People Choose Friends Who Are Genetically Similar to Themselves, Study Finds

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For many of us, good friends are the next closest thing to family-- but you might be surprised to learn just how literal this simple truth is. According to a new controversial study, good friends actually are the next closest thing to family, genetically speaking.

A pair of U.S. researchers have found that we are more genetically similar to our friends than we are to random strangers, suggesting that genetics may factor in to how we choose our friends, reports the BBC.

The study looked at the genetic profiles of nearly 2,000 people, who were recruited from a small U.S. town as part of a larger heart study. Nearly 500,000 single-letter markers from across the genomes were analyzed, revealing that friends share about 0.1 percent more DNA, on average, than strangers do. While that might not sound like much, it's actually roughly equivalent to the genetic similarity of forth cousins.

"It's as if they shared a great-great-great-grandparent in common," explained James Fowler of the University of California at San Diego, one of the study's authors.

Aside from providing DNA samples, participants in the study were also asked who their closest friends were. Because all of the participants hailed from such a small community, there was a lot of crossover between friendship networks and study participation, making this sample population particularly ideal for such a study.

But the fact that all of the samples derived from such a small, tight-knit community has also prompted skepticism. Friendships in small communities might be more likely to be genetically related because such communities have less genetic diversity in general.

"I wonder whether [the methods used in the study can fully account for] factors known to drive friendships, like church membership, sports or other cultural affinities, that would also lead to a correlation with genotype," said Oxford's Dr. Rory Bowden, who was not involved in the study.

Nevertheless, the study's authors remain confident. "Most people don't even know who their fourth cousins are!" said co-author Dr. Nicholas Christakis from Yale University. "Yet we are somehow, among a myriad of possibilities, managing to select as friends the people who resemble our kin."

One interesting finding from the study is that some of the genes that friends were most likely to have in common involve smell. In other words, it seems that the smells we are drawn toward may also facilitate how we gather together socially. This, in turn, may influence how we meet friends.

"You may really love the smell of coffee. And you're drawn to a place where other people have been drawn to who also love the smell of coffee," Fowler explained. "And so that might be the opportunity space for you to make friends. You're all there together because you love coffee and you make friends because you all love coffee."