Adult sex friend
Using the KING algorithm (25), we computed genetic kinships between all pairs of Add Health participants.We then compared kinships among friends to kinships among random pairs of individuals to estimate the degree of genetic similarity among friends (3).First, social networks can influence mating markets, so genetic similarity among friends may be one source of genetic similarity among spouses.Second, there may exist social–genetic effects—the effects of alter’s genotype on ego’s phenotype (1, 14, 15)—which would further suggest that social sorting on genotype may have consequences for the distribution of phenotypes in a population beyond its effect on subsequent generations through assortative mating.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.For these reasons, in the present study, we characterize genetic homophily within adolescent social networks in the United States.
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.
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).
Among non-Hispanic whites in Add Health, KING estimates of genetic homophily were about two-thirds the magnitude of our previous KING estimates of genetic similarity among spouses in the US Health and Retirement Study (friend similarity = 0.031, CI = 0.022–0.036, compared with spousal similarity = 0.045 from ref. REAP estimates of genetic similarity were somewhat smaller.
Our second analysis tested whether friends were more similar to one another on specific phenotype-related genetic dimensions.