Shanahan and Hofer (2005) described three models by which environmental factors moderate genetic variance for behavioral traits. The first, consistent with that proposed by Heath et al (1999), was a social control model, which suggests that people are prevented from behaving in a certain manner as the result of social factors, regardless of genetic predisposition. Consequently, the genetic variance (and heritability) is attenuated in more controlling environments. The second model, social distinction, proposes that genes become more important in the etiology of a phenotype in environments where the trait is rare. The social push perspective (Raine 2002), in which a benign environment (one that neither encourages nor discourages a particular behavior) is associated with a higher heritability, is an example of social distinction. Finally, the third model was a social expression model, where it is proposed that specific environments trigger genetic variance. For instance, exposure to extremes of alcohol using peers (i.e. where all peers drink) may trigger any pre-existing, but previously un-expressed, genetic risk to drink. These models are described in detail elsewhere (Button et al. 2009; Shanahan and Hofer 2005).
