thermoregulation in hominids
Newington Reference Library (fp96@dial.pipex.com)
Tue, 17 Dec 1996 19:31:45 +0000
Thermoregulation in Hominids
by Andrew Lewis
Is it just me or does anyone else have a problem with the application of
Allens rule to hominids? The rule states that mammals adapt to the
temperature of their environment through variations in limb length.
Longer limbs give the body a larger surface area from which heat can be
dissipated more rapidly.
I dont know if this works with most mammals but when it is applied to
hominids it does not seem to make any sense. However, the rule seems to
be accepted by most anthropologists.
Often a Nilotic tribesman is compared to an Eskimo to illustrate the
point. Nilotic tribesmen live on the equator and are tall and slender
with long limbs. Eskimos live in the arctic and are short with short
limbs.
Nilotic tribesmen are not typical of people living in the dry tropics,
they are not even typical of Africans living in the dry tropics. Most
black people in Africa are the same sort of height as anyone else. The
Masaii in Kenya are massively outnumbered by Bantu people such as the
Kikuyu.
Pygmies are the smallest people in the world, but apparently they are an
exception to the rule because they live in a humid environment where
sweating is not an effective means of cooling. The Dinka and Nuer people,
who are possibly the tallest of all, live in the swamps of The Sudd in
the Sudan: would this not also be a humid environment?
What about the Bushmen of the Kalahari desert who are almost as small as
the Pygmies? What about the Scandinavians who are taller than southern
Europeans, (apart from the population in former Yugoslavia who arevery
tall)? Why are there no very tall aborigines in Australia?
The savanna can get very cold at night. It can be cold during the day.
How does this fit into the equation?
The coldest inhabited area of the world is not the home of the Eskimo
anyway. The town with the record winter minimum is Oymyakon in Siberia
which is not inside the Polar Circle. This region is very hot in summer.
It is the home of the Tungus, Yakut and Evenki people.
It should be possible to measure the surface area of people from
different populations around the world together with their weight. This
would be the best way to assess the theory. The brachial index (the ratio
of the length of the upper arm to that of the forearm) and the crural
index (the ratio of the length of the thigh to that of the lower leg) are
used instead, presumably because they are easier to measure. But it seems
very contrived to me, almost as if someone has juggled data to see what
fits the theory best. Another measure is relative body breadth. That
does not seem to make any sense either.
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