nificantly. New studies have allowed more complex views of the multiple dimensions of adolescence, fresh insights into the process and timing of puberty, and new perspectives on the behaviors associated with the second decade of life. At the same time, the field's underlying theoretical assumptions have changed and matured.
Researchers of human development have consistently observed that the second decade of life is a time of dramatic change: a period of rapid physical growth, endocrine (hormone) changes, cognitive development and increasing analytic capability; emotional growth, a time of self-exploration and increasing independence, and active participation in a more complex social universe. For much of this century, scientists and scholars studying adolescence tended to assume that the changes associated with adolescence were almost entirely dictated by biological influences. It has been viewed as a time of storm and stress, best contained or passed through as quickly as possible. Adolescence, a 1904 book by G. Stanley Hall, typified this standpoint. It was Hall who popularized the notion that adolescence is inevitably a time of psychological and emotional turmoil (Hall, 1904). Half a century later, psychoanalytic writers including Anna Freud accepted and augmented Hall's emphasis on turmoil (Petersen, 1988). Even today, "raging hormones" continue to be a popular explanation for the lability, aggression, and sexual activity associated with adolescence (Litt, 1995). Intense conflict between adolescents and their parents is often considered an unavoidable consequence of adolescence (Petersen, 1988). However, this assumption is not supported by scientific evidence. The assumption that turmoil and conflict are inevitable consequences of the teenage years may even have prevented some adolescents from receiving the support and services they needed.
Research is now creating a more realistic view of adolescence. Adolescence continues to be seen as a period of time encompassing difficult developmental challenges, but there is wider recognition that biology is only one factor that affects young people's development, adjustment, and behavior. In fact, there is mounting evidence that parents, members of the community, service providers, and social institutions can both promote healthy development among adolescents and intervene effectively when problems arise.
The study of adolescence is now becoming an increasingly sophisticated science. Thanks to powerful new research tools and other scientific and technological advances, today's theories of adolescent development are more likely to be supported by scientific evidence than in the past. Indeed,