A Graduate Student Writes - Evolution News & Views

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A Graduate Student Writes

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Editor's Note: Since Darwin’s Doubt was published on June 18 more than 65 reviews have been posted on Amazon. In addition, Panda's Thumb, a blog dedicated to the defense of evolutionary theory, published a lengthy critique by Nick Matzke on June 19. On July 3, The New Yorker followed with a review that drew heavily on Matzke’s post. We are delighted that the book has already provoked such a spirited response. With this reply to just some of the questions that Nick Matzke raised in his review, we continue, and will continue, to use ENV as a platform for discussing the issues raised in critical (and other) reviews of the the book. Look for thoughtful and vigorous responses to other critiques of Darwin's Doubt at ENV in the future.

David Berlinski, mathematician and philosopher, is the author most recently of The King of Infinite Space: Euclid and His Elements (Basic). He is also the author of The Deniable Darwin and Other Essays (Discovery Institute Press), The Devil's Delusion: Atheism and its Scientific Pretensions (Basic) and other books.

DebatingDD.jpegNick Matzke has written a critique of Stephen Meyer's Darwin's Doubt. Having for years defended Darwin’s theory as an employee of the National Center for Scientific Education, he has determined to learn something about the theory as a graduate student at the University of California, an undertaking in the right spirit but the wrong order. Would that he had done things the other way around. His animadversions are written with all of the ebullience of a man sure enough of his conclusions not to worry overmuch about his arguments. They are wrong in the small, wrong in the large, and wrong all around. A pity. The Darwinian establishment is hardly without resources of its own, and had Matzke devoted more thought to his critique, he might have spared us the embarrassment of improving his arguments before rejecting his conclusions.

Darwin's Doubt advances three theses: First, that the Cambrian explosion is a real event; second, that the Cambrian explosion has not been explained by neo-Darwinian or other evolutionary mechanisms; and, third, that the Cambrian explosion, is best explained by an inference to intelligent design. Matzke in his critique of Meyer, concentrates on the first of these theses, barely mentions the second, and fails to engage Meyer’s actual arguments for the third.

Darwin's Doubt makes its case for the reality of the Cambrian explosion chiefly, but not entirely, on the basis of the fossil record. Paleontology has pride of place. It is where the bodies are. Representatives of twenty-three of the roughly twenty-seven fossilized animal phyla, and the roughly thirty-six animal phyla overall, are present in the Cambrian fossil record. Twenty of these twenty-three major groups make their appearance with no discernable ancestral forms in either earlier Cambrian or Precambrian strata. Representatives of the remaining three or so animal phyla originate in the late Precambrian, but they do so as abruptly as the animals that appeared first in Cambrian. Moreover, these late Precambrian animals lack clear affinities with the representatives of the twenty or so phyla that first appear in the Cambrian.

An account of their appearance must logically be focused on either the earliest part of the Cambrian or the Precambrian. Where else to look? But in looking there, Meyer argues, there is nothing much to see. Not nothing, of course. The well-known sequence that begins with the acritarchs and gutters into the small shelly fauna is an example, one in which Matzke invests his hopes without sufficiently hedging his bets. “The earliest identifiable representatives of Cambrian ‘phyla,’” Matzke writes, the twitch of misplaced quotation marks around a word that does not need them, “don’t occur until millions of years after the small shelly fauna have been diversifying...” But while the small shelly fauna offer something to see, they reveal nothing of interest. No paleontologist believes that some small shelly fauna are ancestral to all the Cambrian phyla. Trilobites are an example. These strange and complex creatures, their eyes staring hypnotically, appear during the early Cambrian (the Atdabanian stage). Having quite obviously gotten to where they appear in the fossil record, how did they get there? One speculative scenario runs from Precambrian bilaterians or arthropods to the Cambrian arachnomorphs, and then to the trilobites, the arrow of affirmative action in Lin et al. 2006 going from Parvancorina to Skania sundbergi and then wandering to Primicaris larvaformis.1

“What is often missed,” Matzke argues, “is that deposits like the Chenjiang have dozens and dozens of trilobite-like and arthropod-like organisms ....” There follows a burst of exuberant thunder: “These are transitional forms!” Matzke is persuaded that whatever is trilobite-like must be trilobite-lite, and so ancestral to the trilobites themselves. The party line is otherwise:

Early trilobites show all the features of the trilobite group as a whole; there do not seem to be any transitional or ancestral forms showing or combining the features of trilobites with other groups (e.g. early arthropods). Morphological similarities between trilobites and early arthropod-like creatures such as Spriggina, Parvancorina, and other “trilobitomorphs” of the Ediacaran period of the Precambrian are ambiguous enough to make detailed analysis of their ancestry far from compelling.2

If his natural allies in the great cause have refrained from supporting his conclusions, Matzke is prepared to advance them anyway, a policy commanding our admiration if only for its foolhardiness: “All of this is pretty good evidence,” Matzke writes, “for the basic idea that the Cambrian ‘Explosion’ is really the radiation of simple bilaterian worms into more complex worms, and that this took something like 30 million years just to get to the most primitive forms that are clearly related to one or another living crown ‘phyla,’ and occurred in many stages, instead of all at once.”

This is a view championed by Matzke in defiant isolation. The University of California’s Museum of Paleontology makes the obvious case to the contrary:

When the fossil record is scrutinized closely, it turns out that the fastest growth in the number of major new animal groups took place during the as-yet-unnamed second and third stages (generally known as the Tommotian and Atdabanian stages) of the early Cambrian, a period of about 13 million years. In that time, the first undoubted fossil annelids, arthropods, brachiopods, echinoderms, molluscs, onychophorans, poriferans, and priapulids show up in rocks all over the world.

Matzke is pursuing his PhD at the University of California. He is apparently indisposed to visiting museums.

References:

(1) Lin, J. P.; Gon, S.M.; Gehling, J.G.; Babcock, L.E.; Zhao, Y.L.; Zhang, X.L.; Hu, S.X.; Yuan, J.L.; Yu, M.Y.; Peng, J. (2006). "A Parvancorina-like arthropod from the Cambrian of South China". Historical Biology 18 (1): 33-45.

(2) From Wikipedia, a Party Organ, and hardly a source our side is disposed to champion. Why stop there? See Jell, P. (2003), "Phylogeny of Early Cambrian trilobites", in Lane, P. D., Siveter, D. J. & Fortey, R. A., Trilobites and Their Relatives: Contributions from the Third International Conference, Oxford 2001, Special Papers in Palaeontology 70, Blackwell Publishing & Palaeontological Association, pp. 45-57.

Image: Sather Gate, UC Berkeley, Wonderlane/Flickr.


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