Over the last couple of years, scientists have been making fascinating discoveries about human prehistory by squencing anceint DNA. For some time they could infer clues to our past by studying DNA from living humans, but now they’re fleshing out the details by sequencing DNA from bones of those who lived thousands of years ago.
On Sunday, a paper in Nature detailed the results of sequencing a 7000-year-old skeleton of an ancient hunter-gatherer from Spain. Most of Europe was apparently populated by hunter –gatherers until farmers swept in some 8000 years ago, but the transition occurred later in Spain.
Michael Balter has been doing a great job following DNA-based archaeology for Science, and his piece, How Farming Reshaped our Genomes, provides great context and interpretation for this latest advance. Readers get to learn that these hunter-gatherers had not developed our modern adaptations to digest milk and starch, but they did have some immune-associated genes that were thought to have arisen much later.
And the DNA revealed that this man probably had very dark skin and blue eyes – a striking combination to be sure.
New Scientist weighted in with a similar piece, Ancient European Hunter-Gatherer was a Blue Eyed Boy. Livescience, too, ran with a piece that emphasized this ancient person’s skin/eye combination.
There was one point where both Science and even more so Livescience got confusing. Both stories explain that scientists used to think that light skin is an adaptation to the need to get more vitamin D from sunlight. People get less sun exposure in northern and extreme southern latitudes, and lighter skin absorbs UV more readily. But now we find that people were still dark-skinned after living in Europe for thousands of years. One of the researchers, Carles Lalueza-Fox, is quoted in Science and Livescience saying that hunters would have gotten sufficient vitamin D from eating wild fish and game. It’s in the food chain. So the adaptation may have resulted instead from a change to the lower-vitamin D diet people ate after the advent of farming. Both stories quote him suggesting it’s not about sunlight after all.
Well, okay, but if farming and not sunlight is the main factor behind light skin, why didn’t African, South Asian and Native American farmers become white? Could it be that both sunlight and diet are important in evolution of light skin? Maybe it takes both a farming diet and high latitude before light skin mutations are favored enough to spread through the population. This is what seemed to be suggested by the New Scientist story, which included another source. That source also pondered the spread of blue eyes, which have no obvious survival advantage. Could their spread be the result of sexual selection? It’s an intriguing question.