Thursday, April 10, 2008

science works

the remarkable flagellum

I note that in a couple of recent issues of New Scientist they've been having a go - belatedly? - at creationists attempts to undermine evolutionary theory with their two pet objections, irreducible complexity and so-called gaps in the fossil record [which also has a high-falutin moniker I can't currently recall].

The intellectual debate on this matter seems to be over, but a great deal of noise remains of course, and the film Expelled, which I don't think has been released yet even in the US, will add to the static.

For my own sake I'll summarise the objections, via the New Scientist articles. The supposed lack of 'transitional' species 'between' highly distinct species makes a mockery of evolutionary theory, according to the creationists. If they're smart enough, they'll even know that Darwin himself was concerned at this lack. Donald Prothero, author of the March New Scientist article, and of a new book, Evolution: What the fossils say and why it matters, marshals the evidence and the arguments against this objection, pointing to the 'fishibian' record, synapsids [the ancestors of mammals], ceratopsians [horned dinosaurs] and many other 'transitional' forms, from mammals to worms [the term transitional being problematic because it suggests that these were not fully fledged forms in their own right, that they were halfway houses in some sense]. He's pretty conclusive about the richness of the fossil record for all those who don't wish to remain willfully blind to it.

The case of the bacterial flagellum has been claimed as a prime example of designed complexity by creationists, and they attempted to use it to promote their case in Dover, Pennsylvania in 2005. The failure of the creationists in that case, considering the bizarre context of American religious politics, was a great victory for those who respect evidence and reason.

A lot of work has been done recently on the bacterial flagellum, no doubt prompted , at least partly, by the attention devoted to it by the creationists. So what is it? It's a mechanism for moving bacteria about in fluids, and it can be divided into three protein-constructed parts, a basal body, a hook and a filament. The basal body is the key to this mechanism, and it is indeed extraordinarily complex. Embedded in the cell wall, it has been described as a sort of outboard motor for the bacterium. It consists of a series of minuscule rings, with a rotating rod in the centre, attached to a hook...

These manically rotating rods and hooks are driven by the flow of sodium and hydrogen ions. The intricacy of the mechanism has long intrigued biologists, and creationists have latched onto it for their own purposes. However, in the nineties the discovery and analysis of ‘type III secretion systems’ [T3SS] helped in breaking down the mystery. This complex protein system is used in certain bacteria to inject toxins into their hosts. A number of the same proteins are found in the flagellum’s protein export system, and the two systems have subsequently been found to be variants of each other, with probably a common ancestry. It's all about homology - homologies in the bone structure of whales, horses and bats, for example, have led to an understanding of the common ancestry of these apparently unconnected creatures. Homologies in DNA or amino acid sequencing similarly reveal shared descent, and such homologies are regularly being turned up in discoveries that chip away at claims about irreducible complexity.

Analysis continues on the relationship between flagella and their components [there is in fact no one flagellum, there are a number, which differ slightly in detail], and there is much debate about findings - for example, were the flagella a development from the T3SS, or vice versa, or neither. Much of this debate lies beyond my competence to report, but there's no dissension about the fact that gene duplication and diversification are involved. In other words, it's all about evolution. Irreducible complexity can no longer be claimed with regard to these ingenious structures, but the creationists will no doubt find something else to pin their hopes on.

Turning to the more general issue, creationists have nothing testable to offer as an alternative to evolution. God did it, but there is no method, no theory, no direction for research, nothing. Presumably they believe in a return to the fixity-of-species model which proved a dead-end centuries ago. Some seem to be suggesting though, a combination of evolution and fixity. Coherence is a real problem.

There's an interesting discussion of some of these matters here, gathered around the question of whether creationism should be dismissed as total non-science [and non-sense] or critiqued as very bad science. I lean towards the former view. It bears no resemblance to science as currently practiced, it merely tries to ape science-speak and, far less successfully, scientific method, for credibility purposes.


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