NYTimesJerome Kagan's "Aha!" moment came with Baby 19. It was 1989, and Kagan, a professor of psychology at Harvard, had just begun a major longitudinal study of temperament and its effects. Temperament is a complex, multilayered thing, and for the sake of clarity, Kagan was tracking it along a single dimension: whether babies were easily upset when exposed to new things. He chose this characteristic both because it could be measured and because it seemed to explain much of normal human variation. He suspected, extrapolating from a study he had just completed on toddlers, that the most edgy infants were more likely to grow up to be inhibited, shy and anxious. Eager to take a peek at the early results, he grabbed the videotapes of the first babies in the study, looking for the irritable behavior he would later call high-reactive.
No high-reactors among the first 18. They gazed calmly at things that were unfamiliar. But the 19th baby was different. She was distressed by novelty — new sounds, new voices, new toys, new smells — and showed it by flailing her legs, arching her back and crying. Here was what Kagan was looking for but was not sure he would find: a baby who essentially fell apart when exposed to anything new.
Baby 19 grew up true to her temperament. This past summer, Kagan showed me a video of her from 2004, when she was 15. We sat in a screening room in Harvard's William James Hall — a building named, coincidentally, for the 19th-century psychologist who described his own struggles with anxiety as "a horrible dread at the pit of my stomach ... a sense of the insecurity of life." Kagan is elfin and spry, balding and bespectacled. He neither looks nor acts his age, which is 80. He is one of the most influential developmental psychologists of the 20th century.[...]
