Darwin's field notes on the Galapagos: 'A little world within itself'
Charles Darwin's visit to the Galapagos in 1835 is one of the most famous few weeks in the history of science. Scholars today differ in their view of the impact of the islands on the young Darwin; all agree however that the animals and plants he saw there contributed significantly to his becoming an evolutionist. He wrote in Journal of researches, p. 454): 'The natural history of this archipelago is very remarkable: it seems to be a little world within itself.' As is well known, Darwin started to develop his theory of evolution by natural selection within two years of the Beagle's return to England in 1836, and his 1859 book the Origin of species was the pivot about which most of the scientific community was persuaded to accept evolution during the 1860s (see Sulloway 1982b for a full discussion of Darwin's 'conversion').
There is now a considerable body of literature concerning Darwin's visit to the Galapagos, in which the most tightly focused study is Estes et al. 2000. We would also draw attention to the large amount of research on this topic by the late David Stanbury which, although never published in full, is happily now available for study at Christ's College, Cambridge. We believe Stanbury was the first scholar to realise that Darwin probably saw Halley's Comet while in the Galapagos. (The comet was at its minimum distance from Earth on 13 October 1835, while Darwin was on James Island (now Santiago, see below on island names), and he should have been able to see it with the naked eye immediately after sunset on any clear evening at about that time. Since we believe he had access to the Nautical Almanac for 1833 which included a chart showing the comet's predicted path, and he may have had a telescope, the reference to 'Comet' in almost his last field note on the Galapagos (the Galapagos Notebook, p. 50b.) is a strong indication that he saw it.
The basic facts of the Beagle's visit bear retelling. The first suggestion that the ship might visit the Galapagos was made by her captain, Robert FitzRoy, to Admiral Beaufort, Hydrographer to the Royal Navy, before Beaufort issued the Admiralty's instructions for the voyage (letter from FitzRoy to Beaufort of 6 September, 1831, Admiralty Hydrographic Office). Beaufort then suggested that if convenient, Captain FitzRoy 'should run for the Galapagos, and, if the season permits, survey that knot of islands.' (Admiralty instructions and memorandum in Narrative 1.) FitzRoy had Darwin with him on the voyage as ship's naturalist and gentleman companion. At the start of the voyage Darwin was twenty-two; he had some experience of collecting beetles and small sea creatures, and was fast developing a strong interest in geology, but he saw himself rightly as a novice in all other areas of natural history. His plan for the Beagle voyage was twofold — to continue his own investigations of geology and marine invertebrates, and to collect specimens of other organisms that might be new to science, for experts to examine and describe on the Beagle's return to England.
The Beagle was in the Galapagos for five weeks, from 15 September to 20 October 1835, and made a series of charts which were still in use by mariners in the 1940s. Darwin spent about nineteen days ashore, on Chatham Island (now San Cristobal) (Galapagos Notebook, p. 18b), Charles (now Floreana) (p. 34b), Albemarle (now Isabela) (p. 29a) and James (now Santiago) (p. 36b).
Darwin's use of his field notebooks during the voyage is explained in the general introduction to the notebooks. The one he used on the Galapagos is labelled 'Galapagos. Otaheite Lima'. It contains entries he made between January and November 1835 when he was in Chile, Peru, the Galapagos and Tahiti. The Galapagos entries, which comprise about one quarter of the book, consist of one sequence of 34 pages filled in consecutively while Darwin was in the Galapagos (pp. 18b to 51b), and some brief notes on four other pages (inside front cover, inside back cover, p. 29a and p. 31a). The notes on the inside back cover and page 29a refer to the Beagle's sailing between Albemarle and Narborough (now Fernandina) on 29 and 30 September and its arrival at Tagus Cove on Albemarle (known to Darwin as Blonde Cove) on the 30th. The note on the inside front cover gives the generic name of the marine and terrestrial iguanas of the Galapagos which Darwin found in the account of the iguanas in Admiral George Byron's Voyage of HMS Blonde (Byron 1826). The note on page 31a which refers to the specimens of trachyte which Darwin collected during his days on James (p. 47b) may have been inserted some time after the Beagle's departure from the Galapagos.
After the voyage Darwin kept the notebook with his other records of his observations and collections, and he took it with them to Down House in Kent when he went to live there in 1842. The Galapagos Notebook is part of English Heritage's Darwin Collection at Down House, but it was stolen from there in the early 1980s and has yet to be recovered. Most fortunately, a microfilm had been made in 1969 and the transcription has been made from the microfilm.
In line with his practice throughout the Beagle voyage, Darwin's field notes on the Galapagos are not a full record of what he saw when he landed on each island but jottings of particular observations and thoughts that he wanted to include in the full notes and specimen lists he would write later at his work-table back on board the Beagle, and felt a need to note down at once in case he forgot any details. Read in this way, the jottings reveal points that were particularly important to him as he worked energetically to observe and collect all he could in the few days he had on the islands before the Beagle sailed on. The notes make clear his fascination with the volcanic formations he was able to study, and his determination to make worthwhile collections of plants and animals for others. They show clearly and vividly how actively he was observing, investigating, comparing and speculating as he explored the islands.
So what exactly did Darwin do while in the Galapagos? Estes et al. 2000 have detailed his itinerary and make several references to the Galapagos Notebook but do not quote from it, and we offer here a broader account with the emphasis on Darwin's scientific activities and how his eventual historic insight into the possibility that species change came after his days of wide-ranging observation and hurried collecting.
While Darwin was in Lima, before the Beagle set sail towards the Galapagos, he wrote to his sister: 'I am very anxious for the Galapagos Islands. I think both the geology and the zoology cannot fail to be very interesting.' (Letter of July 1835 to Caroline Darwin, Correspondence vol. 1, p. 456.) And to his cousin, W. D. Fox, he wrote: 'I look forward to the Galapagos with more interest than any other part of the voyage. They abound with active volcanoes, and, I should hope, contain Tertiary strata.' (Letter of August 1835, Correspondence vol. 1, p. 458.) Darwin's main interest lay in the opportunity to study the craters and lava flows of active volcanoes, an important first for a young geologist like Darwin in the 1830s. In fact he would find the islands to be entirely volcanic, but as he reported in Volcanic islands, p. 114ff, there were some deposits containing marine shells (probably a few million years old (see Estes et al., 2000) which showed that the islands had probably been partially uplifted from the sea.
Darwin also looked forward to collecting natural history specimens on the islands. A number of English naturalists on previous visits had made collections, but he could hope to discover some new species. His mentor at Cambridge University, Professor John Stevens Henslow, had introduced him to the study of the geographical distribution of species; Henslow had explained the special interest of the strange links between the flora and fauna of oceanic islands and the continents they were close to, and the Galapagos were an obvious case for further study. Darwin made a special effort to collect the plants of the four islands he visited. Darwin wrote to Henslow four months after leaving the Galapagos, that he had 'worked hard' there. 'Amongst other things, I collected every plant which I could see in flower, and as it was the flowering season, I hope my collection may be of some interest to you.' (Correspondence vol. 1, p. 485.)
The Beagle anchored first off Chatham Island. During the eight days Captain FitzRoy spent surveying the coast, Darwin made five landings, starting on Wednesday 16 September near what is now Puerto Baquerizo Moreno (Galapagos Notebook, p. 18b). His entries in the field notebook suggest that his main interest on Chatham was to explore a 'craterised district' that had struck him when he first saw it from a distance. He made detailed geological notes on the craters, their formation and the lava flows around them that appeared to have been frozen in an instant (p. 19b). He noted that three quarters of the plants were in flower (p. 31b), an essential point for botanical collecting. During one landing he found ten plant species though most of them were, as he was to phrase it in Journal of researches, p. 454, 'such wretched-looking little weeds' that they 'would have better become an arctic than an equatorial Flora.' He was very impressed by the reptile life – the tortoises and iguanas, and opened a brief entry on them with a characteristically personal remark: 'Met an immense Turpin; took little notice of me.' (Galapagos Notebook, p. 20b.)
His first field note on a bird of the Galapagos was to prove historic. On the day he studied the craterised district, he also jotted down: 'The Thenca very tame & curious in these Islds. I certainly recognise S. America in ornithology; would a botanist?' (p. 30b.) 'Thenca' is the Spanish name for the thrush-like mockingbird of the west coast of South America with which Darwin had become familiar as the Beagle sailed up from Chile to Peru. He now caught one of the 'tame and curious' birds and recorded later in his list of specimens that it was from Chatham Island (Keynes ed. 2000, p. 414). The point of interest in Darwin's field note is how he linked the Galapagos bird with its counterparts on the mainland, and asked himself at once whether there might be similar likenesses between the plants of the continent and those of the archipelago. The entry shows that as he worked in the field on one of his first landings on the islands, he was already keenly interested in features that might bear on the global issue of species and their geographical distribution, and wanted to be sure to remember one key question that had come to mind as he explored. When he wrote to Henslow three months later about his collection of Galapagos plants, he picked up the point: 'I shall be very curious to know whether the Flora belongs to America, or is peculiar.' (Correspondence vol. 1, p. 485.)
The Beagle sailed next to Charles Island where Darwin spent three days exploring and collecting 'all the animals, plants, insects and reptiles from this Island' (Beagle diary). He made a few short entries in the field notebook to help him recall a number of points for comment in his diary (Galapagos Notebook, p. 34b). He also made an observation and heard a passing remark that were to be significant for his later insight into the species issue. One of the birds he found was another mockingbird and, as he was to record later in Birds, p. 63, he 'fortunately happened to observe' that it differed markedly from his Chatham Island specimen, and from that point on, he paid 'particular attention to their collection'. When he entered the bird in his list of specimens, he recorded the island where he had found it (Keynes ed. 2000, p. 414). The remark was made by the English Vice-Governor, Nicholas Lawson, who met the Beagle crew by chance when they landed. In a conversation about the giant Galapagos tortoises of which there were small numbers on the island, Lawson said that the tortoises on different islands showed 'slight variations in the form of the shell'. He claimed that he could, 'on seeing a tortoise, pronounce with certainty from which island it has been brought' (ibid. p. 291). It is not clear whether Darwin attached any significance to the remark at the time, but he was to remember it later.
On 29 September the Beagle reached Albemarle Island and the next day the ship anchored in the inlet Darwin knew as Blonde Cove, now Tagus Cove. Darwin landed on 1 October to examine the volcanic terrain. As on Charles Island, he collected plants and animals, including another mockingbird which he recorded later in his zoology notes and specimen list (Zoology notes, pp. 298, 416), again identifying the island, but he made only a few brief jottings in his field notebook (Galapagos Notebook inside back cover, p. 29a, p. 34b and p. 35b). On 3 October the Beagle stood round the north end of Albemarle, and then sailed eastwards to survey the coasts of Abingdon (now Pinta), Tower (Genovesa) and Bindloe (Marchena) Islands. On 8 October she reached James Island, and Darwin was able to go ashore with his servant Syms Covington, the Captain's servant Harry Fuller, and the ship's surgeon Benjamin Bynoe, for a stay of nine days while the Beagle returned to Chatham and Charles for water and provisions.
During their time on James Island, Darwin explored inland and collected specimens with help from the others, and from 12 October to the Beagle's departure on 18 October, he made a number of entries in the field notebook (pp. 36b to 51b). He was struck by the extraordinary numbers of giant tortoises; he made detailed observations of their drinking and feeding, and calculated their 'quickness of travelling' with a column of figures. He and his companions were given tortoise meat and found that it was delicious in soup.
Two sets of jottings by Darwin on 12 and 14 October are linked with his eventual glimpse of the key the Galapagos were to provide to the understanding that species change. On page 40b he noticed a 'Thenca' on the island and noted how it 'eats bits of meat'. (The point was significant to him because he remembered seeing a mockingbird on the mainland of South America behaving in just the same way (see Birds, p. 64.)) He opened his entry on page 42b: 'Wandered about Bird collecting. Iguana … Eats much cactus: … Small Finc[h] picking from same piece after alights on back.' Darwin was clearly completing his bird-collecting, but not apparently with any single focus. He was observing mockingbirds on the island; he caught one and added it to his specimen list, yet again noting the island. He was also observing and collecting finches and other birds.
Finally on 17 October the Beagle sent in two boats to bring the shore party back on board for their voyage out into the Pacific and eventually home to England. This is the moment shown in John Chancellor's well-known painting. (See right) (Estes et al. 2000 mention only one boat but the Captain's log is clear on this point.)
As the Beagle sailed for Tahiti, Darwin had a few days to order and record his Galapagos specimens before the next landfall. Ten years later, in the second edition of Journal of researches (2d ed., p. 394), he explained what happened next. When he compared together 'the numerous specimens, shot by myself and several other parties on board, of the mocking-thrushes', 'to my astonishment, I discovered that all those from Charles Island belonged to one species, … all from Albemarle Island to [another] and all from James and Chatham Islands to [a third].' He wrote in his zoological notes (Zoology notes, p. 298: 'This bird which is so closely allied to the Thenca of Chili … is singular from existing as varieties or distinct species in the different islands. … This is a parallel fact to the one mentioned about the tortoises.' The connection with Lawson's remark about the tortoises is the clue to what Darwin had in mind at this juncture — deep patterns in the distribution of species that reach between whole classes of the animal kingdom. He wrote in 1845 (Journal of researches 2d ed., p. 394): 'I never dreamed that islands about 50 or 60 miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted; but we shall soon see that this is the case. It is the fate of most voyagers, no sooner to discover what is most interesting in any locality, than they are hurried from it; but I ought, perhaps, to be thankful that I obtained sufficient materials to establish this most remarkable fact in the distribution of organic beings.'
As the Beagle sailed home towards England during June and July 1836, Darwin had time to prepare those sets of specimens that he would need to hand over to other experts for examination. He took his specimen lists and zoological notes and drew up separate sets of notes for mammals, birds, insects, shells, plants, reptiles, crustaceans and fish, expanding on his former entries when he now had more to say. He needed an expert ornithologist's verdict on his birds, especially his judgement that the three Galapagos mockingbirds should be counted as separate species, and wrote about the mockingbirds in his notes to accompany the specimens ('Ornithological notes', p. 262): 'I have specimens from four of the larger Islands; [two already enumerated], and (3349: female. Albemarle Isd.) and (3350: male: James Isd). The specimens from Chatham and Albemarle Island appear to be the same, but the other two are different. In each island, each kind is exclusively found: habits of all are indistinguishable.' He now developed his brief comment in his zoological notes about the parallel between the mockingbirds and the tortoises.
When I recollect the fact that [from] the form of the body, shape of scales and general size, the Spaniards can at once pronounce from which island any tortoise may have been brought; when I see these islands in sight of each other and possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure and filling the same place in nature; I must suspect they are only varieties. The only fact of a similar kind of which I am aware, is the constant asserted difference between the wolf-like fox of East and West Falkland Islands. If there is the slightest foundation for these remarks, the zoology of archipelagoes will be well worth examining; for such facts would undermine the stability of species.
This passage is generally recognized as Darwin's first statement pointing directly from his findings on the Galapagos towards the possibility that species change, but his meaning is unclear as the wording and grammatical construction are ambiguous. Taking into account what he had been told and found for himself on the Galapagos, and his later conclusions from his findings, he may possibly have been saying at this point that if the remarks made about the Galapagos tortoises and Falklands foxes had any basis in truth, it would be well worth conducting further zoological studies of the Galapagos mockingbirds and any other comparable patterns in other archipelagoes because the facts such studies might reveal of species differences emerging between organisms separated only by island barriers would undermine assumptions about the fixity of species.
On his return to London, Darwin offered his collection of bird specimens to John Gould, an ambitious young bird illustrator who was rapidly building a reputation as an ornithologist. Gould responded quickly and positively with a series of presentations of the specimens at meetings of the Zoological Society of London. Gould confirmed Darwin's suggestion that there were three species of mockingbird in his Galapagos collection, though he changed the grouping of two of the specimens. He also pointed out to Darwin that the many birds he had identified as finches and collected on the different islands, often without recording which, should be grouped together with a number of other birds Darwin had identified as wrens, 'gross-beaks' and 'Icteruses' (relatives of blackbirds) as 'a series of ground Finches which are so peculiar as to form an entire new group containing twelve new species' (Gould 1837, p. 4). Darwin was fascinated at once by what the new grouping revealed about possible evolutionary adaptations in the archipelago but found that he could not study the distribution of the finches between islands because he had failed to identify on which one he had collected many of his specimens. Gould's report was the first account in the long and complicated story of 'Darwin's finches' which has distorted the general understanding of Darwin's work in the Galapagos in recent years. See Sulloway 1982a. Darwin's interest in the finches lies outside the scope of this introduction because, as Sulloway has explained, Darwin did not recognize the issues that they posed while he was on the Galapagos. His primary concern until Gould's report in 1837 was the mockingbirds, as explained above.
Through 1837 and 1838 Darwin thought to himself about the fixity or mutability of species and the implications of the Galapagos mockingbirds for the possibility that they might change. In the summer of 1837 he started a series of private writings on the subject. He wrote in his journal (DAR158.1-76, p. 13)
In July opened first note Book on "transmutation of Species". — Had been greatly struck from about month of previous March on character of S. American fossils—& species on Galapagos Archipelago. — These facts origin (especially latter) of all my views.
He referred to his point about the Galapagos in a passage on the seventh page of the first transmutation notebook: 'Let a pair be introduced [to an area] and increase slowly, from many enemies, so as often to intermarry; who will dare say what result? According to this view, animals on separate islands ought to become different if kept long enough apart, with slightly different circumstances. Now Galapagos tortoises, mockingbirds, Falkland fox, Chiloe fox, English and Irish hare.' And thirty pages later in the notebook, he drew his historic branching diagram showing how different species might be linked to each other by common descent. (Notebook B, pp.172-180.)
Darwin had written in his first note on the 'Thenca' in his field notebook: 'I certainly recognise S. America in ornithology; would a botanist?' When he first noticed the bird on Chatham Island, he thought of parallels with other species and he was already collecting the plants of the island for an analysis of their links with the flora of other regions. As he developed his ideas about evolution in the late 1830s and early 1840s, he became more and more confident in their power to explain, but the evidence on which they were based needed to be built up before he could put them to others. The three species of mockingbirds on three Pacific islands would not be enough to persuade. He had given his collection of Galapagos plants to Henslow shortly after his return to England and had been pressing him ever since to analyse and report on them, but Henslow did not find the time. In 1843 Darwin finally lost patience with his teacher and arranged for the young botanist Joseph Dalton Hooker to take over the task. Darwin was eager to hear how many species were shared with South America, how many were unique to the Galapagos and how many were unique to a single island. Hooker found that the flora had many close and clear links with the plants of South America, and his conclusions on the distinctiveness of the archipelago and individual islands were astonishing. Of a total of 217 species collected, he found that 109 were confined to the archipelago and 85 of those were confined to a single island. (See Journal of researches 2d ed., pp. 395-397.)
Darwin's eventual conclusions stemming from his first question about the birds and plants of the Galapagos were to feature in one of the most important passages in Origin of species (pp. 397-406). The passage ended with one of his key points about evolution by natural selection:
The relations just discussed … [including] the very close relation of the distinct species which inhabit the islets of the same archipelago, and especially the striking relation of the inhabitants of each whole archipelago or island to those of the nearest mainland, are, I think, utterly inexplicable on the ordinary view of the independent creation of each species, but are explicable on the view of colonisation from the nearest and readiest source, together with the subsequent modification and better adaptation of the colonists to their new homes.
We wish to acknowledge the help we have received in the preparation of this article from Cambridge University Library and from Darwin Online. We also thank Thalia Grant for her advice on Darwin's collecting on Charles Island, and English Heritage and the Darwin family for permission to quote from the notebook.
Gordon Chancellor and Randal Keynes