This is the second of three linked Web essays by Bill Butz, president of the Population Reference Bureau. The essays cover the complex challenges of today's population issues and how PRB is responding to those challenges. The first essay was The Double Divide: Implosionists and Explosionists Endanger Progress Since Cairo.

(March 2005) Ask about "the population problem" to people of a certain age, and the first and perhaps only thing that comes to mind is the "population bomb" or "population explosion."

And they would be right—for their time. In the second half of the 20th century, rapid population growth—especially but not exclusively in the developing countries—created unprecedented increases in the number of people on the earth. And this growth was accompanied by crowding, malnutrition, disease, and poverty. Indeed, for many Americans, the coming "population explosion" was, along with the Cold War, the most unsettling fact about our world.

But "population problems" have been part of American discourse for over 100 years. In the 1930s and 1940s, for instance, many observers feared that depopulation due to plummeting birth rates would cause chronic economic depression as the numbers of U.S. consumers and workers declined.

In the 1920s, the U.S. "population problem" was rapid urbanization, reflected in a 1920 census count showing that for the first time more than one-half the population lived in urban areas. Rural incumbents in the House of Representatives, fearing they would be voted out of office by their new urban constituents, succeeded in blocking reapportionment of the House's seats on the basis of the census counts as mandated by the U.S. Constitution.

The century's first "population problem" was mass xenophobia about immigration. Beginning in 1880, wave after wave of European immigrants was creating congestion and social change at an unprecedented rate. In response to widespread anxiety and anger, Congress in 1924 passed the country's most restrictive immigration legislation ever.

So for at least a century, every generation of Americans has seen some aspect of population as a problem. Each problem was based in hard numbers. Each generated private emotions and public fears. Each suffered exaggeration and manipulation. And each commanded the attention of opinion leaders and elected officials.

Why the Population 'Explosion' Was Different

Rapid population growth is quantitatively and qualitatively different from these previous population problems. Its scope is worldwide. It has garnered intense global public attention. It has persisted far longer as a policy issue. And the policy responses to this growth—which have chiefly addressed family planning, women's schooling, and empowerment, and overall economic development—have spanned scores of national governments and dozens of international organizations.

The effectiveness of these policies aimed at reducing fertility and slowing population growth, though maddeningly slow to emerge, has been demonstrable and widespread. Less than 40 years after the term "population bomb" was coined, fertility rates are falling in almost every country. Indeed, below-replacement fertility rates predominate in more than one-third of the world's countries—including China, Japan, and all of Europe—encompassing one-half of the world's people. Among developed countries, only the United States is likely to see significant growth, a result of immigration and a fertility rate higher than other developed nations.

So, Is Everything OK Now?

Far from it. In most countries with below-replacement fertility rates, populations are still increasing because of the large numbers of women of childbearing age. Fertility rates in most of the developing world also continue to exceed replacement levels. Developing countries in Africa and Asia will account for almost all of the increase in world population between now and 2050. And above-replacement fertility rates mean that world population will not stabilize (much less decline) of its own accord. The remarkable fertility declines of the last 40 years in much of the world will not continue without continuing the investments in women, family planning, and development outlined above.

And the world has moved well past the time when just one paradigm or "problem" could encompass the myriad dynamics and issues that fall under the heading "population." Globalization pressures and disparities between the fertility rates of neighboring countries mean that population's interactions with the environment, health, gender, poverty, migration, urbanization, aging, and youth are creating new and complex economic and policy challenges.

Yet policymakers, analysts, and the public often fail to understand these complexities and continue to settle for simple explanations—such as the outmoded monolithic global population explosion (or its fashionable obverse, a population implosion). Instead of clinging to one side or the other of this "demographic divide," these stakeholders need reliable information and fresh thinking to grasp the crosscutting and rapidly changing population problems of the 21st century.

PRB's New Core Themes: A Response to the Confusion

In the midst of these complexities and misunderstandings, PRB has identified a set of core themes that describe and address the population challenges and opportunities of the coming decades.

PRB's core themes are not confined to the misleading focus on a single population problem. Nor do they favor either the United States or the developing world. Instead, they treat phenomena that increasingly cross national borders. The themes also encompass the opportunities—not just the problems—that demographic change may provide, and they illustrate the power of population data to contribute to policy solutions.

Here are PRB's core themes:

Reproductive health and fertility. More than one-half million women still die every year from pregnancy-related causes. Almost one-half the world's women—including 85 percent in sub-Saharan Africa and 28 percent in the United States—still do not use modern contraception. The news on HIV is equally gloomy: Nearly 20 million women worldwide now have HIV, and rates of HIV infection among African women ages 15-19 are five to six times higher than infection rates for their male counterparts. AIDS is also the leading cause of death among African American women ages 25-34. Investments in family planning and reproductive health must continue—reaching the women and couples that are often the hardest to reach—if progress on these issues is to continue.

Children and families. Falling infant and child mortality rates nearly worldwide were a triumph of 20th century science, public health, and economic development. But adequate investment and policy attention to these crucial populations in both the United States and internationally is still lacking. For instance, American children experience teen death rates as high as 236 per 100,000 in the District of Columbia. In sub-Saharan Africa, HIV/AIDS has left 14 million children orphaned. And while falling fertility in developing countries now presents a window of opportunity to invest more in the health, nutrition, and schooling of each child—what demographers call the "demographic dividend"—few national governments are poised to take advantage of this opportunity.

Population and the environment. Around 70 percent of the world's poor rely on the land for income and subsistence. But increasingly, poor rural families worldwide are likely to live in ecologically fragile zones; support themselves with subsistence slash-and-burn agriculture; and use products from increasingly stressed forests as fuel, fodder, and building materials. Abject poverty can push rural residents to destroy the very resources they rely on for their livelihoods, and can leave them unable to meet basic human needs when the prices of environmental goods such as water, land, or marine life increase. Meanwhile, improving incomes and living standards are driving increasing global demand for consumer goods—but this development is also fueling deforestation and environmental degradation. And demographic factors increasingly contribute to environmental problems in the developed world as well, from densely populated coasts that are vulnerable to storms to low water tables in the American Southwest. In all these settings, evidence-based public policy can make a marked difference.

Aging. Coming population declines in many developed countries will accompany very low proportions of youth and high proportions of older people in these societies. The resulting policy challenges of how to support increasing numbers of retirees while maintaining productive economies have already arrived in the European Union and Japan and will in time confront the United States as well as many developing countries. In Thailand, for example, 23 percent of the population is less than 15 years old—a proportion much closer to that of the United States (21 percent) than of sub-Saharan Africa (44 percent).

Migration and urbanization. Brain drain, globalization, coastal crowding, xenophobia and discrimination, dying rural towns: One or several of these manifestations of migration and urbanization permeate life in every country on earth and connect them one with the others as never before. Economic globalization is driving massive international movements of labor, jobs, and income, raising living standards of many in the developing world but threatening the livelihood of others. Developing countries are losing skilled personnel—notably in the health professions—to Europe and North America. The migrants and receiving countries benefit, but the home countries are left with labor shortages. These and other pressures will soon arise between developing countries as neighboring societies such as Chad and the Central Africa Republic experience diverging fertility and population trends. Meanwhile, the proportion of the world's people living in urban areas will exceed 50 percent in 2005.

Poverty and inequality. Poverty and inequality are at the heart of poor health, high mortality, and lack of access to education—and these factors themselves perpetuate and deepen individual poverty and national and global inequality. In the least developed countries, health spending is about $11 per person a year—well short of the World Health Organization's recommended $30 per person needed to cover essential health care. People in poverty also tend to have reduced access to modern contraception, to live in areas of environmental degradation, and to migrate because of the "push" of survival rather than the "pull" of opportunity. In the United States, child poverty rates that vary from 7 percent to 26 percent across the states demonstrate that even some highly industrialized societies have not solved this issue.

Gender. Improving literacy for women in developing countries has been a proven factor in lowering fertility and improving reproductive health. Improving the status of women at home, in the workplace, and in social and political life (as well as involving women and men equally in their reproductive decisions) also foreshadows improved health outcomes as well as overall economic growth. The gap between current realities and progress yet to be made is arguably larger here than in any other of PRB's theme areas. The changes required are legal, economic, and cultural, but the resulting benefits cut broadly across most of our theme areas.

PRB's core themes describe challenges and opportunities that are richly interconnected. For example, improved family planning reduces the number of children to be cared for, thereby increasing the resources available to investing in each child's health and education. Fewer people also alleviate population pressures on the environment. But fewer youth also yield a smaller workforce, leading to the questions of how to support an aging population. Migration and urbanization assure that overcrowding in one country or region affects others, whether desired or not. And evidence-based attention to gender perspectives—particularly the role of women in family and community life—can propel progress in nearly every aspect of the other themes.

My final essay in this series of three will elucidate PRB's special contributions and responsibilities for ameliorating the world's new "population problems."

Bill Butz is president of the Population Reference Bureau.