Demographers now generally agree that the twenty-first century is likely to see the end of world population growth. The cause: significant fertility declines around the world that are unlikely to stop at the replacement level of around 2.1 children per woman.
But before growth levels off and possibly decreases, at least 2 bilion will be added to total world population. Women around the world now have fertility levels well below those needed to reproduce their populations, say Wolfgang Lutz, Warren C. Sanderson, and Sergei Scherbov of the International Institute for Applied Systems Analysis. "Spain and Italy used to be relatively high fertility countries," they write in The End of World Population Growth in the 21st Century. "Today, fertility levels there are so low that, on average, 100 women of reproductive age will produce only 65 daughters to follow them as potential mothers in the next generation."
According to the demographic transition theory, as living standards rise and health conditions improve, mortality rates should decline, followed by a decline in fertility rates sometime later. In more-developed countries, the mortality rate generally began its decline in the late 1700s, while the fertility rate's decline began up to 100 years later.
Different societies experience the demographic transition at different rates; in many developing countries, it began in the latter half of the twentieth century. Furthermore, the decline in the mortality rate in developing nations has occurred very rapidly, from an average of 40.9 years at the end of World War II to 63 years in 2000. The IIASA researchers expect that declines in fertility will follow; zero population growth or even population decline will occur by the end of the twenty-first century, they predict.
Of the world's developing nations, China is furthest along in its demographic transition. Fertility rates there have declined from 4.2 births per woman in 1974 to 1.85 births in 1995. Government family-planning programs have strongly influenced these numbers, but education is an important determinant in fertility reduction. …