COMMENT ON BEHE. PENULTIMATE DRAFT. COMMENTS INVITED
for Notre Dame, April 5, 1997
Daniel C. Dennett
March 19, 1997
A Mystery Solved; a Skyhook Grounded
1. Seeking a Skyhook
Michael Behe's book is an interesting attempt at a frontal assault on Darwinism, based on an analysis of the complexities of molecular structures inside the cell--Darwin's black box.
"The complexity of life's foundation has paralyzed science's attempt to account for it; molecular machines raise an as-yet-impenetrable barrier to Darwinism's universal reach." (p.5)
Behe claims to demonstrate "unbridgeable chasms" (e.g., pp14-15) that Darwinism cannot span. In my 1995 book, Darwin's Dangerous Idea, I characterize skeptics about neo-Darwinism as seeking skyhooks--trying to find wonders of the biosphere that cannot be the product of gradual, mindless, mechanistic natural selection. and these unbridgeable chasms are precisely places you'd need a skyhook to cross--no cranes could build a bridge from the distant side to our side: "you can't get here from there" could be Behe's motto.
In the history of controversy over evolution, many have tried to find skyhooks--and ended up finding cranes, new mechanisms that actually enhance the underlying power of natural selection in heretofore unimagined ways, but that themselves are the products of a history of natural selection. I don't think that Behe has found either a skyhook or a crane. It's refreshing, however, to find as forthright a skyhook-seeker as Behe, and I want to take this opportunity to say that, contrary to what some readers have thought, I do not disparage skyhook seeking. On the contrary, if you're a skeptic about evolutionary theory, a skyhook is just the sort of thing you should look for. What I disparage is obfuscation: clinging to the presumption that there are skyhooks without taking on the burden of proving it, or holding out for skyhooks without acknowledging that this is what you are doing. Behe, to his credit, defines his task clearly. When he asks, quoting Darwin:
What type of biological system could not be formed by "numerous, successive, slight modifications?" (p39)
he is asking what type of biological phenomenon needs a skyhook. His answer is apparently straightforward:
An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. (p39)
But it wears its equivocation on its sleeve. A truly irreducibly complex biological system wouldn't be just a "powerful challenge" to Darwinian evolution; it would be a definitive refutation of it. Anybody who could demonstrate this would be sure of a Nobel Prize. An apparently irreducibly complex biological system, on the other hand, is indeed a powerful challenge to Darwinians. Can they "reduce" it or not? Behe claims to demonstrate that various phenomena are irreducibly complex. His fellow biochemists don't agree, apparently. If they were so much as worried that he might be on to something, they would be frantically scrambling right now to leap-frog his efforts, to overtake him on the road to Stockholm. That's what typically happens these days when scientists smell a revolutionary demonstration in the wind. Remember cold fusion? Behe's book has not triggered any such gold rush. Behe has not come close to demonstrating that any biological systems are irreducibly complex. He has demonstrated, however, that there are some quite challenging phenomena still in store for Darwinians. We already knew that, of course, but Behe gives us the details on some good cases, and enlarges our sense of how much unfinished business there is for Darwinism.
It is time, Behe says, to put the debate squarely in the open, and to disregard public
relations problems. (p.31) I entirely agree. There has been an unfortunate siege mentality on
both sides, with evolutionists often unwilling to criticize each other for fear of letting down the
side in the battle against creationists, and skeptics of evolution being reluctant to declare their
more benighted brethren to be in error. For my part, I have tried to point out where we
evolutionists have been guilty of misrepresentation or obfuscation, and for his part, Behe
disassociates himself from the wilder brands of creationism, by making several key
acknowledgments. Contrary to what the "young-earth" school of creationism maintains, Behe
agrees with his fellow scientists that there is a single family tree, billions of years old, the Tree
of Life, that has on its branches both you and me and every fish and daisy and bacterium. We
are all related; we all descend in common from the earliest inhabitants of this planet, the
single-celled organisms that are our great-great-great. . . . grandparents. We agree, then, that
science has shown that the Genesis creation myth of Adam and Eve is just that, a myth, a
falsehood if taken literally.(1)
Behe's skepticism about evolution concerns a more subtle point; he claims that the fact that all life on earth is connected by common descent over billions of years does not yet prove that no intelligent being--a God or an intergalactic gene-splicer, for instance--played a role in this saga of design innovation and elaboration. I think every evolutionist should agree with him about that much. We cannot positively and definitively rule out the hypothesis that there has been intelligent tampering with our genomes in the past. After all, we ourselves have intelligently tampered with the genomes of many species over the years, and our efforts may well leave no traces that sleuths of the future could detect--if we destroy the written accounts of our tampering, for instance.(2) Behe thinks, however, that he can go beyond this and show that not only has intelligent design not been definitively ruled out; it is rendered at least highly probable by his arguments. This is Behe's central point of disagreement with the establishment.
Behe is right that we won't have a properly completed evolutionary account until the biochemists respond to the challenges he raises. These are huge gaps, I agree, but are they embarrassing flaws, as Behe tries to make out? Are they signs of a theory in trouble? Consider one of his claims on this score: "Although great strides have been made in understanding how the immune system works, we remain ignorant of how it came to be." (p136) This is largely true, but these great strides of which he speaks have almost all been in the last twenty years or so, and one could hardly set out to investigate the evolution of the system before discovering what the system consists in. First things first.
He hints that this ignorance is an embarrassment to scientists, and suggests that it is a taboo topic for scientists because in their hearts they fear they cannot repair it, but this is not at all persuasive. Whether or not scientists ought to be worried, they just aren't, and I can show why. Contemporary evolutionary biologists and biochemists are calmly confident that in due course these evolutionary histories will be filled in--or, to the extent that they are not, they will be shown to be unknowable for tedious reasons, not because of deep theoretical mystery. Historians are not embarrassed by the fact that they cannot yet tell us, and probably never will be able to tell us, whether Alexander the Great arranged for the assassination of Philip II of Macedonia--or closer to the present, whether Oswald acted alone. This unrepairable ignorance does not conceal any abyss, however. It does not open the door, for instance, to the hypothesis that Zeus had a hand in Philip's death, or that Oswald was aided by Martians. In the same spirit, we may encounter unrepairable ignorance of the history of evolution, but this will not open the door to hypotheses about the intervention of an intelligent designer unless somebody can show that the work to be done during this history could not possibly be done by mindless evolution by natural selection. This is a burden of proof that Behe accepts, so let's see how well he carries it. Before looking at his case in detail, however, I want to review, very briefly and superficially, the two main reasons why this burden falls on him.
Why, then, are evolutionary biologists so confident, in the face of so much remaining ignorance? First, consider the difference between a dachshund and a St. Bernard. How different they are! We know, however, that they spring from a common ancestor in the fairly recent past. So we know that this much difference, at least, can accumulate in only a few thousand generations by a process of nothing but differential reproduction. Now since this is a case of natural selection at maximum speed, driven by dog breeders foresightfully aiming at particular goals, one might reserve some doubt about whether a more haphazard regime could achieve the same results at a slower pace. But there are plenty of uncontroversial examples of evolution in which no foresightful selector is at work. The most ominous are the well-studied cases in which viruses or other disease organisms have swiftly developed resistance to antibiotics and other selective forces arrayed against them. We know, for instance, that human beings and chimpanzees spring from a common ancestor of roughly 6 million years ago. and we have an objective measure of just how much mutation has accumulated in each branch in that time. It is unsettling to learn that the AIDS virus, which reproduces so much more swiftly than we do, has accumulated even more mutation in its genome since it was first identified only a few years ago.
The machinery for natural selection exists, and it definitely works. Behe doesn't deny any of this.(3) He holds, however, that we cannot extrapolate from the existence of these uncontested cases to general claims about all the design innovation that has occurred. Science have proved that the machinery works sometimes, but that doesn't show that it works everywhere it must work for the general theory to be true.
How powerful is the machinery of natural selection? How much design work can a blind, mechanical, unforesightful process accomplish? Here is a little imagination-stretcher by Karl Sims.
Sims video
This video doesn't prove that Behe is wrong about anything. I am not claiming, for instance, that anything Behe would describe as irreducibly complex evolves in this computer simulation. It is what an engineer might call a "proof of concept" demo, and all it shows is that it is not impossible for natural selection, under some conditions, to design strikingly effective organs in short order with no helping hands from intelligent bystanders. I wanted to show it to you just to even the playing field of imagination. I find that most people who see it are astonished at how easy it is for a blind algorithmic process to create such well-designed things. I know I was, and I've been a card-carrying Darwinian for years. If you were astonished by it, then had I not shown it, you would have listened to the rest of my talk with an impoverished sense of the power of the process Behe thinks is incapable of executing the tasks he describes.
A picture of a dachshund and a St. Bernard and a brief video--that will have to stand in for the mountains of further grounds I could cite for the scientists' confidence that some evolutionary story or other will fill in all the gaps in the historical record. It is time to turn to Behe's counter-case.
2. Intelligent Authorship or Mindless Plagiarism?
Behe likes to use macroscopic analogies, taking us back and forth between the strange micro-world of biochemistry and our familiar everyday-sized world, and he does it very effectively. He gives us thought experiments about motorcycle factories and vaccine delivery systems and gigantic space ships. There are risks associated with this pedagogical strategy, some of which I will point out in due course, but first I will pursue it myself, using an everyday analogy of my own to show just how hard it is going to be for him to make his case.
Imagine a student accused of plagiarizing his term paper. The student's paper is, with only minor deletions and additions, word for word the same as a published article found in the library. The student admits that he wrote his paper after going to the library in which the (apparent) source article is stored, so a possible path in space and time for the dishonest information transmission is conceded to exist. Moreover, the student admits to having taken his lap-top computer to the library with him, so the necessary copying machinery was available. (If he were blind, and went to the library without so much as paper and pencil or an accomplice, we'd have some challenging questions to answer about how on earth he ever got the information out of the library so intact, but in this case, we have no such problem.) Further, let's suppose, the differences between the published paper and the student's paper all fall in the category of improvements designed to meet the student's current and pressing needs--the student's own name appearing as author, a title more in line with the assignment given by the professor, a reference inserted to one of the course's required texts. Finally, the most damaging evidence of all, we notice that some spelling errors or typographical errors that appear in the original also appear in his paper. Still, insists the student, his paper was an independent Creation, not a copy-with-modifications. Professor Behe's task is strikingly parallel to the difficult task of defending this student against the charge of plagiarism.(4)
In cases of plagiarism, the burden of proof never falls on the prosecutor to show exactly the path by which the copying took place. All the prosecutor has to show is that the copying was possible--the perpetrator did somehow have access to the information. After that, the evidence of similarity speaks eloquently for itself, as it does in all these cases. The reason is simply that the odds are Vast--Very much more than ASTronomical [DDI, p109]--against any such coincidence.
This everyday principle of evidence is relied on by evolutionary theorists to ground their firm belief that evolution by natural selection accounts for the design found in nature, at every level, from the molecular on up: mindless copying with occasional small transformations. You have long sequences of nucleotides in your genome that you share not just with me, but with every mouse, every fruitfly, every fish in the sea--including tell-tale copying errors mindlessly but faithfully reproduced in trillions of copies. These sequences are not a few letters long. Some are term paper length, for instance. The huge flood of new information on gene sequences that is now inundating molecular biology and affecting every walk of life came as no surprise to the evolutionists, of course, but it provided them, for the first time, with the truly voluminous proof that the similarities observable between all species were not just coincidences, but the result of a blind, mechanical copying process.
Now Behe accepts that all this sequence evidence exists, and as he notes, it "strongly supports common descent." Indeed it does; the case for copying is open and shut, and he knows better than to challenge it. But, he goes on to say, "the root question remains unanswered: What has caused complex systems to form?" (p.176) At another point he says "Comparing sequences might be a good way to study relatedness, but the results can't tell us anything about the mechanisms that first produced [my emphasis] the systems." (p.138)(5)
In these passages, Behe grants that there has been copying of designs, and tries to divorce the copying process from the "production" process. In the terms of my analogy, he wants to divert our attention from the mindless copying, and concentrate on the question of how the original paper got written in the first place. Wasn't that first authorship an act of intelligent creation? Of course this divorce of copying from designing is just what the Darwinian theory of evolution denies; it hypothesizes that all creation, all design improvement, all invention is the result of the accumulation of fortuitously sprinkled enhancements that occur within the copying process. We can't isolate a process by which a system was "first produced" from the process by which it gradually came into existence during the copying of its ancestor systems.
Behe highlights the contrast he is intent on making with one of his own analogies:
By way of analogy, the instruction manuals for two different models of computer put out by the same company might have many identical words, sentences, and even paragraphs, suggesting a common ancestry (perhaps the same author wrote both manuals), but comparing the sequences of letters in the instruction manuals will never tell us if a computer can be produced step-by-step starting from a typewriter. (p175)
This analogy may seem to be doing some good work for Behe, but watch how just three minor mutations can make it serve an entirely different purpose.
BEFORE:
By way of analogy, the instruction manuals for two different models of computer put out by the same company might have many identical words, sentences, and even paragraphs, suggesting a common ancestry (perhaps the same author wrote both manuals), but comparing the sequences of letters in the instruction manuals will never tell us if a computer can be produced step-by-step starting from a typewriter. (p175)
AFTER:
By way of analogy, the micro-code for two different models of computer put out by different companies might have many identical words, sentences, and even paragraphs, suggesting a common ancestry . . . , but comparing the sequences of letters in the micro-code will never tell us if a word-processor can be produced step-by-step starting from a computer.
Recall a recent species of artifact that has now just about gone extinct--the so-called "dedicated" word-processor. It looked from the outside like an inexpensive hybrid between an electric typewriter and a personal computer, but when you looked inside the black box, you found that they were actually much more directly descended from the computer, not the typewriter. Inside you'd find an all-purpose CPU chip, such as an 8088 microchip, a full-power computer more powerful that the biggest computer Alan Turing ever saw, but locked into menial service running word-processing software burned into a ROM chip. Vestigial traces of former powers, now no longer expressed in the phenotype! If archeologists of the future discovered this, they might even be able to deduce from tell-tale sequences in the micro-code just how the design of this object had descended by largely mindless copying (with a series of minor modifications) from the design of earlier artifacts. Several cases of such software sleuthing have gone to court, and the existence of tell-tale idiosyncratic similarities in the code have demonstrated clearly to the court that this design was the result of successive acts of relatively mindless plagiarism, not independent, intelligent creation. Manufacturers and publishers sometimes now adopt the tricky policy of deliberately including such idiosyncrasies in their sequences just to trap thieves.(6)
Behe's version of the analogy seems to suggest that studying sequences is no way to make progress on how the design got created "in the first place"; my mutation of his analogy shows that on the contrary, it could be a fine way to study the gradual creation of a design. Behe disagrees.
Mechanical objects can't reproduce and mutate like biological systems, but hypothesizing comparable events at an imaginary factory shows that mutation and reproduction are not the main barriers to evolution of mechanical objects. It is the requirements of the structure-function relationship itself that block Darwinian-style evolution.(47)
This is why biochemistry is, Behe thinks, the Waterloo for Darwin: molecular machines are complex in ways that prevent their coming into existence by any gradual Darwinian process. Here his pedagogical tools are put to dubious use, distorting our sense of what is possible.
An entrancing difference between the macroscopic world of mousetraps and swimming pools on the one hand and the submicroscopic world of cells is that in the tiny world, things have near magical properties: they float around and jump together as if pushed by invisible sprites--or endowed with discerning magnets of a sort unknown to us macroscopic agents. For instance, at one point Behe offers us the analogy of molecules nesting together like cans of tunafish on a supermarket shelf. I don't know about you, but I almost never see random piles of tin cans assembling themselves into neat rows without the intervention of a human stacker, but this is just the sort of thing that happens all the time in the ultra-tiny scenarios of biochemistry.
When conditions are right within the cell (for example, when the temperature is within certain limits and when the concentration of calcium is just right) tubulin--"the 'brick' that makes up the smokestacks--automatically come together to form microtubules. The forces that bring tubulins together are much like those that fold an individual protein into a compact shape: positive charges attract negative charges, oily amino acids squeeze together to exclude water, and so forth. (p.61).
I submit that if we lived in a world where things assembled themselves as readily and frequently as they do in the molecular world, the idea of agentless manufacture--manufacture without any manu (without any helping hands but the molecules themselves)--is one we would find much less dubious.
Behe's macroscopic analogies sometimes permit him to exaggerate the difficulties faced by the Darwinian, ignoring likely paths that would probably not occur to the uninitiated. Here is one instance. Behe asks us to reflect on the impossibility of a bicycle evolving into a motorcycle: "And what part of the bicycle could be duplicated to begin building a motor?" (p.44) It does sound preposterous, doesn't it? Well, here's an even more preposterous idea: instead of imagining the motor to evolve out of a pre-existing part of a functioning bicycle, imagine that the motor evolved separately, somewhere else, serving other purposes in other environments--and then somehow just floated into place on the bicycle! Nothing like that could happen in evolution, could it? At the subcellular level, yes, it could. The mitochondria, which are little energy-machines in each cell of your body, are just such invaders, who, having evolved on their own, joined forces to form eukaryotic cells.
The phenomenon of system parts evolving separately under one selective regime and then coming together fortuitously to form a new selective regime in which the parts acquire (and then grow into) new functions is just one of the powerful cranes that evolutionary biologists have discovered to do this heavy lifting in design space. Behe knows this, of course. In fact, he opens his chapter 2 thus:
Lynn Margulis is highly respected for her widely accepted theory that mitochondria, the energy source of plant and animal cells, were once independent bacterial cells.(p26)
He mentions Margulis favorably so he can quote one of her famous anti-establishment outbursts (somewhat out of context)(7), but he never dwells on the implications of the work that made her famous, and when it comes time to address her more recent, and even more relevant proposals, he dismisses them in less than a page. She has recently been advancing theses to the effect that flagella and cilia, two of Behe's pet examples of irreducibly complex subsystems, also evolved as independent microbes and then joined forces with other cells. These are more radical hypotheses than her theory of the endosymbiotic origin of mitochondria, which is, as Behe notes, widely accepted. They involve the merging of the DNA of these outboard motors with the nuclear DNA of the vessels to which they become attached, and puzzles about how or whether this could have happened have not been resolved. One might think that Behe would set out to demonstrate that her hypotheses--and those of others--could not possibly be correct. Only then would he have any grounds for claiming that he had demonstrated that these systems are irreducibly complex. But instead, he dismisses her work, and that of Cavallier-Smith and Szathmary, as mere "word-pictures." "What is fatal, however, is that neither side has filled in any mechanistic details for its model." (p.69)(8)
3. Some Weaknesses in Behe's Argument: Five Dubious Claims
The argument for irreducible complexity is extremely difficult to make, as generations of previous skeptics have discovered.(9)
Biologists and biochemists who have looked closely at the details of his arguments have been highly critical, but instead of serving as a messenger to relay their criticisms second-hand--I list a few in Appendix B--I will concentrate on a few general assumptions of Behe's that have not been the focus of much attention, but which are, in my opinion, false--or at least highly dubious.
1. It is not true that "without numbers, there is no science." (p95)
As I just noted, Behe rejects one of Margulis's hypotheses as a mere "word-picture," and claims that Cavalier-Smith's scenario lacks "quantitative details" which makes "such a story utterly useless for understanding how a cilium truly might have evolved." (p68) He repeats the same charge often, but although it does sound like an unexceptionable demand for scientific rigor, it is, I think, simply false that "without numbers, there is no science." Leaving out the quantitative details for the time being has often been the best way of proceeding until we could get some clarification of the constraints on a whole class of hypotheses. Balancing the scientific sin of a story without numbers is the scientific sin of premature specificity. When Darwin speculated about how plant seeds, birds and other animals might have been carried by storms to islands from the mainland, he had only the crudest "quantitative details" to constrain his speculations--which seeds floated, how long they could remain in water and still be viable, and so forth. What Darwin did was just what one ought to do in such a circumstance, and what science very often does. When and where it is appropriate to demand "quantitative details" is a variable matter in science, and Behe often seems to be moving the goal-posts to meet the needs of his case. First he calls for serious hypotheses about the possible mechanisms--which have to begin as speculations about possibilities--and then in the next breath he refuses to take seriously any such hypothesis because it doesn't yet have the specificity he demands. To point out that such hypotheses are still far too unconstrained to be proven or disproven is constructive criticism; to hoot them off the stage as unworthy responses to his challenge is obstructionism.(10)
2. No multiplication of improbabilities.
"As the complexity of an interacting system increases, though, the likelihood of such an indirect route drops precipitously. [On the contrary, I think, it becomes ever harder to rule out!] And as the number of unexplained, irreducibly complex biological systems increases, our confidence that Darwin's criterion of failure has been met skyrockets toward the maximum that science allows." (p.40) This is wishful thinking too. In fact, as Behe multiplies examples, and shows their similarity, one sees that if you can solve one of them, you can probably solve them all, with similar means. No multiplication of improbability attaches at all. As he says on page 135, "Like the blood-clotting pathway, the complement pathway is a cascade. Inevitably, in both cases one encounters the same problems trying to imagine their gradual production." All the more reason to suppose that when you solve one, you'll solve them all. Think of watching a stage magician. Is it true that as he does more and more "inexplicable" tricks, your conviction that this is real magic "skyrockets"? Not at all.(11)
3. Exaptation is ignored.
Leaving aside for the moment issues of control and timing of clot formation, upon reflection we can quickly see that even such a slightly simplified system cannot change gradually into the more complex, intact system. If a new protein were inserted into the thrombinless system it would either turn the system on immediately--resulting in rapid death--or it would do nothing, and so have no reason to be selected.(p87)
False. A new protein might be doing something else until coopted for this role.(12)
4. He sometimes forgets his own definition of irreducible complexity.
Because gated transport requires a minimum of three separate components to function, it is irreducibly complex. (p.109)
No. This is not the definition--not Behe's definition--of an irreducibly complex system. He must show that the three components cannot have evolved independently for other functions and then been united seriatim. He knows that this is the loophole, since he sometimes addresses it.
An exhaustive consideration of all possible roles for a particular component can't be done. We can, however, consider a few likely roles for some of the components of the transport system. Doing so shows it is extremely implausible [my emphasis] that components used for other purposes fortuitously adapted to new roles in a complex system.(p.111)
So here he acknowledges that he has nothing but his own sense of the "extreme implausibility" of the alternatives to support his conviction that gated transport is an irreducibly complex system. Faced with an intrepid speculation about how the reduction might go, all he can say is "This may or may not be true." (p115). Exactly right. This tautology is the strongest verdict his book defends.
5. Should we look for conceptual precursors or physical precursors--or both?
In Darwinian evolution, only physical precursors count. (p118).
Behe distinguishes physical precursors from "conceptual" precursors: "A rock and a gun can both be used for defense, but a rock cannot be turned into a gun by a series of small steps." I suppose this is true, but it is not true that it is a mistake to consider "conceptual" precursors when considering an account of "the evolution of defensive systems." An earlier arm's race can set the background conditions of conflict in which an innovation---such as using an alternative weapon--has a fitness advantage. Whether there is selection pressure can depend on the presence of merely conceptual precursors; whether there is anything for selection pressure to shape does depend on physical precursors of course. Behe seems to forget his insistence on the importance of physical precursors when he discusses the evolution of vision.
And rhodopsin, which is used in vision, is similar to a protein found in bacteria, called bacteriorhodopsin, which is involved in the production of energy. Nonetheless, the similarities tell us nothing [sic] about how vision or the immune system could develop step-by-step. (p284-5)
Sure they do. They answer one of Behe's main challenges: how could there be physical (but not "conceptual") precursors?
4. Summary
Behe is right that evolutionary biology will be seriously incomplete until detailed accounts can be found of the actual steps that created the various fascinating molecular phenomena he describes. I must say that I myself had certainly not appreciated how difficult these problems were, or how little had been figured out about them, before reading his book, and I daresay I am not alone. The question is whether this ignorance is ominous--to the Darwinian--or just a measure of the task that lies ahead. I sketched two main reasons why the burden of proof falls on Behe at this point:
(1) We know that evolution by natural selection works in some cases (such as dogs and the AIDS virus), and
(2) We have overwhelming "textual" evidence that the necessary conditions for its always working are met: there are tell-tale traces of mindless copying with mutation, billions of years of plagiarism.
I take it Behe accepts both of these points. It is for those reasons, then, that I likened his task to the job of the defense attorney obtaining an acquittal for the student accused of plagiarism. Turning to that task, Behe attempts to persuade us with a series of analogies, and I found some of them to be seriously misleading: the computer instruction manual, the bicycle-factory, and the stack of tunafish cans. I think this is a serious criticism of Behe's methods, not just of his rhetorical style, because he is trying not just to educate his lay audience about these matters but also to lead them to his opinion of what they show, and in each case I showed how the deficiency in the analogy positively obscured the power of the Darwinian alternative to Behe's view.
In addition to analogies, Behe offers specific arguments about particular phenomena, and I discussed five claims that appear in these arguments that I believe to be mistaken.
[overhead of 5]
His arguments are applications of strategies attempted before, applied to biochemistry. He went seeking skyhooks, and has come up emptyhanded. By his own account, the most he can conclude from his various examinations is that he finds it "extremely implausible" that evolutionary accounts of these phenomena will be forthcoming.
One of the fascinating features of his book, however, is that he does make several tantalizing stabs at finding cranes in spite of himself. In his account of the bombardier beetle (pp35-6), and in his speculations about how flagella might have evolved (p65-66), he raises interesting possibilities, and grants that "All we can conclude at this point is that Darwinian evolution might have occurred." (p36) And as he himself admits, p41, "The frustrating answer is that we can't tell." Well, say I, don't be faint-hearted. Plunge in and take another look at the overlooked details! Maybe something further will occur to you. I'm no expert on these topics, and for all I know the speculations Behe advances have already been tried and found wanting by others, but if not, then Behe may yet someday find himself honored for having located a new crane. I think that would be a fitting triumph.
But I want to end with a different suggestion. If I seriously believed that a great intelligence had been involved somehow in the creation of all these molecular wonders, I would hunt for that intelligence in the domain of biochemistry with a slightly different approach. I would adapt the strategy used by those who are hunting for extra-terrestrial intelligence. Consider the following sequences:
Chris Viger's e in base-4
Do any of these appear regularly--or at all--in the human genome? If so, I would be quite astonished, since these are all different ways you could write the number e, one of the fundamental numbers in all of science, in base 4 notation, which is the obvious choice for our 4-symbol genetic code. It should be a fairly simple matter of bio-informatics to answer this question. A back-of-the-envelope calculation of the probability of any of these strings occurring by chance in any genome of any human being who has ever lived is roughly 1 in 200,000 trillion.(13)
Behe lays down a challenge: If his fellow biologists are so sure about evolution, why don't they attack the problems he has raised? Let me turn the tables: If Behe is so sure there was an intelligent designer, why doesn't he try to find an indisputable signature of the artist in the most likely place on his masterpieces? Behe doesn't offer any specific hypothesis about the nature of this intelligence he thinks he has proven to exist, no "quantitative details" about when or where or even how many intelligent designers might have had a hand in these projects. Behe is in fact carefully neutral on this score: it might be a deity, or it might be a team of intergalactic gene-splicers for whom Earth is a sort of molecular playpen. Why, then, doesn't he look for actual signature mechanisms in the places only a biochemist can see? That would seem to me to be the best scientific way of attempting to prove his conviction.(14)
Appendix A: The Cytochrome C Caper
Philip Johnson is a professor of law at Berkeley who has been arguing, alongside Prof. Behe, that the case for evolution is far from proven. His book, Darwin on Trial (1991, 1993), is mistitled; it really should have a subtitle, The Case for the Prosecution, since it is very one-sided, as one-sided as a good lawyer's case is supposed to be. In his book, Johnson tells about the California Science Framework, an official document of the state Board of Education, a guide to the teaching of biology in public high schools, The Science Framework was created partly in response to the clamor of creationists to have their doctrines taught in public school biology classes. The camel, according to an old joke, is an animal designed by a committee, and the Science Framework, like most committee products, wasn't created under the highest level of quality control, apparently. In a footnote, Johnson tells the amusing story of how one of its authors got his hand caught in the cookie jar. In one section of the document, there appeared a table, showing the amount of variation in the cytochrome c of different species:
The cytochrome c table caused embarrassment to the Framework's authors when it was discovered to contain typographical errors identical to those in a similar table printed in a creationist textbook titled Of Pandas and People. Confronted with the evidence, the consultant responsible for the evolutionary biology sections of the Framework admitted that he had copied the table from the creationist book, reversing the order of the listed organisms but repeating the data verbatim without checking its accuracy. [Johnson, p145n]
Johnson's point in telling this story was to show that the creationist textbook was not such bad science after all--it was good enough to be deemed a worthy source by the authors of the official Science Framework. But I saw a rather better point lurking in this delectable morsel, and, as a good Darwinian, I adapted it for my own purposes. I had occasion to debate Prof. Johnson on a radio program in California a few years ago, and I asked him for his professional opinion as a lawyer. If he had been counsel for the defense, would he have advised his client to 'fess up, as in fact he did, or would he have urged him to hang tough and deny everything, since the prosecution had no concrete evidence of mindless copying? Johnson assured the radio audience that he would have recommended admitting the plagiarism, since it was an open and shut case; it would strain credulity beyond the breaking point to claim that the very same errors had been independently created twice.
I agreed entirely, and pointed out that this was precisely the reasoning that convinced biologists that evolution had taken place: the tell-tale signs of plagiarism in the genomes of every living organism on the planet. Johnson, being a good lawyer, quickly changed the topic. A good scientist would confront the challenge directly.
Appendix B: A few published discussions of Behe by biologists
Tom Cavalier-Smith, 1997, "The Blind Biochemist," Tree, 12, pp.162-3.
Jerry A. Coyne, "God in the details," Nature, 19 September 1996, pp227-8.
Andrew Pomiankowski, "The God of the tiny gaps," New Scientist, 14 September 1996, pp.44-5.
H. Allen Orr, "Darwin v. Intelligent Design (Again)," Boston Review, December/January, 1996-7, pp28-31.
Orr's review was followed in the next issue of Boston Review (Feb/Mar, 1997) with commentaries by several biologists (as well as a reply by Behe, and a further reply by Orr): Jerry Coyne, "More Crank Science," Robert DiSilvestro, "Where's the Evidence?" Russell F. Doolittle, "A Delicate Balance," Douglas J. Futuyma, "Miracles and Molecules," and James Shapiro, "A Third Way." Doolittle's and Coyne's essays are particularly important, since they sharply rebut Behe's treatment of their own work in his book.
James Shapiro, "In the Details . . . What?" National Review, Sept 16, 1996, pp62-65.
James Shreeve, "Design for Living," New York Times Book Review, Aug. 4, 1996, pp8-9.
1. 1Perhaps I am reading too much into Behe's declarations on these matters. He says he knows of "no reason to doubt" (p5) these standard textbook assertions, but he doesn't quite say they are true. They are in fact established beyond any reasonable doubt, but if by some chance he is still agnostic about them, it would help if he would acknowledge this and say what he thinks distinguishes them from such facts as the fact that the earth is round, or the fact that the heart pumps blood.
2. 2As I have said, "It would be foolhardy, however, for any defender of neo-Darwinism to claim that contemporary evolutionary theory gives one the power to read history so finely from present data to rule out the earlier historical presence of rational designers--a wildly implausible fantasy, but a possibility after all." (Darwin's Dangerous Idea, p317-8)
3. 3 Again, I might be reading too much into Behe's silence. He does concede that evolution by natural selection works, and he does concede common descent. There are no cases of common descent better documented than these, so since he never expresses any specific reservations about these cases, I am presuming that he accepts them. If he has reservations about them, he owes us an account.
4. 4 For a real case drawn from the controversy over creationism, see Appendix A.
5. 5 Another passage: "The sequence similarities are there for all to see and cannot be disputed. By itself, however, the hypothesis of gene duplication and shuffling says nothing about how any particular protein or protein system was first produced [my emphasis]--whether slowly or suddenly, or whether by natural selection or some other mechanism." (p.90) But surely the hypothesis of gene duplication and shuffling does say something about how natural selection could do the job (slowly, not suddenly), by showing how some of the requisite materials and methods for such a process were on hand. Like the hypothesis that the student took his laptop to the library, it responds to the challenge: how could this deed have been done?
6. 6"How do the creators of tables or other routine (but labor-intensive) masses of printed data protect themselves from unscrupulous copiers? Sometimes they set traps. I am told, for instance, that the publishers of Who's Who have dealt with the problem of competitors simply stealing all their hard-won facts and publishing their own biographical encyclopedias by quietly inserting a few entirely bogus entries. You can be sure that if one of those shows up on a competitor's pages, it was no coincidence!" (DDI, p.141)
7. 7 She was quoted in a journalistic article as saying that neo-Darwinism would be seen to be "a minor twentieth-century religious sect within the sprawling religious persuasion of Anglo-Saxon biology." C. Mann, "Lynn Margulis: Science's Unruly Earth Mother," Science 1991, 252, pp378-81
8. 8 He goes on to add: "The scientific community at large has ignored both contributions; neither paper has been cited by other scientists more than a handful of times in the years since publication." (p69) This is a risky move, coming from somebody who is protesting that his own challenge is being ignored. Can he be saying that whereas his challenge is worthy of more serious attention by the profession than it is receiving, their responses are not?
9. 9 For one thing, as Behe acknowledges, (p.46), "minimum function is sometimes hard to define." Indeed it is, and that's what makes it so hard to mount a skyhook argument, since functions have a way of creeping up on the unwary skeptic.
10. 10And to misrepresent them as lacking details that they do in fact have is worse still. Behe's book is written for a lay audience, and hence can be excused for not presenting all the technical details, but among the authors he seriously misrepresents in his book are Russell Doolittle, Allen Orr and Jerry Coyne, Lynn Margulis, Elliott Sober, and myself.
11. 11Behe goes in for skyrockets. On page 73: "As the number of required parts increases, the difficulty of gradually putting the system together skyrockets, and the likelihood of indirect scenarios plummets." And again at 203 he reiterates this message, but repetition does not make it more plausible.
12. 12 He makes this mistake more than once. For instance:
But the situation is actually much worse: if a protein appeared in one step with nothing to do, then mutation and natural selection would tend to eliminate it. (p96)
This is true, but irrelevant in the context. He is not entitled to the assumption that such a protein would have nothing to do. What a protein does eventually may be different from what it did when it first appeared.
13. 13Chris Westbury and Chris Viger, my research associates at the Center for Cognitive Studies, worked out the details of this example for me.
14. 14I'm not saying that the discovery of one of these strings in our DNA would instantly confirm intelligent design, but it would be a stunningly good burden shifter, and set us Darwinians scrambling to find an alternative explanation. (Have we calculated the probabilities correctly? Is this as Vastly improbable a finding as I have suggested?)