人口論
In the 20th century, population planning proponents have drawn from the insights of Thomas Malthus, a British clergyman and economist who published "An Essay on the Principle of Population" in 1798. Malthus argued that, "Population, when unchecked, increases in a geometrical ratio. Subsistence only increases in an arithmetical ratio." He also outlined the idea of "positive checks" and "preventative checks." "Positive checks", such as diseases, wars, disasters, famines, and genocides are factors which Malthus believed could increase the death rate.