In the third revision of Genetics and the Origin of Species (1951), Dobzhansky rewrote all ten chapters on: Isolating Mechanisms, Mutation in Populations, Organic Diversity, Heredity and Mutation, Race Formation, Selection, Adaptive Polymorphism, Hybrid Sterility, Species as Natural Units, and Patterns of Evolution. Dobzhansky decided to remove the chapter on Polyploidy in the third edition. The new chapter on Adaptive Polymorphism highlighted Dobzhansky's research since the second edition. He included precise, quantitative evidence on effective natural selection in laboratory and free populations.
