The adaptive response of human skin to the savanna

Abstract

In the early stage of human evolution, as the hominids began to inhabit the savanna mosaic in Africa some three or four million years ago, a functional complex of skin features contributed to their effective exploitation of resources and survival in the new environment. Thermal radiation from the sun combined with internally generated heat from muscular effort posed problems of thermoregulation. As a mechanism for dissipating body heat and maintaining brain temperature, eccrine sweat glands throughout the body surface combined with reduction in body hair enhanced the evaporative cooling effects of sweating. As body hair diminished, deeply pigmented skin was selected for as a protection against harmful ultraviolet radiation. When human populations left the equatorial regions of Africa, the adaptive significance of deeply pigmented skin may have shifted in response to other factors, such as latitude, diet and cultural pratices. We view the structure and function of human skin within a comparative and evolutionary framework that focuses on the environment in which the hominids evolved.