evolution of human hair

I will admit I do not know everything about biology or evolution, so maybe this is a dumb question, but my inquiring mind wants to know.No animal (or at the very least no primate) I know of, has hair that keeps growing endlessly. Even "longhair" species have hair that only gets to a specific length.Yet the hair on human heads just keeps growing. I realize that some get bushy (because it curls), instead of long (if it is straight), but the hair on human heads ultimately grows until it is a detriment to the owner of that hair. It impedes vision, hearing, and mobility.We can ignore that issue these days as we have tools to bind it or cut it. But this trait of our hair has not been a product of having invented tools has it?Does anyone know how long human hair has been out of control, why it would ever get like that, and why is it just the hair on our heads?It seems that would be an evolutionary disadvantage (before tool use), unless early humans were able to hide in bushes better, because they could drape their hair like cousin It from the Addam's Family.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

To EVERYBODY SO FAR... Thanks for backing up the fact that I'm not the only one stumped by what appears to be a human oddity.The only one who debates this so far is Ned, which is why I am responding to him in specific.

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No, in fact, it doesn't. Each folicle grows for a period of time, goes dormant and the hair falls out. After a rest a new hair starts. The length depends on how fast it grows during the growth phase

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Okay, you are kind of right and kind of wrong, but I should have stated it better.The hair on human heads keeps growing for incredibly extensive time periods which dwarf the rest of our hair "growth periods", so much so that it appears to be constant. We know for a fact that it's growth period is in years, and just how many years no one really knows because no one (which I have been able to find) has tested it. I know of one girl that had been letting her hair grow for longer than 10 years (just cutting the very tips) and it was still growing!If you know of any study which has put a definite time limit for human hair growth I would be interested in knowing about it (not challenging your point, I really am interested).So it is not that head hair grows faster than hair on the rest of one's body, it is that it grows for longer periods of time... much much longer. Why would there have been this discordance? What advantage would it serve that it would be selected for?Without ways of controlling the hair (use of tools) it at the very least becomes a disadvantage for perception (which is crucial in hunting/escaping hunters).So far everyone seems to like the sexual selection explanation. I must say that this is what was on my mind as one of the few realistic scenarios. But then I wonder if it was something that was selected for AFTER use of tools. Kind of like it was part of humans domesticating themselves.But then again, this trait is shared by all humans. So that would have had to have been pretty early on. Was the spread of humanity across the planet contigent on enough tool use (for long enough time) that sexual selection criteria would have found its way into our genes?What's more... all humans share this trait DESPITE the fact that we have many many different hair types between races. Africans have the finest and Asians the coarsest. In fact I have heard Asian hair is actually angular instead of round.Hmmmmmmm. More data. We need more data.If mammuthus is reading, is there any input on this based on woolly mammoth hair? How shaggy did they get?

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)< !--UE-->[This message has been edited by holmes, 01-28-2004]

To be fair, take a look at your avatar and then at Ned's. There may be a reason he wouldn't have experienced such things...I kid I kid.But to add my own experiences in, I went with long hair in college. For a while anyway. Unless tied back, it is a terrible distraction and impediment for seeing and hearing what's going on around you.I did have the humorous notion that we could combine the long hair growth with the fact that humans have gripping instincts. Maybe mothers could carry their babies around by attaching their clutching hands to long lengths of hair. It would keep their hands free after all.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

Actually your "condition" doesn't look too disfiguring. It's hard to tell from the pic if you have a comb over going though. If so, I vote for the final solution. I figure that's what I'll do if/when my hair goes away. It actually looks pretty hip.Below is one of the better links I had found before posting my question:
Why do you hear some radio stations better at night? | HowStuffWorksIt says about the same thing, though it points out there is a difference in hair growth times between head and body hair, as well as not capping the growth time. This being why head hair is longer than body hair.However, the growth time period on your link is totally bogus. Or at least it is contrary to all of my experience with hair. 2-6 years? I'm pretty sure all of my girlfriends have grown their hair for longer than that, and it wasn't stopping. My current girlfriend grew hers for 9 years straight, and it was till plugging away. And like I said, I know there was a girl who had grown hers for well over 10 years. It was down to her ankles. Unless all my girlfriends were anomolies... then again they did date me so... hmmmm.I do stand corrected in my statement that it will grow forever. I just am not comfortable with the limits I have seen (esp. on your link). I would love to have a more accurate (ie backed up with data) assessment of what the real growth period is for human hair.Your assessment that hair acts as a good shield, from sun and cold, sounds okay... but then why don't other primates (or mammals) have the same characteristic? They would have to have the same general issue we do.Also, since it is pretty well established the first humans came out of Africa where it is pretty warm, why didn't we just have more melanin? After all, blacks who shave their heads now have no real problems with the sun beating on their heads, and it is for that reason.I could see being white and moving into sunny areas, or moving from hot to cold climates driving the need for hair coverage. But due to the universality of this hair growth, it must have begun while people were still pigmented and living in a warm environment. Right?

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

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I actually heard that Asian hair is round (and hence straight) and the curliest hair is asymetrical.

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Correction of my earlier statement. In horizontal cross section, Asian hair is round, African is oval and Caucasian is in between. In length cross section, Asian is perfectly straight (no asymmetry), African is extremely asymetrical and so kinky, while Caucasian is somewhere between.

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What the heck is with balding then? Where does that fit in with evolution?

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This may have more to do with the aging process than with survival. A long time ago we didn't really live long enough to have that as a major issue in survival or mate selection.

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I know what it is like to inhale hair: I regularly experience it while, er, vigorously exercising with my girlfriend...

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I've also choked on my girlfriend's hair (on her head for you pervs) while "exercising" in certain positions (where she is above obviously).

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And why do women find completely shaven more appealing than the monk (semi-bald) look?

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Who can figure out why women prefer anything? Oh yeah, on that mysogynistic comment, maybe long hair on guys is just superfluous like male nipples. Maybe long hair was important for cavemen to drag cavewomen around by.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

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Why do some guys only have to shave once a fortnight but some of us need to shave twice a day?

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Depends... which area of your body are you talking about?Badump bump crash.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

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I suspect that unwashed hair in its natural state is less of a problem than our groomed variety. Certainly many of the most warlike peoples in history wore their hair long and loose, so it can't be that major a problem.

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I took some time to absorb this info, but on reflection it simply is not true. All nations that we know about have had technology to tie back, or in other ways deal with hair.The Romans cut their hair short, the Vikings tied back their hair or wore helmets, the Japanese shaved/tied back/wore helmets, and most of the Barbarian tribes wre helmets of some kind.I am curious what nations you were referring to because I honestly can't think of any which in the course of combat did not do something to their hair. Maybe the Spartans?And I think this stands to reason. If you have taken martial arts or been part of any martial training/experience, long hair quickly becomes a detriment. If loose, it obscures vision and hearing (which is sometimes more important than sight). It also gives one's opponents something to grab on to.After taking martial arts I decided to keep my hair close cropped from then on. A few years later I weakened for a girlfriend and grew it out. A mugger, who I was in the midst of successfully getting away from, entered the blind spot my hair provided him and then grabbed it. If you have ever been in this position (your long hair grabbed tight) you know that you have lost total control of the fight. Needless to say I got mugged.I managed to outwit him while handing over the cash, but was forced to escape rather than defeat the mugger by force. Out of three attempts I have faced, it was the only mugging that ever worked, and it was all due to that damn long hair of mine. I shaved it shortly after that and never let it grow back.Long hair, especially loose, is a DISTINCT disadvantage in combat.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)[This message has been edited by holmes, 01-30-2004]

Some of this held some interesting ideas. Although once again I am left puzzled as they appear to support evolution, which you have been trying to rip up in other threads.But let's go over some points.1) I think it is already well known that hairgrowth and health depends on diet and stress. I am unsure if this proves anything as far as its connection to why it grows different from other hair on the body, as MOST other physical characteristics are dependent on diet and stress. It still leaves the question why only that area has the longer growth period over all.2) I am not quite convinced that Rohwer's explanations do anything to explain this discordance either. Even assuming his overall theory is correct, why does the hair grow out to such excessive lengths in both males and females, rather than using a less obstructive cue?

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

Thank you very much for a lot of interesting info. However, I still have three issues, which I hope you can address in one way or another.1) While I have seen statements that head hair growth is around what you mentioned, my own experience has defied these studies. Doing the math, I come up with an average maximum hair length of ~30 inches. That is not even 3 feet. It's pretty easy to find pictures of people with hair WELL beyond that length, and I know my girlfriends have had this length.... I should add that it took longer than 5 years to grow that length and so it wasn't that their hair grew faster either.I don't want to seem like my anecdotal evidence trumps a study, but when it's pretty obvious hair can grow longer than 3 feet in length, and has grown longer than 5 years, I start having questions about the accuracy of the study. If you have a link to it I would like to see it. And since you seem to have quite a bit of experience with hair, I would ask haven't you seen anyone with hair still growing past 5 years and longer than 30"?I kind of think the 60's provided major counterevidence to L'Oreal's claims.2) While your explanation of noneccrine sweating makes some amount of sense (after all hair seems to grow where we sweat a lot so maybe that is a benefit), it does not exlain the real problem I am trying to figure out. I wasn't so concerned why hair was differentially distributed, I am wondering why hair has differential maximum growth lengths across the human body.Specifically... even if noneccrine sweating is superior... why would max hair length on the head be so much different than say pubic regions or armpits. It seems that that would become a detriment to the survival of humans before they had the ability to control their hair. Do you have any info suggesting an explanation for this?3) And finally, I was disturbed to see in one of your references that Sonic Hedgehog is now a term in genetics? I can only assume it was named from the video game. Is this true?Thanks again for your informative post and I definitely look forward to your reply.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

I do understand that there is a range of growth rates, probably like a bell curve, and some will be on the ends.While 16 feet is certainly an extremity, 30-36" inches does not seem to be (other than cultural desires to chop it down). And that's why I was saying, according to the study you quoted the average MAXIMUM length would only be 30". While I'll admit maybe I've just hung out with freaks, I would think that is not as likely as I've been pretty multicultural in who I hang out with.I'd say the average maximum I've seen is 36-40 inches (when people let it grow out). This does not just include my gfs.And my assessment is not biased by optical illusion (based on different body heights). And as it is my gfs (with the exception of 2) have all been taller than 5'3".But I guess this is a whole other issue anyway. For sake of argument I'll just assume I have been living around the upper half of the bell curve on hair growth.The real question remains why the difference in growth on head vs body hair. It sounds like you are generating the same hypotheses as we are. Possibly cold/sun protection, or sexual significance.Anything you can find I am totally interested.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

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If the latter is adapted to communicating health or the lack of health, it might amplify those problems, while functional hair just carries on.

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That could be. Maybe Randy has some info along these lines.

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Adaptation, by the way, supports both the theories of creation and evolution.

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That's a new one on me. How does adaptation support both? It stems from evolutionary theory. Creationism simply says God made us the way we are.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

They key words were a LONG TIME AGO.Someone correct me if I am wrong, but the average lifespan (before tool use became common) was well under 30. That meant that most of life and reproduction was carried out before hair loss would become an issue for survival or mate selection.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

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Not sure what the evidence is for shorter lifespans

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Now that you mention it, I've never actually tried to find out what data has been used to make the case that people died so young long long ago. But I do know that I've heard it said a lot in documentaries.Hmmmmmm... maybe a new topic, inquiring minds want to know!

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)

Celts, scottish clansmen, and picts, from what I am aware, wore some type of headcovering/headband. The Goths, vikings, and huns wore helmets whenever they were available. I believe the Vikings also braided their hair.I am willing to accept contrary evidence, but will agree that what you pointed out is part of my argument... once you have weapons and armor, hair length tends to be less of a factor.This is one reason I am wondering whether this difference in max hair length (between head and body hair) came after tool use, where sexual significance would play more of a role than survival.

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holmes
"...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros)