A concept developed by the contemporary philosopher of biology Peter Godfrey Smith to explicate the basic logic of evolutionary processes. A Darwinian population is ‘a collection of causally connected individual things in which there is variation in character, which leads to differences in reproductive output (differences in how much or how quickly individuals reproduce), and which is inherited to some extent’. The evolution of the population through time will depend on the precise details of the form that the variation, fitness, and heredity differences take, as well as external factors. Two notable features of this analysis are that evolutionary processes need not depend on the replication of individual units of stuff from one generation to another, and that there is no difficulty about selection occurring at many different levels. Altruism can evolve in a Darwinian population provided that the benefit conferred falls disproportionately on others likely to pass on the disposition to altruism.