Degeneration theory is, at its heart, a way of thinking, and something that is taught, not innate. A major influence was on the theory was Emil Kraepelin, lining up degeneration theory with his psychiatry practice. The central idea of this concept was that in “degenerative” illness, there is a steady decline in mental functioning and social adaptation from one generation to the other. For example, there might be an intergenerational development from nervous character to major depressive disorder, to overt psychotic illness and, finally, to severe and chronic cognitive impairment, something akin to dementia. This theory was advanced decades before the rediscovery of Mendelian genetics and their application to medicine in general and to psychiatry in particular. Kraepelin and his colleagues mostly derived from degeneration theory broadly. He rarely made a specific references to the theory of degeneration, and his attitude towards degeneration theory was not straightforward. Positive, but more ambivalent. The concept of disease, especially chronic mental disease fit very well into this framework insofar these phenomena were regarded as signs of an evolution in the wrong direction, as a degenerative process which diverts from the usual path of nature.