After months of pestering from my fifteen–year–old daughter I was eventually persuaded to read one of her Harry Potter books. I discovered that Harry Potter has a teacher of the wonderfully imagined subject of 'Defence Against the Dark Arts'. But while students at Hogwarts are fortunate enough to be tutored in countering the dark arts, the average muggle on the street must find his own way to defend himself from the darkest art of all; creationist theory.

Creationist claims range from the banal to the highly technical. The evangelical creationist Ken Hamm entreats his congregations to counter those who 'believe' in evolution with the challenge "Were you there?" on the grounds that if no one was there to measure evolution actually happening no one can prove it happened. The counter–spell to this one is easy. Anyone making this claim should be challenged to say whether they agree with the jury system and whether they think that all criminals should be released from prison unless there was a witness to their crime; if not, they are being inconsistent.

On the more technical side there are 'Intelligent Design' websites made up of what appear to be highly technical articles that quote scientific papers and include actual statements from scientists. Some of these articles imply that what they call 'the evolutionary paradigm' is on the brink of a massive shift. The suggestion is that evolutionary biologists are on the back foot and are reeling as they struggle to explain mounting evidence, which, it is claimed, Darwinian theory fails to explain. The writers of some articles on one particular website claim to have PhDs, but their credibility falls apart at any educated reading of their case. One of the authors even claims that cephalopod (squids and octopuses) eyes look very much like vertebrate eyes and that this is a problem for evolutionary theory because vertebrates are terrestrial animals and cephalopods live in the sea. It seems that they don't know that the first vertebrates were fish.

In another article the same writer argues that the claim that bacteria have evolved in response to the overuse of antibiotics is wrong because natural selection had acted on existing genetic variation rather than actually causing the mutations that have led to evolutionary change. The author might be surprised to learn that natural selection does not magically 'get into' genes and modify them; it only acts on the phenotypic expression of any currently existing available genetic variation. The writer's error here is not just basic — it is absolutely fundamental. This 'expert' clearly did not have even the beginning of an understanding of how evolution by natural selection works.

How do we answer more simple distortions like "evolution is only a theory"? The colloquial meaning of the word 'theory' lends itself to misunderstanding. What a layman calls a theory a scientist calls a hypothesis. A scientific theory is a well–established, systematically organised set of explanations, constructed with reference to empirical evidence, which is often the only set of explanations possible. Although it is fair to say that parts of theories might be modified and clarified in light of new evidence, theories are unlikely ever to be overturned.

The misinformation is not confined to creationism. My daughter was taught at school that Darwin's theory of evolution has never been proved. This statement is either grossly misleading, or completely false, depending on how her teacher meant himself to be understood. Once again, popular misunderstandings come into play. It is a mistake to suppose that the theory of evolution depends on acceptance of Darwin's theory of natural selection. There is a mountain of evidence from a diverse panoply of scientific disciplines, all of which are mutually corroborative, which simply cannot be interpreted in any other way but that evolution happened, whether or not natural selection is taken to be its cause. If the teacher had said that Darwin's theory of natural selection had not been proved he might have had a better basis for his argument. Some scientists think that there might be other causal factors implicated in the evolutionary process but almost no–one thinks that selection has had no role to play. If Darwinian natural selection were to be shown not to be the cause of evolution, science would be compelled to seek another explanation for how it happened, because we know it happened.

It is not possible to explain in detail how evolution worked in respect of every anatomical detail of every organism living or extinct, and as one would expect Intelligent Design devotees and creationists make much of this. It may well be that some aspects of the morphology of some creatures might never be explained. This, paradoxically, is especially true of the simplest unicellular creatures like bacteria, some of which have tiny but perfect little 'outboard motors' called flagella and other equally capable and intricate adaptations. It is also true of the fascinatingly complex biochemical factories, and other extraordinary systems that operate inside the more complex eukareotic cells, of which advanced organisms like ourselves are constructed. This is because, in many cases, those features are some of the most ancient we know of. And there are now no known living organisms which might give us a clue to the evolutionary processes that brought them into being. Many of them must have evolved long before the Cambrian explosion of 560 million years ago when animals first became big enough and complex enough to fossilise. The ancestry of some of these primeval mechanisms might even stretch back billions of years. How do we deal with creationists who argue that scientists can't explain everything?

The mistake is to think that because something has not been explained, even if it may never be explained, this somehow means that it is necessarily beyond rational explanation. A simple backwards extrapolation of evolutionary theory implies that all these devices and systems could have evolved just as easily as it has in the more familiar complex organisms. There will always be gaps into which creationists might try to shoehorn God. The antidote to this 'spell' is to say that if, late one night, an old light bulb goes pop and won't come back on, it is safe to say that the element has become old, brittle and burned out due to natural processes. No reasonable person would say that this was God's punishment for staying up too late or that a bad fairy did it, so why invoke a supernatural explanation for other processes that are, or appear to be, natural ones?

Another creationist bewitchment is the 'Second Law of Thermodynamics' argument. According to the second law, all physical systems decay. Heat flows from the hottest to the coldest areas until the whole system becomes normalised; energy becomes used up, and complex active systems gradually entropy into simpler weaker ones. This — it is alleged — means that evolution could not have happened because, if life on Earth had become more complex over time, the second law would have been violated. It is of course true that the second law — after many billion years — will eventually lead to the 'heat death' of the Universe. All the stars will eventually use up their fuel, and all active systems, including life, will gradually become frozen out of existence, locked into the unrelenting clutch of an eternal deep freeze. But this does not mean that complex systems could not arise temporarily, especially when they are bathed in the vibrant energy of an active star. The law of gravity is ultimately as unyielding as the second law but that doesn't mean that birds, bats and bits of fluff can't defy it.

Creationist conjurers may pull the 'association trick' out of the bag. This argument suggests that if one plank of evolutionary theory is shown to be inadequately supported by evidence, by implication, the whole evolutionary edifice can be thought of as being suspect. For example, creationists are fond of saying that the archaeopteryx is a fake, as if this somehow means that the evolutionary mountain is crumbling. Even if we ignore the fact that the first archaeopteryx was found in 1861 and the latest was found in 1993, so the forger must have been over 150 years old when he faked the last one; and even if —against all the evidence — the scientific provenance of the archaeopteryx were shown to be insecure, then it would mean nothing, because fossilised creatures, showing intermediate anatomical differences between the dinosaurs and the birds, have been found in China. The ancestral link between dinosaurs and birds can still be convincingly made. This particular spell is vulnerable to the loose stone defence: if a piece of evidence were found to be suspect it would be a bit like finding a loose stone on the side of a mountain. Finding one loose stone, or ten, or a thousand, would not mean that the mountain wasn't there. Nor would it mean that there was something intrinsically rotten about the mountain, or that it was about to collapse from within.

Sadly, however compelling the evidence, creationists and Intelligent Design devotees are unlikely to be persuaded by any evidence that undermines their case. After all, in the final evaluation any passing clever, mischievous, omnipotent spirit could have planted the evidence, and to the creationist mind this solution is just as plausible. We need to be ready with the right antidote to the creationist's clever tricks.

Peter Fisher recently completed his first book, The God Machine, a popular science novel