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 use disorders have heritabilities in the range of 50-60% (Verhulst et al., 2015; Kendler et al., 2007; Kendler et al, 2003), and depression, anxiety, and eating disorders have heritabilities that are even more modest (Shimada-Sugimoto et al., 2015, Sullivan et al., 2000). Further, twin data also demonstrate that the importance of genetic influences can vary tremendously as a function of the environment (Hicks et al., 2008, Dick & Kendler, 2012). That is to say that point estimates of heritability are a reflection of the importance of genetic variation specific to the population characteristics at the time of study; changing the environmental context can change the relative importance of genetic variation in contributing to the disease outcome. Thus, although there is clearly a biological, genetic component involved in why some individuals are more at risk than others, there is a significant environmental component as well, with compelling evidence that substance use and psychiatric disorders result from complex interactions of genetic and
