The invention of adolescence

Since the mid-1800s, puberty--the advent of sexual maturation and the starting point of adolescence--has inched back one year for every 25 years elapsed. It now occurs on average six years earlier than it did in 1850--age 11 or 12 for girls; age 12 or 13 for boys. Today adolescents make up 17 percent of the U.S. population and about a third of them belong to racial or ethnic minorities.

It's still not dear exactly what triggers puberty, confides Jeanne Brooks-Gunn, Ph.D., of Columbia University Teachers College, an expert on adolescent development. "The onset of pu-betty has fallen probably due to better nutrition in the prenatal period as well as throughout childhood. Pubertal age--for girls, when their first period occurs--has been lower in the affluent than the nonaffluent classes throughout recorded history. Differences are still found in countries where starvation and malnutrition are common among the poor. In Western countries, no social-class differences are found." Although adolescence is a new phenomenon in the history of our species, thanks to a stable and abundant food supply, we've already hit its limits---it's not likely puberty onset will drop much below the age of 12.

If kids look like adults sooner than ever before, that doesn't mean they are. The brain begins to change when the body does, but it doesn't become a grown-up thinking organ as quickly as other systems of the body mature. The clash between physical maturity and mental immaturity not only throws parents a curve--they forget how to do their job, or even what it is--it catapults teens into some silly situations. They become intensely interested in romance, for example, only their idea of romance is absurdly simple, culminating in notes passed across the classroom: "Do you like me? Check yes or no."

Puberty isn't the only marker of adolescence. There's a slowly increasing capacity for abstract reasoning and relative thinking. Their new capacity for abstraction allows teens to think about big things--Death, Destruction, Nuclear War--subjects that depress them, especially since they lack the capacity to ameliorate them.

The idea that everything is relative suddenly makes every rule subject to debate. As time passes, teens attain the ability to make finer abstract distinctions. Which is to say, they become better at choosing their fights.

Teens also move toward autonomy. They want to be alone, they say, because they have a lot on their minds. Yet much of the autonomy hinges on the growing importance of social relationships. Evaluating the ups and downs of social situations indeed requires time alone. Family ties, however, remain more important than you might expect as teens increase identification with their peers.

Whatever else turns teens into the moody creatures they are, hormones have been given far too much credit, contends Brooks-Gunn. In fact, she points out, the flow of hormones that eventually shapes their bodies actually starts around age seven or eight. "Certain emotional states and problems increase between ages 11 and 14, at the time puberty takes place. These changes are probably due to the increased social and school demands, the multiple new events that youth confront, their own responses to puberty, and to a much lesser extent hormonal changes themselves."

The nutritional abundance that underlies a long adolescence also prompted the extension of education, which has created a problem entirely novel in the animal kingdom--physically mature creatures living with their parents, and for more years than sexually mature offspring ever have in the past. College-bound kids typically depend on their parents until at least age 21, a decade or more after hitting puberty.

Historically, children never lived at home during the teen years, points out Temple University's Laurence Steinberg. Either they were shipped out to apprenticeships or off to other relatives.

Among lower primates, physically mature beasts simply are not welcome in the family den; sexual competition makes cohabiting untenable. But for animals, physical maturity coincides with mental acuity, so their departure is not a rejection.

The formal study of adolescence began in the 1940s, just before James Dean changed our perception of it forever. There is a long-standing tradition of professional observers looking at adolescence as a pathology--and this one really did start with Freud. It continues still.