Your “sister from another mister” might actually share your genes. A new study has found that friends are more genetically similar to each other than to strangers.

In a process similar to how the Sorting Hat groups Hogwarts newbies into houses of like-minded wizards, researchers have found that humans tend to form social relationships with people who resemble them.

It’s part of a new field called sociogenomics that studies “social genomes” to understand human health and behavior.

This evolutionary sorting hat presents a bit of a chicken-or-the-egg situation: do we like our friends because they are like us, or are they like us because we like them? 

Ever wonder why you can miraculously fit into your best friend’s shoes? It's because people are attracted to others with similar shared characteristics like body mass index. Birds of a feather really do flock together – and people form bonds based on physical similarities and backgrounds – thanks to social homophily. 

We’re also influenced by our social structure, a notion that indicates people tend to gravitate towards similar people, like those that live in the same communities or attend the same school.

The two theories are not mutually exclusive and could actually complement each other. 

Researchers from Stanford, Duke University, and the University of Wisconsin examined 5,500 American adolescents using data from the National Longitudinal Study of Adolescent to Adult Health. During the 1994-95 school year, researchers interviewed more than 90,000 Americans aged 12-18. As part of the survey, students were asked to list the names of their friends. In 2008, 12,000 participants later provided DNA samples used to identify social ties between individuals and their friends. The study was published in the Proceedings of the National Academy of Sciences. 

It adds to recent studies that show married couples, classmates, and adult friends are, on average, more genetically similar to each other than pairs of people who don't know one another.

Study author Benjamin Domingue, an assistant professor at the Stanford Graduate School of Education, told Time that these correlations are strong enough to detect but are not as strong as links in siblings.

The social grouping in teens is an important indication of how people sort through genetic selections. Adolescence is a critical developmental period during our lives and our habits, patterns of health behaviors, and overall mental health established during this time will continue throughout our lives.

It also shows how social networks can influence "mating" markets. As it turns out, that friend who set you up on a blind date was actually sorting through genotypes to find your perfect genetic match.

It all points to how a shared environment and background may account for a good chunk of genetic likeness in friends.

That takes your “brother from another mother” to a whole new level.