Born-Again Creationism: Behe's Big Idea
The following excerpt was published in Intelligent Design Creationism and Its Critics (2001).
by Philip Kitcher
saiah Berlin's famous division that contrasts hedgehogs (people with one big idea) and foxes (people with lots of little ideas) applies not only to thinkers but to creationists as well. The two most prominent figures on the neo-creo scene are Michael Behe (a hedgehog) and Phillip Johnson (a fox), both of whom receive plaudits from such distinguished philosophers as Alvin Plantinga and Peter van Inwagen. (Since Plantinga and van Inwagen have displayed considerable skill in articulating and analyzing philosophical arguments, the only charitable interpretation of their fulsome blurbs is that a combination of Schwärmerei for creationist doctrine and profound ignorance of relevant bits of biology has induced them to put their brains in cold storage.)Johnson, a lawyer by training, is a far more subtle rhetorician than Gish, and he moves from topic to topic smoothly, discreetly making up the rules of evidence to suit his case as he goes. Many of his attack strategies refine those of country-bumpkin creationism, although, like the White Knight in Alice, he has a few masterpieces of his own invention.
Behe, by contrast, mounts his case for born-again creationism by taking one large problem, and posing it again and again. The problem isn't particularly new: it's the old issue of "complex organs" that Darwin tried to confront in the Origin. Behe gives it a new twist by drawing on his background as a biochemist, and describing the minute details of mechanisms in organisms so as to make it seem impossible that they could ever have emerged from a stepwise natural process.
Here's the general form of the problem. Given our increased knowledge of the molecular structures in cells and the chemical reactions that go on within and among cells, it's possible to describe structures and processes in exceptionally fine detail. Many structures have large numbers of constituent molecules and the precise details of their fit together are essential for them to fulfill their functions. Similarly, many biochemical pathways require numerous enzymes to interact with one another, in appropriate relative concentrations, so that some important process can occur. Faced with either of these situations, you can pose an obvious question: how could organisms with the pertinent structures or processes have evolved from organisms that lacked them? That question is an explicit invitation to describe an ancestral sequence of organisms that culminated in one with the structures or processes at the end, where each change in the sequence is supposed to carry some selective advantage. If you now pose the question many times over, canvass various possibilities, and conclude that not only has no evolutionist proposed any satisfactory sequences, but that there are systematic reasons for thinking that the structure or process could not have been built up gradually, you have an attack strategy that appears very convincing.
That, in outline, is Behe's big idea. Here's a typical passage, summarizing his quite lucid and accessible description of the structures of cillia and flagella:
…as biochemists have begun to examine apparently simple structures like cillia and flagella, they have discovered staggering complexity, with dozens or even hundreds of precisely tailored parts. It is very likely that many of the parts we have not considered here are required for any cilium to function in a cell. As the number of required parts increases, the difficulty of gradually putting the system together skyrockets, and the likelihood of indirect scenarios plummets. Darwin looks more and more forlorn. (DBB 73)
This sounds like a completely recalcitrant problem for evolutionists, but it's worth asking just why precisely Darwin should took more and more forlorn.
Notice first that lots of sciences face all sorts of unresolved questions. To take an example close to hand, Behe's own discussions of cilia frankly acknowledge that there's a lot still to learn about molecular structure and its contributions to function. So the fact that evolutionary biologists haven't yet come up with a sequence of organisms culminating in bacteria with flagella or cilia might be regarded as signaling a need for further research on the important open problem of how such bacteria evolved. Not so! declares Behe. We have here "irreducible complexity," and it's just impossible to imagine a sequence of organisms adding component molecules to build the structures up gradually.
What does this mean? Is Behe supposing that his examples point to a failure of natural selection as a mechanism for evolution? If so, then perhaps he believes that there was a sequence of organisms that ended up with a bacterium with a flagellum (say), but that the intermediates in this sequence added molecules to no immediate purpose, presumably being at a selective disadvantage because of this. (Maybe the Good Lord tempers the wind to the shorn bacterium.) Or does he just dispense with intermediates entirely, thinking that the Creator simply introduced all the right molecules de novo? In that case, despite his claims, he really does doubt common descent. Behe's actual position is impossible to discern because he has learned Duane Gish's lesson (Always attack! Never explain!). I'll return at the very end to the cloudiness of Behe's account of the history of life.
Clearly, Behe thinks that Darwinian evolutionary theory requires some sequence of precursors for bacteria with flagella and that no appropriate sequence could exist. But why does he believe this? Here's a simple minded version of the argument. Assume that the flagellum needs 137 proteins. Then Darwinians are required to produce a sequence of 138 organisms, the first having none of the proteins and each one having one more protein than its predecessor. Now, we're supposed to be moved by the plight of organisms numbers 2 to 137, each of which contains proteins that can't serve any function, and is therefore, presumably, a target of selection. Only number 1, the ancestor, and number 138, in which all the protein constituents come together to form the flagellum, have just what it takes to function. The intermediates would wither in the struggle for existence. Hence evolution under natural selection couldn't have brought the bacterium from there to here.
But this story is just plain silly, and Darwinians ought to disavow any commitment to it. After all, it's a common theme of evolutionary biology that constituents of a cell, a tissue, or an organism, are put to new uses because of some modification of the genotype. So maybe the immediate precursor of the proud possessor of the flagellum is a bacterium in which all the protein constituents were already present, but in which some other feature of the cell chemistry interferes with the reaction that builds the flagellum. A genetic change removes the interference (maybe a protein assumes a slightly different configuration, binding to something that would have bound to one of the constituents of the flagellum, preventing the assembly). "But, Professor Kitcher [creos always try to be polite], do you have any evidence for this scenario?" Of course not. That is to shift the question. We were offered a proof of the impossibility of a particular sequence, and when one tries to show that the proof is invalid by inventing possible instances, it's not pertinent to ask for reasons to think that those instances exist. If they genuinely reveal that what was was declared to be impossible isn't, then we no longer have a claim that the Darwinian sequence couldn't have occurred, but simply an open problem of the kind that spurs scientists in any field to engage in research.
Behe has made it look as though there's something more here by inviting us to think about the sequence of precursors in a very particular way. He doesn't actually say that proteins have to be added one at a time—he surely knows very well that that would provoke the reaction I've offered—but his defense of the idea that there just couldn't be a sequence of organisms leading up to bacteria with flagella insinuates, again and again, that the problem is that the alleged intermediates would have to have lots of the components lying around like so many monkey-wrenches in the intracellular works. This strategy is hardly unprecedented. Country-bumpkin creos offered a cruder version when they dictated to evolutionists what fossil intermediates would have to be like: the transitional forms on the way to birds would have to have had half-scales and half-feathers, halfway wings—or so we are told.
Behe has made up his own ideas about what transitional organisms must have been like, and then argued that such organisms couldn't have existed. In fact, we don't need to compare my guesswork with his. What Darwinism is committed to (at most) is the idea that modifications of DNA sequence (insertions, deletions, base changes, translocations) could yield a sequence of organisms culminating in a bacterium with a flagellum, with selective advantages for the later member of each adjacent pait. To work out what the members of this sequence of organisms might have been like, our ideas should be educated by the details of how the flagellum is actually assembled and the loci in the bacterial genome that are involved. Until we know these things, it's quite likely that any efforts to describe precursors or intermediates will be whistling in the dark. Behe's examples cunningly exploit our ability to give a molecular analysis of the end product and our ignorance of the molecular details of how it is produced.
Throughout his book, Behe repeats the same story. He describes, often charmingly, the complexities of molecular structures and processes. There would be nothing to complain of if he stopped here and said: "Here are some interesting problems for molecularly minded evolutionists to work on, and, in a few decades time, perhaps, in light of increased knowledge of how development works at the molecular level, we may be able to see what the precursors were like." But he doesn't. He tries to argue that the precursors and intermediates required by Darwinian evolutionary theory couldn't have existed. This strategy has to fail because Behe himself is just as ignorant about the molecular basis of development as his Darwinian opponents. Hence he hasn't a clue what kinds of precursors and intermediates the Darwinian account is actually committed to—so it's impossible to demonstrate that the commitment can't be honored. However, again and again, Behe disguises his ignorance by suggesting to the reader that the Darwinian story must take a very particular form—that it has to consist in something like the simple addition of components, for example—and on that basis he can manufacture the illusion of giving an impossibility proof.
Although this is the main rhetorical trick of the book, there are some important subsidiary bits of legerdemain. Like pre-Reformation creationists, Behe loves to flash probability calculations, offering spurious precision to his criticisms. Here's his attack on a scenario for the evolution of a blood-clotting mechanism, tentatively proposed by Russell Doolittle:
…let's do our own quick calculation. Consider that animals with blood-clotting cascades have roughly 10,000 genes, each of which is divided into an average of three pieces. This gives a total of about 30,000 gene pieces. TPA [Tissue Plasminogen Activator] has four different types of domains. By "variously shuffling," the odds of getting those four domains together is 30,000 to the fourth power, which is approximately one-tenth to the eighteenth power. Now, if the Irish Sweepstakes had odds of winning of one-tenth to the eighteenth power, and if a million people played the lottery each year, it would take an average of about a thousand billion years before anyone (not just a particular person) won the lottery.… Doolittle apparently needs to shuffle and deal himself a number of perfect bridge hands to win the game. (DBB 94)
This sounds quite powerful, and Behe drives home the point by noting that Doolittle provides no quantitative estimates, adding that "without numbers, there is no science" (DBB 95)—presumably to emphasize that born-again creationists are better scientists than the distinguished figures they attack. But consider a humdrum phenomenon suggested by Behe's analogy to bridge. Imagine that you take a standard deck of cards and deal yourself thirteen. What's the probability that you got exactly those cards in exactly that order? The answer is 1 in 4 x 1021. Suppose you repeat this process ten times. You'll now have received ten standard bridge hands, ten sets of thirteen cards, each one delivered in a particular order. The chance of getting just those cards in just that order is 1 in 410 x 10210. This is approximately 1 in 10222. Notice that the denominator is far larger than that of Behe's trifling 1018. So it must be really improbable that you (or anyone else) would ever receive just those cards in just that order in the entire history of the universe. But, whatever the cards were, you did.
What my analogy shows is that, if you describe events that actually occur from a particular perspective, you can make them look improbable. Thus, given a description of the steps in Doolittle's scenario for the evolution of TPA, the fact that you can make the probability look small doesn't mean that that isn't (or couldn't) have been the way things happened. One possibility is that the evolution of blood-clotting was genuinely improbable. But there are others.
Return to your experiment with the deck of cards. Let's suppose that all the hands you were dealt were pretty mundane—fairly evenly distributed among the suits, with a scattering of high cards in each. If you calculated the probability of receiving ten mundane hands in succession, it would of course be much higher than the priority of being dealt those very particular mundane hands with the cards arriving in just that sequence (although it wouldn't be as large as you might expect). There might be an analogue for blood-clotting, depending on how many candidates there are among the 3,000 "gene pieces" to which Behe alludes that would yield a protein product able to play the necessary role. Suppose that there are a hundred acceptable candidates for each position. That means that the chance of success on any particular draw is (1/30)4, which is about 1 in 2.5 million. Now, if there were 10,000 tries per year, it would take, on average, two or three centuries to arrive at the right combination, a flicker of an instant in evolutionary time.
Of course, neither Behe nor I knows how tolerant the blood-clotting system is, how many different molecular ways it allows to get the job done. Thus we can't say if the right way to look at the problem is to think of the situation as the analogue to being dealt a very particular science of cards in a very particular order, or whether the right comparison is with cases in which a more general type of sequence occurs. But these two suggestions don't exhaust the relevant cases.
Suppose you knew the exact order of cards in the deck prior to each deal. Then the probability that the particular sequence would occur would be extremely high (barring fumbling or sleight of hand, the probability would be 1). The sequence only looks improbable because we don't know the order. Perhaps that's true for the Doolittle shuffling process as well. Given the initial distribution of pieces of DNA, plus the details of the biochemical milieu, principles of chemical recombination might actually make it very probable that the cascade Doolittle hypothesizes would ensue. Once again, nobody knows whether this is so. Behe simply assumes that it isn't.
Let me sum up. There are two questions to pose: What is the probability that the Doolittle sequence would occur? What is the significance of a low value for that probability? The answer to the first question is that we haven't a clue: it might be close to 1, it might be small but significant enough to make it likely that the sequence would occur in a flicker of evolutionary time, or it might be truly tiny (as Behe suggests). The answer to the second question is that genuinely improbable things sometimes happen, and one shouldn't confuse improbability with impossibility. Once these points are recognized, it's clear that, for all its rhetorical force, Behe's appeal to numbers smacks more of numerology than of science. As with his main line of argument, it turns out to be an attempt to parlay ignorance of molecular details into an impossibility proof.
( Philip Kitcher, "Born-Again Creationism," In Robert T. Pennock, Intelligent Design Creationism and Its Critics, Cambridge, Massachusetts, The MIT Press, 2001, pp. 261-267. )
Home Page | Further Reading | Site Map | Send Feedback
