The Battle Between the Biometricians and the Mendelians: How Sir Francis Galton’s Work Caused his Disciples to Reach Conflicting Conclusions About the Hereditary Mechanism

Francis Galton, Charles Darwin’s cousin, had wide and varied interests. They ranged from exploration and travel writing to fingerprinting and the weather. After reading Darwin’s On the Origin of Species, Galton reached the conclusion that it should be possible to improve the human stock through selective breeding, as was the case for domestic animals and cultivated plants. Much of the latter half of Galton’s career was devoted to trying to devise methods to distinguish men of good stock and then to show that these qualities were inherited. But along the way he invented two important statistical methods: regression and correlation. He also discovered regression to the mean. This led Galton to believe that evolution could not proceed by the small steps envisioned by Darwin, but must proceed by discontinuous changes. Galton’s book Natural Inheritance (1889) served as the inspiration for Karl Pearson, W.F.R. Weldon and William Bateson. Pearson and Weldon were interested in continuously varying characters and the application of statistical techniques to their study. Bateson was fascinated by discontinuities and the role they might play in evolution. Galton proposed his Law of Ancestral Heredity in the last decade of the nineteenth century. At first this seemed to work well as an explanation for continuously varying traits of the type that interested Pearson and Weldon. In contrast, Bateson had published a book on discontinuously varying traits so he was in a position to understand and embrace Mendel’s principles of inheritance when they were rediscovered in 1900. The subsequent battle between Weldon and Pearson, the biometricians, and Bateson, the Mendelian, went on acrimoniously for several years at the beginning of the twentieth century before Mendelian theory finally won out.