Science of Discworld III

by Terry Pratchett

  Two hours later he went back, woke the Librarian again, and asked for Theology of Species. As he left with it, he heard the door being locked behind him.

  Later still, he fell asleep with his face in a cold pizza and both books open on his desk, dripping with bookmarks and stray pieces of anchovy.

  Beside him, Hex’s writing table whirred. Twenty quill pens flashed back and forth and gyrated on spring-loaded arms, making the table look like several giant spiders on their backs. And, every minute, a page dropped onto the pile that was forming on the floor …

  Ponder dreamed fitfully of dinosaurs trying to fly. They always splashed when they reached the bottom of the cliff.

  He woke up at half past eight, read the accumulated papers, and voided a small scream.

  All right, all right, he thought. There is no actual hurry, as such. We can change it back any time we like. That’s what time travel means.

  But although the brain can think that, the panic gland never believes it. He snatched up the books and as many notes as he could carry and hurried out.

  We have heard the chimes of midnight, the saying goes. The wizards had not only heard them but also the ones at one, two and three a.m. They certainly weren’t interested in hearing anything at half past eight, however. The only occupant of the tables in the Great Hall was Archchancellor Ridcully, who liked an unhealthy breakfast after his early morning run. He was alone at the trestle tables in the big hall.

  ‘I’ve found it!’ Ponder announced, with a certain nervous triumph, and dropped the two books in front of the astonished wizard.

  ‘Found what?’ said Ridcully. ‘And mind where you’re putting stuff, man! You nearly had the bacon dish over!’

  ‘I have put my finger,’ Ponder declared, ‘on the precise split in the Trousers of Time!’

  ‘Good man!’ said Ridcully, reaching for the flagon of brown sauce. ‘Tell me about it after breakfast, will you?’

  ‘It’s a book, sir! Two books in fact! He wrote the wrong one! Look!’

  Ridcully sighed. Against the enthusiasm of wizards there was no defence. He narrowed his eyes and read the title of the book Ponder Stibbons was holding:

  ‘Theology of Species. And?’

  ‘Archchancellor, it was written by a Charles Darwin, and caused rather a row when it was published, since it purported to explain the mechanism of evolution in a manner which upset some widely held beliefs. Vested interests railed against it, but it prevailed and had a significant effect on history. Er … the wrong one.’

  ‘Why? What is it about?’ said Ridcully, carefully taking the top off a boiled egg.

  ‘I’ve only glanced at it, Archchancellor, but it appears to describe the process of evolution as one of permanent involvement by an omnipotent deity.’

  ‘And?’ Ridcully selected a piece of toast and began to cut it into soldiers.

  ‘That’s not how it works on Roundworld, sir,’ said Ponder, patiently.

  ‘That’s how it does here, more or less. There’s a god who sees to it.’

  ‘Yes, sir. But, as I am sure you will remember,’ said Ponder, using the words in the sense of ‘as I know you have forgotten’, ‘we have not found any traces of Deitium on Roundworld.’

  ‘Well, all right,’ the Archchancellor conceded. ‘But I don’t see why the man shouldn’t have written it, even so. Good solid book, by the look of it. Took some thinkin’ about, I’ll be bound.’

  ‘Yes, sir,’ said Ponder. ‘But the book he should have written …’ he thumped another volume onto the breakfast table, ‘… was this.’

  Ridcully picked it up. It had a much more colourful cover than ‘Theology’, and the title:

  Darwin Revisited

  THE ORIGIN OF SPECIES

  by The Rev. Richard Dawkins

  ‘Sir, I think I can prove that because Darwin wrote the wrong book the world took a different leg of the Trousers of Time, and humanity didn’t leave the planet before the big freeze,’ said Ponder, standing back.

  ‘Why did he do that, then?’ said Ridcully, mystified.

  ‘I don’t know, sir. All I know is that, until a few days ago, this Charles Darwin wrote a book that said that evolution all worked naturally, without a god. Now it turns out that he didn’t. Instead, he wrote a book that said it worked because a god was involved at every stage.’

  ‘And this other fella, Dawkins?’

  ‘He said Darwin had pretty much got it right except the god part. You didn’t need one, he said.’

  ‘Didn’t need a god? But it says here he’s a priest of some sort!’

  ‘Er … sort of, sir. In the … history where Charles Darwin wrote Theology of Species, it had become more or less compulsory to take holy orders in order to attend university. Dawkins said evolution happened all by itself.’

  He shut his eyes. Ridcully alone was a much better audience than the senior faculty, who’d taken cross-purposes to the status of a fine art, but his Archchancellor was a practical, sensible man and therefore found Roundworld difficult. It wasn’t a sensible place.

  ‘You’ve foxed me there. How can it just happen?’ said Ridcully. ‘It makes no sense if there isn’t someone who knows what’s going on. There’s got to be a reason.’

  ‘Quite so, sir. But this is Roundworld,’ said Ponder. ‘Remember?’

  ‘But surely this other feller, Dawkins, made it all right again?’ Ridcully floundered. ‘You did say it was the right book.’

  ‘But at the wrong time. It was too late, sir. He didn’t write his book until more than a hundred years later. It caused a huge row—’

  ‘An ungodly one, I suspect?’ said Ridcully cheerfully, dipping the toast in the egg.

  ‘Haha, sir, yes. But it was still too late. Humanity was well on the road to extinction.’

  Ridcully picked up Theology and turned it over in his hands, getting butter on it.

  ‘Seems innocent enough,’ he said. ‘Gods making it all happen … well, that’s common sense.’ He held up a hand. ‘I know, I know! This is Roundworld, I know. But where there’s something as complicated as a watch, you know there must be a watchmaker.’

  ‘That’s what the Darwin who wrote the Theology book said, sir, except that he stated that the watchmaker remained part of the watch,’ said Ponder.

  ‘Oilin’ it, and so forth?’ said Ridcully, cheerfully.

  ‘Sort of, sir. Metaphorically.’

  ‘Hah!’ said Ridcully. ‘No wonder there was a row. Priests don’t like that sort of thing. They always squirm when things get mystical.’

  ‘Oh, the priests? They loved it,’ said Ponder.

  ‘What? I thought you said vested interests were against it!’

  ‘Yes, sir. I meant the philosophers and scientists,’ said Ponder Stibbons. ‘The technomancers. But they lost.’

  FOUR

  PALEY ONTOLOGY

  PALEY’S METAPHOR OF THE WATCH, alluded to by Ridcully, still remains powerful; powerful enough for Richard Dawkins to title his neo-Darwinian riposte of 1986 The Blind Watchmaker. Dawkins1 made it clear that in his view, and those of most evolutionary biologists over the past fifty years, there was no watchmaker for living organisms, in Paley’s sense: ‘Paley’s argument is made with passionate sincerity and is informed by the best biological scholarship of his day, but it is wrong, gloriously and utterly wrong.’ But, says Dawkins, if we must give the watchmaker a role, then that role must be the process of natural selection that Darwin expounded. If so, the watchmaker has no sense of purpose: it is blind. It’s a neat title but easily misunderstood, and it opens the way to replies, such as the recent book by William Dembski, How Blind Is the Watchmaker? Dembski is an advocate of ‘intelligent design’, a modern reincarnation of Paley with updated biology which repeats the old mistakes in new contexts.2

  If you did find a watch on a heath, your first thought would probably not be that there must have been a watchmaker, but a watch-owner. You would either wish to get the owner’s property back to them, or look guiltily
around to make sure they weren’t anywhere nearby before you snaffled it. Paley tells us that if we find, say, a spider on the path, then we are compelled to infer the existence of a spider-maker. But he finds no such compulsion to infer the existence of a spider-owner. Why is one human social role emphasised, but the other suppressed?

  Moreover, we know what a watch is for, and this colours our thinking. Suppose, instead, that our nineteenth-century heath-walker chanced upon a mobile phone, left there by some careless time traveller from the future. He would probably still infer ‘design’ from its intricate form … but purpose? What conceivable purpose would a mobile phone have in the nineteenth century, with no supporting network of transmission towers? There is no way to look at a mobile phone and infer some evident purpose. If its battery has run down, it doesn’t do anything. And if what was found on the path was a computer chip – say, the engine manager of a car – then even the element of design would be undetectable, and the chip might well be dismissed as some obscure crystalline rock. Chemical analysis would confirm the diagnosis by showing that it was mostly silicon. Of course, we know that these things do have a designer; but in the absence of any clear purpose, Paley’s heath-walker would not be entitled to make any such inference.

  In short, Paley’s logic is heavily biased by what a human being would know about a watch and its maker. And his analogy breaks down when we consider other features of watches. If it doesn’t even work for watches, which we do understand, there’s no reason for it to apply to organisms, which we don’t.

  He is also rather unfair to stones.

  Some of the oldest rocks in the world are found in Greenland, in a 25-mile-long band known as the Isua supracrustal belt. They are the oldest known rocks among those that have been laid down on the surface of the Earth, instead of rising from the mantle below. They are 3.8 billion years old, unless we cannot reliably make inferences from observations, in which case the evidence for cosmic design has to be thrown out along with the evidence of the rocks. We know their age because they contain tiny crystals of zircon. We mention them here because they show that Paley’s lack of interest in ‘stones’, and his casual acceptance that they might have ‘lain there forever’, are unjustified. The structure of a stone is nowhere near as simple as Paley assumed. In fact, it can be just as intricate as an organism, though not as obviously ‘organised’. Every stone has a story to tell.

  Zircons are a case in point.

  Zirconium is the 40th element in the periodic table, and zircon is zirconium sulphate. It occurs in many rocks, but usually in such tiny amounts that its presence is ignored. It is extremely hard – not as hard as diamond, but harder than the hardest steel. Jewellers sometimes use it as a diamond substitute.

  Zircons, then, are found in most rocks, but in this instance the important rock is granite. Granite is an igneous rock, which wells up from the molten layers beneath the Earth’s crust, forcing a path through the overlying sedimentary rock that has been deposited by wind or water. Zircons form in granite that solidifies about 12 miles (20 km) down inside the Earth. The crystals are truly tiny: one 10,000th of an inch (2 microns) is typical.

  Over the last few decades we have learned that our apparently stable planet is highly dynamic, with continents that wander around over the surface, carried by gigantic ‘tectonic plates’ which are 60 miles (100 km) thick and float on the liquid mantle. Sometimes they even crash into each other. They move less than an inch (about 2 cm) per year, on average, and on a geological timescale that’s fast. The north-west of Scotland was once part of North America, when the North American plate collided with the Eurasian plate; when the plates later split apart, a piece of America was left behind, forming the Moine thrust. When plates collide, they slide over each other, often creating mountains. The highest mountains on Earth today, the Himalayas, formed when India collided with the Asian mainland. They are still rising today by more than half an inch (1.3 cm) a year, though are often weathered away faster, and India is still moving northwards.

  At any rate, granite deep within the Earth may be uplifted by the collision of continental plates, to appear at the surface as part of a mountain range. Being a hard rock, it survives when the softer sedimentary rocks that surround it weather away. But eventually, even granite weathers, so the mountain erodes. The zircon crystals are even harder, so they survive weathering; they separate out from the granite, to be washed down to the coast by streams and rivers, deposited on the sandy shore, and incorporated into the next layer of sedimentary rock.

  As well as being very hard, zircon is chemically very stable, and it resists most chemical changes. So, as the sediment builds up, and the zircon crystal is buried under accumulating quantities of incipient rock, the crystal is relatively immune to the increasing heat and pressure. Even when the rock is cooked by deep heat, becoming metamorphic – changing its chemical structure – the crystal of zircon survives. Its one concession to the extreme environment around it is that eventually it builds a new layer, like a skin, on its surface. This ‘rim’, as it is called, is roughly the same age as the surrounding rock; the inner core is far older.

  Now the process may repeat. The core of zircon, with its new rim, may be pushed up with the surrounding rocks to make a new mountain range. When those mountains weather, the zircon may return to the depths, to acquire a second rim. Then a third, a fourth … Just as tree rings indicate the growth of a tree, so ‘zircon rims’ reflect a sequence of mountain-building and erosion. The main difference is that each ring on a tree corresponds to a period of one year, whereas the rims on the tiny zircon crystal correspond to geological cycles that typically last hundreds of millions of years. But, just as the widths of tree rings tell us something about the climate in the years that are represented, so the zircon rims tell us something about the conditions that occurred during a given geological cycle.

  By one of those neat coincidences that Paley would interpret as the Hand of God but nowadays we recognise as an inevitable consequence of the sheer richness of the universe (yes, we do see that those statements might be the same), the zirconium atom has the same electric charge, and is much the same size, as an atom of uranium. So uranium impurities can easily sneak into that zircon crystal. This is good for science, because uranium is radioactive. Over time, it decays into lead. If we measure the ratio of uranium to lead then we can estimate the time that has elapsed since any given part of the zircon crystal was laid down. Now we have a powerful observational tool, a geological stopwatch. And we also have a simple prediction that gives us confidence in the hypothesis that the zircon crystal forms in successive stages. Namely, the core should be the oldest part of the crystal, and successive rims should become consistently younger, in separate stages.

  A typical crystal might have, say, four layers. The core might date to 3.7 billion years ago, the next to 3.6 billion years, the third to 2.6 billion years, and the last one to 2.3 billion years. So here, in a simple ‘stone’, we have evidence for geological cycles that last between 100 million and one billion years. The order of the ages agrees with the order in which the crystal must have been deposited. If the general scenario envisaged by geologists were wrong, then it would take only a single grain of sand to disprove it. Of course that doesn’t confirm the huge geological cycles: those are deduced from other evidence. Science is a crossword puzzle.

  Zircons can teach us more. It is thought that the ratio of two isotopes of carbon, carbon-12 and carbon-13, may distinguish organic sources of carbon from inorganic ones. There is carbon in the Isua formation, and the ratio there suggests that life may have existed 3.8 billion years ago, surprisingly soon after the Earth’s surface solidified. But this conclusion is controversial, and many scientists are not convinced that other explanations can be excluded.

  At any rate, for the Isua zircons we know that it is not an option for them to have ‘lain there for ever’. Stones are far more interesting than they might seem, and anyone who knows how to read the rocks can deduce many things about
their history. Paley believed that he could deduce the existence of God from the complexity of an eye. We can’t get God from a zircon, but we can get vast geological cycles of mountain-building and erosion … and just possibly, evidence for exceedingly ancient life.

  Never underestimate the humble stone. It may be a watch in disguise.

  Paley’s position is that what you see is what you get. The appearance is the reality. His title Natural Theology says as much, and his subtitle could scarcely be plainer. Organisms look designed because they are designed, by God; they appear to have a purpose because they do have a purpose: God’s. Everywhere Paley looked, he saw traces of God’s handiwork; everything around him was evidence for the Creator.

  That kind of ‘evidence’ exists in such abundance that there is no difficulty in accumulating examples. Paley’s central example was the eye. He noted its similarity to a telescope, and deduced that since a telescope is designed, so must an eye be. The camera did not exist in his day,3 but if it had existed, he would have found even closer similarities. The eye, like a telescope or a camera, has a lens to bring incoming light to a sharp focus, forming an image. The eye has a retina to receive that image, just as a telescope has an observer, or a screen on to which the image is projected.

  The lens of the eye is useless without the retina; the retina is useless without the lens. You can’t put an eye together piecemeal – you need all of it, at once, or it can’t work. Later supporters of theist explanations of life turned Paley’s subtle arguments into a simplistic slogan: ‘What use is half an eye?’

  One reason to doubt Paley’s explanation of ‘design’ is that in science, you very seldom get what you see. Nature is far from obvious. The waves on the ocean may seem to be travelling, but the water is mainly going round and round in tiny circles. (If it wasn’t, the land would quickly be swamped.) The Sun may appear to orbit the Earth, but actually it’s the other way round. Mountains, apparently solid and stable, rise and fall over geological timescales. Continents move. Stars explode. So the explanation ‘it appears designed because it is designed’ is a bit too trite, a bit too obvious, a bit too shallow. That doesn’t prove it’s wrong, but it gives us pause.