By contributor
updated 1/17/2011 3:00:07 PM ET 2011-01-17T20:00:07

You might have more in common with your BFF than a shared passion for football, politics, or kitty cats. Just like members of the same family, you and your "bestie" could be sharing some very compatible genes, according to a new study published Monday in PNAS, the journal of the U.S. National Academy of Sciences.

Researchers found that choosing folks to hang around with — and not choosing others — can be linked to specific genes. That genetic link provides the beginnings of a scientific explanation for the elusive quality of “chemistry” among friends, explains lead author James Fowler, a professor of medical genetics and political science at the University of California, San Diego.

“The whole idea of friendships is very weird,” says Fowler, whose research focuses on social networks, health and the biological basis of behavior. That’s because humans are one of the only species that forms long-term unions simply because we like each other, not just because we need to reproduce.

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To analyze an association between genes and human relationships, the researchers, with support from the National Institute on Aging, gathered data from two large studies: the National Longitudinal Study of Adolescent Health, and a replication study in an independent sample collected from the Framingham Heart Study. Both of these long-term studies asked participants about their friendship ties and social networks.

Like birds of a feather that actually do flock together, individuals who carry a particular genetic marker for a gene called DRD2, a dopamine receptor that is associated with alcoholism, among other traits, tend to make friends with other DRD2-positive people, according to the study results. Conversely, those who lacked the gene tended to form friendships with people who were also DRD2-negative.

Opposites also attract
But the scientists also found that when it comes to our genes, opposites may indeed attract. According to the research, folks who carried a version of a gene called CYP2A6, associated with an “open” personality, made friends with folks who didn’t carry it.

This idea of heterophily, or the love of the different, existing simultaneously with homophily, the love of the same, “should not be true at the same time,” says Fowler, who believes ongoing research will show that different biomechanisms, such as the sense of smell, might also come into play as we form friendships.

The researchers believe that friendships, when viewed from the genetic level, could provide a better understanding of the way that our genes may shape our social environment, and the way that social environment influences our behaviors.

Continued research may even show that a kind of feedback process happens, in which a person’s genes lead to choosing friends with particular genotypes. That, in turn, may actually influence the expression of a person’s own genes, giving rise to the idea that humans are “metagenomic,” says co-author Dr. Nicholas Christakis, a professor of medicine and sociology at Harvard Medical School.

“Humans live our lives in social networks in a sea of genes,” says Christakis. “And the fact that we’re showing that it’s not just our own genes, but (also) the genes of other people (having) relevance in our lives, has a lot of implications.”

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