several systems used by
parasitic
bacteria for pumping toxic sub- stances through their cell walls to poison their host organism.
Richard-Dawkins-God-Delusion
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 im- probability 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
WHY ri-irRr AI MOST CtRTAINIY IS NO <>oD 123
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', some- times 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 adjust- ing 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 com- plexity'. 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 per cent 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 experi- ment 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 per cent. The forests are replete with gliding or parachuting animals
124 T H E G O D 1> E I U S I O N
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 per cent of an eye would not. Smooth gradients are pro- vided 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, demonstrat- ing 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 care- fully 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
WHY '11IKRK ALMOST (. :FRTA1N[. Y 15 NO (,OI) 125
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 say- ing 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
126 THEI '. > <> I) i> i 1 i S f O N
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 to 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 hes- itate 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 research- ing 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 con- text. 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
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128 T H E G O D I) 1" I. V S I O N
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 inter- spersed 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 justifi- cation. 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
W H Y r H E RE A 1. M O S T C F . R T A I N L Y I S N O G () I) 129
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
62
was invented by the creationist Michael Behe in 1996. He is
130 1IIH t. O1) 1)! ? 1US1ON
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? * 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. ! It has been happily described as a tiny outboard motor (although by engineering standards - and
* There is an example in fiction. The children's writer Philip Pullman, in His Dark Materials, imagines a species of animals, the 'mulefa', that co-exist with trees that produce perfectly round seedpods with a hole in the centre. These pods the mulefa adopt as wheels. The wheels, not being part of the body, have no nerves or blood vessels to get twisted around the 'axle' (a strong claw of horn or bone). Pullman perceptively notes an additional point: the system works only because the planet is paved with natural basalt ribbons, which serve as 'roads'. Wheels are no good over rough country.
f Fascinatingly, the muscle principle is deployed in yet a third mode in some insects such as flies, bees and bugs, in which the flight muscle is intrinsically oscillatory, like a reciprocating engine. Whereas other insects such as locusts send nervous instructions for each wing stroke (as a bird does), bees send an instruction to switch on (or switch off) the oscillatory motor. Bacteria have a mechanism which is neither a simple contractor (like a bird's flight muscle) nor a reciprocator (like a bee's flight muscle), but a true rotator: in that respect it is like an electric motor or a Wankel engine.
I! TRt AI. M15SI' ('. IR! 'Af\1Y '? ? s \{> i,oI) 131
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 atten-
tion to a mechanism called the Type Three Secretory System or
63
TTSS.
several systems used by parasitic bacteria for pumping toxic sub- stances 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
The TTSS is not used for rotatory movement. It is one of
(1
132 "i H I'' ' O I- D V i ! ' S I O N
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 some- thing 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 photo- synthesis 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 research- ing it away. We need those glorious gaps as a last refuge for God. ' St Augustine said it quite openly: 'There is another form of temp- tation, 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
W H Y T H E R E A I . M O S T C H R T A F N I . Y I S NO ( , O I ) 1 3 3
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:
In fact, on cross-examination, Professor Behe was questioned concerning his 1996 claim that science would never find an evolutionary explanation for the immune system. He was presented with fifty-eight peer-reviewed publications, nine books, and several immunology text- book chapters about the evolution of the immune system; however, he simply insisted that this was still not sufficient evidence of evolution, and that it was not 'good enough. '
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 immun- ology 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:
Thankfully, there are scientists who do search for answers to the question of the origin of the immune system . . . It's our defense against debilitating and fatal diseases. The scientists who wrote those books and articles toil in obscurity, without book royalties or speaking engage- ments. Their efforts help us combat and cure serious medical conditions. By contrast, Professor Behe and the entire intelligent design movement are doing nothing to advance scientific or medical knowledge and are telling
64 future generations of scientists, don't bother.
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
134 "! in: i, o D i) 1. 1 U S I O N
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,
Why is God considered an explanation for anything? It's not - it's a failure to explain, a shrug of the shoulders, an 'I dunno' dressed up in spirituality and ritual. If someone cred- its something to God, generally what it means is that they haven't a clue, so they're attributing it to an unreachable, unknowable sky-fairy. Ask for an explanation of where that bloke came from, and odds are you'll get a vague, pseudo-philosophical reply about having always existed, or
65
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 re- current 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
66
THE ANTHROPIC PRINCIPLE: PLANETARY VERSION
Gap theologians who may have given up on eyes and wings, flagellar motors and immune systems, often pin their remaining
being outside nature. Which, of course, explains nothing.
'designed' to escape them. Whose side is God on?
A I. M O S I C 1 R I'A I N M is X <) <? O I) 135
hopes on the origin of life. The root of evolution in non-biological chemistry somehow seems to present a bigger gap than any par- ticular transition during subsequent evolution. And in one sense it is a bigger gap. That one sense is quite specific, and it offers no comfort to the religious apologist. The origin of life only had to happen once. We therefore can allow it to have been an extremely improbable event, many orders of magnitude more improbable than most people realize, as I shall show. Subsequent evolutionary steps are duplicated, in more or less similar ways, throughout millions and millions of species independently, and continually and repeatedly throughout geological time. Therefore, to explain the
evolution of complex life, we cannot resort to the same kind of statistical reasoning as we are able to apply to the origin of life. The events that constitute run-of-the-mill evolution, as distinct from its singular origin (and perhaps a few special cases), cannot have been very improbable.
This distinction may seem puzzling, and I must explain it further, using the so-called anthropic principle. The anthropic principle was named by the British mathematician Brandon Carter in 1974 and expanded by the physicists John Barrow and Frank Tipler in their
67
book on the subject. The anthropic argument is usually applied to
the cosmos, and I'll come to that. But I'll introduce the idea on a smaller, planetary scale. We exist here on Earth. Therefore Earth must be the kind of planet that is capable of generating and supporting us, however unusual, even unique, that kind of planet might be. For example, our kind of life cannot survive without liquid water. Indeed, exobiologists searching for evidence of extra- terrestrial life are scanning the heavens, in practice, for signs of water. Around a typical star like our sun, there is a so-called Goldilocks zone - not too hot and not too cold, but just right - for planets with liquid water. A thin band of orbits lies between those that are too far from the star, where water freezes, and too close,
where it boils.
Presumably, too, a life-friendly orbit has to be nearly circular. A
fiercely elliptical orbit, like that of the newly discovered tenth planet informally known as Xena, would at best allow the planet to whizz briefly through the Goldilocks zone once every few (Earth) decades or centuries. Xena itself doesn't get into the Goldilocks
136 TIIE GOO I)EI. USIGN
zone at all, even at its closest approach to the sun, which it reaches once every 560 Earth years. The temperature of Halley's Comet varies between about 47? C at perihelion and minus 270? C at aphelion. Earth's orbit, like those of all the planets, is technically an ellipse (it is closest to the sun in January and furthest away in July*); but a circle is a special case of an ellipse, and Earth's orbit is so close to circular that it never strays out of the Goldilocks zone. Earth's situation in the solar system is propitious in other ways that singled it out for the evolution of life. The massive gravitational vacuum cleaner of Jupiter is well placed to intercept asteroids that might otherwise threaten us with lethal collision. Earth's single
68
relatively large moon serves to stabilize our axis of rotation,
helps to foster life in various other ways. Our sun is unusual in not being a binary, locked in mutual orbit with a companion star. It is possible for binary stars to have planets, but their orbits are likely to be too chaotically variable to encourage the evolution of life.
Two main explanations have been offered for our planet's peculiar friendliness to life. The design theory says that God made the world, placed it in the Goldilocks zone, and deliberately set up all the details for our benefit. The anthropic approach is very different, and it has a faintly Darwinian feel. The great majority of planets in the universe are not in the Goldilocks zones of their respective stars, and not suitable for life. None of that majority has life. However small the minority of planets with just the right conditions for life may be, we necessarily have to be on one of that minority, because here we are thinking about it.
It is a strange fact, incidentally, that religious apologists love the anthropic principle. For some reason that makes no sense at all, they think it supports their case. Precisely the opposite is true. The anthropic principle, like natural selection, is an alternative to the design hypothesis. It provides a rational, design-free explan- ation for the fact that we find ourselves in a situation propitious to our existence. I think the confusion arises in the religious mind because the anthropic principle is only ever mentioned in the context of the problem that it solves, namely the fact that we live in a life-friendly place. What the religious mind then fails to grasp is that two candidate solutions are offered to the problem. God is one. The anthropic principle is the other. They are alternatives.
* If you find that surprising, you may be suffering from northern hemisphere chauvinism, as described on page 115.
and
WiIY 1IIF. RF A1Vi(. )ST CV. RTAINLY IS NO COD 137
Liquid water is a necessary condition for life as we know it, but it is far from sufficient. Life still has to originate in the water, and the origin of life may have been a highly improbable occurrence. Darwinian evolution proceeds merrily once life has originated. But how does life get started? The origin of life was the chemical event, or series of events, whereby the vital conditions for natural selection first came about. The major ingredient was heredity, either DNA or (more probably) something that copies like DNA but less accurately, perhaps the related molecule RNA. Once the vital ingredient - some kind of genetic molecule - is in place, true Darwinian natural selection can follow, and complex life emerges as the eventual consequence. But the spontaneous arising by chance
of the first hereditary molecule strikes many as improbable. Maybe it is - very very improbable, and I shall dwell on this, for it is central to this section of the book.
The origin of life is a flourishing, if speculative, subject for research. The expertise required for it is chemistry and it is not mine. I watch from the sidelines with engaged curiosity, and I shall not be surprised if, within the next few years, chemists report that they have successfully midwifed a new origin of life in the laboratory. Nevertheless it hasn't happened yet, and it is still possible to maintain that the probability of its happening is, and always was, exceedingly low - although it did happen once!
Just as we did with the Goldilocks orbits, we can make the point that, however improbable the origin of life might be, we know it happened on Earth because we are here. Again as with temperature, there are two hypotheses to explain what happened - the design hypothesis and the scientific or 'anthropic' hypothesis. The design approach postulates a God who wrought a deliberate miracle, struck the prebiotic soup with divine fire and launched DNA, or something equivalent, on its momentous career.
Again, as with Goldilocks, the anthropic alternative to the design hypothesis is statistical. Scientists invoke the magic of large numbers. It has been estimated that there are between 1 billion and 30 billion planets in our galaxy, and about 100 billion galaxies in the universe. Knocking a few noughts off for reasons of ordinary prudence, a billion billion is a conservative estimate of the number of available planets in the universe. Now, suppose the origin of life,
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the spontaneous arising of something equivalent to DNA, really was a quite staggeringly improbable event. Suppose it was so improbable as to occur on only one in a billion planets. A grant- giving body would laugh at any chemist who admitted that the chance of his proposed research succeeding was only one in a hundred. But here we are talking about odds of one in a billion. And yet . . . even with such absurdly long odds, life will still have
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arisen on a billion planets - of which Earth, of course, is one.
This conclusion is so surprising, I'll say it again. If the odds of life originating spontaneously on a planet were a billion to one against, nevertheless that stupefyingly improbable event would still happen on a billion planets. The chance of finding any one of those billion life-bearing planets recalls the proverbial needle in a haystack. But we don't have to go out of our way to find a needle because (back to the anthropic principle) any beings capable of looking must necessarily be sitting on one of those prodigiously
rare needles before they even start the search.
Any probability statement is made in the context of a certain
level of ignorance. If we know nothing about a planet, we may postulate the odds of life's arising on it as, say, one in a billion. But if we now import some new assumptions into our estimate, things change. A particular planet may have some peculiar properties, perhaps a special profile of element abundances in its rocks, which shift the odds in favour of life's emerging. Some planets, in other words, are more 'Earth-like' than others. Earth itself, of course, is especially Earth-like! This should give encouragement to our chemists trying to recreate the event in the lab, for it could shorten the odds against their success. But my earlier calculation demonstrated that even a chemical model with odds of success as low as one in a billion would still predict that life would arise on a billion planets in the universe. And the beauty of the anthropic principle is that it tells us, against all intuition, that a chemical model need only predict that life will arise on one planet in a billion billion to give us a good and entirely satisfying explanation for the presence of life here. I do not for a moment believe the origin of life was anywhere near so improbable in practice. I think it is definitely worth spending money on trying to duplicate the event in the lab and - by the same token, on SETI, because I think it is likely that there is intelligent life elsewhere.
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Even accepting the most pessimistic estimate of the probability that life might spontaneously originate, this statistical argument completely demolishes any suggestion that we should postulate design to fill the gap. Of all the apparent gaps in the evolutionary story, the origin of life gap can seem unbridgeable to brains calibrated to assess likelihood and risk on an everyday scale: the scale on which grant-giving bodies assess research proposals submitted by chemists. Yet even so big a gap as this is easily filled by statistically informed science, while the very same statistical science rules out a divine creator on the 'Ultimate 747' grounds we
met earlier.
But now, to return to the interesting point that launched this
section. Suppose somebody tried to explain the general phenomenon of biological adaptation along the same lines as we have just applied to the origin of life: appealing to an immense number of available planets. The observed fact is that every species, and every organ that has ever been looked at within every species, is good at what it does. The wings of birds, bees and bats are good at flying. Eyes are good at seeing. Leaves are good at photo- synthesizing. We live on a planet where we are surrounded by perhaps ten million species, each one of which independently dis- plays a powerful illusion of apparent design. Each species is well fitted to its particular way of life. Could we get away with the 'huge numbers of planets' argument to explain all these separate illusions of design? No, we could not, repeat not. Don't even think about it. This is important, for it goes to the heart of the most serious mis- understanding of Darwinism.
It doesn't matter how many planets we have to play with, lucky chance could never be enough to explain the lush diversity of living complexity on Earth in the same way as we used it to explain the existence of life here in the first place. The evolution of life is a completely different case from the origin of life because, to repeat, the origin of life was (or could have been) a unique event which had to happen only once. The adaptive fit of species to their separate environments, on the other hand, is millionfold, and ongoing.
It is clear that here on Earth we are dealing with a generalized process for optimizing biological species, a process that works all
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over the planet, on all continents and islands, and at all times. We can safely predict that, if we wait another ten million years, a whole new set of species will be as well adapted to their ways of life as today's species are to theirs. This is a recurrent, predictable, multiple phenomenon, not a piece of statistical luck recognized with hindsight. And, thanks to Darwin, we know how it is brought about: by natural selection.
The anthropic principle is impotent to explain the multifarious details of living creatures. We really need Darwin's powerful crane to account for the diversity of life on Earth, and especially the persuasive illusion of design. The origin of life, by contrast, lies out- side the reach of that crane, because natural selection cannot proceed without it. Here the anthropic principle comes into its own. We can deal with the unique origin of life by postulating a very large number of planetary opportunities. Once that initial stroke of luck has been granted - and the anthropic principle most decisively grants it to us - natural selection takes over: and natural selection is emphatically not a matter of luck.
Nevertheless, it may be that the origin of life is not the only major gap in the evolutionary story that is bridged by sheer luck, anthropically justified. For example, my colleague Mark Ridley in Mendel's Demon (gratuitously and confusingly retitled The Cooperative Gene by his American publishers) has suggested that the origin of the eucaryotic cell (our kind of cell, with a nucleus and various other complicated features such as mitochondria, which are not present in bacteria) was an even more momentous, difficult and statistically improbable step than the origin of life. The origin of consciousness might be another major gap whose bridging was of the same order of improbability. One-off events like this might be explained by the anthropic principle, along the following lines. There are billions of planets that have developed life at the level of bacteria, but only a fraction of these life forms ever made it across the gap to something like the eucaryotic cell. And of these, a yet smaller fraction managed to cross the later Rubicon to consciousness. If both of these are one-off events, we are not dealing with a ubiquitous and all-pervading process, as we are with ordinary, run-of-the-
mill biological adaptation. The anthropic principle states that, since we are alive, eucaryotic and conscious, our planet has to be
W 11 Y '1 11 !
Creationists who attempt to deploy the argument from im- probability 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
WHY ri-irRr AI MOST CtRTAINIY IS NO <>oD 123
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', some- times 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 adjust- ing 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 com- plexity'. 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 per cent 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 experi- ment 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 per cent. The forests are replete with gliding or parachuting animals
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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 per cent of an eye would not. Smooth gradients are pro- vided 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, demonstrat- ing 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 care- fully 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
WHY '11IKRK ALMOST (. :FRTA1N[. Y 15 NO (,OI) 125
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 say- ing 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
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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 to 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 hes- itate 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 research- ing 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 con- text. 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
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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 inter- spersed 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 justifi- cation. 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
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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
62
was invented by the creationist Michael Behe in 1996. He is
130 1IIH t. O1) 1)! ? 1US1ON
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? * 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. ! It has been happily described as a tiny outboard motor (although by engineering standards - and
* There is an example in fiction. The children's writer Philip Pullman, in His Dark Materials, imagines a species of animals, the 'mulefa', that co-exist with trees that produce perfectly round seedpods with a hole in the centre. These pods the mulefa adopt as wheels. The wheels, not being part of the body, have no nerves or blood vessels to get twisted around the 'axle' (a strong claw of horn or bone). Pullman perceptively notes an additional point: the system works only because the planet is paved with natural basalt ribbons, which serve as 'roads'. Wheels are no good over rough country.
f Fascinatingly, the muscle principle is deployed in yet a third mode in some insects such as flies, bees and bugs, in which the flight muscle is intrinsically oscillatory, like a reciprocating engine. Whereas other insects such as locusts send nervous instructions for each wing stroke (as a bird does), bees send an instruction to switch on (or switch off) the oscillatory motor. Bacteria have a mechanism which is neither a simple contractor (like a bird's flight muscle) nor a reciprocator (like a bee's flight muscle), but a true rotator: in that respect it is like an electric motor or a Wankel engine.
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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 atten-
tion to a mechanism called the Type Three Secretory System or
63
TTSS.
several systems used by parasitic bacteria for pumping toxic sub- stances 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
The TTSS is not used for rotatory movement. It is one of
(1
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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 some- thing 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 photo- synthesis 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 research- ing it away. We need those glorious gaps as a last refuge for God. ' St Augustine said it quite openly: 'There is another form of temp- tation, 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
W H Y T H E R E A I . M O S T C H R T A F N I . Y I S NO ( , O I ) 1 3 3
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:
In fact, on cross-examination, Professor Behe was questioned concerning his 1996 claim that science would never find an evolutionary explanation for the immune system. He was presented with fifty-eight peer-reviewed publications, nine books, and several immunology text- book chapters about the evolution of the immune system; however, he simply insisted that this was still not sufficient evidence of evolution, and that it was not 'good enough. '
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 immun- ology 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:
Thankfully, there are scientists who do search for answers to the question of the origin of the immune system . . . It's our defense against debilitating and fatal diseases. The scientists who wrote those books and articles toil in obscurity, without book royalties or speaking engage- ments. Their efforts help us combat and cure serious medical conditions. By contrast, Professor Behe and the entire intelligent design movement are doing nothing to advance scientific or medical knowledge and are telling
64 future generations of scientists, don't bother.
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
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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,
Why is God considered an explanation for anything? It's not - it's a failure to explain, a shrug of the shoulders, an 'I dunno' dressed up in spirituality and ritual. If someone cred- its something to God, generally what it means is that they haven't a clue, so they're attributing it to an unreachable, unknowable sky-fairy. Ask for an explanation of where that bloke came from, and odds are you'll get a vague, pseudo-philosophical reply about having always existed, or
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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 re- current 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
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THE ANTHROPIC PRINCIPLE: PLANETARY VERSION
Gap theologians who may have given up on eyes and wings, flagellar motors and immune systems, often pin their remaining
being outside nature. Which, of course, explains nothing.
'designed' to escape them. Whose side is God on?
A I. M O S I C 1 R I'A I N M is X <) <? O I) 135
hopes on the origin of life. The root of evolution in non-biological chemistry somehow seems to present a bigger gap than any par- ticular transition during subsequent evolution. And in one sense it is a bigger gap. That one sense is quite specific, and it offers no comfort to the religious apologist. The origin of life only had to happen once. We therefore can allow it to have been an extremely improbable event, many orders of magnitude more improbable than most people realize, as I shall show. Subsequent evolutionary steps are duplicated, in more or less similar ways, throughout millions and millions of species independently, and continually and repeatedly throughout geological time. Therefore, to explain the
evolution of complex life, we cannot resort to the same kind of statistical reasoning as we are able to apply to the origin of life. The events that constitute run-of-the-mill evolution, as distinct from its singular origin (and perhaps a few special cases), cannot have been very improbable.
This distinction may seem puzzling, and I must explain it further, using the so-called anthropic principle. The anthropic principle was named by the British mathematician Brandon Carter in 1974 and expanded by the physicists John Barrow and Frank Tipler in their
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book on the subject. The anthropic argument is usually applied to
the cosmos, and I'll come to that. But I'll introduce the idea on a smaller, planetary scale. We exist here on Earth. Therefore Earth must be the kind of planet that is capable of generating and supporting us, however unusual, even unique, that kind of planet might be. For example, our kind of life cannot survive without liquid water. Indeed, exobiologists searching for evidence of extra- terrestrial life are scanning the heavens, in practice, for signs of water. Around a typical star like our sun, there is a so-called Goldilocks zone - not too hot and not too cold, but just right - for planets with liquid water. A thin band of orbits lies between those that are too far from the star, where water freezes, and too close,
where it boils.
Presumably, too, a life-friendly orbit has to be nearly circular. A
fiercely elliptical orbit, like that of the newly discovered tenth planet informally known as Xena, would at best allow the planet to whizz briefly through the Goldilocks zone once every few (Earth) decades or centuries. Xena itself doesn't get into the Goldilocks
136 TIIE GOO I)EI. USIGN
zone at all, even at its closest approach to the sun, which it reaches once every 560 Earth years. The temperature of Halley's Comet varies between about 47? C at perihelion and minus 270? C at aphelion. Earth's orbit, like those of all the planets, is technically an ellipse (it is closest to the sun in January and furthest away in July*); but a circle is a special case of an ellipse, and Earth's orbit is so close to circular that it never strays out of the Goldilocks zone. Earth's situation in the solar system is propitious in other ways that singled it out for the evolution of life. The massive gravitational vacuum cleaner of Jupiter is well placed to intercept asteroids that might otherwise threaten us with lethal collision. Earth's single
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relatively large moon serves to stabilize our axis of rotation,
helps to foster life in various other ways. Our sun is unusual in not being a binary, locked in mutual orbit with a companion star. It is possible for binary stars to have planets, but their orbits are likely to be too chaotically variable to encourage the evolution of life.
Two main explanations have been offered for our planet's peculiar friendliness to life. The design theory says that God made the world, placed it in the Goldilocks zone, and deliberately set up all the details for our benefit. The anthropic approach is very different, and it has a faintly Darwinian feel. The great majority of planets in the universe are not in the Goldilocks zones of their respective stars, and not suitable for life. None of that majority has life. However small the minority of planets with just the right conditions for life may be, we necessarily have to be on one of that minority, because here we are thinking about it.
It is a strange fact, incidentally, that religious apologists love the anthropic principle. For some reason that makes no sense at all, they think it supports their case. Precisely the opposite is true. The anthropic principle, like natural selection, is an alternative to the design hypothesis. It provides a rational, design-free explan- ation for the fact that we find ourselves in a situation propitious to our existence. I think the confusion arises in the religious mind because the anthropic principle is only ever mentioned in the context of the problem that it solves, namely the fact that we live in a life-friendly place. What the religious mind then fails to grasp is that two candidate solutions are offered to the problem. God is one. The anthropic principle is the other. They are alternatives.
* If you find that surprising, you may be suffering from northern hemisphere chauvinism, as described on page 115.
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Liquid water is a necessary condition for life as we know it, but it is far from sufficient. Life still has to originate in the water, and the origin of life may have been a highly improbable occurrence. Darwinian evolution proceeds merrily once life has originated. But how does life get started? The origin of life was the chemical event, or series of events, whereby the vital conditions for natural selection first came about. The major ingredient was heredity, either DNA or (more probably) something that copies like DNA but less accurately, perhaps the related molecule RNA. Once the vital ingredient - some kind of genetic molecule - is in place, true Darwinian natural selection can follow, and complex life emerges as the eventual consequence. But the spontaneous arising by chance
of the first hereditary molecule strikes many as improbable. Maybe it is - very very improbable, and I shall dwell on this, for it is central to this section of the book.
The origin of life is a flourishing, if speculative, subject for research. The expertise required for it is chemistry and it is not mine. I watch from the sidelines with engaged curiosity, and I shall not be surprised if, within the next few years, chemists report that they have successfully midwifed a new origin of life in the laboratory. Nevertheless it hasn't happened yet, and it is still possible to maintain that the probability of its happening is, and always was, exceedingly low - although it did happen once!
Just as we did with the Goldilocks orbits, we can make the point that, however improbable the origin of life might be, we know it happened on Earth because we are here. Again as with temperature, there are two hypotheses to explain what happened - the design hypothesis and the scientific or 'anthropic' hypothesis. The design approach postulates a God who wrought a deliberate miracle, struck the prebiotic soup with divine fire and launched DNA, or something equivalent, on its momentous career.
Again, as with Goldilocks, the anthropic alternative to the design hypothesis is statistical. Scientists invoke the magic of large numbers. It has been estimated that there are between 1 billion and 30 billion planets in our galaxy, and about 100 billion galaxies in the universe. Knocking a few noughts off for reasons of ordinary prudence, a billion billion is a conservative estimate of the number of available planets in the universe. Now, suppose the origin of life,
138 M M : <<. o n i) ! ? ;
the spontaneous arising of something equivalent to DNA, really was a quite staggeringly improbable event. Suppose it was so improbable as to occur on only one in a billion planets. A grant- giving body would laugh at any chemist who admitted that the chance of his proposed research succeeding was only one in a hundred. But here we are talking about odds of one in a billion. And yet . . . even with such absurdly long odds, life will still have
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arisen on a billion planets - of which Earth, of course, is one.
This conclusion is so surprising, I'll say it again. If the odds of life originating spontaneously on a planet were a billion to one against, nevertheless that stupefyingly improbable event would still happen on a billion planets. The chance of finding any one of those billion life-bearing planets recalls the proverbial needle in a haystack. But we don't have to go out of our way to find a needle because (back to the anthropic principle) any beings capable of looking must necessarily be sitting on one of those prodigiously
rare needles before they even start the search.
Any probability statement is made in the context of a certain
level of ignorance. If we know nothing about a planet, we may postulate the odds of life's arising on it as, say, one in a billion. But if we now import some new assumptions into our estimate, things change. A particular planet may have some peculiar properties, perhaps a special profile of element abundances in its rocks, which shift the odds in favour of life's emerging. Some planets, in other words, are more 'Earth-like' than others. Earth itself, of course, is especially Earth-like! This should give encouragement to our chemists trying to recreate the event in the lab, for it could shorten the odds against their success. But my earlier calculation demonstrated that even a chemical model with odds of success as low as one in a billion would still predict that life would arise on a billion planets in the universe. And the beauty of the anthropic principle is that it tells us, against all intuition, that a chemical model need only predict that life will arise on one planet in a billion billion to give us a good and entirely satisfying explanation for the presence of life here. I do not for a moment believe the origin of life was anywhere near so improbable in practice. I think it is definitely worth spending money on trying to duplicate the event in the lab and - by the same token, on SETI, because I think it is likely that there is intelligent life elsewhere.
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Even accepting the most pessimistic estimate of the probability that life might spontaneously originate, this statistical argument completely demolishes any suggestion that we should postulate design to fill the gap. Of all the apparent gaps in the evolutionary story, the origin of life gap can seem unbridgeable to brains calibrated to assess likelihood and risk on an everyday scale: the scale on which grant-giving bodies assess research proposals submitted by chemists. Yet even so big a gap as this is easily filled by statistically informed science, while the very same statistical science rules out a divine creator on the 'Ultimate 747' grounds we
met earlier.
But now, to return to the interesting point that launched this
section. Suppose somebody tried to explain the general phenomenon of biological adaptation along the same lines as we have just applied to the origin of life: appealing to an immense number of available planets. The observed fact is that every species, and every organ that has ever been looked at within every species, is good at what it does. The wings of birds, bees and bats are good at flying. Eyes are good at seeing. Leaves are good at photo- synthesizing. We live on a planet where we are surrounded by perhaps ten million species, each one of which independently dis- plays a powerful illusion of apparent design. Each species is well fitted to its particular way of life. Could we get away with the 'huge numbers of planets' argument to explain all these separate illusions of design? No, we could not, repeat not. Don't even think about it. This is important, for it goes to the heart of the most serious mis- understanding of Darwinism.
It doesn't matter how many planets we have to play with, lucky chance could never be enough to explain the lush diversity of living complexity on Earth in the same way as we used it to explain the existence of life here in the first place. The evolution of life is a completely different case from the origin of life because, to repeat, the origin of life was (or could have been) a unique event which had to happen only once. The adaptive fit of species to their separate environments, on the other hand, is millionfold, and ongoing.
It is clear that here on Earth we are dealing with a generalized process for optimizing biological species, a process that works all
140 THV. C,OL) I)I-iUSION
over the planet, on all continents and islands, and at all times. We can safely predict that, if we wait another ten million years, a whole new set of species will be as well adapted to their ways of life as today's species are to theirs. This is a recurrent, predictable, multiple phenomenon, not a piece of statistical luck recognized with hindsight. And, thanks to Darwin, we know how it is brought about: by natural selection.
The anthropic principle is impotent to explain the multifarious details of living creatures. We really need Darwin's powerful crane to account for the diversity of life on Earth, and especially the persuasive illusion of design. The origin of life, by contrast, lies out- side the reach of that crane, because natural selection cannot proceed without it. Here the anthropic principle comes into its own. We can deal with the unique origin of life by postulating a very large number of planetary opportunities. Once that initial stroke of luck has been granted - and the anthropic principle most decisively grants it to us - natural selection takes over: and natural selection is emphatically not a matter of luck.
Nevertheless, it may be that the origin of life is not the only major gap in the evolutionary story that is bridged by sheer luck, anthropically justified. For example, my colleague Mark Ridley in Mendel's Demon (gratuitously and confusingly retitled The Cooperative Gene by his American publishers) has suggested that the origin of the eucaryotic cell (our kind of cell, with a nucleus and various other complicated features such as mitochondria, which are not present in bacteria) was an even more momentous, difficult and statistically improbable step than the origin of life. The origin of consciousness might be another major gap whose bridging was of the same order of improbability. One-off events like this might be explained by the anthropic principle, along the following lines. There are billions of planets that have developed life at the level of bacteria, but only a fraction of these life forms ever made it across the gap to something like the eucaryotic cell. And of these, a yet smaller fraction managed to cross the later Rubicon to consciousness. If both of these are one-off events, we are not dealing with a ubiquitous and all-pervading process, as we are with ordinary, run-of-the-
mill biological adaptation. The anthropic principle states that, since we are alive, eucaryotic and conscious, our planet has to be
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