It's not just our partners that we choose partly because of their genes, we might pick our friends on that basis too. The finding could have implications for studying links between social behaviour and genetics.
People's choice of reproductive partner is known to carry a genetic aspect. To test whether genetics also influences friend choice, James Fowler at the University of California, San Diego, and colleagues studied more than 3000 pairs of friends for which they had genotype information for both individuals. For each friendship pair, the team compared six genes thought to be associated with social behaviour.
They found that friends tended to be more alike than expected by chance for one gene, DRD2, which has been associated with a tendency to alcoholism. The researchers suggest this might be because those carrying the gene find social drinking convivial. In contrast, friends tended to be less alike than expected by chance for another gene, CYP2A6, which may be associated with an open personality. It is not clear why people should prefer friends with different versions of this gene, says Fowler.
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The genetic preferences may create previously unrecognised feedback loops. If, for instance, those susceptible to alcoholism choose friends with the same propensity, they may be influenced to drink by social as well as genetic factors. A study that omits this social factor may overstate the effect of DRD2 on their behaviour.
Journal reference: Proceedings of the National Academy of Sciences
