# What is the evolutionary benefit for tightly curled hair? **URL:** \ **Category:** Factual Questions\ **Created:** [April 25, 2018, 6:07am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079 "2018-04-25T06:07:48Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Contemplation](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@Contemplation](https://boards.straightdope.com/u/Contemplation)\ **Post date:** [April 25, 2018, 6:07am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/1 "2018-04-25T06:07:48Z")
Why did humans evolve to have tightly curled hair in some places and not in others? Straight hair is extremely rare in native people in sub-saharan Africa. People in other hot climates tend to have loosely curled hair and more variation such as in India, the Phillipines, and Australian aborignes. Andamese people, Papuan new guineans, and Fiji islanders also tightly curled hair, but they have more variation. Think of variation as in natural variation of hair texture and patterns without artificial straightenting, flat irons or hot combs and etc. Strangeley, people native to central and South America usually have very straight hair. So, I was thinking does tightly curled hair trap LESS heat, or help your head stay cooler in hot weather than straight hair? ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 25, 2018, 9:01am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/2 "2018-04-25T09:01:32Z")
That’s the most widely accepted theory, yes. ---
**Author:** ![Contemplation](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@Contemplation](https://boards.straightdope.com/u/Contemplation)\ **Post date:** [April 25, 2018, 9:08am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/3 "2018-04-25T09:08:03Z")
> [@MrDibble](#): > > That’s the most widely accepted theory, yes. But why would native people of central and South America have mostly straight hair? Or Why would the people of Cambodia have mostly straight or wavy hair? There are many places hotter than sub saharan Africa where people have straighter hair. ---
**Author:** ![yendis](https://avatars.discourse-cdn.com/v4/letter/y/ed8c4c/32.png) [@yendis](https://boards.straightdope.com/u/yendis)\ **Post date:** [April 25, 2018, 9:12am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/4 "2018-04-25T09:12:30Z")
> [@Contemplation](#): > > But why would native people of central and South America have mostly straight hair? > There are many places hotter than sub saharan Africa where people have straighter hair. Because the people they descended from had straight hair, having come from the Siberia region. Remember that tightly curled hair is probably the default hair for humans. As people migrated out of Africa they adapted to their environment, straighter hair, paler skin etc. So the question might be better framed as to why human hair changed the way it did from tightly curled, instead of towards tightly curled. ---
**Author:** ![penultima\_thule](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/penultima_thule/32/3833_2.png) [@penultima\_thule](https://boards.straightdope.com/u/penultima_thule)\ **Post date:** [April 25, 2018, 9:22am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/5 "2018-04-25T09:22:14Z")
Consider the “Out of Africa” migration patterns. The other primates don’t have tightly curled hair so that trait evolved in Africa but was lost by the migration waves that left Africa to northern Asia and populated the Americas north to south and the trait hasn’t re-emerged (yet). Conversely the Melanesians are on a shorter evolutionary timeline and similar sub tropical climates and didn’t lose the characteristic. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [April 25, 2018, 10:02am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/6 "2018-04-25T10:02:19Z")
I’ll jump in with an AIUI… AIUI, tightly-curled hair is basically a warm weather adaptation, and it is very effective at blocking heat getting to the scalp and for radiating heat. In terms of why some people native to very hot climates do not have tight curls, I’d WAG it as: 1. Movement of people. 2. Other mechanisms of keeping cool. e.g. maybe the greasiness of the hair helps? Just because A solves problem X, no reason to assume there is no B, C, D that might also be effective. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [April 25, 2018, 10:56am UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/7 "2018-04-25T10:56:51Z")
> [@Mijin](#): > > I’ll jump in with an AIUI… > > AIUI, tightly-curled hair is basically a warm weather adaptation, and it is very effective at blocking heat getting to the scalp and for radiating heat. If that’s the case one would assume a lighter color would have also been selected for. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [April 25, 2018, 12:04pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/8 "2018-04-25T12:04:37Z")
That requires the lighter color to also appear as a mutation and to have positive effects which aren’t balanced or surpassed by negative ones. If a mutation doesn’t happen, it can’t be selected. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [April 25, 2018, 12:17pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/9 "2018-04-25T12:17:03Z")
Maybe it’s neutral. Then there would be no evolutionary pressure to change, no? ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 25, 2018, 12:18pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/10 "2018-04-25T12:18:21Z")
> [@Lucas\_Jackson](#): > > If that’s the case one would assume a lighter color would have also been selected for. not if it’s _less_ selected for than, say, UV protection. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [April 25, 2018, 1:37pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/11 "2018-04-25T13:37:26Z")
> [@Lucas\_Jackson](#): > > If that’s the case one would assume a lighter color would have also been selected for. Not a biologist or understand evolution fully, but there are the Melanesians with dark skin and blonde Afros. [Melanesian Blondes - Black People with Natural Blonde Hair](http://www.odditycentral.com/news/black-and-blond-the-origin-of-blond-afros-in-melanesia.html) ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [April 25, 2018, 1:41pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/12 "2018-04-25T13:41:36Z")
As a biologist, I would first want someone to give me evidence that there IS evolutionary pressure behind this phenotype one way or the other before I start speculating about why. It’s easy and FAR too common to launch into evolutionary just-so stories without bothering first to determine whether such stories are necessary. There are vast numbers of completely neutral genetic variants in the human population. The default assumption should be that this is one of them until someone provides evidence suggesting otherwise (such as population genetic data demonstrating selection at the relevant locus). ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 25, 2018, 1:44pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/13 "2018-04-25T13:44:53Z")
> [@Smeghead](#): > > As a biologist, I would first want someone to give me evidence that there IS evolutionary pressure behind this phenotype one way or the other before I start speculating about why. I think the difference from straight-haired apes is held up as evidence for there being some sort of selection to it, but you’re right, of course there needn’t be anything. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 25, 2018, 2:01pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/14 "2018-04-25T14:01:11Z")
Maybe one proto-human just had a random mutation that led to curly hair, and maybe for completely unrelated reasons that particular proto-human just happened to be really smooth with the ladies, and so ended up having a lot of offspring. Maybe even the other proto-humans saw his descendants with curly hair and said “Look, he looks just like his grandfather the Really Great Guy; he must be a Really Great Guy, too, so we should all mate with him”. And so curly hair becomes more common, for no particular reason beyond random chance. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 25, 2018, 2:13pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/15 "2018-04-25T14:13:15Z")
> [@Chronos](#): > > Maybe one proto-human just had a random mutation that led to curly hair, and maybe for completely unrelated reasons that particular proto-human just happened to be really smooth with the ladies, and so ended up having a lot of offspring. Maybe even the other proto-humans saw his descendants with curly hair and said “Look, he looks just like his grandfather the Really Great Guy; he must be a Really Great Guy, too, so we should all mate with him”. And so curly hair becomes more common, for no particular reason beyond random chance. That was recently confirmed by the new fossil species found that was dubbed _Homo barrywhitensis_. ---
**Author:** ![DrCube](https://avatars.discourse-cdn.com/v4/letter/d/a3d4f5/32.png) [@DrCube](https://boards.straightdope.com/u/DrCube)\ **Post date:** [April 25, 2018, 2:19pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/16 "2018-04-25T14:19:38Z")
> [@Smeghead](#): > > As a biologist, I would first want someone to give me evidence that there IS evolutionary pressure behind this phenotype one way or the other before I start speculating about why. It’s easy and FAR too common to launch into evolutionary just-so stories without bothering first to determine whether such stories are necessary. There are vast numbers of completely neutral genetic variants in the human population. The default assumption should be that this is one of them until someone provides evidence suggesting otherwise (such as population genetic data demonstrating selection at the relevant locus). As an interested layman, that’s my thinking too. As a WAG, it seems to me that head and body hair is mostly a canvas for self expression which was probably sexually selected for. I understand that there’s some sun protection going on too, but then, why don’t we have thick hair on our shoulders or noses for the same purpose? Why would male pattern baldness be a thing? Whatever clothes we wore that made us lose our chimp-like body hair probably included hats, too. So it seems to me that it’s more likely our head hair, facial hair, body hair and pubic hair stuck around for the same reasons we still use them today: self expression and attracting mates. Not any objective physical function like cooling or blocking UV, though those might have been influences too. But again, I’m just guessing. Until there’s some evidence either way, the default should be that it’s random variation. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [April 25, 2018, 3:36pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/17 "2018-04-25T15:36:30Z")
> [@Chronos](#): > > Maybe one proto-human just had a random mutation that led to curly hair, and maybe for completely unrelated reasons that particular proto-human just happened to be really smooth with the ladies, and so ended up having a lot of offspring. Maybe even the other proto-humans saw his descendants with curly hair and said “Look, he looks just like his grandfather the Really Great Guy; he must be a Really Great Guy, too, so we should all mate with him”. And so curly hair becomes more common, for no particular reason beyond random chance. That’s not random chance, that’s sexual selection. Even if the initial two traits are unrelated, by the time it gets to “he looks like…”, it’s not chance anymore. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 25, 2018, 4:11pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/18 "2018-04-25T16:11:29Z")
Once the initial change occurs, sexual selection can reinforce it, but the direction of the original change is still random. It’s like if you turn a bowl over, and put a marble on top of it, in the middle. The marble rolls off the north side of the bowl. Why the north side? You could try to invent some explanation involving Coriolis effects or the Earth’s magnetic field or whatever, but really, it was just random. Once the ball was perturbed a little bit to the north, the slope of the bowl kept it rolling northward, but that doesn’t make the initial perturbation any less random. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [April 25, 2018, 4:17pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/19 "2018-04-25T16:17:35Z")
> [@Smeghead](#): > > As a biologist, I would first want someone to give me evidence that there IS evolutionary pressure behind this phenotype one way or the other before I start speculating about why. It’s easy and FAR too common to launch into evolutionary just-so stories without bothering first to determine whether such stories are necessary. There are vast numbers of completely neutral genetic variants in the human population. The default assumption should be that this is one of them until someone provides evidence suggesting otherwise (such as population genetic data demonstrating selection at the relevant locus). > [@Chronos](#): > > Maybe one proto-human just had a random mutation that led to curly hair, and maybe for completely unrelated reasons that particular proto-human just happened to be really smooth with the ladies, and so ended up having a lot of offspring. Maybe even the other proto-humans saw his descendants with curly hair and said “Look, he looks just like his grandfather the Really Great Guy; he must be a Really Great Guy, too, so we should all mate with him”. And so curly hair becomes more common, for no particular reason beyond random chance. Actually, I think that sexual selection might be the best explanation for the various types of human head hair. After all, humans are the only great apes that have head hair that grows to such long lengths, and male mustaches and beards are clearly sexual ornaments. It’s been said, only partly in jest, that the main reason that humans evolved long head hair was to have something to tie ribbons to. There may be some adaptive benefit to kinky hair, but it’s obscure. Maybe it provides some protection from overheating the skull in tropical sun, but if so one wonders why it doesn’t seem to have evolved independently in tropical regions outside Africa. See [here](http://humanphenotypes.net/metrics/texture.html) for distribution of human hair textures. The most extreme form of curly hair is peppercorn hair, which is found in some lineages that split very early, including the Khoisan of Southern Africa and some pygmies. But it is also found in Andaman islanders, one of the first lineages to leave Africa. The alleged benefit in the tropics is to allow sweat to evaporate from the scalp, but this is sort of the opposite of the benefit attributed to kinky hair. Kinky hair is found mainly in sub-Saharan Africa, but like peppercorn hair it is also found in some lineages that were among the first to leave Africa, like the Negritos of Southeast Asia, some peoples in New Guinea, and even the Tasmanians in temperate Australia. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [April 25, 2018, 4:47pm UTC](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079/20 "2018-04-25T16:47:27Z")
> [@Colibri](#): > > There may be some adaptive benefit to kinky hair, but it’s obscure. Maybe it provides some protection from overheating the skull in tropical sun, but if so one wonders why it doesn’t seem to have evolved independently in tropical regions outside Africa. In the Americas, at least, people haven’t been here long enough for a lot of evolutionary change. The founders groups of the people who became Native Americans (both north and south) were a relatively small pool of people who had straight hair, brown eyes, and sort of medium-dark skin. While there have been some changes, none of the Natives became as pale as people living in, say, Northern Europe, or as dark as sub-Saharan Africa where people have lived ten or perhaps even a hundred times longer. While 10,000 or 12,000 years seems like a long time to us, in evolutionary terms it’s not that long, especially for a long-lived species like ours. There hasn’t been sufficient time to accumulate sufficient mutations to make for much change in the Americas, and most of the present diversity is the result of importing people from elsewhere in massive numbers. [Next page](https://boards.straightdope.com/t/what-is-the-evolutionary-benefit-for-tightly-curled-hair/813079.md?page=2)