What did the fellows make of them? The President reported later that 1858 had been a rather dull year, not `marked by any of those striking discoveries which at once revolutionise, so to speak, our department of science'.

No matter. Darwin's fear of controversy was now irrelevant, because the cat was out of the bag, and there was no chance whatsoever that the beast could be stuffed back in. Yet, as it happened, the anticipated controversy didn't quite materialise. The meeting of the Linnaean Society had been rushed, and the fellows had departed muttering vaguely under their breaths, feeling that they ought to be outraged by such blasphemous ideas ... yet puzzled because the enormously respected (and respectable) Hooker and Lyell clearly felt that both papers had some merit.

And the ideas struck home with some. In particular, the VicePresident promptly removed all mention of the fixity of species from a paper he was working on.

Now that Darwin had been forced to put his head above the parapet, he would lose nothing by publishing the book that he had previously decided not to write, but had constantly been thinking about anyway. He had intended it to be a vast, multi-volume treatise with extensive references to scientific literature, examining every aspect of his theory. It was going to be called Natural Selection (a conscious or subconscious reference to Paley's Natural Theology?). But time was pressing. He polished up his existing essay, changing the title to On the Origin of Species and Varieties by Means of Natural Selection. Then, on the insistent advice of his publisher John Murray, he cut out the `and Varieties'. The first print run of 1250 copies went on sale in November 1859. Darwin sent Wallace a complimentary copy, with a note: `God knows what the public will think.'

In the event, the book sold out before publication. Over 1500 advance orders came in for those 1250 copies, and Darwin promptly started working on revisions for a second edition. Charles Kingsley, author of The Water-Babies, country rector, and Christian socialist, loved it, and wrote a lavish letter: `It is just as noble a conception of Deity, to believe that He created primal forms capable of selfdevelopment ... as to believe that He required a fresh act of intervention to supply the lacunas [1] which He himself had made.' Kingsley was something of a maverick, because of his socialist views, so praise from this source was something of a poisoned chalice.

The reviews, steadfast in their Christian orthodoxy, were distinctly less favourable. Even though Origin hardly mentions humanity, all the usual complaints about men and monkeys, and insults to God and His Church, were trotted out. What particularly galled the reviewers was that ordinary people were buying the thing. It was all right for the upper classes to toy with radical views, it had an attractive frisson of naughtiness and was perfectly harmless among gentlemen of breeding, though not ladies of course; but those same views might put ideas into the common folk's heads, if they were exposed to them, and upset the established order. For Heaven's sake, the book was even selling to commuters outside Waterloo railway station! It must be suppressed!

[1] No, not long-haired South American beasts of burden, but Latin for `gaps'.

Too late. Murray geared up to print 3000 copies of the second edition, whose likely sales were not going to suffer from public controversy. And the people who mattered most to Darwin - Lyell, Hooker, and the anti-religious `evangelist' Thomas Henry Huxley - were impressed, and pretty much convinced. While Charles stayed out of the public debate, Huxley set to with a will. He was determined to advance the cause of atheism, and Origin gave him a point of leverage. The radical atheists loved the book, of course: its overall message and scientific weightiness were enough for them, and they weren't too concerned about fine points. Hewett Watson declared Darwin to be `the greatest revolutionist in natural history of this century'.

In the introduction to Origin, Darwin begins by telling his readers the background to his discovery: When on board H.M.S. Beagle, as naturalist, I was much struck with certain facts, in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species - that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out of this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it.

Apologising profusely for lack of space, and time, to write something more comprehensive than his 150,000-word tome, Darwin then moves towards a short summary of his main idea. Writers on science generally appreciate that it is seldom enough to discuss the answer to a question: it is also necessary to explain the question. And that, of course, should be done first. Otherwise your readers will not appreciate the context into which the answer fits. Darwin was clearly aware of this principle, so he begins by pointing out that: It is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how innumerable species inhabiting this world have been modified, so as to acquire those perfections of structure and coadaptation which most justly excites our admiration.

Already we see a gesture towards Paley - 'perfections of structure' is a clear reference to the watch/watchmaker argument, and `had not been independently created' shows that Darwin doesn't buy Paley's conclusion. But we also see something that characterises the whole of Origin: Darwin's willingness to acknowledge difficulties in his theory. Time and again he raises possible objections - not as straw men, to be knocked flat again, but as serious points to be considered. More than once he concludes that there is more to be learned, before the objection can be resolved. Paley, to his credit, did something similar, though he didn't go as far as admitting ignorance: he knew that he was right. Darwin, a real scientist, not only had his doubts - he shared them with his readers. He would not have arrived at his theory to begin with if he had failed to seek the weaknesses of the hypotheses upon which it was based.

He also, of course, makes it clear what his own work is adding to the speculations of earlier 'transmutationists'. Namely: he has come up with a mechanism for species change. There are advantages in being honest about ,your own limitations: you gain the right to talk about the limitations of others. And now he tells us what that mechanism is. Species, we know, are variable - the domestication of wild species like chickens, cows, and dogs is clear evidence of that. Although that is deliberate selection by humans, it opens the door to selection by nature without human aid: I will then pass on to the variability of species in a state of nature ... We shall, however, be enabled to discuss what circumstances are most favourable to variation. In the next chapter the Struggle for Existence amongst all organic beings throughout the world, which inevitably follows from their high geometrical powers of increase, will be treated of ... The fundamental subject of Natural Selection will be treated at some length in the fourth chapter; and we shall then see how Natural Selection almost inevitably causes much Extinction of the less improved forms of life, and induces what I have called Divergence of Character.