Paul Samuelson made a series of important contributions to population theory for humans and other species, evolutionary theory, and the theory of age structured life cycles in economic equilibrium and growth. The work is highly abstract but much of it was intended to illuminate issues of compelling policy importance, such as declining fertility and population aging. While his work in population economics has been very influential, his work in population and evolution appears to have been largely overlooked, perhaps because he seldom published in demographic journals or went to population meetings. Here I discuss his many contributions in all these areas, but give particular attention to demographic aspects of his famous work on overlapping generation models, social security systems, and population growth.