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Author Topic:   evolution of human hair
Silent H
Member (Idle past 5820 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 1 of 55 (81347)
01-28-2004 1:29 PM


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.

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

Replies to this message:
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Yaro
Member (Idle past 6496 days)
Posts: 1797
Joined: 07-12-2003


Message 2 of 55 (81356)
01-28-2004 2:21 PM
Reply to: Message 1 by Silent H
01-28-2004 1:29 PM


WOW! Good question!
Im stumped
Maybe your right about tool use. Maybe sometime, long in our past, we began cutting our hair. So when the gene that limited it's growth was turned off it didn't matter.
Kinda like the Vitamin C hypothesis.
[This message has been edited by Yaro, 01-28-2004]

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:æ: 
Suspended Member (Idle past 7185 days)
Posts: 423
Joined: 07-23-2003


Message 3 of 55 (81357)
01-28-2004 2:27 PM
Reply to: Message 1 by Silent H
01-28-2004 1:29 PM


Maybe around the time our species diverged from the earlier hominids, long hair on our heads became a reproductive advantage more than it was a survival disatvantage. Something like the large peacock tails -- it doesn't necessarily aid in survival per se (i.e. attain more food, escape predators, etc...), but there's something about it that members of the opposite sex fancy and so that trait benefits from greater reproduction.
Just my $0.02.

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truthlover
Member (Idle past 4059 days)
Posts: 1548
From: Selmer, TN
Joined: 02-12-2003


Message 4 of 55 (81360)
01-28-2004 3:08 PM
Reply to: Message 3 by :æ:
01-28-2004 2:27 PM


I am totally interested in this question. I'm prone to the hippy "if it's natural, it's good" attitude, but it just doesn't work for hair. My mustache grows long enough to just cover my bottom lip, getting in the way of food, but not long enough to comb to the side. My beard stops at a decent enough length, but others have beards that grow to their waist.
I like the reproductive advantage idea. My very unscientific observations of myself and those around me is that long hair does indeed tend to appeal to the opposite sex, male and female.

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 5 of 55 (81361)
01-28-2004 3:12 PM
Reply to: Message 1 by Silent H
01-28-2004 1:29 PM


Yet the hair on human heads just keeps growing.
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.
I'm inclinded to think that the sexual selection idea might explain it if it actually gets to be an impediment. I'm not sure it does and it may also be that we have had some kind of control technology for a very long time. I wonder how long?

Common sense isn't

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truthlover
Member (Idle past 4059 days)
Posts: 1548
From: Selmer, TN
Joined: 02-12-2003


Message 6 of 55 (81362)
01-28-2004 3:22 PM
Reply to: Message 5 by NosyNed
01-28-2004 3:12 PM


if it actually gets to be an impediment. I'm not sure it does
Oh, it does.
The worst time ever was when I was wrestling about six kids and I inhaled some of my hair. Fortunately, they were nine and ten year olds, so I was able to immediately fling them off and retrieve the ends of my hair from my throat. If it were teenagers who could have kept my hands pinned, I might have died.

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Silent H
Member (Idle past 5820 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 7 of 55 (81364)
01-28-2004 3:37 PM
Reply to: Message 5 by NosyNed
01-28-2004 3:12 PM


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.
quote:
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
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?

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]

This message is a reply to:
 Message 5 by NosyNed, posted 01-28-2004 3:12 PM NosyNed has replied

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Silent H
Member (Idle past 5820 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 8 of 55 (81365)
01-28-2004 3:43 PM
Reply to: Message 6 by truthlover
01-28-2004 3:22 PM


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.

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

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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 9 of 55 (81367)
01-28-2004 4:09 PM
Reply to: Message 7 by Silent H
01-28-2004 3:37 PM


I will continue talking to you even though you have made fun of my disfigurement. (and I'm considering taking it to the 'final solution' when the weather warms ).
Skin Beauty - Not Found
Talks about the phases of hair growth (not exactly a primary source but will do for now).
My point was that "hair" as a whole doesn't "keep growing". Each hair folicle is doing it's thing. I think some individuals have managed hair to the ground but I'll bet that there is a firm limit no matter how long they go without cutting (the same does not appear to be true of fingernails - and I've seen pictures of grotesque results).
That doesn't mean your question about how this could be good (or not bad) is answered. Darned if I know.
Do present day hunter gatherers cut their hair? (I'm thinking of, eg, the !Kung ).
That site suggests 2 to 6 years is the time period of active growth. That may itself account for the differences in hair length.
I just had another thought. (amazing 2 in a week! ). We do know that we lose a lot of energy through our busy little heads (about 25% ). Or conversly we risk getting heatstroke if too much heat is applied.
Therefore it is important that we have hair to protect us. (I guess I am one of the "unfit" huh? ). Hair is subject to pretty severe conditions in the wild (not in modern socieity). If it didn't grow fast enough to maintain a covering we could be in trouble.

Common sense isn't

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Silent H
Member (Idle past 5820 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 10 of 55 (81372)
01-28-2004 4:49 PM
Reply to: Message 9 by NosyNed
01-28-2004 4:09 PM


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? | HowStuffWorks
It 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?

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

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Brian
Member (Idle past 4959 days)
Posts: 4659
From: Scotland
Joined: 10-22-2002


Message 11 of 55 (81375)
01-28-2004 5:07 PM
Reply to: Message 10 by Silent H
01-28-2004 4:49 PM


Why do some guys only have to shave once a fortnight but some of us need to shave twice a day?
What's that all about?
Brian.

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Gilgamesh
Inactive Member


Message 12 of 55 (81376)
01-28-2004 5:17 PM
Reply to: Message 6 by truthlover
01-28-2004 3:22 PM


I know what it is like to inhale hair: I regularly experience it while, er, vigorously exercising with my girlfriend but I manage to continue to get enough oxygen to, er, complete the workout. Sometimes.
Maybe your own male hair is much coarser Truthlover!
I actually heard that Asian hair is round (and hence straight) and the curliest hair is asymetrical.
What the heck is with balding then? Where does that fit in with evolution?
And why do women find completely shaven more appealing than the monk (semi-bald) look?

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Gilgamesh
Inactive Member


Message 13 of 55 (81378)
01-28-2004 5:29 PM
Reply to: Message 11 by Brian
01-28-2004 5:07 PM


Brian might have hit the nail on the head (indirectly). Obviously hormones paly a role with not only hair quantity and distribution (between the sexes) but also with variances between the same sex. It is a hormone (linked to testosterone) that cause male pattern baldness: indeed you can stop a person who is predisposed to balding going bald by hormone treatment or castration (a bit extreme). Guys who are overweight and drink heavily have higher levels of estrogen and lower testosterone and therefor are less likely to rapidly lose hair.
Similarly guys with higher testosterone grow facial hair faster.
Testosterone levels are not only genetic but as I indicated above, lifestyle/health related. Bodybuilders produced (naturally and artifically) lots of it and often go bald.
Maybe head hair growth compensated for the loss of bodyhair in hominids associated with the use of clothing. Dunno.

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Silent H
Member (Idle past 5820 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 14 of 55 (81379)
01-28-2004 5:32 PM
Reply to: Message 12 by Gilgamesh
01-28-2004 5:17 PM


quote:
I actually heard that Asian hair is round (and hence straight) and the curliest hair is asymetrical.
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.
quote:
What the heck is with balding then? Where does that fit in with evolution?
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.
quote:
I know what it is like to inhale hair: I regularly experience it while, er, vigorously exercising with my girlfriend...
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).
quote:
And why do women find completely shaven more appealing than the monk (semi-bald) look?
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.

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

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Silent H
Member (Idle past 5820 days)
Posts: 7405
From: satellite of love
Joined: 12-11-2002


Message 15 of 55 (81380)
01-28-2004 5:34 PM
Reply to: Message 11 by Brian
01-28-2004 5:07 PM


quote:
Why do some guys only have to shave once a fortnight but some of us need to shave twice a day?
Depends... which area of your body are you talking about?
Badump bump crash.

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

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