During the final years of the twentieth century, the question of how demographic trends in the near future will affect humanity has received more scrutiny than perhaps ever before. At the 1994 United Nations Conference on Population and Development, for example, representatives from 180 countries addressed the issue of rapid population growth, especially the potential tripling or quadrupling of the world’s 5.5 billion people during the twenty-first century.

Much of the concern about population focuses on the impact of substantial increases in the size of teenage and elderly age-groups. Many corporations, for example, eagerly anticipate the increased global growth and consumer potential of the adolescent age- group, which experts contend will peak in number in the early twenty-first century. Especially appealing to these businesses is what businessman and demographer Peter Schwartz calls the emergence of “global teenagers”—youths with...