Thomas Malthus was one of the three founders of modern economics, alongside Adam Smith and David Ricardo. He was also the founder of modern demography (population studies). In his Essay on the Principle of Population (1798), turned into a greatly expanded and in many ways different book in the second edition of 1803, Malthus laid out his famous laws of population, later amended to tendencies. The influence of this book has been immense, not merely on theoretical discussions in economics and the social sciences, but also in the practical legislation of the early nineteenth century and the policies of those who ruled the British Empire. His theories also provided the key to the idea of natural for both Alfred Russell Wallace and Charles Darwin.