In June 2009, The Atlantic published a cover story on the Grant Study, one of the longest-running longitudinal studies of human development. The project, which began in 1938, has followed 268 Harvard undergraduate men for 75 years, measuring an astonishing range of psychological, anthropological, and physical traits—from personality type to IQ to drinking habits to family relationships to “hanging length of his scrotum”—in an effort to determine what factors contribute most strongly to human flourishing.

Recently, George Vaillant, who directed the study for more than three decades, published Triumphs of Experience, a summation of the insights the study has yielded. Among them: “Alcoholism is a disorder of great destructive power.” Alcoholism was the main cause of divorce between the Grant Study men and their wives; it was strongly correlated with neurosis and depression (which tended to follow alcohol abuse, rather than precede it); and—together with associated cigarette smoking—it was the single greatest contributor to their early morbidity and death. Above a certain level, intelligence doesn’t matter. There was no significant difference in maximum income earned by men with IQs in the 110–115 range and men with IQs higher than 150. Aging liberals have more sex. Political ideology had no bearing on life satisfaction—but the most-conservative men ceased sexual relations at an average age of 68, while the most-liberal men had active sex lives into their 80s. “I have consulted urologists about this,” Vaillant writes. “They have no idea why it might be so.”