As we look back over the development of German criminology from the late nineteenth century to 1945, the most noticeable feature is the predominance of research on the biological causes of crime over research on its social causes. The criminal-biological approach prevailed in large part because most criminological research was conducted by psychiatrists. The field of criminology had originally developed from a conjunction of interests among criminal jurists and psychiatrists. The penal reformers around Franz von Liszt looked to criminological research to provide a scientific foundation for penal policy. Although the penal reformers were inclined to attribute greater importance to social than to biological causes of crime, in practice criminal-sociological investigations soon lagged behind criminal-biological research, both because German sociologists showed little interest in crime and because the penal reformers proved reluctant to undertake criminal-sociological research themselves. This situation changed only after the First World War, when a number of jurists, most notably Exner and Liepmann, did begin to conduct criminal-sociological research. But the resurgence of criminal sociology under Exner's aegis was never enough to overcome the continuing predominance of criminal biology.
Hence most criminological research during this period was conducted by German doctors, primarily psychiatrists. Why did German psychiatrists take such an interest in criminological questions? There were several reasons. First, the late nineteenth-century surge in the medical profession's interest in the etiology of crime came about because Lombroso's theory of the born criminal advanced a biological explanation of crime to which German doctors, especially prison doctors, felt compelled to respond. And when Lombroso equated his "born criminal" with the psychiatric diagnosis of "moral insanity," psychiatrists in general felt called upon to react to his theories.