This article focuses largely on GxE interaction, but discussion of genes and the environment as if they are separate sources of influence represents a clear oversimplification. Genetic and environmental influences are inexorably intertwined. Although some environmental influences may be largely random, such as experiencing a natural disaster, most measures of the environment show some degree of genetic influence, illustrating the active role that individuals play in selecting and creating their environment (Kendler & Baker, 2007). To the extent that these choices are influenced by an individual’s genetically influenced temperament and behavioral characteristics, an individual’s environment is not purely exogenous, but rather, in some sense, is yet another extension and reflection of the individual’s genotype. This concept is called gene–environment correlation.
