Human beings evolved as social animals; social groups provide more protection against predators and infections, provide information and security, and they provide the opportunity for cooperative exchanges. Genes that help humans form friendships are obviously a huge evolutionary advantage. As humans, we also tend to like people who are like us - this is called homophily. So how do you study the genetic similarity between friends? The authors took data from 1 932 people who took part in the Framingham Heart Study, which included genetic information (including common genetic variations, or SNPs) as well as friendship ties. The researchers underwent a genome-wide association study (GWAS) and identified over 460 000 SNPs, looking not at any particular SNPs, but at patterns across the whole genome.
|Genetic similarity is higher between friends (left), and|
genetic dissimilarity is higher between strangers (right).
These findings are still very preliminary. The use of the Framingham Heart Study participants introduced a bias, as these people were predominantly white and of Italian descent. Here, it is possible that genetic similarity and friendship may come from the simple preference for associating with ethnically similar others, especially since the first cohort was recruited in 1948. The authors did control for population stratification in their data analysis, however, so this bias should be minimal.