By the mid-twentieth century, several recognized French geographers had produced research work classifying lifestyles. They had broken with the idea that nomadic and sedentary lifestyles were the successive stages of a universal history of human societies, and claimed that they were the result of human adaptations to specific natural environments. Within this new conceptual framework, nomadism was thus understood as a form of highly evolved lifestyle responding to the particular characteristics of the steppe. The issue concerned the territories of the Empire, and especially those of Colonial Algeria. Indeed, if pastoral nomadism was the best possible adaptation to the dry steppe zone, on which natural basis could the extension of European sedentary agriculture be justified? Through the analysis of a corpus of works published by institutionally-recognized geographers concerning Algeria and Algeria's indigenous lifestyles (theses, articles in the Annales de Géographie, literary reviews, etc.), I would like to show how the concept of the adaptation of Man to his natural environment, when applied to Algeria, generated several intractable divides and deep contradictions.