Some friendships are so strong that you swear you and your BFF were related in another life. Well, it turns out that declaration isn’t too far off: Researchers at Yale University and the University of California at San Diego recently discovered that our friends are as genetically similar to us as fourth cousins—meaning we share around one percent of the same genes.
“The striking thing here is that friends are actually significantly more similar to one another than we were expecting,” says James Fowler, a professor of political science and medical genetics at UCSD, who conducted the study with Dr. Nicholas Christakis, a social scientist at Yale.
“It’s as if they shared a great- great- great-grandparent in common,” Fowler told NPR, and said that among some of the genes that friends were most likely to have in common involve smell. “We tend to smell things the same way that our friends do,” Fowler says.
Interestingly, there’s an evolutionary explanation for that. As humans evolved, the ability to tolerate and be drawn to certain smells may have influenced where people hung out. Today, we might call this the Starbucks effect, as NPR pointed out.
“You may really love the smell of coffee. And you’re drawn to a place where other people have been drawn to who also love the smell of coffee,” Fowler says. “And so that might be the opportunity space for you to make friends. You’re all there together because you love coffee and you make friends because you all love coffee.”
Even more mind-blowing: Researchers also discovered that—while genetically similar in lots of ways—friends (and spouses, as other data has pointed out) have very different genes when it comes to their immune systems, and we have evolution to thank for that, as well.
“One of the reasons why we think this is true is because it gives us extra protection. If our spouses have an immune system that fights off a disease that we’re susceptible to, they’ll never get it, and then we’ll never get it,” Fowler says.
The study’s findings could help to explain lots of things, including how relationships are driven by genetics and how that could be influencing human evolution right now. Of course, it also explains why surrounding ourselves with friends makes us feel comfy and cozy.
“It’s as if we were surrounding ourselves with a new family,” Fowler says. “It’s the family we chose, rather than the family we’re born with.”