One domain in which specific forms of interaction differentiate theoretical positions is the study of GXE interactions. Many GXE studies(e.g., Caspi et al., 2002, 2003) are based on a diathesis-stress model of environmental action (Belsky et al., 2009). Under diathesis-stress (Zuckerman, 1999), individuals with a “ risk or vulnerability” gene are affected negatively by poor environments, whereas individuals with a different version of the same gene are relatively unaffected by environments. In the best environments, persons with differing polymorphisms may exhibit similar levels of behavior, but behavior of the groups diverges with worsening environmental conditions. Diathesis-stress therefore leads to prediction of a GXE interaction with the ordinal form shown in Figure 1A.
