Overpopulation is a generally undesirable condition where an organism's numbers exceed the carrying capacity of its habitat. The term often refers to the relationship between the human population and its environment, the Earth, or smaller geographical areas such as countries.
The population has been growing continuously since the end of the Black Death, around the year 1400, although the most significant increase has been in the last 50 years, mainly due to medical advancements and increases in agricultural productivity.
The recent rapid increase in human population over the past two centuries has raised concerns that the planet may not be able to sustain present or larger numbers of inhabitants. Steve Jones, head of the biology department at University College London, has said, "Humans are 10,000 times more common than we should be". Many environmental problems, such as rising levels of atmospheric carbon dioxide, global warming, and pollution, are aggravated by the population expansion. Other problems associated with overpopulation include the increased demand for resources such as fresh water and food, starvation and malnutrition, consumption of natural resources faster than the rate of regeneration (such as fossil fuels), and a decrease in living conditions. However, some believe that waste and over-consumption, especially by wealthy nations, is putting more strain on the environment than overpopulation.
Limiting birth rates through legal regulations, educating people about family planning, increasing access to birth control and contraception, and extraterrestrial settlement have been suggested as ways to mitigate overpopulation in the future. China and other nations already have regulations limiting the birth rate, with China using the one child policy. Contraception is a response to the fact that nearly 40% of pregnancies are unintended and that in the poorest regions mothers often lack information and the means to control the size of their families.
History of concern
Concern about overpopulation is relatively recent in origin. Throughout history, populations have grown slowly despite high birth rates, due to the population-reducing effects of war, plagues and high infant mortality. During the 750 years before the Industrial Revolution, the world's population increased very slowly, remaining under 250 million. By the beginning of the 19th century, the world population had grown to a billion individuals, and intellectuals such as Thomas Malthus and physiocratic economists predicted that mankind would outgrow its available resources, since a finite amount of land was incapable of supporting an endlessly increasing population. Mercantillists argued that a large population was a form of wealth, which made it possible to create bigger markets and armies.
Demographic transition and Sub-replacement fertility
The theory of demographic transition held that, after the standard of living and life expectancy increase, family sizes and birth rates decline. However, as new data has become available, it has been observed that after a certain level of development the fertility increases again. This means that both the worry the theory generated about aging populations and the complacency it bred regarding the future environmental impact of population growth are misguided. Factors cited in the old theory included such social factors as later ages of marriage, the growing desire of many women in such settings to seek careers outside child rearing and domestic work, and the decreased need of children in industrialized settings. The latter factor 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 decline in birth rates...