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.
A team of researchers from Stanford, Duke and the University of Wisconsin examined 5,500 American adolescents using data from the National Longitudinal Study of Adolescent to Adult Health.
After carrying out a series of genetic comparisons between pairs of friends, they found a slew of genetic similarities between them, far more than between pairs who didn't know each other.
They also found that friends were on average around two-thirds as genetically similar as married couples.
This might be because people are drawn to those with whom they have shared characteristics i.e. having similar backgrounds, levels of education or being of a similar height and/or weight.
The researchers describe this process as social homophily.
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.
They added that social homophily and social structuring are not necessarily mutually exclusive processes and that the two may also complement one another.
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.”