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Author Topic:   Is body hair a functionless vestige?
Blue Jay
Member (Idle past 287 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 61 of 143 (565560)
06-18-2010 12:22 AM
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.

Ken Fabos writes:

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.

I think youve not been reading us very carefully. None of us has argued that hair is not functional. Im not sure why you think any of us would be arguing that hair is non-functional.

We have only been pointing out that, in order for the functions you ascribe to our relative hairlessness to have evolutionary significance, you need to show that functionality is greater under the our situation than under other situations.

-----

Ken Fabos writes:

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

This would be of very little benefit for evaporative cooling.

Sweat works in two ways.

First, the liquid carries some excess heat away from the core and deposits it outside of the body, thus reducing core temperature. The heat shed in this way is not enough to cause the liquid to evaporate, which is why it is exuded as a liquid.

Second, when exuded onto the skin surface, the liquid absorbs heat from the surface, which causes it to evaporate. The net effect is reduced surface temperature. Sweat beads that are wicked away from the skin surface will absorb less (if any) heat from the skin surface, and will thus be less effective at fulfilling this second function than sweat beads that are not wicked away from the surface.

You can test this by putting a drop of water on an arm hair, then blowing it away; and then putting a drop of water on your skin, then blowing it away. Sweat wicked away from the body is of less benefit to evaporative cooling than sweat retained on the surface of the body.

So, completely bare skin should still outperform a thin pelage in terms of sweating.


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

Darwin loves you.


This message is a reply to:
 Message 56 by Ken Fabos, posted 06-14-2010 6:56 PM Ken Fabos has responded

Replies to this message:
 Message 65 by Ken Fabos, posted 06-19-2010 8:48 PM Blue Jay has not yet responded

  
Blue Jay
Member (Idle past 287 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 62 of 143 (565565)
06-18-2010 1:57 AM
Reply to: Message 53 by Ken Fabos
05-20-2010 8:21 PM


Re: More or less sensitive than thick fur?
Hi, Ken.

Ken Fabos writes:

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.

For what purpose?

I dont see a really good reason why detection of parasites requires hairs that are sensitive to even the subtlest breezes when thicker hairs are sufficiently sensitive to detect the movement of parasites on the skin. Fine hairs also result in wide gaps between them, which creates pockets of sensory void that animals with thicker hairs dont have. I just dont see how our sparser hair really makes sense as a sensory adaptation.

Furthermore, I think the heightened sensitivity to touch on your face can be explained at least as well by the increase in the density of nerves in the skin of the face as by the better sensitivity of fine hairs.

Certainly, hairs have important sensory functions for humans. I dont deny this.
But, hairs also have important sensory functions for other mammals. You havent given any good reasons to think that our hairs are better than other hairs at sensory perception, and you havent given any good reasons to think that humans needed or benefited from such an adaptation.

And, finally, how does your sensory hypothesis explain ethnic variation in hair-shaft coarseness?
Do Caucasians have a stronger need for this sensory adaptation than Africans do?


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

Darwin loves you.


This message is a reply to:
 Message 53 by Ken Fabos, posted 05-20-2010 8:21 PM Ken Fabos has not yet responded

  
Taq
Member
Posts: 7263
Joined: 03-06-2009
Member Rating: 3.2


Message 63 of 143 (565599)
06-18-2010 10:35 AM
Reply to: Message 60 by Ken Fabos
06-17-2010 8:28 PM


Re: Anyone disagree that body hair has sensory function?
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.

This is a secondary role for hair, not it's primary function which is insulation. This is why human hair is considered to be vestigial because it has lost its primary function.

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.

Hair also provides cover for ticks. When someone is bitten by a tick they often find them just inside the hair margin. Also, body lice are evolved so that the distance between their pincers is the same as the distance between human pubic hair. The best cure is just to get rid of the hair.


This message is a reply to:
 Message 60 by Ken Fabos, posted 06-17-2010 8:28 PM Ken Fabos has responded

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RAZD
Member
Posts: 19218
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.4


Message 64 of 143 (565666)
06-18-2010 10:40 PM
Reply to: Message 63 by Taq
06-18-2010 10:35 AM


Vestigial?
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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This message is a reply to:
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Ken Fabos
Member (Idle past 1775 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 65 of 143 (565730)
06-19-2010 8:48 PM
Reply to: Message 61 by Blue Jay
06-18-2010 12:22 AM


No-one here says body hair is functionless?
Bluejay - you said...
"Im not sure why you think any of us would be arguing that hair is non-functional."
Perhaps not the people here but it is a widespread meme. Try googling 'useless body parts' and you'll find source after source that includes body hair in the list. Including some that I would have considered reliable. Erector pilori muscles and goosebumps often appear there too, and, since those muscles hold hairs erect during moments of fright and hairs do have sensory function I'm also arguing that goosebumps have a related function by extending touch sensitivity to the furthest distance from the skin.

What I have encountered here is resistance to the idea that body hair, even with acknowledged sensory function, actually provides any significant benefits from this function. A lot seems to depend on the sensitivity; I maintain that hairs provide sensitivity greater than hairless skin as well as do it beyond the surface of the skin and that it has - more than once - enabled me to remove toxic parasites before they could dig in to my flesh. Some here seem convinced that I would have felt those ticks anyway - by direct skin contact. I've watched flies landing on my feet and not felt them until and unless they ventured into the hairy areas so I have to disagree. So, to me it seems obvious that hairs provide a sensitivity to touch that bare skin doesn't. I spend a lot of time outdoors, in a rural environment, where such sensitivity does still retain some usefulness. Without some rigorous, independent experimental evidence that disagreement seems unlikely to be settled here.

Now, the argument that such a function was not directly relevant to the evolution of the modern state of human body hair could have merit - I make no claim to deep knowledge on evolution - but I'm still doubtful that such a - to my mind - useful function could have been irrelevant, if only as cause for retention of what's left. Whether such sensitivity has undergone evolutionary changes is speculative; what isn't is that a thick pelage, with hairs all up against each other, would dampen small movements from further along the hair shafts and tend to reduce sensitivity to low threshold impulses. So in that sense I think that smaller, more widely spaced hairs would indeed provide greater sensitivity than the hairs of a thick pelage.

My opinions regarding thermoregulatory function aren't so strongly held although I think the argument that the change from thick pelage to thin benefits cooling from perspiration seems sound. The part the remaining hair plays seems less clear.


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 Message 61 by Blue Jay, posted 06-18-2010 12:22 AM Blue Jay has not yet responded

  
Ken Fabos
Member (Idle past 1775 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 66 of 143 (565733)
06-19-2010 9:16 PM
Reply to: Message 63 by Taq
06-18-2010 10:35 AM


Re: Anyone disagree that body hair has sensory function?
If, after evolution has reduced or taken away the primary function of a body part, it retains other functions, wouldn't one of those functions then become it's current primary function? Nitpicking? (ha, couldn't resist).
Yes, hair can hide ticks and other parasites. It can also alert us to their presence. In an age of pesticides and high fashion this may be counted as useless, except lots of people still lack ready access to either and could still find it useful to detect ticks prior to being bitten. When it really matters we can pay a lot closer attention to such somatic sensory information; I think the greatest limitation to such a sense is lack of attention and awareness so many people give it.
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Replies to this message:
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barbara
Member (Idle past 2392 days)
Posts: 167
Joined: 07-19-2010


Message 67 of 143 (580910)
09-12-2010 11:36 AM
Reply to: Message 66 by Ken Fabos
06-19-2010 9:16 PM


Re: Anyone disagree that body hair has sensory function?
This reminds of a time when a friend of mine who is mexican had a premature baby. When I went to see her at her home and saw the baby for the first time. My first reaction was this was a baby monkey because her baby had so much dark hair over the entire body that it resembled fur.

Of course, as the baby grew it lost its appearance of being furry and looks human now. This provided strong evidence to me of our ancestrial background of once being apes.


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greyseal
Member (Idle past 1451 days)
Posts: 464
Joined: 08-11-2009


Message 68 of 143 (580942)
09-12-2010 1:35 PM
Reply to: Message 67 by barbara
09-12-2010 11:36 AM


Re: Anyone disagree that body hair has sensory function?
This reminds of a time when a friend of mine who is mexican had a premature baby. When I went to see her at her home and saw the baby for the first time. My first reaction was this was a baby monkey because her baby had so much dark hair over the entire body that it resembled fur.

Of course, as the baby grew it lost its appearance of being furry and looks human now. This provided strong evidence to me of our ancestrial background of once being apes.

Lol, that very nearly sounded racist. That aside, I'll nitpick - technically we not only were we apes, we still are. Scratch that, technically not only were we monkeys, we still are (apes being a type of monkey).

But, and here's the key, we weren't ever chimps, or gorillas, or any other extant species of monkey or ape. We had an "ape-like" ancestor related to modern-days apes and monkeys (albeit it on reasonably distant branches). You probably knew that, but it pays to be sure.

At one point, I'm sure we were very, very hairy. I don't think it's been fur for a while, but we gradually lost that hair. We probably didn't need it. In the future, it's possible we'll evolve away from body-hair entirely if the overall consensus of our species is that hairless is prettier. If not, we won't. Hair being useless for maintaining body-temperature or keeping the sun off our heads doesn't automatically mean it's no longer useful and all our kids will be bald...and that's not how something which once had a function becomes superfluous to find itself no longer positively selected for.

If it doesn't do anything useful (or not so useful) it will no longer be selected for by natural selection, and in that case can change and morph rather freely, until it becomes something else (through many, many steps) or ceases to occur but for random chance (like whale legs).


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Ken Fabos
Member (Idle past 1775 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 69 of 143 (581030)
09-13-2010 3:35 AM
Reply to: Message 68 by greyseal
09-12-2010 1:35 PM


Gradual or rapid change to our hairiness
Greyseal, you said "I don't think it's been fur for a while, but we gradually lost that hair. " I'm curious to know why you think it would have been gradual; if it was the result of a mutation reduced hairiness would have appeared in an individual, apparently out of nowhere. That it is a trait that is strong through childhood until puberty suggests to me that the fundamental 'furless' trait is independent of sexual dimorphism - the male/female differences in adulhood - that is probably a result of sexual selection.
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 Message 68 by greyseal, posted 09-12-2010 1:35 PM greyseal has responded

Replies to this message:
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greyseal
Member (Idle past 1451 days)
Posts: 464
Joined: 08-11-2009


Message 70 of 143 (581039)
09-13-2010 5:34 AM
Reply to: Message 69 by Ken Fabos
09-13-2010 3:35 AM


Re: Gradual or rapid change to our hairiness
Hi Ken,

Greyseal, you said "I don't think it's been fur for a while, but we gradually lost that hair. " I'm curious to know why you think it would have been gradual

I'm sorry, I should make it clear when I'm talking about an individual (and an individual mutation) and a population.

The reason I think it's gradual is because we all are relatively hairless, and modern-day apes are not. As far as I know, our joint ancestor several million years ago was more like the ape - quite probably very hairy.

Unless you think at, say, 5 million BCE there was a sudden rash of bald ape babies, then we have to assume that whatever happened, instantaneous hairloss in one generation in all members of the relevant population wasn't one of them.

You could be right though, and it suddenly appeared and very rapidly speaking became the norm for some reason - I don't know - but it seems unlikely. Most change is gradual, as large amounts of change tend to get selected against whether it's a good thing or not as the single offspring in question with it would probably be less desirable as a mate.


This message is a reply to:
 Message 69 by Ken Fabos, posted 09-13-2010 3:35 AM Ken Fabos has responded

Replies to this message:
 Message 71 by Ken Fabos, posted 09-13-2010 10:15 PM greyseal has responded

    
Ken Fabos
Member (Idle past 1775 days)
Posts: 51
From: Australia
Joined: 05-09-2010


(1)
Message 71 of 143 (581128)
09-13-2010 10:15 PM
Reply to: Message 70 by greyseal
09-13-2010 5:34 AM


Re: Gradual or rapid change to our hairiness
Greyseal, I think that, if a single furless mutant successfully reproduces and has furless descendents the trait could be established within a sub-group. It doesn't have to have provided any net benefit and could even have been an initial disadvantage, so long as it was not so disadvantageous that it prevented reproductive success. Of course if it did confer advantage that makes it more likely they would demonstrate fitness (as in fitness = reproductive success). I don't see why it takes more than one to start things off; the question then becomes why the fully furred lines failed whilst the furless ones succeeded.
There are multiple ways an ugly furless mutant could go on to breed successfully especially if being thin furred confers benefits, such as better health through reduced ecto-parasite loads or better stamina and hunting success through better heat dissipation. Just having greater determination and more aggression could be enough to push more attractive rivals aside to mate successfully; being different can in itself be an incentive to try harder. Or it could be just pure luck and circumstance; the fully furred dominant males fail to return from a hunt and the barely tolerated ugly hairless one got an unexpected opportunity. I think it's a mistake to underestimate the part pure chance would have played within a very small and vulnerable foundation population.

Edited by Ken Fabos, : added a paragraph


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 Message 70 by greyseal, posted 09-13-2010 5:34 AM greyseal has responded

Replies to this message:
 Message 72 by greyseal, posted 09-16-2010 7:49 AM Ken Fabos has responded

  
greyseal
Member (Idle past 1451 days)
Posts: 464
Joined: 08-11-2009


Message 72 of 143 (581540)
09-16-2010 7:49 AM
Reply to: Message 71 by Ken Fabos
09-13-2010 10:15 PM


Re: Gradual or rapid change to our hairiness
Greyseal, I think that, if a single furless mutant successfully reproduces and has furless descendents the trait could be established within a sub-group.

You don't get a sub-group of one. You don't get a breeding subgroup from one family...or if you do it'll probably die out from genetic disease, or just plain interbreeding.

It doesn't have to have provided any net benefit and could even have been an initial disadvantage, so long as it was not so disadvantageous that it prevented reproductive success. Of course if it did confer advantage that makes it more likely they would demonstrate fitness (as in fitness = reproductive success). I don't see why it takes more than one to start things off; the question then becomes why the fully furred lines failed whilst the furless ones succeeded.

yes. You got it.

Now, you're suggesting that this "non-hairy" mutation was large and that it occured in one generation in one specimen and was dominant. You're contesting it didn't happen again directly, but that it didn't need to as because it was dominant, all offspring had it, and slowly but surely there were more of these hairless monkeys until they could divide into a subgroup.

You could be correct, but you're probably wrong for a number of reasons

1) changes that large don't, afaik, usually occur
2) the trait you're talking about would probably not be quite so dominant even if it did happen
3) and once again, you don't get a population of one, and you don't get a breeding population of one family
4) so what you might get is hairless mutants popping up with increasing regularity until it "bred true"

this fits my description of "slowly" and "gradually", even if the mutation itself was sudden. I should have been more specific.

I don't believe in your "sudden in one generation from hairy to hairless ape" for a number of reasons, and I'm certainly not expert enough to say if we have the proof you're wrong - somebody here might, or of course I could google it and see.

interesting theory though.


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 Message 71 by Ken Fabos, posted 09-13-2010 10:15 PM Ken Fabos has responded

Replies to this message:
 Message 73 by Ken Fabos, posted 09-16-2010 9:10 PM greyseal has responded

    
Ken Fabos
Member (Idle past 1775 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 73 of 143 (581672)
09-16-2010 9:10 PM
Reply to: Message 72 by greyseal
09-16-2010 7:49 AM


Re: Gradual or rapid change to our hairiness
Greyseal, I am engaged in speculation and don't insist this was how it must have happened. I've been thinking about how the underlying genetics can become widespread prior to the trait revealing itself in a major way. Yes, a strong characteristic like this would not have to come about as a dominant trait passed directly to furless descendants (although I still think it could be possible).

I still think that mutations must come from single progenitors - but there may not be outward manifestation of it until the mutant gene is widespread enough to recombine with itself. Within a small population that may not be that many generations. Mutations will go on to be 'fixed' within the gene pool when enough members of the population carry it; those will all be descendants of that original mutant individual. Over enough generations it will become a case of interbreeding between members who had that progenitor; that's true of any species after enough generations.

I don't understand the processes well enough, but as I understand it some traits require the same allele to come from both parents - or for different alleles from different evolutionary lines that complement each other to combine to produce a trait. Yet that could still result in a strong change seemingly appearing out of nowhere rather than as a gradual loss of fur. Although it's occurence would be rare at first and seem confined to siblings, it could appear separately amongst groups who would not seem to be closely related.

I'm just not convinced it's purely natural selection at work. Natural selection works with what's already in the gene pool and, without some form of mutation, won't come up with new genetics. Can natural selection be responsible for such a strong divergence? Being fully furred from early childhood - as our closest ape relatives exhibit - seems fundamental; such a big change to that just seems unlikely without some serious genetic change. I really don't know, but our thinned pelage is such a strong and universal characteristic of our species through childhood until puberty that I have doubts that what we have now is purely a result of natural selection. The variations in our adult pelage on the other hand looks more likely to be a result of a subset of natural selection - sexual selection - but to me that looks to be independent of the fundamental furless trait as exhibited through childhood.


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 Message 74 by greyseal, posted 09-20-2010 7:21 AM Ken Fabos has responded

  
greyseal
Member (Idle past 1451 days)
Posts: 464
Joined: 08-11-2009


Message 74 of 143 (582184)
09-20-2010 7:21 AM
Reply to: Message 73 by Ken Fabos
09-16-2010 9:10 PM


Re: Gradual or rapid change to our hairiness
Greyseal, I am engaged in speculation and don't insist this was how it must have happened.

You might be right, but for various reasons I think you're more likely to be wrong.

Namely:

I still think that mutations must come from single progenitors

...is definitely wrong, at least with the application of the word "must", unless you know a hell of a lot more about genetics and mutation than I do, which admittedly wouldn't be difficult

I'm just not convinced it's purely natural selection at work. Natural selection works with what's already in the gene pool and, without some form of mutation, won't come up with new genetics.

well, I don't know how to convince you. It's natural selection working on random mutation that powers the engine of evolution. There is no destination, there is no one right way to do something, there is no pre-defined successful mutation list and I'm quite sure that a million million good mutations didn't make it just because.

that's why i say it takes a population to evolve, and why it takes time for a mutation to become so general that "everybody has it".


This message is a reply to:
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 Message 75 by Ken Fabos, posted 09-21-2010 12:36 AM greyseal has responded

    
Ken Fabos
Member (Idle past 1775 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 75 of 143 (582374)
09-21-2010 12:36 AM
Reply to: Message 74 by greyseal
09-20-2010 7:21 AM


Re: Gradual or rapid change to our hairiness
Greyseal - I don't see how mutations can derive from anything except individuals - whilst a specific mutation can occur independently the chances of that aren't high wheras a mutant gene will be passed to descendents and, as long as that line doesnt die out, will almost certainly become part of the gene pool.

From Introduction to Evolutionary Biology - by Chris Colby - "Substitution is the replacement of an allele by another in a population. This is a two step process: First a mutation occurs in an individual, creating a new allele. This allele subsequently increases in frequency to fixation in the population." Whist allele substitution is one of several forms of mutation the idea that it derives from individuals seems implicit within Colby's writing on it. So I think you will find that I'm correct that mutations arise in individuals and a mutation becomes more common within the gene pool with successive generations through being passed on to direct descendents. For relatively small and isolated groups of proto humans there's no reason to believe very close relatives were necessarily prevented from mating and even if direct incest (parent and offspring or between siblings) was not practiced it doesnt take many generations before a small population shares common ancestors. Also what is beneficial, neutral or deleterious could be skewed by possession of intelligence and ability to use tools; the ability to change behaviour to overcome physical limitations looks to be a long standing trait of our lineage.

Whilst natural selection is the way adaptation happens it is selection between existing variants; (Colby - "The opportunity for natural selection to operate does not induce genetic variation to appear -- selection only distinguishes between existing variants.") Ongoing evolution depends upon genetic variation which ultimately comes from mechanisms other than natural selection of which mutation is the most fundamental. ( "In order for continuing evolution there must be mechanisms to increase or create genetic variation and mechanisms to decrease it. Mutation is a change in a gene. These changes are the source of new genetic variation. Natural selection operates on this variation.")

I find it unlikely that the kind of reduction of fur (that's so strong that it pervades our species but not our nearest relatives) could get that way purely by natural selection from within a fully furred population without some kind of mutation - was our proto human hairiness that variable? Surely we are talking relatively small numbers within a not very fecund species with long maturation times. Whilst mutation would be rare, it would be more likely - so long as not seriously deleterious - to be passed on and become fixed within the gene pool.
Complex traits don't tend to be about genes in isolation, yet a gene that changes the way hair growth responds to biochemical signals during growth maybe could be down to small genetic changes. Note that I said unlikely it's all natural selection; I'd actually like to discuss this with people with a strong grounding in evolutionary biology and the evolution of hair. But most of all I still want to know why the clearest remaining physical function of body hair - it's sensory function - seems to be entirely absent when it comes to understanding how we ended up with a pelage the way it actually is. Isn't the point to understand how we got to be the way we actually are? Evolutionary anthropologists like M.Rantala and N.Jablonski have not, so far as I can discern, correctly identified this function of body hair and seem to discuss body hair like it is vestigial and has no real function. Given how wrong that is how can their speculations on it's evolution be considered to have a sound foundation?


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