The history of human and medical genetics has roots different from those in the study of heredity in plants and animals. Likeness between human parents and offspring and between familial and hereditary diseases always intrigued scientists and physicians throughout the ages. However, few systematic accounts of hereditary diseases in man appear to have been published before the twentieth century.
Occasional brilliant insights into the principles of medical genetics already existed in early times. In 1752, Maupertuis, cited by Glass,1 published an account of a family of polydactylia in four generations and demonstrated that the trait could be equally transmitted by father and mother. He further showed, by probability calculations, that chance alone could not account for the familial concentration of the trait. The striking sex-linked character of traits, such as color blindness and hemophilia, had also been established near the end of the eighteenth century and the beginning of