Senin, 04 Juli 2011

Demographic Trends

Hania Zlotnik

Over the past four centuries the population of the world has increased tenfold, rising from about 580 million persons in 1600 to slightly over six billion in 2000 (Biraben,1979; United Nations, 2001a). Most of that growth occurred during the 20th century when the population nearly quadrupled (Fig. 5.1). Thus, whereas it took three centuries – from 1600 to 1900 – for the population to increase from 0.6 billion to 1.6 billion, between 1900 and 2000 a further 4.4 billion persons were added to the world population. Such rapid population growth, unprecedented in human history, resulted largely from the major reductions of mortality that occurred during the 20th century. Between 1900 and 2000, life expectancy at the world level nearly doubled, reaching 65.5 years by the end of the century. Almost universally mortality reductions preceded changes in fertility. In populations where mortality had been traditionally high, women had to bear large numbers of children to ensure that enough of them survived to adulthood. As mortality declined, populations did not immediately adjust their fertility levels to match the reduced risks of death. As a result, populations grew rapidly when high fertility persisted even as mortality declined. The more developed countries of today were the first to experience sustained declines of mortality. Starting in the 18th century, better hygiene and improving standards of living contributed to reduce mortality rates in those countries. Between 1750 and 1850, for instance, life expectancy in a number of European countries increased from 25 years to 35 years (Vallin, 1989) and during the 19th century, as mortality reductions accelerated, a widespread fertility decline began as well. Although even for Europe the data available on fertility trends over the 19th century are partial, it would appear that fertility in the continent declined from about 5–5.5 births per woman in the early part of the 19th century to about four children per woman in the early part of the 20th century (Clark, 1968). The process whereby reductions of mortality are followed by reductions of fertility sufficient to ensure that overall population growth remains low is known as the demo-graphic transition. During the 20th century, most developing countries embarked on the demographic transition. Indeed, with the discovery of antibiotics and other means
The views and opinions expressed in this chapter are those of the author and do not necessarily represent those of the United Nations.
The Nutrition Transition
Copyright © 2002 Elsevier Science Ltd
ISBN: 0-12-153654-8
All rights of reproduction in any form reserved

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Figure 5.1
Long-term population increase, BC400 to 2000AD.

to combat the spread of the infectious diseases endemic in developing countries, rapid reductions of mortality were achieved in those countries after 1945–1950. As in the more developed countries earlier, the continuation of high fertility as mortality declined gave rise to very rapid population growth, but fertility reductions in the developing world have been occurring more rapidly than in the more developed countries. The availability of modern contraceptives has facilitated such developments. By the end of the 20th century, most developing countries had initiated the transition to lower fertility. According to United Nations (2001a) estimates, by 1995–2000 only 16 developing countries had not yet shown signs of a fertility reduction and they comprised just 3% of the world’s population. Not only did the 20th century witness a rapid rise of population but, in addition, it saw the distribution of the population between rural and urban areas change dramatically. Indeed, although the existence of populous cities with urban attributes dates back several centuries if not millennia depending on the region under consideration, the vast majority of the world’s population has lived in rural settings during most of human history. Even as late as 1800, only 5% of the world population lived in urban areas and by 1900 that proportion had increased to just over 13% (United Nations, 1980). But over the course of the 20th century the proportion urban more than tripled, reaching 47% by 2000 (Fig. 5.2). The process of widespread urbanization started earlier in the more developed regions than in the developing world. Already by 1900 one out of every four inhabitants of more developed countries was an urban dweller whereas in the developing world the equivalent proportion was one in fifteen. Although levels of urbanization have risen markedly in developing countries, by 2000 less-developed regions are still about half as urbanized as more-developed regions. Thus, whereas 76% of the population of the latter lives in cities, just 40% of the population of less-developed countries is made of urban dwellers. This chapter describes in more detail the evolution of the size and growth of the world population and the dynamics of the process of urbanization in the major regions
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World Less-developed regions More-developed regions Series 4
Figure 5.2
Percentage of population in urban areas, 1800–2030.

of the world since 1950. It also discusses future prospects and their implications. The data presented were derived from the 2000 Revision of estimates and projections of national populations prepared by the United Nations Population Division (United Nations, 2001a,b) and from the 1999 Revision of World Urbanization Prospects (United Nations, 2001c). To ensure consistency between the two sets of data, estimates and projections of the urban and rural populations were derived using the national populations produced by the 2000 Revision and the proportions residing in urban areas as estimated and projected by the 1999 Revision of World Urbanization Prospects.


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