Darwin's Doubt: The Explosive Origin of Animal Life and the Case for Intelligent Design

by Stephen C. Meyer

Third, even if representatives of four animal phyla were present in the Ediacaran period, it does not follow that these forms were necessarily transitional or intermediate to the Cambrian animals. The Precambrian sponges (phylum Porifera), for example, were quite similar to their Cambrian brethren, thus demonstrating, not a gradual transformation from a simpler precursor or the presence of an ancestor common to many forms, but quite possibly only an earlier first appearance of a known Cambrian form. The same may be true of whatever kind of worm may be attested by Precambrian tracks and burrows. Moreover, even assuming, as some evolutionary biologists do,34 that later Cambrian animals had a sponge-like Precambrian ancestor, the gap in complexity as measured by the number of cell types alone, to say nothing of the specific anatomical structures and distinct modes of body plan organization that are present in later animals but not in sponges, leaves a massive discontinuity in the fossil record that requires explanation (much like the morphological gap between Spriggina and actual arthropods).