Brad DeLong shows how productive a little evolutionary theory can be in the right hands. Brilliant.
Amanda Schaffer writes in Slate about how a surprisingly large number of people who live here in the northlands far from the equator need more vitamin D. I am very surprised that this is controversial. When we Cro-Magnon types came out of Africa 60,000-100,000 years ago, none of us were white. Now practically all of us, the bulk of whose ancestors stopped for long in northern Europe or northern China, are remarkably pale indeed. I have heard no reason advanced for this other than that melanin in your skin blocks some vitamin D creation. If true, then there must have been a hell of a lot of selection pressure for low-melanin skin, which implies a hell of a large health cost to blocking even a small amount of sun-mediated vitamin D creation.
Addendum: The ever-intelligent Randall Parker points me to this link with further information on Vitamin D, folate and ultraviolet light.
Until the 1980s, researchers could only estimate how much ultraviolet radiation reaches Earth’s surface. But in 1978, NASA launched the Total Ozone Mapping Spectrometer. Three years ago, Jablonski and Chaplin took the spectrometer’s global ultraviolet measurements 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. “This was one of the last barriers in the history of human settlement,” Jablonski says. “Only after humans learned fishing, and therefore had access to food rich in vitamin D, could they settle these regions.”