âNature teaches beasts to know their friends,â wrote Shakespeare. In humans, nature may be less than half of the story, a team led by Âé¶čÊÓÆ” researchers has found.
In the first study of its kind, the team found that genetic similarities may help to explain why human birds of a feather flock together, but the full story of why people become friends âis contingent upon the social environment in which individuals interact with one another,â the researchers write.
People are more likely to befriend genetically similar people when their environment is stratified, when disparate groups are discouraged from interacting, the study found. When environments were more egalitarian, friends were less likely to share certain genes.
Scientists debate the extent to which genetics or environmental factors -- ânatureâ or ânurtureâ -- predict certain behaviors, said Jason Boardman, associate professor of sociology and faculty research associate with the Population Program in CU-Boulderâs Institute of Behavioral Science. âFor all the social demographic outcomes we care about, whether itâs fertility, marriage, migration, health, itâs never nature or nurture.
âItâs always nature and nurture,â he said. âAnd most of the time it has a lot more to do with nurture.â
Boardmanâs team included Benjamin Domingue, research associate in the Population Program at IBS; and Jason Fletcher, associate professor of health policy at the Yale School of Public Health. Their research was recently published in the Proceedings of the National Academy of Sciences.
Early last year, PNAS published a study reporting evidence that certain shared genes might determine peoplesâ choice of friends. Time magazine dubbed this âfriends with (genetic) benefits.â
Boardman is a sociologist who spent five years studying genetics at CU-Boulderâs Institute for Behavioral Genetics to bring insights of the social sciences to the natural sciences. He observed: âYou canât understand the spread of health behaviors -- why people smoke, why they drink, why they may or may not be obese -- unless you understand their genetic liability and also place them in the right social context.â
The research team used data from the National Longitudinal Study of Adolescent Health. Boardmanâs team focused on 1,503 pairs of friends in seventh through 12th grade in 41 schools. As with the earlier study, Boardmanâs group found that some pairs of friends shared certain genetic characteristics.
The team tested the evidence, arguing that if genes were the driving friendship factor, genetically based friendship should emerge most often and easily in schools with the least amount of social friction. âBut we found the exact opposite,â he said.
In the most socially equal environments, genetic homophily (or love of the same) was âpretty weak,â meaning that friends were less likely to share genetic traits. He added, âIt was in the most unequal social environments that we saw the highest level of genetic homophily.â
In a socially stratified school, âStudents from different populations within the school may be effectively âoff limitsâ for friendships,â the team wrote.
While applauding the revolutionary advances in genetics in recent years, Boardman said âwe have to have social scientists at the table, because weâre the ones with the data, methods and theories to characterize the multidimensional and multilevel nature of the social environment.â
Scientists cannot fully understand heritable changes in gene expression unless they understand âwhat kind of schools people go to, what neighborhoods they live inâ and other social factors, Boardman said.
âTo me, to say whether genes predict friendships without understanding the context within which these friendships may or may not occur just doesnât tell the whole story.â
The teamâs research was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the Office of Behavioral and Social Science Research at the National Institutes of Health. Fletcher is also supported by the Robert Wood Johnson Foundation Health and Society Scholars Program.
Boardman and Fletcher host an annual conference called Integrating Genetics and the Social Sciences.
