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“Darwin’s Dilemma”, part II

This is part of a review of the intelligent design movie “Darwin’s Dilemma”, which was shown by the University of Oklahoma IDEA Club. See part I.

The first part of the movie was “mostly harmless”.  Some factual errors, some odd constructs, and a few quotes from Darwin which, given the context, probably misrepresented his thought.  Bad enough, but no worse than you’d encounter on the average documentary of cable tv.  But things began to take a turn for the worse.

With the introducion of Chengjiang fauna, the underlying arguments began to slip more to the forefront. Although the Chengjiang fauna is about 10 million years older than those of the Burgess Shale, it is described as being more diverse. This, the movie argues, narrows the window of time in which these distinct groups of species could have evolved.  The shorter the window of time, the less likely it is that these groups would have evolved “by chance”.  But why should this matter?  Why do a few million years here or there matter?  This is where they bring in Paul Chien.

Paul Chien is a marine biologist at the University of San Francisco and Discovery Institute fellow.  According to the USF website, “Prof. Chien is interested in the physiology and ecology of inter-tidal organisms. His research has involved the transport of amino acids and metal ions across cell membranes and the detoxification mechanisms of metal ions”.  While the movie presents him as someone who has “done research in the renowned fossil beds of Chengjiang, China”, there’s no evidence to suggest that Chien is a palaeontologist or that he has published any of this findings (outside of Discovery Institute publications).  In the movie, Chien is shown visiting the Chengjiang site.  If you listen carefully to the what is said, it appears that he did so simply as an interested member of the public, not as an involved researcher.  But the viewer is left with the distinct impression that he worked at the site.  The movie’s website goes further, claiming that “Dr. Chien has done research in the renowned fossil beds of Chengjiang, China”.  While this is possible, I saw nothing in the movie that actually supports this assertion.

Through Chien, the movie introduces the existence of a layer of phosphatised microfossils of Precambrian origin which lie between the Burgess Shale-type fauna and the older Ediacaran fauna.  Since these fossils are older than the Chengjiang fauna, and since they lack the sort of morphological complexity that characterises the Burgess Shale-type fauna, the implication is that these fossils were deposited before the evolution of complex body plans.  The existence of 600-million-year-old microfossils is pretty amazing, especially when you realise that these aren’t just impressions – the individual cells are preserved.  Chien describes these microfossils as “sponge embryos”; it is later stated in the movie* that sponges are not thought to be ancestral to triploblastic metazoa.(i.e., most animals other than sponges and cnidarians).  The interval between these fossils and the Chengjiang fauna, the movie argues, provides the window in which all the evolution of modern phyla could have occurred.  I don’t recall an actual interval being given, but based on what Meyer said they seem to be thinking of something along the lines of 10-20 million years (as best I recall).

All in all, a pretty good gambit.  Not only have the addressed the “what about the Precambrian fossils?”,** they have actually used their existence to constrain the time frame for the “explosion”.  Very convincing.  Convincing, that is, until you take a closer look at the facts that they have chosen to spin (something that most people who see the movie will never do).  The last time I got a haircut, a History Channel documentary about Bigfoot was on tv while I waited.  It was very convincing, complete with scientific-looking analysis of the Patterson-Gimlin film and that casts of footprints that left no doubt that none of them could be made by humans or any other known species.  I also remember seeing Chariots of the Gods? when I was a child.  That, also, was totally convincing.  Of course, in both cases, I was unable to evaluate the evidence myself.  And films like this depend on that fact.

The first issues are subtle, and it’s hard to know whether they are intentional omissions or just sloppy production.  While it’s clear that the phosphatised fossils are of Chinese origin, the locality was not named.***  I was left with the clear impression that the microfossils underlay the Chengjiang site – they didn’t say so, but the implication was present.  After all, Chien never claims that he worked on the Chengjiang fossils, only on the phosphatised microfossils, but the movie’s website clearly states that Chien had “done research in the renowned fossil beds of Chengjiang, China”.**** So I started looking.  As is often the case, Wikipedia provided an excellent entry-point to the scientific literature.

As best I can determine, Chien is talking about the Doushantuo Formation which is located not in Chengjiang, but in the neighbouring province of Guizhou.  It’s apparently about 40-45 million years older than the Chengjiang fauna, rather than 10-20 million, but Meyer made it clear that they didn’t think that differences of a few tens of millions of years were all that important to their argument.***  Nonetheless, the fact that the Doushantuo Formation appears to be a somewhat singular environment means that you can’t conclude with any certainty that the fossils represented there represent the whole range of life forms or body types that existed at the time it was being deposited.  In fact, since the Doushantuo Formation overlaps with other Ediacaran assemblages, it’s pretty safe to say that it’s not a representative sample of life on earth 590-565 million years ago.  But the real problem arises with Chien’s insistence that the microfossils aren’t ancestral to modern metazoans.  Although most of them appear to be sponges and cnidarians, others have been described as being bilaterally symmetrical organisms like Vernanimicula.  While the identification of Vernanimicula as an early metazoan has been disputed, it isn’t something you can simply ignore, especially if you are trying to use the Doushantuo fossils to make the case that Cambrian metazoans could not have evolved from Precambrian organisms.   (A Google Scholar search for recent articles about Doushantuo shows that there is ongoing debate about the nature of the Duoshantuo fauna, including reports of “annelid-like” fossils.  While there’s plenty of reason to be skeptical of claims like these, it’s pretty clear that the study and interpretation of this field is active and dynamic.)

While the movie spends a lot of time on the Doushantuo microfossils, little is said about the remainder of the Ediacaran fauna.  They’re basically characterised as outliers, unusual organisms that bear little relation to the groups of organisms present in the Cambrian.  And they were said to have disappeared before the beginning of the Cambrian.  Not knowing much about the Ediacarans, I found it hard to evaluate the movie’s claims.  But there’s a vast scientific literature out there, just waiting to be discovered (though, apparently, not by the creators of Darwin’s Dilemma).  A review article published in the January issue of Trends in Ecology & Evolution***** discusses the presence of bilaterally symmetrical organisms among the Ediacaran fauna, and identifies them as likely members of the ‘stem group’ that gave rise to the modern bilateral metazoans.  Despite what the movie suggests, the Cambrian fauna did not appear “as if out of nowhere”.  The presence of the ancestral forms among the Ediacarans appears to be fairly well-established.

Beyond this point the movie stops wandering along the fringe and steps boldly away from modern science.  (More to come).

– – – – – – – – – –
*One of the interviewees says this.  I believe it was Chien, but I’m not 100% certain that it was.
**In addition to the phosphatised microfossils, they also discussed – and dismissed – the Ediacaran fauna.
***As best I can recall.
****There’s no reason to assume that this information is intentionally meant to be misleading.  Rather, that whoever put together the web site for the movie got their information from the movie, and assumed that the microfossils came from “the renowned fossil beds of Chengjiang, China”.
*****Xiao, Shuhai and Mark Laflamme. 2009. On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota. Trends in Ecology & Evolution 24 (1): 31-40


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