The correspondence of Charles Darwin, volume 14: 1866

Edited by Frederick Burkhardt, Duncan M. Porter, Sheila Ann Dean, Samantha Evans, Shelley Innes, Alison M. Pearn, Andrew Sclater, Paul White. (Cambridge University Press 2004)

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The year 1866 began well for Charles Darwin, as his health, after several years of illness, was now considerably improved. His increased vigour was apparent in a busy year that included two trips to London, to the great delight of his friends, the entertaining of a number of scientific admirers at Down, among them Robert Caspary, John Traherne Moggridge, and Ernst Haeckel, and also a meeting with Herbert Spencer, who was visiting Darwin’s neighbour, Sir John Lubbock. In February, Darwin received a request from his publisher, John Murray, for a new edition of On the origin of species (Origin). Darwin set to energetically, and the fourth, and much revised, edition was with the printers in July. Much to Darwin’s annoyance, however, publication was delayed by Murray, who judged that it would sell better if released later in the year. The correspondence includes some pithy remarks on publishers, decried on one occasion by Joseph Dalton Hooker as ‘Penny-wise Pound foolish, Penurious, Pragmatical Prigs’ (letter from J. D. Hooker, [29 December 1866]). But the crowning achievement of the year was the completion of the major part of what was to become The variation of animals and plants under domestication (Variation). Although it was not published until 1868, all but the concluding chapter of the work was submitted by Darwin to his publisher in December. Much of Darwin’s correspondence in 1866 was focussed on issues surrounding the completion of this lengthy work, including further discussion of ‘pangenesis’, his hypothesis of hereditary transmission.

Debate about Darwin’s theory of transmutation continued in various quarters, with important commentaries appearing in France, Germany, and Italy. In the United States, Louis Agassiz renewed his defence of special creation on the basis of alleged evidence of a global ice age, while Asa Gray pressed Darwin’s American publisher for a revised edition of Origin. Closer to home, Darwin’s theory featured in the presidential address by William Robert Grove at the annual meeting of the British Association for the Advancement of Science. Fuller consideration of Darwin’s work was given by Hooker in an evening speech on insular floras at the same meeting. Prior to the event, the details of Hooker’s proposed talk formed the basis of a lengthy and lively exchange of letters between the two friends. The year’s successes and frustrations were punctuated by family bereavement. Two of Darwin’s sisters died, Emily Catherine Langton in January, and Susan Darwin in October. In his correspondence, Darwin responded philosophically to these deaths, regarding both as a merciful release from painful illness.

Among Darwin’s first letters in the new year was a report on his condition to his doctor, Henry Bence Jones: ‘I am able now to walk daily on an average 3½ miles & often one mile at a stretch…. I feel altogether much more vigorous & active. I read more, & what is delightful, I am able to write easy work for about 1½ hours every day’ (letter to H. B. Jones, 3 January [1866]). Darwin had first consulted Jones in July 1865 and attributed his improved health by the end of that year to the diet and exercise he had prescribed. ‘I have not yet much taste for common meat,’ he continued, ‘but eat a little game or fowl twice a day & eggs, omelet or maccaroni or cheese at the other meals & these I think suit me best.’ He sought Jones’s approval to increase his intake of coffee to two cups a day, since coffee, with the ‘10 drops of Muriatic acid twice a day (with Cayenne & ginger)’, appeared to have had a beneficial effect on his troublesome stomach, although he still usually suffered daily bouts of flatulence. Jones replied in encouraging terms, enclosing a revised diet, which unfortunately does not survive, and recommending the addition of an occasional baked potato. He also advised a holiday, and the acquisition of a ‘rough pony’ so that his patient could be ‘shaken once daily to make the chemistry go on better’ (letter from H. B. Jones, 10 February [1866]). Darwin began riding the cob, Tommy, on 4 June 1866, and in a letter to his cousin William Darwin Fox on 24 August [1866], he wrote, ‘I attribute my improvement partly to Bence Jones’ diet & partly, wonderful to relate, to my riding every day which I enjoy much.’ The new exercise regime led to Darwin’s being teased by his neighbour, John Lubbock, about the prospect of riding to hounds: ‘I … fully expect to see you out with our beagles before the season is over’ (letter from John Lubbock, 4 August 1866). More predictably, however, Darwin immediately converted his renewed vigour into scientific work, remarking to Fox, ‘I don’t believe in your theory of moderate mental work doing me any harm—any how I can’t be idle’ (letter to W. D. Fox, 24 August [1866]).

Since the publication of Origin in November 1859, Darwin had continued gathering and organising information on variation in domesticated plants and animals in order to write the first of a projected three volumes detailing the evidence on which his theory of the transmutation of species by natural selection was based. The work relied heavily on Darwin’s extensive correspondence over several decades with plant and animal breeders, such as the pigeon and poultry expert William Bernhard Tegetmeier. In January, Darwin wrote to Tegetmeier that he was getting on with his ‘everlasting volume’, and began a series of detailed queries and instructions, extending over the course of the year, on some of the book’s illustrations, the production of which Tegetmeier had agreed to supervise (letter to W. B. Tegetmeier, 16 January [1866]). Darwin found the evidence of variation in domesticated pigeons the most useful and complete for his purposes, and he took great care to ensure that the visual presentation of this evidence supported his argument for the common descent of all domestic varieties from Columbia livia, the rock pigeon.

In addition to the material on pigeons, the first volume of Variation included discussions of other domesticated animals, and of cultivated plants. The second volume contained chapters on inheritance, reversion, crossing, sterility, hybridism, and the causes and laws of variation. Finally, in an admittedly speculative chapter headed ‘Provisional hypothesis of pangenesis’, Darwin proposed that the various phenomena of development and hereditary transmission could be explained by the operation of ‘gemmules’, minute particles thrown off by the body’s individual cells, and capable of generating new cells when needed. Gemmules circulated in the body’s fluids, and could cohere by mutual attraction in, for example, the reproductive organs, or the tissues of a bud. Darwin had submitted a preliminary sketch of pangenesis to Thomas Henry Huxley in 1865 (see Correspondence vol. 13), and continued to refine his hypothesis in 1866. He wrote to Hooker on 16 May [1866], ‘I … am at work on a Chap. on Reversion which to me is a most interesting subject & brimful of my dear little mysterious gemmules.’ Darwin collected information on anomalous cases of reproduction, such as graft hybrids, soliciting assistance from the American botanist Asa Gray, the nurseryman Thomas Rivers, and the German botanist Robert Caspary. Darwin was particularly interested in recent work by Caspary on a graft hybrid then known as Cytisus adami, in which the scion apparently produced buds with blended characters; Darwin had tried to propagate the species some years before without success.

Darwin had originally intended his work on variation to form just two chapters of the ‘big book’ on species of which Origin was an abstract; but when he completed all but the final chapter of the manuscript in December, he was worried that it was too big. ‘You must congratulate me’, he wrote to Hooker, ‘when you hear that I have sent M.S. (such an awful, confounded pile, two volumes I much fear) of “Domestic Animals & Cult. Plants” to Printers’ (letter to J. D. Hooker, 24 December [1866]). When finally published in 1868, it filled two lengthy volumes, even with much of the text set in small type. The compilation and writing of Variation had been a major task, occupying much of Darwin’s working time since the publication of Origin. Although he was still debating whether to grasp the nettle and insert a chapter on human origins, his relief at its completion is palpable.

There had been, however, one last interruption. On 21 February Darwin received notification from John Murray that stocks of the third edition of Origin were exhausted. Darwin replied the next day, ‘I am much pleased but even more grieved …; for after ten months intermission I am now able to work nearly two hours daily at my next book; but this will be now stopped by the Origin. Natural Hist. progresses so quickly that I must make a good many corrections.’ It had been five years since the third edition was issued. The intervening period had seen the publication of a wide range of researches that Darwin regarded as supportive of his theory of transmutation. These included his own work on botanical dimorphism and trimorphism, published between 1861 and 1864, which raised questions about hybrid sterility as a criterion for species. The implications of Darwin’s botanical research and that of other plant hybridisers had been a subject of debate between Darwin and Huxley, who had asserted the importance of producing new ‘physiological species’ by means of artificial selection as a necessary condition for proof of Darwin’s theory. Shortly after the new edition was published, Darwin wrote to Huxley, ‘do read the Chapt. on Hybridism …, for I am very anxious to make you think less seriously on that difficulty.— I have improved the Chapt. a good deal I think, & have come to more definite views’ (letter to T. H. Huxley, 22 December [1866]).

The fourth edition of Origin also incorporated the work of some of Darwin’s closest scientific friends and correspondents. Hooker’s research on alpine floras, Henry Walter Bates’s article on mimetic butterflies, Lubbock’s observations of diving Hymenoptera and insect metamorphosis, Benjamin Dann Walsh’s theory of phytophagic varieties and species of insects, Fritz Müller’s research on crustacean embryology, and Alfred Russel Wallace’s conclusions on varieties and species of Malayan Lepidoptera were all inserted into Darwin’s ‘long argument’ for descent with modification. Darwin also added material obtained through correspondence in 1866, including observations by the American naturalist Jeffries Wyman on the irregular shape of bee cells, long regarded as works of geometric perfection and therefore of divine design. Finally, the new edition of Origin allowed Darwin to respond to his former friend, and now bitter antagonist, Richard Owen, whose harsh criticism of Origin Darwin had regarded as unjust. Darwin expanded his historical preface to include a lengthy account of Owen’s alleged claim to have discovered the principle of natural selection in 1850: ‘This belief in Professor Owen that he then gave to the world the theory of natural selection will surprise all those who are acquainted with the several passages in his works, reviews, and lectures, published since the “Origin,” in which he strenuously opposes the theory’ (Origin 4th ed., p. xviii).

Much of Darwin’s correspondence in February and early March was also concerned with an extended discussion of glacial theory, prompted in part by the Harvard naturalist Louis Agassiz’s recent claims. Agassiz undertook an ambitious expedition to Brazil in 1865 and 1866, partly with a view to finding support for his hypothesis that the entire earth had been frozen during the Ice Age, destroying all life; this was a direct challenge to Darwin’s theory of descent. Agassiz claimed to have found evidence of glaciation in the Amazon basin. Darwin was sceptical of Agassiz’s findings, however, and allusions to Agassiz’s ‘absurd views’ and his burning desire to disprove Darwin’s theories are reiterated in correspondence throughout the year, as in his remark to Lyell, ‘I quite follow you in thinking Agassiz glacier-mad’ (letter to Charles Lyell, 8[–9] September [1866]).

Darwin had first heard of Agassiz’s views through a letter to Lyell’s wife, Mary Elizabeth Lyell, from Elizabeth Cabot Cary Agassiz, who had accompanied her husband to South America. Lyell circulated this and other letters (several of which have survived and appear in this volume), drawing Darwin, Hooker, and the botanist Charles James Fox Bunbury into the discussion of glacial theory. Lyell’s own interest in the subject was keen, as he was preparing a greatly expanded discussion of climatic change, including a new chapter on astronomical influences, for the tenth edition of his Principles of geology. The discussion partly turned on the weighing of different causes of glaciation, and the relative value attached to different forms of evidence in geology, geography, botany, palaeontology, and physics. Although Darwin never advanced a theory of the glacial epoch, his views on geographical distribution depended upon a ‘mundane cold period’, and he was sceptical of some speculations of physicists against a general cooling of the globe. ‘I am bigotted to the last inch, & will not yield’, he wrote to Hooker, who attached greater weight to physical and astronomical arguments, such as that of the Scottish autodidact James Croll, who traced the glacial epoch to a period of extreme eccentricity of the earth’s orbit. Darwin favoured evidence from observed distributions, such as the presence of the same temperate species on distant mountains, and remarked to Hooker on his strong preference for specific facts over general theories: ‘I will maintain to the death that y r case of Fernando Po & Abyssinia is worth ten times more than the belief of a dozen physicists’ (letter to J. D. Hooker, [28 February 1866]). Darwin also ventured to inform Lyell that he did not support Lyell’s theory of the cause of glaciation, which involved the massing of land at the poles. ‘I must confess that I cannot believe in change of land & water being more than a subsidiary agent’, Darwin wrote on 8 March [1866], prefacing his remark with, ‘I hope you will own that I have generally been a good & docile pupil to you’.

In April Darwin went with his wife, Emma, and daughter Henrietta, to London, staying for two weeks with his brother, Erasmus Alvey Darwin. Owing to improved health, Darwin was able to make a number of social calls, sit for the photographer Ernest Edwards, and visit the gardens of the Zoological Society at Regent’s Park. He also astonished the metropolitan scientific community by attending a reception at the Royal Society of London. Some of his friends did not recognise him owing to the beard he had grown over the past few years. Emma described the Royal Society event in a letter to George: ‘Your father … entered at the same time with Dr B. J. who received him with triumph. All his friends gave him the most cordial reception as soon as they knew who he was, for he had to name himself to all who had not seen him lately. The P. of Wales was there & Gen. Sabine presented your father who made 2 of the best bows he cd muster. The P. muttered some little civility but he cd not hear what, & that was all’ (Stephen Keynes, private collection). Darwin’s friends were indeed delighted at his return to scientific society; Hooker remarked, ‘I am longing to know how you go on, after the startling apparition of your face at R.S. Soirèe—which I dreamed of 2 nights running. Tyndall came up to me in raptures at seeing you—& told me to worship Bence Jones in future—’ (letter from J. D. Hooker, 13 May 1866). Darwin himself was jubilant: ‘I have been so well most days since being in London, like what I was 7 or 8 years ago— one day I paid 3 calls! & then went for ¾ to Zoolog. Garden!!!!!!!!!’ (letter to J. D. Hooker, [28 April 1866]).

Darwin’s increasing renown both within Britain and abroad is evident from his portrayal in various popular publications, and from the visits he received from admirers and followers. A photograph of Darwin by Edwards was published with a biographical sketch in a volume edited by Lovell Reeve and Edward Walford, Portraits of men of eminence in literature, science and art. Another of Edwards’s photographs served as the basis for a handsome engraving that accompanied a lengthy review article in the Quarterly Journal of Science. Though not uncritical, the review described Darwin as ‘one of the noblest, most exalted, and most brilliant intellects of our age’ (Anon 1866, p. 176). At Down, Darwin received a number of visitors whom he had known previously only through correspondence. George Henslow, the son of his Cambridge mentor, John Stevens Henslow, stayed for two days in April and discussed mechanisms for insect pollination in the legume genera Medicago, Indigofera, and Cytisus. Darwin contributed an observational note to Henslow’s paper on the subject, read several weeks later at the Linnean Society of London (Henslow 1866a). In June, Darwin was visited by the orchid specialist John Traherne Moggridge, whose work on the self-pollinating bee ophrys (Ophrys apifera) and related orchids was of particular interest. The visit had been precipitated by a meeting between Moggridge and Henrietta during her travels in France. ‘I have just had the eventful interview with Mogg’, she wrote in May, ‘He didn’t scold me at all about fusca & lutea & we talked orchids very amicably—but the little man wants to see you— I told him that he might come & pay a morning call but that most likely you wdn’t see him & he said he shd be delighted to come on those terms so you are in for it’ (letter from H. E. Darwin, [ c. 10 May 1866]). Henrietta’s letter demonstrates her own interest in Darwin’s botanical work (‘I happened to have an orchid in my hand for him to name & oddly enough it was the other orchis that fertilises itself…. It is rather horrible to have another self fertiliser, isn’t it?’), as well as the role that she and Emma continued to play in safeguarding Darwin’s health and securing his privacy. Similarly, Hooker was called upon to act as intermediary between Darwin and the German botanist Robert Caspary, who wished to visit Down in May: ‘ask him by all means to come & sleep here, if he has spare time, but at same time tell him the truth how little exertion I can stand. I sh d like very much to see him, though I dread all exertion’ (letter to J. D. Hooker, [12 May 1866]). Darwin’s interest in Caspary’s research on graft hybrids and self-pollinating waterlilies prevailed over considerations of health in this case.

Nor could Darwin refuse a request from his most zealous admirer and advocate, Ernst Haeckel. The German zoologist had written to Darwin on 11 January 1866, ‘Every time I succeed in making a new discovery in the intellectual field of the contemplation of nature that you have newly opened up for us, I want to hurry to Down, Bromley, Kent, in order to talk to you about it.’ Haeckel was in England in August en route to Madeira. His visit to Down House is described in a letter from Henrietta to George: ‘when first he entered he was so agitated he forgot all the little English he knew & he & Papa shook hands repeatedly. Papa reiteratedly remarking that he was very glad to see him & Haeckel receiving it in dead silence…. He told us that there are over 200 medallions of Papa made by a man from W ms photo in circulation amongst the students in Jena’ (DAR 245: 269). Haeckel continued to promote Darwinism in Germany. His vast work, Generelle Morphologie, published in 1866, was dedicated to Darwin (as well as to Carl Gegenbaur, Johann Wolfgang von Goethe, and Jean-Baptiste de Lamarck), and credited Darwin with having effected a reformation in descent theory and a new era in science. Darwin received the book with gracious thanks: ‘You confer on my book, the “Origin of Species”, the most magnificent eulogium which it has ever received’ (letter to Ernst Haeckel, 18 August [1866]). Darwin clearly admired parts of the book, but he expressed to Huxley and others certain reservations and worries that its formidable length and difficult language would make its translation into English problematic: ‘I have been able to read a page or two here & there, & have been interested & instructed by parts. But my vague impression is that too much space is given to methodical details, & I can find hardly any facts or detailed new views. The number of new words, to a man like myself weak in his Greek, is something dreadful’ (letter to T. H. Huxley, 22 December [1866]).

Further interest in Darwin’s theory in Germany is indicated by correspondence with several publishers who sought permission to translate Darwin’s works, including a new edition of Origin. A son of the publisher Friedrich Emil Suchsland wrote to Darwin in March asking permission for a new translation of Origin, and claiming that Darwin’s theory had been widely misunderstood as a result of shortcomings in the previous translation. Two German editions of Origin, translated by Heinrich Georg Bronn, had been published in 1860 and 1863 by the firm E. Schweizerbart’sche Verlagsbuchhandlung; these included numerous notes and a critical epilogue that was partly inspired by Bronn’s adherence to Naturphilosophie, the German idealist tradition of science. Some recent German commentaries on Darwin’s theory, such as that of Carl Wilhelm von Nägeli, were also influenced by the authors’ commitments to this tradition, with its assumptions about progressive, teleological development (see for example, letter to C. W. Nägeli, 12 June [1866]). Also in March, however, Christian Friedrich Schweizerbart wrote to Darwin offering to publish a revised edition himself. Negotiations were complicated by debates about a suitable translator, Bronn having died in 1862. Finally, Julius Victor Carus, a naturalist who was sympathetic to Darwin and had previously translated Huxley’s Man’s place in nature, was settled upon. Carus immediately began work on the new translation (Bronn and Carus trans. 1867), incorporating the revisions Darwin had made to the fourth English edition, and corresponding with Darwin about various details.

Less success was achieved across the Atlantic, despite much effort expended by Asa Gray in trying to secure a new American edition of Origin. Gray had negotiated the original contract between Darwin and the New York publisher D. Appleton and Co. in 1860. Unfortunately, Appleton had produced the 1860 edition using stereotypes, solid plates in which the type was permanently fixed. Substantial alterations, such as Darwin had made to the fourth English edition, would consequently require the recasting of the entire volume, a process that Appleton was unwilling to undertake. The firm apparently offered to incorporate some changes, but their proposal was unsatisfactory to Darwin. Gray then approached another American firm, Ticknor & Fields, but they declined Gray’s offer, and a revised American edition was not published until 1870.

Despite the demands of completing Variation and preparing a fourth edition of Origin, Darwin still found time in the spring and summer to continue botanical researches on dimorphism and dichogamy. As he had done since 1862, Darwin relied on assistance from his eldest son, William, who made observations of the common broom (Cytisus scoparius) and the white broom (C. multiflorus) in his botanical notebook (DAR 186: 43). His drawings of C. scoparius, sent to Darwin with his letter of 8 May [1866], allowed detailed comparisons of pollen-grains of long-styled and short-styled forms, and illustrated the floral mechanism peculiar to Cytisus that facilitated cross-pollination by insects. Darwin and William also exchanged over a dozen letters in May and June on the subject of Rhamnus catharticus (now R. cathartica). Darwin had become interested in Rhamnus (buckthorn) in 1861, when Asa Gray informed him that a North American species presented ‘an initial state of dimorphism’ (Correspondence vol. 9, letter from Asa Gray, 11 October 1861). Darwin wished to establish whether dioecious plants had hermaphrodite ancestors, by observing gradation in the development of separate sexes. William gathered numerous specimens of R. catharticus, the only species of Rhamnus native to Britain, and made detailed observations and drawings. He initially reported that the species was ‘merely ordinaryly diœcious’ (letter from W. E. Darwin, [7 May – 11 June 1866]). On examining more specimens later in the season, he detected two floral forms of each sex and speculated: ‘I cannot help thinking the Rhamnus is a case of dimorphic becoming diœcious’ (letter from W. E. Darwin, 20 June [1866]). Darwin was excited by William’s find, and urged him to continue his observations with a view to publishing the results: ‘If your case turns out true … it will be a most interesting discovery & I vow you shall write a paper & publish it; but it must be well worked out first.’ Darwin also counselled his son on the necessary disappointments that accompanied scientific inquiry: ‘Do not be discouraged if the whole case blows up— I am well accustomed to such explosions’ (letter to W. E. Darwin, 22 June [1866]). He urged further observations the following summer, including experiments to assess the relative fertility of the pollen from the different male forms. Darwin evidently continued his observations, planting cuttings sent by William; however, no further correspondence or notes on the subject have been found. When Darwin eventually published the results in Forms of flowers, pp. 293–5, he credited observations of the different flower forms to William, but remarked that the plant showed no evidence of having once been heterostyled.

A more wide-ranging set of discussions engaged Darwin and Hooker for much of the summer, prompted by Hooker’s decision to give a public lecture at the August meeting of the British Association for the Advancement of Science in Nottingham. Hooker had accepted an invitation from the president of the association, William Robert Grove, to speak ‘on the Darwinian theory’, and wrote to Darwin on 16 January 1866, ‘I am utterly disgusted with my bravado…. the difficulty of the subject & impossibility of my doing it justice had charms for me. The Lord have mercy on your bantling in my hand’. The actual subject of Hooker’s address was insular floras, a topic of long-standing interest to both men, and a source of ongoing debate for its bearing both on Darwin’s theory of transmutation, and on competing theories of the geographical distribution of plants. Darwin had consistently argued against migration by means of continental extension, as proposed by Edward Forbes and others. He favoured instead migration by occasional transport, including the dispersal of seeds by wind, sea currents, floating ice, and birds. Hooker had never accepted Darwin’s arguments on this score as conclusive, and raised a host of botanical objections. The preparation of his insular floras lecture offered a new occasion for airing these differences, and for a reassessment of the problem in light of recent evidence. The exchange was often heated, and there were moments when Darwin expressed concern about Hooker’s arguments against his distribution theory: ‘When you exorcise at Nottingham occasional means of transport, be honest, & admit how little is known on the subject’ (letter to J. D. Hooker, 3 and 4 August [1866]). And on the next day: ‘It makes me rather miserable to see how differently we look at every thing’ (letter to J. D. Hooker, 5 August [1866]). Yet both men seemed to relish this fresh opportunity for intense debate. As Darwin remarked to Lyell earlier in the year: ‘a squabble with or about Hooker always does me a world of good, & we have been at it many a long year’ (letter to Charles Lyell, 15 February [1866]). Hooker tried to set Darwin’s mind at ease: ‘You must not let me worry you. I am an obstinate pig—but you must not be miserable at my looking at the same thing in a different light from you’ (letter from J. D. Hooker, 7 August 1866). The two exchanged letters with great rapidity in the weeks leading up to the meeting, their correspondence breaking off only when Hooker visited Down on 18 August, bringing his ‘blessed mss’ (letter from J. D. Hooker, [17 August 1866]). Hooker reported in a letter dated [28 August] 1866: ‘The whole thing went off … in very good style— … I never was so glad to get a thing out of hand & mind.’ In the end, Hooker argued that both theories, continental extension and occasional transport, faced ‘insuperable obstacles’, though he granted that the latter offered a ‘rational solution of many of the most puzzling phenomena’ that oceanic islands presented. Hooker also asserted that the facts regarding oceanic floras strongly supported ‘Mr. Darwin’s derivative theory of species’, and concluded with a humorous reference to the famous Oxford meeting of the British Association in 1860, where the bishop of Oxford, Samuel Wilberforce, had held forth against Origin (J. D. Hooker 1866a, pp. 50, 75–6).

Darwin’s work also featured significantly in another speech at the Nottingham meeting. William Robert Grove had approached Hooker in May for information on recent research supportive of Darwin’s theory for his presidential address. Hooker produced a list of corroborative works, including his own essays on Arctic and Australian floras, Darwin’s Orchids and papers on botanical dimorphism, Bates’s and Wallace’s work on mimetic butterflies, and Wallace’s work on human races. Darwin replied with a modified list, adding Fritz Müller’s Für Darwin, and a recent fossil discovery in pre-Silurian strata; he thought his own work on orchids and Primula of ‘too indirect a bearing to be worth noticing’ (letter to J. D. Hooker, 31 May [1866]). Most of these works and discoveries were mentioned in Grove’s address; however, Darwin’s theory was described only in terms of its general contrast with creationist accounts of species. Darwin was displeased that the address did not discuss what was specific to his theory. In a letter that has not been found, he voiced his criticisms to Grove, who replied that he had wanted the address to be accessible to non-specialists, and that the ‘adaptation view’ was in fact consistent both with the origin of species by natural selection, and with special creation (letter from W. R. Grove, 31 August 1866). Hooker later explained that Grove had shown ‘little appreciation’ of the difficulties of Darwin’s theory and had intended Hooker to be ‘champion of the cause’: ‘I was to “back him up” & “to carry Darwinism through the ranks of the enemy” after he had sounded the charge’ (letter from J. D. Hooker, [4 September 1866]).

Darwin discussed the details of transmutation theory during the year with Alfred Russel Wallace. They corresponded in February on non-blending characteristics with reference to Darwin’s crosses between different varieties of sweetpea and Wallace’s work on different female forms of a Malayan species of butterfly. In July, Wallace sent a lengthy commentary on the term ‘natural selection’. Darwin’s metaphorical use of the expression had been a subject of long discussion in previous years with Lyell, Gray, and Hooker. Wallace’s remarks were prompted by several recent reviews in which Origin had been criticised for inconsistencies with respect to the role of design in nature. A similar criticism had been made by the editor of the Quarterly Journal of Science, James Samuelson, in his letter of 8 April 1866. Wallace argued that the extended analogy that Darwin had drawn between natural selection and artificial or human selection had encouraged readers to attribute intelligent choice to nature. Wallace also pointed out passages in which Darwin had written of nature as ‘favouring’ or ‘seeking’ the good of a species, and warned against personifying nature too much. In place of ‘natural selection’, Wallace suggested that Darwin substitute ‘survival of the fittest’, an expression first used by Herbert Spencer in an 1864 instalment of Principles of biology. (Letter from A. R. Wallace, 2 July 1866.) Darwin agreed that Spencer’s term had merit, but argued that it could not be directly substituted as, unlike the term ‘natural selection’, it could not be used as a substantive governing a verb. Although it was too late to alter the fourth edition of Origin, Darwin did insert Spencer’s expression at numerous places in the fifth edition, as well as in Variation. Darwin continued to read the instalments of Principles of biology, praising ‘its prodigality of original thought’, while noting that ‘each suggestion, to be of real value to science, w d require years of work’ (letter to J. D. Hooker, 30 June [1866]). He met Spencer during a visit to the Lubbocks in October, and remarked on his use of ‘awesomely long words’ (letter to J. D. Hooker, 2 October [1866]). He later expressed amusement at Hooker’s description of Spencer as a ‘thinking pump’: ‘I read aloud your simile of H. Spencer to a thinking pump, & it was unanimously voted first-rate, & not a bit the worse for being unintelligible’ (letter from J. D. Hooker, 14 December 1866, letter to J. D. Hooker, 24 December [1866]).

Fritz Müller, the German naturalist living in Brazil, became a regular correspondent of Darwin’s in 1866. Having sent Müller copies of his earlier botanical publications at the end of 1865, Darwin wrote in January 1866, sending his Journal of researches and offering Müller a copy of the second German edition of Origin. Müller was happy to receive all Darwin’s works and read them carefully. A modest request from Darwin on 23 May 1866, ‘will you be so kind as to observe whether Oxalis with you exhibits different forms’, inspired Müller to make thorough and detailed observations of dimorphism and trimorphism not only in Oxalis, but in several other genera, which he sent to Darwin along with diagrams, drawings, specimens, and seeds. With the rich Brazilian orchid flora at his disposal, Müller was able to send Darwin a wealth of new information on orchid pollination. Some of Müller’s observations were added to Variation, the fifth edition of Origin, and Darwin’s later botanical works. Müller seemed almost to anticipate what would be useful to Darwin, causing the latter to remark, ‘It is quite curious how by coincidence you have been observing the same subjects that have lately interested me’ (letter to Fritz Müller, 25 September [1866]). Not surprisingly, Müller was on Darwin’s list to receive a pre-publication copy of the fourth edition of Origin, and within a few weeks of reading it, he was able to send evidence confirming Darwin’s hypothesis that the lancelet, then classified as a primitive fish, would have an invertebrate as its closest competitor in the struggle for existence (letter from Fritz Müller, 1 December 1866). By the close of the year, Darwin had already planted several of the bulbs and seeds sent by Müller, and began a letter, ‘I have so much to thank you for that I hardly know how to begin’ (letter to Fritz Müller, [before 10 December 1866]).

On occasion, issues of national or international concern were registered in Darwin’s correspondence, and even touched upon the publication of his work. In the summer months, much of the attention of the British press was directed toward war on the continent, as Prussia’s efforts to expand its power and dominions led to armed conflict with other German states and Austria in June and July. Writing on 10 May from Württemberg, one of the states bordering Prussia, Darwin’s German publisher, Christian Friedrich Schweizerbart, warned that should war break out, ‘business would be totally paralysed’. Similarly, John Murray gave as a reason for his decision to delay the publication of Origin until November the distraction of the British public with ‘gaieties travelling & War Bulletins’ (letter from John Murray, 18 July 1866). Slavery, a subject of extensive correspondence between Darwin and Asa Gray for many years, was legally abolished in the United States with the ratification of the Thirteenth Amendment to the Constitution in December 1865. Despite concerns about the ongoing difficulties of reconstruction in the southern states, Darwin rejoiced over this latest development: ‘I declare I can hardly yet realise the grand, magnificent fact that Slavery is at end in your country’ (letter to Asa Gray, 16 April [1866]). Similar sentiments may have been behind Darwin’s decision to support the Jamaica Committee, which had formed in December 1865 to lobby for the criminal prosecution of the colonial governor Edward John Eyre. In his efforts to suppress an uprising of the ex-slave population in Jamaica, Eyre had executed a leading revolutionary without trial. An opposing committee for Eyre’s defence was formed in August 1866, and both sides in the controversy sought to enlist the support of prominent individuals. Darwin was asked by Herbert Spencer to sign a list of those in favour of prosecution on 2 November 1866. Spencer enclosed a letter by Huxley to the Pall Mall Gazette, responding to the imputation that his views on ‘the development of species’ had inclined him to regard ‘the negro’ as well as ‘the ape’ as a brother. ‘I am glad to hear from Spencer’, Huxley wrote on 11 November, ‘that you are on the right (that is my) side in the Jamaica business— But it is wonderful how people who commonly act together are divided about it—’. The issue did in fact divide Darwin and Hooker, who remarked on 3 November that the application of high political principles was absurd when colonial officials were chosen from among ‘heaven born politicians; Geograph. Soc: Lions, & nine days wonders’. Darwin confessed, ‘You will shriek at me when you hear that I have just subscribed to the Jamaica committee. For the more I hear about it the more atrocious the case appears—’ (letter to J. D. Hooker, 20 November [1866]).

The year was marked by several deaths within Darwin’s family and circle of friends, provoking sombre thoughts. Darwin’s younger sister Emily Catherine Langton died in February, and his elder sister Susan Darwin died in October. On learning of Catherine’s poor state of health, Hooker, who had lost his father the previous year, wrote on 23 January 1866: ‘I have been so haunted by death & his dart … that I can hardly bear to look at my children asleep in bed’. Darwin’s two sisters had lived together in the family house in Shrewsbury after their father’s death in 1848 until Catherine married in 1863. Catherine had written shortly before her death that she was ‘grieved indeed at poor Susan’s loneliness’ (letter from E. C. Langton to Emma and Charles Darwin, [6 and 7? January 1866]), and Darwin later remarked to Lyell, ‘We are uneasy about Susan, but she has hitherto borne it better than we c d have hoped’ (letter to Charles Lyell, 7 February [1866]). Susan had been a particular favourite among the family at Down and her company was frequently enjoyed during her visits to Darwin’s brother, Erasmus, in London. When her death seemed near, Darwin wrote to Hooker: ‘we must soon hear of the end of a most sweet & loving character’ (letter to J. D. Hooker, 2 October [1866]). In the following month, the family house and estate were put up for sale, bringing an end to the family’s Shrewsbury era. The disposal of Susan’s property prompted thoughts of the provision Darwin hoped to make for his children at his death, and brought an urgent request that his eldest son William make a will of his own. Another particularly sad loss came in April, when the young daughter of Hooker’s colleague at Kew, Daniel Oliver, died suddenly. ‘How grieved I am to hear about poor Oliver’s loss’, Darwin wrote to Hooker, ‘There is nothing in this world like the bitterness of such a loss,—unless indeed the wife herself’ (letter to J. D. Hooker, [9 April 1866]).

It was against this background that Darwin made a rare statement of his religious views, replying to the educator Mary Everest Boole, who asked whether he thought the theory of natural selection compatible with belief in God as a ‘personal and Infinitely good Being’ (letter from M. E. Boole, 13 December 1866). Darwin answered, ‘it has always appeared to me more satisfactory to look at the immense amount of pain & suffering in this world, as the inevitable result of the natural sequence of events … rather than from the direct intervention of God’ (letter to M. E. Boole, 14 December 1866). But amidst such loss and sober reflection, the year ended on a bright note, with the renewal of old friendships, and enthusiasm over family successes and scientific work. One of the officers on the Beagle voyage, Bartholomew James Sulivan, wrote on 25 December of the achievements of his sons, newly promoted in the navy, and of the Admiralty’s plans to return to the site in Patagonia where he had discovered the fossilised bones of several extinct mammals years before. Darwin replied on the last day of the year, reporting the success of his son George, who had recently won a scholarship to Trinity College, Cambridge. He asked Sulivan about the possibility of obtaining information on the expression of emotions among ‘Fuegians’, and added what was by no means an afterthought, ‘I have just sent off to the printers a great bundle of M.S for a book on “domestic animals”.