SAN DIEGO, CA (CBS) – You might have even more in common with your friends than you think. In fact, you probably share some of the same genes.

That’s according to new research out of Yale and the University of California – San Diego, which shows that friends are about as genetically similar as fourth cousins.

Researchers say they focused on nearly 2,000 subjects from the Framingham Heart Study, one of the largest sets of data that contains both genetic information and information on social relationships between the people it was collected from.

What they found is that people who were friends shared about one percent of the same genes.

And though “One percent may not sound like much to the layperson…most people don’t even know who their fourth cousins are,” co-author Nicholas Christakis, professor of sociology, evolutionary biology, and medicine at Yale, tells the UC San Diego News Center, “We are somehow, among a myriad of possibilities, managing to select as friends the people who resemble our kin.”

Scientists say their findings make sense, as “functional kinship” can produce a number of evolutionary advantages. As they explain it, if your friend wants to make a fire and you’re cold, you both benefit.

And while friends were most alike in genes having to do with sense of smell, they were the most different in terms of their immune systems. This, too, has advantages, since “having connections to people who are able to withstand different pathogens reduces interpersonal spread.”

But perhaps the most fascinating finding gleaned from the study? Genes that were similar between friends seem to be evolving faster than other genes, suggesting that “social environment itself is an evolutionary force.”

“The first mutant to speak needed someone else to speak to. The ability is useless if there’s no one who shares it. These types of traits in people are a kind of social network effect,” explains the study’s co-author James Fowler, who is also a professor of medical genetics and political science at UC San Diego.

The research is published in a recent issue of the journal Proceedings the National Academy of Sciences of the United States of America.

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