Genetic, Environmental Factors Identified in Social Networks

“Birds of a feather,” as the maxim goes, may “flock together,” but a new study by a Yale School of Public Health researcher suggests that a complex array of environmental and genetic factors influence which friendships and social networks people enter into.

Jason M. Fletcher, Ph.D., associate professor in the Department of Health Policy and Management, and colleagues used data on social networks and genetics within middle and high school settings to determine how gene-environment interactions influence complex relationships such as friendships.

The analysis found that specific genetic factors in a region of a receptor gene known as DRD2 predict friendship formation in schools, suggesting that an individual’s basic “social” choices are influenced, at least in part, by biological and genetic underpinnings.

The paper, published this week in the journal PNAS, also shows that formal and stratified settings such as schools play a more fundamental role in shaping friendship opportunities that then allow or disallow genetic factors to determine friendship choices.

“More specifically, we find that in some schools, individuals who have similar genomes are more likely to be friends while in other schools, the opposite is true,” said Fletcher. “This suggests the important role of schools and how they shape and interact with the potential genetic determinants of social behaviors.”

Fletcher and Jason Boardman and Ben Dominque from the University of Colorado, Boulder, also found that schools with higher levels of socioeconomic inequality seem to foster friendships that are based on more genetic similarity, whereas schools with lower levels of inequality produce friendship that are dissimilar. “This indicates that social factors may shape the ability for individuals to act on their genetic influences,” Fletcher said.

The researchers used data from the National Longitudinal Study of Adolescent Health and included genetic samples from 1,503 participants as well as detailed information on their social networks along with their ethnic/racial heritage.

Fletcher said that the findings have a number of public health implications. They suggest that standard genetic analysis is often complicated by gene-environment interactions—that genes may be related to behavior outcomes only in certain environments and not in others. The findings also suggest that social science analysis examining complex behaviors may need to examine both social and genetic characteristics in order to fully understand behaviors.