Close to the Zocalo, Mexico City's great central square, lies the barrio of Morelos, a vast warren of dusty, potholed streets and narrow entryways. The passages lead to a gloomy world. On each side of a roofless patio is a ten- room jumble. Each room holds a family; each family averages five people. The only bathrooms -- two to serve 100 people -- are located at the back of the patio. The odor of grease and sewage permeates the air. Flies buzz relentlessly. The people who live here are considered lucky.
In the shantytowns on Mexico City's outskirts, tens of thousands of people shelter in huts made of cardboard with aluminum roofs. There is no running water and no sanitation. The stench is overpowering: garbage and human waste heap up in piles. Rats roam freely, like stray domestic animals.
To the more privileged, those scenes look like a science-fiction vision of civilization's breakdown, perhaps after a nuclear war. In fact, Mexico City has been described as the anteroom to an ecological Hiroshima. With 20 million residents -- up from 9 million only 20 years ago -- the Mexican capital is considered the most populous urban center on earth. Mexico City has been struck not by military weapons but by a population bomb.
Ultimately, no problem may be more threatening to the earth's environment than the proliferation of the human species. Today the planet holds more than 5 billion people. During the next century, world population will double, with 90% of that growth occurring in poorer, developing countries. African nations are expanding at the fastest rate. During the next 30 years, for example, the population of Kenya (annual growth rate: 4%) will jump from 23 million to 79 million; Nigeria's population (growth rate: 3%) will soar from 112 million to 274 million. Expansion is slower in Brazil, China, India and Indonesia, but in those countries the sheer size of existing populations translates into a huge increase in people.
In the poorest countries, growth rates are outstripping the national ability to provide the bare necessities -- housing, fuel and food. Living trees are being chopped down for fuel, grasslands overgrazed by livestock, and croplands overplowed by desperate farmers. Horrifying images of starvation in northeastern Africa have captured world attention in the past decade. In India, according to government reports, 37% of the people cannot buy enough food to sustain themselves. Warned Shri B.B. Vohra, vice chairman of the Himachal Pradesh state land-use board in northern India: "We may be well on the way to producing a subhuman kind of race where people do not have enough energy to deal with their problems."
Prospects are so dire that some environmentalists urge the world to adopt the goal of cutting in half the earth's population growth rate during the next decade. "That means a call for a two-child family for the world as a whole," explained Lester Brown, president of the Worldwatch Institute. "In some countries there may be a need to set a goal of one child per family." That is a daunting challenge. During the past decade, many of the world's poor nations condemned the notion of family planning as an imperialist and racist scheme touted by the developed world. Yet today virtually all Third World countries are committed to limiting population growth.