This paper discusses the political dimension of Odón de Buen's (1863–1945) expository practices—teaching and popularizing—as a university professor of natural history in Barcelona and later in Madrid at the turn of the nineteenth century. De Buen appropriated Ernst Haeckel's ideas on evolution in order to promote an ambitious political agenda, based on republican, freethinking, anticlerical values. To that end, he moved beyond the confines of academic science within the university and sought to bring modern concepts of natural history into elementary schools, athenaeums, political clubs and associations, scientific trips, popular books, periodicals, and the daily press. In such places, de Buen's natural history acted as an intellectual weapon with which to confront the conservative monarchic attitudes of the Spanish Restoration, but it also provided a moral backing to a society, which felt backward in terms of science and technology and was desperately seeking new sources of inspiration and national pride.