10. In 1798, Thomas Malthus’s Essay on the Principle of Population was published. In it, he wrote: "Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio . . . . This implies a strong and constantly operating check on population from the difficulty of subsistence." Malthus was saying that the growth of the population is limited by the amount of food available to eat; people will live at the subsistence level forever. Why did Malthus's description not apply to the world after 1800? Migration to cities as the factory system grew led to smaller families, and the volume of food required fell as a result. In an agricultural society, proximity to plentiful food resulted in extremely high caloric intake, but migration to cities meant that workers started eating less. Malthus did not know that technological changes would enhance productivity growth beyond any previous levels. As less‑developed areas were colonized and European attitudes dominated foreign cultures, birth rates around the world fell drastically.