Undead: The Myth of the 80-Million-Year Cambrian Explosion - Evolution News & Views

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Undead: The Myth of the 80-Million-Year Cambrian Explosion

Bela_lugosi_dracula.jpg

It's a debater's trick and not a particularly reputable one. When you're the last to speak and time's up, you know your opponent won't have an opportunity to answer you. So in the closing moments you throw in what sounds like an irrefutable zinger. It only sounds irrefutable, though. If it were really all that devastating, you would have brought it up earlier to see your opponent try and fail to deflect the challenge.

DebatingDDsmall.jpegThe fact that you fling it at him when you know the rules won't allow him a reply is usually evidence that you know it's strong only rhetorically, not on substance.

So it was today in the last minute of "skeptic" Michael Shermer's debate with Stephen Meyer on the Medved Show. Michael Medved was commendably welcoming and respectful to Shermer, giving him both the first and the last statements. After all, Shermer was a sport to come on the show, knowing that both Michael and Steve are Discovery Institute fellows. Anyway, in the final few words of his final comment Shermer proffered a favorite, seemingly deathless Darwinian legend.

Groan... Yes, it arises each night from its coffin. It cannot be killed by any natural means. By now, it has extremely bad breath. It is the Myth of the 80-Million-Year Cambrian Explosion.

That again. Summing up, Dr. Shermer pointed listeners to go read geologist Donald Prothero's review of Meyer's book, Darwin's Doubt, posted at Shermer's Skeptic website, where Prothero revisits his contention that the Cambrian "explosion" is no such thing. For Shermer the business about the 80 million years is the killer comeback. Prothero writes:

[W]e now know that the “explosion” took place over an 80 m.y. time frame. Paleontologists are gradually abandoning the misleading and outdated term “Cambrian explosion” for a more accurate one, “Cambrian slow fuse” or “Cambrian diversification.” The entire diversification of life is now known to have gone through a number of distinct steps, from the first fossils of simple bacterial life 3.5 billion years old, to the first multicellular animals 700 m.y. ago (the Ediacara fauna), to the first evidence of skeletonized fossils (tiny fragments of small shells, nicknamed the “little shellies”) at the beginning of the Cambrian, 545 m.y. ago (the Nemakit-Daldynian and Tommotian stages of the Cambrian), to the third stage of the Cambrian (Atdabanian, 530 m.y. ago), when you find the first fossils of the larger animals with hard shells, such as trilobites.

But we also know that Steve Meyer and Casey Luskin have in fact easily deflected this cavil. It comes down to little more than that life has a long history, which no one doubts, and that you can arbitrarily cut an 80-million-year slice containing the actual Cambrian explosion and redefine the whole thing as the “Cambrian slow fuse.” Voila! You now have a mere "diversification" rather than the more dramatic "explosion."

Yet this is all games with words and numbers. The Cambrian event is still there, the Cambrian animals still have no recognizable ancestors, they still defy Darwinian explanations of how the information to build them got there, and the mainstream view among Cambrian experts still recognizes that the explosion indeed is a real event that consumed some 10 million years.

See Casey Luskin's article, "How 'Sudden' Was the Cambrian Explosion? Nick Matzke Misreads Stephen Meyer and the Paleontological Literature; New Yorker Recycles Misrepresentation." Casey explains that the trick is premised on "including as part of the Cambrian explosion (a) the origin of the Ediacaran organisms in the late Precambrian, and (b) the small shelly fossils at the base of the Cambrian and (c) the main pulse of morphological innovation in the early Cambrian, and (d) subsequent diversification events right up until the end of the Cambrian period."

In his review in Science, Charles Marshall also knocked Meyer for saying the Cambrian event lasted 10 million years rather than 22-23 million, a figure arrived at by including the beloved but enigmatic "small shelly" fossils. However, in his final reply to Marshall's review, here at ENV ("More on Small Shelly Fossils and the Length of the Cambrian Explosion: A Concluding Response to Charles Marshall"), Meyer notes that Marshall himself elsewhere excludes the precious small shellies. Meyer concludes:

In any case, treating the first appearance of the small shelly fossils as the beginning of the Cambrian explosion does little to explain the main pulse of the morphological innovation that occurs later during the 10-million-year window that paleontologists commonly designate as "the explosion." As I acknowledge in Darwin's Doubt, it is entirely possible to assign a different duration to the "Cambrian explosion" depending upon how many separate paleontological events scientists choose to include within that designation. Nevertheless, quibbling of that sort reduces the debate to one of semantics. The key question is not how many different events should be included within the designation "Cambrian explosion." Nor is it about the total amount of time that some arbitrarily designated series of separate paleontological events covers. Instead, the key question is what caused the discontinuous appearance of morphological novelty within specific, and measurably narrow, windows of geological time -- whatever we choose to call them. Thus, Darwin's Doubt focuses on the crucial Tommotian and Atdabanian stages of the Cambrian explosion -- where 13-16 new animal phyla arose within a 5-6 million year window -- as a defining challenge to the efficacy of the neo-Darwinian mechanism. Marshall doesn't explain how the origin of the small shelly fossils diminishes the problem of the origin of the morphological novelty within that window of time.

I've already commented on the habit among Darwin defenders of appearing to forget that a key challenge of theirs has actually been addressed and refuted, repeatedly ("A Taxonomy of Evasion: Reviewing the Reviewers of Darwin's Doubt"). It's another case of the Reviewer Who Cannot Remember That His Objections Have Already Been Answered, of which Donald Prothero is the holotype specimen. For goodness sake, if they had better stuff than this to throw at us, they wouldn't hesitate to do so. But when they try to answer Meyer on the scientific merits of the argument, this is about the best they come up with. Where's the lion for their cause who can put up a real fight?

Image: Bela Lugosi as Dracula/Wikipedia.

 


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