NewsSkin

Shedding light on skin color

Science  21 Nov 2014:
Vol. 346, Issue 6212, pp. 934-936
DOI: 10.1126/science.346.6212.934

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Summary

Why do humans have skin of various colors? Anthropologist Nina Jablonski explains that it's all about sunlight. As modern humans spread out of Africa in the past 60,000 years, they adapted to the varying natural light they encountered, from the twilight of northern winters to the blazing sun of the equator, and their originally dark skin evolved into a sepia rainbow. Jablonski has popularized this evolutionary history in countless radio and TV interviews, two popular books, and a TED talk viewed by nearly 700,000 people online. She argues that our skin color has crucial implications for health. In the modern era, as humans of various shades have moved rapidly across hemispheres, their skin has not had time to adapt to different amounts of ultraviolet light, so they are poorly adapted to their environments. For example, most white people know that if they live near the equator, they risk skin cancer unless they use sunscreen. But what is less known is that dark-skinned people who bundle up in frigid northern winters or stay indoors all day in the tropics risk vitamin D deficiency, making them susceptible to rickets, infectious diseases, heart disease, and other health problems. Some of Jablonski's ideas, for example that dark skin evolved to protect folate circulating in the blood, remain unproven. Yet her work is injecting a shot of evolutionary perspective into medicine and influencing researchers to test how sunlight affects health.