Developmental Timing Explains The Woes Of Adolescence
"What was he thinking!" This is the familiar bewildered cry of parents trying to explain why their teenaged children act the way they do. Developmental psychologists, neuroscientists and clinicians have an interesting and elegant explanation for teenage weirdness. It applies to a wide range of adolescent behavior, from the surprisingly admirable, to the mildly annoying, to the downright pathological. The idea is that there are two different neural and functional systems that interact to turn children into adults. The developmental relationship between those two systems has changed, and that, in turn, has profoundly changed adolescence.
First, there is a motivational and emotional system that is very closely linked to the biological and chemical changes of puberty. This is what turns placid ten-year-olds, safe in the protected immaturity of childhood, into restless, exuberant, emotionally intense teenagers, desperate to attain every goal, fulfill every desire, and experience every sensation. And for adolescents, the most important goal of all is to get the respect of your peers. Recent studies show that adolescents aren't reckless because they underestimate risks, but because they overestimate rewards, especially social rewards, or rather that they find rewards more rewarding than adults do—think about the incomparable intensity of first love, the never to be recaptured glory of the high-school basketball championship. (In youth you want things, and then in middle-age you want to want them.)
The second system is a control system that can channel and harness all that seething energy. The prefrontal cortex reaches out to guide and control other parts of the brain. This is the system that inhibits impulses and guides decision-making. This control system depends much more on learning than the motivational system. You get to make better decisions by making not so good decisions and then correcting them. You get to be a good planner by making plans, implementing them and seeing the results again and again. Expertise comes with experience.
In the distant evolutionary past, in fact, even in the recent historical past, these two systems were in sync. Most childhood education involved formal and informal apprenticeships. Children had lots of chances to practice exactly the skills that they would need to accomplish their goals as adults, and so to become expert planners and actors. To become a good gatherer or hunter, cook or caregiver, you would actually practice gathering, hunting, cooking and taking care of children all through middle-childhood and early adolescence—tuning up just the prefrontal wiring you'd need as an adult. But you'd do all that under expert adult supervision and in the protected world of childhood where the impact of your inevitable failures would be blunted. When the motivational juice of puberty kicked in, you'd be ready to go after the real rewards with new intensity and exuberance, but you'd also have the skill and control to do it effectively and reasonably safely.
In contemporary life though, the relationship between these two systems has changed. For reasons that are somewhat mysterious but most likely biological, puberty is kicking in at an earlier and earlier age. (The leading theory points to changes in energy balance as children eat more and move less). The motivational system kicks in with it.
At the same time, contemporary children have very little experience with the kinds of tasks that they'll have to perform as grown-ups. Children have increasingly little chance to even practice such basic skills as cooking and caregiving. In fact, contemporary adolescents and preadolescents often don't do much of anything except go to school. The experience of trying to achieve a real goal in real time in the real world is increasingly delayed, and the development of the control system depends on just those experiences. The developmental psychologist Ron Dahl has a nice metaphor for the result—the adolescents develop a gas pedal and accelerator a long time before they get steering and brakes.
This doesn't mean that adolescents are stupider than they used to be — in many ways, they are much smarter. In fact, there's even some evidence that delayed frontal development is correlated with higher I.Q. The increasing emphasis on schooling means that children know more about more different subjects than they ever did in the days of apprenticeships. Becoming a really expert cook doesn't tell you about the evolution of tool-use or the composition of sodium chloride—the sorts of things you learn in school. But there are different ways of being smart-knowing history and chemistry is no help with a soufflé. Wide-ranging, flexible and broad-based learning may actually be in tension with the ability to develop finely-honed controlled, focused expertise in a particular skill.
Of course, the old have always complained about the young. But the explanation does elegantly account for the paradoxes and problems of our particular crop of adolescents. There do seem to be many young adults who are enormously smart and knowledgeable but directionless, who are enthusiastic and exuberant but unable to commit to a particular work or a particular love until well into their twenties or thirties. And there is the graver case of children who are faced with the uncompromising reality of the drive for sex, power and respect, without the expertise and impulse-control it takes to ward off pregnancy or violence.
I like this explanation because it accounts for so many puzzling everyday phenomena. But I also like it because it emphasizes two really important facts about minds and brains that are often overlooked. First, there's the fact that experience shapes the brain. Its truer to say that our experience of controlling our impulses make the prefrontal cortex develop than it is to say that prefrontal development makes us better at controlling our impulses.
Second, it's increasingly apparent that development plays a crucial role in explaining human nature. The old "evolutionary psychology" picture was that a small set of genes was directly responsible for some particular pattern of adult behavior—a "module". In fact, there is more and more evidence that genes are just the first step in complex developmental sequences, cascades of interactions between organism and environment, and that those developmental processes shape the adult brain. Even small changes in developmental timing can lead to big changes in who we become.