ABSTRACT
Like the eponymous mammary glands, hair is one of the defining features of mammals. It is a remarkable substance: light, flexible, and resilient. A single strand of human hair is capable of supporting 50-100 g, meaning that the total tensile strength of a normal head of hair could support over 12 metric tons ( 1 ). Hair first appeared in nature over 200 million years ago ( 2 ) and conventional wisdom is that hair originated as a part of the development of endothermy, or warm-bloodedness, to assist with insulation ( 3 ). New research however suggests that hair emerged during the complex process of skin evolution that took place during the transition of the mammalian species from aqueous to terrestrial environments ( 2 ). Although the precise evolutionary path remains unclear, the important role that hair plays in nature and society is undisputed.
