Human Variation and Race

Solar radiation is an environmental stress that, in high levels, has had a major impact on the evolution of hominid specie. Extreme solar radiation was a major problem to our predecessors in sub-Saharan Africa, as their skin tone, previously covered by hair or fur, was exposed to the intense rays of the sun. Darker skin tone, which is determined by the levels of melanin present in their cells, helps to absorb the harmful UV rays. UV rays, if not protected against, can cause genetic mutations to skin cells which can lead to cancer and eventually, death. Additionally, folate, a B vitamin essential to cell division in embryonic fetal development, is degraded by UV radiation leading to leading to less reproductive success if affected.

A short term adaptation to solar radiation does not really exist, as our bodies cannot adjust on the fly

to exposure. This is why fair-skinned people burn easily, and are more susceptible to skin cancer.

An example of a facultative adaptation would be how the skin tans, and produces more melanin to protect against over-absorption of UV rays, as h. sapiens migrated away from the tropics out of the intense UV radiation areas, the dark pigmentation gradually lightened as the need for high levels of melanin and UV protection diminished. 

As generation after generation of hominids adapted to living at higher altitudes and further north or south of the equator, they were exposed to less intense UV radiation. As a result, they developed a deficiency of vitamin D. A developmental adaptation was that the reduction in the production of melanin allowed for more efficient absorption of Vitamin D, a building block for bone mass and density, through the skin. This also allows the body to be able to convert Vitamin D to 1,25D, a crucial molecule needed for the prevention of m. tuberculosis and other diseases. An attribute associated with this adaptation with some frequency, which was evidenced as early as  h. neaderthalis, is red hair and freckles. 

Cultural adaptations to solar radiation can be observed around us in our everyday lives. Fair skinned people use sunscreen lotion to form a barrier between their skin and harmful UV rays, along with hats and umbrellas. As many humans work in offices for a large part of their day, the need for Vitamin D supplements will continue to increase. Many nutritional products are fortified with Vitamin D to help meet the recommended daily intake.

The more the scientific community studies genetic adaptations to solar radiation, the better off society will be. If we understand how and why our skin tones are different from our neighbors, we will not see skin tone as a point of differentiation, but, rather, as an indication of equality on our evolutionary tracts. Additionally, the this research can be used for the betterment of society, as new and more advanced treatments and protections against solar radiation can be developed and administered.

If we try to use race to help us understand human variation, we fail miserably. There is no difference at the DNA level between what society refers to as ‘race’, other than variation in phenotypic expression.  Rather, studying the environmental pressures that led to the great variation we observe today helps us to understand where our ancestors came from, what led to their migratory path, and possibly a glimpse into how our descendants will evolve and adapt to their own pressures.