is healthy.
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Old 10-21-2019, 09:47 AM
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I thought head hair was a vestige from when our ancestors were a lot harier?
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Old 10-21-2019, 10:53 AM
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Originally Posted by Hari Seldon View Post
All of the above might be true, but what I have read suggests that when Homo adopted a cursorial (running down game) life style on open grassland we lost most of our body hair to help with cooling, but the hair on the head protects from the sun and was not lost. As for pubic and underarm hair, I cannot even speculate. Also why women lost facial hair and men didn't seems mysterious too.

A slightly related question. Do transwomen go bald like men or mostly don't like women? And what about transmen? Data only please.
This is my understanding too. To shed body heat while basically running marathons to tire out big game, we shed a lot of body hair (or the thickness of it) and living in a central African climate at the time helped. By the time humans moved to colder climates, they had learned to make clothes and hair or lack was less of a concern. As mentioned, hair provides a protection from sun, and insulation in colder times. Unlike the rest of our flesh, the scalp is a very thin layer of flesh over bone, so supplying blood to maintain temperature is more difficult than for thicker fleshy bits, I would think. With less heavy blood flow, it does not aid significantly in shedding internal heat, and similarly that lesser blood flow makes it harder to keep the scalp warm. All in all, head protection is probably better.

The story (true or not) that I heard was that we (males) lose our hair as we get older allow more skin sunshine exposure to generate vitamin D, particularly . That and sun protection might indicate why baldness is more prevalent in temperate climates (if it is).
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Old 10-21-2019, 10:57 AM
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Originally Posted by DrCube View Post
When the question is "why did it evolve" the most likely answer is "to do what it does currently". That is, functions of evolved traits don't usually change. Sometimes they do, like in vestigial traits, but you'll need evidence to determine that they have done so.

From my cursory understanding, human head hair is for cutting and styling into personalized shapes so as to assert certain roles in society and to attract mates. Pubic hair and what other body hair we have retained has a similar function.

Sun blocking and warming functions might be a small part of why we have hair, but I imagine hats were invented at the same time as other clothes (before or around the time we lost our ape-like body hair?), and we'd have hair on a lot more of our bodies than our head if its main function was blocking the sun or maintaining body temperature in cold climates.
If I had to guess, I'd guess this. It's a trait that was sexually selected.
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Old 10-21-2019, 11:04 AM
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Originally Posted by Yllaria View Post
If I had to guess, I'd guess this. It's a trait that was sexually selected.
It's a trait that already existed. Possibly, the minimization of hair on the rest of the body is due to sexual selection. Plenty of animals have adapted to running and living in hot climates without losing their hair*, sexual selection could be a better explanation.

*Noting that people don't have hairless bodies, they just don't have dense coarse hair on most of their bodies. That varies a lot also, some people are hairier than others.

Last edited by TriPolar; 10-21-2019 at 11:05 AM.
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Old 10-21-2019, 11:39 AM
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Does any other primate have head hair that continuously grows?
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Old 10-21-2019, 11:52 AM
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Originally Posted by Hari Seldon View Post
As for pubic and underarm hair, I cannot even speculate.
Pubic and underarm hair both occur in regions where humans have apocrine sweat glands -- these are an entirely different sort of sweat gland than eccrine sweat glands, which is what we have over the rest of our bodies, and which help us to regulate body temperature.

Apocrine glands are apparently an evolutionary remnant of scent glands, and it's theorized that those glands may serve a pheromonal function in sexual attraction, and that the hair in those areas may help in transmission of those pheromones.
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Old 10-21-2019, 12:27 PM
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From a Straight Dope column from 1980:

Quote:
Nobody knows exactly, but some anthropologists believe the purpose of long head hair is to give you something to tie ribbons in. No kidding. Quoth one, “the functional significance of long head hair is almost certainly adornment, providing for the ‘sexual selection’ that Darwin correctly argued was a potent factor in the evolutionary process.” In other words, when you drop sixty bucks at the beauty parlor, don’t feel guilty–you’re helping to advance the species.

- Cecil Adams
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Old 10-21-2019, 12:50 PM
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My WAG for public / armpit hair would be that it captures the scent of the person, and would have been tied to mating preference.

I also remember reading something along the lines that the scent can give clues as to how closely related one is to another, and that modern women can subconsciously choose a scent that isn't father/brother close.
(unless you're from AR or TN obviously :-P)

https://en.m.wikipedia.org/wiki/Body...ual_attraction
See the section "body odour in selection"

ETA

https://www.newscientist.com/article...an-a-stranger/

This is one of the articles I think I remember reading in the ago time regarding avoiding incest or too-close relations.


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Last edited by eldowan; 10-21-2019 at 12:55 PM.
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Old 10-21-2019, 09:12 PM
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Originally Posted by Ashtura View Post
Does any other primate have head hair that continuously grows?
Some primates have pretty mustaches, sideburns, beards, etc, but I don't know of anything quite as flagrant and bizarre as human head hair. There may be some slight truth to the idea of hair as a natural hat, but I would wager that it's largely due to sexual selection and/or species identification. We have the Neanderthal genome so another data point is sitting there on the servers waiting for someone to figure out how to read it. My guess is that Neanderthals' head hair was not much different than their body hair - but maybe they had their own bizarre feature, like flappy ears, or noses that were little trunks.
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Old 10-21-2019, 10:47 PM
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One advantage of having hair on the scalp is that it prevents the scalp from getting sunburnt. Bald-headed men in sunny countries have to wear hats. I'm not sure if that's the evolutionary reason for retaining it, but it's certainly a bonus.
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Old 10-22-2019, 12:58 AM
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Maybe our ancestors never went bald. Didn't they only live into their 30's, which would means most died with their head hair on.
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Old 10-22-2019, 03:58 AM
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Maybe our ancestors never went bald. Didn't they only live into their 30's, which would means most died with their head hair on.
No, you're confused by the average age of death. But it was what is called a bimodal distribution that they averaged. What that means is that there were two times when lots of people died: 1) in infancy and early childhood, and 2) in old age, 60s or 70s. If you average those out, it comes to some time in the late 30s. So if someone in that time made it out of childhood, they usually made it to old age. Yes, some people died of accidents along the way, but those were a small fraction of the total number of deaths.

ETA: the old age of 60s and 70s only applies to humans and not to pre-human populations. The pre-human groups probably reach old age earlier, although I don't think we know enough to say exactly how early. I expect it was a gradual increase in lifespan. But the bimodal stuff applies to all these populations.

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Old 10-22-2019, 04:07 AM
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Some primates have pretty mustaches, sideburns, beards, etc, but I don't know of anything quite as flagrant and bizarre as human head hair.
Cotton-top tamarin (AKA "That monkey that looks like Einstein")

Last edited by MrDibble; 10-22-2019 at 04:08 AM.
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Old 10-22-2019, 07:59 AM
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Originally Posted by Hari Seldon View Post
All of the above might be true, but what I have read suggests that when Homo adopted a cursorial (running down game) life style on open grassland we lost most of our body hair to help with cooling, but the hair on the head protects from the sun and was not lost.
I don't think you can entirely discount sexual/social display - it's not certain how long people have been grooming/shaping/altering their head hair but it's been a very long time and some sort of hair styling seems to show up in every human society.

Quote:
Originally Posted by Hari Seldon View Post
As for pubic and underarm hair, I cannot even speculate.
I've heard a theory that it's to reduce chafing when moving limbs, and also a theory that it helps hold onto sex pheromones.

Quote:
Originally Posted by Hari Seldon View Post
Also why women lost facial hair and men didn't seems mysterious too.
Why do you assume there was a loss? Out closest primate cousins don't have beards regardless of sex, and there are quite a few human groups where the men have little or no beards/mustaches. How do you know that it wasn't that men acquired facial hair in some groups?

Quote:
A slightly related question. Do transwomen go bald like men or mostly don't like women? And what about transmen? Data only please.
Male pattern baldness is triggered by certain levels of male hormones. Transwomen who have had their testicles removed or inactivated do not go bald(er) (if they started male pattern baldness prior to gender transition treatment they may retain the level of baldness they had before). A related phenomena was noted by folks in ancient history who noted that eunuchs did not go bald like their uncastrated brothers. Transmen on hormones to treat their condition with the appropriate genetics will undergo male pattern baldness.

Post-menopausal ciswomen, whose hormone profiles change, may also start to experience thinning hair in a male pattern, although usually not as distinctly as their brothers did.

In other words, hormones determine whether or not any hormone-linked baldness patterns will emerge, but it's your genes that determine that pattern (or lack of it).
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Old 10-22-2019, 10:41 AM
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It's a trait that already existed. Possibly, the minimization of hair on the rest of the body is due to sexual selection. Plenty of animals have adapted to running and living in hot climates without losing their hair*, sexual selection could be a better explanation.

*Noting that people don't have hairless bodies, they just don't have dense coarse hair on most of their bodies. That varies a lot also, some people are hairier than others.
As Hari Seldon said above:
Quote:
All of the above might be true, but what I have read suggests that when Homo adopted a cursorial (running down game) life style on open grassland we lost most of our body hair to help with cooling, but the hair on the head protects from the sun and was not lost
The distinction is that almost all other mammals that run, run sprints. Humans are uniquely adapted to run marathons, to basically chase down four-legged game to the point where it is too exhausted to run. A horse can run a very fast mile when it has to, then it sweats buckets and has to "pee like a racehorse" to recover. In an hours long chase where it is constantly harried by humans and cannot stop to eat or drink, it would eventually fail of exhaustion first. Same with all the other savannah big game. But for most other threats, the short sprint is all that is required of such animals - a lion or cheetah will tire just as fast. (And then be too tired for a fight, whereas we would have spears and rocks).

Part of human adaption for that hunting style is the lack of significant body hair to more easily shed the heat generated. I believe in a different thread it was pointed out we have different muscle makeup than, say, a chimp - so we have endurance muscles at the expense of strength muscles compared to some other animals.

one suggestion I read is that in temperate winters men are more likely to be out and about hunting, so baldness helps them with vitamin D production, while women who stayed in the shelter with the children would not really benefit as much - but again, a "just so story". Certainly don't disregard the roles of sex selection/distinction in the emergence of certain traits.

And pubic or under-arm hair, just like eyebrows, can play a role in managing sweat - ie. channel it, keeping it around to cool the specific region instead of dripping and annoying. Avoiding chafing and airing pheromones - well, plenty of attributes have multiple functions.

Last edited by md2000; 10-22-2019 at 10:44 AM.
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Old 10-22-2019, 10:57 AM
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A
The distinction is that almost all other mammals that run, run sprints. Humans are uniquely adapted to run marathons, to basically chase down four-legged game to the point where it is too exhausted to run. A horse can run a very fast mile when it has to, then it sweats buckets and has to "pee like a racehorse" to recover. In an hours long chase where it is constantly harried by humans and cannot stop to eat or drink, it would eventually fail of exhaustion first. Same with all the other savannah big game. But for most other threats, the short sprint is all that is required of such animals - a lion or cheetah will tire just as fast. (And then be too tired for a fight, whereas we would have spears and rocks).
Sorry, but horses can run fast for much longer than a mile, and carrying a human on their back as well. Humans pale in comparison. The other animals are limited by their tactics, not because of hair on their bodies. If humans sprinted they would tire out just as fast as other animals, lack of hair won't matter at all. Hair is nowhere near as much of a factor as the cardiovascular system. Finally, we do not know how much hair our ancestors had when they started running down game.
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