The social and economic gap between the world’s richest 1 billion people and its poorest 1 billion has no historical precedent. Not only is this gap wide, it is widening. The poorest billion are trapped at a subsistence level and the richest billion are becoming wealthier with each passing year. The economic gap can be seen in the contrasts in nutrition, education, disease patterns, family size, and life expectancy.

World Health Organization (WHO) data indicate that roughly 1.2 billion people are undernourished, underweight, and often hungry. At the same time, roughly 1.2 billion people are overnourished and overweight, most of them suffering from excessive caloric intake and exercise deprivation. So while 1 billion people worry whether they will eat, another billion should worry about eating too much.

Disease patterns also reflect the widening gap. The billion poorest suffer mostly from infectious diseases—malaria, tuberculosis, dysentery, and AIDS. Malnutrition leaves infants and small children even more vulnerable to such infectious diseases. Unsafe drinking water takes a heavier toll on those with hunger-weakened immune systems, resulting in millions of fatalities each year. In contrast, among the billion at the top of the global economic scale, it is diseases related to aging and lifestyle excesses, including obesity, smoking, diets rich in fat and sugar, and exercise deprivation, that cause most deaths.

Education levels reflect the deep divide between the rich and the poor. In some industrial countries—for example, Canada and Japan—more than half of all young people now graduate from college with either two- or four-year degrees. By contrast, in developing countries 115 million youngsters of elementary school age are not in school at all. Although five centuries have passed since Gutenberg invented the printing press, nearly 800 million adults are illiterate. Unable to read, they are also excluded from the use of computers and the Internet. Without adult literacy programs, their prospects of escaping poverty are not good.

Close to 1 billion people live in countries where population size is essentially stable. But another billion or so live in countries where population is projected to double by 2050. The world’s illiterates are concentrated in a handful of the more populous countries, most of them in Asia and Africa. Prominent among these are India, China, Pakistan, Bangladesh, Nigeria, Egypt, Indonesia, and Ethiopia, plus Brazil and Mexico in Latin America. From 1990 to 2000, China and Indonesia made large gains in reducing illiteracy. Other countries also making meaningful progress were Mexico, Nigeria, and Brazil. However, in four other populous countries—Bangladesh, Egypt, Pakistan, and India—the number of illiterates increased.

Illiteracy and poverty tend to reinforce each other because illiterate women typically have much larger families than literate women do and because each year of schooling raises earning power by 10–20 percent. In Brazil, for instance, illiterate women have more than six children each on average; literate women have only two. Additionally, illiterate women are trapped by large families and minimal earning power.

To be poor often means to be sick. As with illiteracy, poverty and ill health are closely linked. Health is closely related to access to safe water, something that 1.1 billion people lack. Waterborne diseases claim more than 3 million lives each year, mostly as a result of dysentery and cholera. These and other waterborne diseases take their heaviest toll among children. Infant mortality in affluent societies averages 8 per 1,000 live births; in the 50 poorest countries, it averages 97 per 1,000—nearly 13 times as high.

The poor and uneducated often do not understand the mechanisms of infectious disease transfer and thus fail to take steps to protect themselves. In addition, those with immune systems weakened by hunger are more vulnerable to common infectious diseases. Poverty also means children are often not vaccinated for routine infectious diseases, even though the cost may be just pennies per child.

The connection between poverty and disease is strong, but it has been broken for most of humanity by economic development. The challenge now is to break this link for that remaining minority who do not have access to safe water, vaccines, education, and basic health care.

Hunger is the most visible face of poverty. The U.N. Food and Agriculture Organization estimates that 852 million of the world’s people are chronically hungry. They are not getting enough food to achieve full physical and mental development and to maintain adequate levels of physical activity.

The majority of the underfed and underweight are concentrated in the Indian subcontinent and sub-Saharan Africa—regions that contain 1.4 billion and 750 million people, respectively. Twenty-five years ago, the nutritional status of Asia’s population giants, India and China, was similar, but since then China has eliminated most of its hunger, whereas India has made limited progress. During this last quarter-century, China has accelerated the shift to smaller families. While gains in food production in India during this period were absorbed largely by population growth, those in China went mostly to raising individual consumption.

Malnutrition takes its heaviest toll among the young, who are most vulnerable during their rapid physical and mental development. In both India and Bangladesh, almost half of all children under five are underweight and malnourished. In Ethiopia, 47 percent of children are undernourished, while in Nigeria the figure is 31 percent—and these are two of Africa’s most populous countries.

Although it is not surprising that those who are underfed and underweight are concentrated in developing countries, it is perhaps surprising that most of them live in rural communities. More often than not, the undernourished are either landless or they live on plots of land so small that they are effectively landless. Those who live on the well-watered plains are usually better nourished. It is those who live on marginal land—land that is steeply sloping or semiarid—who are hungry.