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On Sun, 18 Dec 2005, Jonathan King wrote:
That's the classic theory. There may be other factors at work in
addition to this melanoma-vitamin-D tradeoff. For example, it has been
suggested that darker skin is protective against some kind of fungal
infections.
I don't think we'll really understand what's going on here, though,
until we figure out the mystery of relative human hairlessness.
Interestingly, skin color per se can vary a lot even in primates (chimps
are relatively light skinned, while gorillas are not; both are way
hairier than people). Humans are extreme outliers on the hairiness
continuum, though. For whatever reason, the pressure on genes that had
a main effect (or a side effect) of hairlessness were really strong and
pretty much universal, while skin color can be all over the place.
It seems that the frontrunner there is the theory that we are relatively
hairless because we use sweating to cool ourselves. Fur gets in the way
of that. We retain hair on the head to protect against the sun (or so it
seems to this bald man) and in the axillary and inguinal areas probably to
reduce friction and maybe to spread odorants. Men have more hair than
women probably because men have more testosterone, which causes hair
growth, and there just hasn't been enough selection pressure to further
reduce hairiness.
Mike
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