The correspondence of Charles Darwin, volume 8: 1860

Volume 8, 1860: Edited by Frederick Burkhardt, Janet Browne, Duncan M. Porter, Marsha Richmond. (Cambridge University Press 1993)

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Introduction

On 7 January 1860, John Murray published the second edition of Darwin’s Origin of species, printing off another 3000 copies to satisfy the demands of an audience that surprised both the publisher and the author. One week later Darwin was stunned to learn that the book was on sale even in railway stations (letter to Charles Lyell, 14 January [1860]). By May, with the work continuing to sell well in England and with editions out in the United States and in Germany, he expressed to Asa Gray his astonishment at the widespread interest it had aroused: ‘No doubt the public has been shamefully imposed on! for they bought the book, thinking that it would be nice easy reading.’ (letter to Asa Gray, 22 May [1860]).

But it was the opinion of scientific men that was Darwin’s main concern. He eagerly scrutinised each new review and was heartened to find that many of the early notices were favourable. He later learned that they came from some of those whose support he most wanted: Thomas Henry Huxley, William Benjamin Carpenter, and Joseph Dalton Hooker. Others were not quite as supportive but were nonetheless appreciated for their honest critiques of his views. ‘One cannot expect fairness in a Reviewer’, Darwin commented to Hooker after reading an early notice that gave ‘good and well deserved raps’ on his discussion of the geological record; but this criticism, he told Hooker, did not at all concern his main argument (letter to J. D. Hooker, 3 January [1860]).

Darwin’s magnanimous attitude soon faded, however, when ‘the stones began to fly’. His ‘dearly beloved’ theory suffered a series of attacks, the most vicious of which came from Richard Owen in the April issue of the Edinburgh Review. Indeed, after reading not only critical but ‘unfair’ reviews that misrepresented his ideas, Darwin began to feel that without the early favourable notices his theory would have been ‘utterly smashed’ (letter to T. H. Huxley, 3 July [1860]). (A chronological list of all the reviews mentioned in the volume is given in Appendix VII.)

The difficulties that members of the scientific community found in Origin in the twelve months after its publication make an impressive list. Adam Sedgwick, not surprisingly, attacked the book on a number of fronts. But it was his methodological criticism in the accusation that Darwin had ‘deserted the inductive track, the only track that leads to physical truth’ (Sedgwick 1860) that most wounded Darwin. Having spent years gathering the evidential underpinning for his theory, he had hoped to deflect such criticism. ‘I can perfectly understand Sedgwick or any one saying that nat. selection does not explain large classes of facts; but that is very different from saying that I depart from right principles of scientific investigation.—’ (letter to J. S. Henslow, 8 May [1860]).

Above all else Darwin prided himself on having developed a theory that explained several classes of facts— those of geological succession, geographical distribution, classification, homology, and embryology—which were inexplicable by the theory of creation. Asa Gray’s statement in his March review that natural selection was a hypothesis, not a theory, therefore also displeased Darwin. Comparing natural selection to the undulatory theory of light or to the theory of gravity, he retorted: ‘It seems to me that an hypothesis is developed into a theory solely by explaining an ample lot of facts.’ (letter to Asa Gray, 18 February [1860]). To those who objected that his theory could not be a vera causa, he similarly stated that ‘it seems to me fair in Philosophy to invent any hypothesis & if it explains many phenomena it comes in time to be admitted as real.’ (letter to C. J. F. Bunbury, 9 February [1860]). This helps to explain why Darwin was delighted by the defence of his scientific method by the young Cambridge fellow Henry Fawcett in the December issue of Macmillan’s Magazine. Fawcett asserted that Darwin’s theory accorded well with John Stuart Mill’s exposition of the deductive method of scientific investigation, consisting of direct induction, ratiocination, and then verification.

Specific difficulties were raised against the theory on the basis of existing scientific evidence. Several correspondents, such as his cousin Hensleigh Wedgwood and Heinrich Georg Bronn, expressed their concerns about the question of the origin of life itself, which the theory did not address. Darwin chose to treat this as an entirely separate problem from the origin of species, believing that current knowledge could not illuminate this ‘mystery’. Charles Lyell worried, among other things, about the multitude of still living simple forms. Darwin readily admitted that his failure to discuss this point was a ‘most serious omission’ in his book and explained how natural selection did not necessarily lead to progression (letter to Charles Lyell, 18 [and 19 February 1860]). To this and Lyell’s many other queries he responded carefully and patiently, knowing that Lyell was earnestly attempting to understand natural selection and incorporate it into his method of reasoning about global change. Darwin also knew that Lyell was a powerful potential ally. Indeed, the letters between Darwin and Lyell are some of the most fascinating in the volume.

George Henry Kendrick Thwaites questioned Darwin about how natural selection could explain the production of beauty, pointing to organisms such as the desmids, whose intricate patterned forms seemed to offer no obvious selective advantage to the creatures themselves. The evolutionist Hewett Cottrell Watson argued for the concept of ‘convergence’ of species to join that of divergence. Andrew Murray challenged the explanation of the origin and distribution of blind cave animals. Darwin attempted to answer each of these issues in his letters; several were considered in future editions of Origin. William Henry Harvey wondered, in addition to questioning gradual versus saltatory species change, how natural selection could ever alter and improve various ‘simple’ protozoans that were seemingly identical to one another. Harvey’s letters reveal aspects of Darwin’s theory that gave contemporary naturalists the greatest conceptual difficulty, and theological discomfort. After several long letters were exchanged, Darwin finally decided that Harvey and other working naturalists simply did not yet understand the concept of natural selection.

Even Huxley, an avowed supporter, proved a formidable critic. Huxley extolled the analogy between artificial selection among domestic varieties and natural selection in a lecture before the Royal Institution. Yet he also noted the difficulty that varieties are not sterile when crossed, whereas sterility had long been recognised by naturalists as a criterion of specific difference. He concluded the lecture by asserting that until naturalists could find ‘derivatives from a common stock, whose offspring should be infertile, inter se,’ Darwin’s theory would remain unproven (T. H. Huxley 1860a).

Darwin had long reflected on the origin of sterility between incipient species but knew that much work was needed before the problem could be conclusively resolved. He also recognised that, owing to experimental difficulties, advances were more likely to come from studies of crossing among plant species and varieties than from animal breeding. With Lyell also questioning how interbreeding among animal groups could give rise to new species, Darwin found Huxley’s lecture irritating and ultimately considered it more a failure than a success (see letter to J. D. Hooker, 14 February [1860]).

As Darwin himself well recognised and fully anticipated in Origin, several major criticisms arose from evidence (or the lack thereof) in the geological record. Several critics pointed out that the earliest geological formations already contained relatively advanced forms of life. Many singled out Darwin’s own discussion of the absence of transitional or intermediate forms between related groups and the vast time required for one or more primordial forms to have evolved into the multitude of the earth’s present inhabitants. Darwin agreed, for example, with Alfred Russel Wallace’s assessment that the imperfection of the geological record was one of the weakest parts of his theory. Yet he nonetheless noted that in fact ‘there are almost more Geological converts than of pursuers of other branches of natural science.’ As for why this should be so, he confided to Wallace: ‘I think geologists are more converted than simple naturalists because more accustomed to reasoning.’ (letter to A. R. Wallace, 18 May 1860).

Darwin began to tabulate (and categorise) his various followers as early as March. Dividing up his supporters on the basis of their professional affiliations, he counted among this number four geologists, four zoologists or palaeontologists, two physiologists, and five botanists (see letter to J. D. Hooker, 3 March [1860]). Others, like Franc cois Jules Pictet de la Rive, he judged would eventually be converted, for he found them somewhat ‘staggered’ by his theory—and once staggered, he believed, it was only a matter of time before a person would become an adherent.

Certainly Darwin was disappointed by the small number of physiologists who initially supported his theory. Even Carpenter, whom he included as a proponent in this group, offered only partial support, for he hesitated at going so far as to derive all vertebrates from a single progenitor. The major stumbling block for most anatomists and physiologists was the difficulty of conceiving of the selection of chance variations being able to produce such a marvellously perfected structure as the eye. As Darwin admitted to Lyell, Gray, and others, imagining how selection could account for highly adapted organs had sometimes given even him a ‘cold shudder’. Yet it was more trifling structures, ones for which it was difficult to see clear selective advantages, that caused him greater discomfort. As he readily admitted to Gray: ‘The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!’ (letter to Asa Gray, 3 April [1860]).

By the end of 1860, Darwin was disheartened that so few of his reviewers had noticed what he considered to be ‘the strongest single class of facts in favour of change of form’, namely those of embryology (letter to Asa Gray, 10 September [1860]). Only his theory, he believed, could explain the basis for the correlation of the facts of embryology, homology, morphology, and classification and thereby account, as the creationist view could not, for anomalous structures such as rudimentary organs and the general resemblance of embryos of the same class. But it was precisely the physiologists, steeped in a heavily developmental conception of nature, who had more difficulty reconciling the seemingly directed process of embryogenesis with a theory of change based upon the selection of chance variations. Few could imagine how such a process could actually alter the developmental patterns of species. Darwin took some comfort from news that the doyen of embryology, Karl Ernst von Baer, had expressed support for species change based on his study of the geographical distribution of species (see letter from T. H. Huxley, 6 August 1860). But Baer in fact eventually opposed Darwin’s theory on the grounds that it failed to account for the purposiveness of embryonic development.

Among the formidable array of problems confronting Darwin’s theory, perhaps most telling of all was that arising from the implications it had for human ancestry. Certainly this was a major difficulty standing in the way of Lyell’s acceptance of the theory, as Darwin well knew. Even though he had not discussed this problem explicitly in Origin — only one sentence, he told Lyell, showed that he believed ‘man is in same predicament with other animals’ (letter to Charles Lyell, 10 January [1860])— he and others were well aware that the continuity of humankind with the animal kingdom was an obvious logical consequence of his theory. The question of man’s ‘descent from apes’ was explicitly raised in February in Thomas Vernon Wollaston’s review in the Annals and Magazine of Natural History. The question would not disappear with Darwin’s dismissal of the issue as having more to do with theology than with science. It emerged with force and in full public view in June at the Oxford meeting of the British Association for the Advancement of Science.

Darwin first learned that he and his book had become ‘topics of the day’ at the meeting in a letter from Hooker written from Oxford. Hooker’s letter, one of the few known eyewitness accounts, well captures the excitement of the legendary episode. After avoiding earlier sessions, including the Thursday meeting at which Huxley and Owen ‘had a furious battle over Darwins absent body’, Hooker attended the fabled Saturday session of Section D. He told Darwin how ‘between 700 & 1000 people’ crowded into the as yet unfurnished library of the new Oxford Museum to hear Samuel Wilberforce, the bishop of Oxford, reply to John William Draper’s paper giving a Darwinian view of the development of Western civilisation. Wilberforce, Hooker recounted, responded by shouting ‘for half an hour’, ridiculing Darwin ‘badly & Huxley savagely’. Huxley rose in response and ‘answered admirably’, but ‘could not throw his voice over so large an assembly, nor command the audience’. With his blood boiling and his heart pounding, Hooker threw down the gauntlet and became a ‘referee on Natural Selection’. His performance surprised many: he ‘smashed’ Wilberforce ‘amid rounds of aplause’ and the meeting adjourned, leaving Darwin ‘master of the field after 4 hours battle’ (letter from J. D. Hooker, 2 July 1860). Other correspondents informed Darwin about further, less dramatic incidents, including John Lubbock’s retort to Wilberforce on the embryological evidence supporting Darwin’s views and Robert FitzRoy’s denunciations in both the Saturday meeting and in the geography section. Darwin, who had been kept away by illness, was glad to have avoided such public confrontation. ‘I would as soon have died as tried to answer the Bishop in such an assembly,’ he told Huxley; nonetheless he believed that ‘this row is best thing for subject.—’ (letter to T. H. Huxley, 3 July [1860]). Further details of the meeting, taken from the contemporary report in the Athenæum, are given in Appendix VI.

Wilberforce’s review of Origin, published in the Quarterly Review, appeared shortly after the Oxford meeting. In its arguments Darwin clearly recognised the clever touch of his now arch-foe Owen. It specifically addressed the question of man, among other difficult scientific problems, and set the tone for future theological controversy over evolution theory.

The response to Origin by theologians, however, was not entirely negative, as the approval of the scientifically literate clergymen Baden Powell and Charles Kingsley attested. Moreover, theological opinion has to be gauged as much in terms of the response to the publication of the theological reform tract Essays and reviews in January 1860 as to that of Origin itself. This volume of seven essays, whose authors (six of whom were clergymen) were liberal critics of prevailing Church doctrine, was more inspired by the German movement of historico-literary criticism of biblical texts than it was by new developments in science. But the correspondence shows that the two separate attacks on orthodoxy were related. Sedgwick, for example, stated publicly at a meeting of the Cambridge Philosophical Society in May that ‘his chief attacks were directed against Powell’s late Essay’ in Essays and reviews rather than against Darwin’s book per se. Prodded by Henslow’s defence of the integrity of Darwin’s scientific motivation, Sedgwick admitted that he was distressed that Powell had, in his opinion, ‘accepted all Darwin had suggested, & applied these suggestions (as if the whole were already proved) to his own views.—’ (letter from J. S. Henslow to J. D. Hooker, 10 May 1860). What worried Darwin most about such attacks was what the effect might be ‘of so many heavy guns fired by great men’, believing that they might retard the theory’s gaining any new converts or even cause earlier proponents (like Lyell) to retract their support altogether letters to Charles Lyell, 1 June [1860] and 11 August [1860]).

As the months passed by, Darwin read each review with less trepidation, commenting on each, and the private communications he received, in letters to his closest confidants Hooker, Lyell, and Gray. Initially he found it curious ‘how differently different opposers view the subject’ (letter to Charles Lyell, 15 February [1860]); later he became ‘fairly sick’ of the notices as he increasingly realised that one of the reasons for the paucity of novel objections to his views was that very few reviewers actually understood his theory. Somewhat exasperated after reading William Hopkins’s hostile critique of his geological argument, he wrote to Lyell on 6 June [1860]:

I am beginning to despair of ever making the majority understand my notions. Even Hopkins does not thoroughly . . . I must be a very bad explainer.

This was not, however, his opinion of Asa Gray, who Darwin thought understood his argument perhaps better than anyone else. Having been impressed by Gray’s review in the American Journal of Science and Arts, Darwin was elated by his series of three (unsigned) articles published in the Atlantic Monthly. Although intended to counter the powerful opposition to Origin in America by Louis Agassiz and his followers, Gray’s essays, Darwin believed, could also serve a purpose in Britain. He immediately wrote to Gray on 10 September after studying the first published piece:

I said in a former letter that you were a Lawyer; but I made a gross mistake, I am sure that you are a poet. No by Jove I will tell you what you are, a hybrid, a complex cross of Lawyer, Poet, Naturalist, & Theologian!— Was there ever such a monster seen before?

Gray’s essays attempted to show that the operation of natural selection was compatible with continued belief in Design in nature. Even though unable to believe in design himself, Darwin recognised that Gray’s argument could be a powerful antidote to the theological attacks on his book that were rife in England. He immediately set about arranging for the publication of Gray’s articles in Britain: the first article appeared in the Annals and Magazine of Natural History, and all three pieces were published together under Gray’s name in a pamphlet (Gray 1861) with the publication costs shared equally by Darwin and Gray.

Darwin was not, however, entirely preoccupied in 1860 with his critics and the reception of Origin. This work was, after all, only an ‘abstract’ of his theory. His critics merely reinforced his agenda: their remarks led to detailed arguments in his subsequent works. Only two days after the second edition was issued, on 9 January 1860, he turned to preparing the first part of his planned three-volume work intended to buttress the compressed arguments of Origin. Many of the letters of 1860 pertain to his collection of further facts in support of his postulate of a vast amount of variation among plant and animal species on which natural selection could operate. He wrote to various correspondents in the hope of finding more cases of striping in dray and cart horses, of inheritance in fowls, of the intercrossing among sweet-pea plants, of variation in the nests of bees and wasps, and of a myriad of other phenomena that provided empirical support for his arguments. He recommenced writing his chapter on pigeons (interrupted in 1858 by the receipt of Wallace’s manuscript and the subsequent drafting of Origin ), and he wrote up anew a chapter discussing the origin of various breeds of dogs. By June it was clear that his materials on variation alone would fill one volume exclusively; in the event, they ran to two. The work drained him, yet he persevered, strongly believing in the importance of the task. It would provide evidence in support of his theory that would help to ‘stagger’ the new generation of naturalists, who Darwin felt were crucial to the ultimate triumph of his theory. ‘I can pretty plainly see’, he commented to Huxley on 2 December, ‘that if my view is ever to be generally adopted, it will be by young men growing up & replacing the old workers, & these young ones finding that they can group facts & search out new lines of investigation better on the notion of descent, than on that of creation.—’ The new book on which he laboured was intended to provide just that mass of documentary evidence by which this process could best be advanced.

But Variation was not the only ‘evolutionary tract’ on which Darwin worked in the months after publishing Origin. Turning to pursue a number of topics about which he had long been curious, he began a serious study of several different botanical problems. For more than twenty years, Darwin had observed the role of insects in the fertilisation of plants. In the spring and summer of 1860, he began to investigate the problem in detail, focusing on specific aspects of the structure of the flower parts of various species. He drew up a list of those species in which the pistil appeared to be bent toward the nectar-secreting surface of the flower. ‘Why I care about it,’ he confided in Hooker, ‘is that it shows that visits of insects are so important, that these visits have led to changed structure.’ (letter to J. D. Hooker, 27 April [1860]). Tracing the complicated contrivances by which insects, in getting at the nectar, inadvertently become transporters of pollen (and hence agents effecting cross-pollination between different plants) necessitated meticulous microscopic examination of the fructifying structures of many plant species. Orchids in particular came to his attention as being ‘beautifully adapted’ to insect visitation. The project engrossed Darwin, as he examined one genus after another. ‘I am intensely interested on subject,’ he told Hooker several months later, ‘just as at a game of chess.’ (letter to J. D. Hooker, 19 [July 1860]). With the work halted by the coming of winter, Darwin carried over the investigation to the next year and published the results of the orchid study in 1862.

Another botanical project was a study of primroses and cowslips, which Darwin had discussed in Origin in regard to whether the oxlip, intermediate in form between the two, could be considered as a hybrid offspring and hence an example of an incipient species. But it was the evolution of sex, not speciation, that captured his interest, just as it had in his earlier study of the cirripedes. A chance observation of two different forms of the flower parts of cowslips soon evolved into an extensive piece of botanical research. Keeping Hooker closely informed on the progress and results of his study, he wrote on 7 May [1860]:

I have this morning been looking at my experimental Cowslips & find some plants have all flowers with long stamens & short pistils which I will call ‘male plants’—others with short stamens & long pistils, which I will call “female plants” . . . I cannot help suspecting that the cowslip is in fact dioicous—but it may turn out all blunder, but anyhow I will mark with sticks the so-called male & female plants & watch their seeding. It would be fine case of gradation between an hermaphrodite & unisexual condition.—

He presented the results of his study in a paper of 1862 and in The different forms of flowers on plants of the same species (1877).

Serendipity led to the commencement of what was to become a fifteen-year-long investigation. During visits to Hartfield in July and Eastbourne in September and October, he amused himself by observing how the common sundew of the Sussex heaths, Drosera rotundifolia, was able to capture insects. A casual observation soon turned into a passionate investigation of one very curious point, soon revealed to Hooker: ‘The leaves are first rate chemists & can distinguish even an incredibly small quantity of any nitrogenised substance from non=nitrogenised substances.’ (letter to J. D. Hooker, 31 [August 1860]). Relying in part on his youthful experiences in chemical experimentation (see Correspondence vol. 1), and the tenaciousness exhibited in all his undertakings in natural history, he tested the sensitivity of various insectivorous plants to a large variety of substances, observing their digestive processes at the cellular level. Describing her husband’s current enthusiasm, Emma Darwin wrote to Mary Lyell: ‘At present he is treating Drosera just like a living creature, and I suppose he hopes to end in proving it to be an animal.’ ( Emma Darwin 2: 177). As was so frequently the case with his research topics, Darwin was able to solicit the assistance of a number of other specialists who also became deeply engrossed in his experimental regime. In this instance, he drafted the services not only of Hooker but also of a newly appointed Kew botanist, Daniel Oliver; his old friend and neighbour Edward Cresy; and Cresy’s acquaintances August Wilhelm von Hofmann, the renowned German organic chemist, and Alfred Swaine Taylor, an authority on poisons and tests for chemical sensitivity. After finding ‘one suspicious case’ in his experimental record, however, Darwin abandoned his original intention to publish a short paper on the subject, fearing that his estimate of the astonishing sensitivity of the leaves of these plants to minute quantities of nitrogenous substances would scarcely be believed without further supporting evidence (letter to Edward Cresy, 12 December [1860]). This work was not published until 1875, when Insectivorous plants appeared.

These studies offered naturalists different perspectives of the marvellous adaptive mechanisms of plants; moreover, they showed how the design of such structures could be interpreted on the basis of the theory of natural selection. As the letters between Darwin, Hooker, and Oliver indicate, the novelty of this approach to botanical research was striking even to experts in that field who were favourably disposed to his views. In future years, his botanical work served as models for investigation in natural history, graphically illustrating the conceptual and methodological power of the theory. This is not to say that Darwin himself was conscious of attempting to initiate an evolutionary ‘research programme’. Indeed, he was rather apologetic about having spent so much time on the Drosera study in particular, admitting to Lyell ‘how much better fun observing is than writing.—’ (letter to Charles Lyell, 12 September [1860]). Despite the fact that he cared ‘more about Drosera than the origin of all the species in the world’, he told Oliver he was going to put away his mass of notes, ‘for I am convinced that I ought to work on Variation & not amuse myself with interludes.—’ letters to Charles Lyell, 24 November [1860], and to Daniel Oliver, 20 October [1860]).

In the event, however, Darwin’s work on variation had to be interrupted for other reasons. His health was still a source of continued anxiety and annoyance, disturbing his work and causing him to miss the British Association meeting. But it was the health of his daughter Henrietta that caused the family the greatest concern. Having suffered intermittent bouts of illness for the past few years, Etty fell seriously ill late in April 1860 with what was eventually diagnosed as a form of typhus fever. With the memory of their older daughter Anne’s fatal illness never far from their minds, Charles and Emma did whatever they could to promote Etty’s recovery, even if it meant interrupting his precious studies.

His work was also halted abruptly late in November when Murray again called for a new edition of Origin. This gave Darwin the opportunity to make a number of corrections and additions ‘in the hopes of making my many rather stupid reviewers at least understand what is meant.— I hope & think I shall improve the Book considerably.—’ (letter to John Murray, 5 December [1860]). Although he took Lyell’s advice not to name any names when responding to his reviewers, he nonetheless added a considerable amount of new material in support of his various arguments, as well as including in the third English edition the historical preface (acknowledging naturalists who had propounded views about species change) previously printed in the German and American editions.

In light of the criticism his book had received over the past year, Darwin was determined to do what he could to make his doctrines more generally understood, realising that the process of acceptance would be a long and gradual one. ‘I never expected to convert people under 20 year,’ he told his friend John Innes, ‘though firmly convinced now that I am in the main right.— For a week hardly passes without my hearing of some good judge coming some little way with me.’ (letter to John Innes, 28 December [1860]).