Genes, environment influence social networks

A new study shows friendship formation may be influenced by both genetics and social situations.

In a paper published on Oct. 8 in the scientific journal Proceedings of National Academy of Sciences, Jason M. Fletcher, health policy professor at the Yale School of Public Health, re-explored prior research establishing a correlation between genes and friendship. Entitled “How Social and Genetic Factors Predict Friendship Networks,” the paper concluded that a complex array of environmental influences ­— as well as genetic factors — play a role in influencing people’s decisions about friendships and social networks. The study found that genetic factors on a gene called DRD2 predict friendship formation in schools, suggesting a biological role on friendship formation.

However, selecting friendships is “not strictly a biological phenomenon”, Fletcher said.

The team examined data collected by the National Longitudinal Study of Adolescent Health that included genetic samples from 1,503 participants from 100 schools, as well as information regarding participants’ social networks and ethnic and racial heritage. Fletcher’s study additionally examined whether the correlation between genotypes and friendships persists among students from the same school.

In schools with students from a wider range of socioeconomic backgrounds, students tended to form friendships with people who are genetically similar to them, Fletcher said. Students from schools with a more uniform socioeconomic background tend to make friends who are dissimilar to them genetically, he added.

The research also found a potential correlation between this gene-friendship relationship and schools offering multiple academic or vocational tracks. Students in these tracks, who share similar characteristics, are more likely to befriend each other, Fletcher said.

“Schools with tracks that are hard to cross tend to have kids who spend time together with people just like them,” he added.

The team also explored whether race was a determining factor, but found no evidence to support this hypothesis.

The study’s findings led the authors to believe the friendship selection process happens much “farther upstream” and can be caused by factors such as gender, ethnicity, class and social environment, said Jason Boardman,lead author of the paper and sociology professor at the University of Colorado. In fact, the research discovered that social environment — in this case, the schools they attended — plays an important, if not more direct, role in the friends people select, he added.

Dalton Conley, professor of sociology at Northwestern University, said he believed the October paper puts genetic research in a larger context. Fletcher echoed Conley’s comment and said the research shows how basic genetics studies might be further enriched by including social factors. Understanding the true causes of friendship formation requires a detailed knowledge of both the influencing environmental and genetic factors.

“Rarely with any phenomenon is it either entirely genetic or entirely environment. Most often it is simultaneously nature and nurture, and that’s why biological scientists and social scientists need to work together to find answers,” Boardman said.

The research was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

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