The explosion of the world's population at the end of the twentieth century was largely the result of a dramatic rise in life expectancy, attributable to scientific advances, innovations in communications technology, and economic growth. High fertility, however, which might be linked with increases in population, is not always a propitious sign. Despite a global tendency toward convergence in demographic trends, high fertility in parts of Africa and Asia—as driven by such exogenous variables as infant mortality, women's education, and racial identity—militates against the improvement in living standards generally enjoyed in the more economically developed countries.