Mauro Galetti solved Darwin’s puzzle of the ‘bright seeds’. This is what he told us about becoming an ecologist:

Like every kid, I always liked to be in the woods and watch animals in the zoo. When I decided to start my career in biology in Brazil, I did not really know what kind of job I would take, but I knew that to be successful in any career I needed to do what I enjoyed most. While at university I started studying the behavior of howler monkeys in a forest near my university. Twice a week I spent the whole morning studying what they ate, where they moved, how they divided the space with other animals. This gave me experience and time to watch other organisms in the forest, such as squirrels, birds, capuchin monkeys and, of course, plants. As a zoologist, I never realized how complex and interesting the strategies are that plants have evolved to attract animals for pollination or seed dispersal. I started collecting all kind of fruits in this wood and described for each species the strategy that they used for dispersal. Some fruits are dispersed by wind, a few by ants, but most of them (in Brazil) are dispersed by birds or mammals. My second favorite place was always the library of my university. After coming from the field, I spent one or two hours reading the scientific journals and books. Knowing what the “top scientists” are studying and why they are doing their research is a fundamental step for every student. Since most of the journals or books were in English, it took me a long time to translate each paper, or each book. This is certainly the largest barrier to doing science in non-English-speaking countries. Now, describing fruit strategies is a kind of hobby and job, and I enjoy traveling to new places to compare how plants disperse their fruits. This is relevant to understanding evolution and ecology, and has been a major tool in speeding up the restoration of wild places.

In one of these places I came across an Ormosia tree, full of red and black seeds, with no pulp. I knew from old naturalists, like Darwin, Ridley and van der Pijl, that some fruits ‘tried’ to mislead birds and evolved colourful fruits but no fleshy reward, the so-called mimetic seeds. I never took this idea for granted, and decided to investigate on my own. So, I spent two years coming every month to this place to study this species. First, I marked and mapped all Ormosia trees. I could find no more than eight trees in a 2200 hectare region! They were very rare. In the meantime, I also found several other species with the same strategy: Margaritaria nobilis, Rhynchosia pyramidalis and Abrus precatorius. After marking all the Ormosia, I started watching every morning, to see whether any bird would come to eat its mimetic fruits. After many, many days, no success. In the same place I found some fruiting trees of Copaifera langsdorffii, a leguminous tree, with a very similar fruit display, but with a pulp reward for the dispersers. So, I started my experiments transplanting Copaifera arils to Ormosia seeds and placed them on the ground to see whether wild birds would take them. Later, I decided to try with captive birds. My findings show that it is hard to mislead a bird, but naïve (captive-born) birds are easily misled by Ormosia seeds. Nowadays, I continue studying the adaptations of fruits to dispersal, especially the ones dispersed by extinct megafauna.

As the first of a planned series of collaborations, The Darwin Correspondence Project and Cambridge University’s Centre for Gender Studies hosted a public lecture by Professor Dame Gillian Beer on ‘Darwin and the Descent of Woman’ at the Pitt Building, Cambridge, on 2 June 2010.  The lecture was followed by a discussion with Professor Juliet Mitchell, Emeritus Professor of Psychoanalysis and Gender Studies, chaired by the Project’s Director, Professor Jim Secord.  The lecture and reception were attended by more than one hundred people.  There is more information, including the suggested readings from Darwin’s Descent of Man, available on the Gender Studies website.

Professor Beer used unpublished letters in her lecture the texts of which were provided by the Darwin Correspondence Project.  These included an exchange of letters between Darwin and the poet Emily Pfeiffer (1827–90) in 1871 in which they discussed Darwin’s conclusions in Descent of Man about beauty and aesthetic sense and their role in sexual selection.  Pfeiffer suggested that ‘beauty does not necessarily fascinate, & that fascination does not always imply beauty’ (letter from E. J. Pfeiffer, [before 26 April 1871]).  Their letters will be published in volume 19 of The correspondence of Charles Darwin, and the full texts made available ahead of normal schedule through this website as part of the ‘Darwin and Gender’ project.

Pfeiffer is best known for her poetry exploring the role and status of women, some of it clearly inspired by her reading of Darwin’s works.  Self-taught, she was a supporter of formal education for women and left money to found a number of women’s education initiatives.

Order this volume online from Cambridge University Press.

Introduction

The year 1870 is aptly summarised by the brief entry Darwin made in his journal: ‘The whole of the year at work on the Descent of Man & Selection in relation to Sex’ . Always precise in his accounting, Darwin reckoned that he had started writing on 4 February 1868, only five days after the publication of his previous book, Variation in animals and plants under domestication. In fact, Descent was the culmination of over three decades of observations and reflections on human ancestry, including the origin of language, mind, morals, and religious temperament. Research on sexual selection and emotional expression had predominated in recent years, and the information gathered on each of these topics was far more extensive than Darwin had anticipated. As a result, Descent, like Variation, would require two large volumes, and by June Darwin gave up the idea of including the material on emotion; it would eventually appear as a separate book in 1872 (Expression of the emotions in man and animals). The year was otherwise coloured by controversies, including vigorous objections to the application of natural selection to humans from Alfred Russel Wallace and St George Jackson Mivart, and heated debates sparked by Darwin’s proposed election to the French Academy of Sciences and his nomination for an honorary degree at Oxford. As usual, Darwin tried to avoid involving himself in such controversies, saving his energies for his scientific work and his family. As he was completing corrections to the final proofs of Descent in December, he wrote to his friend Charles Lyell, ‘thank all the powers above & below, I shall be a man again & not a horrid grinding machine’  (letter to Charles Lyell, 25 December [1870]).

Darwin began receiving proofs of some of the illustrations for Descent as early as January, including woodcuts of the heads of chameleons and the tail feathers of snipe, much to his delight: ‘The sight of the proofs has pleased me more than anything which has happened to me for some weeks’  (letter to Albert Günther, 13 January [1870]). Darwin was still working hard on parts of the text, in particular his chapters on the moral sense and the comparative mental powers of humans and animals. He turned, as he had before, to his daughter Henrietta for commentary, sending her parts of the manuscript while she was on holiday in France and Italy: ‘After reading once right through, the more time you can give up for deep criticism or corrections of style, the more grateful I shall be’  (letter to H. E. Darwin, [8 February 1870]). She had previously read proof-sheets of Variation and Orchids, the latter when she was just eighteen years of age. CD clearly expected her to make a considerable contribution, instructing her to write any long corrections on separate slips of paper pinned to the relevant page of manuscript. He worried that parts of the book were ‘too like a Sermon: who wd ever have thought that I shd. turn parson?’ (letter to H. E. Darwin, [8 February 1870]). Henrietta disagreed: ‘Certainly to have you turned Parson will be a change I expect I shall want it enlarging not contracting cos I think you think an apology is wanting for writing abt any thing so unimportant as the mind of man!’ (letter from H. E. Darwin, [after 8 February 1870]). Darwin was also encouraged to expand his discussion of mind and morals by the religious writer and philanthropist Frances Power Cobbe. At Cobbe’s suggestion, Darwin read some of Immanuel Kant’s Metaphysics of ethics, and he remarked on the contrast between the ‘great philosopher looking exclusively into his own mind’, and himself, ‘a degraded wretch looking from the outside thro’ apes & savages at the moral sense of mankind’ (letter to F. P. Cobbe, 23 March [1870?]). Cobbe accused Darwin of smiling in his beard with such remarks, and urged, ‘are you never going to unite your lines of thought & let us see how metaphysics & physics form one great philosophy?’ (letter from F. P. Cobbe, 28 March [1870?]).

Despite Cobbe’s plea, most of Darwin’s scientific attention in 1870 was devoted to the ‘physical’ side of human descent. On 7 March 1870, Darwin made a note on the shape of human ears: ‘W. has seen the tips in women & men. When he was making his figure of Puck he went to Z garden and made drawings of ears of monkeys & shortly afterwards he saw a man with tip & instantly recognized their signification’  (DAR 80: B120). The reference here is to the sculptor Thomas Woolner, and to his statue of Puck, the mischievous fairy in Shakespeare’s A midsummer night’s dream. Darwin obtained a sketch of a human ear from Woolner showing the unusual feature of a pointed tip projecting inward from the folded margin. Darwin, who had posed for the sculptor in 1868, an experience he described as ‘purgatory’ made lighter by Woolner’s ‘wonderfully pleasant’ manner, named the feature after the famous artist. ‘The “Woolnerian tip” is worth anything to me’, he wrote in thanks for the drawing (Correspondence vol. 16, letter to J. D. Hooker, 26 November [1868]; this volume, letter to Thomas Woolner, 10 March [1870]). Darwin included Woolner’s sketch in Descent, and discussed the ‘tip’ as a rudimentary organ, describing its frequency and variability in humans (Descent 1: 22-3).

A more troubling anatomical feature for Darwin was the platysma myoides, a band of muscle in the neck extending from the collar bone to the lower part of the cheek. Darwin had read various accounts of the contraction of this muscle in persons experiencing fear or terror. He studied the photographic album by the French physiologist Guillaume Benjamin Amand Duchenne, whose research involved the mechanical production of expressions by applying electrodes directly to the face and neck. Duchenne had dubbed the platysma the ‘muscle of fright’, and one of his photographs, later used by Darwin in Expression, showed a man whose platysma was severely contracted, his face exhibiting extreme horror. Darwin lent Duchenne’s album to the asylum director James Crichton-Browne, who had become one of Darwin’s most avid observers of facial expression. Browne sent a lengthy account of the movements of the platysma muscle in his asylum patients, but it did not confirm Duchenne’s findings (letter from James Crichton-Browne, 15 March 1870). Indeed, Darwin noted the same longitudinal furrows radiating on the side of the neck of his son Francis when he was playing the flute. Exasperated, Darwin turned to the physician and eye-specialist William Ogle, requesting him to observe the muscle in patients who were having trouble breathing. ‘This muscle’, he complained, ‘is the bane of existence!’ (letter to William Ogle, 9 November 1870).

Darwin’s research on emotions continued to draw on observations from a variety of domains, from the colonial frontier to the household, from the photographer’s studio to the zoological garden. He received more replies to his questionnaire on expression, including four lengthy letters from the explorer William Winwood Reade, who had led an expedition to Africa in search of the source of the Niger river. Reade was sceptical of Darwin’s view that standards of beauty were variable across different cultures and claimed that Africans admired the racial characteristics of Europeans. The nose, he remarked, was ‘the only doubtful point . . . girls have been heard to say “I dont want to marry him he’s got no nose”. Reade noted the strong preference of native peoples for black skin, but attributed this to their belief that all demons and spirits were white (letter from W. W. Reade, 9 November 1870).

Keen for more evidence of the continuity of expressions across species, Darwin asked the zoo-keeper at Regent’s Park to study the squirrel monkey’s screams: ‘does it wrinkle up the skin round the eyes like a Baby always does? . . Could you make it scream without hurting it much?’ (letter to A. D. Bartlett, 5 January [1870]). Darwin made a similar request of a London photographer: ‘I have been trying to get a [photograph] of a young baby screaming or crying badly; but I fear he will not succeed’ (letter to James Crichton-Browne, 8 June [1870]). Darwin’s queries were part of an investigation into the physiology of weeping that had begun with observations on his own children as early as 1839. Darwin now recruited family members with infants, including his niece Lucy Wedgwood, who sent a sketch of a baby’s brows (letter from L. C. Wedgwood, [5 May 1870]). He also wrote to a leading Dutch ophthalmologist, Frans Cornelis Donders. In order to fulfil Darwin’s request, Donders undertook painstaking experiments on the operation of the eye muscles in weeping. He wrote to Darwin when his work was interrupted by the death of his daughter in childbirth: ‘We are living with a sorrow which it seems can never end, and . . . I have found it hard to return to the laboratory and to attend to our occupations. . . . I have examined the circulation of the eye with some care, and all I am lacking is the inclination to finish my note on this subject’  (letter from F. C. Donders, 17 May 1870).

While Darwin was still revising his manuscript of Descent, the public debate over human evolution grew more heated. Alfred Russel Wallace had expressed reservations about the application of natural selection to the development of the higher intellectual faculties of humans the previous year (see Correspondence vol. 17, letter to A. R. Wallace, 14 April 1869). His views were presented more fully in a collection of essays published in April 1870 (Wallace 1870a). Wallace wrote to Darwin in January warning him of the impending publication. Darwin joked about Wallace’s own intellectual descent: ‘I groan over Man – you write like a metamorphosed (in retrograde direction) naturalist’ (letter to A. R.Wallace, 26 January [1870]). Despite their increasing theoretical differences, both men worked as they had in the past to sustain goodwill and mutual respect. Wallace’s new book, titled Contributions to the theory of natural selection, was dedicated to Darwin. When he received the book, Darwin was full of praise for Wallace’s ‘modesty and candour’. ‘I hope it is a satisfaction to you to reflect, – & very few things in my life have been more satisfactory to me – that we have never felt any jealousy towards each other, though in one sense rivals’ (letter to A. R. Wallace, 20 April [1870]). Darwin alluded here to the famous events of 1858,When Wallace had communicated his own version of the theory of descent by natural selection in a letter to Darwin, prompting much anxiety on Darwin’s part over his priority of discovery.

While Darwin and Wallace remained on amicable terms, other supporters of Darwinian theory were concerned about the consequences of Wallace’s book. Henry Walter Bates urged Darwin to respond to it directly in the form of a review: ‘I have been having some conversation with the Editor of the “Academy” about Mr Wallace’s last book & the appearance of backsliding from the Darwinian theory which it contains. . . . The views of friend Wallace are so plausible & suit so well wide-spread prejudices that you no doubt think with me they ought to be controverted. But who is to criticise them? No one but yourself’ (letter from H. W. Bates, 20 May 1870). Darwin very rarely used the periodical press to reply to critics, preferring to address what he considered to be important objections in the revised editions of his own publications. To Bates, he pleaded lack of time and weak health: ‘my chief reason is that I really have not a grain of spare strength. . . . You wd. not readily believe how often & urgently I am pressed to write articles . . . & it is an immense relief to me to be able to say that I never write reviews’ (letter to H. W. Bates, [22 May 1870]).

Another set of objections to the extension of natural selection to human evolution came from the zoologist St George Jackson Mivart. A protégé of Thomas Henry Huxley, Mivart had established a reputation as a leading comparative anatomist through his work on primates. In July 1869, Mivart published the first of a series of articles, titled ‘Difficulties of the theory of natural selection’, in the Roman Catholic journal the Month. He argued that a number of physical structures and homologies could not have arisen through the operation of natural selection alone, and that these were better accounted for by an underlying design. Darwin commented on Mivart’s essay in a letter to William Henry Flower: ‘I am glad you noticed the curiously false argument in the Month. . . . I cd have answered, I think satisfactorily, many of the objections advanced in this article; but my whole time wd be wasted if I once began to answer objectors’ (letter to W. H. Flower, 25 March [1870]). In his letters to Mivart, Darwin remained cordial and supportive, praising his earlier anatomical papers and urging him to resume his research: ‘I hope that you will continue your wonderfully laborious & valuable labours on the Primates’ (letter to St G. J. Mivart, 23 April [1870]). He also tried to recruit Mivart’s expertise, and inquired after a point of human and ape anatomy, hoping to cite Mivart as an authority in Descent. Mivart’s reply, however, underscored their fundamental differences on human ancestry: ‘assuming that zoological classification should be Anatomical– Man forms only a family of the higher division of the Primates. But if we introduce into the consideration his intellectual, moral & religious nature I am convinced he differs more from an Anthropoid Ape than such an Ape differs from a lump of granite’ (letter from St G. J. Mivart, 22 April 1870). Mivart hinted that his criticism of descent theory was not directed at Darwin himself, but at more aggressive champions of Darwinism: ‘For my part I shall never feel anything but gratitude & sincere esteem for the author of “natural selection” but I heartily execrate some who make use of that theory simply as a weapon of offence against higher interests and as a means of impeding Man’s advance towards his “end” whatever may have been his “origin” (letter from St G. J. Mivart, 25 April 1870). In his critical essays (later revised as Genesis of species (Mivart 1871)), Mivart tried to carve out a position between the new evolutionary biology that was being promoted by Huxley and others as an instrument of social reform, and another constituency to which he was equally loyal, the Roman Catholic Church. The relationship between Mivart and Darwin would grow more strained in the next few years and eventually reach breaking point.

Darwin’s name and theory served a number of polemical and political ends. In France, Darwin was proposed for a corresponding membership of the elite Academy of Sciences, prompting an extended debate. The nomination was made by Henri Milne-Edwards and Armand de Quatrefages, both leading zoologists in Paris. Quatrefages had just completed a book, Charles Darwin et ses précurseurs français (Quatrefages 1870), that gave a detailed account, as well as criticism, of Darwin’s theory. On receiving the book, Darwin remarked, ‘many of your strictures are severe enough, but all are given with perfect courtesy & fairness. I can truly say I would rather be criticised by you in this manner than praised by many others’  (letter to Armand de Quatrefages, 28 May [1870]). Quatrefages had corresponded with Darwin regularly since 1859, and viewed his relationship with Darwin as embodying the virtues of scientific community, placing truth above individual or factional differences. ‘Yes, I dare to say it,’ he wrote, ‘we are both pursuing truth and that alone must establish links between us which are stronger than the causes of discord’  (letter from Armand de Quatrefages, 30 March 1870). In proposing Darwin for election, Quatrefages hoped to bring the same non-partisan spirit into the French Academy, ‘rest assured that I shall be a zealous and convinced advocate. . . . Our very dissensions will give more weight to my words’. In fact, the election served as an occasion for attacks not only on Darwin’s theory, but on his scientific methods and his status as a naturalist. ‘It is being said at the Academy’, Quatrefages complained, ‘. . . that you had done no more than collect natural history specimens and that you had called on assistants to describe them’  (letter from Armand de Quatrefages, 18 July 1870). The assertion had been made by Emile Blanchard, who added that Darwin’s pigeon studies were unscientific, and that his various theories, from coral island formation to transformism, were either unoriginal or false. Another detractor, Léonce Elie de Beaumont, referred to Darwin’s work as ‘la science mousseuse’ (a science of froth or bubbles). Quatrefages himself seemed uncertain about some of these charges, and he seemed unaware that Darwin had published any of his geological research from the Beagle voyage.

Darwin lost the election by a narrow margin. The defeat was seized upon as a matter of national pride by the Belgian zoologist Edouard van Beneden when the Belgian Academy elected Darwin an associate member later that year. ‘In this matter the Belgians have taught the members of the Institut de France a lesson,’ he wrote. ‘May all the learned bodies of the world protest, like the Academy of Belgium, against the debate they dared instigate on the question of your scientific merits. Your name summarises the whole scientific movement of recent years and your immortal work is above all attacks’  (letter from Edouard van Beneden, 17 December 1870). A more parochial controversy occurred in Oxford, when Darwin was chosen to receive an honorary degree. Among the other candidates had been Thomas Huxley, who wrote to Darwin about the heated debate that had taken place in the ruling body of the University, and the role played by a leading Anglican conservative, Edward Bouverie Pusey: ‘There seems to have been a tremendous shindy in the Hebdomadal board about certain persons who were proposed; and I am told that Pusey came to London to ascertain from a trustworthy friend who were the blackest heretics out of the list proposed – and that he was glad to assent to your being doctored, when he got back – in order to keep out seven devils worse than that first!’ (letter from T. H. Huxley, 22 June 1870). In the event, Darwin did not receive the degree because it could only be awarded in person, and he declined to attend the ceremony on grounds of weak health: ‘I could have travelled to Oxford,’ he confessed, ‘but could no more have withstood the excitement of a commemoration than I could a ball at Buckingham Palace’ (letter to B. J. Sulivan, 30 June [1870]).

Though Darwin was mostly occupied with the revision of Descent and research on expression, his attention was frequently diverted by correspondents to topics of long-standing interest. The Italian botanist Federico Delpino sent a description of a pollination mechanism in Lotus siliquosus (now L. maritimus), a sample of which had been collected by one of Darwin’s sons: ‘This . . . apparatus, which I have called “papilionaceous pump apparatus” is rather marvellous. It is similar to the instrument with which one makes pasta at the vermicelli-makers.’  Bees settling onto the carina of the flowers caused the pistil and filaments to press upon the pollen-mass, which was then ejected through a small hole in the carina and attached to the insects (letter from Federico Delpino, 20 May 1870). Darwin encouraged the German naturalist Hermann Müller to continue his work on the adaptation of insect structures, in particular the mouth-parts of bees, to the forms of flowers: ‘As far as I know, no one has carefully observed the structure of insects in relation to flowers, although so many have now attended to the converse relation’ (letter to Hermann Müller, 14 March 1870). Darwin received a string of letters from his cousin Francis Galton, reporting on his efforts to alter the colour of rabbits by transfusing the blood of one variety into another and observing the colour of the offspring. The experiments, designed to test Darwin’s hypothesis of pangenesis, sometimes involved unusual procedures: ‘I hope to succeed in making the ears of two young rabbits grow together & to mix their circulations by breaking adjacent veins into one’ (letter from Francis Galton, 25 June 1870). Occasionally Galton reported success: ‘Good rabbit news.! One of the latest litters has a white forefoot’  (letter from Francis Galton, 12 May 1870). But in general the results were discouraging. Darwin’s pangenesis theory also prompted speculation among some of his correspondents about the influence that males could have, both upon later generations of offspring not sired by them, and upon the females with whom they had mated. Some thought that male ‘gemmules’ (the material of hereditary transmission in Darwin’s theory) might be transmitted to the female by the circulation of blood between the mother and foetus during pregnancy. As a case in point, John Jenner Weir described the offspring of a mare that had once mated with a quagga as resembling a donkey; he also added: ‘It may be fanciful on my part but I cannot but think that my theory accounts for what has been so often noticed that persons long married grow like each other’ (letter from J. J. Weir, 17 March 1870). With Joseph Dalton Hooker, Darwin discussed the recent experiments of Henry Charlton Bastian, which Bastian claimed showed evidence of the spontaneous generation of life from inorganic matter: ‘Spontaneous generation seems almost as great a puzzle as preordination; I cannot persuade myself that such a multiplicity of organisms can have been produced, like crystals, in Bastian’s solutions of the same kind’ (letter to J. D. Hooker, 12 July [1870]). Bastian’s results were criticised in a presidential address to the British Association for the Advancement of Science by Thomas Huxley, who had identified bits of the moss Sphagnum in Bastian’s supposedly empty and sealed test tubes. Huxley’s address also discussed recent experiments by Louis Pasteur and John Tyndall that provided evidence for the existence of germs.

Some of the wider implications of evolutionary theory for medicine and society were explored in a campaign that Darwin initiated to gather information about the potentially harmful effects of cousin marriage. Darwin wanted to test the prevalent assumption that marriages to first cousins were injurious to offspring. He wrote initially probably to Henry Hussey Vivian, an MP and fellow of the Geological Society: ‘I have every cause to believe that the time will soon come, when this subject will be . . . highly important for the welfare of mankind’ (letter to [H. H. Vivian?], [April or May 1870?]). Vivian contacted the home secretary, Henry Austin Bruce, about the possibility of inserting a question in the 1871 census about cousin marriage. Darwin believed that if such statistics could be obtained, they could be correlated with figures regarding the frequency of deafness, blindness, and other conditions in the offspring of consanguineous marriages. He enlisted the support of William Farr, a specialist in medical statistics who worked in the registrar-general’s office, in drafting a memorandum. He asked his neighbour, the naturalist John Lubbock, who was now MP for Maidstone, to present the proposal to the House of Commons. Lubbock read Darwin’s letter before the Commons on 26 July, ‘As you are aware, I have made experiments on the subject during several years; & it is my clear conviction that there is now ample evidence of the existence of a great physiological law, rendering an enquiry with reference to mankind of much importance’ (letter to John Lubbock, 17 July 1870). The motion to amend the Census was defeated by a vote of ninety-two to forty-five.

As was usual in periods of reasonably good health, Darwin seldom took breaks from his scientific work except to receive friends and visit family. He confided to his cousin William Darwin Fox, ‘I never pass 6 hours without a fit of extreme discomfort, & so I shall go on to the last of my uncomfortable days’ (letter to W. D. Fox, 18 February [1870]). But he had resumed horse-riding and, subject to the usual qualifications, Darwin’s health was generally good. He did consult Henry Bence Jones, his physician since 1865, regarding ‘pins & needles’. Jones replied, ‘some stopped molecular action I suppose which is somehow related to your indigestion. Altho’ the manner is very dark to me and to every one else I suspect’ (letter from H. B. Jones, 2 August 1870). Darwin had visits from a number of scientific friends and colleagues at Down, including Alexander Agassiz and his family, Anton Dohrn, Albert Günther, Joseph Hooker, Rudolf Albert von Kölliker, Alfred Newton, Robert Swinhoe, and Vladimir and Sofia Kovalevsky. In November, he received a permanent guest in the form of a Scottish deerhound puppy, the pride and joy of George Cupples, who had written to Darwin regularly over the course of the year to apprise him of the dog’s progress and fine breeding: ‘the father is descended from Sir Walter Scott’s celebrated “Maida”’ (letter from George Cupples, 17 September 1870). Darwin reassured Cupples after the dog arrived, ‘Bran is thriving & growing at a wonderful rate – coat sleek, & not too fat. Plays much with Polly & enjoys English life’  (postcard to George Cupples, 27 November [1870]). In addition to receiving many visitors, Darwin was also away from Down more than usual, staying on three occasions in London with his brother Erasmus, a week in Surrey and at Ightam Mote, in Kent, and nearly a fortnight with his son William in Southampton, and making a four-day visit to Cambridge. While in Cambridge, he toured the Woodwardian Museum with his former professor of geology, Adam Sedgwick. ‘He utterly prostrated me,’ Darwin wrote to Hooker, ‘. . . & I have not recovered the exhaustion yet. Is it not humiliating to be thus killed by a man of 86’  (letter to J. D. Hooker, 25 May [1870]). On learning of this, Sedgwick replied: ‘I was truly grieved to find that my joy at seeing you again was almost too robust for your state of nerves. . . . I only speak honest truth when I say that I was overflowing with joy when I saw you; & saw you in the midst of a dear family party & solaced at every turn by the loving care of a dear Wife & Daughters. How different from my position – that of a very old man, living in cheerless solitude!’ (letter from Adam Sedgwick, 30 May 1870).

Darwin continued to take great pride in his children, and to worry about any potential waywardness on their part. He reflected on the responsibilities of finding a course in life for one’s sons to Hooker: ‘God knows it is puzzle enough in every case whatever; & what our Boy Horace is to do, I know no more than the man in the moon’ (letter to J. D. Hooker, 25 May [1870]). Horace had entered Trinity College, Cambridge, in the autumn of 1870. Darwin was concerned that his poor health in previous years had left him behind, and arranged for him to have private instruction in mathematics. He wrote to Horace’s tutor at Trinity to request that he be excused from attending college lectures for the time being (letter to [E.W. Blore], [October 1870 or later]). Leonard continued to have great success in the army. He gained a commission in the Royal Engineers, obtaining the second highest marks among the candidates. Francis completed his studies at Cambridge, taking third place in first-class honours in the natural sciences tripos in December. He had fallen into debt, however, and had kept the matter secret for some months. Darwin was very stern in his advice: ‘I have never known a man who was too idle to attend to his affairs & accounts, who did not get into difficulties; & he who habitually is in money difficulties, very rarely keeps scrupulously honourable. . . . My father, who was the wisest man I ever knew, thought it the duty of every man, young & old, to keep an account of his money; & I very unwillingly obeyed him; for I was not always so bothersome an old fellow as I daresay I appear to you’ (letter to Francis Darwin, 18 October [1870]). The affection and concern of the father for his children were reciprocated. George, who was now a fellow at Trinity College, Cambridge, wrote to Henrietta of his concern that his father, despite suffering a bad fall the previous year, continued to ride the same horse that had thrown him (letter from G. H. Darwin to H. E. Darwin, [21 – 2 February 1870] (DAR 251: 2243)). With some difficulty, he had found a mare so tame that she was ridden by a blind man and used at a school for timid riders. ‘She has a canter like an armchair’, he informed his father (letter from G. H. Darwin, [3 February 1870 or earlier]). George devoted considerable effort to securing the loan of the animal for his father, but the horse did not suit Darwin, and he evidently continued to ride the dangerous Tommy.

Darwin’s European correspondence was disrupted for part of the year owing to the outbreak of war. France had declared war on Prussia on 19 July 1870, and French troops had crossed the border into Prussia at the end of that month. But despite suffering heavy casualties, the Prussian armies won several decisive victories in August. Darwin followed the progress of the war in the press, and to his German correspondents he declared his allegiance to the Prussian cause. ‘I cannot express too strongly how I rejoice at the wonderful success of Germany,’ he wrote to Julius Victor Carus, ‘& I have not hitherto met a single person who has not entirely participated in this feeling’  (letter to J. V. Carus, 18 August 1870). Carus described how he had to abandon his work to care for the wounded, and how he found some ‘philosophic comfort’ in viewing the war as a ‘necessary consequence of natural conditions’, ‘a most dreadful “struggle for existence”’ (letter from J. V. Carus, 2 October 1870). Carus, who had already arranged to translate Descent into German, assured Darwin that the war would not interfere with the success of his book in Germany: ‘People are anxious to find a safe refuge in science’.

As completion of the book drew near, Darwin began to prepare for its reception, and for the disapproval that would greet his conclusions about the ‘origin of man’. ‘I can most truly say’, he wrote to his cousin William Darwin Fox, ‘that I have written nothing without deliberate consideration & acquiring all the knowledge which I possibly could. – I will send it, as I know well that you are a charitable man & do not without good evidence believe in bad motives in others’  (letter to W. D. Fox, 15 November [1870]). Fox reassured him, however, that descent from a monkey was no longer so hard to contemplate, for he had recently learned from the antics of the orang-utans at the Zoological Gardens in Regent’s Park that beasts shared the same vices as humans: ‘the Lady Monkey from the Andamans – drinks & smokes like a Christian; & evidently the Gentleman wd thrash, if not kill the Lady, if he had an opportunity’  (letter from W. D. Fox, 18 [November 1870]).

This volume contains a supplement of more than one hundred letters that have been discovered since the volumes they should have appeared in were published, or that have been redated to before 1870. It also contains some letters with wide date spans that were probably written before 1870. The supplement includes letters to William Kemp between 1840 and 1843, concerning Kemp’s geological discoveries in Scotland; letters to the Arctic explorer John Richardson thanking him for barnacle specimens; a letter to Charles Kingsley written shortly after the publication of Origin; and letters to Henry Fawcett thanking him for his favourable review of Origin, and reflecting on the methodological and theoretical difficulties of Darwin’s early research on species.

During 1870, Darwin was in the final stages of writing and revising Descent of man, and continued working on his next book, Expression of the emotions in man and animals. St George Jackson Mivart and Alfred Russel Wallace published criticisms of the theory of natural selection. Darwin was offered an honorary degree by Oxford University, was nominated for corresponding membership of the French Academy of Science, and was elected an associate member of the Belgian Academy. Translation of his works in Europe was disrupted by the onset of the Franco-Prussian war, but his translators continued to work with a will whenever they could.

Letters from this volume will be made available through this website in due course – by agreement with the publisher this will be four years from publication.   In the meantime, summaries of all the letters are available on this site, and the book can be ordered through libraries and booksellers.

Read the introduction to volume 18 here.

Cocos (Keeling) atoll, where Darwin studied the formation of coral reefs in 1836. Source: Wikimedia Commons

In his autobiographical ‘Recollections,’ Darwin describes how he arrived at his coral reef theory as follows:

No other work of mine was begun in so deductive a spirit as this; for the whole theory was thought out on the west coast of S. America before I had seen a true coral reef. I had therefore only to verify and extend my views by a careful examination of living reefs. But it should be observed that I had during the two previous years been incessantly attending to the effects on the shores of S. America of the intermittent elevation of the land, together with denudation and the deposition of sediment. This necessarily led me to reflect much on the effects of subsidence, and it was easy to replace in imagination the continued deposition of sediment by the upward growth of coral. To do this was to form my theory of the formation of barrier-reefs and atolls.

No statement of the theory that could be described as ‘thought out’ has been found in the extensive notes on geological observations that survive from the time Darwin spent on the west coast of South America. There are, however, several references in the field notebooks and letters of the South American period, which, though fragmentary and indirect, give evidence that Darwin had the main points of the theory clearly in mind before he left that continent, and that he looked forward to verifying it when he could observe the Pacific islands.

The central idea of his theory, as it was later formulated, was that the islands were formed by the upward growth of coral as the Pacific Ocean floor gradually subsided. A letter from Robert Edward Alison, who had assisted Darwin in his observations on the elevation of the Chilean coast, makes clear that by April 1835, when he was still at Valparaiso, Darwin had expressed to his friend his expectation that the Pacific islands would furnish evidence of general subsidence:

‘I wish much’ Alison wrote from Valparaiso, ‘to hear of your report respecting the islands in the Pacific, and it will be curious if you find a sinking of the land there, & a rising here.’

Possibly at about the same time, but certainly before leaving for the Galapagos early in September, Darwin jotted down some notes about coral formations in the field notebook labelled ‘Santiago Book’ (Down House no. 1.18). The medium is ink, which indicates that the notes were made when Darwin was in residence ashore or on board the Beagle and not in the field. His spelling of ‘Pacific’ suggests that he was writing before the late summer of 1835, for about that time he adopted ‘Pacifick’ as his normal spelling. An early date is also suggested by the context, which is concerned with subjects of primary interest to Darwin during his time in Chile: crustal movements, elevation, and subsidence. The passages deal with general geological speculations involving both European and Chilean formations as well as the Pacific coral reefs. Coral formations are treated as evidence for subsidence, rather than as formations whose origin and structure have to be explained. The tone is hypothetical and speculative:

As in Pacific a Corall bed. forming as land sunk. would abound with. Those genera which live near the surface. (mixed with those of deep water) & what would more easily be told the Lamelliform: Corall forming, Coralls.– I should conceive in Pacific. wear & tear of Reefs must form strata of mixed. broken sorts & perfect deep-water shells (& Milleporæ).–

Parts of reefs themselves would remain amidst these deposits, & filled up with infiltrated calcareous matter. — Does such appearance correspond to any of the great Calcareous formations of Europe.–

Is there a large proportion of those Coralls which only live near surface.– If so we may suppose the land sinking: I believe much conglomerate on the other hand is an index of bottom [above del ’land’] coming near the surface. If so Red Sandstone Epoch of England. will point out this: Mountain limestone the epoch of depression.– Do the [over ‘these’] numerous alternations of these two grand classes of rock point out a corresponding opposite & repeated motion of the surface of that part of the Globe. [Notebook no. 1.18: 6-8.]

The discussion of conglomerate formations continues for several pages, then the following entry occurs:

May we not imagine each band of conglomerates marks an epoch when that part of the ocean’s bottom was near to a continent or shoal water; & that having again being depressed. calcareous fine sediments were deposited. (if under circumstances to allow of corall reefs, such would be very abundant).– [Notebook no. 1.18: 12.]

Then, a few pages later, comes the statement:

The Test of depression *in strata[added]. is where great thickness has. shallow. coralls growing in situ: this could only happen. when bottom of ocean was subsiding: [Notebook no. 1.18: 15.]

The emphasis in these notes on global crustal changes strongly suggests that Darwin’s theory of coral reef formation originated as a consequence and corollary of his chief preoccupation at the time: the elevation of the South American continent. Darwin had by that time become a ‘zealous disciple’ of Lyell and, having found ample direct evidence that elevation of the continent had occurred, he invoked Lyell’s principle of compensatory change in the earth’s crust and hypothesised a corresponding subsidence in the Pacific. The coral islands would thus furnish proof both of that subsidence and, indirectly, of the elevation of South America.

Darwin's hand-coloured cross-sectional view of the reef at Cocos (Keeling) atoll.

Paradoxically, Darwin’s adoption of the principle of compensatory crustal changes led him to depart from Lyell’s own view of the geology of the Pacific. In his chapter on coral reefs in the second volume of the Principles of Geology, Lyell had adopted the prevailing view of the time that ‘lagoon islands’ (the annular reefs that we now call atolls) were ‘nothing more than the crests of submarine volcanoes, having the rims and bottoms of their craters overgrown by corals’ (2: 290). This view was based an observation by two French naturalists, J.R. Quoy and J.P. Gaimard, who had shown in their Zoologie of Freycinet’s Voyage (1824), that reef-building corals lived only in shallow water.  The idea that atolls were volcano craters that had merely been encrusted with a thin veneer of corals not only accounted for the ringlike shapes of the reefs, it also explained how such reefs could have been formed in parts of the Pacific where the water was  otherwise far too deep for reef-building corals to grow.

Darwin was certainly familiar with Lyell’s chapter and with the observations of earlier Pacific voyagers, notably the British hydrographer Frederick William Beechey, who had just published the results of his survey of 32 coral islands, and the Frenchmen Quoy and Gaimard.  As Darwin wrote to his sister Catherine, Darwin had begun reading about ‘the South Sea’ in May 1835. The Beagle library was well stocked with works about earlier voyages and the Admiralty orders had specifically recommended surveys and geological descriptions of the channels and lagoons of the islands (Narrative 2: 38-9), so it may be presumed that he was well informed on what was known about them. But of his reading, only one note occurs, in Notebook no. 1.17, written shortly after a visit to Lima in August 1835: ‘Corall rapidly growing in Low islands’.

From his reading Darwin must also have been aware that his view of the relationship of subsidence and coral building, if verified, would be an important contribution to geology. Apparently the first coral reef he saw convinced him that his prediction had been sound, and that he had an explanation of the origin of both annular and barrier reefs. This was in November 1835 at Tahiti and the neighbouring reef of Eimeo (Moorea). It was probably shortly after that visit that he wrote out a draft of his theory in a memorandum headed ‘Coral islands 1835.’ It is the first account of the theory of which there is any record. It begins with the statement: ‘Although I have personally scarcely seen anything of the [‘Corall’ del] Islands in the Pacifick ocean, I am tempted to make a few observations respecting them.–’

After showing that the observable data were best explained by subsidence he continues:

Before finally concluding this subject, I may remark that the general horizontal uplifting which I have proved has & is now [‘activ’ del] raising upwards the greater part of S. America & as it would appear likewise of N. America, would of necessity be compensated by an equal subsidence in some other part of the world.– Does not the great extent of the Northern & Southern Pacifick include this corresponding Area?–  [Stoddart 1962, DAR 41: 22a.]

The impact of Darwin’s first sighting of a coral island is confirmed by a letter to his sister Caroline, written on 29 April 1836 during the Beagle stop at Mauritius, in which he states that ‘The subject of Coral formation has for the last half year, been a point of particular interest to me’, implying that his interest dates from the time of the visit of the Beagle to Tahiti. The letter of 29 April was written shortly after a visit to the Cocos (Keeling) Islands of the Indian Ocean. What Darwin saw there strengthened his conviction that he had a sound theory and one that was worth publishing. The letter continues: ‘I hope to be able to put some of the facts in a more simple & connected point of view, than that in which they have hitherto been considered. The idea of a lagoon Island, 30 miles in diameter being based on a submarine crater of equal dimensions has always appeared to me a monstrous hypothesis.’

While at Cocos (Keeling) Darwin wrote an entry in his diary that combines an eloquent description of his response to what he saw with a succinct statement of his theory:

12th. [April 1836] In the morning we stood out of the Lagoon. I am glad we have visited these Islands; such formations surely rank high amongst the wonderful objects of this world. It is not a wonder which at first strikes the eye of the body, but rather after reflection, the eye of reason. We feel surprised when travellers relate accounts of the vast piles & extent of some ancient ruins; but how insignificant are the greatest of these, when compared to the matter here accumulated by various small animals. Throughout the whole group of Islands, every single atom, even from the most minute particle to large fragments of rocks, bear the stamp of once having been subjected to the power of organic arrangement. Capt. FitzRoy at the distance of but little more than a mile from the shore sounded with a line 7200 feet long & found no bottom. Hence we must consider this Isd as the summit of a lofty mountain; to how great a depth or thickness the work of the Coral animal extends is quite uncertain. If the opinion that the rock-making Polypi continue to build upwards as the foundation of the Isd from volcanic agency, after intervals, gradually subsides, is granted to be true; then probably the Coral limestone must be of great thickness. We see certain Isds in the Pacifick, such as Tahiti & Eimeo, mentioned in this journal, which are encircled by a Coral reef separated from the shore by channels & basins of still water. Various causes tend to check the growth of the most efficient kinds of Corals in these situations. Hence if we imagine such an Island, after long successive intervals to subside a few feet, in a manner similar, but with a movement opposite to the continent of S. America; the coral would be continued upwards, rising from the foundation of the encircling reef. In time the central land would sink beneath the level of the sea & disappear, but the coral would have completed its circular wall. Should we not then have a Lagoon Island?– Under this view, we must look at a Lagoon Isd as a monument raised by myriads of tiny architects, to mark the spot where a former land lies buried in the depths of the ocean.  [Beagle diary, pp. 399-400.]

Shortly after returning to England, Darwin told Lyell of his theory. Lyell was immediately convinced by it. ‘I must give up my volcanic crater theory for ever . . . ,’ he wrote to John Herschel on 24 May 1837, ‘the whole theory is knocked on the head & the annular shape & central lagoon have nothing to do with volcanoes nor even with a crateriform bottom . . . Let any mountain be submerged gradually & coral grow in the sea in which it is sinking & there will be a ring of coral & finally only a lagoon in the centre.’ (Wilson 1972, p. 449).

At Lyell’s urging, Darwin read a paper on his coral theory before the Geological Society in May 1837.  His most fully developed statement of the theory, The Structure and Distribution of Coral Reefs (1842) was based on intensive reading and correspondence with observers of coral reefs in other parts of the world. Though adopted by many geologists, it was a subject of controversy until the 1950s, when test borings in the Marshall Islands confirmed that the foundations of Pacific atolls had indeed sunk many thousands of feet.

Darwin's geological mentor, the Cambridge professor Adam Sedgwick.

Darwin had originally been introduced to the science of geology during his abortive tenure as a medical student at the University of Edinburgh, though he became actively interested in the subject only as he was completing his degree at Cambridge.  Under the influence of the professor of botany (and former professor of mineralogy) John Stevens Henslow, Darwin became fascinated by the thought of travelling to the tropics in emulation of Alexander von Humboldt.  Although Humboldt wrote with authority on subjects from botany to political economy, his background was in mineralogy and he had worked as a mining engineer.  Inspired by Humboldt’s example, Darwin apprenticed himself to the Cambridge professor of geology, Adam Sedgwick, who had invited the young man to join him on an extended field trip to study the stratigraphy of North Wales.  A letter written beforehand to Henslow illustrates Darwin’s unbridled enthusiasm both for the practical work of the geologist and for the invention of geological hypotheses.  Sedgwick gave this enthusiasm direction and discipline and inducted Darwin as an interested participant in geological research, which the young man declared ‘I would not give up for any consideration.’

Sedgwick met up with his protégé at the Darwin family home in Shrewsbury in early August 1831 and together they travelled to the Welsh town of Llangollen.  Their geological excursion took them west-north-west toward Bangor between 5 and 11 August.  Although field notes by both Darwin and Sedgwick have survived, the exact sequence of their movements remains uncertain and is a topic of active research by historians.  On 12 August, Darwin may have accompanied Sedgwick to the island of Anglesey, where Henslow had done geological work.  At some point Darwin and Sedgwick separated and the younger man traversed back inland by himself, visiting the cliff-encircled lake of Cwm Idwal on his way to meet friends in Barmouth.

Darwin returned to Shrewsbury from Wales on 29 August 1831. He had scarcely put down his geological hammer when he learned that the endorsement of his Cambridge mentors had earned him an invitation to join Robert FitzRoy for a surveying expedition to South America aboard H.M.S. Beagle.

This list includes papers read by Darwin to the Geological Society of London, his books on the geology of the Beagle voyage, and other publications on geological topics.  Author-date citations refer to entries in the Darwin Correspondence Project’s cumulative bibliography.  Where appropriate, references are given to reprints available in John van Wyhe ed., Charles Darwin’s shorter publications, 1829-1883 (Cambridge:  Cambridge University Press, 2009).  ‘F’ numbers refer to R. B. Freeman’s standard bibliography of Darwin’s works.

—Extracts from letters addressed to Professor Henslow. Pamphlet printed for private distribution by the Cambridge Philosophical Society, 1 December 1835.  [Shorter publications, pp.  2-15.  F1.]

—Geological notes made during a survey of the east and west coasts of South America, in the years 1832, 1833, 1834, and 1835, with an account of a transverse section of the Cordilleras of the Andes between Valparaiso and Mendoza. Proceedings of the Geological Society of London 2 (1838): 210-12.

—Observations of proofs of recent elevation on the coast of Chili, made during the survey of His Majesty’s Ship Beagle, commanded by Capt. FitzRoy, R.N. Proceedings of the Geological Society of London 2 (1838): 446-9.  [Shorter publications, pp.  32-5.  F1645.]

—A sketch of the deposits containing extinct Mammalia in the neighbourhood of the Plata. Proceedings of the Geological Society of London 2 (1838): 542-4.  [Shorter publications, pp.  35-7.  F1646]

—On certain areas of elevation and subsidence in the Pacific and Indian Oceans, as deduced from the study of coral formations. Proceedings of the Geological Society of London 2 (1838): 552-4.  [Shorter publications, pp.  37-9.  F1647.]

—On the formation of mould. Transactions of the Geological Society of London 2nd ser., pt. 3, 5 (1840): 505-9.  [Shorter publications, pp.  48-50.  F1648.]

—On the connexion of certain volcanic phenomena in South America; and on the formation of mountain chains and volcanos, as the effect of the same power by which continents are elevated. Transactions of the Geological Society of London 2nd ser., pt. 3, 5 (1840): 601-31.  [Shorter publications, pp.  97-124.  F1656.]

—Observations on the parallel roads of Glen Roy, and of other parts of Lochaber in Scotland, with an attempt to prove that they are of marine origin. Philosophical Transactions of the Royal Society of London (1839) pt 1: 39-81. [Shorter publications, pp.  50-91.  F1653.]

—Note on a rock seen on an iceberg in 61° south latitude. Journal of the Royal Geographical Society of London 9 (1839): 528-9.  [Shorter publications, pp.  95-6.  F1652.]

—On a remarkable bar of sandstone off Pernambuco, on the Coast of Brazil. Philosophical Magazine 19 (1841): 257-60.  [Shorter publications, pp.  137-39.  F266.]

—On the distribution of erratic boulders and on the contemporaneous unstratified deposits of South America. Transactions of the Geological Society of London 2nd ser. 6 (1842): 415-31.  [Shorter publications, pp. 147-162.  F1661.]

—The structure and distribution of coral reefs. Being the first part of the geology of the voyage of the Beagle, under the command of Capt. FitzRoy RN, during the years 1832 to 1836. By Charles Darwin. London: Smith, Elder & Co. 1842.  [F271.]

—Notes on the effects produced by the ancient glaciers of Caernarvonshire, and on the boulders transported by floating ice. Philosophical Magazine 21 (1842): 180-8.   [Shorter publications, pp.  140-7.  F1660.]

—Remarks on the preceding paper, in a letter from Charles Darwin, Esq., to Mr. Maclaren. Edinburgh New Philosophical Journal 34 (1843): 47-50.  [Shorter publications, pp.  162-5.  F1662.]

—Geological observations on the volcanic islands, visited during the voyage of HMS Beagle, together with some brief notices on the geology of Australia and the Cape of Good Hope. Being the second part of the geology of the voyage of the Beagle, under the command of Capt. FitzRoy RN, during the years 1832 to 1836. By Charles Darwin. London: Smith, Elder & Co. 1844.  [F272.]

—What is the action of common salt on carbonate of lime. Gardeners’ Chronicle and Agricultural Gazette, 14 September 1844, pp. 628-9.  [Shorter publications, pp.  176.  F1668.]

—Extracts from letters to the General Secretary, on the analogy of the structure of some volcanic rocks with that of glaciers. Proceedings of the Royal Society of Edinburgh 2 (1844-50): 17-18.  [Shorter publications, pp.  188.  F1670.]

—Geological observations on South America. Being the third part of the geology of the voyage of the Beagle, under the command of Capt. FitzRoy RN, during the years 1832 to 1836. By Charles Darwin. London: Smith, Elder & Co. 1846.  [F273.]

—On the geology of the Falkland Islands.  Proceedings of the Geological Society pt. 1, 2 (1846): 267-74.  [Shorter publications, pp.  196-204.  F1674.]

—Origin of saliferous deposits: salt-lakes of Patagonia and La Plata. Proceedings of the Geological Society pt. 2, 2 (1846): 127-8.

—On the transportal of erratic boulders from a lower to a higher level. Proceedings of the Geological Society 4 (1848): 315-23.  [Shorter publications, pp.  209-17.  F1677.]

—Geology. Section VI, pp. 156-95, in A manual of scientific enquiry; prepared for the use of Her Majesty’s Navy: and adapted for travellers in general, edited by John F. W. Herschel. London: John Murray. 1849.  [Shorter publications, pp.  217-35.  F325.]

—On British fossil Lepadidæ.  Proceedings of the Geological Society 6 (1850): 439-40.  [Shorter publications, pp.  241.  F1679.]

—On the power of icebergs to make rectilinear, uniformly-directed grooves across a submarine undulatory surface. Philosophical Magazine 10 (1855):96-8.  [Shorter publications, pp.  244-6.  F1681.]

—On the thickness of the Pampean formation, near Buenos Ayres.  Proceedings of the Geological Society 19 (1863): 68-71.  [Shorter publications, pp.  342-5.  F1724.]

—The structure and distribution of coral reefs. By Charles Darwin. Revised edition. London: Smith, Elder & Co. 1874.  [F275.]

—The formation of vegetable mould, through the action of worms, with observations on their habits. By Charles Darwin. London. 1881.  [F1357.]

—Extracts from two letters: on glacial drift. In Prehistoric Europe: a geologic sketch, edited by James Geikie, pp. 141-2. Also, Life and letters of Charles Darwin, edited by Francis Darwin, 3: 213-15.  [Shorter publications, pp.  436-7.  F135.]

Somerset House, the home of the Geological Society. T.H. Shepherd, 1817. Image in public domain; source: Wikimedia Commons.

The science of geology in the early nineteenth century was a relatively new enterprise forged from the merging of several distinct traditions of inquiry, from mineralogy and the very practical business of mining, to theories of the earth’s origin and the study of its inhabitants through the fossil record.  When Darwin arrived in London in 1836 after the Beagle voyage, he found a thriving collective enterprise centred on the regular evening meetings of the Geological Society at Somerset House.  Darwin’s reputation preceded him at the society as his former geology teacher, Adam Sedgwick, had read out some of his letters from South America at society meetings while Darwin was still on the other side of the world.

Charles Lyell, who was completing a term as president of the society, was quick to befriend the voyager after the Beagle returned.  Between January 1837 and March 1838, Darwin became a central figure in the Geological Society, presenting four papers on his Beagle findings and becoming its secretary (a position he held until 1841).  Taken as a whole, these papers indicated that Darwin believed that separate sections of the earth’s crust shifted vertically in a series of gradual compensatory movements that were associated with the linked phenomena of earthquakes and volcanoes.  He argued, for example, that sections of the Pacific Ocean floor were sinking in association with the elevation of South America.  Such claims ensured that Darwin was known in public as an enthusiastic follower of Lyell’s dictum that great transformations could be effected by the accumulation of small changes over an enormously long time.

Darwin's hand-tinted geological map of southern South America, made during the Beagle voyage.

The primary concern that linked much of Darwin’s geological work in the Beagle years was to understand the changing relation between the levels of land and sea.  In this he followed the example of the Scottish geologist Charles Lyell, whose three-volume Principles of Geology Darwin read during the voyage.  Lyell argued that the history of movements in the earth’s crust should be (and could be) explained as the result of earthquakes, volcanoes, erosion, and other processes operating at the same intensity in the past as they did in the present.  The earth had existed for long enough, Lyell claimed, that an accumulation of small changes could have enormous effects, even the raising of new continents from the ocean.  As Darwin studied the shores of South America and discovered shells inland at thousands of feet above sea level, he became convinced that the continent had been uplifted in just such a gradual manner.  His conviction was strengthened in February 1835, when he was witness to an earthquake that raised the harbour at Concepcion, Chile, several feet out of the Pacific Ocean.

Some of Darwin’s most innovative work during the voyage related to the formation of coral reefs.  For the previous two generations, geologists and navigators had sought to explain the origin of the curious ring-shaped reefs that we now call atolls.  At the time of the Beagle’s departure from England, Lyell and many others believed that these reefs had been formed by the growth of corals around the rim of underwater volcano craters.  Darwin argued that atolls were formed when islands in the tropical ocean gradually sank, in the reverse of the process that raised South America.  Reefs around the shore of such a sinking island could grow upward to keep their surfaces near sea level as long as the island did not recede faster than corals could grow.  Eventually the original island would be submerged entirely out of view, while the location of its former shoreline would be marked by a ring of living coral.  Darwin’s inventive theory of atoll formation proved to be one of the most immediately successful products of the voyage; Lyell himself expressed great admiration for the new explanation and quickly abandoned his previous view.

From the early days of the journey, Darwin had intended to write a book on the geology of the Beagle voyage.  His efforts to write up five years’ worth of geologising eventually expanded and fractured into three volumes:  The structure and distribution of coral reefs (1842), Geological observations on the volcanic islands visited during the voyage of HMS Beagle (1844), and Geological observations on South America (1846).

Walk in Darwin’s footsteps:  Click this link to download a field guide to Glen Roy written by Martin Rudwick (10MB; link opens in a new window).  It is based on the guide prepared for the field trip in Lochaber, Scotland, on 26-29 June 2009, led by Martin Rudwick (University of Cambridge) and Adrian Palmer (Royal Holloway, University of London) to mark the bicentenary of the birth of Charles Darwin.  The guide has been revised to make it usable by anyone wishing to follow the itinerary on their own.

Engraving showing the ‘Parallel Roads’ on either side of Glen Roy, from Darwin’s 1839 paper.

Although Darwin was best known for his geological work in South America and other remote Beagle destinations, he made one noteworthy attempt to explain a puzzling feature of British geology.  In 1838, two years after returning from the voyage, he travelled to the Scottish Highlands to study the so-called parallel roads of Glen Roy.

These ‘roads’ were horizontal terraces on either side of a valley called Glen Roy, and though earlier visitors had supposed that they must be ancient hand-built features, geologists in the last two decades had declared them to be of natural origin.  Two Scotsmen, John MacCulloch and Thomas Dick Lauder, proposed in the late 1810s that the roads had been cut into the hillsides by standing water, and were the beaches of a former highland lake that had once filled the valley.  They supposed the water in the lake to have stood at several distinct levels, each corresponding to the level of one of the roads.

Darwin’s interest in the parallel roads was piqued by his previous study of a series of terraces at Coquimbo, Chile, which he believed were former marine beaches that had since been pushed above sea level by the bulging of the earth beneath South America.  He went to Scotland in hopes of demonstrating that the Glen Roy roads were also former sea beaches.  If this were the case, their existence would indicate that Scotland had been elevated from the sea in a manner similar to the process he believed had lifted the continent of South America.  In each case, the fact that the terraces remained essentially level indicated to Darwin that tectonic movements could be gradual and equable (as the upright pillars of the temple at Serapis had famously suggested to Charles Lyell).

In 1839 Darwin read a paper on the parallel roads to the Royal Society of London.  He dismissed the notion that they were former lake beaches on the grounds that there was no satisfactory explanation for the temporary damming of Glen Roy, which must have occurred for the valley to fill with water and then be emptied.  Instead, he advanced his theory: ‘the whole country has been slowly elevated, the movements having been interrupted by as many periods of rest as there are shelves.’ The roads were of marine origin, and each road represented a former stage in Scotland’s emergence from the sea.

While Darwin was thus able to avoid conjecturing about an event that could have dammed Glen Roy, he instead had to explain why the sea had left no marine fossils on the sides of the glen and why it had not cut similar terraces on other hillsides across Scotland.  He argued that the preservation of both fossils and old sea beaches should be considered the exception rather than the rule.  For instance, Darwin pointed to a number of locations, ranging from his home county of Shropshire to the coasts of Scandinavia, where exposed deposits of undoubted marine origin had been found not to contain any marine shells, presumably because they had been dissolved by acidified rain.  Likewise, he pointed out that durable terraces like the roads might have been formed only where a special combination of currents and tides were acting on a coastline of a particular geological composition.

Scarcely had Darwin’s Glen Roy paper appeared in print than the Swiss geologist Louis Agassiz proposed an explanation for the roads that had not been considered by Lauder, MacCulloch, or Darwin.  Agassiz was convinced that the earth had formerly experienced an ‘epoch of great cold’, and that glaciers had once been much more widespread across Europe.  In 1840 he toured locations in Britain with many leading geologists, pointing out how many familiar phenomena could be reinterpreted with reference to the former action of glaciers.  In the case of Glen Roy, Agassiz provided the missing component of the lake-beach theory of the formation of the parallel roads.  A wall of ice extending across the foot of the valley could have dammed Glen Roy and formed a glacial lake like those seen in the present-day Alps.

In the hands of Agassiz and others in the succeeding decades, glacial theory prompted geologists to reappraise much more than the terraces at Glen Roy.  Darwin was resistant to the glacial explanation for the parallel roads, even as he admitted the action of ice sheets elsewhere.  On his last ever geological field trip, a return visit to North Wales in 1842, Darwin wrote that the signs of glacial action in the valley of Cwm Idwal could not have been more obvious ‘if it had still been filled by a glacier.’  Yet in letters written as late as 1861, Darwin continued to defend, albeit halfheartedly, the marine theory of the formation of the parallel roads (see sidebar to the right).  Darwin was later to write, notoriously, in his autobiographical ‘Recollections’ that his paper on Glen Roy was a great failure: ‘and I am ashamed of it.’

Although Darwin eventually abandoned his original conclusions about Glen Roy, it is well worth trying to retrace Darwin’s footsteps there.  To understand what led Darwin to ‘see’ what he saw in 1838 is to take a glimpse from the perspective of the young geologist when he was giving full expression to the theory of the earth that was his proudest product of the Beagle voyage.