Global Demographic Trends

During the past 50 years, the world's population has increased dramatically-a trend that is projected to continue. Most future growth will occur in less developed countries, where the population is increasing more than five times as fast as that in developed countries.

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The phenomenal growth in world population has occurred despite a marked decline in the growth rate of the world's population-which fell to 1.2 percent a year in 2000-05, and is expected to drop further to 0.38 percent a year by 2045-50-because of the large number of women of childbearing age, a phenomenon known as "population momentum."

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Birth rates have fallen and are expected to drop further in less developed countries, whereas in more developed countries, they are expected to remain fairly constant. At the same time, death rates are holding fairly steady.

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Male/female sex ratios are typically around 105/100 at very young ages because naturally more boys than girls are born, with sex ratios tending to equalize by adulthood, as more males than females die. However, in some countries, female infanticide, neglect of female newborns, and selective abortion of female fetuses have resulted in male/female ratios of over 108/100 at very young ages.

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Declining birth rates, combined with increases in life expectancy, are leading to population aging. The number of people in less developed countries aged 60 or over is expected to exceed the number of 12-to 24-year-olds by 2045, a phenomenon that occurred in more developed countries in the late 1990s.

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Increases in the...