February 14, 2006 | David F. Coppedge

Evolutionists Tackle Cambrian Explosion

You have to give credit to anyone who tackles a big problem head-on, regardless of whether you agree with their solution.  Two recent papers take on one of evolution’s biggest challenges: the Cambrian Explosion.  Assuming the evolutionary timeline, this represents a “brief” 5 million year period back 530 million years ago when most of the major animal phyla appeared.  It was called an “explosion” of evolutionary emergence even decades ago, when scientists thought the interval was eight times longer, or 40 million years.  More refined dating estimates have only exacerbated this problem which was known even in Darwin’s time.  Somewhere between 48% and 82%, most likely around two thirds, of all animal phyla (major groupings) and subphyla appeared in this period, fully formed, and without ancestors.  At most four had possible precursors up to 40 million years earlier in the Precambrian, but these are doubtful (e.g., see 08/19/2004, 12/23/2002).
    How brief was this explosion of life?  According to Meyer, Ross, Nelson and Chien,1 if the entire evolutionary timeline were compressed into a 24-hour day, the Cambrian Explosion would represent one minute, or 0.11% of the timeline.  Even if that estimate were an order of magnitude off – ten minutes, representing 50 million years – the comparative brevity of the interval would be still be remarkable.  In that blink of a geologic eye, the world saw the emergence of molluscs, echinoderms, brachiopods, jellyfish, worms, arthropods (like trilobites) and many other complex organisms, compared to the prior three billion years or more when, except for a few multicelled organisms like flatworms and sponges, single-celled organisms ruled the world.
    To be fair, the Cambrian examples of the new phyla seem primitive by comparison to later representatives.  The first chordates (those with a notochord or simple nerve chord) looked like worms, although representatives of early jawless fish (subphylum vertebrata) have been found recently in the early Cambrian strata (01/30/2003, 08/21/2002).  Think how diverse the vertebrates became: everything from giraffes to turtles to hummingbirds and horses.  Later arthropods in the fossil record include flying insects and lobsters and spiders.  Still, to have over two-thirds of all animal body plans appear so abruptly is astonishing.
    The new Cambrian animals had specialized tissues and organs, presupposing that huge increases in biological information and specialized functions appeared almost overnight.  Evolution isn’t supposed to happen this way.  Darwin’s book presented a slow, gradual tree of life branching from ever more primitive ancestors.  Where are the transitional forms?  Punctuated equilibria theory has a similar problem – just on a more jerky scale.  Since the Origin of Species, evolutionists have admitted that the Cambrian Explosion is one of their most vexing problems (see 07/29/2004, 12/22/2005).  Intelligent design theorists and creationists have not hesitated to remind them that the Cambrian fossil record doesn’t look like evolution; it looks like creation.
    A recent paper tackling this problem was published by Eric Davidson (Caltech) and Douglas Erwin (National Museum of Natural History, DC) in Science.2  They mention the difficulty somewhat delicately: “A notable feature of the paleontological record of animal evolution is the establishment by the Early Cambrian of virtually all phylum-level body plans.”  (Emphasis added in all quotes.)  Their explanation revolves around gene regulatory networks (GRNs).  “Development of the animal body plan is controlled by large gene regulatory networks (GRNs), and hence evolution of body plans must depend upon change in the architecture of developmental GRNs,” they begin.  Some of these networks appear hierarchical, and the “kernels” are resistant to change.  Consequently, they argue, “Conservation of phyletic body plans may have been due to the retention since pre-Cambrian time of GRN kernels, which underlie development of major body parts.”  This, however, seems to focus on what didn’t change, not what did.  Nevertheless, they think they are on the right track, compared with earlier explanations:

Classic evolutionary theory, based on selection of small incremental changes, has sought explanations by extrapolation from observed patterns of adaptation.  Macroevolutionary theories have largely invoked multi-level selection, among species and among clades.  But neither class of explanation provides an explanation of evolution in terms of mechanistic changes in the genetic regulatory program for development of the body plan, where it must lie.

Photos in the article show some of the diverse body plans of Cambrian animals.  Their explanation of body plan diversification takes on a distinctive cybernetic flavor.  By picturing genetic networks as “kernels” resistant to change (because “change in them is prohibited on pain of developmental catastrophe”), with “plug-ins” that get co-opted to developmental programs, “switches” that turn on these programs and so act as “input/output (I/O) devices” within the network, and even “differentiation gene batteries,” they envision a multi-level architecture, in which changes can have anywhere from dramatic to fine-tuning effects depending on what level it occurs.
    All this computer lingo, however, still sounds more like design than evolution.  Smart people design computers and networks.  Do Davidson and Erwin succeed in getting unaided natural forces to surprise the world with the sudden appearance of new complex animals?  A key to their answer lies in assuming a “deep divergence” in genetic networks a hundred million years earlier.  (Another key must, alas, await future discoveries.)

We predict that when sufficient comparative network data are available, there will be found conserved network kernels similar in complexity and character to those of Fig. 2 [examples of “putative GRN kernels”], which program the initial stages of development of every phylum-specific body part and perhaps of superphylum and pan-bilaterian body parts as well.  It would follow [sic] that these kernels must have been assembled during the initial diversification of the Bilateria [animals with bilateral symmetry]and have retained their internal character since.  Critically, these kernels would have formed through the same processes of evolution as affect the other components, but once formed and operating to specify particular body parts, they would have become refractory to subsequent change.  Molecular phylogeny places this evolutionary stage in the late Neoproterozoic when Bilateria begin to appear in the fossil record, between the end of the Marinoan glaciation at about 630 million years ago and the beginning of the Cambrian.  Therefore the mechanistic explanation for the surprising fact that essentially no major new phylum-level body parts have evolved since the Cambrian may lie in the internal structural and functional properties of GRN kernels: Once they were assembled, they could not be disassembled or basically rewired, only built on to.
    Between the periphery of developmental GRNs and their kernels lies the bulk of the network architecture.  Here we see skeins of special cross-regulatory circuitry, plug-ins, and I/O connections; and here is where have occurred the changes in network architecture that account for the evolutionary novelties [sic] attested in the fossil record of animals.

Their conclusion is that there are at least three hierarchical levels of network architecture, “with extremely different developmental consequences and rates of occurrence.”  The alert reader will notice, however, that the explanation above focuses on stasis of the kernels, and elsewhere only assumes that evolution somehow came up with all the highly diverse body plans in the other parts of the network.  Meyer et al. pre-criticized this explanation by saying that the amount of genetic information required would be astronomical, and by saying the “deep time” supposition lacks any fossil evidence.  They also pointed out that the molecular comparisons used to support divergence in deep time give highly different results, depending on whose data compares which genes.
    One notable part of Davidson and Erwin’s conclusion is that it differs markedly from “current microevolutionary thinking” that assumes change occurs in a “temporally homogeneous way.”  They argue, instead, that “different levels of change that have occurred in evolution are imperfectly reflected at different levels of Linnean classification,” i.e., from species up through families up to phyla, “and we think that these inhomogeneous events have been caused by architectural alterations in different locations in the underlying GRNs.”  Architectural alterations – is that a euphemism for mutations?  They use the word alterations for all the other levels of the network, too.  Here comes their cadenza.  Amidst all the machine and network language, look for any unguided mechanisms that explain the origin of new body plans:

To the extent that kernel formation underlies critical morphological innovations, some kernels must indirectly be responsible for major events in Neoproterozoic niche construction.  Motility, predation, digestion, and other canonical features of the Bilateria followed from the evolutionary appearance of the genetic programs [sic] for the respective body parts.  These innovations became an engine of change that irreversibly altered the Earth’s environment and, thus, the probability of success of subsequent evolutionary changes.  We believe that experimental examination of the conserved kernels of extant developmental GRNs will illuminate the widely discussed but poorly understood problem of the origination of animal body plans in the late Neoproterozoic and Cambrian and their remarkable subsequent stability.

So, in other words, we have the framework for a new theory, and a lot of work remains to be done – stay tuned.  But would this answer be enough to silence the ID critics?  Paul Nelson of the Discovery Institute doesn’t think so.  He posted an anecdote on Evolution News about how he had met Eric Davidson years ago and heard him admit that single base-pair mutations would not produce genetic networks.  He also quoted Davidson asserting that “Neo-Darwinism is dead.”  After reading this latest Davidson paper, Nelson noticed a problem for getting new information into the system: “If changing the wiring takes down the whole system, well, then, obviously the wiring can’t change – a developmental instance of what has come to be known as the Principle of Continuity.”     Another, more complete survey of the Cambrian Explosion and possible solutions has been made available in a preprint to the upcoming 2006 Annual Review of Earth and Planetary Science.  Visit a future entry for a look at whether this paper succeeds in countering what Darwin called “the most obvious and serious objection which can be urged against the theory.”3


1Stephen C. Meyer, Marcus Ross, Paul Nelson and Paul Chien, “The Cambrian Explosion: Biology’s Big Bang,” Darwin, Design and Public Education (ed. John Angus and Stephen C. Meyer), Michigan State Univ. Press, 2003, pp. 323-402.  This is a good semi-technical overview of the Cambrian Explosion problem and evolutionary attempts to explain it away.  The timeline analogy by paleontologist Jun-Yuan Chen is mentioned on p. 326.  See also the Discovery Institute Fact Sheet (PDF) about the Cambrian Explosion.
2Eric Davidson and Douglas Erwin, “Gene Regulatory Networks and the Evolution of Animal Body Plans,” Science, 10 February 2006: Vol. 311. no. 5762, pp. 796 – 800, DOI: 10.1126/science.1113832.
3Charles Darwin, Origin of Species, ch. 10: “But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed, be truly enormous.  Why then is not every geological formation and every stratum full of such intermediate links?  Geology assuredly does not reveal any such finely-graduated organic chain; and this, perhaps, is the most obvious and serious objection.  The explanation lies, as I believe, in the extreme imperfection of the fossil record.”  Yet 140 years has not filled in these gaps, as Darwin had hoped; in fact, the situation has only become worse.  Most paleontologists now admit that the fossil record is essentially complete; most new finds fit within existing categories and do not fill in the gaps; see 10/25/2002 2nd entry and 02/14/2005 entry).

Ha!  Another example of Darwinian hand-waving.  It’s worth the effort of learning a little scientific jargon to see how these spinmeisters work their magic.  Imagine some hypothetical “architectural alterations” coming up with the inconceivably complex functions of motility, predation, digestion and every other piece of hardware and software a Cambrian animal needed to live and reproduce.  Unbelievable faith.
    The bottom line: this paper is constructed on euphemisms for random mutations and natural selection, sprinkled with plagiarized jargon about networks, engines, I/O modules, kernels, plug-ins and other intelligent-design concepts.  Any fossil evidence?  Nope.  Any realistic genetic mechanism that could produce a trilobite with complex eyes (09/18/2003) or a starfish, or a calcified shell (06/26/2003), or an animal with a backbone and nervous system?  Nothing but a vivid imagination, verbal magic and the power of belief (e.g., 10/25/2002).  Go get ’em, ID.

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Categories: Fossils, Genetics

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