The Darwinian revolution supposed and imposed a much broader and more complex concept of environment than that which, until that moment, had been considered by most as part of natural history. Until Darwin, the environment of living beings had been regarded, almost exclusively, as the inanimate surroundings. This pre-Darwinian notion of environment included physicochemical and climatic variables: the living beings themselves were scarcely considered, or they were regarded just as food to be assimilated. In contrast, with Darwin, the influence of (...) living surroundings began to be regarded as having decisive importance for understanding the distribution, configuration, and viability of living beings. The relationships established among different living beings became the main and more significant features of the biological environment. This conceptual change was an exigency derived from the formulation and justification of the theory of natural selection. The idea of struggle for existence supposed by that theory requires that the biotic environment be considered critical in determining the viability of each living being. (shrink)