. "Some people have a lot of melanin because it protected their ancestors from the harmful effects of UV radiation; other people have less melanin because they live where there is less UV radiation, and their skin must be lighter in order to permit the available UVR to be used in vitamin D production."
But what about places like Alaska, which is close to the North pole, but where the indigenous peoples are dark? Geologically speaking, these populations have not lived in the region very long. But more importantly, their traditional diet is rich in fish and marine mammal blubber. They've consumed so much vitamin D-3 that they have not required a reduction in pigmentation that would otherwise benefit people living at such high latitudes.
"What's really interesting is that if these people don't eat their aboriginal diets of fish and marine mammals, they suffer tremendously high rates of vitamin D-deficiency diseases such as rickets in children and osteoporosis in adults," Jablonski says. "For years people couldn't understand why dark Indians and Pakistanis living in northern England suffered from vitamin D-deficiency diseases. Now it has become clear that the natural sunscreen in their skins wouldn't allow them to synthesize enough vitamin D from the sunlight."
"One of the interesting findings that our study has thrown up is that in every indigenous population we've examined, females are slightly more lightly colored than males, probably because they need to synthesize more vitamin D in their skin during critical periods of their life history, such as pregnancy and lactation," she adds.
Jablonski arrived at her theory after she and her spouse George Chaplin, also with the California Academy of Sciences, studied data from NASA's Total Ozone Mapping Spectrometer, which was launched in 1978 to measure how much ultraviolet radiation reaches Earth's surface. Jablonski and Chaplin compared that data with published data on skin color in indigenous populations from more than 50 countries. The unmistakable correlation showed that the weaker the UVR in an area, the fairer the skin. Jablonski points out that people living above 50 degrees latitude have the highest risk of vitamin D deficiency. "This was one of the last barriers in the history of human settlement," she says. "Only after humans learned fishing, and therefore had access to food rich in vitamin D, could they settle these regions."
Jablonski hopes her research will 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, and completely disarm it," she says. "We're all the same under the skin."
Many people are "happy and relieved" when they hear about this research, she says. "All of a sudden their own coloration isn't something that was just handed to them. It isn't a social stigma. It's something that evolved in their ancestors for a good set of biological reasons. And it takes the wind out of racism and bigotry."
Jablonski received her PhD in anthropology from the University of Washington in 1981 and then went on to hold teaching positions at the University of Hong Kong (1981-1990) and The University of Western Australia (1990-1994). She has held the Irvine Chair of Anthropology at the California Academy of Sciences since late 1994. She is the author of numerous papers and books on primate and human evolution, conducts fieldwork throughout Asia and Africa, and in 2002 was elected a Fellow of the American Association for the Advancement of Science.
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