Nina Jablonski: Penn State Department of Anthropology

Humans are distinguished from other primates by being functionally hairless over most of their bodies. This condition evolved because hairlessness facilitated cooling of the body by sweating. The evaporative cooling made possible by sweating results in whole-body cooling of blood flowing in superficial vessels, and the maintenance of constant brain temperature. The combination of anatomical, physiological, and new genetic information pertaining to the structure and function human skin have helped to “lay bare” the evolution of human hairlessness and sweatiness. Hairlessness had major consequences for the evolution of skin pigmentation and the communication of visual information and signals through elaborated facial expressions and, later, body painting and decoration.
http://www.bec.ucla.edu/JablonskiTalk.pdf