Hardly did I know what I was getting into when I set out to research this topic. It wasn’t easy. I normally don’t really give much thought to why my skin is dark and apparently, many other people don’t. Based on my informal surveys, I could not find a single explanation. I suppose it’s just one of those things everyone notices, but no one really thinks about. So after wasting hours on the Internet with hundreds of irrelevant links, I went to Baker Library in search of the truth.
Three librarians later, I came across a summary of work done by Nina Jablonski, Chair of the anthropology department at the California Academy of Sciences, who started research on the evolution of skin color about ten years ago. In a nutshell, she says that skin color is largely a matter of vitamins.
Jablonski based her research on work published in the 1960’s by biochemist W. Farnsworth Loomis suggesting that skin color is determined by the body’s need for vitamin D, which depends on ultraviolet light for its production in the body. Loomis believed that people who live in the north, where daylight is weakest, evolved fair skin to help absorb more ultraviolet light and that people in the tropics evolved dark skin to block the light, keeping the body from overdosing on vitamin D, which can be toxic at high concentrations.
By the time Jablonski did her research, in the early 1990’s, Loomis’s hypothesis had been partially disproved, as it was found that a person could never overdose on natural amounts of vitamin D. While Loomis’s theory was disproved, his insight about fair skin held up.
In Loomis’ day, researchers could only estimate how much ultraviolet radiation reaches Earth’s surface. But three years ago, Jablonski and her husband, George Chaplin took global ultraviolent measurements from NASAs’ Total Ozone Mapping Spectrometer and compared them with published data on skin color in indigenous populations from more than 50 countries.
To their delight, there was an unmistakable correlation: the weaker the ultraviolet light, the fairer the skin. Jablonski went on to show that people living above 50 degrees latitude have the highest risk of vitamin D deficiency. As well, an hour of intense sunlight can cut levels of folate, a member of the vitamin B complex, in half if your skin is light.
Humans have spent most of their history moving around the Earth. They’ve had to adapt their tools, clothes, housing, and eating habits to each new climate and landscape. But Jablonski’s work indicates that our adaptations go much further.
So what’s the bottom line of Jablonski’s research? Pay attention to vitamin D and folate in your diet. More importantly, Jablonski hopes her work will begin to change the way people think about skin color. “We can take a topic that has caused so much disagreement, so much suffering, and so much misunderstanding,” she says, “and completely disarm it.”
Jablonski and Chaplin predicted the skin colors of indigenous people across the globe based on how much ultraviolet light different areas receive.
