Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 62 (9094 total)
3 online now:
PaulK, Phat (2 members, 1 visitor)
Newest Member: d3r31nz1g3
Post Volume: Total: 901,672 Year: 12,784/6,534 Month: 67/2,210 Week: 8/390 Day: 8/20 Hour: 1/4


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Is body hair a functionless vestige?
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 1 of 143 (559450)
05-09-2010 6:41 PM


It seems to be widely held that human body hair, being too thin to provide thermal insulation, is essentially functionless. It's my contention that it's probably multifunctional and that it's primary function is sensory. It may still have a role in thermal regulation for those who retain a lot of it and may have a role in carrying pheremones, perspiration as well as water away from the skin - with some impact on how well perspiration cools - however I want to focus specifically on hair's sensory function. I believe it's widely overlooked and I'm interested in how so many people, who live constantly with the sensory input these humble mechano-receptors provide, can fail to consider that function relevant to discussions on the evolution that led to our current (relative and variable) state of sparse hair cover, rather than fur covered, skin.

Replies to this message:
 Message 3 by Dr Adequate, posted 05-10-2010 4:27 AM Ken Fabos has replied
 Message 5 by Phage0070, posted 05-10-2010 7:58 PM Ken Fabos has not replied
 Message 8 by Hyroglyphx, posted 05-11-2010 8:38 AM Ken Fabos has replied
 Message 17 by dennis780, posted 05-11-2010 8:16 PM Ken Fabos has replied
 Message 32 by Larni, posted 05-14-2010 6:02 PM Ken Fabos has not replied
 Message 37 by Larni, posted 05-15-2010 7:23 AM Ken Fabos has not replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 4 of 143 (559621)
05-10-2010 7:00 PM
Reply to: Message 3 by Dr Adequate
05-10-2010 4:27 AM


Body hairs are very sensitive to movement (perceived as touch). Whilst not strictly good science, brushing a fine hair across areas of my own skin that are truly hairless was imperceptible but brushing it across the hairs on skin nearby was clearly perceptibe. ie the threshold sensitivity for hairs is lower than for direct skin touch. I tried shaving a small area just in case those hairless areas - back of knuckles, inside wrist, inside of fingers and palm, hairless areas of feet - were naturally less sensitive. Close shaving was required because even short stubble transmits sensory information, but it convinced me that body hairs do actually provide greater sensitivity to low threshold tactile sensations than hairless skin. Not scientific evidence perhaps, but cause for someone to conduct some experiments. I did find an abstract from a single paper in the obscure field of Haptics that tried to measure the trheshold sensitivity of hairs on the back of a finger to vibrations - paywalled unfortunately. Otherwise it's conspicuous by it's absence.
I would point out that body (vellus) hairs provide sensitivity to touch that extends beyond the surface of the skin - during moments of fright or arousal goose bumps cause them to stand out from the skin and extend that sensitivity even further. 30mm and more on my legs and arms with an occaision hair that extends as far as 50mm. Further on my chest, belly and back.
Eyelashes may be a special case but like all hairs, they are sensitive to touch - extremely sensitive in this case - and detect and sweep away foreign particles and insects. Our outer ears have hairs and they also act to alert us to intrusions by insects. General body hair ... again, personally anecdotal but...
I recently felt a paralysis tick (ixodes holocyclus) making it's way up my leg only because it brushed against the hairs - I've watched insects cross a hairless area on my foot and felt nothing until the moment they reached an area with hairs. Finding that tick before it attached itself saved me from a painful, itchy lump and headaches. For people more sensitive to these creatures the results can be seriously debilitating. I can't consider that to be a function so unimportant as to be irrelevant.
Is it possible to make informed speculation about the evolution of our body hair without consideration of it's sensory function?
Edited by Ken Fabos, : fixed typos and some rephrasing

This message is a reply to:
 Message 3 by Dr Adequate, posted 05-10-2010 4:27 AM Dr Adequate has replied

Replies to this message:
 Message 7 by Dr Adequate, posted 05-11-2010 8:22 AM Ken Fabos has not replied
 Message 10 by Blue Jay, posted 05-11-2010 11:36 AM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 12 of 143 (559817)
05-11-2010 6:34 PM
Reply to: Message 8 by Hyroglyphx
05-11-2010 8:38 AM


Re: More or less important
Hyroglyphx - My understanding is that it's not the number of hairs that's widely variable, just their size - but I could be wrong. Anyone know? Being very fine and short doesn't make them insensitive and may make them more sensitive to even lower threshold stimuli - although within a zone closer to the skin. From personal experience the very fine hairs high on cheeks near my eyes are barely visible yet are extremely sensitive to touch. Seems to me such sensitivity could be variable according to location as well as by the thickness, length and stiffness of the hairs themselves; there'd be advantage to such fine sensitivity around eyes and ear canal over heavier hairs that may not pick up the presence of very small insects.
I'm not sure I'd agree that there's an ongoing across the board trend towards less body hair, either by numbers, by skin area or by size. Seems to be more variable across our species than that. I'm not sure how the results would play out with competitive beard and chest displays amongst males seeking to force away rivals from bare skinned beauties - my understanding of the mechanics of such evolution is a bit thin and I'd hoped to tap some people here who've studied it.

This message is a reply to:
 Message 8 by Hyroglyphx, posted 05-11-2010 8:38 AM Hyroglyphx has not replied

Replies to this message:
 Message 16 by RAZD, posted 05-11-2010 7:53 PM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 14 of 143 (559831)
05-11-2010 7:21 PM
Reply to: Message 10 by Blue Jay
05-11-2010 11:36 AM


bluejay, the pervasiveness of this paradigm is something I am interested in. It seems that general body hair - rather than that of more location specific hair like the pits and crevices, the eyebrows and eyelashes, beard and chest hair - does get widely considered functionless and the sensory function in particular is conspicuous for failing to even rate a mention. From Wikipedia, to the recent SciAm article "The Naked Truth" by Dr Jablonski, the sensory function of body hair fails to get any consideration. Rather than explicitly stating that it's essentially functionless, that paradigm seems implicit and Jablonski even extends it to creatures like mole rats - which very much would be advantaged in their dark tunnels by touch sensitive body hairs. Likewise M. Rantala's paper "The evolution of Nakedness in Homo Sapiens" gives it no consideration.
On whether the hair we retain functions to inhibit or improve evaporation of sweat, I tend to agree with Coragyps; the outer surface of hairs themselves are well suited to carry moisture by capilliary action which would increase the overall surface area. By slowing but not blocking air flow close to the skin a layer of cooler air could develop. Just speculating of course and my focus remains the much neglected sensory function.
To rephrase your final question - what are the functional advantages and disadvantages of the variable pelage we currently possess? Sensory function belongs somewhere in that answer.
Edited by Ken Fabos, : rephrase for clarity

This message is a reply to:
 Message 10 by Blue Jay, posted 05-11-2010 11:36 AM Blue Jay has replied

Replies to this message:
 Message 45 by Blue Jay, posted 05-19-2010 2:04 PM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 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 but not replied

  
Ken Fabos
Member (Idle past 670 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:
 Message 23 by dennis780, posted 05-12-2010 1:55 AM Ken Fabos has not replied

  
Ken Fabos
Member (Idle past 670 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

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 33 of 143 (560375)
05-14-2010 6:35 PM
Reply to: Message 31 by Dr Adequate
05-14-2010 5:16 PM


Re: Anyone disagree that body hair has sensory function?
Dr Adequate, when you brush something across your body hairs -without touching the skin - can't you feel it? I know that I can. My wife and daughter can. I'm very confident that this is universal for normal healthy people. I'd actually say it's self-evident that this function exists. For the purpose of alerting us to the presence of insects and ecto-parasites a whole body covering looks useful. To feel air movements and shift in breeze, likewise.
As for fingertips, they serve other functions than tactile perception, most notably grasping and holding which would possibly be impeded by hair covering - and such hairs would be subject to excessive wear and tear and end up lost anyway.
The sensory input from hairs may merge in our perception with what we feel from direct skin contact but I'm astonished that, even after participation in this discussion, you could think it doesn't exist. Actually I find it surprising that anyone could think that a form of sensory input that's so universal and fundamental and that they've lived with their whole lives doesn't exist. Is the myth of functionless body hair powerful enough to cause people to deny the evidence of their own senses?

This message is a reply to:
 Message 31 by Dr Adequate, posted 05-14-2010 5:16 PM Dr Adequate has replied

Replies to this message:
 Message 34 by hooah212002, posted 05-14-2010 6:59 PM Ken Fabos has not replied
 Message 35 by Dr Adequate, posted 05-15-2010 3:22 AM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 36 of 143 (560430)
05-15-2010 7:18 AM
Reply to: Message 35 by Dr Adequate
05-15-2010 3:22 AM


Re: Anyone disagree that body hair has sensory function?
Dr Adequate, I'm arguing that body hair is more sensitive than bare, hairless skin and hairs can sense insects that bare skin cannot. To me the tickling irritation of buzzing insects is almost all due to the high sensitivity of hairs and when insects cross onto truly hairless skin I can barely feel them. I don't believe I am unique in this respect.
In message 4 I described simple experiments that can demonstrate this relative sensitivity. Let me know how they go.

This message is a reply to:
 Message 35 by Dr Adequate, posted 05-15-2010 3:22 AM Dr Adequate has not replied

Replies to this message:
 Message 38 by nwr, posted 05-15-2010 9:42 AM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 39 of 143 (560529)
05-15-2010 7:41 PM
Reply to: Message 38 by nwr
05-15-2010 9:42 AM


Re: Anyone disagree that body hair has sensory function?
So far one vote for no sensory function revised to functional but not significantly useful .
Two more say functional but not significantly useful.
And me, both functional and useful.
Larni and NWR - I think that in order to assess the relative advantages and disadvantages in an evolutionary fitness sense this function needs due consideration. If you know of any articles, papers or discussions that give the sensory function of hairs due consideration I would like to know. I haven't found any that even mentions sensory function, let alone explores what that means for the evolutionary pressures that led to the way we are.
Possible useful advantages from sensory body hair: Reduced metabolic load and risk of infection from ecto-parasites such as toxic ticks, biting flies, mosquitos etc by alerting people to their presence prior to being bitten: for hunters running down prey (or running to avoid predation) body hairs could help judge how closely one can pass by obstacles by feeling the close encounters (directly by brushing the hairs or indirectly by feeling the air movements that come from objects passing close by): Alerting people to shifts in breezes so that they are aware of the likely approach directions of stalking predators. The fine hairs on face around eyes and on outer ears are particularly sensitive to small intrusions and help prevent damage to those vital organs. I could probably think of some more.
Possible disadvantages of sensory body hair: the tickling annoyance of buzzing insects could make for distraction at the wrong time and increase risk of accident or injury.
I'd be surprised if the advantages to losing sensory sensitivity would outweigh the advantages in keeping it.

This message is a reply to:
 Message 38 by nwr, posted 05-15-2010 9:42 AM nwr has replied

Replies to this message:
 Message 40 by nwr, posted 05-15-2010 8:42 PM Ken Fabos has replied
 Message 41 by Dr Adequate, posted 05-16-2010 1:41 AM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 42 of 143 (561074)
05-18-2010 6:39 PM
Reply to: Message 40 by nwr
05-15-2010 8:42 PM


Re: Anyone disagree that body hair has sensory function?
NWR, whilst the skin on face near eyes might be more sensitive than, say, on forearms or torso I still think that the fine hairs play a greater role than that skin in detecting the presence of insects. I suggest a bit of experiment; try brushing those very fine hairs without touching the skin - I believe you'll find they are highly sensitive to touch.
Very fine hairs as well as thicker ones remain touch sensitive and the wide variation of 'hairiness' is variation of the thickness and length of hairs, not presence or absence.

This message is a reply to:
 Message 40 by nwr, posted 05-15-2010 8:42 PM nwr has seen this message but not replied

  
Ken Fabos
Member (Idle past 670 days)
Posts: 51
From: Australia
Joined: 05-09-2010


Message 43 of 143 (561084)
05-18-2010 7:22 PM
Reply to: Message 41 by Dr Adequate
05-16-2010 1:41 AM


Re: Anyone disagree that body hair has sensory function?
Dr Adequate, I think it's you and others that are asserting that sensory function exists but provides no significant benefit. I've given examples of that functionality being useful; believe me that detecting a paralysis tick (ixodes holocyclus) before it digs into your flesh is very advantageous. This example hinges on body hairs having greater sensitivity than hairless skin - that such a parasite is not normally detectable by direct skin contact but is through the sensitivity of hairs. I've described simple experiments that I believe indicate that greater sensitivity to be the case. I've attempted to find published experimental evidence for that relative sensitivity and failed. (There are some that look at sensitivity for hairs in the field of Haptics but they look to be narrow focused, not exploring the overall nature and variation of such sensitivity, just applying it to sensory feedback for computer control purposes)
For me these are genuine scientific questions - has a significant function of body hair been widely overlooked or underestimated? Does it have significance for understanding the evolutionary process that led to us being the way we are?

This message is a reply to:
 Message 41 by Dr Adequate, posted 05-16-2010 1:41 AM Dr Adequate has not replied

Replies to this message:
 Message 44 by Taq, posted 05-19-2010 12:20 PM Ken Fabos has not replied

  
Ken Fabos
Member (Idle past 670 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:
 Message 62 by Blue Jay, posted 06-18-2010 1:57 AM Ken Fabos has not replied

  
Ken Fabos
Member (Idle past 670 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
 Message 61 by Blue Jay, posted 06-18-2010 12:22 AM Ken Fabos has replied

  
Ken Fabos
Member (Idle past 670 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 but not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2022 by EvC Forum, All Rights Reserved

™ Version 4.1
Innovative software from Qwixotic © 2022