Page "Hair" Paragraph 47

According to the recent single origin hypothesis, anatomically modern humans arose in East Africa approximately 200, 000 years ago.

Then, ~ 150, 000 years later ( i. e. around 50, 000 years ago ), sub-groups of this population began to expand our species ' range to regions outside of, and ( later ) within, this continent ( Tishkoff, 1996 ).

For those members of this group who migrated far north ( i. e. to northern Eurasia, etc.

), the UV light of these regions was too weak to penetrate the highly pigmented skin of the initially ( relatively ) dark-skinned migrants so as 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 less pigmented skin survived and had children at higher rates because their skin allowed more UV light for the production of vitamin D. Thus, the skin of those in the group that left the African continent and went far north gradually developed adaptations for relatively greater translucence compared to equatorial hues.

This enabled the passage of more UV light into the body at high latitudes, facilitating the natural human body-process of manufacturing vitamin D ( which is essential for bone development ) in response to said light.