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The Flagellum Unspun

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August 27, 2009 Tags: Design

Today's entry was written by the BioLogos Editorial Team. You can read more about what we believe here.

The Flagellum Unspun

In his book No Free Lunch, William Dembski makes the case for intelligent design by arguing that the bacterial flagellum, thanks to its apparent irreducible and specified complexity, could never have been produced through evolution. To support his argument, Dembski presents a calculation for the flagellum, which he describes as a "discrete combinatorial object".

According to him, "the probability of assembling such an object can be calculated by determining the probabilities that each of its components might have originated by chance, that they might have been localized to the same region of the cell, and that they would be assembled in precisely the right order", probabilities that he calls Porig, Plocal, and Pconfig.

His calculations find the probability of the flagellum assembling by chance to be 10-1170, a probability far below what he considers a threshold for highly improbably events or "universal probability bound". Thus, argues Demsbki, the flagellum must be the result of an intelligent designer's intervention.

However, in his article "The Flagellum Unspun", biologist Ken Miller points out that Dembski's calculations miss several important aspects of biological evolution. Most importantly, as Miller points out, calculations treating the flagellum as a "discrete combinatorial object" only show that it is highly unlikely that the parts of the flagellum assembled spontaneously. No one has argued, however, that the flagellum was formed this way. Evolution works by using pre-existing structures rather than spontaneously creating entirely new ones.

In the case of the flagellum, the proteins of another bacterial system -- the type III secretory system, which allows the bacteria to translocate proteins directly into a host's cytoplasm -- are directly homologous to the basal portion of bacterial flagellum. This secretory system does not contain all 30 or so proteins that are present in the flagellum, yet this subset serves a purpose on its own. It seems likely, then, that the evolutionary pathway that resulted in the flagellum also includes the type III secretory system. The flagellum, then, is not irreducibly complex.

Miller ends his article by explaining the difference between acknowledging that nature reflects the higher purpose of a divine intelligence, and what the modern theory of "intelligent design" entails:

"Their views demand not a universe in which the beauty and harmony of natural law has brought a world of vibrant and fruitful life into existence, but rather a universe in which the emergence and evolution of life is made expressly impossible by the very same rules. Their view requires that the source of each and every novelty of life was the direct and active involvement of an outside designer whose work violated the very laws of nature he had fashioned. The world of intelligent design is not the bright and innovative world of life that we have come to know through science. Rather, it is a brittle and unchanging landscape, frozen in form and unable to adapt except at the whims of its designer."

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glsi - #64046

August 15th 2011

Trouble is we don’t have a shred of evidence that any simpler, more primitive cells have ever existed.  So it sure doesn’t “seem likely” to me that a type III secrectory system was running around somewhere before the flagellum.  Based on belief in what?  Undemonstrated chemical evolution?  You might want to find some evidence first because your “directly homologous” hypotheses are far from convincing.  

Jon Garvey - #64050

August 16th 2011

I wonder why this article never attracted any comment when it was first published in 2009? Since then, of course, the case has been well made thatt the type III secretory system is quite likely to have developed after the flagellum.

But what annoys me is the rhetoric that colours these issues, which ought to be discussed on the evidence. Just try rephrasing Miller’s final words in terms of our modern technological society:

“The world of human design is not the bright and innovative world of culture that we have come to know through living with high technology and contemporary styling . Rather, it is a brittle and unchanging landscape, frozen in form and unable to adapt except at the whims of its designers and artists.”

If someone wrote that in an article, you’d assume they were barking mad.

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