 Classical genetics is said to derive from Mendel’s experiments with pea plants, however, the story is more complex than this. At the beginning of the 20th Century, there existed several schools in genetics, on both sides of the Atlantic. In England, the Biometric school of Karl Pearson and Raphael Weldon were developing a quantitative approach that took Francis Galton “Law of ancestral heredity” as its point of departure. The Mendelian William Bateson was leading a rival movement. In the United States, Thomas Hunt Morgan and his associates were constructing the first genetic maps of the fruit fly. For a while, William Castle was defending a different approach to genetic mapping, as well as a different theory of the gene. Various approaches were also developed in Continental Europe, for example, in the Netherlands (Hugo de Vries), Germany (Carl Correns) or Austria (Erich Tschermak). The American school of Thomas Hunt Morgan pretty much carried the day. Its approach to mapping genes as well the (ever changing) theory of the gene became widely accepted in the 1930s, and became officially incorporated in the Evolutionary Synthesis of the 1930s and 40s (Mayr 1982; Provine 1971).