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Author Topic:   Is body hair a functionless vestige?
RAZD
Member (Idle past 675 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 16 of 143 (559841)
05-11-2010 7:53 PM
Reply to: Message 12 by Ken Fabos
05-11-2010 6:34 PM


Re: More or less important
Hi again Ken Fabos,

... My understanding is that it's not the number of hairs that's widely variable, ...

Curiously, I looked into this when putting together Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution, see Message 41:

quote:
If loss of hair was an important variable in thermoregulation then we would expect {evolutionary pressure \ natural selection} to show a broad trend of hair thickness variations that could be correlated with the need to {retain\dissipate} heat.

We do see this. From the same source, here discussing the need of larger bodies to {retain less \ dissipate more} heat due to the increase in volume as the cube but skin area as the square of a size dimension:

The obvious solution to this situation is decreased body hair with increasing body size, which is exactly what is seen in anthropoids. When the number of hair follicles present in species per unit of area is compared with body size, all primates (including humans) fit along a regular log linear regression line, along which the density of hair per unit of area decreases as body size increases. Species like chimpanzees and gorillas have relatively fewer hair follicles per unit area of skin compared to the smaller monkeys. Humans fall along this line, and have a relative hair density almost the same as seen in chimpanzees, gorillas and orangutans.

To drive this point home, the number of hairs on the human body are precisely what they should be for the human body size. We are not displaced on the scale. There is no special loss of hair required for thermoregulation, and thus there is no special mechanism needed to provide for the loss of hair: no mutation is needed for the explanation of amount of human body hair.


... just their size - but I could be wrong. Anyone know? ...

Not the size, really, but the developmental stages are interrupted at a younger stage. Again from Message 41:

quote:
The difference between the thick pelage of the Great Apes and humans is not in terms of the density of hair, but in its length and thickness and the production of vellus hair in most humans to the exclusion of terminal hair on the body. Humans are not "hairless", but are merely covered by thinner, smaller and unpigmented hair (Schwartz & Rosenblum 1981; Schultz 1931).

This may seem like an obvious point (although 'underpigmented' might be better than unpigmented: it's not albinoism).

Now to better understand the distinction here, we need to know what vellus hair is and how it differs from terminal hair.

Types of Hair (click)

There are three types of hair:
*lanugo: fetal hair
*vellus: replace lanugo hairs in the peripartum period, unmedullated
*terminal hairs: long, coarse, medullated; typified by scalp and pubic regions

...

Vellus hair is juvenile hair that is best seen in women? Other than facial hair, is there really that much difference in hair patterns between males and females? See information about a medical 'condition' called Masculine Hair Distribution (in a female):

This is excessive hair growth in an androgen dependent pattern. It is applied to females who complain of hair growth in the beard area, around the nipples and in a male pattern on the abdomen. Androgens induce the transformation of fine vellus hair into coarse terminal hair.

Female vellus hair that is transformed into terminal hair in a male pattern. As a bad thing.

Put this together with the "baby-faced-ness" and the issue of run-away sexual selection of
Human Skin hair thinness is seen as two results of the same process: juvenile features selected for in the female of the species. And considering that the bareness of the human female could not get much further developed without some mutation to actually decrease the numbers of hairs on the human body, I would say that it has been carried to the extreme condition that is characteristic of a fully developed run-away mechanism.


I also note that this sexual selection is still continuing, as the prevalence of shaving of body parts shows.

Enjoy.


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by our ability to understand
Rebel American Zen Deist
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This message is a reply to:
 Message 12 by Ken Fabos, posted 05-11-2010 6:34 PM Ken Fabos has replied

Replies to this message:
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dennis780
Member (Idle past 4046 days)
Posts: 288
From: Alberta
Joined: 05-11-2010


Message 17 of 143 (559845)
05-11-2010 8:16 PM
Reply to: Message 1 by Ken Fabos
05-09-2010 6:41 PM


Perfect perfect body hair...
Actually, I think you have 'jumped the guns' so to speak on this subject, in saying that hair provides little to no insulation for an animal. This just isn't true.

In fact, in 2004, Harvard students shaved a camel, and found it's water loss due to sweat increased by over 30%. As well, it would seem logically correct, since physically most animals living in warmer climates have fur, such as Zebras, Giraffes, Lions, Tigers, Apes, Monkeys, Oxen, Antelope, horses, cows, hyenas, etc. You get the point.

There are many reasons that contradict apes `evolving` from quadrupeds to bipeds, losing their fur, etc. But I think for this particular subject, this information seems relevant.

Dennis.


This message is a reply to:
 Message 1 by Ken Fabos, posted 05-09-2010 6:41 PM Ken Fabos has replied

Replies to this message:
 Message 18 by RAZD, posted 05-11-2010 8:40 PM dennis780 has replied
 Message 20 by Ken Fabos, posted 05-11-2010 9:41 PM dennis780 has replied

  
RAZD
Member (Idle past 675 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 18 of 143 (559853)
05-11-2010 8:40 PM
Reply to: Message 17 by dennis780
05-11-2010 8:16 PM


Re: Perfect perfect body hair...
Hi dennis780, and welcome to the fray.

In fact, in 2004, Harvard students shaved a camel, and found it's water loss due to sweat increased by over 30%.

Citation please? Did the camel maintain the same body temperature?

There are many reasons that contradict apes `evolving` from quadrupeds to bipeds, losing their fur, etc. ...

Oh? Care to start a new thread on this?

Go to Proposed New Topics to post new topics.

Enjoy.

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we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 17 by dennis780, posted 05-11-2010 8:16 PM dennis780 has replied

Replies to this message:
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Ken Fabos
Member (Idle past 510 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 19 of 143 (559860)
05-11-2010 9:15 PM
Reply to: Message 16 by RAZD
05-11-2010 7:53 PM


Re: More or less important
RAZD, that did sound a lot like what I said - numbers the same, hair size different and evolution didn't add more follicles in line with increasing size, nor produced thicker heavier hairs. Whether true across the whole human spectrum would still be a question. Seems like the size of those vellus hairs, by whatever mechanism, has reduced, even to the point of near invisibility, but not universally. Seems (from my layman's perspective) likely we've seen hormonal variations to growth of hairs - which is likely to have been evolutionarily easier - rather than actual loss of follicles. But the loss of those hairs completely would take away an array of sensory mechano-receptors that are still potentially advantageous. Can there be evolutionary advantage in reducing our sensory sensitivity? Does a heavier pelage make for more or less sensitivity - or just sensitivity to different kinds of stimuli. eg, longer hairs might be better at detecting air movements and shifts in breeze than shorter lighter ones and lighter ones more able to detect small insects. And does hair held erect by goosebumps transmit those tactile sensations better than in it's relaxed state? They'd be held tighter. Also not sure what adrenalin and the like do to our sense of touch, whether by direct skin contact or through our hairs; increased sensitivity doesn't sound impossible.
There's a lot we don't know and should if we are to make informed speculation about the evolutionary process that's made us how we are.
On shaving I wouldn't think that people plucking and shaving counts in the sexual selection of relative hairiness; even if reduced hairiness is a measure of attractiveness in the modern context those practices are likely to prevent the selection for reduced hair by giving false impressions. Hairy girls can still get the guys, just keep on plucking!

This message is a reply to:
 Message 16 by RAZD, posted 05-11-2010 7:53 PM RAZD has seen this message

  
Ken Fabos
Member (Idle past 510 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 20 of 143 (559866)
05-11-2010 9:41 PM
Reply to: Message 17 by dennis780
05-11-2010 8:16 PM


Re: Perfect perfect body hair...
Hi Dennis. From my perspective functionality with respect to thermoregulation seems very likely, however it must be highly variable as our hairiness is highly variable. I'm hairy enough myself to believe that it can still provide me some insulation from the cold, a smallish amount primarily when at rest in the absence of breeze, by impeding but not stopping air flow. Cooling? See my earlier comments, but sparse human body hair allows air flow across bare skin even if sometimes thick enough to impede it.
Rather than having jumped the gun myself, I think others have; I was commenting on what I believe to be a widespread meme, one I think is overdue for debunking. My own focus remains the sensory function which I think is a serious ongoing omission; whilst I haven't gone through every thread here, I have looked through a lot of discussions of human 'hairlessness' and sensory function looks especially conspicuous by it's absence.

This message is a reply to:
 Message 17 by dennis780, posted 05-11-2010 8:16 PM dennis780 has replied

Replies to this message:
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Dr Adequate
Member (Idle past 321 days)
Posts: 16112
Joined: 07-20-2006


Message 21 of 143 (559884)
05-12-2010 12:44 AM


A Non-Adaptationist Explanation?
I read recently (I think in a book on supernormal stimuli) that the places where we do get hair are also the places where chimps get it first.

So the distribution of hair in humans could be the side effect of a (hormonal?) adaptation towards neoteny that had nothing to do with hair as such but was favored for its effect on something else, such as brain plasticity. It would be what Gould called a spandrel.


  
dennis780
Member (Idle past 4046 days)
Posts: 288
From: Alberta
Joined: 05-11-2010


Message 22 of 143 (559894)
05-12-2010 1:49 AM
Reply to: Message 18 by RAZD
05-11-2010 8:40 PM


Re: Perfect perfect body hair...
Thanks RAZD. I'll try using the quote thing there...lol. I'm old school you know.

Citations for Camels water loss:

http://www.animalcorner.co.uk/...fe/camels/camels_about.html
http://www.solarnavigator.net/...l_kingdom/mammals/camel.htm
http://worldanimalfoundation.homestead.com/adoptacamel.html

Although these sites seem to say 50%. It's been a few years since I first read about it so I am probably mistaken, and they actually sweat 50% more.

And no, I don't care to start a new thread. I just started on this a few hours ago, and don't have enough time to answer the threads that alread exist. I'm sure there is a thread discussing the various subjects....plus I don't know the first thing about starting a thread. The study of evolution and creation is just a hobby for me, and hobbies are supposed to be fun. I much prefer to jump into conversations unannounced and blurt random facts. This is fun.


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dennis780
Member (Idle past 4046 days)
Posts: 288
From: Alberta
Joined: 05-11-2010


Message 23 of 143 (559896)
05-12-2010 1:55 AM
Reply to: Message 20 by Ken Fabos
05-11-2010 9:41 PM


Re: Perfect perfect body hair...
Another point to notice is that generally humans grow hair where apes do not. the face and chest are prime examples, since apes are hairless there, or sparse, but humans (especially males) grow hair in these areas. Even female humans grow chest hair and nipple hair (as much as we would like to ignore it, lol).

I'm a little confused as to the sensory point. It's unclear to me how this would be an advantage or disadvantage either way. More detail??


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Dr Adequate
Member (Idle past 321 days)
Posts: 16112
Joined: 07-20-2006


Message 24 of 143 (559916)
05-12-2010 3:48 AM
Reply to: Message 23 by dennis780
05-12-2010 1:55 AM


Re: Perfect perfect body hair...
Another point to notice is that generally humans grow hair where apes do not. the face and chest are prime examples, since apes are hairless there, or sparse, but humans (especially males) grow hair in these areas.

Well I'm not sure that this is particularly sparse as compared to a human.

Sparse compared to the rest of the chimpanzee, perhaps. But to suggest that we "grow hair where apes do not" seems unjustified.


This message is a reply to:
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Replies to this message:
 Message 25 by dennis780, posted 05-12-2010 4:14 AM Dr Adequate has replied

  
dennis780
Member (Idle past 4046 days)
Posts: 288
From: Alberta
Joined: 05-11-2010


Message 25 of 143 (559922)
05-12-2010 4:14 AM
Reply to: Message 24 by Dr Adequate
05-12-2010 3:48 AM


Re: Perfect perfect body hair...
"Well I'm not sure that this is particularly sparse as compared to a human."

I'm not comparing, I'm pointing out that apes are MORE hairy everywhere but their face and chest. This is the opposite with humans.

thats one hairy ape, how long did it take you to find that one pic of a monkey with a hairy chest? Cause I found lots to show they are FAR more sparse on their face and chest:
http://www.kodak.com/.../en/corp/1000words/pschwartz/ape.jpg
http://www.kuvamaja.com/..._Park_ape_straw_8X10_02720096.jpg
http://www.wildabouttheworld.com/...ery/data/505/Gorilla.jpg
http://www.animalpictures1.com/data/media/65/gorilla-15.gif
http://liliendahl.files.wordpress.com/2009/10/gorilla.jpg
http://www.greendiary.com/images/r_chimpanzee.jpg


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 Message 24 by Dr Adequate, posted 05-12-2010 3:48 AM Dr Adequate has replied

Replies to this message:
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Dr Adequate
Member (Idle past 321 days)
Posts: 16112
Joined: 07-20-2006


Message 26 of 143 (559924)
05-12-2010 4:25 AM
Reply to: Message 25 by dennis780
05-12-2010 4:14 AM


Re: Perfect perfect body hair...
I'm not comparing, I'm pointing out that apes are MORE hairy everywhere but their face and chest.

What you said was "humans grow hair where apes do not".

thats one hairy ape, how long did it take you to find that one pic of a monkey with a hairy chest? Cause I found lots to show they are FAR more sparse on their face and chest:

Most of those pictures don't look that much different.

Edited by Dr Adequate, : No reason given.


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Replies to this message:
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dennis780
Member (Idle past 4046 days)
Posts: 288
From: Alberta
Joined: 05-11-2010


Message 27 of 143 (559935)
05-12-2010 5:04 AM
Reply to: Message 26 by Dr Adequate
05-12-2010 4:25 AM


Re: Perfect perfect body hair...
Less hair on chest and face, more on rest of body.

Humans opposite. Follow?


This message is a reply to:
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Dr Adequate
Member (Idle past 321 days)
Posts: 16112
Joined: 07-20-2006


Message 28 of 143 (559939)
05-12-2010 5:16 AM
Reply to: Message 27 by dennis780
05-12-2010 5:04 AM


Re: Perfect perfect body hair...
Less hair on chest and face, more on rest of body.

Humans opposite. Follow?

Yes. This does not support your claim that "humans grow hair where apes do not". Follow?


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Dr Adequate
Member (Idle past 321 days)
Posts: 16112
Joined: 07-20-2006


Message 29 of 143 (559944)
05-12-2010 5:28 AM
Reply to: Message 22 by dennis780
05-12-2010 1:49 AM


Re: Perfect perfect body hair...
I much prefer to jump into conversations unannounced and blurt random facts.

You seem to be better at the "random" bit than the "fact" bit.


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Ken Fabos
Member (Idle past 510 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 30 of 143 (560237)
05-13-2010 10:09 PM


Anyone disagree that body hair has sensory function?
I'm curious if anyone here thinks the sensory function of body hair is inconsequential or lacks relevance to understanding it's evolution? Also, has anyone come across serious discussion of that evolution that includes due consideration for that sensory function?
I've been accusing the community of academics that study human evolution of (to my mind) a serious oversight. I don't mind being proven wrong, but I've struggled to find evidence that it's gotten any real consideration.

Replies to this message:
 Message 31 by Dr Adequate, posted 05-14-2010 5:16 PM Ken Fabos has replied
 Message 59 by Artemis Entreri, posted 06-16-2010 6:24 PM Ken Fabos has replied

  
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