Ecology in principle is tied to evolution, since communities and ecosystems result from evolution and ecological conditions determine fitness values. Yet the two disciplines of evolution and ecology were not unified in the twentieth-century. The architects of the Modern Synthesis, and especially Julian Huxley, constantly pushed for such integration, but the major ideas of the Synthesis—namely, the privileged role of selection and the key role of gene frequencies in evolution—did not directly or immediately translate into ecological science. In this paper (...) I consider five stages through which the Synthesis was integrated into ecology and distinguish between various ways in which a possible integration was gained. I start with Elton’s animal ecology, then consider successively Ford’s ecological genetics in the 1940s, the major textbook Principles of animal ecology edited by Allee et al., and the debates over the role of competition in population regulation in the 1950s, ending with Hutchinson’s niche concept and McArthur and Wilson’s Principles of Island Biogeography viewed as a formal transposition of Modern Synthesis explanatory schemes. I will emphasize the key role of founders of the Synthesis at each stage of this very nonlinear history. (shrink)