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The Bacterial Flagellum
The bacterial flagellum is an example of what Michael Behe describes
as an irreducibly complex system. In his book, Darwin's Black
Box, he explains that such irreducibly complex systems could
not have arisen by a gradual step-by-step Darwinian process.
Because the bacterial flagellum is necessarily composed of at
least three parts -- a paddle,a rotor, and a motor -- it is irreducibly
complex. Gradual evolution of the flagellum, like the cilium,
therefore faces mammoth hurdles. (p.72)
Behe summarizes the structure of the bacterial flagellum in
Some bacteria boast a marvelous swimming device, the flagellum,
which has no counterpart in more complex cells. In 1973 it was
discovered that some bacteria swim by rotating their flagella.
So the bacterial flagellum acts as a rotary propellor -- in contrast
to the cilium, which acts more like an oar.
The structure of a flagellum is quite different from that
of a cilium. The flagellum is a long, hairlike filament embedded
in the cell membrane. The external filament consists of a single
type of protein, called "flagellin." The flagellin
filament is the paddle surface that contacts the the liquid during
swimming. At the end of the flagellin filament near the surface
of the cell, there is a bulge in the thickness of the flagellum.
It is here that the filament attaches to the rotor drive. The
attachment material is comprised of something called "hook
protein." The filament of a bacterial flagellum, unlike
a cilium, contains no motor protein; if it is broken off, the
filament just floats stiffly in the water. Therefore the motor
that rotates the filament-propellor must be located somewhere
else. Experiments have demonstrated that it is located at the
base of the flagellum, where electron microscopy shows several
ring structures occur. The rotary nature of the flagellum has
clear, unavoidable consequences ... (pp. 70-72)
The consequences Behe refers to are inferred by the nature
of its irreducibly complex components, the discovery of which
undermines a Darwinian explanation of origins. Behe concludes:
In summary, as biochemists have begun to examine apparently
simple structures like cilia and flagella, they have discovered
staggering complexity, with dozens or even hundreds of precisely
tailored parts. It is very likely that many of the parts we have
not considered here are required for any cilium to function in
a cell. As the number of equired parts increases, the difficulty
of gradually putting the system together skyrockets, and the
likelihood of indirect scenarios plummets. Darwin looks more
and more forlorn. New research on the roles of the auxiliary
proteins cannot simplify the irreducibly complex syetem The intransigence
of the problem cannot be alleviated; it will only get worse.
Darwinian theory has given no explanation for the cilium or flagellum.
The overwhelming complexity of the swimming systems push us to
think it may never give an explanation. (p. 73)
Behe concludes that such irreducibly complex systems were ultimately
the result of intelligent design. (It should be pointed out that
Behe has no objections to the concept of universal common ancestry.
His objections to evolution are limited to the rejection of the
neo-Darwinian mechanism as a sufficient explanation for the origin
of all biological systems.)
Copyright © 1998 Michael J. Behe.
All rights reserved. International copyright secured.
File Date: 6.10.98
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