The Science of Discworld I tsod-1

by Terry Pratchett

  The within was the big leap forward, or at least the big slither. Within you can put the things you need to protect, like internal organs. In one sense, you are not part of the environment any more, there is a you as well. And, like someone who now has a piece of property of their very own, you can begin to make improvements. This is a lie-to-children, but as lies go it is a good one. Triploblasts played a crucial role in evolution, precisely because they did have internal organs, and in particular they could ingest food and excrete it. Their excreta became a major resource for other creatures; to get an interestingly complicated world, it is vitally important that shit happens.

  But where did all those triploblasts come from? Were they an offshoot of the Ediacarans? Or did they come from something else that didn't leave fossils?

  It's hard to see how they could have come from Ediacarans. Yes, an extra layer of tissue might have appeared, but as well as that extra layer you need a lot of organization to exploit it. That organization has to come from somewhere. Moreover, there were these occa­sional tantalizing traces of what might have been pre-Cambrian triploblasts, fossils not of worms, which would have clinched it, but of things that might have been trails made by worms in wet mud.

  And then again, might not.

  In February 1998, we found out.

  The discovery depended upon where, and in this case how -you look for fossils. One way for fossils to form is by petrification. There is a poorly known type of petrification that can happen very fast, within a few days. The soft parts of a dead organism are replaced by calcium phosphate. Unfortunately for palaeontologists, this process works only for organisms that are about a tenth of an inch (2 mm) long. Still, some interesting things are that tiny. From about 1975 onwards scientists found wonderfully preserved speci­mens of tiny ancient arthropods, creatures like centipedes with many segments. In 1994 they found fossilized balls of cells from embryos, early stages in the development of an organism, and it is thought that these come from embryonic triploblasts. However, all of these creatures must have come after the Ediacarans. But in 1998 Shuhai Xiao, Yun Zhang, and Andrew Knoll discovered fos­silized embryos in Chinese rock that is 570 million years old -smack in the middle of the Ediacaran era. And those embryos were triploblasts.

  Forty million years before the Cambrian explosion, there were triploblasts on Earth, living right alongside those enigmatic Ediacarans.

  We are triploblasts. Somewhere in the pre-Cambrian, sur­rounded by mouthless, organless Ediacarans, we came into our inheritance.

  It used to be thought that life was a delicate, highly unusual phe­nomenon: difficult to create, easy to destroy. But everywhere we look on Earth we find living creatures, often in environments that we would have expected to be impossibly hostile. It's beginning to look as if life is an extremely robust phenomenon, liable to turn up almost anywhere that's remotely suitable. What is it about life that makes it so persistent?

  Earlier we talked about two ways to get off the Earth, a rocket and a space elevator. A rocket is a thing that gets used up, but a space elevator is a process that continues. A space elevator requires a huge initial investment, but once you've got it, going up and down is essentially free. A functioning space elevator seems to contradict all the usual rules of economics, which look at individual transac­tions and try to set a rational price, instead of asking whether the concept of a price might be eliminated altogether. It also seems to contradict the law of conservation of energy, the physicist's way of saying that you can't get something for nothing. But, as we've seen, you can, by exploiting the new resources that become available once you get your space elevator up and running.

  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.

  25. 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 mas 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 wi
th 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.'[36]

  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[37]. 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.

  26. 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[38]. 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 fauna 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.