The Author analyses the part played by the idea of degeneration in Discours sur l’origine et les fondements de l’inegalite parmi les hommes in the light of the degeneration theory formulated by French physicians and naturalists between the 1740s and the 1760s. Rousseau draws both from the medical and the naturalist traditions of degeneration and applies them to his analysis of human historical development, adding alongside it a theory of moral degeneration, from which proceeds a theory of political degeneration.