Science of Discworld III

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’scoast. 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 twelve 2 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 alsothe 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