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?


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

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 :slight_smile:

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.

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 :

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.

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.

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)

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.

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.

I thought head hair was a vestige from when our ancestors were a lot harier?

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).

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.

Does any other primate have head hair that continuously grows?

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.

From a Straight Dope column from 1980:

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)

See the section “body odour in selection”


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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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.

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.

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.