Such worries about overpopulation and resource scarcity have a long history. The Roman writer Tertullian warned in 200 A.D. that "we men have actually become a burden to the earth" and that "the fruits of nature hardly suffice to support us." In 1798 the Rev. Thomas Robert Malthus published An Essay on the Principle of Population, in which he claimed that population growth would always outstrip food supplies, inevitably resulting in famine, pestilence, and war. Biologist Paul Ehrlich notoriously updated Malthus' gloomy predictions in his 1968 book The Population Bomb, which predicted that hundreds of millions of people would die of famine in the 1970s.