A social theory discussed in the novel in connection with the purpose of the [[orphan trains]]. Text from Wikipedia, citations and some links intact.
Malthusianism is a school of ideas derived from the political/economic thought of the Reverend Thomas Robert Malthus, as laid out in his 1798 writings, An Essay on the Principle of Population, which describes how unchecked population growth is exponential while the growth of the food supply was expected to be arithmetical. 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 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 seem to 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.
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, misanthropy and/or 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, libertarians and free market enthusiasts, social conservatives, feminists and human rights advocates.