Friendship and Natural Selection

TL;DR

This study reveals that human friendships are genetically similar at many loci, with some gene sets showing positive or negative correlations, and that homophilic genotypes are under positive selection, indicating evolutionary advantages.

Contribution

It uncovers the genetic basis of social ties in humans, showing genome-wide genotype correlations among friends and linking these to evolutionary selection pressures.

Findings

Genetic similarity among friends extends across the genome.

Certain gene sets, like olfactory and immune genes, show specific correlation patterns.

Homophilic genotypes are associated with higher positive selection measures.

Abstract

More than any other species, humans form social ties to individuals who are neither kin nor mates, and these ties tend to be with similar people. Here, we show that this similarity extends to genotypes. Across the whole genome, friends' genotypes at the SNP level tend to be positively correlated (homophilic); however, certain genotypes are negatively correlated (heterophilic). A focused gene set analysis suggests that some of the overall correlation can be explained by specific systems; for example, an olfactory gene set is homophilic and an immune system gene set is heterophilic. Finally, homophilic genotypes exhibit significantly higher measures of positive selection, suggesting that, on average, they may yield a synergistic fitness advantage that has been helping to drive recent human evolution.