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.Whether this sorting of like with like arises from historical patterns of migration, meso-level social structures in modern society, or individual-level selection of similar peers remains unsettled.
We linked these genetic data with social network information from the original school-based surveys along with information about personal characteristics and social environments accumulated across Add Health follow-up waves.
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.
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.