The Global and Regional Impact of Mortality and Fertility Transitions, 1950–2000

During the second half of the twentieth century, world population grew at a record pace, both in absolute and relative terms, from 2.5 billion to 6 billion (or 1.75 percent annually). Demographers have long identified rapid mortality declines as the main explanation. This article finds that one‐fourth of today's world population is alive because of mortality improvements since mid‐century. Very rapid growth is unlikely to continue as substantial fertility declines also occurred in recent decades. This article finds that already by the year 2000, these fertility declines have almost exactly compensated for the impact of mortality declines from mid‐century levels. This result may suggest homeostasis, but analyses of underlying trends contradict this impression. First, the impact of fertility declines will soon and significantly exceed that of mortality declines. Second, that mortality and fertility declines jointly affect the size of the world population by less than one percent conceals a significant impact on the population's age composition as well as on regional population sizes.