No need to thank me but you're welcome anyway:
"Almost from the moment/The Origin of Species/was published in 1859,
the opponents of evolution have fought a long, losing battle against
their Darwinian foes. Today, like a prizefighter in the late rounds
losing badly on points, they've placed their hopes in one big punch
– a single claim that might smash through the overwhelming weight of
scientific evidence to bring Darwin to the canvas once and for all.
Their name for this virtual roundhouse right is "intelligent design."
In the last several years, the intelligent design movement has
attempted to move against science education standards in several
American states, most famously in Kansas and Ohio (Holden 1999; Gura
2002). The principal claim made by adherents of this view is that
they can detect the presence of "intelligent design" in complex
biological systems. As evidence, they cite a number of specific
examples, including the vertebrate blood clotting cascade, the
eukaryotic cilium, and most notably, the eubacterial flagellum (Behe
1996a, Behe 2002).
Of all these examples, the flagellum has been presented so often as
a counter-example to evolution that it might well be considered the
"poster child" of the modern anti-evolution movement. Variations of
its image (Figure 1) now appear on web pages of anti-evolution
groups like the Discovery Institute, and on the covers of
"intelligent design" books such as William Dembski's/No Free
Lunch/(Dembski 2002a). To anti-evolutionists, the high status of the
flagellum reflects the supposed fact that it could not possibly have
been produced by an evolutionary pathway.
*Figure 1:*The eubacterial flagellum. The flagellum is an
ion-powered rotary motor, anchored in the membranes surrounding the
bacterial cell. This schematic diagram highlights the assembly
process of the bacterial flagellar filament and the cap-filament
complex. OM, outer membrane; PG, peptidoglycan layer; IM,
cytoplasmic membrane (From Yonekura/et al/2000).
There is, to be sure, nothing new or novel in an anti-evolutionist
pointing to a complex or intricate natural structure, and professing
skepticism that it could have been produced by the "random"
processes of mutation and natural selection. Nonetheless, the
"argument from personal incredulity," as such sentiment has been
appropriately described, has been a weapon of little value in the
anti-evolution movement. Anyone can state at any time
that/they/cannot imagine how evolutionary mechanisms might have
produced a certain species, organ, structure. Such statements,
obviously, are personal – and they say more about the limitations of
those who make them than they do about the limitations of Darwinian
mechanisms.
The hallmark of the intelligent design movement, however, is that it
purports to rise above the level of personal skepticism. It claims
to have found a/reason/why evolution could not have produced a
structure like the bacterial flagellum, a reason based on sound,
solid scientific evidence.
Why does the intelligent design movement regard the flagellum as
unevolvable? Because it is said to possesses a quality known as
"irreducible complexity." Irreducibly complex structures, we are
told, could not have been produced by evolution, or, for that
matter, by any natural process. They do exist, however, and
therefore they must have been produced by something. That something
could only be an outside intelligent agency operating beyond the
laws of nature – an intelligent designer. That, simply stated, is
the core of the new argument from design, and the intellectual basis
of the intelligent design movement.
The great irony of the flagellum's increasing acceptance as an icon
of anti-evolution is that fact that research had demolished its
status as an example of irreducible complexity almost at the very
moment it was first proclaimed. The purpose of this article is to
explore the arguments by which the flagellum's notoriety has been
achieved, and to review the research developments that have now
undermined they very foundations of those arguments.
*The Argument's Origins*
The flagellum owes its status principally to/Darwin's Black
Box/(Behe 1996a) a book by Michael Behe that employed it in a
carefully-crafted anti-evolution argument. Building upon William
Paley's well-known "argument from design," Behe sought to bring the
argument two centuries forward into the realm of biochemistry. Like
Paley, Behe appealed to his readers to appreciate the intricate
complexity of living organisms as evidence for the work of a
designer. Unlike Paley, however, he raised the argument to a new
level, claiming to have discovered a scientific principle that could
be used to prove that certain structures could not have been
produced by evolution. That principle goes by the name of
"irreducible complexity."
An irreducibly complex structure is defined as ". . . a single
system composed of several well-matched, interacting parts that
contribute to the basic function, wherein the removal of any one of
the parts causes the system to effectively cease functioning." (Behe
1996a, 39) Why would such systems present difficulties for
Darwinism? Because they could not possibly have been produced by the
process of evolution:
/"An irreducibly complex system cannot be produced directly by
numerous, successive, slight modifications of a precursor system,
because any precursor to an irreducibly complex system that is
missing a part is by definition nonfunctional. .... Since natural
selection can only choose systems that are already working, then if
a biological system cannot be produced gradually it would have to
arise as an integrated unit, in one fell swoop, for natural
selection to have anything to act on."/(Behe 1996b)
The phrase "numerous, successive, slight modifications" is not
accidental. The very same words were used by Charles Darwin in/The
Origin of Species/in describing the conditions that had to be met
for his theory to be true. As Darwin wrote, if one could find an
organ or structure that could not have been formed by "numerous,
successive, slight modifications," his "theory would absolutely
break down" (Darwin 1859, 191). To anti-evolutionists, the bacterial
flagellum is now regarded as exactly such a case – an "irreducibly
complex system" which "cannot be produced directly by numerous
successive, slight modifications." A system that could not have
evolved – a desperation punch that just might win the fight in the
final round – a tool with which the theory of evolution can be
brought down.
*The Logic of Irreducible Complexity*
Living cells are filled, of course, with complex structures whose
detailed evolutionary origins are not known. Therefore, in
fashioning an argument against evolution one might pick nearly any
cellular structure, the ribosome for example, and claim – correctly
– that its origin has not been explained in detail by evolution.
Such arguments are easy to make, of course, but nature of scientific
progress renders them far from compelling. The lack of a detailed
current explanation for a structure, organ, or process does not mean
that science will never come up with one. As an example, one might
consider the question of how left-right asymmetry arises in
vertebrate development, a question that was beyond explanation until
the 1990s (Belmonte 1999). In 1990 one might have argued that the
body's left-right asymmetry could just as well be explained by the
intervention of a designer as by an unknown molecular mechanism.
Only a decade later, the actual molecular mechanism was identified
(Stern 2002), and any claim one might have made for the intervention
of a designer would have been discarded. The same point can be made,
of course, regarding any structure or mechanism whose origins are
not yet understood.
The utility of the bacterial flagellum is that it seems to rise
above this "argument from ignorance." By asserting that it is a
structure "in which the removal of an element would cause the whole
system to cease functioning" (Behe 2002), the flagellum is presented
as a "molecular machine" whose individual parts must have been
specifically crafted to work as a unified assembly. The existence of
such a multipart machine therefore provides genuine scientific proof
of the actions of an intelligent designer.
In the case of the flagellum, the assertion of irreducible
complexity means that a minimum number of protein components,
perhaps 30, are required to produce a working biological function.
By the logic of irreducible complexity, these individual components
should have no function until all 30 are put into place, at which
point the function of motility appears. What this means, of course,
is that evolution could not have fashioned those components a few at
a time, since they do not have functions that could be favored by
natural selection. As Behe wrote: " . . . natural selection can only
choose among systems that are already working" (Behe 2002), and an
irreducibly complex system does not work unless all of its parts are
in place. The flagellum is irreducibly complex, and therefore, it
must have been designed. Case closed.
*Answering the Argument*
The assertion that cellular machines are irreducibly complex, and
therefore provide proof of design, has not gone unnoticed by the
scientific community. A number of detailed rebuttals have appeared
in the literature, and many have pointed out the poor reasoning of
recasting the classic argument from design in the modern language of
biochemistry (Coyne 1996; Miller 1996; Depew 1998; Thornhill and
Ussery 2000). I have suggested elsewhere that the scientific
literature contains counter-examples to any assertion that evolution
cannot explain biochemical complexity (Miller 1999, 147), and other
workers have addressed the issue of how evolutionary mechanisms
allow biological systems to increase in information content
(Schneider 2000; Adami, Ofria, and Collier 2000).
The most powerful rebuttals to the flagellum story, however, have
not come from direct attempts to answer the critics of evolution.
Rather, they have emerged from the steady progress of scientific
work on the genes and proteins associated with the flagellum and
other cellular structures. Such studies have now established that
the entire premise by which this molecular machine has been advanced
as an argument against evolution is wrong –*the bacterial flagellum
is not irreducibly complex*. As we will see, the flagellum – the
supreme example of the power of this new "science of design" – has
failed its most basic scientific test. Remember the claim that "any
precursor to an irreducibly complex system that is missing a part is
by definition nonfunctional?" As the evidence has shown, nature is
filled with examples of "precursors" to the flagellum that are
indeed "missing a part," and yet are fully-functional. Functional
enough, in some cases, to pose a serious threat to human life.
*The Type -III Secretory Apparatus*
In the popular imagination, bacteria are "germs" – tiny microscopic
bugs that make us sick. Microbiologists smile at that
generalization, knowing that most bacteria are perfectly benign, and
many are beneficial – even essential – to human life. Nonetheless,
there are indeed bacteria that produce diseases, ranging from the
mildly unpleasant to the truly dangerous. Pathogenic, or
disease-causing, bacteria threaten the organisms they infect in a
variety of ways, one of which is to produce poisons and inject them
directly into the cells of the body. Once inside, these toxins break
down and destroy the host cells, producing illness, tissue damage,
and sometimes even death.
In order to carry out this diabolical work, bacteria must not only
produce the protein toxins that bring about the demise of their
hosts, but they must efficiently inject them across the cell
membranes and into the cells of their hosts. They do this by means
of any number of specialized protein secretory systems. One, known
as the type III secretory system (TTSS), allows gram negative
bacteria to translocate proteins directly into the cytoplasm of a
host cell (Heuck 1998). The proteins transferred through the TTSS
include a variety of truly dangerous molecules, some of which are
known as "virulence factors," and are directly responsible for the
pathogenic activity of some of the most deadly bacteria in existence
(Büttner and Bonas 2002; Heuck 1998).
At first glance, the existence of the TTSS, a nasty little device
that allows bacteria to inject these toxins through the cell
membranes of its unsuspecting hosts, would seem to have little to do
with the flagellum. However, molecular studies of proteins in the
TTSS have revealed a surprising fact – the proteins of the TTSS are
directly homologous to the proteins in the basal portion of the
bacterial flagellum. As figure 2 (Heuck 1998) shows, these
homologies extend to a cluster of closely-associated proteins found
in both of these molecular "machines." On the basis of these
homologies, McNab (McNab 1999) has argued that the flagellum itself
should be regarded as a type III secretory system. Extending such
studies with a detailed comparison of the proteins associated with
both systems, Aizawa has seconded this suggestion, noting that the
two systems "consist of homologous component proteins with common
physico-chemical properties" (Aizawa 2001, 163). It is now clear,
therefore, that a smaller subset of the full complement of proteins
in the flagellum makes up the functional transmembrane portion of
the TTSS.
*Figure 2:*There are extensive homologies between type III secretory
proteins and proteins involved in export in the basal region of the
bacterial flagellum. These homologies demonstrate that the bacterial
flagellum is not "irreducibly complex." In this diagram (redrawn
from Heuck 1998), the shaded portions of the basal region indicate
proteins in the/E. coli/flagellum homologous to the Type III
secretory structure of/Yersinia./. OM, outer membrane; PP,
periplasmic space; CM, cytoplasmic membrane.
Stated directly, the TTSS does its dirty work using a handful of
proteins from the base of the flagellum. From the evolutionary point
of view, this relationship is hardly surprising. In fact, it's to be
expected that the opportunism of evolutionary processes would mix
and match proteins to produce new and novel functions. According to
the doctrine of irreducible complexity, however, this should not be
possible. If the flagellum is indeed irreducibly complex, then
removing just one part, let alone 10 or 15, should render what
remains "by definition nonfunctional." Yet the TTSS is indeed
fully-functional, even though it is missing most of the parts of the
flagellum. The TTSS may be bad news for us, but for the bacteria
that possess it, it is a truly valuable biochemical machine.
The existence of the TTSS in a wide variety of bacteria demonstrates
that a small portion of the "irreducibly complex" flagellum can
indeed carry out an important biological function. Since such a
function is clearly favored by natural selection, the contention
that the flagellum must be fully-assembled before any of its
component parts can be useful is obviously incorrect. What this
means is that the argument for intelligent design of the flagellum
has failed.
*Counterattack*
Classically, one of the most widely-repeated charges made by
anti-evolutionists is that the fossil record contains wide "gaps"
for which transitional fossils have never been found. Therefore, the
intervention of a creative agency, an intelligent designer, must be
invoked to account for each gap. Such gaps, of course, have been
filled with increasing frequency by paleontologists – the
increasingly rich fossil sequences demonstrating the origins of
whales are a useful examples (Thewissen, Hussain, and Arif 1994;
Thewissen, Williams, Roe, and Hussain 2001). Ironically, the
response of anti-evolutionists to such discoveries is frequently to
claim that things have only gotten worse for evolution. Where
previously there had been just one gap, as a result of the
transitional fossil, now there are two (one on either side of the
newly-discovered specimen).
As word of the relationship between the eubacterial flagellum and
the TTSS has begun to spread among the "design" community, the first
hints of a remarkably similar reaction have emerged. The TTSS only
makes problems worse for evolution, according to this response,
because now there are two irreducibly-complex systems to deal with.
The flagellum is still irreducibly complex – but so is the TTSS. But
now there are two systems for evolutionists to explain instead of
just one.
Unfortunately for this line of argument, the claim that one
irreducibly-complex system might contain another is
self-contradictory. To understand this, we need to remember that the
entire point of the design argument, as exemplified by the
flagellum, is that only the entire biochemical machine, with all of
its parts, is functional. For the intelligent design argument to
stand, this must be the case, since it provides the basis for their
claim that only the complete flagellum can be favored by natural
selection, not any its component parts.
However, if the flagellum contains within it a smaller functional
set of components like the TTSS, then the flagellum itself cannot be
irreducibly complex – by definition. Since we now know that this is
indeed the case, it is obviously true that the flagellum is not
irreducibly complex.
A second reaction, which I have heard directly after describing the
relationship between the secretory apparatus and the flagellum, is
the objection that the TTSS does not tell us how either it or the
flagellum evolved. This is certainly true, although Aizawa has
suggested that the TTSS may indeed be an evolutionary precursor of
the flagellum (Aizawa 2001). Nonetheless, until we have produced a
step-by-step account for the evolutionary derivation of the
flagellum, one may indeed invoke the argument from ignorance for
this and every other complex biochemical machine.
However, in agreeing to this, one must keep in mind that the
doctrine of irreducible complexity was intended to go one step
beyond the claim of ignorance. It was fashioned in order to provide
a rationale for claiming that the bacterial flagellum couldn't have
evolved, even in principle, because it is irreducibly complex. Now
that a simpler, functional system (the TTSS) has been discovered
among the protein components of the flagellum, the claim of
irreducible complexity has collapsed, and with it any "evidence"
that the flagellum was designed.
*Combinatorial Argument*
At first glance, William Dembski's case for intelligent design seems
to follow a distinctly different strategy in dealing with biological
complexity. His recent book,/No Free Lunch/(Dembski 2002a), lays out
this case, using information theory and mathematics to show that
life is the result of intelligent design. Dembski makes the
assertion that living organisms contain what he calls "complex
specified information" (CSI), and claims to have shown that the
evolutionary mechanism of natural selection cannot produce CSI.
Therefore, any instance of CSI in a living organism must be the
result of intelligent design. And living organisms, according to
Dembski, are chock-full of CSI.
Dembski's arguments, couched in the language of information theory,
are highly technical and are defended, almost exclusively, by
reference to their utility in detecting information produced by
human beings. These include phone and credit card numbers,
symphonies, and artistic woodcuts, to name just a few. One might
then expect that Dembski, having shown how the presence of CSI can
be demonstrated in man made objects, would then turn to a variety of
biological objects. Instead, he turns to just one such object, the
bacterial flagellum.
Dembski then offers his readers a calculation showing that the
flagellum could not have possibly have evolved. Significantly, he
begins that calculation by linking his arguments to those of Behe,
writing: "I want therefore in this section to show how irreducible
complexity is a special case of specified complexity, and in
particular I want to sketch how one calculates the relevant
probabilities needed to eliminate chance and infer design for such
systems" (Dembski 2002a, 289). Dembski then tells us that an
irreducibly complex system, like the flagellum, is a "discrete
combinatorial object." What this means, as he explains, is that 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. Dembski refers to these three
probabilities as*P*orig,*P*local, and*P*config, and he regards each
of them as separate and independent (Dembski 2002a, 291).
This approach overlooks the fact that the last two probabilities are
actually contained within the first. Localization and self-assembly
of complex protein structures in prokaryotic cells are properties
generally determined by signals built into the primary structures of
the proteins themselves. The same is likely true for the amino acid
sequences of the 30 or so protein components of the flagellum and
the approximately 20 proteins involved in the flagellum's assembly
(McNab 1999; Yonekura/et al/2000). Therefore, if one gets the
sequences of all the proteins right, localization and assembly will
take care of themselves.
To the ID enthusiast, however, this is a point of little concern.
According to Dembski, evolution could still not construct the 30
proteins needed for the flagellum. His reason is that the
probability of their assembly falls below what he terms the
"universal probability bound." According to Dembski, the probability
bound is a sensible allowance for the fact that highly improbable
events do occur from time to time in nature. To allow for such
events, he agrees that given enough time, any event with a
probability larger than 10-150might well take place. Therefore, if a
sequence of events, such as a presumed evolutionary pathway, has a
calculated probability less than 10-150, we may conclude that the
pathway is impossible. If the calculated probability is greater than
10-150, it's possible (even if unlikely).
When Dembski turns his attention to the chances of evolving the 30
proteins of the bacterial flagellum, he makes what he regards as a
generous assumption. Guessing that each of the proteins of the
flagellum have about 300 amino acids, one might calculate that the
chances of getting just one such protein to assemble from "random"
evolutionary processes would be 20-300, since there are 20 amino
acids specified by the genetic code. Dembski, however, concedes that
proteins need not get the/exact/amino acid sequence right in order
to be functional, so he cuts the odds to just 20-30, which he tells
his readers is "on the order of 10-39"(Dembski 2002a, 301). Since
the flagellum requires 30 such proteins, he explains that 30 such
probabilities "will all need to be multiplied to form the
origination probability"(Dembski 2002a, 301). That would give us an
origination probability for the flagellum of 10-1170, far below the
universal probability bound. The flagellum couldn't have evolved,
and now we have the numbers to prove it. Right?
*Assuming Impossibility*
I have no doubt that to the casual reader, a quick glance over the
pages of numbers and symbols in Dembski's books is impressive, if
not downright intimidating. Nonetheless, the way in which he
calculates the probability of an evolutionary origin for the
flagellum shows how little biology actually stands behind those
numbers. His computation calculates only the probability of
spontaneous, random assembly for each of the proteins of the
flagellum. Having come up with a probability value on the order of
10-1170, he assures us that he has shown the flagellum to be
unevolvable. This conclusion, of course, fits comfortably with his
view is that "The Darwinian mechanism is powerless to produce
irreducibly complex systems..." (Dembski 2002a, 289).
However complex Dembski's analysis, the scientific problem with his
calculations is almost too easy to spot. By treating the flagellum
as a "discrete combinatorial object" he has shown only that it is
unlikely that the parts flagellum could assemble spontaneously.
Unfortunately for his argument, no scientist has ever proposed that
the flagellum or any other complex object evolved that way. Dembski,
therefore, has constructed a classic "straw man" and blown it away
with an irrelevant calculation.
By treating the flagellum as a discrete combinatorial object he has
assumed in his calculation that no subset of the 30 or so proteins
of the flagellum could have biological activity. As we have already
seen, this is wrong. Nearly a third of those proteins are closely
related to components of the TTSS, which does indeed have biological
activity. A calculation that ignores that fact has no scientific
validity.
More importantly, Dembski's willingness to ignore the TTSS lays bare
the underlying assumption of his entire approach towards the
calculation of probabilities and the detection of "design."/He
assumes what he is trying to prove./
According to Dembski, the detection of "design" requires that an
object display complexity that could not be produced by what he
calls "natural causes." In order to do that, one must first examine
all of the possibilities by which an object, like the flagellum,
might have been generated naturally. Dembski and Behe, of course,
come to the conclusion that there are no such natural causes. But
how did they determine that? What is the scientific method used to
support such a conclusion? Could it be that their assertions of the
lack of natural causes simply amount to an unsupported personal
belief? Suppose that there are such causes, but they simply happened
not to think of them? Dembski actually seems to realize that this is
a serious problem. He writes: "Now it can happen that we may not
know enough to determine all the relevant chance hypotheses [which
here, as noted above, means/all relevant natural processes/(hvt)].
Alternatively, we might think we know the relevant chance
hypotheses, but later discover that we missed a crucial one. In the
one case a design inference could not even get going; in the other,
it would be mistaken" (Dembski 2002, 123 (note 80)).
What Dembski is telling us is that in order to "detect" design in a
biological object one must first come to the conclusion that the
object could not have been produced by any "relevant chance
hypotheses" (meaning, naturally, evolution). Then, and only then,
are Dembski's calculations brought into play. Stated more bluntly,
what this really means is that the "method" first involves/assuming
the absence/of an evolutionary pathway leading to the object,
followed by a calculation "proving" the impossibility of spontaneous
assembly. Incredibly, this/a priori/reasoning is exactly the sort of
logic upon which the new "science of design" has been constructed.
Not surprisingly, scientific reviewers have not missed this point –
Dembski's arguments have been repeatedly criticized on this issue
and on many others (Orr 2002; Charlesworth 2002; Padian 2002).
*Designing the Cycle*
In assessing the design argument, therefore, it only/seems/as though
two distinct arguments have been raised for the unevolvability of
the flagellum. In reality, those two arguments, one invoking
irreducible complexity and the other specified complex information,
both depend upon a single scientifically insupportable position.
Namely, that we can look at a complex biological object and
determine with absolute certainty that none of its component parts
could have been first selected to perform other functions. The
discovery of extensive homologies between the Type III secretory
system and the flagellum has now shown just how wrong that position was.
When anti-evolutionary arguments featuring the bacterial flagellum
rose into prominence, beginning with the 1996 publication of
Darwin's Black Box (Behe 1996a), they were predicated upon the
assertion that each of the protein components of the flagellum were
crafted, in a single act of design, to fit the specific purpose of
the flagellum. The flagellum was said to be unevolvable since the
entire complex system had to be assembled first in order to produce
any selectable biological function. This claim was broadened to
include all complex biological systems, and asserted further that
science would never find an evolutionary pathway to any of these
systems. After all, it hadn't so far, at least according to one of
"design's" principal advocates:
/There is no publication in the scientific literature – in
prestigious journals, specialty journals, or books – that describes
how molecular evolution of any real, complex, biochemical system
either did occur or even might have occurred./(Behe 1996a, 185)
As many critics of intelligent design have pointed out, that
statement is simply false. Consider, as just one example, the Krebs
cycle, an intricate biochemical pathway consisting of nine enzymes
and a number of cofactors that occupies center stage in the pathways
of cellular metabolism. The Krebs cycle is "real," "complex," and
"biochemical." Does it also present a problem for evolution?
Apparently yes, according to the authors of a 1996 paper in the
Journal of Molecular evolution, who wrote:
/"The Krebs cycle has been frequently quoted as a key problem in the
evolution of living cells, hard to explain by Darwin’s natural
selection: How could natural selection explain the building of a
complicated structure in toto, when the intermediate stages have no
obvious fitness functionality?/(Melendez-Hevia, Wadell, and Cascante
1996)
Where intelligent design theorists throw up their hands and declare
defeat for evolution, however, these researchers decided to do the
hard scientific work of analyzing the components of the cycle, and
seeing if any of them might have been selected for other biochemical
tasks. What they found should be a lesson to anyone who asserts that
evolution can only act by direct selection for a final function. In
fact, nearly all of the proteins of the complex cycle can serve
different biochemical purposes within the cell, making it possible
to explain in detail how they evolved:
/In the Krebs cycle problem the intermediary stages were also
useful, but for different purposes, and, therefore, its complete
design was a very clear case of opportunism. . . . the Krebs cycle
was built through the process that Jacob (1977) called ‘‘evolution
by molecular tinkering,’’ stating that evolution does not produce
novelties from scratch: It works on what already exists. The most
novel result of our analysis is seeing how, with minimal new
material, evolution created the most important pathway of
metabolism, achieving the best chemically possible design. In this
case, a chemical engineer who was looking for the best design of the
process could not have found a better design than the cycle which
works in living cells."/(Melendez-Hevia, Wadell, and Cascante 1996)
Since this paper appeared, a study based on genomic DNA sequences
has confirmed the validity of this approach (Huynen, Dandekar, and
Bork 1999). By contrast, how would intelligent design have
approached the Krebs Cycle? Using Dembski's calculations as our
guide, we would first determine the amino acid sequences of each of
the proteins of the cycle, and then calculate the probability of
their spontaneous assembly. When this is done, an origination
probability of less than 10-400is the result. Therefore, the result
of applying "design" as a predictive science would have told both
groups of researchers that their ultimately successful studies would
have been fruitless, since the probability of spontaneous assembly
falls below the "universal probability bound."
We already know, however, the reason that such calculations fail.
They carry a built-in assumption that the component parts of a
complex biochemical system have no possible functions beyond the
completely assembled system itself. As we have seen, this assumption
is false. The Krebs cycle researchers knew better, of course, and
were able to produce two important studies describing how a real,
complex, biochemical system might have evolved – the very thing that
design theorists once claimed did not exist in the scientific
literature.
*The Failure of Design*
It is no secret that concepts like "irreducible complexity" and
"intelligent design" have failed to take the scientific community by
storm (Forrest 2002). Design has not prompted new research studies,
new breakthroughs, or novel insights on so much as a single
scientific question. Design advocates acknowledge this from time to
time, but they often claim that this is because the scientific deck
is stacked against them. The Darwinist establishment, they say,
prevents them from getting a foot in the laboratory door.
I would suggest that the real reason for the cold shoulder given
"design" by the scientific community, particularly by life science
researchers, is because time and time again its principal scientific
claims have turned out to be wrong. Science is a pragmatic activity,
and if your hypothesis doesn't work, it is quickly discarded.
The claim of irreducible complexity for the bacterial flagellum is
an obvious example of this, but there are many others. Consider, for
example, the intricate cascade of proteins involved in the clotting
of vertebrate blood. This has been cited as one of the principal
examples of the kind of complexity that evolution cannot generate,
despite the elegant work of Russell Doolittle (Doolittle and Feng
1987; Doolittle 1993) to the contrary. A number of proteins are
involved in this complex pathway, as described by Behe:
/When an animal is cut, a protein called Hagemann factor (XII)
sticks to the surface of cells near the wound. Bound Hagemann factor
is then cleaved by a protein called HMK to yield activated Hagemann
factor. Immediately the activated Hagemann factor converts another
protein, called prekallikrein, to its active form, kallikrein./(Behe
1996a, 84)
How important are each of these proteins? In line with the dogma of
irreducible complexity, Behe argues that each and every component
must be in place before the system will work, and he is perfectly
clear on this point:
/. . . none of the cascade proteins are used for anything except
controlling the formation of a clot. Yet in the absence of any of
the components, blood does not clot, and the system fails./(Behe
1996a, 86)
As we have seen, the claim that every one of the components must be
present for clotting to work is central to the "evidence" for
design. One of those components, as these quotations indicate, is
Factor XII, which initiates the cascade. Once again, however, a
nasty little fact gets in the way of intelligent design theory.
Dolphins lack Factor XII (Robinson, Kasting, and Aggeler 1969), and
yet their blood clots perfectly well. How can this be if the
clotting cascade is indeed irreducibly complex? It cannot, of
course, and therefore the claim of irreducible complexity is wrong
for this system as well. I would suggest, therefore, that the real
reason for the rejection of "design" by the scientific community is
remarkably simple – the claims of the intelligent design movement
are contradicted time and time again by the scientific evidence.
*The Flagellum Unspun*
In any discussion of the question of "intelligent design," it is
absolutely essential to determine what is meant by the term itself.
If, for example, the advocates of design wish to suggest that the
intricacies of nature, life, and the universe reveal a world of
meaning and purpose consistent with an overarching, possibly Divine
intelligence, then their point is philosophical, not scientific. It
is a philosophical point of view, incidentally, that I share, along
with many scientists. As H. Allen Orr pointed out in a recent review:
/Plenty of scientists have, after all, been attracted to the notion
that natural laws reflect (in some way that's necessarily poorly
articulated) an intelligence or aesthetic sensibility. This is the
religion of Einstein, who spoke of "the grandeur of reason incarnate
in existence" and of the scientist's "religious feeling [that] takes
the form of a rapturous amazement at the harmony of natural
law."/(Orr 2002).
This, however, is not what is meant by "intelligent design" in the
parlance of the new anti-evolutionists. 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.
Certainly, the issue of design and purpose in nature is a
philosophical one that scientists can and should discuss with great
vigor. However, the notion at the heart's of today intelligent
design movement is that the direct intervention of an outside
designer can be demonstrated by the very existence of complex
biochemical systems. What even they acknowledge is that their entire
scientific position rests upon a single assertion – that the living
cell contains biochemical machines that are irreducibly complex. And
the bacterial flagellum is the prime example of such a machine.
Such an assertion, as we have seen, can be put to the test in a very
direct way. If we are able to search and find an example of a
machine with fewer protein parts, contained within the flagellum,
that serves a purpose distinct from motility, the claim of
irreducible complexity is refuted. As we have also seen, the
flagellum does indeed contain such a machine, a protein-secreting
apparatus that carries out an important function even in species
that lack the flagellum altogether. A scientific idea rises or falls
on the weight of the evidence, and the evidence in the case of the
bacterial flagellum is abundantly clear.
As an icon of anti-evolution, the flagellum has fallen.
The very existence of the Type III Secretory System shows that the
bacterial flagellum is not irreducibly complex. It also
demonstrates, more generally, that the claim of "irreducible
complexity" is scientifically meaningless, constructed as it is upon
the flimsiest of foundations – the assertion that because science
has not yet found selectable functions for the components of a
certain structure, it never will. In the final analysis, as the
claims of intelligent design fall by the wayside, its advocates are
left with a single, remaining tool with which to battle against the
rising tide of scientific evidence. That tool may be effective in
some circles, of course, but the scientific community will be quick
to recognize it for what it really is – the classic argument from
ignorance, dressed up in the shiny cloth of biochemistry and
information theory.
When three leading advocates of intelligent design were recently
given a chance to make their case in an issue of/Natural
History/magazine, they each concluded their articles with a plea for
design. One wrote that we should recognize "the design inherent in
life and the universe" (Behe 2002), another that "design remains a
possibility" (Wells 2002), and another "that the natural sciences
need to leave room for design" (Dembski 2002b). Yes, it is true.
Design does remain a possibility, but not the type of "intelligent
design" of which they speak.
As Darwin wrote, there is grandeur in an evolutionary view of life,
a grandeur that is there for all to see, regardless of their
philosophical views on the meaning and purpose of life. I do not
believe, even for an instant, that Darwin's vision has weakened or
diminished the sense of wonder and awe that one should feel in
confronting the magnificence and diversity of the living world.
Rather, to a person of faith it should enhance their sense of the
Creator's majesty and wisdom (Miller 1999). Against such a backdrop,
the struggles of the intelligent design movement are best understood
as clamorous and disappointing double failures – rejected by science
because they do not fit the facts, and having failed religion
because they think too little of God.