When it comes to friendships, it’s important to have some things in common.
However, while enjoying the same films and having similar taste in restaurants might seem important, the real test of a strong friendship could lie in your genetics.
This is because friends are more genetically similar than strangers, claims a new study published in Proceedings of the National Academy of Sciences.
Past research has suggested that people tend to be somewhat genetically similar to their spouses and adult friends, likely because humans naturally gravitate toward people with whom they have something in common. But how and why does this subconscious sorting happen?
Researchers from Stanford, Duke and the University of Wisconsin—Madison studied 5,000 pairs of adolescent friends using data from Add Health, a long-term study of people who were in grades seven through 12 during the 1994-1995 school year. They ran a number of genetic comparisons, seeking to learn more about pairs of friends and schoolmates.
They also found that friends were on average around two-thirds as genetically similar as married couples, reports Time.
This effect may be due to a concept called social homophily, or the idea that individuals form bonds based on shared characteristics, many of which can be traced back to genetics.
Another explanation they suggest is that people tend to form friendships within shared social environments. For example, they may attend the same school or live in the same community. This is known as social structuring, the authors write.
Speaking to Time, lead author and Stanford professor Benjamin Domingue concluded that the latter, which might be more subconscious, could be more influential in terms of friends sharing similar genetics.
“Are individuals actively selecting to be around people who are like them, or is it due to impersonal forces, such as social structures, that we all are affected by?” he asked.
“Our evidence, with respect to friends, suggest that it’s largely the effect of social structures.”