Science of Discworld III

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, hemade 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