Design Arguments Behe vs. Orr

Design Arguments Behe vs. Orr I assume that everyone is familiar with the basic idea of Darwin s theory of evolution by natural selection. While this did not seem to be Darwin s intention, philosophical naturalists (i.e. atheists) claim that Darwin s explanation for the origin of living organisms has greatly weakened the argument from design. What is it about Darwin s theory that weakens the design argument? It is not the thesis that all organisms are descended from a common ancestor, so that taxonomical relationships are a matter of how close the closest common ancestor is. (This idea allows that the process of evolution was guided by God, and could not have happened by itself.) Rather, the challenge comes from the fact that Darwin s main mechanism for the evolutionary process, natural selection, is unguided, lacking any goal or purpose. Natural selection is basically a filter that chooses (selects for) some biological characteristics and rejects others. Some characteristics will, in a given context, cause the organisms that have them to produce more offspring, on average. For example, sharp eyesight will help predators, especially if their prey is well camouflaged. Now, if such traits are inherited, then the offspring of these animals will likely have the same traits. Such beneficial traits will therefore become prevalent in the population, over a period of some generations. As the name suggests, natural selection is a natural process that does not seem to require the action of a creator. Moreover, the source of the small changes between parents and offspring is thought to be random sexual recombination and occasional random genetic mutations (copying errors). Random events are the opposite of purposeful, intelligent acts. Naturalists argue, therefore, that not only is there a continuous line of descent with modification, from bacteria to humans, but that the whole process happened by purely natural processes, namely the accumulation of small changes, filtered by natural selection. Some theists are happy with this picture, but others (now often called intelligent design advocates, I.D. theorists) argue that it is inadequate. The most common line of attack from ID theorists is that some complex structures would be very difficult to make by a sequence of small improvements. Note that, for natural selection to approve of a mutation, it must cause increased offspring right now, not at some time in the future. Biochemist Michael Behe developed a version of this argument, which is summarised below. Behe writes How can we decide if Darwin's theory can account for the complexity of molecular life? It turns out that Darwin himself set the standard. He acknowledged that: If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, 1

slight modifications, my theory would absolutely break down. But what type of biological system could not be formed by "numerous, successive, slight modifications"? Well, for starters, a system that is irreducibly complex. Irreducible complexity is just a fancy phrase I use to mean a single system which is composed of several interacting parts, and where the removal of any one of the parts causes the system to cease functioning. Let's consider an everyday example of irreducible complexity: the humble mousetrap. The mousetraps that my family uses consist of a number of parts. There are: 1) a flat wooden platform to act as a base; 2) a metal hammer, which does the actual job of crushing the little mouse; 3) a spring with extended ends to press against the platform and the hammer when the trap is charged; 4) a sensitive catch which releases when slight pressure is applied, and 5) a metal bar which connects to the catch and holds the hammer back when the trap is charged. Now you can't catch a few mice with just a platform, add a spring and catch a few more mice, add a holding bar and catch a few more. All the pieces of the mousetrap have to be in place before you catch any mice. Therefore the mousetrap is irreducibly complex. An irreducibly complex system cannot be produced directly by numerous, successive, slight modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. Since natural selection can only choose systems that are already working, then if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on. Demonstration that a system is irreducibly complex is not a proof that there is absolutely no gradual route to its production. Although an irreducibly complex system can't be produced directly, one can't definitively rule out the possibility of an indirect, circuitous route. However, as the complexity of an interacting system increases, the likelihood of such an indirect route drops precipitously. 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. The Cilium Now, are any biochemical systems irreducibly complex? Yes, it turns out that many are. A good example is the cilium. Cilia are hairlike structures on the surfaces of many animal and lower plant cells that can move fluid over the cell's 2

surface or "row" single cells through a fluid. In humans, for example, cells lining the respiratory tract each have about 200 cilia that beat in synchrony to sweep mucus towards the throat for elimination. What is the structure of a cilium? A cilium consists of bundle of fibers called an axoneme. An axoneme contains a ring of 9 double "microtubules" surrounding two central single microtubules. Each outer doublet consists of a ring of 13 filaments (subfiber A) fused to an assembly of 10 filaments (subfiber B). The filaments of the microtubules are composed of two proteins called alpha and beta tubulin. The 11 microtubules forming an axoneme are held together by three types of connectors: subfibers A are joined to the central microtubules by radial spokes; adjacent outer doublets are joined by linkers of a highly elastic protein called nexin; and the central microtubules are joined by a connecting bridge. Finally, every subfiber A bears two arms, an inner arm and an outer arm, both containing a protein called dynein. But how does a cilium work? Experiments have shown that ciliary motion results from the chemically-powered "walking" of the dynein arms on one microtubule up a second microtubule so that the two microtubules slide past each other. The protein cross-links between microtubules in a cilium prevent neighboring microtubules from sliding past each other by more than a short distance. These cross-links, therefore, convert the dynein-induced sliding motion to a bending motion of the entire axoneme. Now, let us consider what this implies. What components are needed for a cilium to work? Ciliary motion certainly requires microtubules; otherwise, there would be no strands to slide. Additionally we require a motor, or else the microtubules of the cilium would lie stiff and motionless. Furthermore, we require linkers to tug on neighboring strands, converting the sliding motion into a bending motion, and preventing the structure from falling apart. All of these parts are required to perform one function: ciliary motion. Just as a mousetrap does not work unless all of its constituent parts are present, ciliary motion simply does not exist in the absence of microtubules, connectors, and motors. Therefore, we can conclude that the cilium is irreducibly complex; an enormous monkey wrench thrown into its presumed gradual, Darwinian evolution. And in another essay, Behe writes about the bacterial flagellum, which is a rotating version of the cilium, driven by a little motor The rotary nature of the flagellum has been recognized for about 25 years. During that time not a single paper has been published in the biochemical literature even attempting to show how such a machine might have developed by natural selection. Darwin's theory is completely barren when it comes to explaining the origin of the flagellum or any other complex biochemical system. The sterility of Darwinism indicates that it is the wrong framework for understanding the basis of life. As I argue in my book, an alternative hypothesis is both natural and obvious: systems such as the flagellum were intentionally 3

designed by an intelligent agent. Just as in the everyday world we immediately conclude design when we see a complex, interactive system such as a mousetrap, there is no reason to withhold the same conclusion from interactive molecular systems. This conclusion may have theological implications that make some people uncomfortable; nonetheless it is the job of science to follow the data wherever they lead, no matter how disturbing. H. Allen Orr criticizes Behe, claiming that his science is completely wrong. Orr does regard Behe s claim as a scientific one, however, and offers a scientific rebuttal. Other scientists dismiss Behe as a creationist, whose work doesn t count as science at all. Orr writes, for example: Although Behe discusses his religious sentiments he notes his Roman Catholicism, is disturbed by the ill will between science and theology, and is subtly (but clearly) offended by biologist Richard Dawkins's atheism he never places himself squarely in the creationist camp. 3 He maintains that his position is strictly scientific and that the data have driven him ineluctably to his views. As though to prove his scientific restraint, Behe even refuses to speculate on the identity of the designer. Although his last chapter offers many hints of the designer's divinity, the door is left open ever so slightly to some variety of alien intervention (although one wonders who designed them). It's hard to say if Behe's reluctance to utter "God did it" is tactical or sincere. On the one hand, creationists learned long ago to be discreet about religious motive. But on the other, Behe seems sophisticated enough to see that Darwinism never threatened any but the most literal-minded of religious creeds anyway (as dramatically confirmed by Pope John Paul II's recent acceptance of evolution as "more than just a hypothesis"). In any case, I will take Behe at his word. His arguments should and must be dealt with on scientific grounds, just as he has requested. For, in the end, Behe is simply right or wrong. And I am convinced that he is very wrong. What is wrong with Behe s argument? Here is Orr s response. The first thing you need to understand about Behe's argument is that it's just plain wrong. It's not that he botched some stray fact about evolution, or that he doesn't know his biochemistry, but that his argument as an argument is fatally flawed. To see this we need to first get clear about what kinds of solutions to irreducible complexity are not open to Darwinism. First it will do no good to suggest that all the required parts of some biochemical pathway popped up simultaneously by mutation. Although this "solution" yields a functioning system in one fell swoop, it's so hopelessly unlikely that no Darwinian takes it seriously. As Behe rightly says, we gain nothing by replacing a problem 4

with a miracle. Second, we might think that some of the parts of an irreducibly complex system evolved step by step for some other purpose and were then recruited wholesale to a new function. But this is also unlikely. You may as well hope that half your car's transmission will suddenly help out in the airbag department. Such things might happen very, very rarely, but they surely do not offer a general solution to irreducible complexity. Behe's colossal mistake is that, in rejecting these possibilities, he concludes that no Darwinian solution remains. But one does. It is this: An irreducibly complex system can be built gradually by adding parts that, while initially just advantageous, become because of later changes essential. The logic is very simple. Some part (A) initially does some job (and not very well, perhaps). Another part (B) later gets added because it helps A. This new part isn't essential, it merely improves things. But later on, A (or something else) may change in such a way that B now becomes indispensable. This process continues as further parts get folded into the system. And at the end of the day, many parts may all be required. The point is there's no guarantee that improvements will remain mere improvements. Indeed because later changes build on previous ones, there's every reason to think that earlier refinements might become necessary. The transformation of air bladders into lungs that allowed animals to breathe atmospheric oxygen was initially just advantageous: such beasts could explore open niches like dry land that were unavailable to their lung-less peers. But as evolution built on this adaptation (modifying limbs for walking, for instance), we grew thoroughly terrestrial and lungs, consequently, are no longer luxuries they are essential. The punch line is, I think, obvious: although this process is thoroughly Darwinian, we are often left with a system that is irreducibly complex. I'm afraid there's no room for compromise here: Behe's key claim that all the components of an irreducibly complex system "have to be there from the beginning" is dead wrong. It's worth noting that our scenario is neither hypothetical nor confined to the often irretrievable world of biological history. Indeed it's a common experience among computer programmers. Anyone who programs knows how easy it is to write yourself into a corner: a change one makes because it improves efficiency may become, after further changes, indispensable. Improvements might be made one line of code at a time and, at all stages, the program does its job. But, by the end, all the lines may be required. This programming analogy captures another important point: If I were to hand you the final program, it's entirely possible that you would not be able to reconstruct its history that this line was added last and that, in a previous version, some other line sat between these two. Indeed, because the very act of revising a program has a way of wiping out clues to its history, it may be impossible to reconstruct the path taken. Similarly, we have no guarantee that we can reconstruct the history of a biochemical pathway. But even if we can't, its irreducible complexity cannot count against its gradual 5

evolution any more than the irreducible complexity of a program does which is to say, not at all. ----------------- Behe responds Declining the opportunity to address my biochemical arguments, Orr questions the concept of irreducible complexity on logical grounds. He agrees with me that "You cannot... gradually improve a mousetrap by adding one part and then the next. A trap having half its parts doesn't function half as well as a real trap; it doesn't function at all." So Orr understands the point of my mousetrap analogy-- but then mysteriously forgets it. He later writes, "Some part (A) initially does some job (and not very well, perhaps). Another part (B) later gets added, because it helps A." Some part initially does some job? Which part of the mousetrap is he talking about? A mouse has nothing to fear from a "trap" that consists of just an unattached holding bar, or spring, or platform, with no other parts. I do sympathize with Orr's muddling of the analysis. The concept of irreducible complexity is new, and can be difficult to grasp for people who have always assumed without demonstration that small, continuous changes could produce virtually any biological structure. Perhaps in the future that assumption will not have such a strong hold on the minds of evolutionary biologists. Behe obviously doesn t think much of Orr s criticism. To see what Orr is talking about, let s think about a structure called a free-standing arch. It s made of stones that are slightly tapered, so that they don t require any mortar to stay together, but are held in place by gravity. If you remove any one of the stones, then the whole arch will collapse. It therefore fits Behe s definition of an irreducibly complex system. How could such a system have evolved, through a sequence of small, individually-advantageous changes? You certainly can t build one by adding one stone at a time! Well, you might start with a small pile of dirt. This might, let us suppose, have something of the arch s eventual function. The pile of dirt gradually gets bigger, thus gradually increasing its function. It then develops, by gradual increments, into a nice hemispherical mound. Finally, stones are added to the top of the mound, which slightly improve the function of the mound. (At this point the stones aren t really necessary, and the system isn t irreducibly complex.) Then, since the stones are now doing the job, the dirt isn t needed, and slowly withers away. Thus the stones are left in place, supporting each other, in an irreducibly complex system. Behe acknowledges such possible evolutionary pathways, saying, Although an irreducibly complex system can't be produced directly, one can't definitively rule out the possibility of an indirect, circuitous route. [My emphasis.] 6

The disagreement between Orr and Behe seems largely centred on the question of the extent to which such indirect routes are biologically important. Orr thinks they re at work everywhere in evolution, whereas Behe regards them as exceptional. 7