科学美国人60秒:Light Skin Variant Arose in Asia Independent of Europe

A new genetic study of Latin Americans provides evidence that gene variants for lighter skin color came about in Asia as well as in Europe. Christopher Intagliata reports.

In Latin America, Native Americans, Africans, and Europeans have intermixed for centuries. So, a few years back, researchers sought to learn more about the ancestry of more than 7,300 people from Brazil, Chile, Colombia, Mexico and Peru. The volunteers provided DNA samples. And they also answered the question: what do you think your background is? 

Turns out that what they thought—that is, their predicted ancestry—told a different story than their genes did—with skin color a key factor. 

“Their predicted ancestry is actually very well correlated with their skin color, but poorly with their actual genetic ancestry. So that showed us people are actually trying to predict their whole ancestry by just looking at their skin color, which is a pretty crude thing to do, but that's how the attitude is in Latin America." Kaustubh Adhikari, who studies human genetics at University College London. 

In particular, lighter-skinned volunteers tended to overestimate their European ancestry whereas darker-skinned subjects overestimated their Native American or African backgrounds.

Now a new study by Adhikari and his colleagues offers a reason for the mismatch. The skin color data and the DNA sequences led the researchers to identify a genetic variant for lighter skin that arose in Asia 20- to 30-thousand years ago. That event appears to be independent of the evolution of lighter skin in Europe. 

What’s it all mean? Well, light skin color in Latin Americans could still reflect European ancestry. But it could also indicate Native American ancestry—by way of the original Asian immigrants carrying the trait who crossed the temporary Beringia land bridge into what’s now Alaska and became the first Americans. 

The researchers were also able to show that this gene variant for lighter skin pigmentation is more prevalent in parts of Asia that do not get much sunlight—indicating a possible way this genetic variant could have been selected for. The new study is in the journal Nature Communications. [Kaustubh Adhikari et al., A GWAS in Latin Americans highlights the convergent evolution of lighter skin pigmentation in Eurasia]

Adhikari says the findings could help modify Latin Americans' social views. "We know for example there's a big socioeconomic stratification in Latin America, and that correlates, because of the history of colonization, to people's European ancestry. And a proxy of European ancestry is often taken to be light skin color. So what we are trying to show is that such a blind attitude to social aspects is also wrong genetically, that there's also big variation of skin color from the native side that such kinds of simplistic attitudes would be ignoring."

A reminder that ancestry, like so much else, is more than skin deep.

—Christopher Intagliata