Population momentum

The lack of balance between birth and death rates is particularly pronounced in many developing countries experiencing population momentum. This phenomenon occurs when a large proportion of a country’s population is of childbearing age. Even if the fertility rate of people in developing countries reaches replacement level, that is if couples have only enough children to replace themselves when they die, for several decades the absolute numbers of people being born still will exceed the numbers of people dying.

Charts 3.1 and 3.2

Charts 3.1 and 3.2 show the composition of the population by age and gender in 2000 and 2030 for low- and high-income economies. As can be seen in Chart 3.1, there is a large difference in low-income countries between the percentage of people of childbearing age and more elderly adults. Once this young group moves beyond childbearing age, however, the momentum will decrease, and population can begin to stabilize so that births and deaths balance (assuming fertility rates remain at or below replacement levels). The reverse is true in many high-income countries where birth rates have already been low for several decades and populations have either stabilized or in some cases begun to decline.

How does the age of its population affect a country?

In low-income countries more than a third of the population is under age 15, compared with less than a fifth in high-income countries. This means that a larger portion of the low-income countries’ population is too young to work and, in the short run, is dependent upon those who can.

Photo 1.

But the transition to lower population growth rates can pose problems, too. As growth slows, the average age of the population rises and eventually the proportion of elderly, nonworking people will increase. This puts great pressure on the working-age population and on a country’s pension, health care, and social security systems. This is an issue facing some high-income countries today and one that may face developing countries in the future as their population growth rates continue to decline.

People in motion

International migration has important social, economic and political significance. This is as true for countries that lose citizens to immigration as it is for the countries in which immigrants make their new homes. Although attention is often given to the numbers of people migrating from developing to industrial countries, most migration in the world today occurs between developing countries.

Urbanization is also significant. The rapid growth of cities in developing countries is nearly universal. Whereas less than 22 percent of the developing world’s population was urban in 1960, by 1990 it had increased to 34 percent. By 2015 it is expected to reach 48 percent.

The movement of people from rural to urban areas can result in greater production of goods and services, but it can also create congestion, pollution, and a greater demand for housing, clean water, sanitation facilities, recreation areas, public transport, health care and education. When rapid migration to cities strains the capacities of governments to provide these necessary services, the result may be a lower standard of living for everyone.