Abstract
Humans tend to form social relationships with others who resemble them. Whether this sorting of like with like, homophily, may arise from historical patterns of migration, macro-level social structures in modern society, or individual-level peer selection remains unsettled. We analyzed data from 9,500 adolescents from the National Longitudinal Study of Adolescent to Adult Health to examine genetic similarities among pairs of friends. While there is some evidence that friends have correlated genotypes, both at the whole-genome level as well as at trait-associated loci (via polygenic scores), further analysis suggests that macro-level forces, such as school assignment, are a principal source of genetic similarity between friends. We also observe associations of an individual’s educational attainment and the polygenic scores of those in their broader social environment (e.g., school) and of their friends (net of their own score). In contrast, individual BMI and height are largely unassociated with the genetics of peers.