2007), so often genetic and environmental influences do not represent independent sources of influ-ence. This also makes it difficult to determine whether the genes or the environment is the causal agent. If, for example, individuals are genetically predisposed toward sensation seeking, and this makes them more likely to spend time in bars (a gene-environment correlation), and this increases their risk for alcohol problems, are the predisposing sensation-seeking genes or the bar environment the causal agent? In actuality, the question is moot—they both played a role; it is much more informative to try to understand the pathways of risk than to ask whether the genes or the environment was the critical factor. Though this review focuses on gene-environment interaction, it is important for the reader to be aware that this is but one process by which genetic and environmental influences are intertwined. Additionally, gene-environment correlation must be taken into account when studying gene-environment interaction, a point that is mentioned again later in this review. Excellent reviews covering the nature and importance of gene-environment correlation also exist (Kendler 2011).
