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Malthus' theory

Early in the 19th century, Thomas Malthus argued in An Essay on the Principle of Population that, if left unrestricted, human populations would continue to grow until they would become too large to be supported by the available agricultural land. At that point, the population would be restrained though mass famine and starvation. Malthus argued for population control, through "moral restraint", to avoid this happening.

Over the two hundred years which followed, famine has overtaken numerous individual regions; proponents of this theory state that these famines were examples of Malthusian catastrophes. On a global scale, however, food production has grown faster than population. It has often been argued that future pressures on food production, combined with threats to other aspects of the earth's habitat such as global warming, make overpopulation a still more serious threat in the future. Perhaps the best-known example of such an argument is The Limits to Growth, a report produced for the Club of Rome in the early 1970s.

Other studies have countered with the claim that the current population level of over six billion may be supported by current resources, or that the global population may grow to ten billion and still be within the Earth's carrying capacity. The assumptions that underlie these claims, however, have been strongly criticised.

The world's current agricultural production, if it were distributed evenly, would be sufficient to feed everyone living on the Earth today. However, many critics hold that, in the absence of other measures, simply feeding the world's population well would only make matters worse, natural growth will cause the population to grow to unsustainable levels, and will result in famines.

However, others contend that within a generation after the standard of living and life expectancy starts increasing, family sizes start dropping in what is termed the demographic transition. In support they point to the contention that every estimate of maximum global population since the 1960s, when the "population explosion" became a worry, has been significantly lower than the previous estimates. Among those holding this view are the ecologist Paul Colinvaux, who writes on the topic in Why Big Fierce Animals are Rare, and The Fates of Nations.

Another point of view on population vs. the standard of living is that of Virginia Abernathy in Population Politics, in which she shows evidence that this effect only holds true in nations where women enjoy a relatively high status, and in strongly-patriarchal nations where women enjoy few rights, a higher standard of living tends to result in population growth.

Some approach overpopulation with a "survival-of-the-fittest," "laissez-faire" attitude, arguing that if the Earth's ecosystem becomes overtaxed, it will naturally regulate itself. In this mode of thought, disease or starvation are "natural" means of lessening population. Others argue that economic development is the best way to reduce population growth. Many developed countries in the world today, such as Italy, now have declining populations (ignoring the effects of immigration).

In either case, it is often held that the most productive approach is to provide a combination of help targeted towards population control and self-sufficiency. One of the most important measures proposed for this effort is the empowerment of women educationally, economically, politically, and in the family. The value of this philosophy has been substantially borne out in cases where great strides have been taken to this goal: where women's status has dramatically improved, there has generally been a drastic reduction in the birthrate to more sustainable levels. Other measures include effective family planning programs, local renewable energy systems, sustainable agriculture methods and supplies, reforestation, and measures to protect the local environment.

There are some examples from history suggesting that when population pressures become too great, the results may, indeed, include war, famine, epidemic disease, and environmental devastation. On the other hand, in many other cases countries with large populations relative to their resources, such as Japan and the Netherlands, have achieved high living standards with limited immediate environmental impact.

Overpopulation as social issue

The density of population has an impact on a broad range of social and economic issues, such as land prices and housing costs. For example, relatively densely populated countries such as Japan have higher land prices than less densely populated countries such as Australia, and even in that country, land prices have doubled and redoubled as the population has increased. It is sometimes argued that reducing the populations of some areas, such as large cities, would have positive benefits for these reasons.

See also Paul Ehrlich, Julian Simon, population density, Underpopulation