At some point in the past, then, as our large brain evolved, our ancestors lost the characteristic hairiness of the apes and acquired our typically naked skin. The hot climate of Africa, where our ancestors evolved, must have been a key factor in that development. A relatively hairless skin with many sweat glands would make heat diffusion of the chemical energy generated by physical effort much more efficient, thus allowing our ancestors to run further and faster without harming their brains from over-heating. Some scientists have suggested that the danger of heat-stroke in this environment are significant enough to have driven the tendency toward larger brains by itself: they argue that the initial advantage of bigger brains was not greater intelligence, as we have long believed, but having "redundant circuits" to protect us from heat stroke.Bigger brains, in this view, created the opportunity for intelligence, but that was only a by-product of their initial advantage to our ancestors.
If naked skin developed as an efficient way to diffuse body heat under an equatorial sun, the skin itself would have been protected by melanin, the dark pigment in human skin that forms a barrier to ultra-violet rays.
Until the development of fire, however, the loss of body hair with its insulating and heat-retaining qualities would have prevented expansion of Hominid or human populations into cooler environments. The ability to survive sudden temperature drops, such as those which occur at night at moderate elevations or away from the equator, would have been a problem for humans. It seems reasonable, in fact, to suppose that the need for warmth at night may have driven the discovery of the uses of fire. Using fire for cooking may, in fact, have been a subsequent invention.
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