Do your friends all know each other? Researchers in the U.S. have found that how interconnected your friends are to each other, depends on your genes. Some of us introduce our friends to each other, and some of us isolate friends from each other. These tendencies are genetic.

Researchers in Boston and California have previously found that obesity, smoking and happiness spread in networks.

On an evolutionary basis, social-network builders may be survivors because they are always at the centre of a group that can provide food and other necessities. On the other hand, they are more likely to be exposed to germs from all sides.

The study was written up in the Proceedings of the National Academy of Sciences.