Yes, suggests a new study on the genetic similarity between people in the same social networks.
"Our ability to make friends and keep friends is a part of humans that makes us unique," says James Fowler of the University of California at San Diego, yet "the biology of social networks is relatively unstudied."
“How and why do we make friends," he asks. To that end, Fowler and his colleagues studied 6 different types of genetic makeups – or genotypes – using data on thousands of people from the National Longitudinal Study of Adolescent Health and the Framingham Heart Study.
They mapped out specific genetic markers within social networks and found that people tend to forge friendships with people who share 2 of the 6 tested markers.
Birds of a feather:
People who carry the DRD2 marker – which is associated with alcoholism – tend to friend other DRD2-positive peers. Similarly, those who lacked the gene formed friendships with other DRD2-negative individuals.
Because drinkers are likely to surround themselves with people who are "slightly more likely to have a well-stocked liquor cabinet or meet you in a bar," the finding is not all that surprising in and of itself, Fowler says. But the fact that the genetic landscape of human populations may be affected by these friendships is a new and interesting concept, he adds.
Fowler points out that some people who know they are predisposed to drinking often have to work harder to change those behaviors. "When you find out your friends are susceptible," he says, "it should have a similar impact on you."
There might be an evolutionary benefit to having friends with compatible genes, even if you don't have any offspring with them. For example, if people who are naturally less susceptible to bacterial infection hang around together, their collective health as a group multiplies because the bacteria have no vulnerable hosts.
On the other hand, they also found that people with the gene CYP2A6 – which is associated with an open personality – tend to be friends with those who do not have that genotype.
"We live in a sea of the genes of others,” Fowler says. “We shouldn't just be thinking of the impact our genes have on our outcomes, but what the impact of our friends' genes are on our outcomes."