„Between 1937 and 1941, Dobzhansky went from being able to allow for the possibility of evolutionary mechanisms other than those he favored to a position in which everything that did not fit his definition of evolution was rejected.
In the midst of his outpouring of anger at and dismissal of Goldschmidt, Dobzhansky neglected to consider the fact that while Goldschmidt's systemic mutations may not have been observed, neither had the mechanisms of speculation that he, or anyone else, for that matter, had proposed…. it was and still is the case that, with the exception of Dobzhansky's claim about a new species of fruit fly, the formation of a new species, by any mechanism, has never been observed.“
— Theodosius Dobzhansky
Jeffrey H. Schwartz, Sudden Origins: Fossils, Genes, and the Emergence of Species (1999)