Why do humans have (pretty much) no body hair

from an evolutionary perspective, what's the point?

http://s.ecrater.com/stores/16290/4aa6f55c6ac40_16290f.jpg

Read this.

that doesn't help at all - I'm not shaving any chimps

B/c without hair, we can sweat better and don't have to burn as much energy up in losing the heat.

Hairy chests

The most compelling argument I've seen following paleoanthropology for a few decades is that human ancestors were persistence hunters, running after savannah animals less adapted to endurance running till they collapsed from overheating. Our upright posture, relative hairlessness, and quite unusual ability to sweat profusely all allow us to dissipate heat better, and hence make us the best endurance runners on the planet.

A few Kalahari still practice persistence hunting.

https://www.youtube.com/watch?v=52k6FdApB94

Once hairless bodies became visible, I'm sure sexual selection set in to reduce body hair further than strictly advantageous.

From The Naked Ape by Desmond Morris

"The hunting ape became an infantile ape. This evolutionary trick is not unique; it has happened in a number of quite separate cases. Put very simply, it is a process (called neoteny) by which certain juvenile or infantile characters are retained and prolonged into adult life.

....

If you examine an infant chimpanzee at birth you will find that it has a good head of hair, but that its body is almost naked. If this condition was delayed into the animal's adult life by neoteny, the adult chimpanzee's hair condition would be very much like ours.

....

What, then, was the survival value of naked skin? One explanation is that when the hunting ape abandoned its nomadic past and settled down at fixed home bases, its dens became heavily infested with skin parasites. The use of the same sleeping places night after night is thought to have provided abnormally rich breeding-grounds for a variety of ticks, mites, fleas and bugs, to a point where the situation provided a severe disease risk. By casting off his hairy coat, the den-dweller was better able to cope with the problem."

He says another theory is that the cultivation of fire led to hairless (no need to stay warm by hair alone). Another theory is that after leaving the treetops and forests we went through an aquatic phase, hunting mostly in the water, losing most of our hair like other aquatic mammals. He points out that we are nimble under water while our closest living relatives the chimps, are helpless. Morris puts across a number of other theories and says this,

"Perhaps the most commonly held explanation of the hairless condition is that it evolved as a cooling device. By coming out of the shady forests the hunting ape was exposing himself to much greater temperatures than he had previously experience, and it is assumed that he took off his hairy coat to prevent himself from becoming over-heated."

Throughout, he gives pros and cons of all the theories, pointing out the flaws as soon as he points out the evidence. I highly recommend this book, it's a great read!

And yeah, I'd say sex appeal probably played the biggest role.

http://letterstorob.files.wordpress.com/2009/08/tomselleck.jpg

http://www.gothamjournal.com/wp-content/uploads/img/2009/06/burt72.jpg

I've always wondered about the evolutionary purpose of armpit hair. We've retained strategically placed eyebrows and nasal hairs and pubic hair and etc. to offer some protection and warmth to all the really important parts and various orifices. What's so important about the armpits?

pheromone factories, hair under there helps "spread the word"

Also maybe prevents chafing.

also important to note that not every feature of an organism is necessarily a direct adaptation to something. many are neutral side effects of other adaptations.

tho i don't know if it applies in this case or not.

is it something to do with humans evolving into wearing clothes, so over time the clothes have replaced the bodies need to self warm with a layer of hair?

Parental Selection: A Third Selection Process in the Evolution of Human Hairlessness and Skin Color (2006 Horrobin Prize for medical theory)

It is proposed that human hairlessness, and the pale skin seen in modern Europeans and Asians, are not the results of Darwinian selection; these attributes provide no survival benefits. They are instead the results of sexual selection combined with a third, previously unrecognized, process: parental selection. The use of infanticide as a method of birth control in premodern societies gave parents – in particular, mothers – the power to exert an influence on the course of human evolution by deciding whether to keep or abandon a newborn infant. If such a decision was made before the infant was born, it could be overturned in the positive direction if the infant was particularly beautiful – that is, if the infant conformed to the standards of beauty prescribed by the mother’s culture.

The use of infanticide as a method of birth control in premodern societies gave parents – in particular, mothers – the power to exert an influence on the course of human evolution by deciding whether to keep or abandon a newborn infant.

Emphasis mine. I wonder what the justification is for putting more of that on mothers.

Judith Harris's argument is that infantcide was the primary means by which mothers could control birth spacing in early cultures, when a new child could mean the death of its not quite weaned elder sibling.

Interesting. Would depend on the mothers' level of subversion, I guess, considering the number of societies in which children were considered the property of the husband/father and potentially kept a close eye on for marriageability/inheritance purposes.

Among the until quite recently nomadic !Kung bushmen (her primary example), there's precious little property to protect. We've had a few million years of evolution of distinctly human culture, and language (and hence ability to transmit cultural abstractions of beauty), as defined by descent of larynx and more visible Broca's and Wernicke's areas in cranial casts, since homo habilis (2.3 to 1.4 mya). In hunter-gatherer societies with defined sex roles, women provide the majority of calories. In contrast, plant and food animal domestication only dates back 10k years (wolf/human cohabitation date back 30k to 100k ago, though).

So I wouldn't assume property and patriarchal responses date that far back into our evolutionary past.

Oh yeah, that's a good point! I never really think about how far back evolution actually GOES.

6k years, IIRC.

barely tangentially related, but since I was about 8 I've had the idea in my head that 38,000 years ago was a significant time for the emergence of the human race, yet in trying to look this up I haven't been able to find anything that could've been what I was thinking about. Anyone?

that was when Dick Clark was born

Also John McCain.

don't remember it being that, but I'll accept it.

Upper paleolithic. Bow and arrow invented, great flourishing of artwork, including painting and figurines, possibility of susbstative leap in complexity of human languages and technologies.

That Harris article is really interesting.

~40K years ago is about the start of Cro-Magnon, right?

^ya that is probably it, thnkyu.

that harris thing seems like...not science. i mean parental selection could totally be a thing but it's prefaced with notion that hairlessness and skin color "provide no survival benefits" when there's plenty of stuff like this that at least provide cogent arguments for why that's not true.

Harris does deal with the vitamin D issue (the only advantage of lighter skin offered by the National Geographic article) here:

In far northern regions, paleness might even have provided some benefit, by enabling the skin to synthesize Vitamin D even when the sun was not overhead or was partly obscured by clouds.

But by making the paler members of our species vulnerable to sunburn and malignant melanoma, in most environments the negative consequences of light skin would have outweighed the positives. The combination of hairlessness and depigmentation has produced a mammal that takes its life in its hands whenever it ventures into the noonday sun.