Huge demographic shifts are under way throughout the world, and their economic, political, and social impacts will be enormous. Most of the changes reflect the demographic transition from high-fertility, rural agrarian societies to low-fertility, urban industrialized societies. The more developed countries, including those in Europe and Northern America, have generally completed the transition, while less developed countries are currently in different stages. As a result, demographic changes are projected to unfold differentially across countries, reflecting variations in the countries’ underlying demographics, particularly the timing and pace of their fertility declines and longevity gains.

Fertility Is Declining
The divergent patterns of growth worldwide stem from large variations in two key demographic drivers: declining fertility and increasing longevity. The number of births per woman worldwide has dropped by about half, from 5.0 in 1955 to 2.7 in 2005. In the industrialized world, the already low fertility rate has dropped from 2.8 in 1955 to just 1.6 in 2005, well below the replacement rate of 2.1 births per woman.

In the less developed countries, fertility has dropped by more than half, from 6.2 in 1955 to 2.9 in 2005, but patterns of fertility decline show significant variation. China experienced one of the world’s sharpest declines, with fertility dropping to less than 2.0 in 1995. South Korea’s steep fertility decline began ten years before China’s and has continued longer, dropping to 1.2, one of the world’s lowest rates. In contrast, India’s fertility, currently at 3.1, has been declining more gradually.

The world’s youngest countries, however, still have high fertility that has only recently begun to decline. The timing and pace of its fertility decline, illustrated in Exhibit 1, will largely determine both a country’s population growth and its population aging.

Longevity Is Increasing
Longevity has increased significantly almost everywhere in the world, with especially dramatic gains in developing regions (Exhibit 2). Life expectancy worldwide increased from 46 years in 1955 to 66 in 2005, with an increase to75 projected for 2050. Since 1950, developing countries have enjoyed a 23 year gain in life expectancy, from 41 to 64, with continued gains to 74 projected for 2050.

In several countries, including China, the increase in life expectancy was especially sharp during the late 1960s and early 1970s, while gains in other countries were more gradual. In the more developed countries, the already high life expectancy has steadily increased, reaching 76 in 2005, with 82 projected for 2050. Life expectancy in Japan, now the world’s highest at 82 years, surpassed the U.S. rate in the late 1960s.

There are several exceptions to this upward trend: The HIV/AIDS epidemic has reduced life expectancy in many African countries, and poor health and failing health-care systems have reduced life expectancy in Russia and several other former Soviet republics.

Note: The definitions and data used in this article are from the United Nations World Population Prospects: The 2006 Revision.

Excerpted from Hayutin, Adele (2007). Demographic shifts create challenges and opportunities. PREA Quarterly (Fall), 46–53. For the full article, click here.