Genome-wide analysis reveals genetic similarities among friends

If you consider your friends family, you may be on to something. A study from the University of California, San Diego, and Yale University finds that friends who are not biologically related still resemble each other genetically.

Published in the Proceedings of the National Academy of Sciences, the study is coauthored by James Fowler, professor of medical genetics and political science at UC San Diego, and Nicholas Christakis, professor of sociology, evolutionary biology, and medicine at Yale.

“Looking across the whole genome,” Fowler said, “we find that, on average, we are genetically similar to our friends. We have more DNA in common with the people we pick as friends than we do with strangers in the same population.”
The findings are not, the researchers say, an artifact of people’s tendency to befriend those of similar ethnic backgrounds. The Framingham data is dominated by people of European extraction.
How similar are friends? On average, Fowler and Christakis find, friends are as “related” as fourth cousins or people who share great-great-great grandparents. That translates to about 1 percent of our genes.

“One percent may not sound like much to the layperson,” Christakis said, “but to geneticists it is a significant number. And how remarkable: Most people don’t even know who their fourth cousins are! Yet we are somehow, among a myriad of possibilities, managing to select as friends the people who resemble our kin…”

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It does not sound good for the “Diversity is strength” crowd (even though the data was restricted to people of European extraction).

Common sense tells you that people like to be with those that they have something in common with.

And I keep reading news reports (anecdotes only, of course) about how kids at university “self-select” their friends by ethnicity.