Tuesday, November 22, 2011

A Short History of Humans and Vitamin D

The Philadelphia Enquirer has an article on the research done by Nina Jablinski on humans’ evolution of skin color as a response to the need for vitamin D. Most of this is not unknown, the higher in latitude a population is, the lighter the skin color to maximise the amount of Vitamin D that is absorbed from the sun. In a nut shell, this is why equatorial populations are dark-skinned as well. Response to the amount of Vitamin D that is needed for a given population is subject to very high degrees of selection. Faye Flam writes:
Originally, humans made more than enough in skin, Holick said. When some of our ancestors left Africa, they adjusted their skin tone to allow in more sunlight. Penn State's Jablonski found that around the world, the skin color of native people maps almost perfectly onto a map of UV radiation; the more UV, the darker the average skin.

In 2005, Penn State professor Mark Shriver and colleagues isolated a genetic mutation that contributed to Europeans' having white skin, a mutation that in zebra fish leads to absence of the characteristic stripes.

Shriver, a professor of anthropology and genetics, said the original human skin color was probably light, because other apes are light-skinned under their fur. Dark skin became advantageous in Africa when we lost our fur.

Genetic evidence suggests that light-skin-related mutations arose recently, less than 15,000 years ago, and spread fast through Europeans.

Jablonski said that when scientists scraped bits of DNA from Neanderthal skeletons, they found a mutation of another skin-color-related gene. Neanderthals lived in Europe and the Middle East long before our ancestors left Africa, and apparently they independently evolved light skin.

In the Arctic, the Inuit never developed light skin, which scientists at first considered a paradox until they discovered how much Vitamin D is in a traditional Inuit diet, which included oily fish and whale blubber.
That Neandertals underwent a slightly different mutation and selection to the need for Vitamin D suggests that there was at least some separation between them and the incoming modern humans. One wonders what gene was involved in the Denisova DNA.

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