Popular? Tight with your friends? Maybe it's your genes

Social butterflies at the center of attention, and wallflowers on the social fringes, may have their genes to thank not only for how popular they are but also for how connected their friends are, new research from social network scholars suggests.

Dr. Nicholas A. Christakis of Harvard and James. H. Fowler of the University of California, San Diego -- the same researchers who explored social networks to explain how obesity, smoking, and happiness spread among groups -- have turned their attention to the connections people make in social groups. Writing in the Proceedings of the National Academy of Sciences, they conclude that people inherit not only a tendency to be shy or gregarious but also a likelihood to have tightly knit or diffuse groups of friends.

"This paper is the first paper to show a genetic basis for human social network structure," Christakis said in an interview. "Where someone is positioned in a social network, and how interconnected their friends are, depends significantly on their genes."

To see if people inherit traits that place them in a social network, the researchers studied 1,110 twins from a sample of more than 90,000 high-schoolers. They compared identical twins, all of whose genes are the same, to fraternal twins, who share 50 percent of their genes. The researchers tracked how many students named a particular student as a friend, how many friends the particular student listed, and whether the friends named by the student were also friends with one another.

Identical twins were significantly more likely to show the same patterns of social ties than fraternal twins, the researchers concluded.

"We have genes that make us popular and genes that make us act like yentas, making friendship matches among people we know," Christakis said. "If Tom knows Dick and Harry, whether Dick knows Harry depends on Tom's genes (and not just Dick and Harry's)."

The structure of social networks has implications beyond friendships, according to Matthew O. Jackson of Stanford University.

"Given that social networks play important roles in determining a wide variety of things ranging from employment and wages to the spread of disease, it is important to understand why networks exhibit the patterns that they do," he writes in a commentary on the Christakis article.