<P> Malthusianism is the idea that population growth is potentially exponential while the growth of the food supply is linear . It derives from the political and economic thought of the Reverend Thomas Robert Malthus, as laid out in his 1798 writings, An Essay on the Principle of Population, Malthus believed there were two types of "checks" that in all times and places kept population growth in line with the growth of the food supply: "preventive checks", such as moral restraints (abstinence, delayed marriage until finances become balanced), and restricting marriage against persons suffering poverty or perceived as defective, and "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 . Malthusianism has been linked to a variety of political and social movements, but almost always refers to advocates of population control . </P> <P> Neo-Malthusianism is the advocacy of 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 organizations such as the Malthusian League . Neo-Malthusians differ from Malthus's theories mainly in their enthusiasm for contraception . Malthus, 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 . </P> <P> Malthusianism has attracted criticism from a diverse range of differing schools of thought, including Marxists and socialists, libertarians and free market enthusiasts, social conservatives, feminists and human rights advocates, characterising it as excessively pessimistic, misanthropic or inhuman . Many critics believe Malthusianism has been discredited since the publication of Principle of Population, often citing 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 . </P>

What is the most effective measure of population control according to malthus