Life is full of surprises—no less so for specialists in population studies than for those engaged in other sorts of analytic endeavors. In fact, it may be that life holds more surprises for the demographer than for other students of the social sciences. While population specialists can bring to bear complex and sophisticated mathematical technique in their labors, the predictive and explanatory models that undergird this elegant superstructure are strikingly limited, and indeed rather shaky. There are good reasons, moreover, to imagine that demography’s predictive properties will remain distinctly limited into the future—so long as the mysterious matters of human agency and human desires continue to shape our population patterns. Under such circumstances, students of population would appear to be consigned forever to playing catch-up with reality.

Be all that as it may, contemporary demography can nonetheless be said to adhere to a sort of general worldview. That worldview is represented in the notion of the ‘‘demographic transition,’’ a concept that the great demographer Frank Notestein introduced to the field several generations ago. The ‘‘demographic transition’’ offered a stylized description of the great shifts in population patterns in the modern era. In this schema, death rates and birth rates start out high, but more or less in equilibrium. Then, advances in knowledge and improvements in income result in broad, general, and continuing declines in mortality, precipitating rapid population increase. Finally, somewhat later, socioeconomic development brings about sustained fertility reductions via voluntary, deliberate changes in childbearing patterns—at which point births and deaths once more come into balance.

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