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Argument Analysis 5: Evolution versus Creation
T here a re 2 a rg uments here, be s ure to rea d both a nd dec i de who ha s the better a rg ument.
A r g u men t 1:
Mi c ha el B ehe a g a i ns t evol uti on
In his seminal work On the Origin of Species, Darwin hoped to explain what no one had been able to explain before—how the variety and complexity of the living world might have been produced by simple
natural laws. His idea for doing so was, of course, the theory of evolution by natural selection...
It was an elegant idea, and many scientists of the time quickly saw that it could explain many things about
biology. However, there remained an important reason for reserving judgment about whether it could actually account for all of biology: the basis of life was as yet unknown. In Darwin's day, atoms and molecules were still theoretical constructs—no one was sure if such things actually existed. Thus the intricate molecular basis of Iife was utterly unknown to Darwin and his contemporaries. In the past hundred years, science has learned much more about the cell and, especially in the past fifty years, much about the molecular basis of life.
In light of the enormous progress made by science since Darwin first proposed his theory, it is reasonable to ask if the theory still seems to be a good explanation for life. In Darwin's Black Box: The Biochemical Challenge
to Evolution (Behe 1996), I argued that it is not. The main difficulty for Darwinian mechanisms is that many systems in the cell are what I termed "irreducibly complex." I defined an irreducibly complex system as: a
single system that is necessarily composed of several well-matched, interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease
functioning (Behe 2001). As an example from everyday life of an irreducibly complex system, I pointed to a mechanical mousetrap such as one finds in a hardware store. Typically, such traps have a number of parts: a spring, a wooden platform, a hammer, and other pieces. If one removes a piece from the trap, it can't catch mice.
Irreducibly complex systems seem very difficult to fit into a Darwinian framework, for a reason insis ted
upon by Darwin himself. In the Origin, Darwin wrote that "if it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory
would absolutely break down. But I can find out no such case" (Darwin 1859, 158). Here Darwin was emphasizing that his was a gradual theory. Natural selection had to improve systems by tiny steps, over a long period of time.
However, it is hard to see how something like a mousetrap could arise gradually by something akin to a Darwinian process. For example, a spring by itself, or a platform by itself, would not catch mice, and adding a
piece to the first nonfunctioning piece wouldn't make a trap either. So it appears that irreducibly complex biological systems would present a considerable obstacle to Darwinian evolution.
The question then becomes, are there any irreducibly complex systems in the cell? Are there any irreducibly
complex molecular machines? Yes, there are many. In Darwin's Black Box, I discussed several biochemical systems as examples of irreducible complexity: the eukaryotic cilium, the intracellular transport system, and more. Here I will
just briefly describe the bacterial flagellum. . . . The flagellum can be thought of as an outboard motor that bacteria use to swim. It was the first truly rotary structure discovered in nature. It consists of a long
filamentous tail that acts as a propeller; when it is spun, it pushes against the liquid medium and can propel the bacterium forward. The propeller is attached to the drive shaft indirectly through something called the hook region, which acts as a universal joint. The drive shaft is attached to the motor, which uses a flow of acid or sodium ions from the outside to the inside of the cell to power rotation. Just as an outboard motor has to be kept stationary on a motorboat while the propeller turns, there are proteins that act as a stator struc ture to
keep the flagellum in place. Other proteins act as bushings to permit the drive shaft to pass through the bac terial membrane. Studies have shown that thirty to forty proteins are required to produce a functioning flagellum
in the cell. In the absence of almost any of the proteins—in the absence of the parts that act as the propeller, drive shaft, hook, and so forth—no functioning flagellum is built.
As with the mousetrap, it is quite difficult to see how Darwin's gradualistic process of natural selection sift-
ing random mutations could produce the bacterial flagel lum, since many pieces are required before its function a ppea rs .... T he probl em of a c c ounti ng f or the ori g in of the flagellum is not limited to the flagellum
itself but extends to associated control systems as well.
Second, a more subtle problem is how the parts assemble themselves into a whole. The analogy to an outboard motor fails in one respect: an outboard motor is generally assembled under the direction of a human—
an intelligent agent who can specify which parts are attached to which other parts. The information for assembling a bacterial flagellum, however (or, indeed, for assembling any biomolecular machine), resides in the component proteins of the structure itself. Thus, even if we had a hypothetical cell in which proteins
homologous to all of the parts of the flagellum were present (perhaps performing jobs other than propulsion) but were missing the information on how to assemble themselves into a flagellum, we would still not get the
structure. The problem of irreducibility would remain.
Because of such considerations, I have concluded that Darwinian processes are not promising explanations
for many biochemical systems in the cell. Instead, I have noted that, if one looks at the interactions of the components of the flagellum, or cilium, or other irreducibly complex cellular system, they look like they were
designed—purposely designed by an intelligent agent.
Rather than showing how their theory could handle the obstacle, some Darwinists are hoping to get around irreducible complexity by verbal tap dancing. Kenneth Miller actually claimed ... that a mousetrap isn't irreducibly complex because subsets of a mousetrap, and even each individual part, could still "function" on their own. The holding bar of a mousetrap, Miller observed, could be used as a toothpick, so it still has a "function" outside the mousetrap. Any of the parts of the trap could be used as a paperweight, he continued, so
they all have "functions." And since any object that has mass can be a paperweight, then any part of anything has a function of its own. Presto, there is no such thing as irreducible complexity!
Of course, the facile explanation rests on a transparent fallacy, a brazen equivocation. Miller uses the word "function" in two different senses. Recall that the defini tion of irreducible complexity notes that removal of a
part "causes the system to effectively cease functioning?' Without saying so, in his exposition Miller shifts the focus from the separate function of the intact system itself to the question of whether we can find a different use (or "function") for some of the parts. However, if one removes a part from the mousetrap I have pictured, it can no longer catch mice. The system has indeed effectively ceased functioning, so the system is irreducibly complex.
With the problem of the mousetrap behind him, Miller then moved on to the bacterial flagellum—and
again resorted to the same fallacy. In recent years, it has been shown that the bacterial flagellum is an even more sophisticated system than had been thought. Not only does it act as a rotary propulsion device, it also contains within itself an elegant mechanism used to transport the proteins that make up the outer portion of the machine from the inside of the cell to the outside (Aizawa 1996). Without blinking, Miller asserted that the flagellum is not irreducibly complex because some proteins of the flagellum could be missing and the
remainder could still transport proteins, perhaps independently. (Proteins similar—but not identical—to some
found in the flagellum occur in the type III secretory system of some bacteria.) Again, he was equivocating, switching the focus from the function of the sys tem, acting as a rotary propulsion machine, to the ability of a subset of the system to transport proteins across a membrane. However, taking away the parts of the flagellum certainly destroys the ability of the system to act as a rotary propulsion machine, as I have argued. Thus, contra Miller, the flagellum is indeed irreducibly complex. What's more, the function of transporting proteins has as
little directly to do with the function of rotary propulsion as a toothpick has to do with a mousetrap.
Future Prospects of the Intelligent Design Hypothesis
The misconceived arguments by Darwinists that I have recounted here offer strong encouragement to me that
the hypothesis of Intelligent Design is on the right track. After all, if well-informed opponents of an idea attack it by citing data that, when considered objectively, actually demonstrate its force, then one is entitled to be
confident that the idea is worth investigating.
The important point here for a theory of Intelligent Design is that molecular machines are not confined
to the few examples that I discussed in Darwin's Black Box. Rather, most proteins are found as components of complicated molecular machines. Thus design might extend to a large fraction of the features of the cell, and perhaps beyond that into higher levels of biology.
Progress in twentieth-century science has led us to the design hypothesis. I expect progress in the twenty- first century to confirm and extend it.
References
Behe, M. J. 1996. Darwin's Black Box. The Biochemical challenge to Evolution. New York: The Free Pres s .
--. 2001. Repl y to my cri ti cs : A res pons e to revi ews of Darwin's Black Box: The Biochemical Challenge to Evolution.. Biology and Philosophy 16: 685-709.
Darwi n, C. 1859. The Origin of Species. New York: Bantam Books .
Argument 2: Kenneth Miller criticizing Behe and defending evolution.
One of the things that make science such an exhilarating activity is its revolutionary character. As science advances, there is always the possibility that some investigator, working in the field or at a laboratory bench,
will produce a discovery or experimental result that will completely transform our understanding of nature...
In 1996, Michael Behe took a bold step in this scientific tradition by challenging one of the most useful,
productive, and fundamental concepts in all of biology—Charles Darwin's theory of evolution. Behe's provocative claim, carefully laid out in his book, Darwin's Black Box, was that whatever else Darwinian evolution can explain successfully, it cannot account for the biochemical complexity of the living cell.
Behe's argument is crafted around the existence of complex molecular machines found in all living cells. Such machines, he argues, could not have been produced by evolution, and therefore must be the products of intelligent design. What I propose to do in this brief review is to put this line of reasoning to the test. I will
examine both the scientific evidence for this claim and the logical structure of the biochemical argument from design, and will pose the most fundamental question one can ask of any scientific hypothesis—does it fit the
facts?
An Exceptional Claim
For nearly more than a century and a half, one of the clas sic ways to argue against evolution has been to point to an exceptionally complex and intricate structure and then to challenge an evolutionist to "evolve this!" examples of such challenges have included everything from the optical marvels of the human eye to the chemical defenses of the bombardier beetle. At first glance, Behe's examples seem to fit this tradition… As he realizes, however, the mere existence of structures and pathways that have not yet been given step-by-step
Darwinian explanation does not make much of a case against evolution.
Given that the business of science is to provide and test explanations, the fact that there are a few things that have, as yet, no published evolutionary explanations is not much of an argument against Darwin. Rather, it means that the field is still active, vital, and filled with scientific chal lenges. Behe realizes this, and therefore his principal claim for design is quite different. He observes, quite correctly, that science has not explained the evolution of the bacterial flagellum, but then he goes one step further. No such explanation is even possible,
according to Behe. Why? Because the flagellum has a characteristic that Behe calls "irreducible complexity."
Irreducible complexity is the key to Behe's argument against Darwin, Why? Because it opens a chain of
reasoning that allows the critic of evolution to reach the conclusion of design. It alone allows one to state that the notion of an evolutionary origin for any complex biochemical structure can be ruled out in principle. To make his point perfectly clear, Behe uses a common mechani cal device, the mousetrap, as an example of
irreducible complexity.
Since every part of the mousetrap must be in place before it is functional, this means that partial
mousetraps, ones that are missing one or two parts, are useless —you cannot catch mice with them. Extending the analogy to irreducibly complex biochemical machines, they also are without function until all of their parts
are assembled. What this means, of course, is that natural selection could not produce such machines
gradually, one part at a time. They would be non-functional until all of their parts were assembled, and natural selection, which can only select functioning systems, would have nothing to work with, . .
In Behe's view, this observation, in and of itself makes the case for design. If the biochemical machinery of the cell cannot be produced by natural selection, then there is only one reasonable alternative—design by an intelligent a g ent.
If Behe's arguments have a familiar ring to them, they should. They mirror the classic "Argument from Design," articulated so well by William Paley nearly 200 years ago in his book Natural Theology. Darwin was well aware of the argument, so much so that he devoted special care to answering it when he wrote On the Origin of the Species. Darwin's answer, in essence, was that evolution produces complex organs in a series of fully functional intermediate stages. if each of the intermediate stages can be favored by natural selection, then so can the whole pathway.
Getting to the Heart of the Matter
To fully explore the scientific basis of the biochemical argument from design, we should investigate the
details of some of the very structures used in Behe's book as examples of irreducibly complex systems. One of these is the eukaryotic cilium, an intricate whip-like structure that produces movement in cells as diverse as
green algae and human sperm.
Remember Behe's statement that the removal of any one of the parts of an irreducibly complex system
effectively causes the system to stop working? The cili um provides us with a perfect opportunity to test that assertion. If it is correct, then we should be unable to find examples of functional cilia anywhere in nature that lack the cilium's basic parts. Unfortunately for the argument, that is not the case. Nature presents many examples of fully functional cilia that are missing key parts. One of the most compel ling is the eeI sperm flagellum, which lacks at least three important parts normally found in the cilium: the central doublet, central spokes, and the dynein outer arm (Wooley 1997).
The key element of Behe's claim was that "any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional." But the individual parts of the cilium, including tubulin, the motor protein dynein, and the contractile protein actin, are fully functional elsewhere in the cell. What this means, of course, is that a selectable function exists for each of the major parts of the and therefore that the argument is wrong.
Disproving Design
If the biochemical argument from design is a scientific hypothesis, as its proponents claim, then it should make
specific predictions that are testable in scientific terms. The most important prediction of the hypothesis of irreducible complexity . . . is that components of irreducibly complex structures should not have functions that can
be favored by natural selection.
As we have seen, these facts demonstrate that the one system most widely cited as the premier example of
irreducible complexity contains individual parts that have selectable functions. What this means, in scientific terms, is that the hypothesis of irreducible complexity is falsified.
Caught in the Mousetrap
Why does the biochemical argument from design collapse so quickly upon close inspection? I would suggest that this is because the logic of the argument itself is flawed. Consider, for example, the mechanical mousetrap as an analogy of irreducibly complex systems. Behe has written that a mousetrap does not work if even one of
its five parts is removed. However, with a little ingenuity, it turns out to be remarkably easy to construct a working mousetrap after removing one of its parts, leaving just four.
Are subsets of the five-part trap useful (selectable) in different contexts? Considering the following examples: for my personal use I sometimes wear a tie clip consisting of just three parts (platform, spring, and hammer) and use a key chain consisting of just two (platform and hammer). It is possible, in fact, to imagine a host of uses for parts of the "irreducibly complex" mousetrap.
The meaning of this should be clear. If portions of a supposedly irreducibly complex mechanical structure are fully functional in different contexts, then the central claim built upon this concept is incorrect. Natural
selection could indeed produce elements of a biochemical machine for different purposes. The mousetrap example provides, unintentionally, a perfect analogy for the way in which natural selection builds complex
structures.
Breaking the Chain
Critics of evolution are fond of claiming they have "dis covered" evidence of intelligent design in biochemical systems, suggesting that they have found positive evidence of the work of the designer.
What, exactly, is the source of this "loud, piercing cry"? It turns out not to be any direct evidence, but rather
a chain of reasoning—beginning with the observation of "irreducible complexity" and leading, step by step, to a conclusion of design (see below)—that is well removed from experimental evidence.
What Is the "Evidence" for Design?
What follows is the logical chain of reasoning leading from the observation of biochemical complexity to the
conclusion of intelligent design.
1. Observation: the cell contains biochemical machines in which the loss of a single component may abolish function. Definition: such machines are therefore said to be "irreducibly complex."
2. Assertion: any irreducibly complex structure that is missing a part is by definition non-functional, leaving natural selection with nothing to select for.
3. Conclusion: therefore, irreducibly complex structures could not have been produced by natural selection.
4. Secondary conclusion: therefore, such structures must have been produced by another mechanism. Since the only credible alternate mechanism is intelligent design, the very existence of such structures must be evidence of intelligent design.
When the reasoning behind the biochemical argument from design is laid out in this way, it becomes easy to spot the logical flaw in the argument. The first statement is true—the cell does indeed contain any number
of complex molecular machines in which the los s of a single part may affect function. However, the second statement, the assertion of non-functionality, is demonstrably false. As we have seen, the individual parts of
many such machines do indeed have well-defined functions within the cell. Once this is realized, the logic of the argument collapses. If the assertion in the second statement is shown to be false, the chain of reasoning is broken and both conclusions are falsified.
The cell does not contain biochemical evidence of design.
Re fe rences
Be he, M. (1996a) Darwin's Black Box, New York: The Free Press.
Huyne n, MA., Dandekar, T., and Bork, P. (1999) "Variation a nd evolution of the citric acid cycle: A genomic perspective," Trends in Microbiology 7:281-91,
Me l e ndez-llevia, E., Wa ddell, TG., a nd Ca scante, M. (1996) "The puzzle of the Kre bs citric acid cycl e: Assembling the pieces of che mically
fe a sible re actions, a nd opportunism i n the design of metabolic pathways during evolution," Journal of Molecular Evolution 431293-303.
Mus ser, S.M. and Chan, S.I. (1998) "Evolution of the cytochrome e oxidase proton pump," Journal of Molecular Evolution 46:508-20.
Wooley, D.M. (1997) "Studies on the eel sperm flagellum," Journal of Cell Science 110:85-94.