Genes had been linked to temperaments before: the extraordinary, otherworldly sweetness of children with Down syndrome had long been noted by psychologists, and other genetic syndromes had been linked with outbursts of violence and aggression. But Ebstein was not interested in the outer bounds of pathology; he was interested in normal variants of temperament. Extreme genetic changes could evidently cause extreme variants of temperament. But were there “normal” gene variants that influenced normal subtypes of personality?
