Thomas Malthus's essay on the Principle of Population is well known among Darwinism's followers as well as Social Darwinists. It discusses the idea of overpopulation, which is something wasn't thought about in depth before this essay.

Malthus applied many of his ideas to the human population. He talked about how the population of humans would outgrow the resources available to them, and how this would cause problems and increased competition within the human race.

Malthusian theories, as his ideas would become known, are relating to Malthus' ideas about the population and how to keep it in check. He suggested two types of checks, positive and preventive. Positive checks were more natural causes of keeping the population down like war, disease, misery, and famine. Preventive checks were more manmade things like controlling the birth and marriage rates. He said people needed moral restraint, vice, and birth control. These preventive checks varied depending on if you were in higher or lower social classes.