Degeneration Theory Claude-Olivier Doron 1 (1)Histoire et Philosophie des Sciences, Université de Paris/SPHERE, Paris, France Claude-Olivier Doron Email: colivierdoron@gmail.com Introduction To devote section of this Encyclopedia to the notion of degeneration may sound odd, as this notion has been pictured as a typically “Fin de siècle” theme, related to the theories of evolution or to psychiatry and criminology after 1850 (Pick 1989; Coffin 2003). Before this period, it is sometimes claimed that degeneration was rather a common place, as old and vague as the complaint celebrating old times as a golden age, and not a scientific or political problem. Historians of modern life sciences and medicine know, though, that, at least from the eighteenth century, the question of the degeneration of the species has been both a significant object of scientific investigations and a haunting biopolitical issue (Sloan 1973; Quinlan 2007). Degeneration of plants or animals referred to a process of alteration of the species over generations that could transform the specific type in such a way that it raised questions about the stability of the species and their possible transformation one into another. The same process of alteration could affect human species, threatening its quality, degrading it over generations, or producing very different races from an original type. It gave rise to various programs and politics to prevent the degeneration of species and regenerate them. But, as we’ll see, many elements related to the notion of degeneration can actually be traced back into early modern period, in a variety of discursive and practical fields, in which the notion of degeneration was widely used. This is why, after a section devoted to a conceptual reflection on degeneration, we will delineate its different uses in the sixteenth and early seventeenth centuries. We will then analyze how the question of degeneration of the species has been defined as an object of natural science and biopolitical programs from the late seventeenth century onward. Definition(s) Even if the notion of degeneration has been used with a wide range of meanings, in relation to heterogeneous fields, we can identify some resemblances that give a relative coherence to these uses. A) First, degeneration ( degeneratio) belongs to a semantic field referring to a process of alteration ( alloiôsis in Aristotle’s words), i.e., the transformation of one quality into another while preserving (or not, this being a matter of debate) the unity of the substance (Aristotle, On generation and Corruption, I, 4). Inside this semantic field, degeneration is close to a whole range of other notions such as alteration, mutation, transformation, or perversion. In this case, degeneration can refer to any kind of transformation of one quality into another. It is generally used in a transitive way: “to degenerate from X into Y.” To degenerate means to lose its quality, to deviate from an original state, and to transform itself while maintaining nonetheless a kind of identity and continuity with the