They found that as individuals develop, genes become increasingly important in influencing how peer groups are chosen. The finding, the researchers insist, is important as it offers an insight into which individuals may be at risk for future substance use or other externalising behaviours such as conduct and antisocial personality disorder.
"As we grow and move out of our own home environment, our genetically influenced temperament becomes more and more important in influencing the kinds of friends we like to hang out with," said Kenneth S. Kendler, M.D., a professor of psychiatry and human genetics in VCU's School of Medicine and lead author on the study.
"The study shows how genetic and family environmental factors influence the ways in which we create our own social environment as we grow," he added.
As a part of their study, the researchers examined peer group deviance among approximately 1,800 male twin pairs from mid-childhood to early adulthood, between 1998 and 2004.
Through a series of interviews, researchers found that genetic factors increasingly impact how male twins make choices as they mature and develop their own social groups.
"The road from genes to externalising behaviours like drug use and antisocial behaviours is not entirely direct or biological," Kendler said.
"An important part of this pathway involves our genetics influencing our own social environment, which in turn impacts on our risk for a whole host of deviant behaviours.
"Our results demonstrate clearly that a complete understanding of the pathway from genes to antisocial behaviours, including drug abuse, has to take into account self-selection into deviant versus benign environments.
"The effects of peers in adolescence can be quite powerful, either encouraging or discouraging deviant behaviours. Peers also provide access to substances of abuse," he added.
Supported by the National Institutes of Health, the study appears in the August issue of the Archives of General Psychiatry, a journal of the American Medical Association.