For forty years, in a variety of books and articles, Gerhard Lenski has become the most influential proponent of ecological and evolutionary explanations of human societies, their development and transformations, from the Stone Age to the present. In his newest book, Lenski offers a succinct but comprehensive statement of the full body of his theory followed by demonstration of how it can be used to generate new and valuable insights when applied to a set of highly diverse issues. These include debates concerning the origin of ancient Israel and its distinctive culture, the rise of the West in the modern era, the highly varied trajectories of development of Third World nations in recent decades, and the failure of Marxist efforts to transform society in the Soviet Union and elsewhere. In the concluding chapter, Lenski discusses a number of other issues and areas where ecological-evolutionary theory may be fruitfully applied in the future.