Sunday, October 4, 2009

The Cambrian Explosion, the Discovery Institute, and Cambrian Diversity

I intend to write a set of blog posts addressing the comments and thoughts on Darwin’s Dilemma from people who have seen the film. This is useful because people who do not have a background in the Cambrian Explosion or palaeontology are the people that the Discovery Institute is hoping to mislead. So what such people are taking away from the film, the messages that the Discovery Institute is hoping to instill, the questions raised in people’s minds, etc., are worth addressing.

Previous posts can be found here.

This post is in response to Ian’s comments here, and addresses what appears to be a failure to understand the basics about the environment of deposition of the Burgess Shale and the Chengjiang faunas. This is a bit of a side bar, but does illustrate the modus operandi of the Discovery Institute, which can be described as ‘the Art of the Superficial’
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”.
OK, to describe the difference in diversity between the two faunas as anything meaningful is to look at the issue purely from a simplistic, superficial view. But then Intelligent Design is a monument to the superficial viewpoint, based as it is on the idea that, ‘gee willikers, that there fla-gell-um looks toooo complex to have e-volved, it must have been de-signed’.

Detailed investigation (i.e. science) is the antithesis of the Art of the Superficial. Detailed investigation blew away the myth that the flagellum was irreducibly complex, and showed that it was similar to a type III secretion system.

Detailed investigation shows that the Chengjiang fauna is more diverse that the Burgess Shale fauna for reasons that have nothing to do with the diversity of life at the time. It is known that the Burgess Shale fauna, while spectacular, is a restricted fauna. It does not represent the breadth of life at the time. The fauna has been washed in over a steep limestone escarpment into deep, oxygen poor, water over 160 metres deep (see for example Briggs et al 1994).

The Chengjiang fauna, while also predominately a washed-in fauna, was positioned in open water at the foot of a delta at around 100 metres deep (see for example Chen and Zhou 1997, Hou et al 2004). A much more open system and so would be expected to sample a greater range of organisms.

One datum point from one location in Chengjiang and Burgess Shale time does not tell us about overall diversity during either time, unless you use the Art of the Superficial.

Briggs, D.E.G., Erwin, D.H. and Collier, F.J. (1994) The Fossils of the Burgess Shale. Smithsonian Institute Press. 238pp.

Hou, X-G; Aldridge, R.J., Bengstrom, J, Siveter, D. J., Feng, X-H (2004) The Cambrian Fossils of Chengjang, China. Blackwell Science. 233pp.

Junyuan Chen and Guiqing Zhou (1997) Biology of the Chengjiang fauna. Bulletin of the National Museum of Natural Science. 10. p.11-106.

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