The late 1960s witnessed a key conjunction between political activism and the history of science. Science, whether seen as a touchstone of rationality or of oppression, was fundamental to all sides in the era of the Vietnam War. This essay examines the historian Robert Maxwell Young's turn to Marxism and radical politics during this period, especially his widely cited account of the ‘common context’ of nineteenth-century biological and social theorizing, which demonstrated the centrality of Thomas Robert Malthus's writings on population (...) for Charles Darwin's formulation of the theory of evolution by natural selection. From Young's perspective, this history was bound up with pressing contemporary issues: ideologies of class and race in neo-Darwinian evolutionary theory, the revival of Malthusian population control, and the role of science in military conflict. The aim was to provide a basis for political action – the ‘head revolution’ that would accompany radical social change. The radical force of Young's argument was blunted in subsequent decades by disciplinary developments within history of science, including the emergence of specialist Darwin studies, a focus on practice and the changing political associations of the history of ideas. Young's engaged standpoint, however, has remained influential even as historians moved from understanding science as ideology to science as work. (shrink)