The contribution of genetic factors to the development of alcohol and other drug dependence has been consistently supported by numerous family, twin, and adoption studies in general population samples. Although the mode of transmission of this increased risk is unclear, most investigators favor a model where a genetic predisposition interacts with environmental variables to produce an overall risk for the disorder. It is also likely that complex disorders like substance dependence are influenced by a large number of genes of small effect. While many of these genes may be specific to the etiology of these disorders, others likely overlap with other psychiatric and metabolic disorders. For example, substance dependence and obesity both occur more frequently in some Native American populations. One theoretical assumption concerning Native people is that the long history of dependence on foraging and subsistence agriculture may have led to selective enrichment of traits that improve genetic fitness, so called ‘thrifty’ or ‘fat sparing’ genes. It has been suggested that this same selective pressure may have enriched for genetic variants that increase the risk for consumption of alcohol
