Population Growth

The Demographic Transition

Accompanying the development process that transforms traditional agricultural societies into modern industrial ones is a distinct pattern of secular population growth and demographic change called the “demographic transition.” Before the transition's onset, population growth is near zero as high death rates more or less offset the high birth rates typically found in traditional societies. Population growth is again near zero after the completion of the transition, as birth and death rates both reach low levels in modern developed societies. During the intervening transition period, population growth is positive, as the death rate drops before the birth rate. Over the course of the transition, the population size typically grows by an order of magnitude.

Until the mid-18th century, global birth and death rates were both high, at approximately 4 percent per year, and growth rates were close to zero. Over the past two and a half centuries, the death rate declined steadily, to below 1 percent per year by 2000. The birth rate changed little from its historic high levels until the early 1970s, when a precipitous drop began that demographers expect to continue in future decades. The population growth rate of the world peaked at 2.1 percent per year in the late 1960s, when the birth and death rates stood at 3.4 and 1.3 percent per year, respectively. Since the 1960s, the growth rate has declined, reaching an estimated 1.1 percent per year in 2000–2005. In contrast, the annual additions to the population of the world peaked later and will remain high for longer (above 70 million per year until about 2020), because the slowly declining growth rate applies to a rapidly expanding population base. The half-century from 1970 to 2020 represents the period of most rapid expansion of human numbers ever, with the addition of nearly 4 billion people.

The timing of the onset of the transition, the duration of its different phases, and the levels of birth, death, and growth rates differ widely among countries and regions. The developed world, also called the North, was the first to enter the demographic transition in the late 18th century with a decline in mortality, and the birth rate began its decline in the late 19th and early 20th centuries. Today the North has reached the end of the demographic transition, and growth averages near zero. The transition in Africa, Asia, and Latin America, also called the South, started much later than in the North. A sustained reduction in the death rate did not occur until the beginning of the 20th century, and the birth rate remained high until about 1970. Since 1970, fertility in Asia and Latin America declined sharply, while Africa's birth rate remains relatively high.

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