According to contemporary evolutionary theory, which is predominantly neo-Darwinist, life diversifies gradually. As favorable mutations accumulate over generations, preserved by natural selection, they produce new limbs, tissues and organs. Given enough time, species may change so radically that they bear almost no resemblance to their ancestors, or each other. This kind of change is often depicted as a branching tree of life.
Neo-Darwinists portray the fossil evidence as a bulwark of support for their theory. For example, the National Academy of Sciences educational guidebook, Teaching about Evolution and the Nature of Science states, The progression of species found in the fossil record provides powerful evidence for evolution.
As evidence, they offer various examples of evolutionary transitions: land mammals to whales, apes to humans, the development of the mammalian hearing structures from reptilian jawbones, and so on.
However, the scientific literature shows that the rock record, far from supporting neo-Darwinism, has always been something neo-Darwinists have had to explain away. What the evidence shows is not gradual change, but sudden appearance and stability: Most fossils species appear all at once, fully formed, and exhibit no directional change throughout their stay in the rocks.
The same is true above the species level. Paleontologist Robert L. Carroll notes that the most striking features of large-scale evolution are the extremely rapid divergence of lineages near the time of their origin, followed by long periods in which basic body plans and ways of life are retained. What is missing are the many intermediate forms hypothesized by Darwin...
This feature reaches an extreme in what paleontologists call the Cambrian explosion, an event that began 530 million years ago. Over a period of only five to 10 million years, a flash of geological time, virtually every major animal group (phylum) seems to suddenly appear from nowherea grave challenge for neo-Darwinism.