English economist Thomas Malthus (1766-1834) contributed to the Enlightenment debate about the perfectibility of human society with works on poverty and overpopulation. Aware of the population growth that Europe had experienced in the late eighteenth century, he theorized that populations cannot grow without at some point reaching a limit defined by available resources, especially food. When this limit is reached, Malthus argued in his first Essay on Population (1798), populations would naturally decline through starvation and impaired fertility.

I think I may fairly make two postulata.
First, That food is necessary to the existence of man.
Second, That the passion between the sexes is necessary and will remain nearly in its present state.

These two laws, ever since we had any knowledge of mankind, appear to have been fixed laws of our nature, and, as we have not hitherto seen any...