Can there be any student of palaeontology who does not have some awareness of the fossils from the Burgess Shale? With their exquisite preservation, including soft body parts, these animals have provided a window into Middle Cambrian life that has only recently been supplemented by other material. Charles Doolittle Walcott is the person who discovered the most significant fossil site. By 1917, his collection numbered 65,000 fossils. His publications set the scene for subsequent debates about the significance of these animals.
"Walcott's 1909 discovery was not the first, but the best Burgess Shale site. By his collections and publications, Walcott contributed more than anyone, before or since, to drawing back the curtain obscuring our view of the life of the Cambrian world. For this alone, he deserves the glory of this month's centennial celebrations."
The Darwinian model of evolutionary transformation does not explain the explosion of life in Cambrian seas (source here)
My interest in this blog is not the history of the discovery, but the significance these fossils have for palaeontological thinking. Three phases of understanding can be identified.
1. Walcott's interpretations. From today's vantage point, it is easy to underestimate the challenge facing this pioneer. Numerous fossil animals were collected by Walcott that had no identifiable living descendants. Nevertheless, he made every effort to find meaningful links to defend his classification of the organisms. Collins draws attention to a 1911 paper on soft-bodied animals: 4 sea cucumbers, 1 jellyfish and some annelid worms.
"Walcott's identifications did not fare well. Only one of the sea cucumbers is still thought to be a sea cucumber, and the jellyfish is now known to be part of an extraordinary arthropod. Of the 12 annelid worms, only one is still recognized as such. Walcott was on more familiar ground with his publication of arthropods in 1912 but, even here, many of the 8 genera he described are now known to belong to classes different to those which he assigned them."
2. Whittington's reinterpretations. For over 40 years, little work was done on Walcott's collection. Then, in the late 1960s, Harry Whittington and colleagues took up the challenge. They were more ready to recognise "unknown affinities" and acknowledge the weirdness of some Cambrian animals.
"This was the first time that anyone had questioned Walcott's implicit assumption that Cambrian animals belonged to groups alive today. [. . .] None of Walcott's contemporaries, nor indeed the scientists who followed him, questioned Walcott's assumption that the Burgess Shale animals belonged to living animal groups; not until Whittington."
Enter Stephen Jay Gould in 1989 with the publication of Wonderful Life. Apart from retelling the story of the Burgess Shale fauna to a new generation of readers, Gould developed three major arguments, summarised below.
The first pointed out significant human factors affecting the way palaeontological work is done. Walcott was criticised "for 'shoehorning' his animals into known groups, so delaying the true understanding of the Burgess Shale fossils".
Second, Gould claimed to recognise new body plans (phyla) in the "weird wonders" revealed by the Whittington group. This, he claimed, pointed to contingency and chance being dominant factors in the history of life. It did not escape the notice of some that this perspective fitted well into Gould's Marxist/atheist worldview.
Third, Gould wanted to point out the incompatibility between the history of life as revealed by the fossils (the sudden appearance of new body plans) and the theoretical understanding of life's diversity provided by Darwinism (which requires gradualism and incremental branching patterns).
3. Desmond Collins' fieldwork and revised classifications. Starting in 1975, Collins (the author of the Nature essay) led "18 seasons of fieldwork and excavation in the Burgess Shale". Many new localities were found, 3 new faunas, plus "a flood of new specimens" in the period 1983-2000. New forms were described and old forms were re-described.
"Today, we have returned mostly to Walcott's practice of classifying Burgess Shale animals in living animal groups, but the groups are different. There are some extinct classes, such as the Dinicarida, but very few extinct phyla. Five of Gould's weird wonders have been classified, only one in a new phylum."
Collins has provided us with a helpful overview with which as assessment of the issues raised by Gould can be made. We shall look at each of the three arguments in turn.
First, the issue of Walcott's "shoehorning". Collins choice of word is different: he refers to Walcott's "misadventures". Clearly, mistakes were made - but not only by Walcott! It can be argued that Gould himself shoehorned the Burgess Shale data to fit a story that matched his 'contingency' worldview. He wanted to be able to say that if the tape of life were ran again, life's history would look very different.
Second, the dramatic explosion of novel body plans in the Cambrian, many of which went nowhere and became extinct. The re-classification of Collins' et al has reduced the number of new phyla to one. This undermines Gould's contingency argument. If the logic of Gould's argument is valid, then the re-evaluation of the data implies that we have no grounds for thinking that re-running the tape of life will lead to the emergence of unfamiliar phyla. Gould drew conclusions relating to humanity:
"Homo sapiens, I fear, is a "thing so small" in a vast universe, a wildly improbable evolutionary event well within the realm of contingency. Make of such a conclusion what you will." (page 291).
Significantly, arguments against contingency have been developed by one of Whittington's colleagues - and one of the characters appearing in Wonderful Life - Simon Conway Morris, Professor of Evolutionary Palaeobiology at the University of Cambridge. These arguments, based partly on the Burgess Shale fossils and partly on the phenomenon of convergence, appear in his book The Crucible of Creation (1998). It should not be necessary to say that a design-orientated understanding of these data is entirely consistent with the approach taken by Conway Morris.
"I hope that by now I have persuaded you that whatever importance is attached to the Burgess Shale, it is not in the operation of either historical contingency or in the fable of re-running the film of the history of life." (page 205)
Thirdly, the challenge to Darwinism because of the Cambrian Explosion of life forms. Although Gould's claims regarding additional phyla are no longer defensible, this particular argument still stands. Darwinism predicts gradualism and increasing diversification (Gould's cone of increasing diversity in Chapter 1). The pattern of diversification and decimation (Gould's inverted cone) is still to be found in the Burgess Shale organisms. The fundamental incompatibility between the evidence and Neodarwinism means that Darwin's theory have very little to offer us as an explanation of the origin of diversity and organic complexity.
"Additional Cambrian material is now coming from the Chengjiang fauna in China (particularly new chordates, the group that includes humans), and the Sirius Passet fauna in Greenland. Along with the Burgess Shale animals, they demonstrate that virtually all animal groups alive today were present in Cambrian seas."
Gould drew conclusions of a theological nature when he argued from science that we live in the realm of contingency and are ourselves the product of contingency. Yet few challenged his philosophy of history. And few pointed out that his advocacy of purposelessness in the Cosmos was incompatible with his promotion of the strict separation of science and religion (as non-overlapping magisteria). Now that the consensus in science has moved on, we can see that Gould's Burgess Shale argument for contingency was flawed and that the opposite conclusion is warranted: that the history of life suggests purpose and meaning in the Cosmos. For more on these issues, please refer to Meyer's paper on the evidences for design apparent in the Cambrian Explosion and also the film Darwin's Dilemma.
Misadventures in the Burgess Shale (Restricted access)
Nature 460, 952-953 (20 August 2009) | doi:10.1038/460952a
One hundred years after Charles Doolittle Walcott found a wealth of Cambrian fossils in the Rocky Mountains of British Columbia, Desmond Collins reflects on the bumpy road of their classification.
Gould, S.J. Wonderful Life, Hutchinson Radius, 1989.
Morris, S.C. The Crucible of Creation, Oxford University Press, 1998.
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