The Reverend Thomas Robert Malthus (1766-1834) was an English scholar, influential in political economy and demography. Malthus is chiefly remembered for his theories about population and its increase or decrease in response to various factors. The six editions of his An Essay on the Principle of Population, published from 1798 to 1826, observed that sooner or later population gets checked by famine and disease. "The power of population is indefinitely greater than the power in the earth to produce subsistence for man". The Malthusian growth model is an exponential growth based on a constant rate of compound interest and is widely regarded in the field of population ecology as the first principle of population dynamics. Malthusianism became an intellectual stepping-stone to the idea of natural selection. Malthus popularized the economic theory of rent. His students affectionately referred to him as "Pop" or "Population" Malthus. He died in 1834 at the age of 68.