Science of Discworld III

by Terry Pratchett

  Charles decided to accept the offer, but his father, forewarned by Charles’s sisters, refused permission. Darwin could have gone against his father’s wishes, but the thought made him feel very uncomfortable, so he wrote to the Navy and turned the job down. Then, uncharacteristically, his father opened a loophole – our first example of what looks suspiciously like wizardly interference. Charles might yet be allowed to go, he said, provided ‘some person of good standing’ recommended it. Both Charles and his father knew who was meant: Uncle Jos (Wedgwood, grandson of the founder of the pottery company). Jos was an industrialist, and Dr Darwin trusted his judgement. So Charles and his uncle sat up very late, composing a suitable letter. Jos told Dr. Darwin that such a voyage would be the making of the young man. And, slyly, he added that it would improve his knowledge of natural history, which would be very useful for a subsequent career in the clergy.

  Darwin Senior relented (score one to the wizards). Excited beyond measure, Charles hurriedly wrote another letter to the Navy, this time accepting. But then he heard from FitzRoy, who told him that the post was no longer vacant. The captain had given it to a friend. However, Darwin was top of the list if his friend changed his mind.

  Darwin went to London, to make contingency plans in case he got lucky, and to keep an appointment with FitzRoy. He arrived to be told that the captain’s friend had changed his mind, not five minutes earlier. (Wizards again?) His wife had objected to the length of the voyage, then planned to be three years. Did Darwin still want the job?

  Lost for words, Charles nodded.

  Darwin’s heart sank when he saw the ship. The Beagle was a rotting, eleven-year-old brig, with ten guns. It was being rebuilt, partly at FitzRoy’s own expense, so it would be seaworthy enough. But the ship was cramped, a mere 90 feet (30m) long by 24 feet (8m) wide. Could his companionship with the captain survive such a lengthy voyage in such close contact? Fortunately, he was allocated one of the larger cabins.

  The Beagle’s assignment was to survey the southern end of South America, in particular the complicated islands around Tierra del Fuego. The Admiralty had provided 11 chronometers for navigation, because the trip would be the first attempt to circumnavigate the Globe using marine chronometers to find longitude. FitzRoy borrowed five more, then bought six himself. So the Beagle sailed with a massive 22 chronometers on board.

  The voyage started badly. Darwin was sick as a dog, crossing the Bay of Biscay, and had to endure the sound of sailors being flogged as he lay nauseated in his hammock. FitzRoy was hot on discipline, especially at the beginning of a voyage. Privately, the captain expected his ‘companion’ to jump ship the moment it touched land, and hotfoot it back to England. The ship was supposed to put in at Madeira to take on fresh food, which would be the perfect opportunity. But the Madeira landing was cancelled because the sea was too heavy and there was no pressing need (score 3 to the wizards?). Instead, the Beagle headed for Tenerife in the Canaries. If Charles jumped ship there, he could see the volcanoes and the Great Dragon Tree. But the consul in Santa Cruz was scared that visitors from England might introduce cholera to his islands, and he refused the Beagle permission to put into port without undergoing quarantine (score 4? We’ll see). Unwilling to wait off land for the required two weeks, FitzRoy ordered the Beagle south, to the Cape Verde Islands.

  It may not have been the wizards at work, but something was determined that Charles should stay on the Beagle. And now, a fifth coincidence, involving his great love, geology, made it impossible for him to do anything else. As the Beagle sailed westward, the ocean grew calm, the air warm. Darwin could trawl for plankton and jellyfish with home-made gauze nets. Things were looking up. And when they finally touched land, the island of St Jago in the Cape Verde Islands, Darwin found it hard to believe his luck. St Jago was a rugged volcanic outcrop, with conical volcanoes and lush valleys. Charles could do geology. And natural history.

  He collected everything. He noticed that an octopus can change colour, and mistakenly thought this was a new discovery. After two days, he had worked out the geological history of the island, using the principles he had learned from Lyell. Lava had flowed over the seabed, trapping shells and other debris, and had later been raised to the surface. All of this must have happened relatively recently, because the shells were just like the fresh ones lying on the beach. This was not the conventional theory of the day, which held that volcanic structures were incredibly old.

  The young man was coming into his own.

  In the end, the voyage lasted five years, and in the whole of that time, poor Darwin never found his sea-legs. Even on the final run home, he was still seasick. But he contrived to spend most of the voyage on land, and only 18 months at sea. And while on land, he made discovery after discovery. He found fifteen new species of flat-worm in Brazil. He studied rheas, giant flightless birds related to the ostrich, in Argentina. There, too, he found fossils, including the head of a giant armadillo-like glyptodont. In Tierra del Fuego he turned anthropologist, and studied the people. ‘I shall never forget how savage & wild one group was,’ he wrote, on encountering ‘naked savages’. He found more fossils, among them bones of the ground-sloth Megatherium and the llama-like Macrauchenia. In Chile, he studied the geology of the Andes and decided that they, and the plains beyond, had been thrust skyward in some gigantic geological upheaval.

  From the South American mainland, the Beagle went north-west to the Galápagos, a tight group of a dozen or so islands, far out into the Pacific ocean. The islands had fascinating geology, mainly volcanic, and a great variety of animals that were not found anywhere else. There were the spectacular giant tortoises that had given the islands their name. Darwin measured the circumference of one as seven feet (2m). There were iguanas, and birds – boobies, warblers, finches. The finches had beaks of different shapes and sizes, depending on the food they ate, and Darwin divided them up into a series of subfamilies. He did not notice that different types of animals occurred on different islands, until Nicholas Lawson pointed this out. (The wizards again? Oh yes, this will have happened soon …) But he did notice that the mockingbirds of Charles and Chatham islands (now Santa Maria and San Cristobál) were different species, and when, now alerted, he looked on James Island (San Salvador), he found yet a third species. But Darwin was not greatly interested in small variations in species, or how those variations corresponded to the local geography. He was vaguely aware of some theorising about species change, or ‘transmutation’, if only from his grandfather Erasmus, but the topic didn’t interest him and he saw no reason to collect evidence for or against it.

  And so the Beagle continued to Tahiti, New Zealand, and Australia. Darwin had seen wonders that would shortly revolutionise the world. But he did not yet understand what he had seen.

  In Tahiti, though, he glimpsed his first coral reef. Before leaving Australia, he was determined to find out how coral islands came into being. Lyell had suggested that because the coral animals live only in shallow waters, with ample sunlight, the reefs must be built on top of submerged volcanoes. This also explained their ringed shape. Darwin didn’t believe Lyell’s theory. ‘The idea of a lagoon island, 30 miles in diameter being based on a submarine crater of equal dimensions, has always appeared to me to be a monstrous hypothesis.’ Instead, he had his own theory. He already knew that land could rise, he’d seen that in the Andes. He reasoned that if some land went up, then other land ought to go down, to maintain the balance of the Earth’s crust. Suppose that when the reef started to form, the water was shallow, but then the ocean floor started descending slowly, while the coral polyps at the surface continued building the reef. Then eventually you would get a huge mountain of coral rising from what was now the ocean depths – all built by tiny creatures, always in shallow water while the building was going on. The shape? That was the result of an island with a fringing reef collapsing. The island would sink, leaving a hole in the middle, but the reef would continue to grow.

  Five years and three days after
the Beagle set sail from Plymouth, Darwin walked into the family home. His father glanced up from his breakfast. ‘Why,’ he said, ‘the shape of his head is quite altered.’

  Darwin did not come up with the concept of evolution during his Beagle voyage. He was too busy amassing specimens, mapping geology, taking notes, and being seasick, to have time to organise his observations into a coherent theory. But when the voyage was over, he was promptly elected to the Royal Geological Society. In January 1837 he presented his inaugural paper, on the geology of Chile’s coast. He suggested that the Andes mountains had originally been the ocean floor, but had later been uplifted. His diary records amazement at ‘the wonderful force which has upheaved these mountains, & even more so the countless ages [needed] to have broken through, removed & levelled whole masses of them’. Much later, the Chilean coast became part of the evidence for ‘continental drift’: we now think that these mountains result from subduction, as the Nazca tectonic plate slides underneath the South American plate.

  Darwin could certainly spot them.

  His interest in geology had other, less obvious, implications. He was starting to wonder about the finches of the Galápagos. They seemed to contradict Lyell’s view that local geological conditions determined what species were created. It was a puzzle.

  In fact, it was more of a puzzle than Darwin thought, because he had misunderstood the finches completely. He thought they all fed on the same food, in big flocks. He had not noticed important differences among their beaks, and he even had trouble identifying different species. Some, he believed, were not finches at all, but wrens and blackbirds. He was so baffled by the birds, and so indifferent to the specimens he had collected, that he donated the lot to the Zoological Society. Within ten days the Society’s bird expert John Gould had worked out that they were all finches, all very closely related, forming a tightly knit grouping that nonetheless contained twelve2 distinct species. This number was surprisingly large for such a small group of tiny islands. What had caused such diversity? Gould wanted to know, but Darwin didn’t care.

  By 1837, Paley’s logic was no longer in vogue. The scientifically literate theist now believed that God had set up the laws of nature at the time of Creation, and that those laws included not just the ‘background’ laws of physics, to which Paley subscribed, but also the development of living creatures, which Paley had denied. The laws of the universe were fixed for all eternity. They had to be, otherwise God’s creation was flawed. Paley’s analogies were used against him. What kind of artificer made such bad machinery that He had to keep tinkering with it all the time to keep it working?

  Science and theology were ripping asunder. The political corruption of the Church was becoming undeniable; now its intellectual claims were also corning under fire. And some radical thinkers, often medics who had studied comparative anatomy and noticed remarkable similarities between the bones of entirely different animals, were engaged in speculation that changed the view of creation itself. According to the Bible, God had created each type of animal as a one-off item – whales and winged fowl on the fifth day, cattle and creeping things and humans on the sixth. But these medical types were starting to think that species could change, ‘transmute’. Species were not fixed for all time. They realised that there was a rather big gap between, say, a banana and a fish. You couldn’t cross that gap in one step. But given enough time, and enough steps …

  Darwin slowly became caught up in the flow. His Red Notebook, where he recorded anything that he saw or that came to mind, began to hint at the ‘mutability of species’. The hints were incomplete and ill-assorted. Deformed babies resembled new species. The beaks of Galápagos finches were of different shapes and sizes. Rheas were a puzzle, though: two distinct species of the giant birds had overlapping ranges in Patagonia. Why didn’t they merge into a single species?

  By July, he had secretly started a new notebook, his B Notebook.

  It was on the transmutation of species.

  By 1839 Darwin was building up a complete picture, and he wrote a 35-page summary of his thinking. A crucial influence was Thomas Malthus, whose 1826 Essay on the Principle of Population pointed out that the unchecked growth of organisms is exponential (or ‘geometric’, in the old-fashioned phrase of the time), whereas that of resources is linear (‘arithmetic’). Exponential growth occurs when each step multiplies the size by some fixed amount, for example 1, 2, 4, 8, 16, 32, where each number is twice the previous one. Linear growth adds some fixed amount at each step, for instance 2, 4, 6, 8, 10, where each number exceeds the previous one by 2. However small the multiplier is in exponential growth, provided it is bigger than 1, and however large the number added in linear growth may be, it turns out that in the long run exponential growth always beats linear. Though it does take some time if the multiplier is close to 1 and the number being added is huge.

  Darwin had taken on board Malthus’s argument, and he had realised that in practice what keeps populations down is competition for resources, such as food and a place to live. This competition, he wrote, leads to ‘natural selection’, in which those creatures that are victorious in the ‘war of nature’ are the ones that produce the next generation. Individual creatures within a species are not exactly identical; those differences make it possible for the force of natural selection to produce slow, gradual changes. How far might such changes go? In Darwin’s view, very far indeed. Far enough to lead to entirely new species, given enough time. And thanks to geology, scientists now knew that the Earth was very, very old.

  Darwin, following family tradition, was a Unitarian. This particular branch of Christianity has been aptly described as ‘people who believe in at most one God’. As a sound Unitarian, he believed that the Deity must work on the grandest of scales. So he finished his summary with a powerful appeal to the Unitarian view of the Deity:

  It is derogatory that the Creator of countless systems of worlds should have created each of the myriads of creeping parasites and slimy worms which have swarmed each day of life on land and water on this one globe. We cease being astonished, however much we may deplore, that a group of animals should have been directly created to lay their eggs in bowels and flesh of others – that some organisms should delight in cruelty … From death, famine, rapine, and the concealed war of nature we can see that the highest good, which we can conceive, the creation of the higher animals has directly come.

  God surely has better taste than to create nasty parasites directly. They exist only because they are a necessary step along the path that leads to cats, dogs, and us.

  Darwin had his hypothesis.

  Now he began to agonise about how to bring it to the waiting world.

  1 In 1865 FitzRoy did exactly the same, having been turned down for a promotion. Narrativium at work?

  2 Now considered to be thirteen, plus a fourteenth on the Cocos Islands. (Look, people write and complain if we don’t point this kind of thing out.)

  ELEVEN

  WIZARDS ON THE WARPATH

  IN THE GLOOM OF THE High Energy Magic building, Hex wrote. Every minute another page slid off the writing table.

  ‘“Boat sunk by collision with Spanish fishing vessel”,’ Ponder Stibbons read out, a tremor in his voice. ‘“Boat shipwrecked on uncharted reef near Madeira. Boat found drifting minus all crew, with the table laid for a meal. Boat catches fire, all lost. Boat struck by meteorite. Darwin accidentally shot by ship’s surgeon and naturalist during a collecting expedition on the island of St Jago. Darwin accidentally shot by ship’s captain. Darwin accidentally shot by himself. Darwin loses place on boat. Darwin leaves boat because of seasickness. Darwin loses notebooks. Darwin stung to death by wasps! Darwin bangs head on underside of table and loses memory …”’ He put down the paper. ‘And these are the more sensible causes.’

  ‘The stone dropping out of the sky was sensible?’ said Ridcully.

  ‘Compared to the attack of the giant squid, Archchancellor, I would say so,’ said Ponder. ‘And the enormou
s waterspout. And the shipwreck off the coast of Norway.’

  ‘Well, ships do get wrecked,’ said the Dean.

  ‘Yes, sir. But the country known as Norway is in the wrong direction. The Beagle would only get there by sailing backwards. Hex is right, sir. This is insane. The moment that we decided to change one simple little history, the whole of the universe is trying to stop the voyage happening! And mathematically speaking, this is illegal!’

  Ponder thumped the table, his face red. The senior wizards shied. This was as unnerving as hearing a sheep roar.

  ‘My word!’ said Ridcully. ‘Is it?’

  ‘Yes! There must be room in phase space for the possibility that Origin gets written! It’s not against the physical laws of this universe!’

  ‘That a young inexperienced man takes a voyage around this world and has an insight that changes mankind’s view of itself?’ said the Dean. ‘You must admit it looks a bit unlikely – sorry, sorry, sorry!’ He backed away as Ponder advanced.

  ‘One of the biggest religions on Roundworld was founded by a carpenter’s son!’ Ponder snarled. ‘For years, the most powerful person on the planet was an actor! There’s got to be room for Darwin!’