As William Bateson conceived it when he coined the term "genetics" in 1906, this new field would combine the approaches used to study heredity and variation and their relation to evolution. At first heredity and variation were thought to be separate phenomena, involving different mechanisms. The confusion of these two concepts was not cleared up by sweeping these items under the rug called genetics. It was not until 1921 that the current view, formulated by Hermann Joseph Muller, was forcefully expressed:
It is commonly said that evolution rests upon two foundations -inheritance and variation; but there is a subtle and important error here. Inheritance by itself leads to no change, and variation leads to no permanent change, unless the variations themselves are heritable. Thus it is not inheritance and variation which bring about evolution, but the inheritance ofvaxiation, and this in turn is due to the general principle of gene construction which causes the persistence of autocatalysis despite the alteration in structure of the gene itself)
The conviction which Muller maintained in 1921 was not possible in 1906. It required the union of cytology, breeding analysis, and Darwinism. Thisunion took place between 1910 and 1915 at Schermerhorn Hall at Columbia University under the leadership of Thomas Hunt.
Morgan and his students using the fruit fly, Drosophila melanogaster, and it culminated in the publication of The Mechanism of Mendelian Heredity (1915) by the chief contributors to that union: Morgan, Alfred Henry Sturtevant, Muller, and Calvin Blackman Bridges.
The key to the success of the Drosophila group was the theory of the gene. The unit of heredity was assigned to the chromosome and numerous phenomena became explainable through the combined cytological and genetic observations and experiments carried out by the group. The gene itself was named earlier, by Wilhelm Ludwig Johannsen