The view that human beings are inexorably outstripping the globe's capacity to sustain them is one of the most vivid, powerful and enduring economic notions of the modern era. Since T. R. Malthus' 1798 treatise on population, the argument that the exponential growth of people and their demands will eventually exceed the earth's capacity has convinced successive generations of concerned scientists and laypersons that a serious "population problem" is imminent, and requires immediate action.

At first glance, this looks intuitively obvious. The planet, after all, is of a fixed size, and at some point will necessarily be unable to meet a continually rising demand upon its resources.

Human beings, however, are not like other animals. The Malthusian population-resource calculus does not consign our species to brutish subsistence, because our species, unlike all others, can consciously apply problem-solving techniques to the project of expanding its resource base and tempering its immediate environment.

Human beings can purposely transform their survival prospects, and they have done so dramatically, across the entire planet. Life expectancy today, for example, is over twice as high as a century ago. In the places conventionally deemed most prone to Malthusian calamity, moreover, improvements in longevity have been especially striking. During the past half-century, life expectancy in the less developed regions has jumped dramatically while the overall infant-mortality rate has significantly decreased. This "health explosion" not some improvident shift in procreation patterns entirely accounts for the unprecedented "population explosion" of the 20th century.

The same factors that have made our health revolution possible advances in scientific and technological knowledge, the spread of education, improvements in organizational technique, and the like have also supported a spectacular, and ongoing, increase in human productivity. Human beings, unlike any other living creatures, can progressively and intentionally augment the "resource base" that sustains them.

The point is illustrated vividly by the race between population and food over the course of the 20th century. Between 1900 and 2000, the world's population is thought to have nearly quadrupled. But this extraordinary population explosion did not consign humanity to mounting hunger. Just the opposite: Mankind enjoys a far better diet today than it did when the Earth's population was only one-fourth as large.

Although millions live under the threat of deadly hunger, the inescapable fact of the matter is that humanity has never before been as well-fed as it is today, and that our improvements in nutritional well-being coincided with the most massive and rapid increase in population in the human experience. In fact, despite our species´ exponentially increasing demand for food, there is compelling evidence that foodstuffs are actually growing ever less scarce: Real prices for corn, wheat and rice have plummeted by more than 70 percent since 1900.

A sophisticated neo-Malthusian may reason that food happens to be only one of the many resources upon which people depend and given its insatiable desire for improved consumption, mankind's appetite for resource use, which spirals upward even more rapidly than its population levels, must eventually come into disastrous collision against some limiting natural constraint.

The picture of the recent past, however, does not comport with the neo-Malthusian's proposed tableau of a world being steadily denuded of resources by unchecked population growth and consumerism. Paradoxically, despite humanity's burgeoning and indeed accelerating demand for consumption, global natural resource constraints over the past century have not obviously been tightening - and by some important indications, even appear to have been loosening. Since 1900, global gross domestic product, and thus global demand for goods and services, has increased almost 20-fold. Despite this staggering increase in demand, however, the relative price of primary commodities dropped markedly an unfathomable and inexplicable result by Malthusian logic.

Looking toward the future, the Malthusian camp and its followers in the media imagine that human demands upon a fragile planet are poised to rise indefinitely. Yet even this assumption may be wrong. For one thing, patterns of economic activity around the globe have changed radically over the past century. With affluence, the shares in overall output of agriculture and manufacturing which draw heavily upon natural resources decrease progressively, and the share accounted for by services rises correspondingly.

Second, it is far from certain that the human population will be growing throughout the coming millennium, even if humanity were to enjoy all the benefits of orderly progress. In every industrial democracy in the contemporary world, fertility levels are below the replacement level in some of them, far below it. Sub-replacement fertility, moreover, is increasingly prevalent in low-income countries as well. If the pace of global fertility decline observed over the past 35 years were to continue for another quarter-century, human numbers would peak around the year 2040, and a world depopulation would commence thereafter.

None of this is to suggest that concern with humanity's current and prospective impact on the global environment is unwarranted. Quite the contrary. Strident and confident assertions by Malthusians and eco-activists notwithstanding, we understand all too little today about this extraordinarily complex dynamic. The case for conservation of, and stewardship over, natural resources would seem compelling but cannot be promoted by a worldview that strips mankind of its unique human dignity, any more than the Earth's "carrying capacity" for human beings can be established through rules and parameters derived from populations of fruit flies.