The degree to which genetics are implicated in the formation and consequences of social relationships is of growing interest to the new field of sociogenomics (1, 2).
Analysis of spousal genotypes suggests that spouses are more genetically similar to one another compared with random pairs of individuals in the population (3–9). In previous analyses, we estimated that genetic homogamy was about one-third the magnitude of educational homogamy (3), even when specifically examining education-associated genotypes (8).
However, even modest genetic homogamy can have implications for statistical and medical genetic models of inheritance and social models of spousal effects (10–12).
Marriage is not the only social grouping to evidence genetic selection.
We also observe apparent social–genetic effects in which polygenic scores of an individual’s friends and schoolmates predict the individual’s own educational attainment.
In contrast, an individual’s height is unassociated with the height genetics of peers.
Responses were collated within schools to identify social ties between individuals and their friends (24).
Of the adolescents surveyed, 20,745 were enrolled in a longitudinal study that included in-home interviews with the adolescents and their parents and that followed the adolescents prospectively across four waves of interviews spanning 14 y.
Although 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 meso-level forces, such as school assignment, are a principal source of genetic similarity between friends.Adult friends are, on average, more genetically similar than random pairs from the population (13).Genetic similarity among friendship networks is important for at least two reasons.Our study reported significant findings of a “social genome” that can be quantified and studied to understand human health and behavior.In a national sample of more than 5,000 American adolescents, we found evidence of social forces that act to make friends and schoolmates more genetically similar to one another compared with random pairs of unrelated individuals.In step 3, we evaluate a potential implication of genetic similarity among friends: social–genetic effects, or the association between the genotypes of one’s social peers and one’s own phenotype (net of own genotype).We tested whether friends were more genetically similar to one another compared with random pairs of individuals.This subtle genetic similarity was observed across the entire genome and at sets of genomic locations linked with specific traits—educational attainment and body mass index—a phenomenon we term “social–genetic correlation.” We also find evidence of a “social–genetic effect” such that the genetics of a person’s friends and schoolmates influenced their own education, even after accounting for the person’s own genetics.Humans tend to form social relationships with others who resemble them.Analyses focus on a group of genetically homogeneous respondents identified as being of ancestral European origin (. In step 1, we test whether friends are more genetically similar to one another than to randomly selected peers.In step 2, we ask about the role of school assignment in observed genetic similarity among friends.