The correct answer is Population. • According to Malthusian theory, the population grows in geometric progression. • The Malthusian Theory of Population is the theory of exponential population and arithmetic food supply growth. • The theory was proposed by Thomas Robert Malthus. He believed that a balance between population growth and food supply can be established through preventive and positive checks. Explanation & Key Takeaways: • Malthusian Theory of Population Growth: • Among the most famous theories of demography is the one associated with the English political economist Thomas Robert Malthus (1766-1834). • Malthus's theory of population growth - outlined in his Essay on Population (1798) - was a rather pessimistic one. • He argued that human populations tend to grow at a much faster rate than the rate at which the means of human subsistence (especially food, but also clothing and other agriculture-based products) can grow. Therefore humanity is condemned to live in poverty forever because the growth of agricultural production will always be overtaken by population growth. • While population rises in geometric progression (i.e., like 2, 4, 8, 16, 32 etc.), agricultural production can only grow in arithmetic progression (i.e., like 2, 4, 6, 8, 10 etc.). • Because population growth always outstrips growth in the production of subsistence resources, the only way to increase prosperity is by controlling the growth of the population. • Unfortunately, humanity has only a limited ability to voluntarily reduce the growth of its population (through 'preventive checks' such as postponing marriage or practicing sexual abstinence or celibacy). • Malthus believed therefore that positive checks' to population growth - in the form of famines and diseases - were inevitable because they were nature's way of dealing with the imbalance between food supply and increasing population.