As the world's population continues to grow at a frighteningly rapid rate, Malthus's classic warning against overpopulation gains increasing importance. An Essay on the Principle of Population (1798) examines the tendency of human numbers to outstrip their resources, and argues that checks in the form of poverty, disease, and starvation are necessary to keep societies from moving beyond their means of subsistence. Malthus's simple but powerful argument was controversial in his time; today his name has become a byword for active concern about humankind's demographic and ecological prospects.