The evolution of bipedality and loss of functional body hair in hominids

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The large relative brain size of hominids, and their lack of an effective carotid rete, means they are vulnerable to thermal damage during elevations of body temperature. This would account for the well developed whole-body cooling system of man, provided by a functionally naked skin and associated cutaneous sweat glands. It is argued that the lower direct solar radiation fluxes incident upon a bipedal mammal made possible the reduction of body hair, and explains the absence of this characteristic among savannah quadrupeds. The major thermoregulatory advantages conferred by bipedality, to an animal extremely sensitive to hyperthermia, could also account for the initial evolution of this unusual form of locomotion.

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