Richard Dawkins disagrees with the view that new phyla suddenly appeared in the Cambrian, arguing that for a new phylum "to spring into existence, what actually has to happen on the ground is that a child is born which suddenly, out of the blue, is as different from its parents as a snail is from an earthworm. No zoologist who thinks through the implications, not even the most ardent saltationist, has ever supported any such notion." In the "Structure of Evolutionary Theory" Gould stresses the difference between phyletic splitting and large anatomical transitions, noting that the two events may be separated by millions of years. Gould argues that no paleontologist regards the Cambrian explosion "as a genealogical event—that is as the actual time of initial splitting", but rather it "marks an anatomical transition in the overt phenotypes of bilaterian organisms."