world’s net gain of elderly individuals from July 1999 to July 2000 (615,000 people monthly). Despite this increase, Europe remains the region with the highest proportion of population aged 65 and over (15.5 percent in 2000), while sub-Saharan Africa has the lowest proportion (2.9 percent).

Life expectancy has increased enormously in the United States since the beginning of the twentieth century (see Figure 3-5). In developed countries, the average national gain in life expectancy at birth was 66 percent for males and 71 percent for females between 1900 and 1990 (Kinsella and Velkoff, 2001). Increases were more rapid in the first half than in the second half of the century because of the expansion of public health services and infectious disease control programs that greatly reduced death rates, particularly among infants and children in developed countries. Estimates of life expectancy in developing countries in the early part of the 1900s are generally unreliable. Since World War II, changes in life expectancy in developing regions have been fairly uniform. Some exceptions include Latin America and, more recently, Africa as a result of the HIV/AIDS epidemic. In 2000, life expectancy in developing countries ranged from 38 to 80 years, as compared with 66 to 81 years in developed nations.


The mass relocation of rural populations to urban areas is one of the defining demographic trends of the latter half of the twentieth century. The world’s cities are currently growing at four times the rate of their rural counterparts, and at least 40 percent of their expansion is the result of migration rather than natural increase. Each day about 160,000 people move from the countryside to metropolitan areas, and almost 50 percent of the world’s population lives “in town” for significant periods (United Nations Population Fund, 2001; United Nations Population Division, 2002). The movement of people to cities has accelerated in the past 50 years (see Figure 3-6). The world’s urban population was 2.9 billion in 2000 and is expected to climb to 5 billion by 2030. Urbanization is greater in the more developed regions of the world, where 75 percent of the population lived in urban settings in 2000. Although the percentage of urban dwellers in less-developed regions had increased to 40 percent in 2000 from 18 percent in 1950, the level and pace of urbanization differed markedly among the major constituent areas. Latin America and the Caribbean as a whole became highly urbanized, with 75 percent of their populations living in urban settlements in 2000. Conversely, only 37 percent of the populations of Africa and Asia lived in urban areas in 2000; however, this number is expected to increase more than 50 percent for both continents by 2030. With 26.5 million inhabitants, Tokyo was the most populated urban agglomeration in the world in 2001 (see Table 3-1).

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