Re: Why is Homo sapiens hairless?
John Waters (jdwaters@dircon.co.uk)
15 Nov 1996 03:30:23 GMT
Susan S. Chin <susansf@netcom.com> wrote in article
<susansfE0qpt3.6M7@netcom.com>...
>
> This is something I learned from an introductory Phys
Anthro class a long
> long time ago (well, ten years), but the hypothesis was
that hominids
> lost their hair gradually as they left the forrested
environments that
> the ancestors of todays great apes lived in (modern
descendants being
> gorillas, chimps, and orangutan). Once this bipedal ape
was out in the
> open, not necessarily a savannah, but not a covered
arboreal setting
> either, the need for heat loss was such that selection
favored loss of
> hair which apes living in forrested environments still
have. Makes sense
> to me...
JW: Ummm. Trouble is that the only mammal species with
limited hair which live in a comparable environment are the
Elephant and Rhinoceros. In their case, their surface to
mass ratio can explain the condition. Hominids were
somewhat smaller and lighter. All other species of mammals
in these environments have a full coat of hair/fur. Why
should the hominids have been any different?
Similar species, with similar physiologies living in
similar habitats, should have similar degrees of hairiness.
Chimpanzees in Senegal live in similar habitats, but have
not become hairless. If anything, bipedalism would have
reduced their exposure to solar radiation, so they should
have got more hairy to compensate.
It is not clear to me how much bipedalism would lead to
increased solar heating of the skull ( viz a viz a
Chimpanzee). Hot adapted people have frizzy hair. This
reduces the impact of solar radiation on the skull, while
allowing maximal flow of air over the head. I would expect
this kind of adaptation in the hominids.
But reduced body hair? No chance. Until the development of
the female subcutanous fat, there is no reason to think
that the hominids would have been any less hairy than their
hominoid cousins.
John.
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