Failure to include racially and ethnically diverse samples in twin studies is problematic because twin estimates of the importance of genetic and environmental influences are necessarily specific to the population under study. Individuals belonging to socially-subordinated groups are disproportionately exposed to a variety of environmental stressors, including higher rates of poverty, lower socioeconomic status, and decreased employment opportunities, in comparison to socially-dominant groups.23–25 For example, a survey of children in the 100 largest metropolitan areas in the United States reported that 76% of AA children lived under worse circumstances with respect to neighborhood poverty than the worst off EAs in those areas.26 Twin studies have robustly demonstrated that the importance of genetic and environmental influences can vary as a function of the environment,27–29 and the profound differences that exist in environments experienced by AAs suggests that the degree to which genetic and environmental influences impact substance use may vary in AA populations, just as the rates of alcohol use vary in AA populations.30 In other words, the etiological pathways that influence risk for complex behavioral outcomes could vary across groups.
