Although not the focus of this paper, it is important that we mention the environment as a key factor that provides the context in which biological systems operate. Environmental exposure plays a critical role in the liability to AD; according to twin/family studies, roughly one-half of the liability to AD is attributable to environmental factors. Environments that influence the risk for AD differ in both proximity to the disorder and mechanism of action. The risk for AD is elevated among (1) children that were prenatally exposed to alcohol, (2) children that grow up in a home with an alcoholic parent, and (3) children that are poorly monitored by their parents, to name a few (Sher et al., 2005). Many of these environments are thought to interact or correlate with the individual’s biological/genetic background resulting in an increased/decreased risk for the development of AD. For instance, genetic effects on drinking has been shown to be greater in urban versus rural residential settings (Dick et al., 2001; Rose et al., 2001), possibly because of differences in the level of social control between
