It is common to designate Lamarck and Lamarckism as the main historical references for conceptualizing the relationship between organisms and the environment. The Lamarckian principle of the inheritance of acquired characters is often considered to be the central aspect of the “environmentalism” developed in this lineage, up to recent debates concerning the possible Lamarckian origins of epigenetics. Rather than focusing only on heredity, this article will explore the materialist aspect of the Lamarckian conception of the environment, seeking to highlight that (...) the life-supporting function of physicochemical milieux was its cornerstone. Indeed, compared to the Darwinian conception of the environment, which focuses on interindividual and interspecific relationships in a given habitat, Lamarck’s emphasis on the dependencies of organisms on physicochemical environments appears to have given rise to a very active philosophical environmentalism. Studying the environmental Lamarckism of 19th-century philosophers and social scientists in France, Great Britain, and the United States, such as Comte, Quatrefages, Spencer, and Ward, I propose to analyze their contribution to the conceptualization of the environment. The social, moral, or psychological conceptions of human environments that proliferated in the second half of the 19th century deviated from Lamarck’s more material approach, but they were still referencing Lamarck. Examining the scope of their “Lamarckism,” this article seeks to highlight the common context of life sciences and social philosophy, in which the environment emerged as a central issue in the 19th century. (shrink)