We're Driven to Pick Friends Who Share Our Genes, Scientists Learn

The nature vs. nurture debate is sort of a misnomer to begin with. It’s not as if nature and nurture are fighting one another to exert influence on human behavior — but rather, the two forces are married and work together to guide our growth and actions.

Nevertheless, we’re starting to learn that nature is probably a much bigger factor in our lives than we thought. Our genes, it turns out, can have effects on everything from our economic status to who how we choose spouses. And now it seems, even how we choose friends is influenced by our genetics.

In a study published Tuesday in Proceedings of the National Academy of Sciences, a team of American researchers illustrate how social forces driven by genes and reinforced by the structure of society cause people to make friends and go to school with those that are genetically similar to them. There exists, according to the study’a authors, a “social genome” that play an extraordinarily key role in human health and behavior.

To get to this conclusion, the researchers took an analysis of 5,000 American adolescents, whose social and genomic information was collected through the National Longitudinal Study of Adolescent Human Health. Between 1994 and 2008 the study participants provided the team samples of their DNA and gave interviews about who their closest friends were. Responses were collected from adolescents who went to the same schools, in order to identify social ties, and each person was of an ancestral European origin.

The researchers collected genetic profiles of the friends of participants, to determine how similar these social groups were at a genetic level. The team discovered that adolescents were more often genetically similar to friends and schoolmates, which in turn augured specific traits like their body mass index and levels of education.

This correlation likely happens for two reasons that stem back to the conversation about nature versus nurture. One hypothesis focuses around a process called “social homophily,” in which people form relationships, consciously or not, on the basis of shared characteristics that often have genetic origins. Two individuals who are friends, for example, are tall, or possess similar temperaments.

The other hypothesis suggests friends and schoolmates are genetically similar because environments are socially stratified, so people tend to grow up and exist in localized social bubbles. This “social structuring” reinforces genetic similarities among groups, which in turn reinforces common behaviors and personalities.

What is most likely happening, the researchers write, is a “complementary process” between both of these hypotheses. The natural forces underlying social homophily combines with the environmental forces behind social structuring. These findings are actually similar to previous research where Duke University professor Daniel Belsky, (also a co-author of this new paper) found that people who shared genetic variants linked to education had more prestigious jobs and earned more money than those who did not.

“All of that does suggest our genes can affect our future,” Belsky explained in a 2017 interview with the Harvard Business Review. “But we also know that human development stems from a complex interaction of the genes we inherit and the environments we encounter.”

The next step in this field of study is to pinpoint observable characteristics that can be linked to genetic expression — whether that’s the psychological makeup of a friend group or their behavior when it comes to drugs and alcohol. People have the free will to make their own choices, but genes still have a whisper of influence when it comes down to pulling the trigger.