Is body hair a functionless vestige?

Hi Phage & Ken Fabos,

Hair around the genitals and joints (such as armpits) can serve to prevent chafing.

I can verify this, as when I lost all my body hair (chemo) I had to use talc powder to lubricate the skin or it got raw.

Thin body hair can still act as a partial barrier against insects, or ...

... as a means to detect insects (mosquitos that carry diseases?) as a survival benefit.

Enjoy.

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Hi Dr Adequate,

After all, you didn't chafe in these areas when you were prepubescent, did you?

I thought about this, and considered that perhaps I didn't chafe because I was a scrawny kid, or that I lost whatever tough skin conditioning I had acquired as a child, once the hair was in place, or I never noticed as a kid, not having anything to compare it to.

The fact that such hair is acquired at puberty suggests to me that it has something to do with sex; if it had any other purpose it would develop earlier.

Plus any explanation for why hair is useful (or not) needs to explain the sexual dichotomy, just as any explanation for hair loss needs to explain the sexual dichotomy (as sexual selection does).

Enjoy

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Hi Bluejay,

But, hair would tend to hamper the movement of things like volatiles and perspiration away from the body. Pheromones would be less effective with hair covering the glands then with bare skin. Perspiration is also less effective when there is hair interfering with convective heat transfer.

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 ...

Enjoy.

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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:

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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.

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... 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:

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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.

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

Enjoy.

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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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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.

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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

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answer here Message 189 why is the lack of "fur" positive Progression for humans?

Enjoy

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.

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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.

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Hi Taq,

I am not certain that this is so:

This is why human hair is considered to be vestigial because it has lost its primary function.

What we have is hair development arrested in a juvenile stage of development. We don't have less hair than juveniles would have, and they would need to survive with that amount of hair in order to reach reproductive age.

Key here would be knowing what the environment was like for early hominids. If it were similar to Africa today in seasonal variation, the daytime temps could get down to ~65 with little discomfort, and nesting at nighttime (like other apes do) would take care of lower nighttime temps.

IIRC, this is approximately what is thought to have been the case for Ardi to Lucy.

We could still have as much insulation as we would need to survive in that environment, and it would be unfair to say that it isn't enough to survive in the arctic, because adaptation was not for that environment.

I'm also not certain that a feature that is arrested in development at an earlier stage due to a mutation in the development sequencing can really be considered vestigial, because the "disuse" is forced by the change in development sequencing rather than being a feature that is no longer necessary and falls into disuse.

Enjoy.

Edited by RAZD, : subtitle, last p

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