A new study suggests Europeans developed lighter skin, hair, and eyes due to their ancestors’ sexual preferences, and not just natural selection.
Homo sapiensfirst arose in Africa about 200,000 years ago, and anthropologists assume that those early humans resembled present-day Africans because dark skin carries advantages in that environment.
Higher levels of the skin pigment melanin block out UV light and protect against its damages, including DNA damage that causes skin cancer and the breakdown of vitamin B.
But melanin also blocks out UV light needed to produce vitamin D, so prehistoric humans needed less of the pigment for protection as they move further north of the equator.
Recent DNA analysis of ancient skeletons suggests that human factors, including diet and sexual attraction, may have caused the lightening of Europeans’ skin over the past 5,000 years, in addition to environmental factors.
Anthropologists at Johannes Gutenberg University Mainz and geneticists at University College London, working with archaeologists from Berlin and Kiev, published their findings this week in the journal Proceedings of the National Academy of Sciences.
The researchers compared DNA from archaeological skeletons with contemporary Europeans using computer simulations, and they inferred positive selection played a role when genetic changes could not be explained by the randomness of inheritance.
The darker phenotype seems to have been preferred by evolution for hundreds of thousands of years and caused prehistoric Europeans to be consistently darker than their present-day descendants.
But that began changing about 50,000 years ago as prehistoric humans migrated further north, although research suggests Europeans remained mostly dark-skinned until much later.
“Most people of the world make most of their vitamin D in their skin as a result UV exposure,” said Professor Mark Thomas, of University College London. “But at northern latitudes and with dark skin, this would have been less efficient. If people weren’t getting much vitamin D in their diet, then having lighter skin may have been the best option.”
But that evolutionary explanation is less convincing for hair and eye color, the researchers said.
“It may be that lighter hair and eye color functioned as a signal indicating group affiliation, which in turn played a role in the selection of a partner,” said researcher Sandra Wilde, of Johannes Gutenberg University Mainz (JGUM).
This sort of sexual selection is common in animals, but the researchers said it may have been one of the driving forces behind human evolution for several thousand years.
While pigmentation genes may have been favored by natural selection to “a surprising degree” over the past 10,000 years, the study’s senior author said their findings should not show that every characteristic selected in the past remains beneficial today.
“The characteristics handed down as a result of sexual selection can be more often explained as the result of preference on the part of individuals or groups rather than adaptation to the environment,” said Joachim Burger, of JGUM.
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