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Jason Fletcher (Cohort 8) Robert Wood Johnson Foundation Blog

Jason M Fletcher, PhD, MS, is an alumnus of the Robert Wood Johnson Foundation (RWJF) Health & Society Scholars program (2010-2012) and an associate professor of health policy at Yale School of Public Health.   Fletcher was recently lead author of the study, “How Social and Genetic Factors Predict Friendship Networks,” published October 17 in the journal PNAS (Proceedings of the National Academy of Sciences). Fletcher and his colleagues found that important interactions between genetics and the social environment help determine friendship formation during high school.

For our study, we used a national survey of adolescent friendships (Add Health, or the National Longitudinal Study of Adolescent Health) to follow up on and expand a study published last year that showed that specific genes, including a dopamine receptor gene (DRD2), may determine friendships among teens.

We found the idea of a biological basis for, in our view, the very sociologically driven outcomes of friendship formation to be too narrow and to not take into account the social and geographic constraints that underlie friendship links.  So in our research we show, using the same data as the previous study, that once we take account of schools and social environments, the previous genetic story is not confirmed by our data.

Indeed, we show that some schools produce friendships that are genetically similar, and others produce friendships that are genetically dissimilar.  And specific aspects of schools, like socioeconomic inequality, appear to partially determine the types of friendships that we observe school-by-school.

Digging deeper, our preliminary finding was that schools with higher levels of socioeconomic inequality actually produce friendships that are more genetically similar; and that relatively egalitarian school populations are related to genetically dissimilar friendship.  This could be counter-intuitive—one might think that having access to individuals who differ (i.e. in unequal schools) may allow genetically dissimilar friendships to form.  But we found the opposite pattern and think this may be the result of social norms within highly unequal schools, where heterophily (friendships among dissimilar individuals) may not be socially accepted.  These findings add complexity to the idea of a biological basis to social ties and remind us how important the social environment may be, even in studies of genetics.

Our paper directs attention back to the importance of the social environment in thinking about which kids become friends.  We already know that the way schools are structured matters, including whether or not the school tracks students into vocational or college-bound curricula. 

Our study adds a new direction by considering both genetics and social aspects, and their interplay, in determining friendship ties.  The implications of this work for teen’s mental health are the subject of ongoing work.  But we should not expect simple answers because of the complexities of the interplay between social environments and genetics.    

It is true that the increasing diversity of the United States has allowed more diversity in friendship and romantic relationships.  However, there is also evidence that suggests that opportunities for diverse friends do not always produce strong patterns of diversity in friends.  It might take a mix of opportunity as well as planning by parents, school administrators, and others to create environments where having a diverse set of friends is normative and valued. 

Learn more about the RWJF Health & Society Scholars program.

Tags: Social determinants of health, Genomics, Research, Adolescents (11-18 years), Human Capital, Voices from the Field, Health & Society Scholars, Research & Analysis