The Science of Discworld Revised Edition

by Terry Pratchett

  There is an analogy between space elevators and life. Life seems to contradict the usual rules of chemistry and physics, especially the rule known as the second law of thermodynamics, which says that things can’t spontaneously get more complicated. Life does this because, like the space elevator, it has lifted itself to a new level of operation, where it can gain access to things and processes that were previously out of the question. Reproduction, in particular, is a wonderful method of getting round the difficulties of manufacturing a really complicated thing. Just build one that manufactures more of itself. The first one may be incredibly difficult – but all the rest come with no added effort.

  What is the elevator for life? Let’s try to be general here, and look at the common features of all the different proposals for ‘the’ origin of life. The main one seems to be the novel chemistry that can occur in small volumes adjacent to active surfaces. This is a long way from today’s complex organisms – it’s even a long way from today’s bacteria, which are distinctly more complicated than their ancient predecessors. They have to be, to survive in a more complicated world. Those active surfaces could be in underwater volcanic vents. Or hot rocks deep underground. Or they could be seashores. Imagine layers of complicated (because that’s easy) but disorganized (ditto) molecular gunge on rocks which are wetted by the tides and irradiated by the sun. Anything in there that happens to produce a tiny ‘space elevator’ establishes a new baseline for further change. For example, photosynthesis is a space elevator in this sense. Once some bit of gunge has got it, that gunge can make use of the sun’s energy instead of its own, churning out sugars in a steady stream. So perhaps ‘the’ origin of life was a whole series of tiny ‘space elevators’ that led, step by step, to organized but ever more complex chemistry.

  1 Everyone knows what science fiction is – until you start asking questions like ‘Is a book set five years in the future automatically SF? Is it SF just because it’s set on another world, or is it simply fantasy with nuts and bolts on the outside? Is it SF if the author thinks it isn’t? Does it have to be set in the future? Does the presence of Doug McClure mean that a movie is SF, or merely that the men-in-rubber-monster-suits quotient is going to be high?’ One of the best SF books ever written was the late Roy Lewis’s The Evolution Man; there is no technology in it more sophisticated than a bow, it’s set in the far past, the characters are barely more than ape-men … but it is science fiction, nonetheless.

  2 They were fortunate, given the names of some places in Australia, that they ended up merely sounding like a minor Star Trek species.

  TWENTY-FIVE

  UNNATURAL SELECTION

  THE LIBRARIAN KNUCKLED swiftly through the outer regions of the University’s library, although terms like ‘outer’ were hardly relevant in a library so deeply immersed in L-space.

  It is known that knowledge is power, and power is energy, and energy is matter, and matter is mass, and therefore large accumulations of knowledge distort time and space. This is why all bookshops look alike, and why all second-hand bookshops seem so much bigger on the inside – and why all libraries, everywhere, are connected. Only the innermost circle of librarians know this, and take care to guard the secret. Civilization would not survive for long if it was generally known that a wrong turn in the stacks would lead into the Library of Alexandria just as the invaders were looking for the matches, or that a tiny patch of floor in the reference section is shared with the library in Braseneck College where Dr Whitbury proved that gods cannot possibly exist, just before that rather unfortunate thunderstorm.

  The Librarian was saying ‘ook ook’ to himself under his breath, in the same way that a slightly distracted person searches aimlessly around the room saying ‘scissors, scissors’ in the hope that this will cause them to re-materialize. In fact he was saying ‘evolution, evolution’. He’d been sent to find a good book on it.

  He had a very complicated reference card in his mouth.

  The wizards of UU knew all about evolution. It was a self-evident fact. You took some wolves, and by careful unnatural selection over the generations you got dogs of all shapes and sizes. You took some sour crab-apple trees and, by means of a stepladder, a fine paintbrush and a lot of patience, you got huge juicy apples. You took some rather scruffy desert horses and, with effort and a good stock book, you got a winner. Evolution was a demonstration of narrativium in action. Things improved. Even the human race was evolving, by means of education and other benefits of civilization; it had began with rather bad-mannered people in caves, and it had now produced the Faculty of Unseen University, beyond which it was probably impossible to evolve further.

  Of course, there were people who occasionally advanced more radical ideas, but they were like the people who thought the world really was round or that aliens were interested in the contents of their underwear.

  Unnatural selection was a fact, but the wizards knew, they knew, that you couldn’t start off with bananas and get fish.

  The Librarian glanced at the card, and took a few surprising turnings. There was the occasional burst of noise on the other side of the shelves, rapidly changing as though someone was playing with handfuls of sound, and a flickering in the air. Someone talking was replaced with the absorbent silence of empty rooms was replaced with the crackling of flame and displaced by laughter …

  Eventually, after much walking and climbing, the Librarian was faced with a blank wall of books. He stepped up to them with librarianic confidence and they melted away in front of him.

  He was in some sort of study. It was book-lined, although with rather fewer than the Librarian would have expected to find in such an important node of L-space. Perhaps there was just the one book … and there it was, giving out L-radiation at a strength the Librarian had seldom encountered outside the seriously magical books in the locked cellars of Unseen University. It was a book and father of books, the progenitor of a whole race that would flutter down the centuries …

  It was also, unfortunately, still being written.

  The author, pen still in hand, was staring at the Librarian as if he’d seen a ghost.

  With the exception of his bald head and a beard that even a wizard would envy, he looked very, very much like the Librarian.

  ‘My goodness …’

  ‘Ook?’ The Librarian had not expected to be seen. The writer must have something very pertinent on his mind.

  ‘What manner of shade are you …?’

  ‘Ook.’1

  A hand reached out, tremulously. Feeling that something was expected of him, the Librarian reached out as well, and the tips of the fingers touched.

  The author blinked.

  ‘Tell me, then,’ he said, ‘is Man an ape, or is he an angel?’

  The Librarian knew this one.

  ‘Ook,’ he said, which meant: ape is best, because you don’t have to fly and you’re allowed sex, unless you work at Unseen University, worst luck.

  Then he backed away hurriedly, ooking apologetic noises about the minor error in the spacetime coordinates, and knuckled off through the interstices of L-space and grabbed the first book he found that had the word ‘Evolution’ in the title.

  The bearded man went on to write an even more amazing book. If only he had thought to use the word ‘Ascent’ there might not have been all that unpleasantness.

  But, there again, perhaps not.

  HEX let itself absorb more of the future … call it … knowledge. Words were so difficult. Everything was context. There was too much to learn. It was like trying to understand a giant machine when you didn’t understand a screwdriver.

  Sometimes HEX thought it was picking up fragmentary instructions. And, further away, much further away, there were little disjointed phrases in the soup of concepts which made sense but did not seem to be sensible. Some of them arrived unbidden.

  Even as HEX pondered this, another one arrived and offered an opportunity to make $$$$ While You Sit On Your Butt!!!!! He considered this unlikely.

/>   The title brought back by the Librarian was The Young Person’s Guide to Evolution.

  The Archchancellor turned the pages carefully. They were well illustrated. The Librarian knew his wizards.

  ‘And this is a good book on evolution?’ said the Archchancellor.

  ‘Ook.’

  ‘Well, it makes no sense to me,’ said the Archchancellor. ‘I mean t’say, what the hell is this picture all about?’

  It showed, on the left, a rather hunched-up, ape-like figure. As it crossed the page, it gradually arose and grew considerably less hairy until it was striding confidently towards the edge of the page, perhaps pleased that it had essayed this perilous journey without at any time showing its genitals.

  ‘Looks like me when I’m getting up in the mornings,’ said the Dean, who was reading over his shoulder.

  ‘Where’d the hair go?’ Ridcully demanded.

  ‘Well, some people shave,’ said the Dean.

  ‘This is a very strange book,’ said Ridcully, looking accusingly at the Librarian, who kept quiet because in fact he was a little worried. He rather suspected he might have altered history, or at least a history, and on his flight back to the safety of UU he’d seized the first book that looked as though it might be suitable for people with a very high IQ but a mental age of about ten. It had been in an empty byway, far off his usual planes of exploration, and there had been very small red chairs in it.

  ‘Oh, I get it. This is a fairy story,’ said Ridcully. ‘Frogs turnin’ into princes, that kind of thing. See here … there’s something like our blobs, and then these fishes, and then it’s a … a newt, and then it’s a big dragony type of thing and, hah, then it’s a mouse, then here’s an ape, and then it’s a man. This sort of thing happens all the time out in the really rural areas, you know, where some of the witches can be quite vindictive.’

  ‘The Omnians believe something like this, you know,’ said the Senior Wrangler. ‘Om started off making simple things like snakes, they say, and worked his way up to Man.’

  ‘As if life was like modelling clay?’ said Ridcully, who was not a patient man with religion. ‘You start out with simple things and then progress to elephants and birds which don’t stand up properly when you put them down? We’ve met the God of Evolution, gentlemen … remember? Natural evolution merely improves a species. It can’t change anything.’

  His finger stabbed at the next page in the brightly coloured book.

  ‘Gentlemen, this is merely some sort of book of magic, possibly about the Morphic Bounce Hypothesis.2 Look at this.’ The picture showed a very large lizard followed by a big red arrow, followed by a bird. ‘Lizards don’t turn into birds. If they did, why have we still got lizards? Things can’t decide for themselves what shape they’re going to be. Ain’t that so, Bursar?’

  The Bursar nodded happily. He was halfway through HEX’s write-out of the theoretical physics of the project universe and, so far, had understood every word. He was particular happy with the limitations of light speed. It made absolute sense.

  He took a crayon and wrote in the margin: ‘Assuming the universe to be a negatively curved non-Paramidean manifold – which is more or less obvious – you could deduce its topology by observing the same galaxies in several different directions.’ He thought for a moment, and added: ‘Some travel will be involved.’

  Of course, he was a natural mathematician, and one thing a natural mathematician wants to do is get away from actual damn sums as quickly as possible and slide into those bright sunny uplands where everything is explained by letters in a foreign alphabet, and no one shouts very much. This was even better than that. The hard-to-digest idea that there were dozens of dimensions rolled up where you couldn’t see them was sheer jelly and ice cream to a man who saw lots of things no one else saw.

  1 ‘Reddish-brown’.

  2 … which had engrossed wizards for many years. The debate ran like this: it was quite easy to turn someone into a frog, and fairly easy to turn them into, say, a white mouse. Strangely, considering the basic similarity of size and shape, turning someone into an orangutan took a vast amount of power and it was only an explosion in the intense thaumic confines of the Library which had managed the trick. Turning someone into a tree was much, much harder even than that, although turning a pumpkin into a coach was so easy that even a crazy old woman with a wand could do it. Was there some kind of framework into which all this fitted?

  The current hypothesis was that most Change spells unravelled the victim’s morphic field down to some very basic level and then ‘bounced’ them back. A frog was quite simple, so they wouldn’t have to bounce far. An ape, being quite human-like in many respects, would mean a very long return journey indeed. You couldn’t turn someone into a tree because there was no way to get there from here, but a pumpkin could be turned into a wooden coach because it was quite close to it in vegetable space.

  The wizards agreed that this all seemed to fit nicely, and was therefore true.

  If William of Occam had been a wizard at Unseen University, he would have grown a beard.

  TWENTY-SIX

  THE DESCENT OF DARWIN

  THE WIZARDS MET the God of Evolution in The Last Continent. He made things the way a god ought to:

  ‘“Amazin’ piece of work,” said Ridcully, emerging from the elephant. “Very good wheels. You paint these bits before assembly, do you?”’

  The God of Evolution builds creatures piece by piece, like a butcher in reverse. He likes worms and snakes because they’re very easy – you can roll them out like a child with modelling clay. But once the God of Evolution has made a species, can it change? It does on Discworld, because the God runs around making hurried adjustments … but how does it work without such divine intervention?

  All societies that have domestic animals, be they hunting dogs or edible pigs, know that living creatures can undergo gradual changes in form from one generation to the next. Human intervention, in the form of ‘unnatural selection’, can breed long thin dogs to go down holes and big fat pigs that provide more bacon per trotter.1 The wizards know this, and so did the Victorians. Until the nineteenth century, though, nobody seems to have realized that a very similar process might explain the remarkable diversity of life on Earth, from bacteria to bactrians, from oranges to orangutans.

  They didn’t appreciate that possibility for two reasons. When you bred dogs, what you got was a different kind of dog – not a banana or a fish. And breeding animals was the purest kind of magic: if a human being wanted a long thin dog, and if they started from short fat ones, and if they knew how the trick worked (if, so to speak, they cast the right ‘spells’) then they would get a long thin dog. Bananas, long and thin though they might be, were not a good starting point. Organisms couldn’t change species, and they only changed form within their own species because people wanted them to.

  Around 1850, two people independently began to wonder whether nature might play a similar game, but on a much longer timescale and in a much grander manner – and without any sense of purpose or goal (which had been the flaw in previous musings along similar lines). They considered a self-propelled magic: ‘natural’ selection as opposed to selection by people. One of them was Alfred Wallace; the other – far better known today – was Charles Darwin. Darwin spent years travelling the world. From 1831 to 1836 he was hired as ship’s naturalist aboard HMS Beagle, and his job was to observe plants and animals and note down what he saw. In a letter of 1877 he says that while on the Beagle he believed in ‘the permanence of species’, but on his return home in 1836 he began to think about the deeper meaning of what he had seen, and realized that ‘many facts indicated the common descent of species’. By this he meant that species that are different now probably came from ancestors that once belonged to the same species. Species must be able to change. That wasn’t an entirely new idea, but he also came up with an effective mechanism for such changes, and that was new.

  Meanwhile Wallace was studying the flora and fau
na of Brazil and the East Indies, and comparing what he saw in the two regions, and was coming to similar conclusions – and much the same explanation. By 1858 Darwin was still mulling over his ideas, contemplating a grand publication of everything he wanted to say about the subject, while Wallace was getting ready to publish a short article containing the main idea. Being a true English gentleman, Wallace warned Darwin of his intentions so that Darwin could publish something first, and Darwin rapidly penned a short paper for the Linnaean Society, followed a year later by a book, The Origin of Species – a big book, but still not on the majestic scale that Darwin had originally intended. Wallace’s paper appeared in the same journal shortly afterwards, but both papers were officially ‘presented’ to the Society at the same meeting.

  What was the initial reaction to these two Earth-shattering articles? In his annual report for that year, the President of the Society, Thomas Bell, wrote that ‘The year has not, indeed, been marked by any of those striking discoveries which at once revolutionize, so to speak, the department of science in which they occur.’ However, this perception quickly changed as the sheer enormity of Darwin’s and Wallace’s theory began to sink in, and they took a lot of stick from Mustrum Ridcully’s spiritual brethren for daring to come up with a plausible alternative to Biblical creation. What was this epoch-making alternative? An idea so simple that everybody else had missed it. Thomas Huxley is said to have remarked, on reading Origin: ‘How extremely stupid not to have thought of that.’

  This is the idea. You don’t need a human being to push animals into new forms; they can do it to themselves – more precisely: to each other. This was the mechanism of natural selection. Herbert Spencer, who did the important journalistic job of interpreting Darwin’s theory to the masses, coined the phrase, ‘survival of the fittest’ to describe it. The phrase had the advantage of convincing everybody that they understood what Darwin was saying, and it had the disadvantage of convincing everybody that they understood what Darwin was saying. It was a classic lie-to-children, and it deceives many critics of evolution to this day, causing them to aim at a long-disowned target, besides giving a spurious ‘scientific’ background to some extremely stupid and unpleasant political theories.