Friday, June 27, 2003

Hair brained

Hmm, several things wrong with this, though parts of it are interesting. More later.

"Professors Pagel and Bodmer write in the Royal Society journal Biology Letters that past humans were able to respond flexibly and effectively to their environment by producing fire, shelter and clothing.

So hairlessness became possible and desirable as clothes and shelter could be cleaned or changed if infected with parasites.

The pair say their theory also has a better answer to why there are differences between hair covering in men and women.

'Hairlessness would have allowed humans to convincingly 'advertise' their reduced susceptibility to parasitic infection and this trait therefore became desirable in a mate and the greater loss of hair in women follows to stronger sexual selection from men to women.

Yeah, okay. And it's nice that this reduces our need for flea collars, but I don't know if I buy it since they are so wrong, in my opinion, about headhair.

But first, I will agree that facial hair, pubes, and pit hair were kept for their sexual usefulness.

Here's Marvin Harris theorising why we kept our headhair and lost most body hair :

"A bigger brain made it possible for erectus to run in the midday sun, at a time of day when most predators seek shade and water and refrain from the persuit of game. Fialkowski bases this theory [growth of brain size] on the assumption that by having extra brain cells, the brain of erectus was less likely to break down while experiencing heat stress during long distance running. Individual brain cells are more susceptible to heat stress than are the cells of other organs. Their breakdown leads to cognitive disorientation, convulsions, stroke, then death. A basic principle of information theory holds that in an information system that has elements prone to breakdown (such as the human brain), the reliability of the system can be increased by increasing the number of elements that perform the same function and by increasing the connections among them. The brain of erectus may therefore have contained a large amount of neural redundancy selected as a means of achieving fail-safe operation under heat stress, which is generated during the persuit of game over long distances.

..when it comes to covering long distances, humans can outrun every other animal."

So once our brains became able to function under heat stress, we established ourselves as niche predators, not built for the sprint but for the grind of marathon hunts while extending the range of our foraging. Naturally, anything that helped our brains keep this advantage was selected by nature...

" .. heat stress as an explanation for the enlargement of the erectus brain dovetails with the presence of several other heat-regulating features that are peculiar to humans... We cool ourselves by wetting our skin with moisture exuded by our eccrine sweat glands. Humans have as many as five million of these glands -- far more than any other mammal."

Right. Since it was successful to run, in order to hunt, anything impeding that ability would be selected away. Sweating is the perfect cooling system for distance runners.

"Forest-dwelling apes do not engage in the intense physical effort that prolonged running requires. Their principle thermodynamic challenge is not to dissapate excess heat but to avoid being chilled, especially at night, by exposure to high humidity and heavy rainfall. Hence the luxuriant, slightly oily, and downward-pointing hairy coats of the great apes. The development of erectus as a long-distance runner and the evolution of the evaporative cooling system were incompatible with the preservation of this coat. Air had to pass unobstructed over the film of moisture exuded by the eccrine glands. Hence the peculiar 'nakedness' of the human body. Although we actually have as many hair follicles as the great apes, the hairs that emerge are too thin and short to form a coat. But the vestiges of the water-shedding function of the fur are preserved in the downward pointing orientation of the hairs on our arms and legs."

That makes much more sense as a primary reason for our nakedness, though I don't doubt that parasite control could have played a supplementary factor.

"Running upright on two legs, erectus presented an oblique target for the sun's rays except for the top of the head. While this minimised the heat load for the body in general as compared with that of animals that ran on all fours, it posed a special threat to the brain. Bald men, even Englishmen, are well advised not to go out in the noonday sun. And if we are doomed to earn our keep by the sweat of our brows, it is because our brows have a dense concentration of sweat glands and no hair.

So head hair was kept because it, with intense face and forehead sweating, and the adapted redundancy systems of the enlarged brain, helped to thwart the effects of heat, so that in turn we could keep running after game. It should be noted that this theory is Konrad Fialkowski's which Harris merely synthesised and perhaps perfected.


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