5.1. The enhancement of skin
A million years ago, in the mild environment of the inter-glacial periods, upright 2-legged proto-humans (hominids) began to roam the fields and forests of Africa, or East Asia, as foragers and collectors of seeds, nuts and fruit, with an occasional meat supplement when they encountered a recently killed beast and could scare away its killer. At some point the proto-humans learned to hunt larger animals, always in groups because they were physically slower and weaker than any of the other predators.
But it seems that (thanks to organization) they developed a capacity to run for longer distances than the faster four legged creatures (like antelopes) that they hunted. The antelope would run away when the hunting party came close, but only far enough to be out of sight. Then the antelope would pause to rest until the hunters came again. And so it continued until the chosen antelope was exhausted and could run no further.
For purposes of long-distance running, heat dissipation by evaporation is crucial – as any long distance runner will tell you – and bare skin is far more efficient at heat dissipation than fur. Bare skin and widely distributed sweat glands became an evolutionary advantage. It enabled hairless hominids to hunt (and travel) during the heat of the day when the large predators with inefficient heat dissipation mechanisms were inactive and the large animals like rhinos, hippos and elephants lounged in the water. (N.B. have you noticed that your dog can only sweat through his tongue?)
It is true that we humans, like other animals, come into the world naked. But we do not stay that way for long. At some later time back in the ice ages, our increasingly hairless ancestors, being cold when they were not running, had the bright idea of covering their bare skins with the skins of other animals. Thus clothing was invented. I know not when this happened, but the link between hairlessness and the use of animal skins seems obvious.
The caves where hairless hominids lived during the glacial epoch were, of course, also another form of protection from large predators of the night. When the ice melted, people learned how to create artificial caves, or huts. Groups of huts became villages, which soon acquired walls. Skin by another name, also thanks to organization and communication.
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