Genes and social networks: new research links genes to friendship networks

A conversation with James Fowler

Posted Feb 14, 2011

James Fowler, a professor at UC-San Diego, is engaged in highly innovative and important research at the crossroads of political science and biology.  His recent paper in the Proceedings of the National Academy of Sciences, "Correlated Genotypes in Friendship Networks", represents an important new study in an emerging research field that is exploring the genetic and biological foundations for our political and social behavior.  

In this paper, James and his colleagues Jaime Settle and Nicholas Christakis demonstrate that there is what they call "genotypic clustering in social networks", by statistically examining the association between markers for six different genes and the reported friendship networks from respondents in data from the National Longitudinal Study of Adolescent Health and the Framingham Heart Study Social Network.  They show that one of these genes (DRD2) is positively associated with in friendship networks, meaning that those who have this gene are more likely to be friends with others who have this gene, controlling for demographic similarities and population stratification; another gene, CYP2A6 has a negative association in friendship networks.

Recently James and I had an email conversation about this research, and here are my questions and his answers.  

Mike:  What is the most important implication of demonstrating that specific genes are associated with who we affiliate with in our friendship networks?

James: What happens to us may depend not only on our own genes but also on the genes of our friends.  This has been shown already in hens, whose feathers change depending on the genetic constitution of the hens that are caged near them.  But something similar may happen in humans. We each live in a sea of the genes of others.  In fact, we are metagenomic.

Mike:  Why did you study the six specific genes in your study, and are there others that might be important for understanding friendship networks?

James: Replication is very important in genetic studies, so we used this first paper to focus on those genes we could test in two independent samples (though, Add Health will probably expand its data in the next year or two to encompass all genes).  We intend to do a genome-wide study in the future, though,and we are especially interested in genes that regulate neuronal development and the immune system.

Mike: As you mention in your study, two of the genes you study (DRD2 and CYP2A6) have been studied by others, and in particular, DRD2 has been shown to have some association with alcoholism.  Why might these same genes also be associated with the development of friendship networks?

James: An important caveat is that there may be processes besides friendship choice that create correlated genotypes.  Our genes may cause us to be drawn to certain environments where we are more likely to meet similar people.  For example, people with the same DRD2 genotype might both find themselves in a bar where they then become friends.  But this cannot explain *negative* correlation.  The "opposites attract" result with CYP2A6 is more likely to be due to friendship choice.

Mike: Genetic factors, like those that you study in this recent paper, are not typically included in previous studies of social networks. What are the implications of this for the study of social networks --- are conclusions from previous studies problematic in the wake of your paper?

James: I wouldn't say they are problematic, since in our social network studies we usually control for static characteristics (like genes) by comparing a current measure and a baseline measure from the same person.  But it is true there can be feedback effects -- our genes not only influence us, but they may influence the genes of our friends, which in turn has an additional effect on us.  For example, the DRD2 gene variant we study has been associated with alcoholism, and if you have this gene variant, your friends are likely to have it, too.  So you are not only more susceptible to alcoholism yourself, but you are likely to be surrounded by friends who are susceptible, too.  Thus, ignoring genes means we might miss important heterogeneity in the network that would obscure strong social effects.

Mike:  Social networks have formed an important part of your ambitious research agenda in recent years, and in other work you have studied genetic influences on social and political behavior.  What led you to merge these lines in inquiry, what insight led you to think that genes might play a role in the development of friendship networks?

James: In our book CONNECTED, Nicholas Christakis and I argue that "social networks are in our nature."  We have discovered some regularities in our studies of human social networks that suggest their structure may be universal, such as the tendency for many of our friends also to be friends with one another, and the tendency for influence to spread to about three degrees of separation.  We conjecture that we have coevolved with these networks as our brains have gotten bigger, and genetic variation might give us a clue about which systems have undergone the most recent evolutionary changes.

Mike:  What advice would you have for a colleague, or graduate student, who has read this paper and is considering research in this area?

James:  I get this question a lot these days!  There is a great conference run by Jason Boardman for social scientists at Boulder: the conference will be followed by a workshop.

I want to thank James for answering these questions about his work, and to point readers to his book, Connected:  How Your Friends' Friends' Friends Affect Everything You Feel, Think, And Do.  In August I wrote about Connected on The Psychology Behind Political Debate, naming it one of my five books to read before the end of summer.

Note:  Image from the U.S. Department of Energy Genome Programs (