The Portable Atheist

The Ultimate Boeing 747

The argument from improbability is the big one. In the traditional guise of the argument from design, it is easily today’s most popular argument offered in favor of the existence of God and it is seen, by an amazingly large number of theists, as completely and utterly convincing. It is indeed a very strong and, I suspect, unanswerable argument—but in precisely the opposite direction from the theist’s intention. The argument from improbability, properly deployed, comes close to proving that God does not exist. My name for the statistical demonstration that God almost certainly does not exist is the Ultimate Boeing 747 gambit.

The name comes from Fred Hoyle’s amusing image of the Boeing 747 and the scrapyard. I am not sure whether Hoyle ever wrote it down himself, but it was attributed to him by his close colleague Chandra Wickramasinghe and is presumably authentic. Hoyle said that the probability of life originating on Earth is no greater than the chance that a hurricane, sweeping through a scrapyard, would have the luck to assemble a Boeing 747. Others have borrowed the metaphor to refer to the later evolution of complex living bodies, where it has a spurious plausibility. The odds against assembling a fully functioning horse, beetle, or ostrich by randomly shuffling its parts are up there in 747 territory. This, in a nutshell, is the creationist’s favourite argument—an argument that could be made only by somebody who doesn’t understand the first thing about natural selection: somebody who thinks natural selection is a theory of chance whereas—in the relevant sense of chance—it is the opposite.

The creationist misappropriation of the argument from improbability always takes the same general form, and it doesn’t make any difference if the creationist chooses to masquerade in the politically expedient fancy dress of “intelligent design” (ID).[28] Some observed phenomenon—often a living creature or one of its more complex organs, but it could be anything from a molecule up to the universe itself—is correctly extolled as statistically improbable. Sometimes the language of information theory is used: the Darwinian is challenged to explain the source of all the information in living matter, in the technical sense of information content as a measure of improbability or “surprise value.” Or the argument may invoke the economist’s hackneyed motto: there’s no such thing as a free lunch—and Darwinism is accused of trying to get something for nothing. In fact, as I shall show in this chapter, Darwinian natural selection is the only known solution to the otherwise unanswerable riddle of where the information comes from. It turns out to be the God Hypothesis that tries to get something for nothing. God tries to have his free lunch and be it too. However statistically improbable the entity you seek to explain by invoking a designer, the designer himself has got to be at least as improbable. God is the Ultimate Boeing 747.

The argument for improbability states that complex things could not have come about by chance. But many people define “come about by chance” as “a synonym for come about in the absence of deliberate design.” Not surprisingly, therefore, they think improbability is evidence of design. Darwinian natural selection shows how wrong this is with respect to biological improbability. And although Darwinism may not be directly relevant to the inanimate world—cosmology, for example—it raises our consciousness in areas outside its original territory of biology.

A deep understanding of Darwinism teaches us to be wary of the easy assumption that design is the only alternative to chance, and teaches us to seek out graded ramps of slowly increasing complexity. Before Darwin, philosophers such as Hume understood that the improbability of life did not mean it had to be designed, but they couldn’t imagine the alternative. After Darwin, we all should feel, deep in our bones, suspicious of the very idea of design. The illusion of design is a trap that has caught us before, and Darwin should have immunized us by raising our consciousness. Would that he had succeeded with all of us.

Natural Selection as a Consciousness-Raiser

In a science-fiction starship, the astronauts were homesick: “Just to think that it’s springtime back on Earth!” You may not immediately see what’s wrong with this, so deeply ingrained is the unconscious northern hemisphere chauvinism in those of us who live there, and even some who don’t. “Unconscious” is exactly right. That is where consciousness-raising comes in. It is for a deeper reason than gimmicky fun that, in Australia and New Zealand, you can buy maps of the world with the South Pole on top. What splendid consciousness-raisers those maps would be, pinned to the walls of our northern hemisphere classrooms. Day after day, the children would be reminded that “north” is an arbitrary polarity which has no monopoly on “up.” The map would intrigue them as well as raise their consciousness. They’d go home and tell their parents—and, by the way, giving children something with which to surprise their parents is one of the greatest gifts a teacher can bestow.

It was the feminists who raised my consciousness of the power of consciousness-raising. “Herstory” is obviously ridiculous, if only because the “his” in “history” has no etymological connection with the masculine pronoun. It is as etymologically silly as the sacking, in 1999, of a Washington official whose use of “niggardly” was held to give racial offence. But even daft examples like “niggardly” or “herstory” succeed in raising consciousness. Once we have smoothed our philological hackles and stopped laughing, herstory shows us history from a different point of view. Gendered pronouns notoriously are the front line of such consciousness-raising. He or she must ask himself or herself whether his or her sense of style could ever allow himself or herself to write like this. But if we can just get over the clunking infelicity of the language, it raises our consciousness to the sensitivities of half the human race. Man, mankind, the Rights of Man, all men are created equal, one man one vote—English too often seems to exclude woman.[29] When I was young, it never occurred to me that women might feel slighted by a phrase like “the future of man.” During the intervening decades, we have all had our consciousness raised. Even those who still use “man” instead of “human” do so with an air of self-conscious apology—or truculence, taking a stand for traditional language, even deliberately to rile feminists. All participants in the Zeitgeist have had their consciousness raised, even those who choose to respond negatively by digging in their heels and redoubling the offence.

Feminism shows us the power of consciousness-raising, and I want to borrow the technique for natural selection. Natural selection not only explains the whole of life; it also raises our consciousness to the power of science to explain how organized complexity can emerge from simple beginnings without any deliberate guidance. A full understanding of natural selection encourages us to move boldly into other fields. It arouses our suspicion, in those other fields, of the kind of false alternatives that once, in pre-Darwinian days, beguiled biology. Who, before Darwin, could have guessed that something so apparently designed as a dragonfly’s wing or an eagle’s eye was really the end product of a long sequence of non-random but purely natural causes?

Douglas Adams’s moving and funny account of his own conversion to radical atheism—he insisted on the “radical” in case anybody should mistake him for an agnostic—is testimony to the power of Darwinism as a consciousness-raiser. I hope I shall be forgiven the self-indulgence that will become apparent in the following quotation. My excuse is that Douglas’s conversion by my earlier books—which did not set out to convert anyone—inspired me to dedicate to his memory this book—which does! In an interview, reprinted posthumously in The Salmon of Doubt, he was asked by a journalist how he became an atheist. He began his reply by explaining how he became an agnostic, and then proceeded:

The concept of stunning simplicity that he was talking about was, of course, nothing to do with me. It was Darwin’s theory of evolution by natural selection—the ultimate scientific consciousness-raiser. Douglas, I miss you. You are my cleverest, funniest, most open-minded, wittiest, tallest, and possibly only convert. I hope this book might have made you laugh—though not as much as you made me.

That scientifically savvy philosopher Daniel Dennett pointed out that evolution counters one of the oldest ideas we have: “the idea that it takes a big fancy smart thing to make a lesser thing. I call that the trickle-down theory of creation. You’ll never see a spear making a spear maker. You’ll never see a horse shoe making a blacksmith. You’ll never see a pot making a potter.” Darwin’s discovery of a workable process that does that very counterintuitive thing is what makes his contribution to human thought so revolutionary, and so loaded with the power to raise consciousness.

It is surprising how necessary such consciousness-raising is, even in the minds of excellent scientists in fields other than biology. Fred Hoyle was a brilliant physicist and cosmologist, but his Boeing 747 misunderstanding, and other mistakes in biology such as his attempt to dismiss the fossil Archaeopteryx as a hoax, suggest that he needed to have his consciousness raised by some good exposure to the world of natural selection. At an intellectual level, I suppose he understood natural selection. But perhaps you need to be steeped in natural selection, immersed in it, swim about in it, before you can truly appreciate its power.

Other sciences raise our consciousness in different ways. Fred Hoyle’s own science of astronomy puts us in our place, metaphorically as well as literally, scaling down our vanity to fit the tiny stage on which we play out our lives—our speck of debris from the cosmic explosion. Geology reminds us of our brief existence both as individuals and as a species. It raised John Ruskin’s consciousness and provoked his memorable heart cry of 1851: “If only the Geologists would let me alone, I could do very well, but those dreadful hammers! I hear the clink of them at the end of every cadence of the Bible verses.” Evolution does the same thing for our sense of time—not surprisingly, since it works on the geological timescale. But Darwinian evolution, specifically natural selection, does something more. It shatters the illusion of design within the domain of biology, and teaches us to be suspicious of any kind of design hypothesis in physics and cosmology as well. I think the physicist Leonard Susskind had this in mind when he wrote, “I’m not an historian but I’ll venture an opinion: Modern cosmology really began with Darwin and Wallace. Unlike anyone before them, they provided explanations of our existence that completely rejected supernatural agents…Darwin and Wallace set a standard not only for the life sciences but for cosmology as well.” Other physical scientists who are far above needing any such consciousness-raising are Victor Stenger, whose book Has Science Found God? (the answer is no) I strongly recommend, and Peter Atkins, whose Creation Revisited is my favourite work of scientific prose poetry.

I am continually astonished by those theists who, far from having their consciousness raised in the way that I propose, seem to rejoice in natural selection as “God’s way of achieving his creation.” They note that evolution by natural selection would be a very easy and neat way to achieve a world full of life. God wouldn’t need to do anything at all! Peter Atkins, in the book just mentioned, takes this line of thought to a sensibly godless conclusion when he postulates a hypothetically lazy God who tries to get away with as little as possible in order to make a universe containing life. Atkins’s lazy God is even lazier than the deist God of the eighteenth-century Enlightenment: deus otiosus—literally God at leisure, unoccupied, unemployed, superfluous, useless. Step by step, Atkins succeeds in reducing the amount of work the lazy God has to do until he finally ends up doing nothing at all: he might as well not bother to exist. My memory vividly hears Woody Allen’s perceptive whine: “If it turns out that there is a God, I don’t think that he’s evil. But the worst that you can say about him is that basically he’s an under-achiever.”

Irreducible Complexity

It is impossible to exaggerate the magnitude of the problem that Darwin and Wallace solved. I could mention the anatomy, cellular structure, biochemistry, and behaviour of literally any living organism by example. But the most striking feats of apparent design are those picked out—for obvious reasons—by creationist authors, and it is with gentle irony that I derive mine from a creationist book. Life—How Did It Get Here?, with no named author but published by the Watchtower Bible and Tract Society in sixteen languages and eleven million copies, is obviously a firm favourite because no fewer than six of those eleven million copies have been sent to me as unsolicited gifts by well-wishers from around the world.

Picking a page at random from this anonymous and lavishly distributed work, we find the sponge known as Venus’ Flower Basket (Euplectella), accompanied by a quotation from Sir David Attenborough, no less: “When you look at a complex sponge skeleton such as that made of silica spicules which is known as Venus’ Flower Basket, the imagination is baffled. How could quasi-independent microscopic cells collaborate to secrete a million glassy splinters and construct such an intricate and beautiful lattice? We do not know.” The Watchtower authors lose no time in adding their own punchline: “But one thing we do know: Chance is not the likely designer.” No indeed, chance is not the likely designer. That is one thing on which we can all agree. The statistical improbability of phenomena such as Euplectella’s skeleton is the central problem that any theory of life must solve. The greater the statistical improbability, the less plausible is chance as a solution: that is what improbable means. But the candidate solutions to the riddle of improbability are not, as is falsely implied, design and chance. They are design and natural selection. Chance is not a solution, given the high levels of improbability we see in living organisms, and no sane biologist ever suggested that it was. Design is not a real solution either, as we shall see later; but for the moment I want to continue demonstrating the problem that any theory of life must solve: the problem of how to escape from chance.

Turning Watchtower’s page, we find the wonderful plant known as Dutchman’s Pipe (Aristolochia trilobata), all of whose parts seem elegantly designed to trap insects, cover them with pollen and send them on their way to another Dutchman’s Pipe. The intricate elegance of the flower moves Watchtower to ask: “Did all of this happen by chance? Or did it happen by intelligent design?” Once again, no of course it didn’t happen by chance. Once again, intelligent design is not the proper alternative to chance. Natural selection is not only a parsimonious, plausible, and elegant solution; it is the only workable alternative to chance that has ever been suggested. Intelligent design suffers from exactly the same objection as chance. It is simply not a plausible solution to the riddle of statistical improbability. And the higher the improbability, the more implausible intelligent design becomes. Seen clearly, intelligent design will turn out to be a redoubling of the problem. Once again, this is because the designer himself (/herself/itself) immediately raises the bigger problem of his own origin. Any entity capable of intelligently designing something as improbable as a Dutchman’s Pipe (or a universe) would have to be even more improbable than a Dutchman’s Pipe. Far from terminating the vicious regress, God aggravates it with a vengeance.

Turn another Watchtower page for an eloquent account of the giant redwood (Sequoiadendron giganteum), a tree for which I have a special affection because I have one in my garden—a mere baby, scarcely more than a century old, but still the tallest tree in the neighbourhood. “A puny man, standing at a sequoia’s base, can only gaze upward in silent awe at its massive grandeur. Does it make sense to believe that the shaping of this majestic giant and of the tiny seed that packages it was not by design?” Yet again, if you think the only alternative to design is chance then, no, it does not make sense. But again the authors omit all mention of the real alternative, natural selection, either because they genuinely don’t understand it or because they don’t want to.

The process by which plants, whether tiny pimpernels or massive wellingtonias, acquire the energy to build themselves is photosynthesis. Watchtower again: “‘There are about seventy separate chemical reactions involved in photosynthesis,’ one biologist said. ‘It is truly a miraculous event.’ Green plants have been called nature’s ‘factories’—beautiful, quiet, nonpolluting, producing oxygen, recycling water and feeding the world. Did they just happen by chance? Is that truly believable?” No, it is not believable; but the repetition of example after example gets us nowhere. Creationist “logic” is always the same. Some natural phenomenon is too statistically improbable, too complex, too beautiful, too awe-inspiring to have come into existence by chance. Design is the only alternative to chance that the authors can imagine. Therefore a designer must have done it. And science’s answer to this faulty logic is also always the same. Design is not the only alternative to chance. Natural selection is a better alternative. Indeed, design is not a real alternative at all because it raises an even bigger problem than it solves: who designed the designer? Chance and design both fail as solutions to the problem of statistical improbability, because one of them is the problem, and the other one regresses to it. Natural selection is a real solution. It is the only workable solution that has ever been suggested. And it is not only a workable solution, it is a solution of stunning elegance and power.

What is it that makes natural selection succeed as a solution to the problem of improbability, where chance and design both fail at the starting gate? The answer is that natural selection is a cumulative process, which breaks the problem of improbability up into small pieces. Each of the small pieces is slightly improbable, but not prohibitively so. When large numbers of these slightly improbable events are stacked up in series, the end product of the accumulation is very very improbable indeed, improbable enough to be far beyond the reach of chance. It is these end products that form the subjects of the creationist’s wearisomely recycled argument. The creationist completely misses the point, because he (women should for once not mind being excluded by the pronoun) insists on treating the genesis of statistical improbability as a single, one-off event. He doesn’t understand the power of accumulation.

In Climbing Mount Improbable, I expressed the point in a parable. One side of the mountain is a sheer cliff, impossible to climb, but on the other side is a gentle slope to the summit. On the summit sits a complex device such as an eye or a bacterial flagellar motor. The absurd notion that such complexity could spontaneously self-assemble is symbolized by leaping from the foot of the cliff to the top in one bound. Evolution, by contrast, goes around the back of the mountain and creeps up the gentle slope to the summit: easy! The principle of climbing the gentle slope as opposed to leaping up the precipice is so simple, one is tempted to marvel that it took so long for a Darwin to arrive on the scene and discover it. By the time he did, nearly three centuries had elapsed since Newton’s annus mirabilis, although his achievement seems, on the face of it, harder than Darwin’s.

Another favourite metaphor for extreme improbability is the combination lock on a bank vault. Theoretically, a bank robber could get lucky and hit upon the right combination of numbers by chance. In practice, the bank’s combination lock is designed with enough improbability to make this tantamount to impossible—almost as unlikely as Fred Hoyle’s Boeing 747. But imagine a badly designed combination lock that gave out little hints progressively—the equivalent of the “getting warmer” of children playing Hunt the Slipper. Suppose that when each one of the dials approaches its correct setting, the vault door opens another chink, and a dribble of money trickles out. The burglar would home in on the jackpot in no time.

Creationists who attempt to deploy the argument from improbability in their favour always assume that biological adaptation is a question of the jackpot or nothing. Another name for the “jackpot or nothing” fallacy is “irreducible complexity” (IC). Either the eye sees or it doesn’t. Either the wing flies or it doesn’t. There are assumed to be no useful intermediates. But this is simply wrong. Such intermediates abound in practice—which is exactly what we should expect in theory. The combination lock of life is a “getting warmer, getting cooler, getting warmer” Hunt the Slipper device. Real life seeks the gentle slopes at the back of Mount Improbable, while Creationists are blind to all but the daunting precipice at the front.

Darwin devoted an entire chapter of the Origin of Species to “Difficulties on the theory of descent with modification,” and it is fair to say that this brief chapter anticipated and disposed of every single one of the alleged difficulties that have since been proposed, right up to the present day. The most formidable difficulties are Darwin’s “organs of extreme perfection and complication,” sometimes erroneously described as “irreducibly complex.” Darwin singled out the eye as posing a particularly challenging problem: “To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.” Creationists gleefully quote this sentence again and again. Needless to say, they never quote what follows. Darwin’s fulsomely free confession turned out to be a rhetorical device. He was drawing his opponents towards him so that his punch, when it came, struck the harder. The punch, of course, was Darwin’s effortless explanation of exactly how the eye evolved by gradual degrees. Darwin may not have used the phrase “irreducible complexity,” or “the smooth gradient up Mount Improbable,” but he clearly understood the principle of both.

“What is the use of half an eye?” and “What is the use of half a wing?” are both instances of the argument from “irreducible complexity.” A functioning unit is said to be irreducibly complex if the removal of one of its parts causes the whole to cease functioning. This has been assumed to be self-evident for both eyes and wings. But as soon as we give these assumptions a moment’s thought, we immediately see the fallacy. A cataract patient with the lens of her eye surgically removed can’t see clear images without glasses, but can see enough not to bump into a tree or fall over a cliff. Half a wing is indeed not as good as a whole wing, but it is certainly better than no wing at all. Half a wing could save your life by easing your fall from a tree of a certain height. And 51 percent of a wing could save you if you fall from a slightly taller tree. Whatever fraction of a wing you have, there is a fall from which it will save your life where a slightly smaller winglet would not. The thought experiment of trees of different height, from which one might fall, is just one way to see, in theory, that there must be a smooth gradient of advantage all the way from 1 per cent of a wing to 100 percent. The forests are replete with gliding or parachuting animals illustrating, in practice, every step of the way up that particular slope of Mount Improbable.

By analogy with the trees of different height, it is easy to imagine situations in which half an eye would save the life of an animal where 49 percent of an eye would not. Smooth gradients are provided by variations in lighting conditions, variations in the distance at which you catch sight of your prey—or your predators. And, as with wings and flight surfaces, plausible intermediates are not only easy to imagine: they are abundant all around the animal kingdom. A flatworm has an eye that, by any sensible measure, is less than half a human eye. Nautilus (and perhaps its extinct ammonite cousins who dominated Paleozoic and Mesozoic seas) has an eye that is intermediate in quality between flatworm and human. Unlike the flatworm eye, which can detect light and shade but see no image, the Nautilus ‘“pinhole camera” eye makes a real image; but it is a blurred and dim image compared to ours. It would be spurious precision to put numbers on the improvement, but nobody could sanely deny that these invertebrate eyes, and many others, are all better than no eye at all, and all lie on a continuous and shallow slope up Mount Improbable, with our eyes near a peak—not the highest peak but a high one. In Climbing Mount Improbable, I devoted a whole chapter each to the eye and the wing, demonstrating how easy it was for them to evolve by slow (or even, maybe, not all that slow) gradual degrees, and I will leave the subject here.

So, we have seen that eyes and wings are certainly not irreducibly complex; but what is more interesting than these particular examples is the general lesson we should draw. The fact that so many people have been dead wrong over these obvious cases should serve to warn us of other examples that are less obvious, such as the cellular and biochemical cases now being touted by those creationists who shelter under the politically expedient euphemism of “intelligent design theorists.”

We have a cautionary tale here, and it is telling us this: do not just declare things to be irreducibly complex; the chances are that you haven’t looked carefully enough at the details, or thought carefully enough about them. On the other hand, we on the science side must not be too dogmatically confident. Maybe there is something out there in nature that really does preclude, by its genuinely irreducible complexity, the smooth gradient of Mount Improbable. The creationists are right that, if genuinely irreducible complexity could be properly demonstrated, it would wreck Darwin’s theory. Darwin himself said as much: “If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.” Darwin could find no such case, and nor has anybody since Darwin’s time, despite strenuous, indeed desperate, efforts. Many candidates for this holy grail of creationism have been proposed. None has stood up to analysis.

In any case, even though genuinely irreducible complexity would wreck Darwin’s theory if it were ever found, who is to say that it wouldn’t wreck the intelligent design theory as well? Indeed, it already has wrecked the intelligent design theory, for, as I keep saying and will say again, however little we know about God, the one thing we can be sure of is that he would have to be very very complex and presumably irreducibly so!

The Worship of Gaps

Searching for particular examples of irreducible complexity is a fundamentally unscientific way to proceed: a special case of arguing from present ignorance. It appeals to the same faulty logic as “the God of the Gaps” strategy condemned by the theologian Dietrich Bonhoeffer. Creationists eagerly seek a gap in present-day knowledge or understanding. If an apparent gap is found, it is assumed that God, by default, must fill it. What worries thoughtful theologians such as Bonhoeffer is that gaps shrink as science advances, and God is threatened with eventually having nothing to do and nowhere to hide. What worries scientists is something else. It is an essential part of the scientific enterprise to admit ignorance, even to exult in ignorance as a challenge to future conquests. As my friend Matt Ridley has written, “Most scientists are bored by what they have already discovered. It is ignorance that drives them on.” Mystics exult in mystery and want it to stay mysterious. Scientists exult in mystery for a different reason: it gives them something to do. More generally, as I shall repeat in Chapter 8, one of the truly bad effects of religion is that it teaches us that it is a virtue to be satisfied with not understanding.

Admissions of ignorance and temporary mystification are vital to good science. It is therefore unfortunate, to say the least, that the main strategy of creation propagandists is the negative one of seeking out gaps in scientific knowledge and claiming t fill them with “intelligent design” by default. The following is hypothetical but entirely typical. A creationist speaking: “The elbow joint of the lesser spotted weasel frog is irreducibly complex. No part of it would do any good at all until the whole was assembled. Bet you can’t think of a way in which the weasel frog’s elbow could have evolved by slow gradual degrees.” If the scientist fails to give an immediate and comprehensive answer, the creationist draws a default conclusion: “Right then, the alternative theory, ‘intelligent design,’ wins by default.” Notice the biased logic: if theory A fails in some particular, theory B must be right. Needless to say, the argument is not applied the other way around. We are encouraged to leap to the default theory without even looking to see whether it fails in the very same particular as the theory it is alleged to replace. Intelligent design—ID—is granted a Get Out Of Jail Free card, a charmed immunity to the rigorous demands made of evolution.

But my present point is that the creationist ploy undermines the scientist’s natural—indeed necessary—rejoicing in (temporary) uncertainty. For purely political reasons, today’s scientist might hesitate before saying: “Hm, interesting point. I wonder how the weasel frog’s ancestors did evolve their elbow joint. I’m not a specialist in weasel frogs, I’ll have to go to the University Library and take a look. Might make an interesting project for a graduate student.” The moment a scientist said something like that—and long before the student began the project—the default conclusion would become a headline in a creationist pamphlet: “Weasel frog could only have been designed by God.”

There is, then, an unfortunate hook-up between science’s methodological need to seek out areas of ignorance in order to target research, and ID’s need to seek out areas of ignorance in order to claim victory by default. It is precisely the fact that ID has no evidence of its own, but thrives like a weed in gaps left by scientific knowledge, that sits uneasily with science’s need to identify and proclaim the very same gaps as a prelude to researching them. In this respect, science finds itself in alliance with sophisticated theologians like Bonhoeffer, united against the common enemies of naive, populist theology and the gap theology of intelligent design.

The creationists’ love affair with “gaps” in the fossil record symbolizes their whole gap theology. I once introduced a chapter on the so-called Cambrian Explosion with the sentence, “It is as though the fossils were planted there without any evolutionary history.” Again, this was a rhetorical overture, intended to whet the reader’s appetite for the full explanation that was to follow. Sad hindsight tells me now how predictable it was that my patient explanation would be excised and my overture itself gleefully quoted out of context. Creationists adore “gaps” in the fossil record, just as they adore gaps generally.

Many evolutionary transitions are elegantly documented by more or less continuous series of gradually changing intermediate fossils. Some are not, and these are the famous “gaps.” Michael Shermer has wittily pointed out that if a new fossil discovery neatly bisects a “gap,” the creationist will declare that there are now twice as many gaps! But in any case, note yet again the unwarranted use of a default. If there are no fossils to document a postulated evolutionary transition, the default assumption is that there was no evolutionary transition, therefore God must have intervened.

It is utterly illogical to demand complete documentation of every step of any narrative, whether in evolution or any other science. You might as well demand, before convicting somebody of murder, a complete cinematic record of the murderer’s every step leading up to the crime, with no missing frames. Only a tiny fraction of corpses fossilize, and we are lucky to have as many intermediate fossils as we do. We could easily have had no fossils at all, and still the evidence for evolution from other sources, such as molecular genetics and geographical distribution, would be overwhelmingly strong. On the other hand, evolution makes the strong prediction that if a single fossil turned up in the wrong geological stratum, the theory would be blown out of the water. When challenged by a zealous Popperian to say how evolution could ever be falsified, J. B. S. Haldane famously growled: “Fossil rabbits in the Precambrian.” No such anachronistic fossils have ever been authentically found, despite discredited creationist legends of human skulls in the Coal Measures and human footprints interspersed with dinosaurs’.

Gaps, by default in the mind of the creationist, are filled by God. The same applies to all apparent precipices on the massif of Mount Improbable, where the graded slope is not immediately obvious or is otherwise overlooked. Areas where there is a lack of data, or a lack of understanding, are automatically assumed to belong, by default, to God. The speedy resort to a dramatic proclamation of “irreducible complexity” represents a failure of the imagination. Some biological organ, if not an eye then a bacterial flagellar motor or a biochemical pathway, is decreed without further argument to be irreducibly complex. No attempt is made to demonstrate irreducible complexity. Notwithstanding the cautionary tales of eyes, wings, and many other things, each new candidate for the dubious accolade is assumed to be transparently, self-evidently irreducibly complex, its status asserted by fiat. But think about it. Since irreducible complexity is being deployed as an argument for design, it should no more be asserted by fiat than design itself. You might as well simply assert that the weasel frog (bombardier beetle, etc.) demonstrates design, without further argument or justification. That is no way to do science.

The logic turns out to be no more convincing than this: “I [insert own name] am personally unable to think of any way in which [insert biological phenomenon] could have been built up step by step. Therefore it is irreducibly complex. That means it is designed.” Put it like that, and you immediately see that it is vulnerable to some scientist coming along and finding an intermediate; or at least imagining a plausible intermediate. Even if no scientists do come up with an explanation, it is plain bad logic to assume that “design” will fare any better. The reasoning that underlies “intelligent design” theory is lazy and defeatist—classic “God of the Gaps” reasoning. I have previously dubbed it the Argument from Personal Incredulity.

Imagine that you are watching a really great magic trick. The celebrated conjuring duo Penn and Teller have a routine in which they simultaneously appear to shoot each other with pistols, and each appears to catch the bullet in his teeth. Elaborate precautions are taken to scratch identifying marks on the bullets before they are put in the guns, the whole procedure is witnessed at close range by volunteers from the audience who have experience of firearms, and apparently all possibilities for trickery are eliminated. Teller’s marked bullet ends up in Penn’s mouth and Penn’s marked bullet ends up in Teller’s. I [Richard Dawkins] am utterly unable to think of any way in which this could be a trick. The Argument from Personal Incredulity screams from the depths of my prescientific brain centres, and almost compels me to say, “It must be a miracle. There is no scientific explanation. It’s got to be supernatural.” But the still small voice of scientific education speaks a different message. Penn and Teller are world-class illusionists. There is a perfectly good explanation. It is just that I am too naive, or too unobservant, or too unimaginative, to think of it. That is the proper response to a conjuring trick. It is also the proper response to a biological phenomenon that appears to be irreducibly complex. Those people who leap from personal bafflement at a natural phenomenon straight to a hasty invocation of the supernatural are no better than the fools who see a conjuror bending a spoon and leap to the conclusion that it is “paranormal.”

In his book Seven Clues to the Origin of Life, the Scottish chemist A. G. Cairns-Smith makes an additional point, using the analogy of an arch. A free-standing arch of rough-hewn stones and no mortar can be a stable structure, but it is irreducibly complex: it collapses if any one stone is removed. How, then, was it built in the first place? One way is to pile a solid heap of stones, then carefully remove stones one by one. More generally, there are many structures that are irreducible in the sense that they cannot survive the subtraction of any part, but which were built with the aid of scaffolding that was subsequently subtracted and is no longer visible. Once the structure is completed, the scaffolding can be removed safely and the structure remains standing. In evolution, too, the organ or structure you are looking at may have had scaffolding in an ancestor which has since been removed.

“Irreducible complexity” is not a new idea, but the phrase itself was invented by the creationist Michael Behe in 1996. He is credited (if credited is the word) with moving creationism into a new area of biology: biochemistry and cell biology, which he saw as perhaps a happier hunting ground for gaps than eyes or wings. His best approach to a good example (still a bad one) was the bacterial flagellar motor.

The flagellar motor of bacteria is a prodigy of nature. It drives the only known example, outside human technology, of a freely rotating axle. Wheels for big animals would, I suspect, be genuine examples of irreducible complexity, and this is probably why they don’t exist. How would the nerves and blood vessels get across the bearing?[30] The flagellum is a thread-like propeller, with which the bacterium burrows its way through the water. I say “burrows” rather than “swims” because, on the bacterial scale of existence, a liquid such as water would not feel as a liquid feels to us. It would feel more like treacle, or jelly, or even sand, and the bacterium would seem to burrow or screw its way through the water rather than swim. Unlike the so-called flagellum of larger organisms like protozoans, the bacterial flagellum doesn’t just wave about like a whip, or row like an oar. It has a true, freely rotating axle which turns continuously inside a bearing, driven by a remarkable little molecular motor. At the molecular level, the motor uses essentially the same principle as muscle, but in free rotation rather than in intermittent contraction.[31] It has been happily described as a tiny outboard motor (although by engineering standards—and unusually for a biological mechanism—it is a spectacularly inefficient one).

Without a word of justification, explanation or amplification, Behe simply proclaims the bacterial flagellar motor to be irreducibly complex. Since he offers no argument in favour of his assertion, we may begin by suspecting a failure of his imagination. He further alleges that specialist biological literature has ignored the problem. The falsehood of this allegation was massively and (to Behe) embarrassingly documented in the court of Judge John E. Jones in Pennsylvania in 2005, where Behe was testifying as an expert witness on behalf of a group of creationists who had tried to impose “intelligent design” creationism on the science curriculum of a local public school—a move of “breathtaking inanity,” to quote Judge Jones (phrase and man surely destined for lasting fame). This wasn’t the only embarrassment Behe suffered at the hearing, as we shall see.

The key to demonstrating irreducible complexity is to show that none of the parts could have been useful on its own. They all needed to be in place before any of them could do any good (Behe’s favourite analogy is a mousetrap). In fact, molecular biologists have no difficulty in finding parts functioning outside the whole, both for the flagellar motor and for Behe’s other alleged examples of irreducible complexity. The point is well put by Kenneth Miller of Brown University, for my money the most persuasive nemesis of “intelligent design,” not least because he is a devout Christian. I frequently recommend Miller’s book, Finding Darwin’s God, to religious people who write to me having been bamboozled by Behe.

In the case of the bacterial rotary engine, Miller calls our attention to a mechanism called the Type Three Secretory System or TTSS. The TTSS is not used for rotatory movement. It is one of several systems used by parasitic bacteria for pumping toxic substances through their cell walls to poison their host organism. On our human scale, we might think of pouring or squirting a liquid through a hole; but, once again, on the bacterial scale things look different. Each molecule of secreted substance is a large protein with a definite, three-dimensional structure on the same scale as the TTSS’s own: more like a solid sculpture than a liquid. Each molecule is individually propelled through a carefully shaped mechanism, like an automated slot machine dispensing, say, toys or bottles, rather than a simple hole through which a substance might “flow.” The goods-dispenser itself is made of a rather small number of protein molecules, each one comparable in size and complexity to the molecules being dispensed through it. Interestingly, these bacterial slot machines are often similar across bacteria that are not closely related. The genes for making them have probably been “copied and pasted” from other bacteria: something that bacteria are remarkably adept at doing, and a fascinating topic in its own right, but I must press on.

The protein molecules that form the structure of the TTSS are very similar to components of the flagellar motor. To the evolutionist it is clear that TTSS components were commandeered for a new, but not wholly unrelated, function when the flagellar motor evolved. Given that the TTSS is tugging molecules through itself, it is not surprising that it uses a rudimentary version of the principle used by the flagellar motor, which tugs the molecules of the axle round and round. Evidently, crucial components of the flagellar motor were already in place and working before the flagellar motor evolved. Commandeering existing mechanisms is an obvious way in which an apparently irreducibly complex piece of apparatus could climb Mount Improbable.

A lot more work needs to be done, of course, and I’m sure it will be. Such work would never be done if scientists were satisfied with a lazy default such as “intelligent design theory” would encourage. Here is the message that an imaginary “intelligent design theorist” might broadcast to scientists: “If you don’t understand how something works, never mind: just give up and say God did it. You don’t know how the nerve impulse works? Good! You don’t understand how memories are laid down in the brain? Excellent! Is photosynthesis a bafflingly complex process? Wonderful! Please don’t go to work on the problem, just give up, and appeal to God. Dear scientist, don’t work on your mysteries. Bring us your mysteries, for we can use them. Don’t squander precious ignorance by researching it away. We need those glorious gaps as a last refuge for God.” St. Augustine said it quite openly: “There is another form of temptation, even more fraught with danger. This is the disease of curiosity. It is this which drives us to try and discover the secrets of nature, those secrets which are beyond our understanding, which can avail us nothing and which man should not wish to learn” (quoted in Freeman 2002).

Another of Behe’s favourite alleged examples of “irreducible complexity” is the immune system. Let Judge Jones himself take up the story:

Behe, under cross-examination, by Eric Rothschild, chief counsel for the plaintiffs, was forced to admit that he hadn’t read most of those fifty-eight peer-reviewed papers. Hardly surprising, for immunology is hard work. Less forgivable is that Behe dismissed such research as “unfruitful.” It certainly is unfruitful if your aim is to make propaganda among gullible laypeople and politicians, rather than to discover important truths about the real world. After listening to Behe, Rothschild eloquently summed up what every honest person in that courtroom must have felt:

As the American geneticist Jerry Coyne put it in his review of Behe’s book: “If the history of science shows us anything, it is that we get nowhere by labelling our ignorance ‘God.’” Or, in the words of an eloquent blogger, commenting on an article on intelligent design in the Guardian by Coyne and me,

Darwinism raises our consciousness in other ways. Evolved organs, elegant and efficient as they often are, also demonstrate revealing flaws—exactly as you’d expect if they have an evolutionary history, and exactly as you would not expect if they were designed. I have discussed examples in other books: the recurrent laryngeal nerve, for one, which betrays its evolutionary history in a massive and wasteful detour on its way to its destination. Many of our human ailments, from lower back pain to hernias, prolapsed uteruses and our susceptibility to sinus infections, result directly from the fact that we now walk upright with a body that was shaped over hundreds of millions of years to walk on all fours. Our consciousness is also raised by the cruelty and wastefulness of natural selection. Predators seem beautifully “designed” to catch prey animals, while the prey animals seem equally beautifully “designed” to escape them. Whose side is God on?