As for why the hair loss occurred, Greaves said that it was "almost certainly to facilitate heat loss by sweating in physically very active hunters, especially in the more open, dry and hot Savannah."
Indigenous humans from East Africa and throughout sub-Saharan Africa today all have black skin, however, and DNA reveals that these individuals evolved a gene, MC1R, associated with skin pigment production. Many scientists over the years, including Charles Darwin, theorized that black skin was acquired early in human evolution as an adaptation to limit UV radiation damage from sun exposure.
To test that theory, Greaves studied African albinos, meaning people who have a congenital absence of pigment in their skin, hair and eyes. He found that they were highly susceptible to developing skin cancer.
"Almost all albinos in equatorial Africa develop skin cancer in their 20's," Greaves told Discovery News. "A few -- maybe 10 percent -- escape, and these are mainly females with a more indoor lifestyle."