III. World Population Growth

Population dynamics are one of the key factors to consider when thinking about development. In the past 50 years the world has experienced an unprecedented increase in population growth (see Figure 3.1). Do you know why?

Grouping Countries by Their Level of Development

A "natural population increase" occurs when the birth rate is higher than the death rate. While a country's population growth rate depends on the natural increase and on migration, global population growth is determined exclusively by the natural increase.

Around the world, death rates gradually decreased in the late 19th and the 20th centuries, with death rates in developing countries plummeting after World War II thanks to the spread of modern medicine that allowed control of infectious diseases. In much of the developing world the decline in death rates preceded the decline in birth rates by 20 years or more (see Figure 3.2), resulting in record-high rates of population growth of 3 percent or even 4 percent a year. Since the 1960s birth rates have also been declining rapidly in most developing countries except those in Sub-Saharan Africa and the Middle East. This decrease in birth rates in the developing world is even more rapid than that characteristic of Europe and the United States in the 19th century.

Today's low-income countries still have the world’s highest birth rates (see Map 3.1), although women tend to have fewer children than before. The reasons for lower fertility are varied, but most are related to developing countries' economic growth and development (see Figure 3.3; see also Chapters 4, 7, 8). Parents choose to have smaller families when health conditions improve because they no longer have to fear that many of their babies might die, and when they do not have to rely on their children to work on the family farm or business or to take care of them in their old age. In addition, more parents are sending their daughters to school, which is important because women with basic education tend to produce healthier children and smaller families. More women now have opportunities to work outside the home, so they are starting their families later and having fewer children. On top of all that, access to modern contraceptives for family planning is improving, making it easier for parents to control the number and spacing of their children.

Lower fertility rate does not immediately lead to lower birth rate and lower population growth rate if a country has a larger proportion of men and women in their reproductive years than before. Population growth caused by more women giving birth even though each has the same number of or fewer children is called "population momentum." Population momentum is particularly significant in developing countries that had the highest fertility rates 20 to 30 years ago.

The decline in birth rates over the past few decades has lowered population growth rates in developing countries despite a continuing decline in death rates. Population growth is even slower in developed countries (Figure 3.4). Stabilizing birth rates and increasing death rates (the latter being a result of aging populations; see Chapter 8) have already led to a natural population decrease in Italy and Germany. Japan and Spain are expected to follow soon (see birth rates and death rates in Data Table 1).

The formerly socialist countries of Central and Eastern Europe present a major exception to the broad similarity of demographic trends in developed and developing countries. The rapid decline in death rates that occurred in the 1950s and 1960s slowed down in the 1970s and 1980s. In the 1990s death rates actually increased in Russia and some other transition countries, including Belarus, Bulgaria, Estonia, Latvia, Lithuania, Moldova, Romania, and Ukraine. In the late 1990s death rates in these middle-income countries exceeded the average death rate for low-income countries and approached the rates in Sub-Saharan Africa.

This dramatic and historically unprecedented reversal in mortality trends is primarily explained by higher adult male mortality: among older men mainly because of the increase in cardiovascular disease, among younger men because of more accidents, suicides, and murders. Many of these factors can be related to stress and substance abuse (heavy drinking and smoking), which in turn can be linked to the increased unemployment, worsening living conditions, and greater economic uncertainty that have accompanied the transition. But rapid economic reforms have not necessarily been detrimental to people's health in all transition countries. For example, in the Czech Republic the death rate has continued to decline (see Figure 3.5), while in Hungary and Poland it has held steady.

Birth rates in the transition countries of Europe have dropped sharply in the past 5 to 10 years, just as the death rates were on the increase. The reasons for that drop are different from those in most developing countries: they are believed to be closely associated with a lower quality of life and the uncertainties caused by the social and economic crisis of transition. As a result fertility rates in these countries are now far below the "replacement level" (the level at which population size would become stable, considered to be slightly more than two children per family) and lower than those in most developed countries (see Figure 3.3).

Because of these unusual demographic trends—increasing death rates combined with dropping birth rates—many of the transition countries of Europe have already experienced natural decreases in population.

On the global scale, falling fertility rates already have decreased the population growth rate--from more than 2.0 percent to 1.5 percent a year over the past 30 years. Experts expect this trend to continue, so that by the end of this century the world’s population will stabilize at 9 to 10 billion people. But in the meantime, in absolute numbers it is still growing faster than ever before—by about 230,000 people a day. This is happening because of the larger-than-ever population base -- in 2000 there were about 6 billion people on earth, about twice as many as in 1970.

The projected increase of the world’s population from the current 6 billion to 9-10 billion at the end of the century will be attributable almost entirely to population growth in developing countries. Thus the share of developing countries in the world’s population is expected to increase from the current 84 percent to 88 percent or more. Rapid growth of the developing countries’ population, particularly in the next 50 years, poses many economic, social, and environmental challenges, not only for these countries but also for the entire global community. Whether these additional billions of people get access to adequate education and health services, are able to find gainful employment, and manage to avoid poverty and hunger will be critical for the possibility of global sustainable development.