A new study says that how we choose our friends is strongly influenced by genetic factors.

The researchers studied the peer groups of approximately 1,800 male twins, having each subject describe the level of social deviance among their friends, such as how many of their friends got drunk, used or sold drugs, or damaged property. The research showed that an individual's selection of friends--whether they chose to socialize with fewer or more socially deviant peers--was shaped by genetic factors. Not only did the researchers find that selection of friends has a genetic basis, but also that the influence of genes actually increased over time, as individuals gain autonomy in selecting their peers and building their social world.