American Socialists and Evolutionary Thought, 1870-1920 demonstrates how evolutionary theories fundamentally shaped, and ultimately undercut, the American socialist movement. Mark Pittenger examines the attempts of radicals in the late 19th and early 20th centuries to synthesise the evolutionary ideas of Charles Darwin and Herbert Spencer with socialist philosophy, social theory and political practice. In contrast to authors who have shown the influence of Darwinism on conservative and progressive political ideologies, Pittenger establishes that radicals also took scientific ideas seriously and wanted to link the public fascination with evolution to their own cause. Looking at theoretical, political and fiction writing by American socialists, Pittenger identifies debates among factions during two distinct periods: the Gilded Age, during which socialism was a fragmented aggregation of largely non-Marxist individuals and organisations; and the Progressive Era, when socialism coalesced into a distinctly Marxist movement, seeking political and economic power via the American Socialist Party. Many activists of both eras saw evolutionary science as the necessary foundation for socialist theory and practice. Some tried in various ways to incorporate pragmatism, cultural relativism, and rights for blacks and women into their programmes, or worked to democratise scientific knowledge in service of the class struggle. But, as a result of the social pressure on socialists to adopt less radical positions and of their own desires to appeal to a broader constituency, the Marxist call for a workers' revolution receded in importance, replaced by the less painful notion that socialism would arrive as the result of natural and inevitable processes. As socialists broadened their message it became difficult to distinguish it from other types of progressive reform. Pittenger's insights regarding the role of evolutionary science in American socialist thought are an important contribution to understanding why socialism has not had more of an impact on modern American society.