Beginning on 27 December 1831, the voyage lasted almost five years and, as FitzRoy had intended, Darwin spent most of that time on land investigating geology and making natural history collections, while the Beagle surveyed and charted coasts. 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 journal for his family. 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. 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 plankton collected in a calm spell.
On their first stop ashore at St. Jago, 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, and Darwin saw things Lyell's way, theorising and thinking of writing a book on geology. In Brazil Darwin was delighted by the tropical forest, but detested the sight of slavery.
At Punta Alta in Patagonia he made a major find of fossil bones of huge extinct mammals in cliffs 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 like a giant version of the armour on local armadillos. The finds brought great interest when they reached England. On rides with gauchos into the interior to explore geology and collect more fossils he 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. 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.
Three Fuegians on board, who had been seized during the first Beagle voyage and had spent a year in England, were taken back to Tierra del Fuego as missionaries. Darwin found them friendly and civilised, yet their relatives seemed "miserable, degraded savages", as different as wild from domesticated animals. To Darwin the difference showed cultural advances, not racial inferiority. Unlike his scientist friends, he now thought there was no unbridgeable gap between humans and animals. 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.
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 reefs round them grew to form atolls.
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 tortoise shells showed which island they came from, but failed to collect them, even after eating tortoises taken on board as food. In Australia the marsupial rat-kangaroo and the platypus seemed so unusual that Darwin thought it was almost as though two distinct Creators had been at work. He found the Aborigines "good-humoured & pleasant", and noted their depletion by European settlement.
The Beagle investigated how the atolls of the Cocos (Keeling) Islands had formed, and the survey supported Darwin's theorising. FitzRoy began writing the official Narrative of the Beagle voyages, and after reading Darwin's diary he proposed incorporating it into the account. Darwin's Journal was eventually rewritten as a separate third volume, on natural history.
In Cape Town Darwin and FitzRoy met John Herschel, who had recently written to Lyell praising his uniformitarianism as opening bold speculation on "that mystery of mysteries, the replacement of extinct species by others" as "a natural in contradistinction to a miraculous process". When organising his notes as the ship sailed home, Darwin wrote that if his growing suspicions about the mockingbirds, the tortoises and the Falkland Islands Fox were correct, "such facts undermine the stability of Species", then cautiously added "would" before "undermine". He later wrote that such facts "seemed to me to throw some light on the origin of species"
Inception of Darwin's evolutionary theory
When the Beagle reached Falmouth, Cornwall, on 2 October 1836, Darwin was already a celebrity in scientific circles as in December 1835 Henslow had fostered his former pupil's reputation by giving selected naturalists a pamphlet of Darwin's geological letters. Darwin visited his home in Shrewsbury and saw relatives, then hurried to Cambridge to see Henslow, who advised on finding naturalists available to catalogue the collections and agreed to take on the botanical specimens. Darwin's father organised investments, enabling his son to be a self-funded gentleman scientist, and an excited Darwin went round the London institutions being fêted and seeking experts to describe the collections. Zoologists had a huge backlog of work, and there was a danger of specimens just being left in storage.
Charles Lyell eagerly met Darwin for the first time on 29 October and soon introduced him to the up-and-coming anatomist Richard Owen, who had the facilities of the Royal College of Surgeons to work on the fossil bones collected by Darwin. Owen's surprising results included other gigantic extinct ground sloths as well as the Megatherium, a near complete skeleton of the unknown Scelidotherium and a hippopotamus-sized rodent-like skull named Toxodon resembling a giant capybara. The armour fragments were actually from Glyptodon, a huge armadillo-like creature as Darwin had initially thought. These extinct creatures were related to living species in South America.
In mid-December Darwin took lodgings in Cambridge to organise work on his collections and rewrite his Journal. He wrote his first paper, showing that the South American landmass was slowly rising, and with Lyell's enthusiastic backing read it to the Geological Society of London on 4 January 1837. On the same day, he presented his mammal and bird specimens to the Zoological Society. The ornithologist John Gould soon announced that the Galapagos birds that Darwin had thought a mixture of blackbirds, "gros-beaks" and finches, were, in fact, twelve separate species of finches. On 17 February Darwin was elected to the Council of the Geological Society, and Lyell's presidential address presented Owen's findings on Darwin's fossils, stressing geographical continuity of species as supporting his uniformitarian ideas.
Early in March, Darwin moved to London to be near this work, joining Lyell's social circle of scientists and experts such as Charles Babbage, who described God as a programmer of laws. Darwin stayed with his freethinking brother Erasmus, part of this Whig circle and close friend of writer Harriet Martineau who promoted Malthusianism underlying the controversial Whig Poor Law reforms to stop welfare from causing overpopulation and more poverty. As a Unitarian she welcomed the radical implications of transmutation of species, promoted by Grant and younger surgeons influenced by Geoffroy. Transmutation was anathema to Anglicans defending social order, but reputable scientists openly discussed the subject and there was wide interest in John Herschel's letter praising Lyell's approach as a way to find a natural cause of the origin of new species.
Gould met Darwin and told him that the Galápagos mockingbirds from different islands were separate species, not just varieties, and what Darwin had thought was a "wren" was also in the finch group. Darwin had not labelled the finches by island, but from the notes of others on the Beagle, including FitzRoy, he allocated species to islands. The two rheas were also distinct species, and on 14 March Darwin announced how their distribution changed going southwards.
By mid-March, Darwin was speculating in his Red Notebook on the possibility that "one species does change into another" to explain the geographical distribution of living species such as the rheas, and extinct ones such as the strange Macrauchenia which resembled a giant guanaco. His thoughts on lifespan, asexual reproduction and sexual reproduction developed in his "B" notebook around mid-July on to variation in offspring "to adapt & alter the race to changing world" explaining the Galápagos tortoises, mockingbirds and rheas. He sketched branching descent, then a genealogical branching of a single evolutionary tree, in which "It is absurd to talk of one animal being higher than another", discarding Lamarck's independent lineages progressing to higher forms.
Coyne, Jerry A. (2009). Why Evolution is True. Viking. pp. 8–11. ISBN 978-0-670-02053-9.
Larson 2004, pp. 79–111
Coyne, Jerry A. (2009). Why Evolution is True. Oxford: Oxford University Press. p. 17. ISBN 0-19-923084-6. "In The Origin, Darwin provided an alternative hypothesis for the development, diversification, and design of life. Much of that book presents evidence that not only supports evolution but at the same time refutes creationism. In Darwin's day, the evidence for his theories was compelling but not completely decisive."
Glass, Bentley (1959). Forerunners of Darwin. Baltimore, MD: Johns Hopkins University Press. p. iv. ISBN 0-8018-0222-9. "Darwin's solution is a magnificent synthesis of evidence...a synthesis...compelling in honesty and comprehensiveness"
The Complete Works of Darwin Online – Biography. darwin-online.org.uk. Retrieved on 2006-12-15
As Darwinian scholar Joseph Carroll of the University of Missouri–St. Louis puts it in his introduction to a modern reprint of Darwin's work: "The Origin of Species has special claims on our attention. It is one of the two or three most significant works of all time—one of those works that fundamentally and permanently alter our vision of the world...It is argued with a singularly rigorous consistency but it is also eloquent, imaginatively evocative, and rhetorically compelling." Carroll, Joseph, ed. (2003). On the origin of species by means of natural selection. Peterborough, Ontario: Broadview. p. 15. ISBN 1-55111-337-6.
Leff 2000, About Charles Darwin
Desmond & Moore 1991, pp. 210, 284–285
Desmond & Moore 1991, pp. 263–274
van Wyhe 2007, pp. 184, 187
Beddall, B. G. (1968). "Wallace, Darwin, and the Theory of Natural Selection" (PDF). Journal of the History of Biology 1 (2): 261–323. doi:10.1007/BF00351923.
Leff 2000, Darwin's Burial
van Wyhe 2008b, pp. 60–61
"Special feature: Darwin 200". New Scientist. Retrieved 2 April 2011.
Hart, Michael H. (2000). The 100: A Ranking of the Most Influential Persons in History. New York: Citadel. ISBN 0-89104-175-3.
John H. Wahlert (11 June 2001). "The Mount House, Shrewsbury, England (Charles Darwin)". Darwin and Darwinism. Baruch College. Retrieved 26 November 2008.
Gordon Chancellor; Randal Keynes (October 2006). "Darwin's field notes on the Galapagos: 'A little world within itself'". Darwin Online. Retrieved 16 September 2009.
"Darwin Online: 'Hurrah Chiloe': an introduction to the Port Desire Notebook". Retrieved 24 October 2008.
"Darwin Online: Coccatoos & Crows: An introduction to the Sydney Notebook". Retrieved 2 January 2009.
"Darwin Correspondence Project – Letter 301 – Darwin, C.R. to Darwin, C.S., 29 Apr 1836"
Colp, Ralph. "Darwin's Illness". Retrieved 24 June 2012-2014.
Darwin, Emma (1882). "[Reminiscences of Charles Darwin's last years. CUL-DAR210.9"]. Retrieved 8 January 2009.
"Darwin Correspondence Project – Letter 346 – Darwin, C. R. to Darwin, C. S., 27 Feb 1837". Retrieved 19 December 2008. proposes a move on Friday 3 March 1837, Darwin's Journal (Darwin 2006, pp. 12 verso) backdated from August 1838 gives a date of 6 March 1837
Desmond & Moore 1991, pp. 201, 212–221
Sulloway 1982, pp. 9, 20–23
Browne 1995, p. 360
"Darwin, C. R. (Read 14 March 1837) Notes on Rhea americana and Rhea darwinii, Proceedings of the Zoological Society of London". Retrieved 17 December 2008.