The Science of Discworld Revised Edition

by Terry Pratchett

  What we must not do, then, is to look back at past events and find significance in the inevitable few that look odd. That is the way of the pyramidologists and the tea-leaf readers. Every pattern of raindrops on the pavement is unique. We’re not saying that if one such patterns happens to spell your name, this is not to be wondered at – but if your name had been written on the pavement in Beijing during the Ming dynasty, at midnight, nobody would have noticed. We should not look at past history when assessing significance: we should look at all the other things that might have happened instead.

  Every event is unique. Until we place that event in a category, we can’t work out which background to view it against. Until we choose a background, we can’t estimate the event’s probability. If we consider the sample space of all possible DNA codes, for instance, then we can calculate the probability of a human being having exactly your DNA code – which is vanishingly small. But it would be silly to conclude that it is impossible for you to exist.

  1 Indeed, it is a fundamental part of story telling. If the hero did not overcome huge odds, what would be the point?

  2 Possibly he was holding a large axe at the time.

  THIRTY-FIVE

  STILL BLOOD LIZARDS

  ‘THE FUTURE IS lizard,’ said Ridcully. ‘Obviously.’

  It was a few days later. The omniscope was focused on a mound of leaves and rotting vegetation a little way from the banks of the river. There was a large depression hanging over the Senior Wrangler, and the Dean had a black eye. The war between land and sea had just entered a terminal stage.

  ‘Little portable seas,’ said Ponder. ‘You know, I never thought of them like that.’

  ‘An egg is an egg, however you look at it,’ said Ridcully. ‘Look, you two, I don’t want to see a scuffle like that again, d’you hear?’

  The Senior Wrangler dabbed at his bleeding nose.

  ‘He goaded be,’ he said. ‘Id’s still osuns, howeber you look at id.’

  ‘A private ocean full of food,’ said Ponder, still entranced. ‘Hidden in a heap of … well, compost. Which heats up. That’s like having private sunshine.’

  The little lizard-like creatures that had hatched from the eggs in the mound slithered and slid down the bank into the water, bright-eyed and hopeful. The first few were instantly snapped up by a large male lying in wait among the weeds.

  ‘However, the mothers still have something to learn about postnatal care,’ said Ridcully. ‘I wonder if they’ll have time to learn? And how did they know how to do this? Who’s telling them?’

  The wizards were depressed again. Most days started that way now. Creatures seemed to turn up in the world randomly, and certainly not according to any pictures in a book. If things were changing into other things, and no one had seen that happen yet, why were the original things still the original things? If the land was so great, why were any fish left in the sea?

  The air-breathing fishes that Rincewind had seen still seemed to be around, lurking in swamps and muddy beaches. Things changed, but still stayed the same.

  And if there was any truth at all in Ponder’s tentative theory that things did change into other things, it led to the depressing thought that, well, the world was filling up with quitters, creatures which – instead of staying where they were, and really making a go of life in the ocean or the swamp or wherever – were running away to lurk in some niche and grow legs. The kind of fish that’d come out of water was, frankly, a disgrace to the species. It kept coughing all the time, like someone who’d just given up smoking.

  And there was no purpose, Ridcully kept saying. Life was on land. According to the book, there should be some big lizards. But nothing seemed to be making much of an effort. The moment anything felt safe, it stopped bothering.

  Rincewind, currently relaxing on a rock, rather liked it. There were large animals snuffling around in the greenery near the rock he was sitting on; in general shape and appearance, they looked like a small skinny hippopotamus designed in the dark by a complete amateur. They were hairy. They coughed, too.

  Things that were doing sufficiently beetle-like things for him to think of them as beetles ambled across the ground.

  Ponder had told him the continents were moving again, so he kept a firm grip on his rock just in case.

  Best of all, nothing seemed to be thinking. Rincewind was convinced that no good came of that sort of thing.

  The last few weeks of Discworld time had been instructive. The wizards had tentatively identified several dozen embryo civilizations, or at least creatures that seemed to be concerned about more than simply where their next meal was coming from. And where were they now? There was a squid one, HEX said, out in the really deep cold water. Apart from that, ice or fire or both at once came to the thinkers and the stupid alike. There was probably some kind of moral involved.

  The air shimmered, and half a dozen ghostly figures appeared in front of him.

  There were, in pale shadowy colours, the wizards. Silvery lines flickered across their bodies and, periodically, they flickered.

  ‘Now, remember,’ said Ponder Stibbons, and his voice sounded muffled, ‘You are in fact still in the High Energy Magic building. If you walk slowly HEX will try to adjust your feet to local ground level. You’ll have a limited ability to move things, although HEX will do the actual work –’

  ‘Can we eat?’ said the Senior Wrangler.

  ‘No, sir. Your mouth isn’t here.’

  ‘Well, then, what am I talking out of?’

  ‘Could be anyone’s guess, sir,’ said Ponder diplomatically. ‘We can hear you because our ears are in the HEM, and you can hear the sounds made here because HEX is presenting you with an analogue of them. Don’t worry about it. It’ll seem quite natural after a while.’

  The ghost of the Dean kicked at the soil. A fraction of a second later, a little heap of earth splashed up.

  ‘Amazing!’ he said, happily.

  ‘Excuse me?’ said Rincewind.

  They turned.

  ‘Oh, Rincewind,’ said Ridcully, as one might say ‘oh dear, it’s raining’. ‘It’s you.’

  ‘Yes, sir.’

  ‘Mister Stibbons here’s found a way of getting HEX to operate more than one virtually-there suit, d’you see? So we thought we’d come down and smell the roses.’

  ‘Not for several hundred million years, sir,’ said Ponder.

  ‘Dull, isn’t it,’ said the Lecturer in Recent Runes, looking around. ‘Not a lot going on. Lots of life, but it’s just hanging around.’

  Ridcully rubbed his hands together.

  ‘Well, we’re going to liven it up,’ he said. ‘We’re going to move things forward fast while we’re here. A few prods in the right place, that’s what these creatures need.’

  ‘The time travelling is not much fun,’ said Rincewind. ‘You tend to end up under a volcano or at the bottom of the sea.’

  ‘We shall see,’ said Ridcully firmly. ‘I’ve had enough of this. Look at those damn sloppy things over there. ‘He cupped his hands and shouted, ‘Life in the sea not good enough for you, eh? Skiving off, eh? Got a note from your mother, have you?’ He lowered his hands. ‘All right, Mister Stibbons … tell HEX to take us forward, oh, fifty million years – hang on, what was that?’

  Thunder rolled around the horizon.

  ‘Probably just another snowball landing,’ said Rincewind morosely. ‘There’s generally one around just when things are settled. It was in the sea, I expect. Stand by for the tidal wave.’ He nodded at the browsing creatures, who had glanced up briefly.

  ‘The Dean thinks all this hammering from rocks is making the life on this world very resilient,’ said Ridcully.

  ‘Well, that’s certainly a point of view,’ said Rincewind. ‘But in a little while a wave the size of the University is going to wash this beach on to the top of those mountains over there. Then I expect the local volcanoes will all let go … again … so stand by for a country-sized sea of lava coming the other way. A
fter that there’ll probably be outbreaks of rain that you could use to etch copper, followed by a bit of a cold spell for a few years and some fog you could cut up in lumps.’ He sniffed. ‘That which does not kill you can give you a really bad headache.’

  He glanced at the sky. Strange lightning was flickering between the clouds, and now there was a glow on the horizon.

  ‘Damn,’ he said, in the same tone of voice. ‘This is going to be one of the times when the atmosphere catches fire. I hate it when that happens.’

  Ridcully gave him a long blank look, and then said, ‘Mister Stibbons?’

  ‘Archchancellor?’

  ‘Make that seventy thousand years, will you? And, er … right now, if you would be so good.’

  The wizards vanished.

  All the insects stopped buzzing in the bushes.

  The hairy lizards carried on placidly eating the leaves. Then, something made them look up –

  The sun jerked across the sky, became very briefly a reddish-yellow band across a twilight hemisphere, and then the world was simply a grey mist. Below Rincewind’s feet it was quite dark, and above him it was almost white. Around him, the greyness flickered.

  ‘Is this what it always looks like?’ said the Dean.

  ‘Something has to stand still for a couple of thousand years before you see it at all,’ said Rincewind.

  ‘I thought it would be more exciting –’

  The light flickered, and sun exploded into the sky, the wizards saw waves around them for a moment, and then there was darkness.

  ‘I told you,’ said Rincewind. ‘We’re under water.’

  ‘The land sank under all the volcanoes?’ said Ridcully.

  ‘Probably just moved away,’ said Rincewind. ‘There’s a lot of that sort of thing down here.’

  They rose above the surface as HEX adjusted to the new conditions. A landmass was smeared on the horizon, under a bank of cloud.

  ‘See?’ said Rincewind. ‘It’s a pain. Time travel always means you end up walking.’

  ‘HEX, move us to the nearest land, please. Inland about ten miles,’ said Ponder.

  ‘You mean I could have just asked?’ said Rincewind. ‘All this time, I needn’t have been walking?’

  ‘Oh, yes.’

  The landscape blurred for a second.

  ‘You could have said,’ said Rincewind accusingly, as they were rushed past, and sometimes through, a forest of giant ferns.

  The view stabilized. The wizards had been brought to the edge of the forest. Low-growing shrubs stretched away towards more ferns.

  ‘Not much about,’ said Ridcully, leaning against a trunk. ‘Can I smoke my pipe here, Stibbons?’

  ‘Since technically you’ll be smoking in the High Energy Building, yes, sir.’

  Rincewind apparently struck a match on the tree trunk. ‘Amazing,’ he said.

  ‘That’s odd, sir,’ said Ponder. ‘I didn’t think there would be any proper trees yet.’

  ‘Well, here they are,’ said Ridcully. ‘And I can see at least another three more …’

  Rincewind had already started to run. The fact that nothing can harm you is no reason for not being scared. An expert can always find a reason for being scared.

  The fact that the nearest trunk had toenails was a good one.

  From among the ferns above, a large head appeared on the end of too much neck.

  ‘Ah,’ said Ridcully calmly. ‘Still bloody lizards, I see.’

  THIRTY-SIX

  RUNNING FROM DINOSAURS

  WALKING WITH DINOSAURS was a very popular television series in the UK in 2000-2001, and it was equally popular on US television soon afterwards. It portrayed dozens of kinds of dinosaur, all beautifully realised as computer animations in the most intimate detail. And it told us things like ‘These doofersaurs were herbivorous, and they were brightly coloured to break up their outline, as protection against predation by thingumosaurs. They were monogamous, rearing their well-protected offspring by living in caves and permitting the children only very restricted access to computer games.’

  All this from just two fossil bones – one for each beast.

  Walking with Dinosaurs was the latest in a series of popularisations of dinosaurs, from H.G. Wells’s Outline of History and Arthur Conan Doyle’s The Lost World to Walt Disney’s Fantasia and Michael Crichton’s Jurassic Park. Dinosaurs are redolent with mana; they ooze charisma. They are the PR person’s wildest dream. What gives dinosaurs such potency?

  The psychologist Helen Haste has taken over from palaeontologist Beverley Halstead the theme of dinosaurs as icons of power and sex in our civilised myth-making. Both have shown that by mythologising them into such potent symbols, we have made it very difficult to work out what it must really have been like when dinosaurs walked the Earth. Our mental images of dinosaurs carry a lot of excess baggage, and it’s hard to get away from the lies-to-children involved in those images.

  We’ll do our best, nonetheless. Whatever it was like, we’re sure that Running from Dinosaurs is a more apt image.

  We have a good idea of what it wasn’t like. We’ve all seen the standard filmic shot of dinosaur ‘ecology’, and it wasn’t like that. The camera homes in on some archaic-looking trees, and we discover a clearing with a lake and some enormous vegetarian reptiles. A few little birdy creatures get into the picture doing their little birdy things; there are pterodactyls flying about … Then there’s a great roar, and a tyrannosaur comes crashing in from stage left. He (nobody can believe it’s a ‘she’ as portrayed: we have to be informed of that in the Jurassic Park sequel) jumps on to a brontosaur or a hadrosaur or whatever, and wrestles it to the ground. Or he has a great teeth-against-horns fight with a triceratops, or some other armoured vegetarian like the stegosaur in Disney’s Fantasia.

  In the natural history books of the late nineteenth and early twentieth centuries, the drawings always show these creatures in mortal combat, too (labelled, for example ‘Ideal Scene of the Middle Oolitic Period’). Wells’s Outline of History was atypical in this regard; the drawings and Plates showed the animals simply going about their business, without the drama.

  What was it really like?

  For a start, there wasn’t an ‘it’. Dinosaurs, and other great reptiles, had nearly two hundred million years of being the most interesting, most important – well, the biggest, at least – land animals, and they re-invaded the sea and even produced the largest flying creatures that have ever been. Dinosaurs began, about two hundred and forty million years ago, with a single species. The earliest descendants of which we have fossils are the herbivore Pisanosaurus, about three feet (1m) long, and Eoraptor, a predator of similar size, which date from about 230 million years ago.

  By 215 million years ago the dinosaurs had diversified considerably. There were big sprawling amphibians, heavily-built and three or four feet long, as well as a great variety of little ones looking more like big salamanders. There were the synapsid reptiles, which were bigger and held up by sturdy legs: some had great bony sails on their backs, some of them were vegetarians as big as donkeys, some were carnivores as big as hyaenas. There were many kinds of more active dog-sized beasties.

  Their therapsid descendants would be the mammals’ ancestors, little guys called morganucodontids, which we talk about later. These were small beasties, because most of the action by then was dinosaur. For 150 million years, between 215 and 65 million years ago, any land animal more than three feet (1m) long was a dinosaur.

  Among these mammal-like reptiles in the forests were a few active predators the size of kangaroos and wallabies. These unprepossessing creatures were the earliest dinosaurs. You wouldn’t have marked them out as having a great future; they were just part of the land fauna that came out of the dark wet Carboniferous forests and began to make a living in the drier Permian era. If you had walked about in those forests you would probably have seen some of these beasts; they were rather slow and stupid, and perhaps they would have attacked you in a rather
leisurely, crocodilian way. They weren’t as bright as crocodiles, though, nor as quick.

  At least as important as the dinosaurs was something far less filmic: soil. By then, soil had developed much of its complex ecosystem: at least fifty interacting species of bacteria, several very different kinds of fungi, insects, worms, protozoans during the Carboniferous. Soil had become a great basis for land plant growth. These forests were not starved, like the modern rainforests with their six inches of soil and no net oxygen production. Oh, no. The coal that we burn for heat and power was deposited in the Carboniferous, and every ton of coal that was deposited by the forests released more than twice its weight of oxygen into the air. Just as each ton of coal we burn now uses that much oxygen to make carbon dioxide again.

  In those days, plants grew fast, like modern herbs, but many of them grew big, as well. These plants didn’t have woody trunks, they were like great tree-ferns, and the creatures that fed on them made a big input into the terrestrial ecology. Until grass really took over, well after the demise of the dinosaurs, and made savannah and pampas the vegetable basis of the great herds of mammalian herbivores, this thick-soiled forest was the nutritional basis of all land fauna. And the ancient land fauna diversified in these forests, at their edges and in the swamps that they so often became.