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Who Owns the Argument from Improbability?

"Life is too improbable to be due to chance" is the old standby, the creaking warhorse of all creationists, from naive Bible-jocks who don't know better, to comparatively well-educated Intelligent Design 'theorists' who should. There is no other creationist argument (if you discount absurdities such as "Evolution violates the second law of thermodynamics" and falsehoods such as "There aren't any intermediate fossils").

However superficially different the arguments may appear, under the surface the deep structure is always the same. In Fred Hoyle's version, the spontaneous emergence of life is as improbable as a hurricane, blowing through a junkyard, having the luck to assemble a Boeing 747. Something in nature ? an eye, a biochemical pathway or a cosmic constant ? is too improbable to have come about by chance. (So far, the argument is impeccable. Now comes the false step.) Therefore it must have been designed. A watch demands a watchmaker. As a gratuitous bonus, the watchmaker always turns out to be the Christian God (or Yahweh, or Allah, or Lord Krishna, or whichever deity happened to dominate the speaker's personal childhood).

Not only is it wrong to assume that deliberate design is the only alternative to chance. Deliberate design is not an alternative to chance at all. The only known alternative to chance as an explanation for living complexity is natural selection. And, to those that understand it , it is a brilliantly successful alternative.

Intelligent design 'theory' (ID) has none of the innocent charm of its old-style, revival-tent parent. Sophistry dresses the venerable watchmaker up in two cloaks of ersatz novelty: 'irreducible complexity', and 'specified complexity', both wrongly attributed to recent ID authors and both much older. 'Irreducible complexity', which creationists attribute to Michael Behe, is nothing more than the familiar 'What is the use of half an eye?' argument, even if it is now applied at the biochemical or the cellular level. Darwin himself anticipated and demolished the general form of the argument in The Origin of Species. For a splendid anthology of replies to it in its biochemical and cellular guise, see "Behe's Empty Box" by John Catalano (

'Specified complexity' takes care of the sensible point that any particular rubbish heap is improbable with hindsight, in the unique disposition of its parts. A pile of detached watch parts tossed in a box is, with hindsight, as improbable as a fully functioning, genuinely complicated watch. What is special about a watch is that it is improbable in the specified direction of telling the time. Creationists fondly imagine that 'specified complexity' is William Dembski's recent coining. Here is how I expressed it 18 years ago:

"Complicated things have some quality, specifiable in advance, that is highly unlikely to have been acquired by random chance alone. In the case of living things, the quality that is specified in advance is, in some sense, 'proficiency'; either proficiency in a particular ability such as flying, as an aero-engineer might admire it; or proficiency in something more general, such as the ability to stave off death . . ." (The Blind Watchmaker, page 9).

Behe and Dembski correctly pose the problem of specified improbability as something that needs explaining. But the explanation they offer ? 'intelligent design' ? is not even a good candidate solution. It is a lazy cop-out, which is most kindly described as a restatement of the problem. And, worse, it shoots itself in the foot.

First, ID theory is lazy. It poses a problem (statistical improbability) and, having recognized that the problem is difficult, lies down under the difficulty. "I can't see any solution to the problem. Therefore a Higher Power must have done it". When people write to me, bemused by one or other of the ID books, I invite them to imagine a fictional conversation between the lazy alter egos of two scientists working on a hard problem, say A L Hodgkin and A F Huxley who in real life won the Nobel Prize for their brilliant elucidation of the biophysics underlying the nerve impulse.

"I say Huxley, this is a terribly difficult problem. I can't see how the nerve impulse works, can you?"

"No Hodgkin, I can't, and these differential equations are fiendishly hard to solve. Why don't we just give up and say that the nerve impulse propagates by Nervous Energy?"

"Excellent idea Huxley, let's write the Letter to Nature now, it'll only take one line, then we can turn to something easier."

Andrew Huxley's elder brother Julian made a similar point when, long ago, he lampooned Henri Bergson's élan vital as tantamount to explaining that a railway engine was propelled by élan locomotif. Lamentably, by the way, the only scientist ever to win the Nobel Prize for Literature is Bergson, the arch vitalist.

With the best will in the world, I can see no difference between the laziness of my hypothetical Hodgkin and Huxley, and the really lazy luminaries of ID. Yet, so successful is their 'wedge strategy', they are managing to subvert the schooling of young Americans in state after state, and they are even invited to testify before congressional committees: all this, while ignominiously failing to come up with a single research paper worthy of publication in a proper scientific journal.

More importantly, the argument from improbability, quite apart from being lazy, backfires fatally against the design inference. Conscientiously pursued, the statistical improbability argument leads to a conclusion diametrically opposed to the fond hopes of the creationists. There may be good reasons for believing in a supernatural being (admittedly, I can't think of any) but the argument from improbability is emphatically not one of them. Indeed, the argument from improbability is the most powerful argument I know in favour of atheism and against agnosticism.

The design argument is fatally wounded by infinite regress. The more improbable the specified complexity, the more improbable the god capable of designing it. Darwinism comes through the regress unscathed, indeed triumphant. Improbability, the phenomenon we seek to explain, is more or less defined as that which is difficult to explain. It is obviously self-defeating to try to explain it by invoking a creative being of even greater improbability. Darwinism really does explain complexity in terms of something simpler ? which in turn is explained in terms of something simpler still, and so on back to primeval simplicity. It is the gradual, escalatory quality of nonrandom natural selection that arms the Darwinian theory against the menace of infinite regress. I suspect that 'inflation theory' may perform a parallel role in cosmology, but I should need to be more learned in theoretical physics before attempting a confident defence of my conjecture. My colleague Daniel Dennett uses the vivid word 'crane' for theories that do this kind of explanatory lifting work.

Design is the temporarily correct explanation for some particular manifestations of specified complexity such as a car or a washing machine. It could conceivably turn out, as Francis Crick and Leslie Orgel once facetiously suggested, that evolution was seeded by deliberate design, in the form of bacteria sent from a distant planet in the nose cone of a space ship. But the alien designers then require their own explanation: ultimately they must have evolved by gradual, and therefore explicable, degrees. It is easy to believe that the universe houses creatures so far superior to us as to seem like gods. I believe it. But those godlike beings must themselves have been lifted into existence by natural selection or some equivalent crane. The argument from improbability, properly applied, rules out their spontaneous existence de novo.

Sooner or later, in order to explain the illusion of design, we are going to have to terminate the regress with something more explanatory than design itself. Design can never be an ultimate explanation. And ? here is the point of my title ? the more statistically improbable the specified complexity, the more inadequate does the design theory become, while the explanatory work done by the crane of gradualistic natural selection becomes correspondingly more indispensable. So, all those calculations with which creationists love to browbeat their na?ve audiences ? the mega-astronomical odds against an entity spontaneously coming into existence by chance ? turn out to be exercises in eloquently shooting themselves in the foot.

The argument from improbability firmly belongs to the evolutionists. It is our strongest card, and we should instantly turn it against our political opponents (we have no scientific opponents) whenever they try to play it against us. If ever you find yourself arguing with a creationist and he tries to hit you with the astronomical improbability of living organization, don't deny the improbability and don't apologise for it. Rejoice in it and go one better, while echoing the sotto voce response of Thomas Huxley to Bishop Wilberforce: "The Lord hath delivered him into mine hand." The Argument from Improbability belongs to us, and with a vengeance. God is the ultimate Boeing 747.



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