Since the academic institutionalization of psychiatry in the decades around 1900, there existed a strong assumption, if not conviction, of many representatives of the discipline that psychiatric disorders are essentially caused by heredity and that it was therefore a central task of psychiatric research to clarify the exact hereditary factors and mechanisms of such conditions. It was assumed that, based on the derived knowledge, it would be possible to develop scientifically based strategies of preventative or therapeutic interventions. Starting with the first systematic research program in psychiatric genetics around 1910 and the related institutionalization of the field in the context of the German Psychiatric Research Institute (Deutsche Forschungsanstalt für Psychiatrie) through the Human Genome Project and up to today’s Genome Wide Association Studies, such scientific endeavors made use of a broad range of methodical approaches and an enormous investment of resources. In this perspective, it is remarkable that in the example of schizophrenia, one of the most frequent and severe psychiatric conditions, representatives of the field conceded even recently that “overall, the details of the etiopathogenesis […] and the genotype environment interactions remain to a large extent unknown” (Henrikson et al 2017).
This situation implies that in relevant parts of psychiatry as well as in medical genetics, there exists a strong assumption, or even conviction regarding the hereditary nature of psychiatric conditions, which is, however, accompanied by weak and almost completely inferential scientific evidence supporting this assumption—in spite of intensive research for more than a century. In this situation, the project addresses the following questions: What kind of evidence have psychiatrists and medical geneticists used to formulate their claims on the heredity of psychiatric disorders? Who were the specific addressees of such claims, and which strategies of creating evidence were used in the shifting constellations of political and economic resources? The project focuses on the period between the formation of first research program in psychiatric genetics around 1910 until the emergence of linkage studies as a new methodological paradigm in the early 1980s.