mutations and must be isolated from others of its species by time, geography, habitat, or breeding season. Historical impact Genetics and the Origin of Species provided the outline for a synthesis of genetics with evolution, and was enthusiastically received by both geneticists and naturalists. Dobzhansky laid out an advanced account of the evolutionary process in genetic terms, and he backed up his work with experimental evidence supporting the theoretical arguments. This led to the stimulation of the field of evolutionary genetics, and contributions to the theory soon began to follow. This had a powerful impact on naturalists and experimental biologists, who quickly embraced this new understanding of the evolutionary process as one of genetic change in populations. It was not long before the synthesis was broadened to include paleontology, systematics and botany in a series of notable books: Systematics and the Origin of Species (1942) by Ernst Mayr; Tempo and Mode in Evolution (1944) by George Gaylord Simpson; and Variation and Evolution in Plants (1950) by G. Ledyard Stebbins. The emerging synthesis was called the evolutionary synthesis by Julian Huxley in his book, Evolution: The Modern Synthesis. In 1947, a diverse collection of biologists met at a symposium in Princeton and declared their acceptance of this synthesis. However, it was not yet complete. Developmental biologists did not accept that the theory explained their observations, and it was not until the 1970s and 1980s that molecular biology bridged the gap. Also, for decades there was disagreement over whether the unit of selection was the gene or the individual as a whole. In 1974 all the living founders of the modern synthesis (with the exception of Simpson and Bernhard Rensch) met with historians of biology in a conference to evaluate their work. All acknowledged Genetics and the Origin of Species as the direct instigator of all the work that followed. Ernst Mayr, in The Growth of Biological Thought, said that it was "clearly the most decisive event in the history of evolutionary biology since the publication of the Origin of Species in 1859. Awards Dobzhansky was plagued by a form of leukemia in his later years, but he remained vigorously active until the day before his death on December 18, 1975. During his lifetime he was the recipient of many honors and awards. For Genetics and the Origin of Species Dobzhansky was awarded the Daniel Giraud Elliot Medal from the National Academy