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Overpopulation

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Map of countries by population —showing the population of the China and India in the billions. (See List of countries by population.)
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Map of countries by population —showing the population of the China and India in the billions. (See List of countries by population.)

Areas of high population densities, calculated in 1994.
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Areas of high population densities, calculated in 1994.

Overpopulation is the condition of any organism's numbers exceeding the carrying capacity of its ecological niche. In common parlance, the term usually refers to the relationship between the human population and its environment, Earth.

Contents

Introduction

Overpopulation is not simply a function of the number or density of the individuals, but rather the number of individuals compared to the resources (ie. food production) they need to survive. In other words, it is the ratio of population divided by resources. If a given environment has a population of ten, but there is food and drinking water enough for only nine, then that environment is overpopulated, while if the population is 100 individuals but there are food and water enough for 200, then it is not overpopulated.

Overpopulation can result from increases in births, a decline in mortality rates, which is linked to increases in life expectancy, or from an unsustainable use and depletion of resources. Advances in technology theoretically can mitigate overpopulation by increasing the productivity of natural resources.

Resources to be taken into account when evaluating when an ecological niche is overpopulated include clean water and air, food, shelter, warmth, or other issues related to survival. In the case of human beings, there are others such as arable land and medical care; for all but tribes with primitive lifestyles, lesser resources such as employment, money or other economic resources, education, fuel, electricity, healthcare, proper sewage treatment, waste management, and transportation. The problem of waste may yet prove the most limiting factor of overpopulation.

In the context of human societies, overpopulation occurs when the population density is so great as to actually cause an impaired quality of life, serious environmental degradation, or long-term shortages of essential goods and services. Of course, it is possible for very sparsely-populated areas to be "overpopulated", as the area in question may have very meagre or non-existent capability to sustain human life (ie the middle of the Sahara desert). Sometimes, overpopulation is not necessarily an imbalance between the number of individuals compared to the resources needed for survival, or a ratio of population over resources. This is because such an imbalance may be caused by any number of other factors such as bad governance, war, corruption or endemic poverty. When other such factors come into play in a certain locale, and population density cannot be shown to be the major cause, overpopulation cannot be conclusively said to occur.

By the standards of existence without misery; adequate drinking water, adequate food, and adequate sewage treatment capacity, the human race has been in a state of overpopulation for decadesRon Nielsen, The little green handbook, Picador, New York (2006) ISBN 0-312-42581-4. The world's human population has quadrupled in the course of the last hundred years. It is currently growing by more than 75 million people per year, down from a peak numerical growth of about 88 million per year in the late 1980s. About half the world lives in nations with sub-replacement fertility, and population growth in those countries is due to immigration.

Malthus' theory

Thomas Malthus argued in An Essay on the Principle of Population, first published in 1798, that if left unrestricted, human populations would continue to grow until they would become too large to be supported by the food grown on available agricultural land. He proposed that, while resources tend to grow linearly, population grows exponentially. At that point, the population would be restrained through mass famine and starvation. Malthus argued for population control, through "moral restraint", to avoid this happening. As the population of a species exceeds the amount of available resources, it decreases, sometimes sharply, since the lack of resources causes mortality (deaths) to increase. This process keeps the population in check and ensures it doesn't exceed the amount of resources.

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. More recent examples also exist [link].

Population as a function of food availability

Some recent research and experiments question the contemporary belief that human populations are a naturally explosive independent variable. Thinkers such as David Pimentel, a professor from Cornell University, Virginia Abernethy, Alan Thornhill, Russell Hopffenberg and author Daniel Quinn propose that like other animals, human populations predictably grow and shrink according to their available food supply – populations grow in an abundance of food, and shrink in times of scarcity. 
Proponents of this theory indicate that every time food production is intensified to feed a growing population, the population responds by increasing even more. Some human populations throughout history support this theory, as consistent population growth began with the Neolithic Revolution, followed by subsequent agricultural revolutions, and thus food supply began consistently increasing and continues to do so in the present. This can be observed in cultural contexts, as populations of hunter-gatherers fluctuate in accordance with the amount of available food and are significantly smaller than populations of agriculturalists, who increase the amount of food available by putting more land under agriculture.


Critics of this idea point out that birth rates are lowest in developed nations, which also have the highest access to food. In fact, some developed countries have both a diminishing population and an abundant food supply (Italy and Japan). Thus human populations do not always grow to match the available food supply. Factors cited in the decline of birth rates include such social factors: increased access to contraception; later ages of marriage; the growing desire of many women in such settings to seek careers outside of child rearing and domestic work; and the decreased need of children in industrialized settings. The latter explanation stems from the fact that children perform a great deal of work in small-scale agricultural societies, and work less in industrial ones; it has been cited to explain the drop-off in birth rates worldwide in all industrializing regions.


Food production has outpaced population growth, meaning that there is now more food available per person than ever before in history (although as with other resources this is distributed very unevenly; rich nations have a super-abundance of food, while poor nations often suffer famines). Studies project that food production can continue to increase until at least 2050.   Net growth by mid century is predicted by optimistic sources to be 34 million per year in contrast to the roughly 76 million per year that was seen from 2000 to 2005. [link] Another United Nations report projects that world population will peak at 9.2 billion around 2075 [link][link].



Population projections




United Nation's medium variant population projections by location.

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United Nation's medium variant population projections by location.






According to projections by the Population Division of the United Nations revised in 2004 [link], the population of the world will stabilize at 9.1 billion by 2050 due to demographic transition. The UN has consistently revised its population projections downwards over the last 10 years. Birth rates are now falling in some developing countries, while the population in many developed countries would also fall without immigration [link].


David Pimentel, a professor of ecology and agricultural sciences at Cornell University, predicts that population outcomes for the 22nd century range from 2 billion people (characterised as thriving in harmony with the environment), to 12 billion people (characterised as miserable and suffering a difficult life with limited resources and widespread famine). [link]



Effects of overpopulation

The world's current agricultural production is defacto not sufficient to feed everyone living on the earth today, given the realities of capital distribution and logistics of food supply.  Moreover, many analysts 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 directly in famines and deforestation and indirectly in pandemic disease and war.


Some other problems which are associated with or exacerbated by human overpopulation:




The demographic transition

The theory of demographic transition holds that within a generation after the standard of living and life expectancy increases, family sizes start dropping.  In support of this theory is the contention that many estimates of maximum global population since the 1960s, when the "population explosion" became a worry, has been lower than 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.


Today about half the world lives in nations with sub-replacement fertility. All the nations of East Asia, with the exceptions of Mongolia, the Philippines, and Laos are below this level. Russia and Eastern Europe are in most cases quite clearly having a birth dearth.  Western Europe also is below replacement fertility levels. In the Middle East Iran, Tunisia, Algeria, Turkey, and Lebanon are below replacement. Canada, Australia, and New Zealand are similar to Western Europe, while the United States is just barely below replacement with about 2.0 births per female. All four of these nations still have growing populations due to high rates of immigration. The countries having the lowest fertility are Hong Kong, Macao, Singapore and Lithuania.


Another version of demographic transition is that of Virginia Abernethy in Population Politics, in which she claims that the demographic transition is primarily in effect for nations where women enjoy a special status (see Fertility-opportunity theory). In strongly patriarchal nations, where she claims women enjoy few special rights, a high standard of living tends to result in population growth.  She argues that foreign aid to poor countries must include significant components designed to improve the education, human rights, political rights, political power, and also to equalize the economic and sexual status and power of women.


Her theory runs counter to some of the available empirical evidence. For example Iran had a Total Fertility Rate of 1.82 children per couple in 2005, which is below the replacement rate of 2.1 to 2.3 children per couple needed to maintain population. Iran is widely perceived as a patriarchal nation, and yet any population growth that occurred there came not from increased birth rates, but from decreased mortality rates, i.e. not from a lack of reproductive rights.


"Demographic entrapment" is a concept developed by Maurice King that has not gained acceptance. King describes a country stuck in an early stage of the demographic transition, with a persistently high birth rate despite economic growth and/or increased life expectancy.  Many sub-Saharan countries are quoted as examples of demographic entrapment (e.g. Uganda), where the total fertility rate stands at 6.71 children born per woman, even though the economy has shown steady growth since 1990 and life expectancy stands at 53 (figures from the 2006 edition of the CIA world factbook).  Other African countries, such as Zimbabwe, have seen their population growth slow down, but not stop, on account of a decrease in life expectancy and an increase in emigration, with the birth rate remaining high: the democratic transition in reverse[link].



Overpopulation as a social issue

The density of population has an impact on a broad range of social and economic issues, such as land prices, housing costs and access to medical care. 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.


The growth of medical schools is arguably not keeping up with population expansion. A shortage of educated doctors and medicine per capita aggravates the worldwide problems of unnecessarily high mortality rates (especially infant mortality), adds to human misery and also adds to medical costs. Fewer doctors per capita causes the price of medical services to rise. This can either cause a government subsidised healthcare system to be unsustainable, or lead to increased medical bills and health insurance costs.



Optimistic viewpoints on population growth

Optimists believe that the 2006 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. In The Skeptical Environmentalist, Bjørn Lomborg argued that because of the falling rate of population growth in some regions, and because of new technologies, there is little problem with overpopulation. The assumptions that underlie these claims, however, have been strongly criticisedM. Wackernagel, C. Manfreda and D. Deumling, Ecological Footprint of Nations, November 2002 Update: How Much Nature do they Use? How Much Nature do they Have?'', Redefining Progress, San Francisco, Ca. (2002).  One criticism is that poor people can't afford such technologies.  One counterargument is that meat production is very energy inefficient, so that food availability would increase if protein sources like soybeans were used in lieu of meat, since humans would then be eating lower on the food chain.  However, given that this would require enough people giving up meat for soy and other plant based protein to make an agricultural shift in production meaningful, this argument may be unrealistic.  It also assumes that the grain fed to livestock is fit for human consumption. [link]


Optimists claim that there will be no mass starvation due to a shortage of arable land.  About 21% of the earth's land is arable. In the past, 160 acres (650,000 m²) of farm land crops fed one person. Hydroponics in autonomous building gardens and greenhouses grow more food in less space, although the requirement for fresh water may limit this technology. Most food production experiments have used vegetable farming because it can support an adult from as little as 15 m² of land. High crop yield vegetables like potatoes and lettuce do not waste space with inedible plant parts, like stalks, husks, vines, and inedible leaves. New varieties of selectively bred and hybrid plants have larger edible parts (fruit, vegetable, grain) and smaller inedible parts. With new technologies, it is now possible to grow crops on some unarable land under certain conditions. Aquaculture could theoretically dramatically increase available area. Hydroponics and food from bacteria and fungi, like Quorn, may allow the growing of food without having to consider land quality, climate, or even available sunlight, although such a process may be very energy-intensive.


In defending these new technologies, optimists, also called cornucopians, can overlook the fact that not all arable land will remain so if it is used for agriculture, as some marginal land can only be made to produce food by unsustainable practices like slash-and-burn agriculture.  They have also been criticized for failing to account for future shortages in fossil fuels, required for modern agriculture.  (See Hubbert peak) They often counter that there will be ample fossil fuel supplies until  after fossil fuel-reliant technologies have been phased out, [link] or even that Hubbert's "peak oil" theory is wrong and that we will never run out of oil in the foreseeable future [link].



Extra-terrestrial population projections


Even as far back as 1798, Thomas Malthus stated in An Essay on the Principle of Population:


"The germs of existence contained in this spot of earth, with ample food, and ample room to expand in, would fill millions of worlds in the course of a few thousand years." 


Gerard O'Neill has suggested that, taking the completion of his proposed Island One as year zero, maximum population growth could then result in a population of 7.3 billion within 35 years*The High Frontier (1976, 2000) Gerard O'Neill, Apogee Books ISBN 1-896522-67-X.  Space advocates and others have made various projections regarding future human population growth in outer space. Marshall Savage (1992, 1994) has projected a population of five quintillion throughout the solar system by 3000, with the majority in the asteroid beltMarshall Savage, (1992, 1994) . Little, Brown. ISBN 0-316-77163-5. Clarke, a fervent supporter of Savage, now argues that by 2057 there will be humans on the Moon, Mars, Europa, Ganymede, Titan and in orbit around Venus, Neptune and  Pluto*Reader's Digest February 2001[link].  Freeman Dyson (1999) favours the Kuiper belt as the future home of humanity, suggesting this could happen within a few centuriesFreeman Dyson, The Sun, The Genome, and The Internet  (1999) Oxford University Press. ISBN 0-19-513922-4.


K. Eric Drexler, famous inventor of the futuristic concept of Molecular Nanotechnology, has suggested in Engines of Creation that colonising space will mean breaking the Malthusian limits to growth forever for the human species.  Considered to be the most mind boggling prediction is that of John S. Lewis in . Bordering on the overpopulation of the solar system itself, Lewis suggests that the staggering resources of the solar system could support 10 quadrillion (10^15) people.


Many authors (eg. Carl Sagan, Arthur C. ClarkeGreetings, Carbon-Based Bipeds! (1999) Arthur C. Clarke, Voyager ISBN 0-00-224698-8, Isaac AsimovThe Good Earth Is Dying (1971) Isaac Asimov (published in Der Spiegel)) have argued that shipping the excess population into space is no solution to human overpopulation, saying that (Clarke, 1999) "the population battle must be fought or won here on Earth."  It is not the lack of resources in space that they see as the problem (as books such as Mining the sky demonstrate (1996) John S. Lewis. Addison Wesley. ISBN 0-201-47959-1); it is the sheer physical impracticality of shipping vast numbers of people into space to "solve" overpopulation on Earth that these authors and others regards as absurd.



Overpopulation as a theme in fiction


In 1729, Jonathan Swift wrote the satirical essay "A Modest Proposal" where he suggests one solution for both the problem of overpopulation and the growing numbers of undernourished people in Ireland can be solved by the breeding of infants as food.


Science fiction writers have frequently made famous predictions in which they portrayed dystopian futures in which the world has become massively overpopulated. This became a major theme in the 1950s and 1960s. One of the first depictions of future megacities was The Caves of Steel by Isaac Asimov (1954). The 1960s saw increasing anxiety about the prospect of the exponential growth of world population, underscored by the publication of Paul R. Ehrlich's non-fiction The Population Bomb, in 1968. 


In the same year, John Brunner's science-fictional Stand on Zanzibar was published. This is perhaps the definitive overpopulation novel to date, though others such as Harry Harrison's Make Room! Make Room! also became a powerful movie (Soylent Green). Logan's Run is a novel by William F. Nolan and George Clayton Johnson (1967), describing a dystopian future society in which the population is kept young by euthanizing everyone who reaches a certain age, thus neatly avoiding the problem of overpopulation. A 1972 film called  [Z.P.G.] featured an overpopulated, very polluted future Earth, whose world government practices Zero Population Growth, executing persons who violate the 30-year ban on procreation.


J. G. Ballard's story "Billennium" pictures a future in which every individual has four, then just three, square metres of living space. Frederik Pohl in "The Space Merchants" described a future in which even public staircases are rented out as living spaces. Robert Silverberg's The World Inside imagines a future with mile high towers holding a million people each. James Blish and Norman L. Knight in A Torrent of Faces imagine a nightmarish future of 1,000 billion living in just 100,000 cities on Earth.


From the 1980s, there has been an evident lessening of such fears in science fiction. Cyberpunk fiction, such as that of William Gibson, often depicts huge, sprawling cities. Yet these are as remarkable for their energy and diversity as for their more dystopian characteristics.



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