QUOTE : Ebstein's original study has been corroborated by several other groups. Interestingly, as one might suspect from the Minnesota twin studies, D4DR does not "cause" a personality or temperament. Instead, it causes a propensity toward a temperament that seeks stimulation or excitement-the first derivative of impulsivity. The precise nature of stimulation varies from one context to the next. It can produce the most sublime qualities in humans-exploratory drive, passion, and creative urgency-but it can also spiral toward impulsivity, addiction, violence, and depression. The D4DR-7 repeat variant has been associated with bursts of focused creativity, and also with attention deficit disorder-a seeming paradox until you understand that both can be driven by the same impulse. The most provocative human studies have cataloged the geographic distribution of the D4DR variant. Nomadic and migratory populations have higher frequencies of the variant gene. And the farther one moves from the original site of human dispersal from Africa, the more frequently the variant seems to appear as well. Perhaps the subtle drive caused by the D4DR variant drove the "out-of-Africa" migration, by throwing our ancestors out to sea. Many attributes of our restless, anxious modernity, perhaps, are products of a restless, anxious gene.