Zero to 3. For ages, this window dominated the field, and it still does today, in part for reasons of convenience: Birth is the easiest time to capture a large population to study, and, as Levitt points out, “it’s easier to understand something as it’s being put together”—meaning the brain—“than something that’s complex but already formed.” There are good scientific reasons to focus on this time period, too: The sensory systems, like hearing and eyesight, develop very early on. “But the error we made,” says Levitt, “was to say, ‘Oh, that’s how all functions develop, even those that are very complex. Executive function, emotional regulation—all of it must develop in the same way.’ ” That is not turning out to be the case. “If you’re interested in making sure kids learn a lot in school, yes, intervening in early childhood is the time to do it,” says Laurence Steinberg, a developmental psychologist at Temple University and perhaps the country’s foremost researcher on adolescence. “But if you’re interested in how people become who they are, so much is going on in the adolescent years.”
In the past couple of decades, studies across the social sciences have been designed around this new orientation. It has long been known, for instance, that male earning potential correlates rather bluntly with height. But it was only in 2004 that a trio of economists thought to burrow a little deeper and discovered, based on a sample of thousands of white men in the U.S. and Britain, that it wasn’t adult height that seemed to affect their subjects’ wages; it was their height at 16. (In other words, two white men measuring five-foot-eleven can have very different earning potential in the same profession, all other demographic markers being equal, just because one of them was shorter at 16.) Eight years later, Deborah Carr, a sociologist at Rutgers, observed something similar about adults of a normal weight: They are far more likely to have higher self-esteem if they were a normal weight, rather than overweight or obese, in late adolescence (Carr was using sample data that tracked weight at age 21, but she notes that heavy 21-year-olds were also likely to be heavy in high school). Robert Crosnoe, a University of Texas sociologist, will be publishing a monograph with a colleague this year that shows attractiveness in high school has lingering effects, too, even fifteen years later. “It predicted a greater likelihood of marrying,” says Crosnoe, “better earning potential, better mental health.” This finding reminds me of something a friend was told years ago by Frances Lear, head of the eponymous, now defunct magazine for women: “The difference between you and me is that I knew in high school I was beautiful.”
Our self-image from those years, in other words, is especially adhesive. So, too, are our preferences. “There’s no reason why, at the age of 60, I should still be listening to the Allman Brothers,” Steinberg says. “Yet no matter how old you are, the music you listen to for the rest of your life is probably what you listened to when you were an adolescent.” Only extremely recent advances in neuroscience have begun to help explain why.
It turns out that just before adolescence, the prefrontal cortex—the part of the brain that governs our ability to reason, grasp abstractions, control impulses, and self-reflect—undergoes a huge flurry of activity, giving young adults the intellectual capacity to form an identity, to develop the notion of a self. Any cultural stimuli we are exposed to during puberty can, therefore, make more of an impression, because we’re now perceiving them discerningly and metacognitively as things to sweep into our self-concepts or reject (I am the kind of person who likes the Allman Brothers). “During times when your identity is in transition,” says Steinberg, “it’s possible you store memories better than you do in times of stability.”
At the same time, the prefrontal cortex has not yet finished developing in adolescents. It’s still adding myelin, the fatty white substance that speeds up and improves neural connections, and until those connections are consolidated—which most researchers now believe is sometime in our mid-twenties—the more primitive, emotional parts of the brain (known collectively as the limbic system) have a more significant influence. This explains why adolescents are such notoriously poor models of self-regulation, and why they’re so much more dramatic—“more Kirk than Spock,” in the words of B. J. Casey, a neuroscientist at Weill Medical College of Cornell University. In adolescence, the brain is also buzzing with more dopamine activity than at any other time in the human life cycle, so everything an adolescent does—everything an adolescent feels—is just a little bit more intense. “And you never get back to that intensity,” says Casey. (The British psychoanalyst Adam Phillips has a slightly different way of saying this: “Puberty,” he writes, “is everyone’s first experience of a sentient madness.”)