|Flagellum controversy continues|
The bacterial flagellum is a miniature motor that propels bacteria through watery environments. Over ten years ago, biochemist Michael Behe identified the flagellum as a biological structure whose evolution would face “mammoth hurdles.”
Since then, it has been suggested by many Darwinists that the bacterial flagellum has evolved from a simpler structure, the Type Three Secretory System (TTSS). In 2006, Richard Dawkins wrote: “To the evolutionist, it is clear that TTSS components were commandeered for a new, but not wholly unrelated function when the flagellar motor evolved.” This single step was the only step that Dawkins could suggest in an evolutionary pathway to the flagellum, so he added “a lot more work needs to be done, of course, and I’m sure it will be.”
More work has now been done, and it is published here in the current issue of PNAS (Proceedings of the National Academy of Sciences of the USA).
Two scientists at the University of Arizona, Renyi Liu and Howard Ochman claim to show how the flagellum could have evolved from simple beginnings in a paper titled “Stepwise formation of the bacterial flagellar system.”
The introduction of their paper is very clear that the evolution of the bacterial flagellum is an unsolved problem. “Although several scenarios have been posited to explain how this organelle might have been originated, the actual series of evolutionary events that have given rise to the flagellum, as might be inferred from the relationships of all genes that contribute to the formation and expression of this organelle across taxa, has never been accomplished,” (p. 7116).
The authors disagree with the idea that the flagellum has evolved from the TTSS, and write that TTSS genes are “derived from” (p. 7120) flagellar genes. There is some evidence that the simpler structure of the TTSS could have evolved from the more complex structure of the flagellum, not vice versa.
In order to show how the bacterial flagellum might have evolved, the authors carried out a series of comparisons of the genes involved in the flagellar structure, both between 41 species of bacteria and within the species Escherichia coli. At the end of the paper they claim “we have shown the bacterial flagellum…originated from ‘‘so simple a beginning,’’ in this case, a single gene that underwent successive duplications and subsequent diversification during the early evolution of Bacteria.” (p. 7120).
This conclusion is “most mystifying” according to Darwinist Nick Matzke at Panda’s Thumb, who provides a detailed analysis of the paper. “There is just no way that the flagellum evolved by diversification of a single gene,” he writes. Matzke is on the staff of the National Center for Science Education and has written papers himself seeking to solve the problem of the flagellum’s evolution. But he is very unconvinced by Liu and Ochman’s contribution, saying it contains “totally mystifying rhetoric” and “many dubious interpretations on specific points.”
Protagonists on the other side of the controversy are equally dismissive. ID-advocate Michael Behe says here, “despite the authors’ apparent confusion, the paper does not even try to address the irreducible complexity of the flagellum or its need for intelligent design.”
The main take-home message from the new paper seems to be that the origins of the bacterial flagellum remain unexplained in Darwinian terms. Both the one step favoured by Richard Dawkins, and the new conclusions of Lui and Ochman appear to be unsubstantiated by evidence.
The bacterial flagellum features in a lesson plan available on the TiS website here.
A fair result can be obtained only by fully stating and balancing the facts and arguments on both sides of each question.