The scientific results of the Beagle voyage still dominated Darwin's working life, but throughout these years he broadened his continuing investigations into the nature and origin of species and varieties. In contrast to the received image of Darwin as a recluse in Down, the letters show him to be an established and confident naturalist at the heart of British scientific society, travelling often to London and elsewhere to attend meetings and confer with colleagues, and involved in the social and political activities of the community of savants as well as in its philosophical and scientific pursuits. At home, time was filled with copious natural history work, writing, and gathering information from an ever-expanding network of correspondents. Down House was altered and extended to accommodate Darwin’s growing family and the many relatives and friends who came to stay; and, with his father’s advice, Darwin began a series of judicious financial investments to ensure a comfortable future for all those under his care.
The geological publications
In these years, Darwin published two books on geology, Volcanic islands (1844) and Geological observations on South America (1846), which completed his trilogy on the geological results of the Beagle voyage, and extensively revised his Journal of researches for a second edition in 1845, having already provided corrections in 1844 for a German translation of the first edition. He continued as an officer of the Geological Society of London, acting as one of four vice-presidents in 1844 and remaining on the council from 1845 onwards; he was a conscientious member of the Royal Geographical Society and the Royal Society; he regularly attended meetings and refereed papers for all these organisations. Between 1844 and 1846 Darwin himself wrote ten papers, six of which related to the Beagle collections. Among these were some studies of invertebrates that at first had been intended for publication in The zoology of the voyage of H.M.S. Beagle (1838–43) but were deferred when the Government grant was exhausted (Correspondence vol. 2, letter to A. Y. Spearman, 9 October 1843, n. 1).
Darwin's inner circle: first discussions of species change
In addition, Darwin threw himself into analysing the results emerging from the examination of Beagle plant specimens by the young botanist and traveller, Joseph Dalton Hooker. More than 1200 letters between the two men survive, fully documenting a life-long friendship.
species are not (it is like confessing a murder) immutable
Darwin’s earlier scientific friendships were not neglected either, as the correspondence with Charles Lyell, George Robert Waterhouse, John Stevens Henslow, Leonard Horner, Leonard Jenyns, Edward Forbes, and Richard Owen shows. These friends, with the addition of Hooker, were important to Darwin for—among other things—they were the first people he turned to when he wished to discuss the problems and various scientific issues that arose out of his work on species. Darwin discussed his ideas on species mutability with Hooker, Horner, Jenyns, Lyell, Owen, and Charles James Fox Bunbury; he may well have broached the subject with others. Only two months after their first exchange, early in 1844, Darwin told Hooker that he was engaged in a ‘very presumptuous work’ which had led to the conviction that ‘species are not (it is like confessing a murder) immutable’ (letter to J. D. Hooker, [11 January 1844]). Nine months later, in his letter of 12 October , he explained to Jenyns: 'I have continued steadily reading & collecting facts on variation of domestic animals & plants & on the question of what are species; I have a grand body of facts & I think I can draw some sound conclusions. The general conclusion at which I have slowly been driven from a directly opposite conviction is that species are mutable & that allied species are co-descendants of common stocks. I know how much I open myself, to reproach, for such a conclusion, but I have at least honestly & deliberately come to it.'
It is clear from the correspondence that his close friends were not outraged by Darwin’s heterodox opinions and later in the year both Jenyns and Hooker were invited to read a manuscript essay on his species theory (DAR 113; Foundations, pp. 57–255), an expanded version, completed on 5 July 1844, of a pencil sketch he had drawn up some two years earlier. But although eager for the views of informed colleagues, Darwin was naturally protective of his untried theory and seems to have shied away from the risk of pushing it too early into the open. In the event, it was not until the beginning of 1847 that Hooker was given a fair copy of the essay of 1844 to read (see Correspondence vol. 4, letter to J. D. Hooker, 8 [February 1847]). Darwin can be seen as a cautious strategist, sometimes confident, but often uneasy about his work, and always attempting to gauge the kind of response that his theory of transmutation would generate. In particular, he anxiously watched the controversy seething around an evolutionary book, Vestiges of the natural history of creation, published anonymously in 1844. His old friend Adam Sedgwick attacked the work vehemently in the Edinburgh Review (1845), while other colleagues like Edward Forbes ridiculed the theories employed there, caring only to join in the popular guessing-game about the identity of the author. One candidate, known to be working on species and varieties, was Darwin himself: as he told his cousin William Darwin Fox in a letter of [24 April 1845], he felt he ought to be both ‘flattered & unflattered’ to hear that other naturalists attributed the book to him. But, as his letters to Hooker show, Darwin carefully considered and then rejected almost all of the contents of Vestiges, and he feared that the reaction to his own work would be prejudiced by the arguments aroused by its skilful but scientifically unsound reasoning.
Perhaps the most interesting letter relating to Darwin’s species theory, which also bears on his concern for the future, is that addressed to his wife Emma, dated 5 July 1844, just after Darwin had completed the final draft of his essay on the subject. He asked her to ensure that the essay would be published in the event of his death and stipulated a sum of money to be bequeathed, together with his extensive library and portfolios of notes on species, to an editor who would undertake to see the work through the press. Darwin also listed possible editors: at first he proposed any one of Lyell, Henslow, Edward Forbes, William Lonsdale, Hugh Edwin Strickland, or Owen—the last with the caveat that he would probably not wish to take on the work. But the list was subsequently altered after Darwin’s second, and possibly third, thoughts on the choice of the right person. The names of Lonsdale, Forbes, and Owen were deleted, Henslow’s was queried, and J. D. Hooker’s was added. Much later, by the autumn of 1854 when Darwin began sorting out his notes in preparation for writing up his ‘big book’ on species (Natural selection), he had decided that Hooker was by far the best man for the task and added a note on the cover to that effect.
The full consideration that Darwin gave to the future editing and publication of his essay, and the way in which he wrote to colleagues and friends about his work, show clearly his intention to publish his theory. His instructions to Emma may, perhaps, as some scholars have thought, indicate a reluctance to take the responsibility for publishing upon himself, but, more plausibly, they portray a man faced with the task of establishing a theory and its consequences, and fearful lest both the energy and time necessary to achieve this end should be denied him. After prolonged illnesses in 1841 and 1842, years poorly represented in the Correspondence because he was for much of the time too ill even to write letters, Darwin felt that his life was only too likely to be cut short. Moreover, even when at his best, Darwin could never work as intensively as he felt he ought to, or needed to, for fear of inducing another breakdown in his health.
Volcanoes, rocks, and fossils
Darwin’s published work during this period secured his position as one of Britain’s foremost naturalists. His study of the volcanic islands visited during the Beagle voyage was based on a wide range of rock and mineral specimens, including his own, and considerable research into contemporary theories of volcanic activity, mountain formation, and the elevation of extensive tracts of land relative to the sea. Darwin put forward a new explanation of the origin of so-called ‘craters of elevation’, which formed the basis of discussions with Charles Lyell and Leonard Horner in letters in this volume. His observations on the lamination of volcanic rocks prompted an exchange with James David Forbes on the analogous structure of glacier-ice. In South America he proposed that the tension generated in molten rock before final consolidation, which he believed gave rise to this lamination, could also explain and link the widespread phenomena of cleavage and foliation, observable in some metamorphic rocks. His description and explanation of cleavage and foliation in the clay-slates and schists of South America benefitted from the mathematical expertise of William Hopkins and aroused the interest of Daniel Sharpe, whose subsequent work led to the general acceptance of Darwin’s views. South America drew together all the geological and palaeontological results of Darwin’s travels through that area and, like Volcanic islands, demonstrated how the structure of the land could best be explained by elevation. Darwin presented a wholeheartedly Lyellian picture of the geology of this vast area, reflecting the influence of Lyell’s Principles of geology (1830–3) and a commitment to Lyell’s idea of gradual geological change taking place overimmensely long periods of time; a commitment that transcended Darwin’s purely geological thought and influenced his speculations in all fields of natural history. But despite this clear and acknowledged debt, Darwin’s independence of mind was never in doubt and is well evidenced by the skilled and determined defence of his theories he invariably made against rivals of whatever standing. Through the pages of South America Darwin pursued an argument against the French palaeontologist Alcide d’Orbigny, insisting that the vast pampas formation could not have been laid down at a single moment through the action of a great débâcle, as Orbigny proposed. Darwin not only used his personal notes and records but, by letter, marshalled the resources of experts such as palaeontologists Edward Forbes and George Brettingham Sowerby, and the German naturalist Christian Gottfried Ehrenberg, to support his own opinion that the pampas formations had been deposited successively under mostly brackish or estuarine conditions.
Journal of researches: Darwin's story of the Beagle voyage
In addition to writing up his geology, Darwin undertook the revision of his Journal of researches for a second edition in 1845. At Lyell’s recommendation, arrangements were made for the rights of the work to be transferred from Henry Colburn, the original publisher, to John Murray, and throughout 1845 Darwin worked hard to provide manuscript copy to be published in three parts during the year. Though the text was reduced in volume, Darwin went to considerable trouble to add the latest descriptions of the Beagle collections, to alter and expand some of his previous suggestions about the causes of extinction, and to supplement the original account of the three Fuegians carried on board the Beagle back to Tierra del Fuego. By 1845, Darwin was in full command of a sophisticated theory of species transmutation and there is much interplay between the information supplied in letters to Darwin, the contents of the new edition of the Journal of researches, and his species work.
Joseph Hooker and the Beagle plant collections
The botany of the Beagle voyage was a topic still relatively unexplored by Darwin, even though he had collected plants extensively. Henslow, who had undertaken to describe the collection, was overwhelmed by ever-increasing parish and local concerns in Cambridge and Hitcham and apparently relieved to handover Darwin’s plants to Hooker, who had just returned from accompanying James Clark Ross’s Antarctic surveying expedition and who hoped to publish a detailed account of the flora of the Southern Hemisphere. Darwin was quick to spot in Hooker a man he judged could become the ‘first authority in Europe on that grand subject, that almost key-stone of the laws of creation, Geographical Distribution’ (letter to J. D. Hooker, [10 February 1845]) and quick to make use of the young man’s already large fund of botanical knowledge and his extensive connections with other British and European botanists. Darwin’s questions challenged Hooker to apply his particular knowledge to more general problems, always relating, directly or indirectly, to the question of the origin and nature of species. There is little in contemporary botany and botanical systematics that is not touched upon in their correspondence. Hooker’s observations on classification provided Darwin with a professional judgment on the plant world to place beside that of Waterhouse with respect to the animal kingdom. Hooker was also ready to discuss contemporary ideas on transformism in Britain and France and was a constant source of useful references and books. Some indication of the intellectual value that both men placed on their correspondence is found in the fact that they independently kept practically all the letters received from each other. The letters also document aspects of Hooker’s life: his search for a paid position, involving an unsuccessful campaign for the chair of botany at Edinburgh University and a period of half-hearted work with the Geological Survey of Great Britain. Like Darwin, he obtained Government aid to publish the results of his own four-year voyage and struggled to keep up to the time-table. And like Darwin, he was deeply committed to philosophical natural history.
Mr Arthrobalanus - Darwin's work on barnacles
It was also Hooker who helped Darwin in the first stages of his barnacle work, a study commenced towards the end of 1846. Hooker, ready with advice on microscopes and microscopic technique, assisted Darwin with drawings of his first dissection. The barnacle—‘Mr Arthrobalanus’ in Hooker’s and Darwin’s letters—was a minute, aberrant species collected by Darwin in the Chonos Archipelago, off southern Chile, which lived inside the shell of the mollusc, Concholepas. Unusual sexual dimorphism, with the male virtually a parasite on the female, a complex life-cycle, and difficult taxonomic considerations, combined to intrigue Darwin, and he launched himself into a survey of related species to elucidate some of the problems presented by the animal. The cirripedes were to remain central to Darwin’s working life for the next eight years.