These are clearly important and laudable goals. Substance use and psychiatric disorders have a tremendous societal and personal cost (Kazdin & Blase, 2011), and the need to understand the underlying etiology of these disorders and develop better treatments cannot be understated. Because many of the large gene-finding efforts in psychiatric genetics are being led by medical professionals, it is not surprising that the implications of gene identification (understanding biology, identifying drug targets, informing clinical practice) is often discussed in the context of a biomedical model. For a disorder like schizophrenia, with a high heritability indicating a strong biological component, effective therapeutic treatments are likely to be critical in controlling disease symptoms. However, even for a highly heritable disorder like schizophrenia, the risk of developing the disorder in a genetically-identical co-twin of an affected individual is only about 50% (Gottesman, 1991). Thus, genetics is clearly only part of the story, and the environment plays an important role in disease etiology, even in a highly heritable disorder like schizophrenia. Most psychiatric and behavioral disorders are not nearly as heritable as schizophrenia. Substance
