It is also assumed in the classical twin design that genetic and environmental influences combine additively (i.e., do not interact) and are uncorrelated. It is possible, however, that some genetic predispositions may be associated with certain kinds of social environments or experiences, leading to a correlation between genes and environments. (G × E interactions are also discussed at length in a later section of this chapter.) Such G × E correlations (rGE) can arise in three different ways (Scarr and McCartney, 1983): (i) Passive rGE occurs when genes overlap between parents and their offspring. For example, a child with aggressive parents inherits genetic susceptibility for aggression as well as experiences an adverse rearing environment. An example of passive rGE was reported in a study comparing genetic and environmental influences on mothering. Passive rGE correlations were suggested for mother's positivity and monitoring. For mother's negativity and control, primarily nonpassive rGE correlations were suggested (Neiderhiser et al., 2004). (ii) Evocative/reactive rGE can arise when a specific child characteristic elicits a particular response from the environment. For example, aggressive children tend to elicit
