Re: Brains size and sweat

Glenn Morton (
Thu, 09 Jan 1997 00:31:38

>I've been working up a sweat trying to follow this discussion, and I
>think my brain is overheating!
>A question: Man may sweat profusely, but isn't the cooling effect
>dependent on how much of this water is actually evaporated from the
>skin? That's the way the heat energy is removed, by using it to
>dissociate the liquid water molecules into water vapor. Agreed, the more
>you sweat, the more water is available for evaporation, but I wonder, is
>there an optimum rate for sweating where you achieve the maximum cooling
>effect with the minimum loss of bodiy water? The point being that merely
>the rate of sweat production is not the whole story in the cooling
>effect. Much sweat simply drops off.
You are correct. However, the Savanna, where man is believed to have evolved
is relatively dry. When you work in a dry region much more of the sweat
evaporates quickly and less drops off. When I have worked outdoors in the
western US I ususally don't drip with sweat. But when I lived in Louisiana, I
would drip sweat simply sitting on my back porch reading.

>And re the Watusi... don't forget the Pygmies! Africans come in varied
>body styles!
Pygmies live in an entirely different climate than the Watusi's. Chris Ruff

"It is interesting and instructive that all present-day populations
exhibiting the extreme linearity of body build illustrated by the Nilotic in
Figure 1 inhabit not only hot environments, but also relatively open, dry
environments, such as savannah grasslands. As Wheeler has demonstrated
theoretically, a tall linear body is a distinct advantage when moving about in
the open during the day. Relative to its mass, such a body leads to less heat
gain from the sun, particularly near mid-day, and greater convective heat loss
from the body, particularly in the morning and late afternoon. In contrast,
in a closed, forested environment with little direct sunlight and little air
movement, this kind of physique loses these advantages. In addition, the
usefulness of a relatively large surface area for evaporative cooling by
sweating is decreased in a humid environment. Thus, given the fact that heat
production is related to body size, the best way to avoid overheating under
such conditions may be to limit body size itself. This is one interpretation
of why present-day Pygmies, whether in Africa or elsewhere are universally
found in rainforest environments."~Christopher B. Ruff, "Climatic Adaptation
and Hominid Evolution: The Thermoregulatory Imperative," Evolutionary
Anthropology, 2:2 (1993), p. 53-60, p. 56

By the way the earliest complete Homo erectus skeleton shows that H.erectus
was extremely Nilotic. In otherwords, he was adapted to an even greater heat
than current Africans. (Alan Walker and Pat Shipman, The Wisdom of the
Bones, (New York: Alfred Knopf, 1996), p. 196)

"In hot, wet climates. like rain forests, sweating is less effective.
People adapted to those environments often have the same body width as those
in hot, dry areas but are short, like Pygmies, to keep their body mass
low."~Alan Walker and Pat Shipman, The Wisdom of the Bones, (New York: Alfred
Knopf, 1996), p. 196

"Because of the lack of fossils in the acid African soils-which dissolve
the main bone component, calcium phosphate-it is impossible to specify exactly
the geographic distribution of Pygmies at earlier times. There is practically
no Pygmy fossil record from dry areas where bones would have been preserved,
confirming the belief that Pygmies represent a long-term adaptation to the
tropical forest."~L. Luca Cavalli-Sforza, Paoli Menozzi and Alberto Piazzi,
The History and Geography of Human Genes, (Princeton: Princeton University
Press, 1994), p. 180

Are you the guy who bought a book from me in early 1994? If so I think you
have the first copy out there.

>Just wondering...
>--Bill Yates


Foundation,Fall and Flood