Between 1980 and 1995 total world population grew from 4.4 billion to almost 5.7 billion. By 2010, at least another billion people will be added for a total of almost 6.9 billion. Chart 1 shows that most of this growth has been, and will continue to be, in the developing world. In 1995, 84 percent of the world’s people—more than 4 out of 5—lived in low- and middle-income countries; by 2010, it will be 6 out of 7.

Death and birth rates have declined over the past several decades. People are living longer in both industrial and developing countries because of increased access to immunization, primary health care, and disease eradication programs. Many parents are realizing that as health conditions improve, more of their children are likely to survive, so they are choosing to have fewer babies. Increased access to family planning is helping parents control the number and spacing of their children. In addition, with greater access to education and jobs, more women are starting their families later and are having fewer, healthier children.

Due to the slowing of birth rates, population growth rates have started to decline in the many countries, although they still remain high in some countries because birth rates have not fallen as rapidly as death rates. As Chart 2 shows, population growth rate still tends to be higher in low- and middle-income countries than in high-income countries. Even as the population growth rate has been decreasing in these countries, the number of people added to the population each year has been increasing because the population base has become larger.

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 show the composition of the population by age and gender in 1995 and 2025 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.

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.

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.

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 exceed 50 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.

Rapid population growth rates can make it difficult for countries to raise standards of living and protect the environment because the more people there are, the greater the need for food, health care, education, houses, land, jobs, and energy. Adding more people to a country’s population means that the wealth must be distributed among more people, causing GNP per capita to decrease at least in the short term.

Responding to the needs of a rapidly growing population can challenge a country’s ability to manage its natural resources on a sustainable basis. For example, people may not be able to get access to safe water because more and more households, farms and factories are using increasing amounts of water. Deforestation may occur as trees are cut to provide fuel for cooking, building materials, or land for grazing and agriculture. Desertification may occur as land that has been intensively farmed becomes depleted of its nutrients or eroded when trees whose roots systems once anchored the soil are gone. The air may become polluted as people crowd into cities, the number of cars increases, people use more and more energy, and economies continue to industrialize.

Parents tend to have larger families when they fear that many of their babies may die, when they need laborers to work on the family farm or business, when they want to ensure that they themselves will be cared for in their old age, and when they lack access to education and to family planning if they want it.

Experience shows that three of the most successful strategies to reduce fertility rates are to ensure that people 1) have greater access to primary health care and family planning services, 2) receive a basic education, especially girls and women, and 3) have government services that help protect them when they are sick, old or unemployed.

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