The world has three broad ecological classes: the consumers, the middle income, and the poor. The world's poor--some 1.1 billion people--includes all households that earn less than $700 a year per family member. They are mostly rural Africans, Indians, and other South Asians. They eat almost exclusively grains, root crops, beans, and other legumes, and they drink mostly unclean water. They live in huts and shanties, they travel by foot, and most of their possessions are constructed of stone, wood, and other substances available from the local environment. This poorest fifth of the world's people earns just 2% of world income.

The 3.3 billion people in the world's middle-income class earn between $700 and $7,500 per family member and live mostly in Latin America, the Middle East, China, and East Asia. This class also includes the low-income families of the former Soviet bloc and of western industrial nations. With notable exceptions, they eat a diet based on grains and water, and lodge in modest buildings with electricity for lights, radios, and, increasingly, refrigerators and clothes washers. They travel by bus, railway, and bicycle and maintain a small stock of durable goods. Collectively, they claim 33% of world income.

The consumer class--the 1.1 billion members of the global consumer society--includes all households whose income per family member is above $7,500. We dine on meat and processed, packaged foods, and imbibe soft drinks and other beverages from disposable containers.

We have refrigerators, clothes washers and dryers, abundant hot water, dishwashers, microwave ovens, and a plethora of other electric-powered gadgets. We travel in private automobiles and airplanes, and surround ourselves with a profusion of short-lived, throwaway goods. The consumer class takes home 64% of world income--32 times as much as the poor.

The consumer class counts among its members most North Americans, West Europeans, Japanese, Australians, and the citizens of Hong Kong, Singapore, and the oil sheikdoms of the Middle East. Perhaps half the people of Eastern Europe and the Commonwealth of Independent States are in the consumer class, as are about one fifth of the people in Latin America, South Africa, and the newly industrializing countries of Asia, such as South Korea.

The top fifth of the consumer class--the rich--makes the lowly consumers seem deprived. In the U.S., for example, the highest paid fifth of income-earners takes home more than the remaining four-fifths combined, and top corporate executives earn 93 times as much as the factory workers they employ. The relation between the rich and the consumer class is a microcosm of that between the consumer class and all people. The rich earn more, consume more natural resources, and disturb ecological systems more than average consumers do.

Still, on a global scale, in terms of ecological impacts, the greatest disparities are not between the rich and the consumers but between the consumers and the middle-income class.

If our grandchildren are to inherit a planet as bounteous and beautiful as we have enjoyed, we in the consumer class must--without surrendering the quest for advanced, clean technology--eat, travel, and use energy and materials more like those on the middle rung of the world's economic ladder. The future of life on earth depends on whether we among the richest fifth of the world's people, having fully met our material needs, can turn to non-material sources for fulfillment.

This article and the box on page 8 were excerpted with permission from chapters two and ten of How Much Is Enough by Alan Durning. Norton: New York , 1992.