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SAN DIEGO — Friends don’t just feel like family members, they are also genetically similar to them, according to a new study.
The friends people pick tend to share a significant amount of gene variants with themselves, according to the study from Yale University and the University of California-San Diego. On average, researchers found close friends are the genetic equivalent of fourth cousins.
“Looking across the whole genome, we find that on average we are genetically similar to our friends,” said co-author James Fowler in a statement. “We have more DNA in common with the people we pick as friends than we do with strangers in the same population.”
Researchers analyzed 1.5 million markers of gene variation from a dataset that included 1,932 people and their relationship information. They compared pairs of unrelated friends to pairs of unrelated strangers for the study.
Friends typically share about 1 percent of their genes, according to findings from the study. Co-author Nicholas Christakis said that may seem like a small percentage, but it is a highly significant number among geneticists.
Sharing genes can provide evolutionary benefits, according to researchers. They found the genes friends have in similar are also the gene variants experiencing the most evolutionary activity.
The first mutant to speak needed someone else to speak to. The ability is useless if there's no one who shares it.
–Fowler
“The first mutant to speak needed someone else to speak to,” Fowler said. “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.”
Using the findings from the study, Fowler and Christakis were able to create a “friendship score” that enabled them to predict who will be friends. The level of confidence for the friendship protections they made based on genes is the same as that for obesity or schizophrenia, according to the study.
Ethnic identity was not a factor in the findings, according to researchers. The dataset was taken from a population with mostly European descent, but geneticists said even within an ethnically similar population, people still chose people who were more genetically similar to them to be friends.
“This gives us a deeper accounting of the origins of friendship,” Christakis said. “Not only do we form ties with people superficially like ourselves, we form ties with people who are like us on a deep genetic level. They’re like our kin, though they’re not.”
The study was published in the Proceedings of the National Academy of Sciences.
