At your next family gathering, take a look around. Although you might not want to admit it, you can often see genetic similarities between your relatives. It might be as obvious as inheriting your grandfather’s propensity towards male pattern baldness, or as subtle as also inheriting his enjoyment of a good Scotch. Like it or not, however, your family is your family and there’s not a damn thing you can do about it.
Friends are different. You can pick and choose your friends, and you can do your best to avoid the genetic foibles you and your family are stuck with.
But a new study published today in PNAS shows that your friends are also likely to share your genetics. The study, led by James Fowler and Nicholas Christakis, found that people with certain gene variants were more likely to have friends with that variant. The reverse was also true: people without the allele were more likely to have friends without that allele.
It’s interesting, but previous studies have shown that when it comes to friends, “birds of a feather flock together.” That is, people tend to befriend others who are like them. Barflies and boy band fans tend to come in packs. But there isn’t a “barfly” or “boy band” gene, so researchers didn’t know whether these behavioral tendencies also tracked on the genetic level.
Fowler and Christakis used data from the the National Longitudinal Study on Adolescent Health and the Framingham Heart Study Social Network. Each of these studies asked participants to name several friends, and obtained genetic data from all of the people involved. From this data, the researchers could look at the relationships between friendship, genotype (which of the gene variants the person had), and phenotype (how the friends behaved).
The authors used two well-researched genes to categorize the study participants. One gene, known as DRD2, is a receptor for dopamine, a neurotransmitter that works in the brain’s reward system. DRD2 has two major variants, one of which is linked to an increased risk for alcoholism. A 2007 study in Drugs and Chemical Toxicology found that some variants of CYP2A6 were associated with openness to new experience. People who score high in openness show a higher appreciation of art and music, have more vivid imaginations, and are more likely to think critically about issues of politics and religion.
Ultimately, the authors found that a person’s friends were much more likely to have the same DRD2 and CYP2A6 variants. Write Fowler and Christakis:
People’s friends may not only have similar traits, but actually resemble each other on a genotypic level, even at the level of specific alleles and nucleotides.
The authors say that these results change what scientists think about how the genetics of a population is structured. Before, scientists believed that long-term partnerships and reproduction were the main things that affected which genes a group of people had. These results, however, show that friendship also plays a role.
Carrie Arnold 