On 14 May 1856, Charles Darwin recorded in his journal that he ‘Began by Lyell’s advice writing species sketch’ (‘Journal’; Appendix II). For the next two years and more, his working life was completely dominated by the preparation of this manuscript. Although advised by Lyell to publish only a brief outline—probably more for the sake of priority than anything else—Darwin was reluctant to squeeze his expansive material into such a small compass and soon abandoned Lyell’s idea in favour of a full-length work that would do greater justice to his views. He had been pondering the question of species for nearly twenty years, gathering vast quantities of information, pursuing his own experiments in a variety of different areas, analysing and altering his arguments in the light of recent results across the spectrum of nineteenth-century natural history, but never relinquishing the belief that his theory of natural selection could explain the structure of the living world. The moment had come, he accepted, to marshall his facts and put his theory before the public. His book was to be called Natural selection.
Determined as he was to publish, Darwin nevertheless still felt cautious in expressing his views before a large scientific audience and anxious to ensure that his facts were correct, his conclusions valid. As always, his correspondents played a crucial role in this process. Still prominent in his immediate circle were Charles Lyell and Joseph Dalton Hooker, who were joined in 1856 by Hooker’s friend the American botanist Asa Gray and then by the specialist in Madeiran entomology, Thomas Vernon Wollaston. Darwin also came to rely on the caustic yet considered botanical opinions of Hewett Cottrell Watson. Similarly—with only occasional protestations about his argumentative habits—he increasingly valued the views of Thomas Henry Huxley, at that time a somewhat precariously placed lecturer and palaeontologist in the School of Mines in London.
Not all of Darwin’s manuscript on species has been preserved and not all of it found its way into On the origin of species (1859). His letters are often the only source of information about his preoccupations during 1856 and 1857. They reveal little noticed aspects of his work and particularly highlight the importance of his investigations of pigeons, poultry, and other domesticated animals. As Darwin explained to Lyell, his studies, particularly those on pigeons, were intended to provide an illustration of how selection might work in nature (letter from Charles Lyell, 1–2 May 1856, n. 10). He was surprised that no naturalist had thought of comparing wild and domesticated species in this way before. ‘How very odd it is that no zoologist sh d. ever have thought it worth while to look to the real structure of varieties’, he remarked to Hooker (letter to J. D. Hooker, 8 September ).
I mean to make my Book as perfect as ever I can
William Bernhard Tegetmeier continued to help Darwin acquire much of the material for his practical work. This work was supported by considerable research in published and unpublished sources. Edward Blyth needed little encouragement to send prolix memorandums on domestic animals in India and elsewhere. William Darwin Fox supplied information about cats, dogs, rabbits, and geese, as well as his customary anecdotes about domestic ducks and poultry; Thomas Campbell Eyton was questioned about pigs, dogs, and cattle; Carl Johann Andersson about native Swedish ponies; Hugh Falconer about Tibetan mastiffs. The disparate facts were correlated and checked by Darwin, who adroitly used letters, published sources, and his own experiments at Down to confirm each detail. ‘I am like Crœsus overwhelmed with my riches in facts,’ he told Fox, ‘& I mean to make my Book as perfect as ever I can.’ (letter to W. D. Fox, 8 February ).
Darwin also attempted to test ideas emerging from his work on domestic animals by conducting experiments on plants. Expanding projects set up during 1855 and 1856 (see Correspondence vol. 5), he tried to ‘break the constitution of plants’ by altering the external conditions under which plants grew to see whether he could induce hereditable changes. He carried out comparative studies of germination under different conditions and interbred garden species with their wild congeners.
Many of Darwin’s conclusions about the variation of animals and plants under domestication were written up in the first two chapters of his species book, completed by October 1856 (‘Journal’; Appendix II). Unfortunately, these chapters are not extant. It seems likely that Darwin used the manuscript when compiling The variation of animals and plants under domestication (1868) and that it was destroyed or lost during the process. Before the publication of Darwin's correspondence from these years, Variation was the only published source for many of Darwin’s views on domestic animals and plants and this, since it was composed so many years later, is not a safe guide to his pre-Origin thinking. The letters, on the other hand, are richly informative and cast a great deal of light on the role that these ideas were intended to play in Darwin’s formal exposition.
Asking questions; getting answers
Since natural selection could not act without varieties to act upon, Darwin wanted to know where, how, and in what way variations appeared in animals and plants. Making the fullest possible use of his botanical friends, Darwin cross-examined them on different aspects of the question. Did naturalised plants, he asked Asa Gray, vary in the United States (letter to Asa Gray, 2 May 1856)? What about weeds? Did they vary? Plants introduced by early travellers or horticulturists were roughly comparable to domestic animals: did they ever run wild? What correlations could be established between variations and conditions of existence? One useful example that Darwin intended to include in his book was the apparent tendency of alpine plants to be more hairy than their lowland relatives. But a last-minute check with Hooker revealed that Darwin was mistaken: ‘You have shaved the hair off the alpine plants pretty effectually’ complained Darwin in 1857 (letter to J. D. Hooker, [2 May 1857]).
The largest project Darwin undertook along these lines was an arithmetical survey of the frequency of plant varieties. Using published catalogues of the floras of particularly well-worked countries, he attempted to show that varieties—as identified by the authors of the catalogues—tended to occur more frequently in species and genera that were geographically widespread or otherwise abundant. He wrote at length about this project, his ups and downs with the calculations and different ways of working, in letters to Hooker, Gray, and Watson. The results seemed to corroborate his general point that variation, providing abundant raw material for natural selection, led to adaptation and thence to more successful, individually numerous, and widely spread species. The significance that he placed on these results is clearly demonstrated by the shock he acknowledged when told by his neighbour and young protégé John Lubbock that his method of calculation was wrong (letter to John Lubbock, 14 July ). Darwin thought his results showed that variable species occurred more frequently in large genera than in small, but all they actually showed was the self-evident fact that a large genus was more likely to contain a variable species than was a small one. Rather than relinquish the results achieved after so much effort, Darwin began the whole laborious project again, using a statistically valid method explained to him by Lubbock.
The origin of sex
Such perseverance is perhaps the key to this period in Darwin’s life. He brought the same quality of doggedness to the resolution of the single most important question revealed by his work on varieties and variation. This was the origin and function of sex in nature. Darwin had always been intrigued by the theoretical issues raised by the existence of two sexes and had long held the idea that the variations seen in individual organisms arose predominantly as the result of sexual reproduction between the parents. For that reason he believed that all organisms, even hermaphrodites, must occasionally be cross-fertilised by other individuals. Darwin sought information on this problem from many different quarters, turning to Huxley to ask him whether there were any necessarily self-fertilising hermaphrodites among marine invertebrates. His request led Huxley to make a note for future reference, ‘Darwin, an absolute & eternal hermaphrodite’ (letter to to T. H. Huxley, 1 July ), which became a source of amusement in later letters. But Huxley could not give a categorical answer. Nor could the botanists that Darwin asked about plants whose flowers seemed consistently to fertilise in the bud or whose structure seemed to preclude crossing. The possibility of the cross-fertilisation of plants that grew under water was an equally difficult problem that he took in turn to Watson, Hooker, George Bentham, and the Belfast botanist George Dickie. Darwin’s theoretical notions also encouraged him to predict that trees would tend to show a separation of the sexes, a proposal that Asa Gray and Hooker confirmed during the course of 1856.
Science at home: the botanical experiments
Darwin’s researches into the purpose and results of sexual reproduction were pursued, as in all his lines of investigation, by experiments at Down. His letters show that he was involved with many different experiments on plants through the summers of 1856 and 1857, particularly with garden vegetables like peas and beans. These plants posed great theoretical difficulties in that none of the available sources, published or practical, could agree on whether the structure of papilionaceous flowers would allow for cross-fertilisation. Darwin carried out his researches with relish and published a short notice about the problem in Gardeners’ Chronicle and Agricultural Gazette in October 1857, to be followed by a second notice in 1858.
Geographical distribution: seeds and salt-water
The Leguminosae question was never fully resolved to Darwin’s satisfaction. Indeed, several of his experiments failed to give him the results he wanted: seeds would not germinate; beans failed to cross; pigeon crosses did not yield conclusive results; newly-hatched molluscs refused to do what he hoped. One set of experiments, in particular, exhibits the steely inner resources that Darwin brought to his work and his indomitable will to succeed in wresting facts out of nature. Having long argued against the existence of former land connections between oceanic islands and their neighbouring continents (see Correspondence vol. 3), he had begun in 1855 a series of researches designed to explain how animals and plants might have been transported to islands without needing to travel over dry land. The centre-piece of his study was the series of experiments begun in 1855 based on soaking a wide variety of seeds in salt water in order to show that they could be transported across oceans without losing their ability to germinate. Even when he noticed, late into the project, that seeds usually sank and therefore could not be floated out to islands by ocean currents, the set-back was only temporary. Darwin rethought the question and began alternative experiments, including feeding seeds to fish. When the fish refused to eat their designated meals, he filled up the carcases of small animals with seeds and fed them to ocean-going birds in the zoological gardens in London. As he cheerfully explained to Hooker: ‘I must tell you another of my profound experiments. Franky said to me, “why shd not a bird be killed (by hawk, lightning, apoplexy, hail &c) with seeds in crop, & it would swim.” No sooner said, than done: a pigeon has floated for 30 days in salt water with seeds in crop & they have grown splendidly & to my great surprise even tares (Leguminosæ, so generally killed by sea-water) which the bird had naturally eaten have grown well.’ (letter to J. D. Hooker, 10 December ).
His faith in his ideas and his unfailing ingenuity led him to speculate on various other possible means of dispersal. He felt that the mud on birds’ feet probably had a role to play in the distribution of seeds and carried out some unusual studies that required Joseph Parslow, the butler, to shoot partridges after a heavy rainfall so that Darwin could count the number of seeds in the earth between their toes. During outings in his carriage, Darwin also made frequent stops at local ponds and ditches to collect scoops of mud to analyse for seeds. Similar experiments were carried out on the possible means of transport of live ova or newly hatched animals such as land snails. Further to these, Darwin also investigated the length of time that seeds could ordinarily retain their ability to germinate, as, for example, in the case of seeds long-buried under the roots of trees (see letters to William Erasmus Darwin, [26 February 1856] and to Charles Lyell, 3 May ).
Darwin’s family was amused and patient about these researches, following his successes and failures with interest. It is clear from the correspondence published here that life at Down revolved around Darwin’s work. Darwin emerges as a typical Victorian patriarch, retiring to his study for the day’s work on his book, emerging only to visit the greenhouse and walk in the garden, the children accompanying him on the daily round of experimental plots, the pigeon houses, and the ‘Sandwalk’. Like any father of his wealth and social position he was also anxious that his boys should be adequately schooled and worried about their future professions. His concern is well evidenced in the encouragement and occasional parental reprimand given to his eldest son William, then aged 17 and coming to the end of his time at Rugby school. ‘I am very glad indeed to hear that you are in the sixth; & I do not care how difficult you find the work: am I not a kind Father?’ Darwin wrote in 1857, soon followed by the complaint ‘You want a jobation about your handwriting—dreadfully bad & not a stop from beginning to end!’ (letters to W. E. Darwin, [17 February 1857] and 21 [July 1857]). The problem of careers for his six boys (Charles Waring Darwin, the sixth and last, was born on 6 December 1856) was a constant worry, particularly since Darwin seems to have felt that the children were poorly equipped to compete in the crowded professions of Britain. He looked to the space and opportunities of the colonies with some regret and envy: ‘What a much better prospect you have for your sons . . . compared to what they could have been in this old burthened country, with every soul struggling for subsistence’, he wrote to Syms Covington in New South Wales (letter to Syms Covington, 9 March 1856).
Many other topics, intellectual and personal, surface in this volume. Darwin exerted a considerable influence on the awarding of the Royal Society’s medals and he took time and trouble trying to get friends and relations into the Athenæum Club. Several letters touch on the publication of John Tyndall’s theory concerning the dynamics of glacial flow, with which Huxley was closely involved. Darwin discussed the geological phenomenon of cleavage, still unresolved in 1856, with John Phillips and entered into a useful correspondence with Samuel Pickworth Woodward on the variability and geographical distribution of fossil shells, stimulated by an appreciative reading of Woodward’s Manual of the Mollusca (1851–6). The letters also reveal some of the views that contemporary naturalists held about Darwin.
Alfred Russel Wallace
Most significant in terms of Darwin’s future, however, was the beginning of his correspondence with Alfred Russel Wallace. The first few letters exchanged between the two have been lost, but it is clear from the surviving correspondence that Darwin initially wrote to Wallace in order to obtain specimens of Malaysian fowls. Seen in the context of other letters written at this time, Darwin’s remarks to Wallace about his work on species and the preparation of his manuscript (letter to A. R. Wallace, 1 May 1857) seem innocuous and hardly the veiled threat that some historians have read into his words. Darwin may indeed have been writing in part to establish his priority in this area, for Charles Lyell thought that Wallace’s 1855 paper implied some kind of belief in transmutation (see Wilson ed. 1970, pp. 54–5), but Darwin had no reason to suspect that Wallace was in any way a direct competitor or about to pre-empt his views on natural selection. All the available material seems to indicate that it was Lyell rather than Darwin who feared the transmutationist implications of Wallace’s paper.
Lyell’s advisory role in the public presentation of Darwin’s theories is also clarified by the publication of their correspondence. Darwin’s manuscript on species was begun only after Lyell had urged him to publish a preliminary sketch, but it seems that this famous advice may have been given on an occasion other than the one previously supposed. Charles and Mary Elizabeth Lyell certainly visited the Darwins at Down House for several days in April 1856, and Darwin took this opportunity to explain his theory of natural selection to Lyell. Yet the suggestion of composing a preliminary sketch was apparently first made in a letter written by Lyell from London on 1–2 May 1856. Darwin took the suggestion seriously and went up to London to see Lyell to discuss it further (letter to Charles Lyell, 3 May ). It was after this meeting that Darwin wrote to Hooker to say that Lyell had pressed him to write up his views (letters to J. D. Hooker, 9 May ).
Darwin had also received unsolicited encouragement from rather different quarters in the interval between these meetings with Lyell. At a second weekend party held at Down on 26 and 27 April 1856, he had discussed the question of species at length with his guests, Hooker, Huxley, and Wollaston. Hearing about the party afterwards, Lyell reported in a letter to his brother-in-law that, ‘When Huxley, Hooker, and Wollaston were at Darwin’s last week, they (all four of them) ran a tilt against species farther I believe than they are deliberately prepared to go. Wollaston, least unorthodox. I cannot easily see how they can go so far, and not embrace the whole Lamarckian doctrine.’ (letter from Charles Lyell, 1–2 May 1856, n. 7). The excitement and intellectual stimulation of that weekend, combined with Lyell’s astute advice, undoubtedly convinced Darwin that he should begin writing.
The theory complete
The labour of composition, the search for authenticated information, the zest for practical researches, and above all the determination to succeed are all vividly displayed in Darwin's letters. By the end of 1857, Darwin was well on the way towards completing his manuscript and felt confident enough in his views to explain them in explicit detail in a long letter to Asa Gray (letter to Asa Gray, 5 September ). From this letter it is evident that Darwin had brought together all the diverse intellectual components of his theory, including the relatively new concept of a ‘principle of divergence’ which Darwin believed necessary to account for the diverging, tree-like relationships of organisms. With the theory complete, he was anxious to press on with its exposition.