The beginnings of biometrical psychiatric genetics: Studies of the insane diathesis 1905-1909.

The year 1900 saw not only the rediscovery of Mendel's hybridization studies but also the publication by Karl Pearson of his newly developed tetrachoric correlation which he used to study the parent-offspring resemblance for the "insane diathesis" in 1905. This was followed by more detailed reports by two of his students/associates: Heron in 1907 and Goring in 1909. Both calculated the tetrachoric correlation for insanity in parent-offspring and Heron for sib-sib pairs. Estimates ranged from approximately +0.30 to +0.60. These papers were statistically sophisticated but demonstrated minimal interest in the phenotype being studied. They are of historical interest because they laid the groundwork for biometrical psychiatric genetics which emerged as a major research paradigm in latter third of the 20th century. In a biting critique of Heron's paper by a young Ernst Rüdin, we see the beginnings of a long-running argument in psychiatric genetics about the relative value of detailed phenotyping versus novel statistical methods and of Mendelian versus Biometrical methods. While much interest has focused on the eugenic orientation of German psychiatric genetics in the early 20th century, these early British biometrical geneticists, like the majority of geneticists of that day, were also ardent advocates of the eugenic application of their research results.