Popularity, or the number of times an individual was named as a friend, and the likelihood that those friends know one another were both strongly heritable, according to the study by researchers from Harvard University and the University of California in San Diego (UCSD).
By examining national data from the National Longitudinal Study of Adolescent Health for the social networks of 1,110 adolescent twins, both fraternal and identical, the researchers compared the social networks of the identical twins to those of the fraternal twins and found greater similarity between the identical twins' social network structure than the fraternal twins' networks.
This is the first study to examine the inherited characteristics of social networks and to establish a genetic role in the formation and configuration of these networks.
While it might be expected that genes affect personality, these findings go further and illustrate a genetic influence on the structure and formation of an individual's social group, according to the study published in the January issue of the Proceedings of the National Academy of Sciences.
Additionally, location within the network, or the tendency to be at the center or on the edges of the group, was also genetically linked, the study said.
There may be an evolutionary explanation for this genetic influence and the tendency for some people to be at the center while others are at the edges of the group, according to the researchers.
If a deadly germ is spreading through a community, individuals at the edges are least likely to be exposed to it. However, to gain access to important information about a food source, being in the center of the group has a distinct benefit, the study said.
"We were able to show that our particular location in vast social networks has a genetic basis," Nicholas Christakis, professor of sociology in the Faculty of Arts and Sciences and professor of medical sociology at Harvard Medical School, said in the study report.
"In fact, the beautiful and complicated pattern of human connection depends on our genes to a significant measure," the professor added.
The findings also illuminate a previously unknown limitation of existing social network models, which had assumed that all members behave as interchangeable cogs. To address these intrinsic differences in human beings that contribute to the formation of social networks, the researchers have created a new mathematical model, called the "attract and introduce" model, which is also explained in the study and supports the genetic variation of members.
"One of the things that the study tells us is that social networks are likely to be a fundamental part of our genetic heritage," said James Fowler, an associate professor of political science at UCSD.
"It may be that natural selection is acting on not just things like whether or not we can resist the common cold, but also who it is that we are going to come into contact with," Fowler noted.
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