Our Cooling System

As I sit at home in Mtwara sweltering in the heat and humidity with nothing on but underwear and sandals and with an electric fan blowing on me, I try to take comfort from the fact that we human beings have a whole-body cooling system that is far more efficient than that of any other mammal.

The book AFRICA: A Biography of the Continent has a very interesting chapter on this. Our upright stance may have come about as a way to reduce the amount of body surface that is directly exposed to the sun during the hottest part of the day. Being off the ground also puts us up into air that is windier, cooler, and less humid compared to a quadraped.

The other component is well-developed sweat glands together with bare skin. Actually, we have as many hairs per unit area of skin as a chimpanzee -- but those hairs are mostly so fine that we are functionally naked. As a result sweating is an extremely effective way of removing heat from the body as the sweat evaporates.

Here in East Africa being able to stay cooler and more active allows humans to reduce their water requirements and be able to forage farther for food in the open savanna. This would have been the immediate advantage.

But the longer term consequence might have been that this unique system removed a physiological constraint on the development of a large brain! Brain tissue is expensive in terms of its continuous need for oxygen, fuel, and a narrow temperature range in which to operate. The brain runs hot. A researcher is quoted: "it is probably no coincidence that today the mammal with the most highly developed brain and social behavior is the species which possesses the most elaborate cooling system".

If we had not evolved a body that is so good at staying cool I might not now be expressing myself in such an intricate language as an act of a shared complex culture and doing so on a machine. 8-D

- Earl