A series of essays examines parallels and distinctions between evolutionary biology and socialist theory, tracing how Darwinian concepts of variation and adaptation have been applied to social questions. The author summarizes Marxist analysis of production, class relations, and technological change as engines of social development and contrasts these social mechanisms with biological explanations. Individual chapters treat the class struggle, critiques of social Darwinism, natural law and social theory, human sociability, the development of tools, language and thought, and comparisons between organs and implements. Throughout, the work urges careful separation of biological and social causation while exploring useful analogies and implications for critiques of capitalism.