fell into two camps: the geneticists, who mostly worked in the laboratory; and naturalists, who studied natural populations in the field and museums, and put much of their effort into taxonomy. Each contributed concepts that were essential to the understanding of evolution. Naturalists introduced the biological species concept, the definition of species as a community that is reproductively isolated and occupies a distinctive ecological niche. They also recognized that species are polytypic, having variations in time and space; and that behavior and change of function can give rise to evolutionary change. The two groups used such different methods and terminology that it was difficult for them to communicate. They were often battling over the same scarce academic resources, and each was often scornful of the other. As the paleontologist George Gaylord Simpson put it, paleontologists believed that "a geneticist was a person who shut himself in a room, pulled down the shades, watched small flies disporting themselves in milk bottles, and thought that he was studying nature." Meanwhile, naturalists were "like a man who undertakes to study the principles of the internal combustion engine by standing on a street corner and watching the motor cars whiz by." Publication The book began as a series of lectures at Columbia University in October and November 1936. Dobzhansky decided to attend the summer 1936 meeting of the Genetics Society of America in Woods Hole, Massachusetts. When the geneticist Leslie Dunn learned of this, he invited Dobzhansky to give a series of lectures at Columbia. He sent the invitation in April, and within a month he had suggested that the lectures be a springboard for writing a general treatise on evolutionary genetics. Dobzhansky was enthusiastic, and in May he wrote back, proposing the title "Genetics and the Origin of Species". He envisioned two parts – "part I containing data on the sources of evolutionary change, and part II containing a discussion of their interactions leading to race- and species formation." After the lectures (for which he received $500), Dobzhansky returned to Pasadena, and in December Columbia University Press accepted his proposal for a book. The pace of writing was helped by a riding accident in February 1937 in which he crushed his knee, rendering him immobile; and by April he was able to send a manuscript to Dunn for his perusal. While reading the manuscript, Dunn persuaded the university to revive the Jesup lectures,