Why Am I Hairy?

[Donk]

I had a bright idea today. Not unusual, of course: bright ideas are constantly cascading through my head ;)

 

Today was a warm day for the time of year, so I was wearing just a pair of shorts. An eyelash came loose and started bothering me, so I pulled it off my eyelid and dropped it. And felt it land on my leg! I mean, seriously – how much does an eyelash weigh? Yet I felt it hit.

 

A little thought indicated that it landed in the right place to bend one or more of my leg hairs, and that was what I felt. That's what the hair is for: it magnifies the sense of touch by a very large factor.

 

Next problem: why? What's the evolutionary imperative? For the parts that really matter, like fingertips and mouth, the touch sense is magnified by crowding together a lot of nerve cells. This isn't necessary on the rest of the body, so it doesn't happen. It's some sort of a “backup plan”, giving amplified touch without the fine detail. I couldn't think of a good reason why we'd need such a thing, or if it was so useful why women didn't have it. Then it came to me: the slightest breath of wind will stir those hairs, giving a precise indication of wind speed and direction. Early man would have found it very useful for getting downwind of prey in a hunt. And the women didn't hunt, so they didn't need it.

 

This explanation seems much more satisfying than the traditional “secondary sexual characteristic” one. If a biologist can't explain a feature, they assign it to sexual display and forget about it.

 

I'd rather have had an insight into Life, the Universe and Everything, but you take your insights where you can. This, ladies and gentlemen, has been mine for today :)

[Don Blazys]

I agree, it does seem to be a more satisfying explanation,

and like any good theory, it brings up new and important questions.

 

Are razors, tweezers, wax and other assorted womens hair removal products

relatively recent evolutionary developements in our species?

 

Also, while it is true that most women do not hunt, there are a few rare exeptions

that still need to be properly explained, such as our next president, Sarah Palin,

who has indeed been known to go hunting once or twice.

 

Don.

[Boerseun]

Possible - quite possible. But I think humanity is on the way to complete hairlessness, and our current state is an in-between state between the hairy apes we were, covered in full fur, and the naked state we will eventually find ourselves in, as hair serves less and less of a purpose. I think fully-furred animals have less of this touch-sense than half-haired beasts like we do, because a thicker mat of hair will support each other and you will need more force to bend them than with sparse hair. For instance, you feel a light breeze on your arms and legs, but rarely on your head - you need quite a force for moving your head hair around.

That being said, I think that the mere ability to do so is quite accidental and merely transient - a few hundred or thousand generations down the line, and we might sprout just a whisker or two and the temporary benefit of having had a magnified sense of touch through hair will have disappeared, together with the hair.

But interesting, nonetheless.

[Moontanman]

She asks me why, I'm just a hairy guy

I'm hairy noon and night, hair that's a fright

I'm hairy high and low, don't ask me why, don't know

It's not for lack of bread, like the Greatful Dead, darlin'

 

Give me a head with hair, long beautiful hair

Shining, gleaming, streaming, flaxen, waxen

Give me down to there, hair, shoulder length or longer

Here baby, there, momma, everywhere, daddy, daddy

 

 

Sarah Palin can not be the first female president, her penis is too big...

[Vox]

I had a bright idea today. Not unusual, of course: bright ideas are constantly cascading through my head ;)

 

Today was a warm day for the time of year, so I was wearing just a pair of shorts. An eyelash came loose and started bothering me, so I pulled it off my eyelid and dropped it. And felt it land on my leg! I mean, seriously – how much does an eyelash weigh? Yet I felt it hit.

 

A little thought indicated that it landed in the right place to bend one or more of my leg hairs, and that was what I felt. That's what the hair is for: it magnifies the sense of touch by a very large factor.

 

Next problem: why? What's the evolutionary imperative? For the parts that really matter, like fingertips and mouth, the touch sense is magnified by crowding together a lot of nerve cells. This isn't necessary on the rest of the body, so it doesn't happen. It's some sort of a “backup plan”, giving amplified touch without the fine detail. I couldn't think of a good reason why we'd need such a thing, or if it was so useful why women didn't have it. Then it came to me: the slightest breath of wind will stir those hairs, giving a precise indication of wind speed and direction. Early man would have found it very useful for getting downwind of prey in a hunt. And the women didn't hunt, so they didn't need it.

 

This explanation seems much more satisfying than the traditional “secondary sexual characteristic” one. If a biologist can't explain a feature, they assign it to sexual display and forget about it.

 

I'd rather have had an insight into Life, the Universe and Everything, but you take your insights where you can. This, ladies and gentlemen, has been mine for today :)

 

I would add 2 more possible functions for body hair;

 

- Controlling and creating the microclimate to the surface of the skin

- Body hair would act as absorbent to stop skin to reabsorb toxins contained in sweat, especially in the areas of armpit, genitals and chest (men)

[dr4g0n0k]

'But I think humanity is on the way to complete hairlessness'

 

Really? I'm not sure that I'm aware of any real selection pressure with regards to hair, or hairlessness for that matter.

 

Could you please enlighten me as to why you think so?

[Rade]

Then it came to me: the slightest breath of wind will stir those hairs, giving a precise indication of wind speed and direction. Early man would have found it very useful for getting downwind of prey in a hunt. And the women didn't hunt, so they didn't need it. This explanation seems much more satisfying than the traditional “secondary sexual characteristic” one.

You have made a nice hypothesis. Human adult males, being more the hunter than human females, have more body hair because the hair gives selective advantage for prey capture because it allows one to detect wind direction (at very low velocity). One possible way to falsify your hypothesis would be to test a range of human males, from those with no hair, to those very hairy, to see if those with hair can detect wind direction (at very low velocity) better than those without hair.

 

In his book, The Naked Ape, Desmond Morris asks this question: "Why on earth should the hunting ape have become a naked ape?". What Morris concludes is that loss of body hair in humans is related to the process of neoteny. Both the infant chimpanzee and new born human have little body hair (except on top of head). Hair production is genetically repressed in humans, as compared to chimps, as they age. The difference between adult humans and adult chimps is that human body hair, while present in same density as adult chimps, is mostly very small (most of the human hairs are like peach fuzz).

 

Morris suggests that the course dark hair that does develop in human males, is closely timed to the the age of sexual maturity, (11-14 years old) and serves as a sexual stimulus, perhaps in helping to maintain skin pheromones that are attractive to females. Females at age of sexual maturity allocate energy to breast development rather than production of body hair, another sexual stimulus. Notice how some human females as adults remove body hair on legs for sexual reasons, others maintain hair under arms for same reason, others various combination of the two, so, to suggest that presence/absence of hair in humans does not have sexual aspects is not supported by the modern day facts. There is no reason to suspect that females 300,000 years ago were not sexually motivated by presence/absence of hair.

 

What would be the selective advantage of genetically repressing hair production in humans until sexual maturity in males, and even then, allowing only minor density of dark course hair as compared to the chimp ? If being a little hairy is an advantage to detect wind direction for hunting males, should not being very hairy (say as hairy as a chimp) be even better to detect wind ? If the wind detection hypothesis had merit, I would expect that human males when they reached age of being able to hunt, say between 12-20 years old, would be covered with hair, since young and fast running and healthy males would be active in hunting. But, this is not what we see. What we see is that human males become more hairy as they age, and are most hairy well past prime hunting age. There does not appear to be any correlation to hair density and hunting ability, if anything the correlation is negative, hairy old men would be poor hunters if they had to run after their prey (rather than let a bullet or arrow do the running).

 

So, there must be some strong selective pressure to suppress hair development during prime hunting age of human males (~ 12-20 years of age), yet allow some to grow for secondary sexual signals. What Morris suggests is that the genetic repression of hair development in young males was adaptive because loss of hair provided selective advantage to expose more skin and sweat gland to allow for cooling of body while young males were running to capture prey, an activity that produces lots of heat. Very hairy young males just could not run as fast or as far or as long as their mostly hairless relatives. In times of intense food competition, hairy young males would not be the ones coming home with the deer, and young females would have no reason to mate with them.

 

Finally, consider that the young mating age human females were very hairless, and, well, maybe they just liked to mate with someone that looked like they did, and not looking like the hairy chimp living in the forest over the hill.