Donald Prothero, a paleontologist, knows his fossils. And, in 2007, Columbia University Press published his book, Evolution: What the Fossils Say and Why It Matters. For it’s scope, clarity of writing, and visual attractiveness (it has lots of illustrative drawings, photographs, and charts), it’s certainly one of the best book on the subject of evolution vs. creationism out there.
Here’s part of what Prothero says about the Cambrian explosion (he devotes a whole chapter of his book to the subject):
Of all the distortions of the fossil record that the creationists promote, the worst is their version of the “Cambrian explosion.” . . . The major group of invertebrate fossils do not appear suddenly at the base of the Cambrian but are spaced out over strata spanning 80 million years—hardly an instantaneous “explosion”!
Donald Prothero emphasizes that early evolution followed a logical progression from a world of “pond scum” to multicellular life (represented by “The Garden of Ediacara”) to shells to “mineralized, fossilizable skeletons.” According to Prothero:
. . . the earliest stages of the Cambrian (known as the Nemakit-Daldynian and the Tommotian stages, from 520 to 545 million years ago) are dominated by tiny (only a few millimeters) fossils nicknamed the ‘little shellies’ . . .
And things become larger and more mineralized from there. Prothero sums up this way:
[T]he Cambrian explosion is a myth. It is better described as the Cambrian slow fuse. It takes from 600 to 520 million years ago before the typical Cambrian fauna of largely shelly organisms (especially trilobites) finally develops. . . . Apparently, creationists persist in presenting a version of the Cambrian that is at least fifty years out of date either because they don’t know any better (the ‘clueless’ hypothesis) or because they do know better (the ‘deceiver hypothesis). Either way, it is bad science.
So, are we done? For the reasonable lay person, should the case be effectively closed on the Cambrian explosion?
In 1993, Stephen Gould edited a book for Norton titled The Book of Life: An Illustrated History of the Evolution of Life on Earth. Like Prothero’s book from a decade later, it’s an attractive and high production affair. And the chapter that includes a discussion of the Cambrian was written by a paleobiologist of equivelent expertise to Prothero, John Sepkoski of the University of Chicago. In general terms, the chapter hits the same bases as Prothero, but there are some tantalizing qualifiers to the tidy picture that Prothero draws. Here’s what Sepkoski writes:
The new story is more coherent than the old, but it raises new questions, and it still leaves hundreds of millions of years of metazoan ancestry during the late Precambrian without a fossil history.
Metazoa is a synonym for the kingdom of Animalia (or animals), so what Sepkoski is saying is the following: prior to the Cambrian, we really don’t see all that much evidence of animals in the fossil record. But the ancestry of Cambrian animals, for mutation and natural selection to do its magic, must surely go back “hundreds of millions of years.”
And the tidy picture of “The Garden of Ediacara” that Prothero depicts as an evolutionary stepping stone toward at least some Cambrian animals may not, in fact, be all that easy to establish. Sepkoski notes that the Edicarian fauna may be “a separate development, not related to modern animal phyla.”
In other words, “The Garden of Ediacara” may have been largely an evolutionary dead-end (or, in any case, not a very big piece in the puzzle of the evolution of metazoa; that is, of animals).
So, maybe the Cambrian explosion was an explosion. Sepkoski, at least in 1993, was willing to use the term:
What is extraordinary about animal phyla is that nearly all of them seem to have evolved around the Cambrian-Precambrian boundary. Furthermore, that evolutionary explosion also produced a horde of unique and sometimes outlandish-looking animals whose fossils cannot be assigned to any living phylum.
So, at the Cambrian-Precambrian boundary, a tipping point was reached in which animal phyla suddenly, and quite dramatically, radiated, but prior to this period the fossil record for the ancestors of metazoa is just not that good (even though it should span hundreds of millions of years).
That sounds like an explosion to me.
But maybe it was an explosion driven, not directly by God, but by simple biomineralization. Here’s a recent speculation offered for the Cambrian explosion in a Physorg.com science news article:
[E]arly shell-bearing creatures help to resolve Charles Darwin’s concern over the sudden appearance of so many new animal species during the Cambrian explosion. The fossil record gives the impression of a “Creation” event, but in reality, animals had evolved prior to the explosion. They just didn’t leave much for paleontologists to find until they developed the skeleton-making trait.
And once a few animals started building with minerals, a “housing boom” erupted across the animal kingdom.
I’m sorry, but this sounds like an assumption in want of proof: did animals have a vastly long and gradual evolutionary history prior to the Cambrian or not? If, after all, the fossil record is almost wholly absent, then on what is the article’s confident pronouncement based?
It appears to be nothing.
So, I’ll try again: did the Cambrian constitute an evolutionary explosion or not? In search of an answer, I’m now opening yet another very attractive coffee-table style book on evolution, published by the University of California in 2009 (Evolution: the Story of Life, by Cambridge lecturer Douglas Palmer). Like Gould’s book from the 1990s and Prothero’s book from 2007, it’s suffused with helpful visuals.
But what does Douglas Palmer say about the Cambrian? Here it is (page 48):
Right from the earliest times, around 542 million years ago, an extraordinary explosion of life in the seas prompted an arms race between predators and prey. Within 20 million years or so, most major groups of animals had evolved, including our remotest vertebrate ancestors.
Houston, we have a problem. Palmer (2009) says it took 20 million years for the evolution of the various phyla of the Kingdom of Metazoa (animals); Prothero (2007) says it took 80 million years (and calls the evolution of animal phyla a “slow fuse”); and Gould and Sepkoski (1993) say it must have taken “hundreds of millions of years.”
What’s a lay person like me, dipping into science websites like Physorg.com and books produced by highly esteemed academic presses (Columbia, Norton, and the University of California), to make of this?
- Physorg.com is blowing blue pipe smoke.
- Donald Prothero overstates his case (that the Cambrian explosion is a misleading myth, and ought to be called a “slow fuse”);
- John Sepkoski is even-handed: the Cambrian explosion really was an explosion, but, if evolutionary gradualism is true, then animals have an unpreserved evolutionary history that goes back “hundreds of millions of years” before the Cambrian.
- Palmer tells it like it really appears to be: the period between 542-522 million years ago constituted “an extraordinary explosion of life.”
Can evolution by random variation and undirected natural selection (absent any target whatsoever) really account for what happened during the Cambrian explosion?
Why should anyone believe it?