`What's that one?' said the Dean, pointing to a red circle with his staff.

`We must make certain he doesn't get off the boat at an island called Tenerife,' said Ponder. `Seasickness again, you see. Quite a few Darwins got off there.'

The tip of the staff moved. `And that one?'

`He must get off the boat at the island of St Jago. He has valuable insights there.'

`Sees things evolvin', that kind of thing?' said Ridcully.

`No, sir. You can't see things evolving, even when they're doing it.' `We saw them on Mono Island,' said the Lecturer in Recent Runes.

`You could practically hear them!'

`Yes, sir. But we have a god of evolution. Gods aren't patient. On Roundworld, evolution takes time. Lots of time. Darwin was raised in the belief that the Roundworld universe was created in six days -'

`Which is correct, as I have pointed out,' said the Dean proudly.

`Yes,' said Ponder, `but I have also pointed out that on the inside it took billions of years. It is vital that Darwin realises that evolution has got lots of time to work in.'

Before the Dean could protest, Ponder turned back to the shining, twisting tangle of light.

'There is where the mast falls on his head in the port of Buenos Aires,' he said, pointing. `The Beagle was shot at. It was meant to he a blank, fired from a cannon, but for some reason it had been loaded. The British were very upset about it, and issued a stern diplomatic protest by sending a warship to bombard the port to rubble. This one is where Darwin bludgeons himself into unconsciousness with his own bolas in Argentina. This one is where he's severely injured putting down an insurrection-'

`He got about a bit for a man who collected flowers and things,' said Ridcully, with a touch of admiration.

`Look, I've been thinking about all this,' said the Dean. `This "science" is all about the search for truth, yes? Why don't we just tell them the truth?'

`You mean tell them that their universe was accidentally started by you, Dean, sticking your hand into some raw firmament created to use up spare power from the thaumic reactor?' said Ridcully.

`Put like that it seems a bit unlikely, I admit, but-'

`No direct contact, Dean, we agreed about that,' said Ridcully. `We just clear his way. What's that nodality, Stibbons? It's flashing.'

Ponder looked at where the Archchancellor's staff was pointing.

`That's a tricky one, sir. We will have to ensure that Edward Lawson, a British official in the Galapagos Islands, isn't struck by a meteorite. It's a new malignity, Hex says. In a number of histories, it happens a few days before he meets Darwin. Remember, sir? I mentioned it in my yellow folder that was delivered to your office this morning.' Ponder sighed. `He draws Darwin's attention to some interesting facts.'

`Ah, I read that one,' said Ridcully, his happy tone indicating that this was a lucky coincidence. `Darwin seemed to be too busy runnin' around like a monkey in a banana plantation to spot the clues, eh?'

`It would be true to say that his full theory of natural selection was evolved on mature reflection some time after his voyage, yes,' said Ponder, carefully answering a slightly different question.

`And this chap Lawson was important?'

`Hex believes so, sir. In a way, everyone Darwin met was important. And everything he saw.'

`And then whoosh, this chap was hit by a rock? I call that suspicious.'

`Hex does too, sir.'

`I'll be jolly glad when we've got this Darwin to the damn islands, then,' said the Archchancellor. `We'll need a holiday after this. Oh well, I'll address the wizards now. I hope we'll have enough for-'

`Er, we haven't just got to get him to the islands. We've got to get him all the way home, sir,' said Ponder. `He'll be away from home for nearly five years.'

`Five years?' said the Dean. `I thought visiting the wretched islands was what it was all about!'

`Yes and then again, in a very real sense, no, Dean,' said Ponder. `It would be more correct to say they later became what it was all about. He was actually there for a little more than a month. It was a very long voyage, sir. They went all around the world. I'm sorry, I hadn't made that clear. Hex, show the entire timelines, please.'

The display began to recede, drawing from nowhere more and more tangles and loops, as if half a dozen cosmic kittens had been given stars to play with instead of balls of wool. There was a gasp from the throng of wizards.

The tangles were still streaming away overhead when the Dean said: `There's millions of the wretched things!'

`No, Dean,' said Ponder. `It looks like that, but there are only 21,309 important nodalities at this point. Hex can deal with almost all of them. They involve quite minute changes at the quantum level.'

The wizards continued to stare upwards as the whorls and loops flashed by and dwindled.

`Someone really doesn't want that book,' said the Lecturer in Recent Runes, his face illuminated by the multi coloured glow.

`In theory there isn't a someone in charge,' said Ponder.

`But the odds against Darwin writing Origin are getting bigger by the minute!'

`The odds against anything actually happening are huge, when you come to think about it,' said Ridcully. `Take poker, for example. The odds against four aces are huge, but the odds of having any four cards at all are really big.'

`Well put, Archchancellor!' said Ponder. `But this is a crooked game.'

Ridcully strode out into the centre of the Great Hall, his face illuminated by the glowing map.

`Gentlemen!' he bellowed. `Some of you already know what this is about, eh? We're going to force a history on Roundworld! It's one that should be there already! Something is trying to kill it, gentlemen. So if someone wants to stop it happening, we want to make it happen all the more! You will be sent into Roundworld with a series of tasks to do! Most of them have been made very simple so that wizards can understand them! Shortly our missions for tomorrow, should you chose to accept them, will be given to you by Mr Stibbons. If you do not choose to accept them, you are free to choose dismissal! We're starting at dawn! Dinner, Second Dinner, Midnight Snack, Somnambulistic Nibbles and Early Breakfast will be served in the Old Refectory! There will be no Second Breakfast!'

Over a chorus of protest he went on: `We are taking this seriously, gentlemen!'

THE WRONG BOOK

OUR FICTIONAL DARWIN HAS A lot more in common with the `real' one - the Darwin of the particular timeline that you inhabit, the one who wrote The Origin and not The Ology - than might at first be apparent. Or plausible. The irresistible force of narrativium induces us to imagine Charles Darwin as an old man with a beard, a stick, and a faint but definite hint of gorilla. And so he was, in his old age. But as a young man he was vigorous, athletic, and engaged in the kind of exuberant and not always politically correct activities that we expect of young men.

We've already learned of the real Darwin's amazing fortune in getting on board the Beagle and remaining there, culminating in his boundless delight at the geology of the coral island of St Jago. But there are other crucial nodalities, points of intervention, and thaumic occlusions in that version of Roundworld's historical record, and the wizards are exercising extreme care and attention in the hope of steering history through, past, and around these causal singularities.

For example, the Beagle really did come under fire from a cannon. When the ship tried to enter the harbour at Buenos Aires in 1832, one of the local guard ships fired at it. Darwin was convinced that he heard a cannonball whistle over his head, but it turned out that the shot was a blank, intended as a warning. FitzRoy, muttering angrily about insults to the British flag, sailed on, but was stopped by a quarantine boat: the harbour authorities were worried about cholera. Incensed, FitzRoy loaded all of the cannons on one side of his ship. As he sailed back out of the harbour he aimed them all at the guard ship, informing its crew that if they ever fired at the Beagle again, he would send their `rotten hulk' to the seabed.