Is body hair a functionless vestige?

It seems to me that if it had a sensory function, then the best place for it would be on the fingertips. Its actual distribution doesn't suggest a sensory function, does it?

Here's a sensory homunculus.

That's how brain function is distributed over the body. It's not how hair's distributed, is it?

And chimps and moneys have hands which are naked on the inside. The one place where the sense of touch is most important ... no hair.

Edited by Dr Adequate, : No reason given.

My chest thatch seems to give me some protection from one of my cat's claws when he crawls into bed with me and starts being Clawry Haim on me.

That's a good function, I reckon.

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?

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

When someone puts their finger in your ass (or you do it yourself) and "milks" your prostate, doesn't it feel good? You are fucking A right it does! (don't knock it 'til you've tried it). Does that mean that at one time men were actually the recipient of sexual intercourse? Or that we are supposed to be homosexual? or could it be just a (very welcome) side effect?

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Not a sunrise, but a galaxy rise
A morning filled with 400 billion suns
The rising of the milky way"
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Dr Adequate, when you brush something across your body hairs -without touching the skin - can't you feel it? I know that I can.

Yes, but I can't say that I've ever found this particularly useful.

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.

Bare skin would do just as well.

To an animal with thick fur, doubtless it is useful that hair follicles are innervated. But in us this too could be a vestige.

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.

But no-one has said that the sensory input doesn't exist. Just that it's not particularly functional.

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.

It's my contention that it's probably multifunctional and that it's primary function is sensory.

So to clarify you are saying that the primary function of the body hair humans have is sensory.

Where would this be of use to increase the fitness of the organism?

Ken Fabos writes: I'm arguing that body hair is more sensitive than bare, hairless skin and hairs can sense insects that bare skin cannot.

I agree with that. It greatly helps me avoid being bitten by mosquitoes.

Ken Fabos writes (in Message 1): 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.

While I agree that the sensory function of body hairs is useful, I seriously doubt that it is useful enough for that to have been significant in the evolution of our species.

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.

Ken Fabos writes: 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.

This isn't anything that I have gone out of my way to study, so I don't know of any articles.

There is a lot of variability between people over the amount of body hair, and that variability argues against it being of evolutionary significance.

Ken Fabos writes: 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.

In my case, I am inclined to think that the sensitivity of the skin in those regions is sufficient protection against insects. Where I mainly benefit is on the arms and legs where there is less skin sensitivity and the sensitivity of the hairs is what alerts me to mosquitoes and other insects.

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.

What distinction are you trying to draw between useful and functional?

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.

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?

Dr Adequate, I think it's you and others that are asserting that sensory function exists but provides no significant benefit.

The problem seems to be that you think vestigial means functionless. It doesn't. Vestigial means having a secondary or rudimentary function compared to the same feature in another species. The sensory function of hair on humans is a secondary or rudimentary function compared to the primary function of thermal regulation. Hair is vestigial on humans. We depend on sweat and clothing for thermal regulation.

Hi, Ken.

Ken Fabos writes: By slowing but not blocking air flow close to the skin a layer of cooler air could develop.

Heat radiating from the body (conductive heat loss) becomes trapped in the boundary layer and keeps the air immediately around the skin warm. Blocking air flow would only increase the amount of heat accumulating at the skin's surface.

Air currents moving across the skin are what move the heat away from the body (convective heat loss) and result in cooling of the skin. Hair and fur function to prevent air currents from moving across the skin, and thereby hamper convective heat loss. Without convective heat loss, we only shed excess heat by conduction, which is slow and generally cannot outpace the production of heat that comes from working our muscles.

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Ken Fabos writes: what are the functional advantages and disadvantages of the variable pelage we currently possess? Sensory function belongs somewhere in that answer.

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

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