Right of Reply: Our Response to Jerry Coyne

Jerry Coyne has offered a response in the pages of Quillette to David Gelernter’s provocative article, “Giving Up Darwin.” Gelernter rejected the standard model of neo-Darwinian evolution for a simple reason: he looked at three pieces of scientific evidence that appeared to be incompatible with that model:

• The sudden appearance of new body plans in the fossil record.
• The extreme rarity of protein folds.
• The absence of early-acting beneficial mutations, the kind that would be needed to generate new animal body plans.

In knowing where to look, Gelernter had help from Stephen Meyer’s Darwin’s Doubt, and David Berlinski’s The Deniable Darwin. These books both contain many references to the literature. Gelernter also highlighted the book Debating Darwin’s Doubt, which responded in detail to all notable critiques of the arguments that swayed him. For all that, Coyne faulted Gelernter for not examining counter-arguments to his own position. “One simply can’t do good science,” Coyne wrote, “by spouting only one side of an argument and ignoring the claims of the other.” A certain measure of irony is conveyed by this unjustified remark. Had Coyne followed it more faithfully, he would have spared himself some embarrassment.

The Cambrian Explosion, Coyne argues, “is an explosion only in geological terms, and allows for a lot of biological evolution to take place, (after all, modern whales evolved from small terrestrial deerlike organisms in just 12 million years).”

This is wrong in its first assertion, it is wrong in its second assertion; and it is wrong all around. The Cambrian Explosion is an abrupt event in geological and biological terms. The average longevity of marine invertebrate species is 5-10 million years. This is standard evolutionary biology. Thus, the transition from an assumed worm-like ancestor to all of the Cambrian animal phyla took place during the lifespan of, at most, a few successive species. (The phyla represent the largest division of animal classification exemplifying the most significant differences in biological form, whereas species which represent the smallest divisions and exemplify much more minor differences). Yet neo-Darwinists envision the new body plans that characterize the animal phyla arising as the result of an accumulation of many, many species-level changes and transitions over long periods of time—indeed, far more time than the Cambrian paleontological record allows. Consequently, the Cambrian Explosion is called the Cambrian explosion for a very good reason: something dramatic happened in a very short period of time.

The whales? And in twelve million years? Not likely. The available window of time for the transition from the terrestrial pakicetids to fully marine basilosaurids (Pelagiceti) is only 4.5 million years. This corresponds to the lifespan of a single larger mammal species, as Donald Prothero correctly notes. Prothero is Coyne’s ideological ally. They should be better friends. Short time spans give rise to a generic waiting time problem — a much-discussed issue in mainstream population genetics. It is easy to see why. The time required for even a single pair of coordinated mutations to originate and spread in a population is, at least, an order of magnitude longer than the window of time established by the fossil record. Either the fossil record must go, or the waiting time must go, but they cannot go on together. The whales are the least of it. The emergence of a single pair of coordinated mutations in the human lineage required a waiting time of 216 million years. The separation of the chimpanzee and human lineages took place only six or seven million years ago. These figures are clearly in conflict. This is the standard view, the one held by mainstream evolutionary biologists.

If the Cambrian Explosion cannot be contained by a play on words, perhaps it may be constrained by a sleight of hand? The very concept of an explosion, Coyne argues, “is disappearing, with paleontologists increasingly speaking of a ‘Cambrian diversification’.” Are they? Are they really? A search on Google Scholar for academic publications between 2000 and 2019 yields 13,400 matches for the term ‘Cambrian Explosion’ but only 392 matches for ‘Cambrian Diversification.’ The Cambrian Explosion continues to explode: “Evidence is converging,” paleontologists have written recently, “towards picturing the Cambrian explosion as even swifter than what we thought.” This does not look like a disappearing concept at all. Some scholars should leave sleights of hand alone.

David Gelernter accepted the conclusion that there were no putative ancestors of the Cambrian phyla in the preceding Ediacaran strata. He is in good company. So do most paleontologists who specialize in this field. This conclusion is not controversial, and it is obviously at odds with Darwin’s theory. Coyne is unpersuaded, maintaining that, yes, we have found Ediacaran “animals that appear to be arthropods, muscle-clad cnidarians (the group that includes modern jellyfish and anemones), echinoderms, mollusks, and probable sponges.”

This is pure fantasy. Coyne is unacquainted with the facts. There are no Ediacaran arthropods. There are no Ediacaran echinoderms either. Akarua adami, it is true, was initially attributed to the echinoderms. But apart from pentaradial symmetry, Akarua adami lack all of the synapomorphic characteristics of the echinoderms. The Cambrian fossil record contains stem echinoderms in helicoplacoids and homalozoans (carpoids) after all; and we know from reconstructed phylogenetic trees that pentaradial symmetry does not belong to their ground plan. The mollusks to which Coyne confidently appeals as friends of the family? They belong to the Ediacaran fossil genus Kimberella. First described as a jellyfish, Kimberella was later indeed sometimes associated with early mollusks. This attribution remained controversial: several characteristics contradicted it. A comprehensive paper recently reviewed the “problem of Kimberella” and concluded that “the possibility that Kimberella is coelenterate grade should therefore not be excluded.” Although likely a metazoan, they went on to write, “its placement remains problematic; it may be on the bilaterian stem group rather than within the stem group of any particular phylum.”