by Niall Shanks and Karl Joplin

Abstract: In this essay we take creationist biochemist Michael Behe to task for failing to make an evidentially grounded case for the supernatural intelligent design of biochemical systems. In our earlier work on Behe we showed that there were dimensions to biochemical complexity—redundant complexity—that he appeared to have ignored. Behe has recently replied to that work. We show here that his latest arguments contain fundamental flaws.

Introduction

Michael Behe has argued that biochemists have uncovered a kind of biochemical complexity that could only result from intelligent design.¹ We have criticized his reasoning in two essays.² Behe has recently responded to our first essay in ways that are simultaneously interesting enough and misleading enough to warrant further analysis.³ Since Behe’s work takes place in the context of the intelligent design branch of the creationist movement, we will begin with some comments on the very enterprise of explaining biochemical phenomena through appeals to supernatural intelligent design. We will then address some specific issues that have arisen in the context of our exchange.

Behe and the Invisible Hand of God

Behe has argued that biochemical systems exhibit a species of complexity—irreducible complexity—that he believes cannot possibly arise from natural processes but must have arisen from deliberate, intelligent design. Behe tells us that an irreducibly complex system is one consisting of several well-matched, interacting parts, with all the parts contributing to the achievement of function, and doing so in such a way that the removal of any one of the parts causes the system to cease functioning.⁴

Like William Paley before him, he compares the complexity observed in biological systems to that of mechanical contrivances. For Paley the mechanical metaphor was that of a pocket watch, for Behe it is the mousetrap. Mousetraps have several interconnected parts (spring, base, hammer, catch, holding bar), and all are necessary for the achievement of function—catching mice.

If organisms are artifacts, it is natural to both assume they were designed (more or less intelligently), and if they are designed then we should identify the designer and the methods and materials used. Perhaps we organisms are the result of an experiment by space aliens from a galaxy far, far away. . . . But, as Behe notes, “Most people, like me, will find these scenarios entirely unsatisfactory, but they are available for those who wish to avoid unpleasant theological implications.”⁵ Hovering unmentioned over the text is the suggestion that a supernatural, undesigned designer could provide a suitable invisible hand, not to mention the necessary expertise in biochemistry.

Behe, like others in the intelligent design movement, is cagey about identifying the intelligent designer, contenting himself with the following comments:

Inferences to design do not require that we have a candidate for the role of designer. We can determine that a system was designed by examining the system itself, and we can hold the conviction of design much more strongly than a conviction about the identity of the designer. In several of the examples above, the identity of the designer is not obvious. . . .  Nonetheless, we know that all of these things were designed because of the ordering of independent components to achieve some end.⁶

We do not think Behe’s caginess is satisfactory. We think it is incumbent upon him to say more.

To see why, imagine you are strolling across a heath and you stumble upon an old pocket watch. Knowing antecedently that watches are artifacts, you know it is the fruit of intelligent human design, though being ignorant of horological history you know not how or by whom. The hand of the human designer is a mystery. And perhaps your interest in the matter ends here. It is a nice watch, and whoever made it did a good job.

But suppose you are inquisitive. You will then want answers to what we shall term the intelligent design questions. These are: 1) What is it? 2) Who made it? 3) When was it made? 4) How was it made? 5) For what purpose was it made? All of these questions can be asked about the fruits of design, be they watches, crop circles, stone tools, or signals from outer space.

For example, a little research at the museum of the National Association of Watch and Clock Collectors suggests that your watch might be a quarter repeater, made by Abraham-Louis Breguet, in 1814, in Paris, France. Studies of the watch itself reveal that it is a quarter repeater on gongs with push pendant, ruby cylinder escapement, gilt finish, serial number 2371 (so it must once have been owned by Napoleon’s sister, Caroline).

Careful studies into the anatomy of the watch itself reveal a silver engine turned dial with Breguet secret signatures. The watch bears the mark of Breguet. Research into the records of Breguet Atelier lists twenty artisans who were paid to make parts for this watch. Finally, through careful investigations into the history of technology, you are able to uncover the nature of the materials and methods employed by Breguet and his band of helpers.

You may even conclude that the watch is so beautiful it was intended to be a work of art as well as a timekeeper. But most importantly, you do not have to pursue the intelligent design questions for watches (or mousetraps) because they are known antecedently to be artifacts, and hence to be the fruits of intelligent human design, even if the identities and methods of the designers remain obscure. For artifacts such as watches and mousetraps, Behe is right, “The inference to design can be held with all the firmness that is possible in this world, without knowing anything about the designer.”7

Suppose now you are strolling across the same heath and you come across a human cell. Microscopic examination reveals that it, like the watch, is a complex system with many interacting parts. But there is a crucial difference. Because for all of the use of mechanical metaphors to make sense of intracellular processes and structures, it is not known antecedently that the cell is the fruit of intelligent design.

Saying biochemical systems are like familiar artifacts such as mousetraps or watches, or behave as if they were machines or designed artifacts, does not make them so. And in fact, from the standpoint of complexity of organization and dynamic interaction, they are utterly unlike anything in everyday human experience of designed artifacts. Mechanical metaphors and analogies may render biochemical systems familiar and more tractable to thought, but they do not transform these systems into artifacts. As Rosenblueth and Wiener have noted, “The price of metaphor is eternal vigilance.”⁸

The claim that biochemical systems are intelligently designed systems is a claim that needs evidential justification. The very issue of design itself—an issue we did not have to confront for watches—is an issue that must be confronted here. About the only way to provide hard evidence that these systems are in fact the fruit of intelligent design is to provide a lot of high-quality evidence to support specific and unambiguous answers to the intelligent design questions. Settling the very issue of the intelligent design of biochemical systems is thus inextricably intertwined with the provision of evidentially grounded answers to the intelligent design questions precisely because it is not known antecedently that biochemical systems result from deliberate design by a nonhuman agent (or agents) of supernatural origin.

As Behe himself has noted,⁹ it is possible for humans to intelligently design human proteins, and even novel proteins that have never been seen before. We speculate that one day it will be possible for a clever biochemist to intelligently design a functioning cell indistinguishable from a human cell. Even if this were so, it would not demonstrate that our cells were the results of intelligent design. Moreover, whether a given cell was extracted from a human subject, or intelligently designed in the laboratory, could be settled only through analysis of its causal history. The judgment would be in favor of human intelligent design, if the trail led back to the laboratory, to identifiable human designers with the biochemical and biological wherewithal to accomplish the feat. The judgment would favor intelligent design precisely if the design questions could be appropriately answered and justified.

Behe has tried to argue that irreducible complexity is a mark of supernatural intelligent design. Here, Behe makes himself a hostage to fortune because the history of science is littered with the corpses of phenomena believed to be inexplicable by natural means. For example, the complex motion of the heart was believed by Fracastorius to be a mystery known only unto God. William Harvey unraveled the mystery. Likewise, crop circles were believed by many to be the fruits of extraterrestrial or supernatural agency, yet human ingenuity with planks of wood and lengths of rope turned out to be the answer.

And we have been mistaken about the very signs of intelligent design before. When Anthony Hewish and Jocelyn Bell discovered the first pulsar in 1967 (an astronomical object emitting bursts of microwaves every 1.33730109 seconds), they wondered whether it was a beacon—a sort of cosmic lighthouse—signaling the existence of an alien intelligence. The objects were even referred to as LGMs (“Little Green Men”).¹⁰

The intelligent design theory of pulsars dropped from sight partly because plausible answers to the intelligent design questions were not forthcoming (e.g., Why broadcast in such a messy part of the electromagnetic spectrum? Why expend so much energy? And, as more objects were discovered, why send signals to Earth from so many different places using similar frequencies?). And also because it was discovered that there were natural, unintelligent explanations for the same phenomenon—rapidly rotating neutron stars.¹¹

Behe’s design inference in fact exhibits an appeal to ignorance. He cannot see how irreducible complexity could have arisen in a natural, unguided manner, so it must have arisen in an unnatural, supernatural manner, though we know not how, by whom, when, or for what purpose. But within the cell we have nothing analogous to the Breguet secret signatures. And, moreover, the examples of irreducible complexity in biochemical processes will not suffice as evidence either. Irreducible complexity is a phenomenon for which there exist naturalistic, unguided evolutionary explanations. We will discuss one below in connection with some of Behe’s favorite examples.

The upshot is that the very features of biochemical systems that Behe points to cannot simply be viewed as either the trademark, or even the fingerprints, of an intelligent designer. For these features, the inference to design cannot be separated from the provision of evidence about the designer and its methods. Behe has made an extraordinary claim, and its validation will require extraordinary evidence. Behe makes no attempt to meet this essential, evidential requirement.

The Invisible Hand of the Laws of Nature

How could a complex system such as an economy, with many interacting parts, manifest stability and order? As the economic collapse of the former Soviet Union has shown, the attempt to intelligently design economic order through centralized planning was a huge failure. The older tradition of laissez faire capitalism had a very different answer to the origins of economic order.

Commenting on the origins of adaptative order in economic systems, Stephen Jay Gould has pointed out:

To achieve the goal of a maximally ordered economy in the laissez faire system, you do not regulate from above by passing explicit laws for order. You do something that, at first glance, seems utterly opposed to your goal: You simply allow individuals to struggle in an unfettered way for personal profit. In this struggle the inefficient are weeded out and the best balance each other to form an equilibrium to everyone’s benefit.¹²

Adam Smith, one of the architects of classical economic theory, explained how an individual agent in a laissez faire economy makes his contribution to the emergence of order in the following way:

He generally indeed neither intends to promote the public interest, nor knows how much he is promoting it. . . . He intends only his own gain, and he is in this, as in many other cases, led by an invisible hand to promote an end which was no part of his intention [our italics].¹³

The invisible hand that produces the economic order is in the interaction dynamics of a group of individuals attempting to maximize personal profits and gains, and who have no broader view of the public interest. Economic order emerges as an unintended, undesigned consequence of the operation of this invisible hand.

Could another invisible hand, this time the invisible hand of chemical interaction dynamics, explain the emergence of a system manifesting irreducible complexity? In our initial commentary on Behe’s claims, we argued that this was indeed the case.¹⁴ We there presented and discussed a chemical system known as the Belousov-Zhabotinski (BZ) reaction. The BZ reaction, we argued, manifested irreducible complexity as a consequence of self-organization. It did not require an intelligent designer.

The BZ system self-organizes into an orderly sequence of reactions, with the products of one reaction in the sequence forming the substrates for the next, and which eventually cycles round so that the products of the last reaction in the sequence form the substrates for the first reaction, thus beginning the process all over again. Thus, the system will cycle or oscillate until chemical equilibrium is achieved, at which point the system can be reactivated by the provision of further “food” molecules from outside.

That the reaction manifests self-organization means nothing more than that the invisible hand of the chemical interactions between molecules brings about highly ordered behavior of the system as a whole in the form of regular temporal oscillations (and the formation of elaborate spatial patterns under certain circumstances). The explanation of this behavior does not require the intervention of a deus ex machina, either physical or metaphysical. The oscillations are typically observed in the form of color changes—for example from red to blue to red . . . and so on. The system behaves like a chemical clock—a sort of Breguet repeater in a beaker!

We argued that the BZ system manifested irreducible complexity because it satisfies all the requirements of the mousetrap model of irreducible complexity. Behe tells us that there are three steps to be satisfied. The system must have a function. Behe tells us, “The function of the system is determined from the system’s internal logic.”¹⁵ In the light of this, the function of the BZ reaction—determined by the logic of the chemical interaction dynamics internal to the system—is to oscillate.

The next requirement is that the system consist of several components.¹⁶ The BZ system consists of several key reactions. Behe does not appear to dispute this part of our example. Finally we must ask whether all the components so identified are required for the achievement of function. The key components of the BZ reaction are all needed for the oscillatory cycle to exist. The disruption of any of these key reactions results in the catastrophic failure of the system. Apparently, the unguided laws of chemistry will generate irreducibly complex systems.

Yet Behe has objected to our example. It is instructive to examine his reasoning. Commenting on the BZ system, he notes, “Although it does have interacting parts that are required for the reaction, the system lacks the crucial feature—the components are not well-matched”(our italics).¹⁷ He tells us that only systems, “that require well-matched components are irreducibly complex.”¹⁸ He then adds,

As an illustration, contrast the greater complexity of a mechanical mousetrap with the much lesser complexity of a lever and fulcrum. Together a lever and fulcrum form an interactive system which can be used to move weights. Nonetheless, the parts of the system have a wide variety of shapes and sizes and still function. Because the system is not well-matched, it could easily be formed by chance [our italics].¹⁹

To be irreducibly complex, then, involves well-matched components, and this means components that cannot easily form into a complex system by chance.

Noting that the distinction between systems with well-matched components and those without is not very sharp, Behe adds:

. . . no law of physics automatically rules out the chance origin of even the most intricate IC [irreducibly complex] system. As complexity increases, however, the odds become so abysmally low that we reject chance as an explanation.²⁰

Behe is thus arguing that the BZ reaction does not have well-matched components, and this means that the self-organization of the components of the system into an oscillating complex system could easily occur by chance! If it was truly irreducibly complex, the probability that the molecular components would self-organize to form an integrated, complex system just by chance would be abysmally low.

And now Behe’s error becomes quite apparent. We agree with Behe that the probability that irreducibly complex systems self-assemble just by chance is abysmally low. But the probability that the BZ system self-organizes and oscillates just by chance is also abysmally low. However, it does not occur just by chance. It occurs as the result of chemical mechanisms operating in accord with the laws of chemistry—the unaided, unguided, but lawlike invisible hand of the chemical interactions internal to the system. Ignorance, sometimes wilful ignorance, of the organizing power of natural mechanisms operating in accord with laws of nature, is an old creationist failing.

Similarly, ignorance of the lawlike invisible hand of gravitational interactions led medieval design theorists to postulate the invisible hand of God as the source of the order we observe in celestial motion. And, as Darwin showed, we do not require the invisible hand of God to explain the adaptations we find in organisms. Natural selection, acting on heritable variation in populations of organisms, sculpts the beaks of finches just as surely as it shapes other features of organisms. You cannot conclude that complex structures and processes must occur just by chance if they are not the result of intelligent design.

Behe bolsters his attack on the BZ reaction with a truly bizarre argument derived from the fact that the reagents in the BZ reaction have a wide variety of uses—in Behe’s terminology, they have low specificity. For example, one ingredient, sodium bromate, is a general purpose oxidizing agent, and ingredients other than the ones we mentioned can be substituted. In our reaction, we mentioned the use of cerium ions, but iron or manganese ions will work just as well. He points out that the reaction is easy to set up and runs over a wide range of concentrations.²¹

If this is the case, then mousetraps are not irreducibly complex either. The steel used in their construction has a wide range of uses, as does the wood used for the base. You can substitute plastic for wood, and any number of metals for the spring and hammer. Mousetraps are easy to make (which is why they are cheap) and will work with metals manifesting a wide range of tensile strengths. But the fact that they are easy to make does not mean they assemble just by chance. Mousetraps need a maker just as much as the BZ system needs chemical mechanisms governed by the laws of chemistry. Either the BZ system is an irreducibly complex system, or the complexity of mousetraps is not a model for irreducible complexity. Take your pick, for you cannot have it both ways.

This matter is made all the more acute because crucial components of Behe’s own examples of irreducible complexity have multiple uses and lack substrate specificity (interact with a wide variety of substrates). For example, plasminogen (a component of the irreducibly complex blood-clotting cascade) has been documented to play a role in a wide variety of physiological processes, ranging from tissue remodeling, cell migration, embryonic development, and angiogenesis, as well as wound healing.²² And though Behe tells us that plasmin (the activated form of plasminogen), “. . . acts as scissors specifically to cut up fibrin clots,”²³ we learn in one of the very papers he cites that, “Plasmin has a relatively low substrate specificity and is known to degrade several common extracellular-matrix glycoproteins in vitro.”²⁴

Redundant Complexity (Again)

Behe’s discussion of our concept of redundant complexity really takes us to the heart of the matter.²⁵ In our initial analysis of Behe’s work we proposed that many real biochemical systems exhibited redundant complexity rather than irreducible complexity. Behe’s characterization of our view of redundant complexity is fair and accurate. He explains our view of redundancy as follows:

By this they mean that biochemical pathways overlap and are interconnected, so that removal of one or even several components does not completely destroy the function. In support of their position they cite a diverse array of biological examples. . . . Their initial illustration is the metabolic pathways for the synthesis of glucose-6-phosphate. They point out that the molecule can be made by “several different isoforms or variants of hexokinase, and all are present, as a result of gene duplication, in varying proportions in different tissues.” What’s more, “Knock out one enzyme isoform and the other isoforms in the tissue can take over its function.”²⁶

And Behe agrees with us that biochemical systems can indeed exhibit redundant complexity.²⁷

Our original purpose in introducing the concept of redundant complexity was twofold. First, this sort of redundancy is a hallmark of evolutionary processes. Gene duplication, for example, is one of the ways in which the number of genes in a genome can be increased, with the result that one of the genes can continue the original function, while the other is freed up to be coopted in evolutionary time to serve new, and novel functions. The redundancy we observe today in effect represents the biochemical and molecular footprints of evolutionary processes in action. Second, we felt that Behe’s analysis of biochemical complexity had obscured the significance of this important evidence.

But Behe observes, “The observation that some biochemical systems are redundant does not entail that all are. And in fact, some are not redundant.”²⁸ Behe goes on to give some interesting and examples to make his case. Let’s suppose he is right. This merely raises the question of the origins of this irreducible complexity. Although we did not explicitly address this question in our original commentary, we have subsequently.²⁹

In terms of redundant complexity we have the tools to provide a naturalistic, evolutionary explanation of the source of irreducible complexity. Behe’s metaphor for an irreducibly complex system was that of the mousetrap. We think a better metaphor is found in the architectural image of a free-standing arch. This image was first suggested by A.G. Cairns-Smith, a biochemist interested in the origins of biochemical complexity.³⁰ Cairns-Smith’s own interests were in the origins of life, but the complexity problem he confronted was essentially identical to that raised a decade later by Behe—though couched in different terminology. It is instructive to examine Cairns-Smith’s reasoning a bit more closely.

Cairns-Smith’s complexity problem was discussed under the heading of the unity of biochemistry, but it is clearly very similar to Behe’s problem. Cairns-Smith comments:

For example, proteins are needed to make catalysts, yet catalysts are needed to make proteins. Nucleic acids are needed to make proteins, yet proteins are needed to make nucleic acids. Proteins and lipids are needed to make membranes, yet membranes are needed to provide protection for all the chemical processes going on in the cell. . . . The interlocking is tight and critical. At the center everything depends on everything.³¹

Cairns-Smith thinks this complexity must be explained. However, unlike Behe, Cairns-Smith thinks a natural, rather than a supernatural, explanation will suffice.

Consider a free-standing arch of stones. It manifests irreducible complexity in that the keystone at the top of the arch is supported by all the other stones in the arch, yet these stones themselves cannot stand without the keystone. In other words, the arch stands because all the component stones depend on each other. Take away a stone, and the arch collapses.

However, Cairns-Smith notes, not all the stones, nor all the functional biological structures must be there from the beginning:

It is clear that not all such functions were hit on at once. Some would have been later discoveries. If new uses may be found for old structures, so, too, can old needs be met by more recently evolved structures. There is plenty of scope for the accidental discovery of new ways of doing things that depend on two or more structures that are already there. . . . This is typical at all levels of organization, from organs to molecules.³²

He adds:

There is plenty of scope for accidental discoveries of effective new combinations of subsystems. It seems inevitable that every so often an older way of doing things will be displaced by a newer way that depends on a new set of subsystems. It is then that seemingly paradoxical collaborations may come about.³³

Why does he think these collaborations are paradoxical?

Referring back to the stone arch, Cairns-Smith comments, “This might seem to be a paradoxical structure if you had been told that it arose from a succession of small modifications, that it had been built one stone at a time.”³⁴ This is especially true if, as in biochemistry, the arch is multidimensional, with central “stones” each touching more than the two stones touched by the keystone in our arch.³⁵

Nevertheless, it is possible to construct an arch in gradual stages. You cannot, of course, gradually build a self-supporting, free-standing arch using only the component stones, piling them up, one at a time. But if you have scaffolding—and a pile of rocks will suffice to support the growing structure—you can build the arch one stone at a time until the keystone is in place, and the structure becomes self-supporting. When this occurs, the (now redundant) scaffolding can be removed to leave the irreducibly complex, free-standing structure.

The study of developmental processes suggests that an important biological role is indeed played by removable scaffolding, in the formation of all manner of elaborate structures including body parts and neural pathways. For example, developmental scaffolding, in the form of an initial superabundance of cells, can be removed by programmed cell death (apoptosis), and this process plays a crucial role in the developmental sculpting of such structures as fingers and toes.³⁶

Behe concedes the existence of redundantly complex biochemical systems. This is an important concession because natural evolutionary processes give rise to the redundant complexity we observe in biochemical systems. These redundancies then provide, in concert with extant functional systems and structures, the biochemical and molecular scaffolding to support the gradual evolution of systems that ultimately manifest irreducible complexity when the scaffolding is removed or reduced. The resulting biochemical arches may then achieve functions as integrated wholes that could not be achieved by the parts acting independently. Natural selection will result in some of these biochemical arches being retained for further evolutionary elaboration, while others will be eliminated by the same mechanism.

In his reply, Behe himself comes close to achieving our crucial insight. Discussing our work, he writes, “They then go on to argue that biochemical systems are ‘redundantly complex’—that is, contain components that can be removed without entirely eliminating function.”³⁷ He is right. And irreducibly complex systems can be viewed simply as limiting cases of redundantly complex systems. Reduce redundancy to the point where further reduction results in loss of function and the system is now irreducibly complex.

As noted above, gene duplication is one route to redundant complexity, but how could redundancy be reduced to give rise to irreducible complexity? One way is through the transformation of functional genes into pseudogenes—nonfunctional members of gene families. “Pseudogenes are DNA sequences that were derived from functional genes but have been rendered nonfunctional by mutations that prevent their proper expression. Since they are subject to no functional constraints, they are expected to evolve at a high rate.”³⁸ If a functional gene becomes a pseudogene, its product will no longer be available to the biochemical pathways in which it formerly participated.

The transformation of a gene to a pseudogene will not have catastrophic consequences if the biochemical pathways in which its product formerly participated are redundantly complex—other products can take over the role of the missing product. Perhaps not as efficiently, but efficiency is something that can be improved by selection. In this way, redundant scaffolding can be reduced, ultimately to the point where a system or pathway is irreducibly complex. There may be strong selection against further reductions at this point of evolution. But not necessarily, as we shall see below.

Behe’s Examples Revisited

Now that we have an evolutionary framework within which we can explain the origins of irreducibly complex systems, we can usefully re-examine Behe’s examples. Behe cites as an example of an irreducibly complex system, the synthetic pathway that makes vitamin C in other mammals, but which in humans (and certain other animal species) is disrupted by the lack of a functional gene for L-gulono-gamma-lactone oxidase. As he notes, in humans a pseudogene is present.³⁹ The vitamin C mousetrap ceases to function in humans when a functional component is lost. But this is hardly a shocking observation. The pathway in humans has simply been disrupted by a continuation of the same sorts of process that reduce redundancy to yield irreducibly complex systems in the first place.

From an evolutionary standpoint, this example looks like a case of “Use it or lose it.” As Nesse and Williams comment:

Our ancestral shift to a high-fruit diet, rich in vitamin C, had the incidental consequence about forty million years ago of allowing the degeneration of the biochemical machinery for making this vitamin. Our frugivorous close relatives share our requirement for dietary vitamin C.⁴⁰

In this case, loss of a functional pathway was preceded by adaptation to a niche rich in vitamin C.

Mutational events called “deletions”—whereby bases are deleted from genes (often a single base or a few bases, but sometimes several thousand)—occur naturally, and can result in dysfunction. A special kind of deletion, however, is artificially induced in a knockout experiment. In a knockout experiment, a gene is deliberately deleted from a genome, and hence all the causal roles played by that gene are halted. We have here a tale of two knockouts.

In our original article we pointed to the gene coding for the protein p53. Lab mice have been created in which this gene has been knocked out. In support of our claims about the existence of redundancy in biochemical systems, we pointed out that, though this protein was involved in a number of important biochemical and biological processes, its removal did not result in a catastrophic disruption of the developmental process. There was redundancy, and other proteins could conspire to do the work of the missing protein.

Behe acknowledges this case, but draws his reader’s attention to the blood-clotting cascade originally discussed in his book:

Yet contrast this case [p53] with that of mice in which the gene for either fibrinogen, tissue factor, or prothrombin has been knocked out. . . . The loss of any one of those proteins prevents clot formation—the clotting cascade is broken. Thus Shanks and Joplin’s concept of redundant complexity does not apply to all biochemical systems.⁴¹

Again, suppose this point is right. What is its relevance when the role of redundant complexity lies in its ability to account, in natural, evolutionary terms, for the origins of irreducible complexity? And origins, as Behe points out, is the central issue. Loss of functional genes reduces redundancy to yield an irreducibly complex system. All Behe’s example shows is that further losses at this point can catastrophically disrupt the system.

We also think, however, that Behe has oversold the irreducible complexity of the blood-clotting cascade. The cascade itself has features that manifest redundant complexity. The real situation is thus more complex than Behe’s carefully massaged description would lead you to believe. Plasminogen deficient (Plg-/-)—hence plasmin deficient—mice have been studied. As noted earlier, plasmin is needed for clot degradation (it cuts up the fibrin), yet:

Plasmin is probably one member of a team of carefully regulated and specialized matrix-degrading enzymes, including serine-, metallo-, and other classes of proteases, which together serve in matrix remodeling and cellular reorganization of wound fields. . . . However, despite slow progress in wound repair, wounds in Plg-/- mice eventually resolve with an outcome that is generally comparable to that of control mice. Thus an interesting and unresolved question is what protease(s) contributes to fibrin clearance in the absence of Plg?⁴²

Behe cited this very paper, so we must assume that he, too, knows that parts of his clotting-cascade are redundantly complex. In this case, healing delayed is not healing denied!

Evolution and Biochemical Novelty

Behe says that he accepts much that has been uncovered through the study of organismal evolution:

I find the idea of common descent (that all organisms share a common ancestor) fairly convincing, and have no particular reason to doubt it. I greatly respect the work of my colleagues who study the development and behavior of organisms within an evolutionary framework, and I think that evolutionary biologists have contributed enormously to our understanding of the world.⁴³

But he adds, “I do not believe it explains molecular life.”⁴⁴

Behe accepts evolution at the organismal level, yet denies it at the level of biochemistry. Yet, though the basic pattern of metabolism is common to all species, biochemical evolution has occurred, and in ways that reflect the evolution of organic diversity. The various mammalian species, for example, are not exactly the same molecular animal dressed up in different organismal clothes. Thus, as noted by Caldwell, there are several pathways whose occurrence is restricted to primate species (e.g., the aromatization of quinic acid; C-Glucuronidation of pyrazolones; and carbamate acyl glucuronidation, among others).⁴⁵ Since there has been life on Earth for more than 3 billion years, the original design event must have been at least that long ago. But primates appear late in life’s history—about 65 million years ago.⁴⁶ If these unique primate pathways are not the fruits of biochemical evolution, then are we to believe they are the result of subsequent intelligent redesign of primate biochemistry? And if so, when, by whom, and for what purpose?

Since primates are not the only evolved organisms to display biochemical novelty, we suspect Behe will have to introduce, on an ad hoc basis, many such redesign events. The situation is not unlike that which confronted the catastrophist geologists of the eighteenth century who had to postulate a multiplicity of floods and re-creations of life to explain the fossil record in the stratified geological column, with Noah’s flood being the last!

Conclusion

It seems, then, that it is simply wrong to suggest that there is no possible unguided, naturalistic explanation of irreducible complexity. Self-organization is one route, and redundant complexity is another. If Behe wishes to disagree, he would do well to formulate precise and unambiguous answers to the intelligent design questions we have proposed, and then to justify his answers about the identity, methods, and materials of his hypothetical designer with the provision of high-quality evidence. Scientists do not rule out of court all talk of supernatural beings, but they do require high-quality evidence before they will take such talk seriously. After all, as Carl Sagan said, extraordinary claims require extraordinary evidence.

Acknowledgments

We would like to thank Hugh LaFollette (Philosophy) and Foster Levy (Biological Sciences) of East Tennessee State University, Massimo Pigliucci (Botany) University of Tenessee–Knoxville, and George Gale (Philosophy) of the University of Missouri-Kansas City for helpful discussions and comments on earlier versions of this essay.

Notes

1. See Michael J. Behe, Darwin’s Black Box: The Biochemical Challenge to Evolution, (New York: The Free Press, 1996).

2. See Niall Shanks and Karl H. Joplin, “Redundant Complexity: A Critical Analysis of Intelligent Design in Biochemistry,” Philosophy of Science 66, (1999): 268–82. See also Niall Shanks and Karl H. Joplin, “Of Mousetraps and Men: Behe on Biochemistry,” forthcoming in Reports of the National Center for Science Education (2000).

3. See Michael J. Behe, “Self-Organization and Irreducible Complexity: A Reply to Shanks and Joplin,” Philosophy of Science 67 (2000): 155–62.

4. See Behe, Darwin’s Black Box, 39.

5. Ibid., 249.

6. Ibid., 196.

7. Ibid., 107.

8. Quoted in Richard Lewontin, The Triple Helix: Gene, Organism and Environment (Cambridge, Mass.: Harvard University Press, 2000), 4.

9. See Behe, Darwin’s Black Box, 200–01.

10. See Robert Dixon, Dynamic Astronomy (New Jersey: Prentice-Hall, 1980), 402.

11. See Isaac Asimov, The Universe: From Flat Earth to Quasar (Baltimore: Penguin, 1971), 306–8.

12. See Stephen J. Gould, Eight Little Piggies (New York: W.W. Norton, 1993), 149.

13. Ibid.

14. See Shanks and Joplin, “Redundant Complexity.”

15. See Behe, Darwin’s Black Box, 196.

16. Ibid., 42.

17. See Behe, “Self-Organization and Irreducible Complexity,” 157.

18. Ibid., 157.

19. Ibid.

20. Ibid., 157–58.

21. Ibid., 158–59.

22. See Thomas H. Bugge, Keith W. Kombrinck, Matthew J. Flick, Cynthia C. Daugherty, Mary J. Danton, Jay L. Degan, “Loss of Fibrinogen Rescues Mice for the Pleiotropic Effects of Plasminogen Deficiency,” Cell 87 (1996): 709–19.

23. See Behe, Darwin’s Black Box, 88.

24. See Bugge, et al., “Loss of Fibrinogen Rescues Mice,” 709.

25. See Behe, “Self-Organization and Irreducible Complexity,” 160–61.

26. Ibid., p. 160.

27. Ibid.

28. Ibid.

29. See Shanks and Joplin, “Of Moustraps and Men.”

30. See Alexander G. Cairns-Smith, Seven Clues to the Origin of Life: A Scientific Detective Story (Cambridge: Cambridge University Press, 1986), 59–60.

31. Ibid., 39.

32. Ibid., 59.

33. Ibid.

34. Ibid.

35. Ibid., 60.

36. See Neil A. Campbell, Biology (New York: Benjamin Cummings, 1996), 980. See also Ricki Lewis, “Apoptosis Activity: Cell Death Establishes Itself as a Lively Research Field,” The Scientist 9 (1995): 15.

37. Ibid., 156.

38. Wen-Hsiung Li, Molecular Evolution (Sunderland, Mass.: Sinauer Associates, 1997), 187.

39. See Behe, “Self-Organization and Irreducible Complexity,” 160.

40. See Randolph M. Nesse and George C. Williams, Why We Get Sick: The New Science of Darwinian Medicine (New York: Random House, 1994), 130.

41. See Behe, “Self-Organization and Irreducible Complexity,” 161.

42. See Bugge, et al. “Loss of Fibrogen Rescues Mice,” 717.

43. See Behe, Darwin’s Black Box, 5.

44. Ibid.

45. See John Caldwell, “Species Differences in Metabolism and their Toxicological Significance,” Toxicology Letters 64/65 (1992): 651–59.

46. See Monroe W. Strickberger, Evolution (Boston: Jones and Bartlett, 1990).

Niall Shanks is Professor of Philosophy and Adjunct Professor of Biological Sciences at East Tennessee State University. E-mail: shanksn@etsu.edu. Karl H. Joplin is Associate Professor of Biological Sciences at East Tennessee State University. E-mail: joplin@etsu.edu.