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Author Topic:   Is body hair a functionless vestige?
Blue Jay
Member (Idle past 1968 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 46 of 143 (561234)
05-19-2010 2:10 PM
Reply to: Message 15 by RAZD
05-11-2010 7:24 PM


Re: horse sweat and scents work quite well with hair.
Hi, RAZD.

RAZD writes:

I've heard this argument before, often as part of a "why humans lost hair" argument, and it seems somewhat logical at first ... but it doesn't explain horses. They sweat, and they have lots of horse scents ...

Play on words: I like it.

In terms of sweating, surface cooling isn't the only thing it does: heat is removed from the core in sweat too, so, even if it doesn't evaporate away, it's still helping dissipate heat.

About pheromones and other scents, I admit less understanding. It may be that the slower dispersal of scents caused by hair is advantageous in some cases, and can actually concentrate the scent more.

I know that some moths actually collect pheromones in their hairs, then spread the hairs and fan them in the wind to disperse them, so hair can serve a pheromonal purpose.

The thing that bugs me about the way Ken presented this suggests that our body hair is superior to both total nakedness and heavier pelage in terms of perspiration and pheromonal dispersal, which doesn't make a lot of sense to me.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 15 by RAZD, posted 05-11-2010 7:24 PM RAZD has replied

Replies to this message:
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Coyote
Member (Idle past 1376 days)
Posts: 6117
Joined: 01-12-2008


Message 47 of 143 (561235)
05-19-2010 2:22 PM
Reply to: Message 46 by Blue Jay
05-19-2010 2:10 PM


Hair loss
My guess on this is that the selection pressure was to remove hair to promote cooling. One old idea was that this may have been needed for persistence hunting, where people simply ran their prey to exhaustion.

If this is the case, the selection pressure to reduce hair would work up to the point where it didn't matter much any more; the selection pressure would end when the cooling was just good enough.


Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.

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


Message 48 of 143 (561313)
05-19-2010 10:10 PM
Reply to: Message 47 by Coyote
05-19-2010 2:22 PM


What Hair loss?
Hi Coyote,

My guess on this is that the selection pressure was to remove hair to promote cooling.

(1) There has been no removal of hair - the apparent bareness is due to hair being arrested in an immature stage, vellus hairs, common on juveniles before puberty.

One old idea was that this may have been needed for persistence hunting, where people simply ran their prey to exhaustion.

(2) IF this were true THEN the most hairless appearing humans would be the hunters and not the gatherers. Conclusion: women did the hunting while the men did the gathering. Please compare this to what you know about anthropology.

(3) This also explains why other cursorial hunters, like wild dogs and wolves, are naked ... ?

If this is the case, the selection pressure to reduce hair would work up to the point where it didn't matter much any more; the selection pressure would end when the cooling was just good enough.

(4) OR the selection pressure would prevent total loss of hair when it reaches levels that endanger survival of the organisms, because the nights are a considerably different temperature, to say nothing about seasons. Curiously, the subcutaneous fat layer in humans is thicker than in other apes, perhaps in order to replace hair as insulation as the hair was lost for other reasons ....

(5) OR the selection pressure would work up to the point where it didn't matter much any more; the selection pressure would end when the appearance of bareness was just good enough. There is vast evidence of sexual selection of females for youthful appearance, and thus juvenile hair patterns would meet that selection criteria, without requiring that bareness be achieved.

(6) Selection pressure would work more on the sex that benefits from the apparent loss of hair: in humans the females are much more advanced in apparent bareness than the males, and the hair pattern in women is fairly consistent, while in men it varies considerably.

... the selection pressure would end when the ...

... selection goal is met, and the evidence is that it still continues:

(7) The evidence is that bare skin is still a factor in sexual selection, by the vast industry in hair removal equipment, salves, and treatements, some for men, but much more for women (also see Venus razor ads).

(8) Male hair pattern in women is seen as an unfortunate medical condition, female hair pattern in men is not.

(9) The porn industry is populated with fully shaved bodies, and a google for "hairy naked women" only shows women that have not shaved armpits and crotch, not women with beards.

Enjoy.


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 47 by Coyote, posted 05-19-2010 2:22 PM Coyote has seen this message

Replies to this message:
 Message 49 by Dr Jack, posted 05-20-2010 4:29 AM RAZD has replied

  
Dr Jack
Member (Idle past 1375 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 49 of 143 (561364)
05-20-2010 4:29 AM
Reply to: Message 48 by RAZD
05-19-2010 10:10 PM


Re: What Hair loss?
(2) IF this were true THEN the most hairless appearing humans would be the hunters and not the gatherers. Conclusion: women did the hunting while the men did the gathering. Please compare this to what you know about anthropology.

African men are considerably more hairless than european men. It is quite plausible that the increased hairiness of men in Europe represents a trend of adaptation to colder conditions.

quote:
(3) This also explains why other cursorial hunters, like wild dogs and wolves, are naked ... ?

Those aren't persistance hunters. Humans are the only species in the world known to persistant hunt, AFAIK.

quote:
(7) The evidence is that bare skin is still a factor in sexual selection, by the vast industry in hair removal equipment, salves, and treatements, some for men, but much more for women (also see Venus razor ads).

(8) Male hair pattern in women is seen as an unfortunate medical condition, female hair pattern in men is not.

(9) The porn industry is populated with fully shaved bodies, and a google for "hairy naked women" only shows women that have not shaved armpits and crotch, not women with beards.


Using recent, predominantly western european fashions as evidence for long term evolutionary trends strikes me as absurd in the extreme.


This message is a reply to:
 Message 48 by RAZD, posted 05-19-2010 10:10 PM RAZD has replied

Replies to this message:
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Blue Jay
Member (Idle past 1968 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 50 of 143 (561408)
05-20-2010 11:46 AM
Reply to: Message 49 by Dr Jack
05-20-2010 4:29 AM


Re: What Hair loss?
Hi, Mr Jack.

RAZD and I had this debate awhile back on why is the lack of "fur" positive Progression for humans?, starting around Message 156.

Mr Jack writes:

African men are considerably more hairless than european men.

I argued this, as well, but it turns out to not be entirely correct. I even looked up the most basal groups of humans and found them to be the least hairy of the Africans, but it turns out that they've got admixture with Asian populations, so hairlessness may not be a plesiomorphic trait (I don't think there's any evidence on this at the present time, though).

-----

Mr Jack writes:

RAZD writes:

This also explains why other cursorial hunters, like wild dogs and wolves, are naked ... ?

Those aren't persistance hunters. Humans are the only species in the world known to persistant hunt, AFAIK.

Actually, this isn't true. All the big Canidae are built for endurance hunting: they hunt in long chases until their prey are exhausted. Other examples are hyenas (particularly the extinct "hunting hyenas"), stoats and possibly even the thylacine.

-----

Since Ken Fabos wants to focus on sensory functions of hair, maybe we could continue this discussion on why is the lack of "fur" positive Progression for humans?: I think there's still potentially a lot to be said for thermoregulatory functions of hairlessness.


-Bluejay (a.k.a. Mantis, Thylacosmilus)

Darwin loves you.


This message is a reply to:
 Message 49 by Dr Jack, posted 05-20-2010 4:29 AM Dr Jack has taken no action

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


Message 51 of 143 (561423)
05-20-2010 1:55 PM
Reply to: Message 49 by Dr Jack
05-20-2010 4:29 AM


Re: What Hair loss?
Hi Mr Jack,

To add to what Bluejay said,

African men are considerably more hairless than european men. It is quite plausible that the increased hairiness of men in Europe represents a trend of adaptation to colder conditions.

The telling issue is now how much different populations of men have different grades of apparent bareness, but the sexual dichotomy.

If an increase in apparent hairiness in men occurred as an adaptation to colder conditions, then why does it not also appear in women?

Any explanation for the apparent bareness of humans is incomplete at best if it does not explain the sexual dichotomy.

Sexual selection is the only mechanism I am aware of that explains the sexual dichotomy.

We know that many features of humans compared to chimps are due to neoteny. It is not logical that the selection for neoteny only selected facial features, rather than overall juvenile appearance, including the retention of juvenile hair patterns.

Again, there is no loss in the number of hair follicles, what we have is development of hair, particularly in women, arrested in a juvenile - vellus hair - stage.

Using recent, predominantly western european fashions as evidence for long term evolutionary trends strikes me as absurd in the extreme.

Riiight, I wouldn't dream of claiming that the present is the key to the past, and that, just because something is existing today, that it could have been existing in the past. ...yes?

Bluejay Message 50
Since Ken Fabos wants to focus on sensory functions of hair, maybe we could continue this discussion on why is the lack of "fur" positive Progression for humans?: I think there's still potentially a lot to be said for thermoregulatory functions of hairlessness.

I agree, and would be happy to discuss this further on that thread with anyone.

Enjoy


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 49 by Dr Jack, posted 05-20-2010 4:29 AM Dr Jack has replied

Replies to this message:
 Message 52 by Dr Jack, posted 05-20-2010 3:01 PM RAZD has replied

  
Dr Jack
Member (Idle past 1375 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 52 of 143 (561443)
05-20-2010 3:01 PM
Reply to: Message 51 by RAZD
05-20-2010 1:55 PM


Re: What Hair loss?
Riiight, I wouldn't dream of claiming that the present is the key to the past, and that, just because something is existing today, that it could have been existing in the past. ...yes?

Sure, but using something we know has changed within the last hundred years and isn't culturally uniform as the basis for an argument is profoundly flawed.


This message is a reply to:
 Message 51 by RAZD, posted 05-20-2010 1:55 PM RAZD has replied

Replies to this message:
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Ken Fabos
Member (Idle past 511 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 53 of 143 (561482)
05-20-2010 8:21 PM
Reply to: Message 45 by Blue Jay
05-19-2010 2:04 PM


More or less sensitive than thick fur?
Bluejay, you asked

Do you think our pelage is better at sensory perception than the thicker pelages of other animals?

I think it's possible, particularly with respect to low threshold stimuli such as needed to detect small parasites. Without some experimental evidence it's speculation but I would point out again that very fine vellus hairs retain a lot of sensitivity and I would not be surprised if they can detect impulses smaller and finer than thick heavy hairs of a thick pelage.
On thermoregulatory function and perspiration, again some experimental evidence looks to be required. I think that the consequences of slowed air flow are very different to blocked air flow and I suspect that flow rates would be critical. My own speculation is that it's not as straightforward as you suggest and that even relatively sparse hairs still increase the overall surface area for evaporation. Wouldn't that cool the air close to the skin? We'd get a hot body warming that air, which is already cooled somewhat, increasing the temperature gradient and resulting in more rapid cooling.
If you want to split off discussion of this from discussion of sensory function that's fine but not necessary for my sake; whilst sensory function has been my primary focus I didn't set out to limit discussion to that alone.

This message is a reply to:
 Message 45 by Blue Jay, posted 05-19-2010 2:04 PM Blue Jay has replied

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


Message 54 of 143 (561487)
05-20-2010 8:56 PM
Reply to: Message 52 by Dr Jack
05-20-2010 3:01 PM


issue taken to another thread

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


Message 55 of 143 (564880)
06-13-2010 1:02 PM
Reply to: Message 46 by Blue Jay
05-19-2010 2:10 PM


Re: horse sweat and scents work quite well with hair.
Hi Bluejay, thanks.

The thing that bugs me about the way Ken presented this suggests that our body hair is superior to both total nakedness and heavier pelage in terms of perspiration and pheromonal dispersal, which doesn't make a lot of sense to me.

Recent article on wiki on hair mentions that the hair follicles relax so the hairs lie next to the skin when sweating. This would facilitate sweating as a means of thermoregulation to disburse excess body heat regardless of how thick the hair was. This would then correlate with males having highly variable degrees of hairiness.

I've also been thinking that being arrested at a juvenile stage of development in body hair does not necessarily result in a loss of the insulation value of hair for thermoregulation to retain body heat at night or during cold snaps, as the juveniles survive with this same degree of hair development.

I know that some moths actually collect pheromones in their hairs, then spread the hairs and fan them in the wind to disperse them, so hair can serve a pheromonal purpose.

And I have some problem considering pheromones at all, when the sensory organ in other mammals and primates is vestigial or missing in apes, including humans, with no nerve inputs. See Message 261 by Coragyps.

Enjoy.


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:
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Replies to this message:
 Message 56 by Ken Fabos, posted 06-14-2010 6:56 PM RAZD has replied

  
Ken Fabos
Member (Idle past 511 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 56 of 143 (565111)
06-14-2010 6:56 PM
Reply to: Message 55 by RAZD
06-13-2010 1:02 PM


Re: horse sweat and scents work quite well with hair.
Bluejay, RAZD - I think I was referring more to the hairy pits and crevices for pheromones - and pointing out that hairs, generally, are part of the mechanism of such dispersal and therefore functional. This appears to be included in existing literature, including wikepedia - not something purely speculative. I didn't intend to suggest thinned out body (vellus) hair is superior in this regard although I don't see reason to think it doesn't function that way. As for perspiration - I've already pointed out mechanisms that would allow relatively thin hair to have a significance for carrying sweat and impact cooling. How significant this might be is probably only going to be made clear with some experimentation and I'm not in any position to do so. This function, to wick away moisture - with and without pheromones - is also known in the scientific literature - David Wolfgang-Kimball's "Pheromones in Humans - Myth or reality" for example. This has to impact temperature regulation. But I don't see that the hairs need to lay flat against the skin to carry sweat; the surface of hairs is able to draw moisture away from the skin by capillary action and the greater surface area, above the skin's surface (where air flow is greater) would facilitate increased evaporation. Thinned out hair might actually be superior in this regard than a thick, heavy pelage.

This message is a reply to:
 Message 55 by RAZD, posted 06-13-2010 1:02 PM RAZD has replied

Replies to this message:
 Message 57 by RAZD, posted 06-14-2010 8:57 PM Ken Fabos has replied
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RAZD
Member (Idle past 675 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 57 of 143 (565121)
06-14-2010 8:57 PM
Reply to: Message 56 by Ken Fabos
06-14-2010 6:56 PM


Re: horse sweat and scents work quite well with hair.
Hi Ken,

... I think I was referring more to the hairy pits and crevices for pheromones ...

You still hae the problem of the sensory apparatus being vestigial in humans and apes. With this lack of ability to sense the pheromones in apes as well as humans, the differences in hair development becomes relatively inconsequential.

Thinned out hair might actually be superior in this regard than a thick, heavy pelage.

But the hair is not thinned out, rather the individual hairs are slightly thinner, generally straight (rather than curly), and transparent, none of which would affect the issue of sweating.

To me this means that the evolution of sweating in humans is not necessarily linked in any way to the arresting of the development of hair at a juvenile stage.

Enjoy.


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 56 by Ken Fabos, posted 06-14-2010 6:56 PM Ken Fabos has replied

Replies to this message:
 Message 58 by Ken Fabos, posted 06-15-2010 8:17 PM RAZD has seen this message

  
Ken Fabos
Member (Idle past 511 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 58 of 143 (565289)
06-15-2010 8:17 PM
Reply to: Message 57 by RAZD
06-14-2010 8:57 PM


Re: horse sweat and scents work quite well with hair.
RAZD, for pheromones I am repeating what others - published scientists - have suggested. I was merely trying to point out that body hair can have varied functions beyond the sensory one that published scientists have failed to give consideration to and that inspired me to start this discussion. If there is clear evidence that humans have completely lost the capability to sense such pheromones then those scientists need to review and revise.

On thermo-regulation and perspiration my terminology may be imprecise but the reduced size - length and thickness - of our body hairs allows air flow in the zone close to the skin that a thick pelage does not, therefore it affects the rate of evaporation in that zone. How significant existing variable 'amounts' of hair is with respect to that air flow or how much moisture is carried along the hair shafts - individually or when laid together - and how that impacts subsequent cooling is a discussion that can suggest areas of enquiry but not give us clear answers. It looks unlikely there'll be any clear conclusions without some experimental or other evidence.
Which leaves me concluding that evolutionary as well as medical science knows a lot less about these matters than I first imagined; it's not just the sensory function of hair that looks to be neglected. Not that there aren't higher priority questions than these; I shouldn't complain that more important scientific questions get preferential treatment.


This message is a reply to:
 Message 57 by RAZD, posted 06-14-2010 8:57 PM RAZD has seen this message

  
Artemis Entreri 
Suspended Member (Idle past 3499 days)
Posts: 1194
From: Northern Virginia
Joined: 07-08-2008


(1)
Message 59 of 143 (565433)
06-16-2010 6:24 PM
Reply to: Message 30 by Ken Fabos
05-13-2010 10:09 PM


Re: Anyone disagree that body hair has sensory function?
It should be pointed out that there are some ethnic groups of Africans who don't have any body hair at all, not even the fine fuzz that most people have (that is, they have the normal concentrations of hair on the head, armpits, and pubic area, but none on their arms, legs, etc). I write this from memory, so I can't give a reference. I've also seen it for myself.
They seem to get by without it.

Dang I was really hoping for a link. Depending on which group of Africans this is, could be evidence that body hair is not a vestige, at all, but more of an adaptation. For example if it was the Khoisan then this could be the case rather than if it was the Moroccans.
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 see where you are coming from, but No I do not think hair is an adaptation to better help with sensory functions. All I can think of right now is arachnids, and how they use their hairs for sensory information, but those hairs are placed in places to better serve that cause, like on the ends of their legs (spiders), or on the body to detect vibrations in still dark places (scorpions). The only Mammals that I can think of that use hairs for the purpose of sensory information are felines (whiskers). I know that the whiskers of a cat help with its equilibrium, and its ability to navigate when its superior vision cannot be used. Humans on the other hand seem to not have hair on there hands, and feet, nor whiskers. I realize this is a simple observation.

Dr Adequate, when you brush something across your body hairs -without touching the skin - can't you feel it?

Only if the brush if forceful enough to be felt at the skin level. Only if it vibrates to the root, otherwise you could feel dust landing on your hair.

Edited by Artemis Entreri, : No reason given.


This message is a reply to:
 Message 30 by Ken Fabos, posted 05-13-2010 10:09 PM Ken Fabos has replied

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Ken Fabos
Member (Idle past 511 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 60 of 143 (565552)
06-17-2010 8:28 PM
Reply to: Message 59 by Artemis Entreri
06-16-2010 6:24 PM


Re: Anyone disagree that body hair has sensory function?
Artemis Entreri - Sorry, but my hairs are able to sense things at a threshold much lower than my bare skin. I don't believe I am unusual in this respect. I've described simple experiments that show this to be the case - a hair too fine to feel brushed across skin but can be felt by body hairs is hardly brute force. Yes, the nerves involved are within the skin and almost certainly include the feedback of erector pilori muscles. By the physics of levers even small forces can move a fine hair enough to be sensed. Clearly there is a threshold - that a speck of dust is below.

For detection of insects and ticks I have no choice, given my own everyday experiences, to conclude that vellus hairs are superior to hairless skin - and very fine vellus hairs are superior to thick heavy hairs - for detection of very small stimuli. Try brushing the very fine hairs high over cheekbones or on your nose or ears; in my case its an effort to not have the irritating tickling cause me to rub or scratch. I think the tactile sensations of skin and hairs tend to merge in our perception and I suggest you may be attributing most of what you perceive to direct skin touch rather than to the movements and vibrations of hairs. The sensations are subtly different and by paying close attention it is possible to learn to discriminate between them. The sensory function of hair insignificant? I don't think so.


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