One of the most significant facts revealed by the fossil record is that living species appeared in a single moment, together with all their characteristics. In other words, there is no sign any species that developed from a primitive form and slowly began to acquire all its limbs. All living species were flawless and fully formed from the moment they emerged, and those species that have survived are still identical to their original form. The book The Origin of Species Revisited describes how this represents a serious dilemma for Darwinism: The abrupt manner in which whole groups of species suddenly appear in certain formations, has been urged by several palaeontologists—for instance, by Agassiz, Pictet, and Sedgwick—as a fatal objection to the belief in the transmutation of species. If numerous species, belonging to the same genera or families, have really started into life at once, the fact would be fatal to the theory of evolution through natural selection. (The Origin of Species Revisited, p. 46)