Overpopulation refers to a situation in which the human population exceeds the carrying capacity of a city, a region or the earth in general.

Position: The entire planet and virtually every nation is already vastly overpopulated.

Paul Erlich, Biologist, author of the The Population Explosion

Argument: overpopulation is not about population density but rather carrying capacity.

Overpopulation is about the numbers of people in an area relative to its resources and the capacity of the environment to sustain human activities; that is, to the area's carrying capacity. When is an area overpopulated? When its population can't be maintained without rapidly depleting nonrenewable resources (or converting renewable resources into nonrenewable ones) and without degrading the capacity of the environment to support the population. In short, if the long-term carrying capacity of an area is clearly being degraded by its current human occupants, that area is overpopulated.

By this standard, the entire planet and virtually every nation is already vastly overpopulated. Africa is overpopulated now because, among other indications, its soils and forests are rapidly being depleted and that implies that its carrying capacity for human beings will be lower in the future than it is now. The United States is overpopulated because it is depleting its soil and water resources and contributing mightily to the destruction of global environmental systems. Europe, Japan, the Soviet Union, and other rich nations are overpopulated because of their massive contributions to the carbon dioxide buildup in the atmosphere, among many other reasons.

Position: There is no foreseeable limit to human population.

Julian Simon, Libertarian Economist, author of The Ultimate Resource

Argument: Population growth does not constitute a Ponzi scheme

There is no reason to expect resources to run out. Instead, as Part I of this book demonstrates (on the basis of the history of long-run price declines in all natural resources, plus theory that fits the data), resources may be expected to become more available rather than more scarce. Hence there is no reason to think that consumption in the present is at the expense of future consumers, or that more consumers now imply less for consumers in the future. Rather, it is reasonable to expect that more consumption now implies more resources in the future because of induced discoveries of new ways to supply resources, which eventually leave resources cheaper and more available than if there were less pressure on resources in the present. There is a second important difference between a Ponzi scheme and this book's view of population and resources. As the Ponzi scheme begins to peter out, the price of franchises falls as sellers find it more difficult to induce more buyers to purchase, and the system begins to fall apart. But if a resource becomes in shorter supply in any period, price rises in a fashion that reduces usage (and presumably reduces population growth), and hence it constitutes a self-adjusting rather than a self-destructing system. Of course this view of population and resources runs against all "common sense" — that is, against conventional belief. But science is only interesting when it gives us knowledge that is not arrived at by common sense alone.

Related issues:
contraception, women's rights, equality, poverty, developing world