T: The Story of Testosterone, the Hormone that Dominates and Divides Us

Male pets, eunuchs in the imperial harems of Ancient China, and castrato singers in 18th-century Italy helped people understand that male traits are determined by the presence of testicles that produce testosterone. This hormone affects male physiology, behavior, aggression, and the drive for privileges. Observations of animals showed that high testosterone levels help males produce offspring and compete with other males. Testosterone levels also influence human behavior, though the reasons for sex differences are disputed. Biology, genetics, and culture create enormous variety in male and female behavior, and understanding the mechanics of how testosterone works will help us better understand ourselves and other people.