Utilizing hitherto unexplored material that has become available only after the dismantling of the Berlin Wall, this book examines the Monist philosophy of the German zoologist Ernst Haeckel, and its role in stimulating the birth of Fascist ideology in Italy and France. Focusing on the relevance of evolutionary science, Fascist thought is revealed as intimately related to Haeckel's scientific Monism - an approach that differs from most interpretations that tend to voice skepticism about the existence of a specific intellectual origin for Fascist ideology.