In 2007 a friend told me of an encounter at a seminar where L. L. Cavalli-Sforza seem to offer agriculture almost reflexively as a solution to the conundrum of signals of positive selection in the genome of humans. Basically, all paths led to agriculture. I have to say that nearly ten years later Cavalli-Sforza’s deep intuition on these issues seems to be vindicated. Agriculture was an enormously big deal.
Carl Zimmer in The New York Times has a write up of Matheison et al. (it’s in Nature), Agriculture Linked to DNA Changes in Ancient Europe. There aren’t a whole lot of surprises, as the pre-print has been around for a year or so. But, having the work written up in a newspaper allows researchers to engage in some extemporaneous speculation. Ergo, you have:
Why? Scientists have long thought that light skin helped capture more vitamin D in sunlight at high latitudes. But early hunter-gatherers managed well with dark skin. Dr. Reich suggests that they got enough vitamin D in the meat they caught.
He hypothesizes that it was the shift to agriculture, which reduced the intake of vitamin D, that may have triggered a change in skin color.
This was to some extent Cavalli-Sforza’s idea, and I’ve proposed it as well. Then there is the model of sexual selection. These theories aren’t always exclusive, and pigmentation may have multi-causal underpinnings. It is very interesting that the best methods and ancient DNA seem to be suggesting lots of very recent change and likely adaptation. But ultimately, we still have no clear idea.