Research: Genes play role in friendship

The researchers looked at six genetic markers in two long-running US studies, the National Longitudinal Study of Adolescent Health and the Framingham Heart Study, which contain both genetic data and information on friends.

With one gene, called DRD2, which has been associated with alcoholism, they found clusters of friends with the very same marker.

Another gene called CYP2A6, which has a suspected role in the metabolism of foreign bodies including nicotine, appeared more divisive. People with this gene seemed to steer clear of those who also carry the gene.

Why, the researchers don't know, but they speculate it could form part of a defensive ploy.

They say similar patterns have been observed among couples, with individuals avoiding prospective partners who are susceptible to the same diseases.

The gene CYP2A6 has also been associated with an openness to new ideas and situations, they say.