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According to the recent single origin hypothesis (the one most supported by the empirical data), anatomically modern humans (Homo sapiens) arose in East Africa approximately 200,000 years ago (Tishkoff, 1996). Anatomically modern behavior in terms of innovation in hunting instruments and artistic expression arose within the past 100,000-70,000 years in Africa. It was just after this period that modern humans began to expand their range to regions outside of (and within) this continent (Tishkoff, 1996). Among those in the group who left the African continent, some migrated to northern regions such as central and northeast Asia. It is hypothesized that, given their original sub-Saharan origin, these groups initially faced a special dilemma. Their dark African skin and 'kinky' African hair, both of which had evolved to minimize entry of UV light into the body, were ill-suited to the weak sunlight of these regions. This is because, some time during the period in which humanity was in Africa, their skin had developed the ability to manufacture vitamin D (which was essential for bone development) upon exposure to UV light (Jablonski, 2006). However the UV light of northern regions was too weak to penetrate the highly pigmented skin of the initial migrants in order to provide enough vitamin D for healthy bone development. Malformed bones in the pelvic area were especially deadly for women in that they interfered with the successful delivery of babies. Hence, those with lighter skin gradually survived and had children at higher rates because their skin allowed more UV light for the production of vitamin D (Jablonski, 2006). It is probable that, during the transition period from dark to light skin, the need for vitamin D grew so intense that northerners with mutations for straight hair survived and had children at higher rates. This is likely because straight fibers better facilitate the passage of UV light into the body compared to 'kinky' hair. This, again, is in accord with Iyengar's (1998) findings that UV light can pass through straight human hair roots in a manner similar to the way that light passes through fiber optic tubes.
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