Our results are inconsistent with the notion that psychiatric problems can be divided accurately into those which are “biologically” caused and involuntary versus those which involve choices. That is, our findings support the proposition that biological/genetic factors influence volitional behavior, though it seems unlikely that genes simply evoke particular problem behaviors. The mechanisms through which genetic factors influence behavior are probably numerous. For example, genes can alter the hedonic and/or adverse effects of cannabis (Lyons et al., 1997) and alcohol (Thomasson and Li, 1993), making it more or less pleasant to consume these substances. Genes can also influence levels of sensation-seeking (Agrawal et al., 2004), making some individuals more prone to behaviors like drug use that are rewarding in the short term but harmful in the long term. Other heritable temperamental traits may similarly influence the development of eating disorders (Wade et al., 2008). While personal decisions are no doubt important in behavioral disorders, genes clearly influence their development. Thus, genes apparently do not respect the boundary between “free will” and “determinism.”
