Greater African genetic heritage was not related to a higher risk of substance dependence among 490 African Americans studied by Ducci et al. (CME, p. 1031). In fact, the degree of African ancestry was somewhat lower among African American patients with cocaine, opiate, or alcohol dependence than among African American comparison subjects. Substance dependence showed a large association with a childhood history of emotional, physical, or sexual abuse or emotional or physical neglect. African genetic heritage was not related to childhood abuse or neglect but was linked to living in an impoverished neighborhood. In an editorial on p. 967, Dr. Robert Freedman examines these nature versus nurture issues.