After a week with student friends at Barmouth, Darwin returned home on 29 August to find a letter from Henslow proposing him as a suitable (if unfinished) gentleman naturalist for a self-funded supernumerary place on HMS Beagle with captain Robert FitzRoy, more as a companion than a mere collector. The ship was to leave in four weeks on an expedition to chart the coastline of South America.[33]Robert Darwin objected to his son's planned two-year voyage, regarding it as a waste of time, but was persuaded by his brother-in-law, Josiah Wedgwood, to agree to (and fund) his son's participation.[34]Darwin took care to remain in a private capacity to retain control over his collection: the ship's surgeon Robert McCormick expected to be the official naturalist.[35]
After delays, the voyage began on 27 December 1831; it lasted almost five years. As FitzRoy had intended, Darwin spent most of that time on land investigating geology and making natural history collections, while the Beagle surveyed and chartedcoasts.[9][36] He kept careful notes of his observations and theoretical speculations, and at intervals during the voyage his specimens were sent to Cambridge together with letters including a copy of his journalfor his family.[37] He had some expertise in geology, beetle collecting and dissecting marine invertebrates, but in all other areas was a novice and ably collected specimens for expert appraisal.[38] Despite suffering badly from seasickness, Darwin wrote copious notes while on board the ship. Most of his zoology notes are about marine invertebrates, starting with planktoncollected in a calm spell.[36][39]
On their first stop ashore at St Jago in Cape Verde, Darwin found that a white band high in the volcanic rock cliffs included seashells. FitzRoy had given him the first volume of Charles Lyell's Principles of Geology, which set out uniformitarian concepts of land slowly rising or falling over immense periods,[II]and Darwin saw things Lyell's way, theorising and thinking of writing a book on geology.[40]
When they reached Brazil, Darwin was delighted by the tropical forest,[41] but detested the sight of slavery.[42] McCormick left the ship at this point, feeling that Darwin had supplanted him as naturalist.[35]
The survey continued to the south in Patagonia. They stopped at Bahía Blanca, and in cliffs near Punta AltaDarwin made a major find of fossil bones of huge extinct mammals beside modern seashells, indicating recent extinction with no signs of change in climate or catastrophe. He identified the little-known Megatherium by a tooth and its association with bony armour, which had at first seemed to him to be like a giant version of the armour on local armadillos. The finds brought great interest when they reached England.[43][44]
On rides with gauchos into the interior to explore geology and collect more fossils, Darwin gained social, political and anthropological insights into both native and colonial people at a time of revolution, and learnt that two types of rhea had separate but overlapping territories.[45][46] Further south, he saw stepped plains of shingle and seashells as raised beaches showing a series of elevations. He read Lyell's second volume and accepted its view of "centres of creation" of species, but his discoveries and theorising challenged Lyell's ideas of smooth continuity and of extinction of species.[47][48]
Three Fuegians on board had been seized during the first Beagle voyage, then during a year in England were educated as missionaries. Darwin found them friendly and civilised, yet at Tierra del Fuego he met "miserable, degraded savages", as different as wild from domesticated animals.[49] He remained convinced that, despite this diversity, all humans were interrelated with a shared origin and potential for improvement towards civilisation. Unlike his scientist friends, he now thought there was no unbridgeable gap between humans and animals.[50]A year on, the mission had been abandoned. The Fuegian they had named Jemmy Button lived like the other natives, had a wife, and had no wish to return to England.[51]
Darwin experienced an earthquake in Chile and saw signs that the land had just been raised, including mussel-beds stranded above high tide. High in the Andes he saw seashells, and several fossil trees that had grown on a sand beach. He theorised that as the land rose, oceanic islands sank, and coral reefsround them grew to form atolls.[52][53]
On the geologically new Galápagos Islands, Darwin looked for evidence attaching wildlife to an older "centre of creation", and found mockingbirds allied to those in Chile but differing from island to island. He heard that slight variations in the shape of tortoiseshells showed which island they came from, but failed to collect them, even after eating tortoises taken on board as food.[54][55] In Australia, the marsupial rat-kangaroo and the platypus seemed so unusual that Darwin thought it was almost as though two distinct Creator