A US study of the social networks of identical and non-identical twins concluded that a person’s popularity (as measured by the number of times his or her name was mentioned by friends and the extent to which those friends also knew each other), was an inherited trait.
The study was the work of researchers from Harvard University and the University of California, San Diego, and was published online before print on January 26 in the Proceedings of the National Academy of Sciences.
Principal investigator Nicholas Christakis, who is professor of sociology at Harvard’s Faculty of Arts and Sciences and professor of medical sociology at Harvard Medical School, said:
“We were able to show that our particular location in vast social networks has a genetic basis.”
“In fact, the beautiful and complicated pattern of human connection depends on our genes to a significant measure,” he added.
The study is thought to be the first to look at inherited factors in social networks and to show that genes play a part in forming and configuring them.
Christakis and colleagues Christopher Dawes and James Fowler, both of University of California (UC) San Diego, found that popularity (the number of times a person was named as a friend, and the likelihood that those friends also knew one another) was strongly heritable. They also found that whether a person was at the centre or the edge of his or her network also had a strong genetic link, but surprisingly, the number of people the individual named as friends did not.
For the study, the researchers used data from the National Longitudinal Study of Adolescent Health and identified the social networks of 1,110 identical and non-identical adolescent twins. On comparing the network of each twin to that of his or her sibling, the researchers found greater similarities among those of identical twins than among those of non-identical twins.
Perhaps there is an evolutionary explanation, said the researchers. There could be a survival advantage to being at the edges of a social group: for instance when deadly infectious diseases spread in a community, fewer social contacts reduces exposure. And on the other hand, being in the middle of the group exposes a person to more information that could also confer survival advantages, such as finding out about new food sources.
As Fowler, an associate professor of political science at UC San Diego, explained:
“One of the things that the study tells us is that social networks are likely to be a fundamental part of our genetic heritage.”
“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,” he added.
The researchers tested their findings using the existing theories of networks and found that none was able to explain the genetic variations they observed. These assume that members of the network are like interchangeable cogs. What was needed was a model that took into account intrinsic differences among members, differences that could influence the development of the network itself.
So they developed their own model, which they called “Attract and Introduce” and showed it was better able to explain how human social networks develop and behave when members vary genetically. Run as a computer simulation, their model showed close resemblance to real human networks, such as when an individual was added to any network, they eventually ended up in the same place within the network, depending on their genetic characteristics.
The researchers said their findings could help us better understand how health habits, health information, and diseases spread in social networks and thereby better inform public health initiatives on large scale issues like obesity and flu.
Fowler said:
“I think that going forward, we are going to find that social networks are a critical conduit between our genes and important health outcomes.”
Fowler and Christakis have writte other papers about social networks, including the spread of obesity, smoking cessation and happiness.
The National Institute on Aging and the National Science Foundation paid for the study.
“Model of genetic variation in human social networks.”
James H. Fowler, Christopher T. Dawes, and Nicholas A. Christakis.
Proceedings of the National Academy of Sciences, published online before print January 26, 2009.
doi:10.1073/pnas.0806746106.
Sources: UC San Diego, journal abstract.
Written by: Catharine Paddock, PhD