When Fisher started his career, genetics was not a well-understood science. There were biologists who did not see how evolution by natural selection could happen with heredity as they understood it. The main effect of the book was to to show the small changes in genes could indeed lead to the large changes seen in the fossil record. Fisher's second chapter, the "Fundamental theory of natural selection", convinced most biologists that Darwin's idea and modern genetics were compatible (could work together). Fisher's view was reinforced by Julian Huxley, J.B.S. Haldane, Sewell Wright, Theodosius Dobzhansky, and G. Ledyard Stebbins. All of these men were in touch with genetics. With the addition of two field biologists, Ernst Mayr and Bernhard Rensch and a palaeontologist, George Simpson, the group put together the modern synthesis.