The publication of Origin of Species in 1859 changed the way in which nature and man’s place in it were regarded. In Argentina, more than anything, the new evolutionism challenged the perceptions of inherited romantic ideas about nature and politics. In a world of competition, struggle, and perpetual transformation it was difficult to accommodate the ideas of harmony and unity. The debate that followed only showed the confusion that existed in terms of how pre-Darwinian ideas could continue in the context of Darwinian science. More than anything, there was a philosophical gap that had to be filled since a theory based on the analysis of divergence over time disputed the hope that unity awaited in a certain future. The changes mentioned in the previous paragraph show us how the philosophical system that had served those who defended European ideas before 1859 started to be less coherent once that the true impact of the new science was understood, around 1870. In this essay, I will analyze how the synthetic philosophy of Herbert Spencer was used to correct what was perceived as the intrinsic materialism, and philosophical poverty, of Darwin’s theory in order to allow the continuity of the ideology that was forming the ideology of the nation. The second part of the essay will explain the transition from Spencer’s philosophy to the Monism of Ernst Haeckel. In it, I will show how synthetic thought was conceived, particularly regarding notions of aesthetics and race, and how the crisis of Spencerianism after 1890 triggered a revision of evolutionism that ended in the affirmation of a spiritual and romantic typology that will connect both Spencer’s and Haeckel’s ideas.