Blonde Girl With Long Hair Posing On The Tree

Further, some interpret the ideas of Charles Darwin as suggesting that some traits, such as hair texture, were so arbitrary to human survival that the role natural selection played was trivial. They argue that Darwin's explanation which was that sexual selection may be responsible for such traits. However, the concept of "triviality" is a human value judgment, and hair texture still may have played a role. In fact, while the sexual selection hypothesis cannot be ruled out, the asymmetrical distribution of this trait vouches for environmental influence. Specifically, if hair texture were simply the result of adaptively arbitrary human aesthetic preferences, one would expect that the global distribution of the various hair textures would be fairly random. Instead, the distribution of Afro-hair is strongly skewed toward the equator. Further, it is notable that the most pervasive expression of this hair texture can be found in sub-Saharan Africa; a region of the world that abundant genetic and paleo-anthropological evidence suggests, was the relatively recent (~200,000 year old) point of origin for modern humanity. In fact, although genetic findings (Tishkoff, 2009) suggest that sub-Saharan Africans are the most genetically diverse continental group on Earth, Afro-textured hair (along with a small cluster of other physical features) approaches ubiquity is this region. This points to a strong, long-term selective pressure that, in stark contrast to most other regions of the genomes of sub-Saharan groups, left little room for genetic variation at the determining loci. Such a pattern is, again, not indicative of human sexual aesthetics.
Straight hair
According to the recent single origin hypothesis, anatomically modern humans arose in East Africa approximately 200,000 years ago (Tishkoff, 1996). Then, ~150,000 years later, modern humans began to expand their range to regions outside of (and within) this continent (Tishkoff, 1996). The skin of those in the group that left the African continent had developed the ability to manufacture vitamin D (which was essential for bone development) upon exposure to UV light. 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 because they interfered with the successful delivery of babies; leading to the death of both the mother and the infant during labor. Hence, those with lighter skin survived and had children at higher rates because their skin allowed more UV light for the production of vitamin D.