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Why Does a Blonde Have Light Hair?

Blonde jokes aside, scientists want to know

Researchers in Scotland want to study blondes. No, they're not out to find why blondes cross the road or uncover the truth behind other countless blonde jokes. Instead, they hope to unravel a bigger puzzle: No one yet can explain why people have different hair colors.

Skin color, for example, seems easy to explain. Scientists theorize that it's a trade off between the risk of skin cancer and the demand for vitamin D, which our bodies create when the skin is exposed to sunlight.

The Lexington, Ky. Herald-Leader says as humans migrated to higher latitudes, lighter skin allowed them to produce more vitamin D. But as tribes moved to northern climates with cloudy skies, the lack of strong sunlight reduced the amount of vitamin D in their systems. Indeed, studies have shown that people who live above 50 degrees latitude face the greatest risk of vitamin D deficiency. (As a reference, the United States and Canada share a border at 49 degrees latitude.)

But that doesn't explain blond hair, which doesn't play any role in vitamin D synthesis in the skin. "For all the jokes about dumb blondes, we can hardly say anything sensible about blond hair," says Jonathan Rees, a dermatology professor at the University of Edinburgh. Ditto for redheads. Biologists can't figure out why evolution would create red hair, either.

The BBC News describes Rees' planned research.

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