By Robert Deyes
The public view of science has often been a romantic one and to some extent justifiably so. Paleontology, for example, has often conjured up images of "rough and tumble field expeditions to remote and often harsh climes" with a "Raiders of the Lost Ark machismo" being commonplace among many of today's fossil collectors (Ref 1, p.43). Even the well-known 'reussites de la science'- those accomplishments of science that marked the 20th century- carry with them no less an amount of intrigue and suspense. Einstein's first conceptualization of the extension of his 'special theory of relativity', for example, came to him as a sudden flash of genius while he was sitting in the patent office in Berne. Einstein would later describe his idea as the 'glucklichste Gedanke meines Lebens' (translated as "the happiest thought of my life" Ref 2, p.178).
There is one accomplishment that stands out as spectacular for the simple reason that it changed the way scientists looked at the origins of multicellular life. The discovery of the Burgess Shale in the Canadian Rockies by the American geologist Charles Doolittle Walcott in the summer of 1909 was an occurrence that required both good fortune and opportunity (Ref 3, p.42). It likewise satisfies our romantic view of scientific discovery. According to folklore, Walcott was riding on horseback together with his wife Helena and son Stuart when his wife's horse stumbled on a rock. Dismounting his horse, Walcott broke open the rock to reveal a host of soft-bodied fossils (Ref 3, p.42). In the days that followed Walcott and his party found more fossils amongst the pieces of broken shale that covered the neighboring hillside. So it was that several years later, after a number of return expeditions to the Burgess Shale, Walcott would describe his finding as "the finest and largest series of Middle Cambrian fossils yet discovered" (Ref 3, p.44).
The relevance of Walcott's discovery becomes all too clear when we consider that it represents an apparently sudden origin of multi-cellular organisms during a period of the earth's history known as the Cambrian (Ref 4, p.97). Furthermore, almost all extant animal phyla appeared in a 5-10 million year period (Ref 4, p.97). Seen in the context of earth's history, such a time span is "but a blink of an eye" (Ref 4, p.97).
In an article that appeared in the Proceedings Of The Biological Society Of Washington, philosopher Stephen Meyer and colleagues noted how during the Cambrian, "many novel animal forms and body plans (representing new phyla, subphyla and classes) arose in a geologically brief period of time" (Ref 5). Paleontologist Niles Eldredge described the Cambrian explosion as a global event in which, "very suddenly, and at about the same horizon the world over, life showed up in the rocks with a bang" (Ref 6, p.24). Biophysicist Cornelius Hunter talked about the Cambrian explosion as, "one of the major 'big bangs' of biology"- a narrow window within which, "the major groups in the fossil record made abrupt appearances" (Ref 7, p.69). Evolutionists David Raup and Steven Stanley similarly drew attention to the abrupt appearance of fossils at the beginning of the Cambrian (Ref 8, p.8).
The most puzzling aspect about the Cambrian explosion lies in the observation that very few organisms present in the strata leading up to the event are in any way ancestral to the Cambrian fauna (Ref 4, p.98). There are now numerous sites around the world that confirm the findings of the Burgess shale including the Maotianshan shales in the Yunning Province in China, well known for their well-preserved, soft-bodied fossils (Ref 9). In the words of biologist Casey Luskin, the emerging picture of phyletic disparity and complex body architecture in the absence of preceding transitional forms "strains traditional evolutionary explanations" (Ref 4, p.98).
Fighting against the evidence and relying simply on the preconceived expectations of what the record should show, some scientists today still promote the viewpoint that the Cambrian explosion was preceded by an extensive period of unrecorded evolution from a small number of common ancestors (Ref 8, p.22). Others posit that an increase in atmospheric oxygen following the evolution of photosynthetic plants allowed animals to grow to a larger size (Ref 9). And yet rather than providing a mechanism through which the Cambrian fauna evolved from simpler organisms, such a stance does little more than cite a hypothetical environmental trigger. The detail of how evolution took place remains conspicuously absent.
Charles Darwin dedicated a section in the latter chapters of The Origin of Species to deal specifically with the rather serious problem that the Cambrian posed to his theory of natural selection. He wrote:
"If the theory be true, it is indisputable that before the lowest Cambrian stratum was deposited long periods of time elapsed, as long as, probably far longer than, the whole interval from the Cambrian age to the present day..To the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer" (Ref 10, pp.438-439).
While Darwin struggled with the facts, he made brave attempts to get around the problem. His initial approach was simply to dismiss the apparent explosion of life as an unsurprising consequence of an imperfect fossil record (Ref 10, pp.441-442). Darwin built a hypothesis based on oscillating sea levels. He proposed that the shifting of sea sediments had forever removed the evolutionary continuum of Precambrian life (Ref 10, pp.441-442). To Darwin the sudden emergence of the Cambrian fauna could thus be considered as a mere artifact of the shifting of sediments (Ref 10, pp.441-442). Indeed plate subduction is a real phenomenon and might have forever destroyed the Precambrian record of history (Ref 3, p.32). But such facts hardly give us permission to let our imaginations run rampant over what evolution might or might not have done before the Cambrian.
Darwin's hope was that further research would unearth the presence of preceding transitional animal forms in the underlying strata. As of yet, these transitional forms have not been found. Nevertheless, in other areas of research the incompleteness of the fossil record has been latched onto as a given from which to subsequently define how all animal life evolved from one or a few common ancestors. One such area involves looking at the similarities in genes of diverse animals and, from these, establishing possible ancestral links between them (Ref 12). Perhaps unreasonably, the assumptions that are made in these phylogenetic comparisons are (i) that differences in specific genes have arisen through the process of mutation (Ref 11) and (ii) that the rate of mutation can be used as a 'molecular clock' of sorts from which to trace back the existence of common ancestral forms (Ref 12).
Several studies have been published using molecular phylogenetic comparisons that suggest a period of animal divergence far earlier than the Cambrian (Ref 11, 13). Gregory Wray and colleagues for example have published genetic sequence data that, they conclude, shows phyletic divergence having occurred almost 1 billion years ago (Ref 11). Their data was based on the sequence analysis of seven genes and involved comparing sequences for each of these genes in chordates and seven invertebrate phyla. In another study, Russell Doolittle and his team from the Center of Molecular Genetics at UCSD compared amino acid sequences from 57 enzymes and likewise concluded that animals had diverged considerably earlier than the Cambrian explosion (Ref 13).
Attractive as it may seem, the picture painted by both Wray's and Doolittle's groups faces a serious problem- it assumes a huge period of unrecorded evolution between the proposed ancestor and the Cambrian fauna. Furthermore, estimates on when such a divergence actually occurred vary dramatically depending upon which genes are sequenced and analyzed. For example Doolittle and his team predicted a deep divergence of 670 million years for the initial divergence of animal phyla (Ref 13) while Wray and his colleagues opted for a much deeper origin- approximately 1.2 billion years ago (Ref 11).
Defining a single 'molecular clock' is problematic in itself given that mutations in DNA do not occur at a constant rate (Ref 3, p.143). This clearly makes it very difficult to draw any conclusions about a possible deep divergence of fauna as David Bottjer, former president of the US Paleontological Society, noted:
"To estimate the timing of the origin of various major animal groups, Gregory Wray of Duke University and colleagues used a molecular clock rate based on vertebrates (animals that have a backbone). Their results, published in 1996, postulated that bilaterians diverged from more primitive animals deep into the Precambrian era, as much as 1.2 billion years ago. Follow-up studies using the molecular clock produced estimates for this split that varied significantly, ranging from as old as one billion years ago to as young as just before the Cambrian period. Such discrepancies naturally generated doubts about the technique, and a more recent study...placed the last common ancestor of bilaterian animals at...somewhere between 573 and 656 million years ago. But even this data sparked controversy. It had become clear that only actual fossils would furnish incontrovertible evidence for the time at which bilaterians had emerged" (Ref 14)
Given such uncertainty, it seems paradoxical that zoologist Richard Dawkins should write about an impending enlightenment from the "one true tree of life" that will be obtained from current and future genome research (Ref 15, p.112). Dawkins lays down his bold claims, seemingly oblivious to the questionable nature of molecular clocks:
"A spin-off benefit, which will perhaps have its greatest impact in the United States, is that full knowledge of the tree of life will make it even harder to doubt the fact of evolution. Fossils will become by comparison irrelevant to the argument, as hundreds of separate genes, in as many surviving species as we can bear to sequence, are found to corroborate each other's accounts of the one true tree of life." (Ref 15, p.112)
Of course some evolutionary biologists have answered the clocks irregularity by proclaiming the broadest range of possible outcomes,
"natural selection should work at markedly varying rates in different lineages at different times: very rapidly in complex forms adapting to rapidly changing environments, very slowly in stable, well adapted populations" (Ref 16, p.129).
The extension of this proclamation has been that, over vast periods of time, the molecular clock should smooth out thereby increasing the accuracy of measurements. Why then do Wray's and Doolittle's estimates on a hypothetical origin of multicellular life differ so dramatically?
Obviously the idea of common descent amongst members of the animal kingdom formed an integral part of Darwin's main thesis (Ref 10, pp.149-160). In the only diagram that appears in the entirety of The Origin Of Species, Darwin himself drew a 'tree of life' in which he proposed that species would produce new varieties. In keeping with his theory of natural selection, Darwin proposed that only those variations that were somehow beneficial would be "preserved or naturally selected" (Ref 11, p.150). Darwin was well aware that such a tree of life would require huge amounts of time perhaps as much as "a thousand or more generations" between defined varieties (Ref 11, p.151). The climactic conclusion to his tree of life was that after many thousands of generations, the amount of variation would be so significant so as to justify defining the new variants as individual species (Ref 11, p.153).
Darwin's tree of life invariably called for a series of varieties or transitional intermediate forms leading up to the Cambrian. Yet the fossil record does no where show this fundamental requirement. Such an absence of intermediates is by no means trivial. To re-iterate the paleontological viewpoint made above, we cannot simply claim as fact 500-700 million years of unrecorded evolution. In short, the Cambrian explosion threatens at least one of the key pillars of Darwinism- that of gradual change over time.
1. Niles Eldredge (1985), Time Frames: The Rethinking of Darwinian Evolution and the Theory of Puctuated Equilibria, Published by Simon and Schuster, New York
2. Abraham Pais (1982), Subtle is the Lord, The Science and the Life of Albert Einstein, Oxford University Press, New York
3. Simon Conway Morris (1998), The Crucible of Creation; The Burgess Shale And the Rise of Animals, 1st Ed, Oxford University Press
4. Michael Behe, Eddie N. Colanter, Logan Paul Gage, Phillip Johnson, Casey Luskin, J.P. Moreland, Jay W. Richards (2008), Intelligent Design 101: Leading Experts Explain The Key Issues, Kregel Publications, Grand Rapids, Michigan
5. Stephen Meyer (2004), The Origin of Biological Information and the Higher Taxonomic Categories, Proceedings of the Biological Society of Washington Volume 117, no. 2, pp.213-239
6. Niles Eldredge (1987) Life Pulse: Episodes From The Story of The Fossil Record, Facts On File Publications, New York
7. Cornelius Hunter (2001) Darwin's God, Evolution and the Problem of Evil, Brazos Press, A division of Baker Book House Company, Grand Rapids, Michigan
8. David Raup and Steven Stanley (1971), Principles of Paleontology, W. H. Freeman and Company, San Francisco
9. Early Cambrian Chengjiang; China Fossils- "A Window Into The Cambrian Explosion", See http://www.fossilmuseum.net/Fossil_Sites/Chengjiang.htm
10. Charles Darwin (1859), The Origin of Species By Means of Natural Selection Or The Preservation of Favored Races In the Struggle For Survival Modern Library Paperbacks Edition (1998), New York
11. Gregory Wray, Jeffrey Levinton, Leo H. Shapiro (1996), Molecular Evidence For Deep PreCambrian Divergences Among Metazoan Phyla, Science, Vol.74, pp.568-573
12. Laura E Maley and Carles R Marshall (1998), The Coming of Age of Molecular Systematics, Science, Vol 279, pp.505-506
13. Russell F. Doolittle, Da-Fei Feng, Simon Tsang, Glen Cho, Elizabeth Little (1996), Determining Divergence Times of the Major Kingdoms of Living Organisms with a Protein Clock, Science Vol 271, pp.470-477
14. David Bottjer (2005), The Early Evolution of Animals, Scientific American, August 10th, 2005
15. Richard Dawkins (2003), A Devil's Chaplain, Published by Weidenfeld and Nicolson London, UK
16. Stephen Jay Gould (1992), The Panda's Thumb- More Reflections In Natural History, Published by W.W Norton and Company, New York
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