evolution of human hair

And women have evolved small feet so they can stand closer to the sink! Brian.PS post 15, MY FACE LOL, I use Immac for my 'BSC'[This message has been edited by Brian, 01-28-2004]

I doubt it, as my hair is very fine. However, I think you will find that standing upright is the best way to get a large amount of hair down your throat, and wrestling helps that. A violent jerk of the head, combined with a deep breath, can get a whole handful of hair to go down your throat (a lock, not just several loose strands). It has happened to me twice, separated by three or four years. (I have six children, so wrestling with lots of children is not a rare occurrence for me.)I don't find that I whirl my head and shoulders violently, putting large amounts of hair in front of my mouth, when I'm "wrestling" my wife (maybe others do, I don't know) so strands are all I have to worry about there.It seems to me, though, that the jerking of wrestling with kids would simulate fighting that might well be faced in an uncivilized society, and it would be very detrimental to choke on your own hair and have to pause to pull it out. Especially if we hadn't evolved speech yet, and your couldn't say "time out" to your opponent.

I think I should have had a smiley face in that last post at least a couple times. :-)

Oh, my smilies don't work, because I'm putting an nose in them. I should have read that smilies legend a long time ago .(edited to change my 0 to and O and make the embarrassed smiley work )[This message has been edited by truthlover, 01-28-2004][This message has been edited by truthlover, 01-28-2004]

I don't claim to know much about mammalian hair growth, but I have been told that horse's tails also grow "continually". I know that this doesn't answer the question, but it may help explain why some people can act so much like a horses ass ().

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 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]

Truthlover,The following:Nebulasearch.comsummarizes a handicap theory that may be useful in understanding human hair growth. Especially when we consider the role hair plays in sexual attraction, and the way it responds to stress (bad hair days) and poor diet. Clearly, someone who has it all together can communicate this by displaying abundant, well groomed hair, that reflects months or years of good diet, and a currently peaceful life-style. Thus, they are a good candidate for reproduction.Predictions:1. Split ends will be reduced by a high protein diet, especially one rich in sulfur.2. The length of time hair grows before it falls out will be diet and stress dependent.3. Human cultures where sexual selection has played a greater role will have potentially longer periods of hair growth.Beards, sexual dimorphism, testosterone factors might be inversely related to male hair growth, since these appear to reflect male aggression as the determiner to sexual choices, instead of sexual selection in the form of female choice of males.Rohwer's studies on territorial behavior and these sorts of signals are also relevant. Basically, the idea is that territorial genotypes all maximise the plumage marker, while "flocking" or "group living" genotypes let the marker vary, so that everyone in the group can find their place according to age and fitness. Territorial individuals are always the top dominant in their territory, and so always have the marker that communicates this. All chickadees (territorial, mostly), for example, have completely black throats. But Harris' Sparrows, which travel in flocks, have variably black throats.Rohwer noted that human females appear to be territorial, while the males tend to hunt in groups. The males have age markers (beards, greying, and balding, that change continually after puberty), while the reproductive females, at least, do not.A lot could be done scientifically with this problem, to generate a most interesting analyis!Stephen

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)

Human hair does indeed grow in cycles. I have measured human hair growth rates on the head, legs and face and growing hair tends to grow at about 0.4 mm/day on all these sites. The growing phase of hair is anagen and head hair tends to stay in anagen 3-5 years. I don’t have the paper here but I recall work for L’Oreal measuring the length of time hair stayed in anagen in several people over several years and the longest number I recall was 5.5 years. In histology it is easy to tell an anagen hair from a resting (telogen) hair. Anagen hairs are rooted well below the skin but telegen hair roots move well up into the middle of the skin. Hairs that are shed during combing are virtually all telogen hairs and mostly from follicles that have new anagen hairs starting to grow. Most people shed about 35 hairs per day. The 100 hairs per day number that you see quoted sometimes is derived from a back of the envelope calculation and is not correct. The real measured number is about 35.The density of hair follicles on the human body is about the same as chimpanzees and maybe a little more than gorillas IIRC. Every sebaceous (oil gland) on the body has a hair in it somewhere though they may be very fine and hard to find They can grow as the Ramos Gomez brothers show.
ForbiddenHuman hair is elliptical in cross section and even Asian hair has an ellipticity ratio (major axis/minor axis) of about 1.2. Caucasian hair tends to run from 1.3-1.4 and African hair may have a ratio as high as 1.8 and is not purely elliptical. It usually has a variety of shapes.The factors that control the cycling of hair are not completely understood. The wnt signaling pathway, long known through work on fruit flies is involved. http://www.chembio.uoguelph.ca/educmat/chm736/devsig.htm
http://www.chembio.uoguelph.ca/educmat/chm736/devsig.htm
Researchers Identify Signals that Cause Hair Follicles to Sprout | HHMI and wnt signaling clearly shows up during anagen onset
Reddy et. al. Mech. Devel. (2001) 107 69-82.There is a good article on hair growth in the June 2001 issue of Scientific American (pages 71-79)
The hormone that most effects hair growth is dihydro-testosterone (DTH), produced from testosterone by the enzyme 5 alpha reductase. This enzyme plays a key role in the development of sexual dimorphism during fetal development. At puberty DHT triggers fine vellus hairs in the underarms and pubic regions of both sexes and the face of males to become thicker, longer terminal hairs. Later in life the same hormone can trigger terminal hairs on the head to become fine vellus hairs leading to the development of baldness. In males baldness is patterned but in females hair loss is usually diffuse and may not start until after menopause. I have seen women with classic male pattern baldness but it is rare. The animal model for pattern baldness is the stump tailed macaque. Both males and females develop pattern baldness that responds to treatment similarly to humans.
Page not found - Regrowth. Your Source Of Hair NewsFinasteride is a 5 alpha reductase inhibitor originally developed for the treatment of benign prostate hyperplasia. It is used in a lower dose to treat baldness (Propecia).As to why humans evolved relative hairless, there are competing theories. I suspect it has to do with maintaining a proper thermal balance with a bipedal posture and that the development of eccrine sweating to help cool the body also played a role. Eccrine sweating will not be as efficient for cooling the body in a hairy animal. I don’t have any of the papers on that subject here today. I will look for some references later.Added in Edit: One of the few known differences in gene expression between humans and chimps is in hair keratins. The gene for Phi-hHaA is a pseudo gene in humans but functional in chimps and gorillas. SeeLangbein et al. Human type I hair keratin pseudogene phihHaA has functional orthologs in the chimpanzee and gorilla: evidence for recent inactivation of the human gene after the Pan-Homo divergence, Hum Genet. 2001 Jan;108(1):37-42.Randy[This message has been edited by Randy, 02-01-2004][This message has been edited by Randy, 02-01-2004]

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)

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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.

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There is always a distribution with biological responses. If you measured the height of 50 Chinese selected at random you probably wouldn’t find any that are 7 feet tall and probably not many over 6 feet tall, but then there is Yao Ming.

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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"?

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According to the Guinness Book of World records there is a guy with hair 16 feet long but that is obviously an anomoly.There are a few people who have been able to grow their hair beyond 30 inches. The longest I have ever seen personally was about three feet long on a woman 5 feet tall and she could sit on her braid. I have seen pictures of hair about 4 feet long. Hair 36 inches long will hang nearly to the knees of a women who is 5’3 , so you may be overestimating actual lengths that you have seen.

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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.

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Actually I was talking about eccrine sweating. Non eccrine sweat is apocrine sweating which occurs in association with hair follicles. Horses sweat by apocrine sweating. Eccrine glands are distributed over the whole body including the palms and soles where there are no hair follicles. Humans are not the only animals with eccrine sweat glands but we do seem to be the only ones who use them for major temperature regulation.

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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?

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Hair on the head may be there to help protect the head from the sun. It may also have played some role in maintaining body temperature during cool nights since heat loss from the head is higher than from any other area of the body. It is also possible that sexual selection played a role in maintaining head hair for some reason. I am not suggesting that the evolution of our relative hairlessness is well understood. It is still a controversial area of research as I said. I will look up some references on this subject when I have time.

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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?

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The signaling factors in fruit flies are named for their effects on the fly when perturbed. One of these is known as hedgehog. When the vertebrate factor that is homologous to hedgehog was discovered it was named sonic hedgehog(Shh) apparently after the video game.Medicine & Health - UNSW SydneyRandy

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)

H.You note: Should we then predict from the signalling hypothesis that body, non-signaling hair will be less dependent on dietary deficiencies, or stress, than head or signalling hair? If the latter is adapted to communicating health or the lack of health, it might amplify those problems, while functional hair just carries on.Adaptation, by the way, supports both the theories of creation and evolution.S.

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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)