In this article, I argue that the problematic of "race and medicine", which has been the object of many recent debates, has a long history that it may be useful to understand better. I show more specifically that, from the very first uses of the concept of "race" in natural history during the XVIIIth century, medical concepts and analogies served as important models. These medical models were especially useful to analyze "races" as alterations from an original identity. Different analogies are studied here. 1. The analogy between races' peculiar temperaments and morbid alterations of human constitution. 2. The analogy between the transmission of the alterations along generations and hereditary diseases. In this second analogy, I differentiate between two models: the degeneration of the human type and the transmission of a molecular alteration of one character.