Table of Contents

Introduction

Fertility

Mortality

Migration

Population Size and Growth

Population Composition

Population Distribution

Population Growth Issues

Concern About Population

Conclusion

Suggested Resources

References

Related Publications

Population: A Lively Introduction

Population Growth Issues

• Figure 11: World Population Growth Through History
• Demographic Transition
• Figure 12: The Classic Stages of Demographic Transition
• Future Prospects
• Population Decline

For most of human history, world population never exceeded 10 million people. The death rate was about as high as the birth rate, and the rate of population growth was scarcely above zero. Significant population growth began about 8000 B.C., when humans began to farm and raise animals (see Figure 11). By 1650, world population had expanded about 50 times—from 10 million to 500 million. Then world population shot up another 500 million people in just 150 years, reaching its first billion around 1800. It achieved its second billion by 1930, 130 years later; a third billion by 1960, only 30 years later; and a fourth billion by 1975, just 15 years later. The fifth billion, reached in 1987, took only 12 years. World population will exceed 6 billion by 1999, and another billion persons will be added every 11 to 13 years until about the middle of the 21st century. It took virtually all of human history for the world's population to reach the first billion; now each new billion is added in just over a decade.

But the population explosion, as it is often termed, is not just an awe-inspiring demographic phenomenon. It has many demographic and societal consequences, such as international and internal migration and the emergence of gigantic cities and shantytowns. While some analysts downplay the negative impact of population growth,⁷⁵ most believe that population growth multiplies the damage created by other world problems.⁷⁶ For example, population growth exacerbates environmental degradation and resource depletion, and puts unmanageable pressures on government institutions, national economies, and virtually all other resources.

Population growth is not solely responsible for these social problems. Environmental degradation, for example, is brought about not only by the number of people, but by how much they consume and the degree to which their consumption damages the environment. Poverty is often produced by the uneven distribution of income within a country, not just by large numbers of people. Solving these social and economic ills often requires direct action by policymakers. Just slowing population growth cannot solve such problems, but it can contribute to their solution.

Demographic Transition

The unprecedented growth of world population in the modern era arose because births began to outnumber deaths. In ancient times, the birth rate and the death rate fluctuated around a relatively high level, and essentially cancelled each other out. This formed the first stage of a process described by the theory of the demographic transition (see Figure 12).

This theory evolved from the history of population growth in Europe and the United States and has been applied to populations everywhere.

In Stage 1 of the classic demographic transition, the death rate was extremely high because of poor health and harsh living conditions. Life expectancy at birth was less than 30 years. If birth rates had not also been high, societies would simply have died out — and many did!

The cultures in these societies encouraged high birth rates through religious teachings and social pressure, essentially encouraging people to "be fruitful and multiply." Socially, a man's virility and a woman's status often were linked to the number of children they had. But large families also served a practical function in these societies. Children furnished labor for family farms and supported elderly parents. Large families also increased the economic, political, and military power of their tribe or nation.

Stage 2 of the demographic transition began when the death rate began to drop, probably because of improved living conditions and health practices. The birth rate remained high and may even have increased because women were healthier. The excess of births over deaths in the second stage of the transition ignited a population explosion.

Why didn't the birth rate fall in tandem with the death rate? Most societies eagerly accept technological and medical innovations, as well as other aspects of modernization, because of their obvious utility against the universal enemy: death. Social attitudes, such as the high value attached to having many children, are slower to change. It also takes time for people to recognize that rapid population growth creates pressures on food and land and that the pressure can be eased by having fewer children. It can take generations for people accustomed to high childhood mortality to recognize that low mortality means that they no longer need to have eight children to ensure that four will survive to adulthood.

In Stage 3 of the demographic transition, the birth rate moves downward, eventually catching up with the death rate. Population growth remains relatively high during the early part of the third stage, but falls to near zero in the latter part.

In Stage 4 of the demographic transition, the birth rate and the death rate are close together again, but they fluctuate around a relatively low level.

Developed countries in Europe and elsewhere have completed the four stages of demographic transition. Most developing nations are still in Stage 2 or the early part of Stage 3 of the transition. Excluding China, the growth rate for developing countries in 1998 was 2.0 percent. If growth were to continue at that rate, the population of these countries would double in only 35 years.

Will developing countries eventually complete the demographic transition to low fertility and mortality? They already have deviated from the path followed by Europe and the United States. The importation of medical supplies and technology caused death rates to plummet in many parts of the developing world after World War II; in contrast, mortality declines in Europe had occurred slowly. The rapid decline in death rates, but not in birth rates, caused unprecedented rates of natural increase in these countries beginning in the 1950s and accelerating in the 1960s. Growth slowed in many countries in the 1980s and 1990s. Brazil, Mexico, South Korea, and Thailand, for example, experienced dramatic declines in birth rates. Fertility rates dropped in many African countries as well, but they are still high enough to keep the region's growth rate near 3 percent annually.

Many demographers question whether Europe's demographic transition is a realistic model for developing countries in this century and the next. Even if all countries eventually undergo a demographic transition (and most population experts assume they will), it is clear that individual countries are following very different timetables and paths for achieving it. The timing of fertility declines in developing countries is key to the ultimate size of the world's population. Population and policy experts debate just which actions or policies, such as improving the educational levels of women or making contraceptives easily available, will initiate declines in the birth rate.⁷⁷

Future Prospects

If the present rate of population growth were to continue, world population would rocket to 12 billion by 2050, 24 billion by 2100, 96 billion by 2200, and so on. Humanity would outweigh the Earth and then the solar system in a remarkably short period of time if the present growth rate continued indefinitely. But no rate of growth can be sustained indefinitely. A positive growth rate of +0.00001 ultimately would yield a population whose mass would expand at the speed of light, while a negative rate of -0.00001 ultimately would carry humanity back past Adam and Eve.⁷⁸ Zero population growth (ZPG), which characterized human population for more than 99 percent of its history, must be achieved once again, at least as a long-term average, if the human species is to survive.

In order for the world to reach ZPG (assuming that mortality remains low or sinks lower, as expected), the global TFR would need to drop from its present 2.9-child per woman average to a two-child average, which is replacement-level fertility.

The global TFR will not fall to replacement level immediately for two reasons. First, the fundamental social beliefs and cultural practices that produce high fertility in many countries (through the variables in Box 1) do not change quickly. Second, the world's current age structure will generate massive growth even if a relatively small family size becomes the norm in the near future.

Almost one-third of the world's inhabitants are below age 15, and they inevitably will become the parents of the largest birth cohorts in history. But, like any explosion, the population explosion will eventually fizzle, probably by the end of the 21st century. By then, the demographic transition will have run its course in most countries of the world and the world growth rate will probably be near zero. Most recent estimates of how large world population will actually be when it stops growing are in the 11 billion to 13 billion range.

Can the Earth support such huge populations? The Earth's ultimate carrying capacity is unknown.⁷⁹ As new technologies are devised and as resource management techniques are improved, the carrying capacity of the Earth expands, making it impossible to predict the ultimate number of people the world can support. But many experts think that a world population of 10 billion may be the maximum that could be supported comfortably. Other scholars believe that the world's basic biological systems—its forests, grasslands, croplands, and fisheries—and energy resources are insufficient to maintain a population of 10 billion. They foresee major systems failures long before the 10 billion mark is attained, and they predict that societies will be forced to restrict individual childbearing to stabilize growth.⁸⁰

Whatever the peak carrying capacity of the Earth, world population might stabilize and remain uncomfortably close to that maximum level once population growth has ceased. Or, more optimistically, world population might decline to a lower, more manageable level for both humans and the environment.

Population Decline

There is no homeostatic mechanism that maintains a society at ZPG. Societies can easily slip into population decline, sometimes termed negative population growth (NPG). Indeed, some population experts and interest groups would welcome such a population implosion.

But zero growth or population decline brings its own set of problems. One is that the proportion of the population made up of older people rises dramatically. Older people consume a disproportionate share of medical and other costly public services. Labor force shortages also may develop.⁸¹ If population declines rapidly, severe social and economic problems can result.

Natural decrease (fewer births than deaths) is already a reality in Germany, Sweden, Russia, and most former Soviet republics. The rate of decline is extremely slow, but many European leaders fear that their falling populations eventually will threaten their economies, their defense systems, and even their national identities.

Some European governments have tried various economic incentives to encourage couples to have more children. Some couples receive housing or other benefits if they have children. Women can receive a percentage of their salaries while they are on maternity leave and are guaranteed a job when they return. But these financial incentives are expensive and they have not boosted birth rates enough to ward off population decline. Massive immigration is not an acceptable solution to population decline in most countries either. Virtually all European countries have imposed strict controls against immigration, and some have encouraged immigrants to leave. Long-term population decline appears inevitable for most of Europe, but it will occur very slowly.⁸² Were it not for high immigration levels, the United States also would be facing population decline in the 21st century, because of low mortality and below-replacement fertility.