Despite a late partition of the two disciplines, geography and ethnology long appeared as complementary and practically interchangeable sciences. The earth and man belong to the same system. In Enlightenment anthropology the “theory of climates” determined the dominant representations of the co-determination link between physical circumstances and the “way of life.” The idea of man’s integration into the world takes shape in the following century. In the perspective of the geographer Humboldt, the question of the spatial distribution of the species draws the attention of naturalists to local “harmonies” that make of each country a “center of creation.” The study of these mutual adaptations reveals an “inter-field” that could be called “geography of man.” This tradition has disappeared with the emergence of the “transformist” debate. But Vidal de La Blache's geography remains responsible for the theory of the “oecumen” (called “environment” today) and the concepts used to consider the economy of nature. The intersected institutional evolutions of these “twin” sciences are analyzed here.