Malthusianism refers primarily to ideas derived from the political/economic thought of Reverend Thomas Robert Malthus, as laid out initially in his 1798 writings, An Essay on the Principle of Population, which describes how unchecked population growth is exponential (1→2→4→8) while the growth of the food supply was expected to be arithmetical (1→2→3→4). Malthus believed there were two types of "checks" that could then reduce the population, returning it to a more sustainable level. He believed there were "preventive" checks such as moral restraints (abstinence, delayed marriage until finances become balanced), and restricting marriage against persons suffering poverty and/or defects. Malthus believed in "positive checks", which lead to 'premature' death: disease, starvation, war, resulting in what is called a Malthusian catastrophe. The catastrophe would return population to a lower, more "sustainable", level. The term has been applied in different ways over the last two hundred years, and has been linked to a variety of other political and social movements, but almost always refers to advocates of population control.
Neo-Malthusianism generally refers to people with the same basic concerns as Malthus, who advocate for population control programs, to ensure resources for current and future populations. In Britain the term Malthusian can also refer more specifically to arguments made in favour of preventive birth control, hence organisations such as the Malthusian League. Neo-Malthusians seem to differ from Malthus's theories mainly in their enthusiasm for contraceptive techniques. Malthus, as a devout Christian, believed that "self-control" (abstinence) was preferable to artificial birth control. In some editions of his essay, Malthus did allow that abstinence was unlikely to be effective on a wide scale, thus advocating the use of artificial means of birth control as a solution to population "pressure". Modern "neo-Malthusians" are generally more concerned than Malthus was with environmental degradation and catastrophic famine than with poverty.
Many critics believe that the basis of Malthusian theory has been fundamentally discredited in the years since the publication of Principle of Population, often citing major advances in agricultural techniques and modern reductions in human fertility. Many modern proponents believe that the basic concept of population growth eventually outstripping resources is still fundamentally valid, and "positive checks" are still likely in humanity's future if there is no action to curb population growth.
Malthusian terms can carry a pejorative connotation indicating excessive pessimism and inhumanity. Some proponents of Malthusian ideas believe that Malthus's theories have been widely misunderstood and misrepresented; these proponents believe his reputation for pessimism and inhumanity is ill deserved. Malthusian ideas have attracted criticism from a diverse range of differing schools of thought, including Marxists and socialists to Fascists, libertarians and free market enthusiasts, American conservatives, feminists and human rights advocates.
Malthus was not the first to outline the problems he perceived. The original essay was part of an ongoing intellectual discussion at the end of the 18th century regarding the origins of poverty. Principle of Population was specifically written as a rebuttal to thinkers like William Godwin and the Marquis de Condorcet, and Malthus's own father who believed in the perfectibility of humanity. Malthus believed humanity's ability to reproduce too rapidly doomed efforts at perfection and cause various other problems.
His criticism of the working class's tendency to reproduce rapidly, and his belief that this, rather than exploitation by capitalists, led to their poverty, brought widespread criticism of his theory.
Malthusians perceived ideas of charity to the poor typified by Tory paternalism were futile, as these would only result in increased numbers of the poor, and was developed into Whig economic ideas exemplified by The Poor Law Amendment Act of 1834. The Act was described by opponents as "a Malthusian bill designed to force the poor to emigrate, to work for lower wages, to live on a coarser sort of food", which initiated the construction of workhouses despite riots and arson.
Malthus revised his theories in later editions of An Essay on the Principles of Population, taking a more optimistic tone, although there is some scholarly debate on the extent of his revisions. According to Dr. Dan Ritschel of the Center for History Education at the University of Maryland,
The great Malthusian dread was that "indiscriminate charity" would lead to exponential growth in the population in poverty, increased charges to the public purse to support this growing army of the dependent, and, eventually, the catastrophe of national bankruptcy. Though Malthusianism has since come to be identified with the issue of general over-population, the original Malthusian concern was more specifically with the fear of over-population by the dependent poor!
One of the earliest critics was David Ricardo. Malthus immediately and correctly recognised it to be an attack on his theory of wages. Ricardo and Malthus debated this in a lengthy personal correspondence.
Another one of the 19th century critics of Malthusian theory was Karl Marx who referred to it as "nothing more than a schoolboyish, superficial plagiary of De Foe, Sir James Steuart, Townsend, Franklin, Wallace" (in Capital, see Marx's footnote on Malthus from Capital - reference below). Marx and Engels described Malthus as a "lackey of the bourgeoisie." Socialists and communists believed that Malthusian theories "blamed the poor" for their own exploitation by the capitalist classes, and could be used to suppress the proletariat to an even greater degree, whether through attempts to reduce fertility or by justifying the generally poor conditions of labour in the 19th century.
One proponent of Malthusianism was the novelist Harriet Martineau whose circle of acquaintances included Charles Darwin, and the ideas of Malthus were a significant influence on the inception of Darwin's theory of evolution. Darwin was impressed by the idea that population growth would eventually lead to more organisms than could possibly survive in any given environment, leading him to theorise that organisms with a relative advantage in the struggle for survival and reproduction would be able to pass their characteristics on to further generations. Proponents of Malthusianism were in turn influenced by Darwin's ideas, both schools coming to heavily influence the field of eugenics. Henry Fairfield Osborn advocated "humane birth selection through humane birth control" in order to avoid a Malthusian catastrophe by eliminating the "unfit."
Malthusianism generally became a less common intellectual tradition as the 19th century advanced, mostly as a result of technological increases, the opening of new territory to agriculture, and increasing international trade. In 1888, political economist William Petty wrote that larger populations should be a benefit to society, claiming “[I]t is more likely that one ingenious curious man may rather be found out amongst 4,000,000 than 400 persons.” Although a "conservationist" movement in the United States concerned itself with resource depletion and natural protection in the first half of the twentieth century, Desrochers and Hoffbauer write, "It is probably fair to say... that it was not until the publication of Osborn’s and Vogt’s books  that a Malthusian revival took hold of a significant segment of the American population."
Modern Malthusianism 
Malthusian theory is a recurrent theme in many social science venues. John Maynard Keynes, in Economic Consequences of the Peace, opens his polemic with a Malthusian portrayal of the political economy of Europe as unstable due to Malthusian population pressure on food supplies. Many models of resource depletion and scarcity are Malthusian in character: the rate of energy consumption will outstrip the ability to find and produce new energy sources, and so lead to a crisis.
In France, terms such as "politique malthusienne" ("Malthusian politics") refer to population control strategies. The concept of restriction of population associated with Malthus morphed, in later political economic theory, into the notion of restriction of production. In the French sense, a "Malthusian economy" is one in which protectionism and the formation of cartels is not only tolerated but encouraged.
One critic of Neo-Malthusian theory (but not of birth control and abortion in general), was Vladimir Lenin, the leader of the Bolshevik Party and main architect of the Soviet Union. India was the first country to start a population control policy in 1952.
"Neo-Malthusianism" may be used as a label for those who are concerned that overpopulation may increase resource depletion or environmental degradation to a degree that is not sustainable with the potential of ecological collapse or other hazards. The term is also often immediately connected with eugenics.
The rapid increase in the global population of the past century exemplifies Malthus's predicted population patterns; it also appears to describe socio-demographic dynamics of complex pre-industrial societies. These findings are the basis for neo-malthusian modern mathematical models of long-term historical dynamics.
There was a general "neo-Malthusian" revival in the 1950s, 60s and 70s after the publication of two influential books in 1948 (Fairfield Osborn's Our Plundered Planet and William Vogt's Road to Survival). During that time the population of the world rose dramatically. Many in environmental movements began to sound the alarm regarding the potential dangers of population growth. The Club of Rome published a famous book entitled The Limits to Growth in 1972. The report and the organisation soon became central to the neo-Malthusian revival. Paul R. Ehrlich has been one of the most prominent neo-Malthusians since the publication of The Population Bomb in 1968. Other prominent Malthusians include the Paddock brothers, authors of Famine 1975! America's Decision: Who Will Survive?.
Many journalists, academics and other commentators have criticized the neo-malthusian revival. In light of the green revolution, which has brought substantial increases in food production sufficient to keep up with rapid population growth, some of the more dramatic Malthusian warnings now appear to have been overstated or premature. Julian Simon, a noted cornucopian has written that contrary to neo-malthusian theory, the earth's "carrying capacity" is essentially limitless. Responding to Simon, Al Bartlett forcefully reiterates the potential of population growth as an exponential (or as expressed by Malthus, "geometrical") curve to outstrip both natural resources and human ingenuity. Bartlett writes and lectures particularly on energy supplies, and describes the "inability to understand the exponential function" as the "greatest shortcoming of the human race".
Prominent neo-malthusians such as Paul Ehrlich maintain that ultimately, population growth on Earth is still too high, and will eventually lead to a serious crisis. The increase in food prices from 2007 to present has inspired further Malthusian arguments regarding the prospects for global food supply.
In fiction 
In Aldous Huxley's classic novel (published 1932) about a fictional Brave New World, he integrates Malthusianism as a central theme, replete with numerous mentions of "Malthusian belts". In his future world, recreational sex is an integral part of society. According to the World State, sex is a social activity, rather than a means of reproduction (sex is encouraged from early childhood). The few women who can reproduce are conditioned to use birth control, even wearing a "Malthusian belt" (which resembles a bandolier and holds "the regulation supply of contraceptives") as a popular fashion accessory. The maxim "everyone belongs to everyone else" is repeated often, and the idea of a "family" is considered pornographic; sexual competition and emotional, romantic relationships are rendered obsolete because they are no longer needed. Marriage, natural birth, parenthood, and pregnancy are considered too obscene to be mentioned in casual conversation. Thus, society has developed a new idea of reproductive comprehension.
See also 
- Cornucopianism: a counter-Malthusian school of thought
- Food Race
- Garrett Hardin
- Law of Rent
- Malthusian trap
- NSSM 200: a National Security Council Study advocating population reduction in selected countries for U.S. security and interests
- Peak Oil
- Political demography
- Population ecology
- Risks to civilization, humans and planet Earth
- Subsistence theory of wages
- "The dismal science"
- Tragedy of the Commons
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