Tightly coiled hair

Jablonski (2006) agrees that it was evolutionarily advantageous for pre-humans (Homo erectus) to retain the hair on their heads in order to protect the skin there as they walked upright in the intense African (equatorial) UV light (Jablonski, 2006). In addition, axilliary hair (in the underarms) was likely retained as a sign of sexual maturity. During the process of going from fur to naked skin, hair texture putatively changed gradually from straight (the condition of most mammals, including humanity's closest cousins--chimpanzees), to Afro-like or 'kinky' (i.e. tightly coiled). This is supported by Iyengar's (1998) findings that the roots of straight human hair may act as fiber optic tubes that allow UV light to pass into the skin, while it is notable that 'kinks' in fiber optic tubes are known to prevent UV light from passing through. In this sense, during the period in which humans were gradually losing their straight body hair and thereby exposing the pale skin underneath their fur to the sun, straight hair would have been an evolutionary liability. Hence, tightly coiled or 'kinky' natural afro-hair may have evolved to prevent the entry of UV light into the body during the gradual transition period towards the evolution of dark skin.