Forgive me for late entry into the discussion of Dembski's paper. I
have been "out of the loop" (and off the list) for a while, and have
not paid enough attention recently: when did the bacterial flagellum
become the prime biological example of Irreducible Complexity? Where
does Dembski get the certainty that "we know the flagellum is
irreducibly complex"? I suggest it's no better an example than Behe's
terrible choice (in Darwin's Black Box) of the eukaryotic flagellum -
one of the MOST COMPLEX motile organelles known!
(For the non-biologists, the two classes of flagellum are utterly
different in design and function; the bacterial one is like a rigid
corkscrew/propellor powered by a rotary motor inserted in the cell
wall; the eukaryotic one is an undulating structure based on the much
used motor+track system of motility).
As I understand Ken Miller has observed (I haven't read his Finding
Darwin's God), too little is known about the bacterial flagellum to be
able to say what's required for its function. I observed some of
DeRosier's structural work on the bacterial flagellum over the 20+
years he and I worked in the same structure lab, where I was working
on the best characterized motor+track system - the muscle cell. For
the flagellum, the structures of none of the (as I recall more than
20) gene products are yet known at high resolution, and the nature of
the rotor/stator interaction remains unclear. DeRosier rightly says
that the "mechanism of the flagellar motor" is still unknown.
If Dembski (and Behe) want to identify IRREDUCIBLE COMPLEXITY in
motility, logically they would do well to ask what is known about the
LEAST COMPLEX motile systems. Start from the muscle cell, every bit as
"machine-like" as the flagellum, and ask what it's essential
components are: two proteins, myosin (the motor) and actin (the
track); four genes (myosin heavy chain, two classes of myosin light
chains, actin). Muscle myosin is just one member of the myosin
"superfamily," which (when I left the field 5 yrs ago) comprised about
13 myosin families, found in everything from plant cells to yeast to
muscles to the human brain. Actin is found in almost all cells.
(Motor+track systems include not only myosins that move along or tug
on actin tracks, but kinesin and dynein motors (both protein
superfamilies) that move on tubulin (microtubule) tracks).
Unlike the flagellum, how myosin+actin motile systems work is known in
detail. From crystallography, the atomic structure of muscle myosin in
the presence of several nucleotide species (motor+track systems are
ATP-driven) is known, and the changes of structure that drive the
motions of myosin's "lever-arm" are now largely understood. The atomic
structure of actin is also known; the structure of the myosin-actin
complex is known at sufficient resolution to map the protein-protein
interactions at the level of amino acid residues.
So it's possible to guess with some degree of confidence what an
"irreducible" motile system of the motor+track type would look like.
Indeed we have probably seen something like it in one of the dozens of
known myosin-actin complexes. A "minimal" myosin-like motor would
probably be a protein no bigger than 200kD; actin is a ubiquitous
globular protein around 50kD that self-assembles into
filaments/tracks. The "irreducible" basis of the most common form of
motility would then be the directional interaction of two small
proteins, fueled by ATP.
What "complexity" is left at this point? The sequence of two
proteins? But if that's what's "irreducible", the flagellum (or a
muscle cell) are straw men, and Intelligent Design in biology amounts
to the argument that "you can't produce a protein by chance," which
seems to be Dembski's main theme.
So I would argue, for the case of motility that I know most about,
that "irreducible complexity," (in any but the sense of specific
DNA/protein sequences) remains an unproved assertion.
Grace and peace,
Peter Vibert
----------------------------------
wrcc@i-2000.com
Pastor
Wading River Congregational Church
PO Box 596
Wading River, NY 11792
Guest Senior Scientist
Biology Department
Brookhaven National Laboratory
Upton, NY 11973
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