The Science of Discworld

by Terry Pratchett

  So Archaeopteryx was a bit 'late', and in the 1950's zoologists thought that it probably represented a primitive reptile-bird lineage hanging on, perhaps contemporary with much more bird-like creatures. That's another scenario that doesn't make sense now. Many bird-like dinosaurs have been found recently, fossils from South America and, especially, Caudipteryx and Protoarchaeopteryx from China, and these make the problems worse.* They have feathers, but they didn't fly. They have no wings, but they have arms with hands, sometimes with only two digits.

  So what were feathers 'for'?

  Feathers are really remarkably complicated. They're not at all like the scales of lizards and snakes, and it's not easy to invent an evolutionary route by which feathers (or hairs, come to that) can have developed from scales. Some biologists who haven't looked at feathers very carefully have imagined scales growing rather like the stage witch's fingernails, so that they stick out like a pangolin's scales. (That's that silly mammalian tree-climbing anteater that looks like a big pine cone.)

  Feathers aren't like that, though. They develop as cylinders: you can see baby feathers, called pin-feathers, on a plucked chicken from the supermarket. The scales on birds' legs are respectable reptilian scales; perhaps surprisingly, no modern birds have structures that are halfway between feathers and scales, even though their remote ancestors had scales all over. Probably ... we can't be sure from those very old fossils. Scales are, and probably were in those ancestors, patches of keratin very like fingernails; sometimes they overlap like roof tiles. Feathers are cylinders sitting in follicles, deep pits in the skin. About a millimetre up from their deep end, they have a ring of dividing cells, called the collar, which produce the cylinder by growing it outwards. As the products move up the follicle, they turn all the cells' productivity into making keratin, the protein of horn, nails, hair and feathers. And the cylinder wall becomes horny in a strange pattern.

  The side of the feather facing backwards on the bird produces creases that pass around on both sides of the cylinder toward the front-facing side, diving into the follicle so that they are almost parallel with the length of the cylinder. They don't quite meet, and the tissue between their deep ends will become the stalk of the feather. The other side splits open, and the barbs of the feather - between the creases - unfurl to make the feather vane. They are much longer than the cylinder's circumference, so a narrow pin-feather can generate a feather with a broad vane.

  Not a bit like a scale. And far more complicated. Evolution had to work hard to come up with feathers.

  And they must have evolved for a good reason, because lots of dinosaurs had feathers in various versions. Some were like down-feathers, others more like paintbrushes or feather dusters. They could have evolved for warmth. Adult velociraptors and young tyrannosaurs may have been covered in down, like baby chicks. Palaeontologist Mark Norell says that 'We have as much evidence that velociraptors had feathers as we do that Neanderthals had hair'. But other scientists disagree.

  Perhaps feathers were sexual ornaments. More likely, we haven't yet thought of whatever function they had.

  So much for stories that 'some reptiles got feathers and became birds'.

  There's a very general problem here, and it's the problem the wizards are having all the time. The overall pattern of evolution, of the birds say, or of tyrannosaurs, looks very sensible. But at a deep level, deeper than the 'common-sense story' that the wizards are trying to use for Roundworld, we don't understand it. We have stories to explain it, all right, but that isn't what understanding means.

  In fact, we're not altogether sure what it does mean, in a scientific sense. We know that apparently quite ordinary historical events 'come to pieces' when you try to analyse them from several directions. John F. Kennedy's assassination is a perfect example: the bullets seem to have come from different directions, and there doesn't appear to be one consistent story that means we can 'understand' what happened. We can describe the events, but the underlying causalities, like the physicists' quantum theory and relativity theory, don't match up.

  Evolution doesn't just happen to one creature at a time. The entire ecosystem evolves, and as it does so, new tricks may become worth using, for a limited period of time and in a limited region of geography. A few of those tricks turn out to have useful effects that •ire quite different from the 'reason' why they evolved to begin with, and those effects may continue to be worth having long after i lie original reason for their appearance has ceased to apply.

  It's not surprising, in that frame, that historical events as far back as the origin of feathers, or of birds, don't make detailed sense either. That's why we can't imagine what it was like in the Late Cretaceous. Walking with Dinosaurs was beautifully made and based on up-to-date science, but ultimately it was unconvincing. The need to tell a story distorted what was actually known, and mixed it up with guesswork and wishful thinking. (You can't be sure what colour an animal's skin was when all you've got is fossil bones. And assuming it was a bit like something vaguely similar that's alive today is cheating, not science.) Anything televisual was automatically preferred to some more mundane scenario. So we got a dinosaur soap, with everything over-dramatised.

  So we can't imagine ourselves walking with dinosaurs. Neither, to be fair, can we imagine ourselves running from them. We simply can't understand what it was like to be there, much as we'd like to believe we can. Still, what can you expect from a slightly brainy ape? We can give ourselves an excuse, an evolutionary one, and it's this: we're only halfway from Australopithecus (Lucy) to human. It's not surprising that we keep finding limits to what our brains can comprehend. Neither is it surprising that our mental models won't fit together to offer a convincing understanding of past events. We're not smart enough. Yet.

  Wait another million years. Then we'll show you.

  Some pterodactyls were sparrow-sized, and their wings could have carried them easily; but pteranodons can't have taken off from the sea surface, or climbed up cliffs to hang-glide! Although Quetzalcoatlus has been modelled, and flown as a radio-controlled glider, that doesn't tell us how it lived. Was there perhaps aerial plankton for it to eat?

  Though some palaeontologists think that such creatures were not feathered dinosaurs, but flightless birds. According to John Ruben, Caudipteryx was merely 'a Cretaceous turkey, so to speak'.

  THIRTY-SEVEN

  I SAID, DON’T LOOK UP!

  PONDER WAS WORKING THE RULES AGAIN. Now they read:

  THE RULES

  1 Things fall apart, but centres hold

  2 Everything moves in curves

  3 You get balls

  4 Big balls tell space to bend

  5 There are no turtles anywhere

  (after this one he'd added Except ordinary ones)

  6 Life turns up everywhere it can

  7 Life turns up everywhere it can't

  8 There is something like narrativium

  9 There may be something called bloodimindium (see rule 7)

  10...

  He stopped to think. Behind him, a very large lizard killed and ate a slightly smaller one. Ponder didn't bother to turn around. They'd been watching lizards for more than a hundred million years, all day, in fact, and even the Dean was giving up on them.

  'Too well adapted,' he said. 'No pressure on them, you see,'

  'They're certainly very dull,' said Ridcully. 'Interesting colours, though.'

  'Brain the size of a walnut and some of them think with their backsides,' said the Senior Wrangler.

  'Your type of people, Dean,' said Ridcully.

  'I shall choose to ignore that, Archchancellor,' said the Dean coldly.

  'You've been interfering again, haven't you,' Ridcully went on. 'I saw you pushing some of the small lizards out of that tree.'

  'Well, you've got to admit that they look a bit like birds,' said the Dean.

  'And did they learn to fly?'

  'Not in so many words, no. Not horizontally.'

  'Eat, fight, mate and die,'
said the Lecturer in Recent Runes. 'Even the crabs were better than this. Even the blobs made an effort. When they come to write the history of this world, this is the page everyone will skip. Terribly dull lizards, they'll be called. You mark my words.'

  'They have stayed around for a hundred million years, sir,' said Rincewind, who felt he had to stand up for non-achievers.

  'And what have they done? Is there a single line of poetry? A building of any sort? A piece of simple artwork?'

  'They've just not died, sir.'

  'Not dying out is some kind of achievement, is it?' said the Lecturer in Recent Runes.

  'Best kind there is, sir.'

  'Pah!' said the Dean. 'All they prove is that species go soft when there's nothing happening! It's nice and warm, there's plenty to eat ... it's just the sea without water. A few periods of vulcanism or a medium-sized comet would soon have them sitting up straight and paying attention.'

  The air shimmered and Ponder Stibbons appeared.

  'We have intelligence, gentlemen,' he said.

  'I know,' said the Dean.

  'I mean, the omniscope has found signs of developing intelligence. Twice, sir.'

  The herd was big. It was made up of large, almost hemispherical creatures, with faces that had all the incisive cogitation of a cow.

  Much smaller creatures were trotting along at the edges. They were dark, scrawny and warbled to one another almost without cease.

  They also carried pointed sticks.

  'Well ...' Ridcully began, dismissively.

  'They're herding them, sir!' said Ponder.

  'But wolves chase sheep ...'

  'Not with pointy sticks, sir. And look there ...'

  One of the beasts was towing a crude travois, covered with leaves. Several herders were lying on it. They were pale around the muzzles.

  'Are they sick, d'you think?' said the Dean.

  'Just old, sir.'

  'Why'd they want to slow themselves down with a lot of old people?'

  Ponder dared a short pause before answering.

  'They're the library, sir. I suppose. They can remember things. Places to hunt, good waterholes, that sort of thing. And that means they must have some sort of language.'

  'It's a start, I suppose,' said Ridcully.

  'Start, sir? They've nearly done it all!' Ponder put his hand to his ear. 'Oh ... and HEX says there's more, sir. Er ... different.'

  'How different?'

  'In the sea again, sir,'

  'Aha,' said the Senior Wrangler.

  In fact on the sea was more accurate, he had to admit. The colony they found stretched for miles, linking a chain of small rocky islands and sandbanks as beads on a chain of tethered driftwood and rafts of floating seaweed.

  The creatures inhabiting it were another type of lizard. Still extremely dull, the wizards considered, compared to some of the others. They weren't even an interesting colour and they had hardly any spikes. But they were ... busy creatures.

  'That seaweed ... does it look sort of regular to you?' said the Lecturer in Recent Runes, as they drifted over a crude wall. They're not farming, are they?'

  'I think ...' Ponder looked down. The water washed over the wall of rocks. 'It's a big cage for fish. The whole lagoon. Er ... I think they've built the walls like that so the tide lets the fish come in and then they're stuck when it goes down.'

  Lizards turned their heads as the semi-transparent men floated past, but seemed to treat them as no more than passing shadows.

  'They're harnessing the power of the sea?' said Ridcully. 'That's clever.'

  Lizards were diving at the far side of the lagoon. Some were busy around rock pools on one of the lower islands. Small lizards swam in the shallows. Along one stretch of driftwood walkways, strips of seaweed were drying in the breeze. And over everything was a yip-yipping of conversation. And it was conversation, Ponder decided. Animals didn't wait for other animals to finish. Nor did wizards, of course, but they were a breed apart.

  A little way away, a lizard was carefully painting the skin of another lizard, using a twig and some pigments in half-shells. The one doing the painting was wearing a necklace of different shells, Ponder realized.

  'Tools,' he murmured. 'Symbols. Abstract thought. Things of value ... is this a civilization, or are we merely tribal at the moment?'

  'Where's the sun?' said the Senior Wrangler. 'It's always so hazy, and it's hard to get used to directions here. Wherever you point, it's at the back of your own head.'

  Rincewind pointed towards the horizon, where there was a red glow behind the clouds.

  'I call it Widdershins,' he said. 'Just like at home.'

  'Ah. The sun sets Widdershins.'

  'No. It doesn't do anything,' said Rincewind. 'It stays where it is. The horizon comes up.'

  'But it doesn't fall on us?'

  'It tries to, but the other horizon drags us away before it happens.'

  'The more time I spend on this globe, the more I feel I should be holding on to something,' the Dean muttered.

  'And the light isn't reflected around the world?' said the Senior Wrangler. 'It is at home. It's always very beautiful, the glow that comes up through the waterfall.'

  'No,' said Rincewind. 'It just gets dark, unless the moon is up.'

  'And there's still just the one sun, isn't there?' said the Senior Wrangler, a man with something on his mind.

  'Yes.'

  'We didn't add another one?'

  'No.'

  'So ... er ... what is that light over there?'

  As one wizard, they turned towards the opposite horizon.

  'Whoops,' said the Dean, as the distant thunder died away and lights streamed high across the sky.

  The lizards had heard it too. Ponder looked around. They were lining the walkways, watching the horizon with all the intelligent interest of a thinking creature wondering what the future may hold...

  'Let's get back to the High Energy Magic building before the boiling rain, shall we?' said Ridcully. 'This really is too depressing.'

  THIRTY-EIGHT

  THE DEATH OF DINOSAURS

  LIFE TURNS UP EVERYWHERE IT CAN.

  Life turns up everywhere it can't.

  And just when it seems to have got itself going really comfortably, with a sustainable lifestyle and gradual progress towards higher things, along comes a major catastrophe and sets it back twenty million years. Yet, paradoxically, those same disasters also pave the way to radically new lifeforms ...

  It's all rather confusing.

  Life is resilient, but any particular species may not be. Life is constantly devising new tricks. The one with eggs is brilliant: provide the developing embryo with its own personal life-support machine. Inside, the environment is tailored to the needs of that species — and what's outside doesn't matter much, because there's a barrier to keep it out.

  Life is adaptable. It changes the rules of its own game. As soon as eggs make their appearance, the stage is set for the evolution of egg-eaters ...

  Life is diverse. The more players there are, the more ways there are to make a living by taking in each others' washing.

  Life is repetitious. When it finds a trick that works, it churns out thousands of variations on the same basic theme. The great biologist John (J.B.S.) Haldane was once asked what question he would like to pose to God, and replied that he'd like to know why He has such an inordinate fondness for beetles.*

  There are a third of a million beetle species today — far more than in any other plant or animal group. In 1998 Brian Farrell came up with a possible answer to Haldane's query. Beetles appeared about 250 million years ago, but the number of species didn't explode until about 100 million years ago. That happens to be just when flowering plants came into existence. The 'phase space' available for organisms suddenly acquired a new dimension — a new resource became available for exploitation. The beetles were beautifully poised to take advantage by eating the new plants, especially their leaves. It used to be thought that
flowering plants and pollinating insects drove each other to wilder and wilder diversity, but that's not true. However, it is true for beetles. Nearly half of today's beetle species are leaf-eaters. It's still an effective tactic.

  Sometimes natural disasters don't just eliminate a species or two. The fossil record contains a number of 'mass extinctions' in which a substantial proportion of all life on Earth disappeared. The best-known mass extinction is the death of the dinosaurs, 65 million years ago.

  In order not to mislead you, we should point out at once that there is no scientific evidence for the existence of any dinosaur civilization, no matter what events are going on in the Roundworld Project. But... whenever a scientist says 'there is no scientific evidence for', there are three important questions you should ask — especially if it's a government scientist. These are: 'Is there any evidence against?, 'Has anyone looked?', and 'If they did, would they expect to find anything?'*

  The answers here are 'no,' 'no', and 'no'. Deep Time hides a lot, especially when it's assisted by continental movement, the bulldozing ice sheets, volcanic action and the occasional doomed asteroid. There are few surviving human artefacts more than ten thousand years old, and if we died out today, the only evidence of our civilization that might survive for a million years would be a few dead probes in deep space and various bits of debris on the Moon. Sixty-five million? Not a chance. So although a dinosaurian civilization is pure fantasy — or, rather, pure speculation — we can't rule it out absolutely. As for dinosaurs who were sufficiently advanced to use tools, herd other dinosaurs ... well, Deep Time would wash over them without a ripple.