Beyond Fur: Sweating and Barrier Features of Human Skin

The evolution of hairlessness in humans was driven primarily by the requirements of keeping cool. The evolution of a high density of eccrine sweat glands was the keystone of our whole-body cooling mechanism. Maintenance of thermal homeostasis during exertion under hot environmental conditions was a precondition for encephalization in the human lineage because the brain is highly temperature sensitive. The loss of functional body hair associated with the evolution of hairlessness necessitated modifications of the epidermis to protect against desiccation and abrasion. The surface layer of the epidermis of human skin called the stratum corneum is characterized by multiple barriers, to physical injury, permeability, and to chemical and biotic insult. Some of the genes associated with these enhanced barrier functions are unique to the human lineage, and have evolved since we shared a common ancestor with our closest living relative, the chimpanzee. Naked skin has been a canvas for self-expression for tens of thousands of years and remains one of humanity's most salient outlets for personal expression.