A pair of researchers have explored the biological influence behind human friendship.
(John Minchillo/Invision via AP)
Friends often look alike. The tendency of people to forge friendships with people of a similar appearance has been noted since the time of Plato. But now there is research suggesting that, to a striking degree, we tend to pick friends who are genetically similar to us in ways that go beyond superficial features.
For example, you and your friends are likely to share certain genes associated with the sense of smell.
Our friends are as similar to us genetically as you’d expect fourth cousins to be, according to the study published Monday in the Proceedings of the National Academy of Sciences. This means that the number of genetic markers shared by two friends is akin to what would be expected if they had the same great-great-great-grandparents.
“Your friends don’t just resemble you superficially, they resemble you genetically,” said Nicholas A. Christakis, a physician and social scientist at Yale University and a co-author of the study.
The resemblance is slight, just about 1 percent of the genetic markers, but that has huge implications for evolutionary theory, said James Fowler, a professor of medical genetics and political science at the University of California at San Diego.
This is not a settled science. Research on genetic factors in friendships is still in a preliminary stage. But if the reasoning of Christakis and Fowler is correct, friendship, and hyper-social behavior more generally, is a significant factor in the recent evolution of the human species, which they describe as having accelerated in the past 30,000 years.
We think of evolution as a process driven by natural selection among individual organisms. But natural selection pivots on the fitness, or reproductive success, of specific genes. It’s long been understood that this requires us to look at kinship groups when thinking about the reproductive success of those genes.
This new theory says that it doesn’t look broadly enough at how evolution works. Our friends are also in the Darwinian pool with us.
Your evolutionary fitness “depends not only on your own genotype, but also on the genotype of your friends,” Christakis said.
“Social networks are an important engine for human evolution,” Fowler said. “Our friends are sort of like family members. They’re functional kin.”
