Darwin's Backyard

by James T. Costa

  Soret was at a loss for words. There is no question whom Goethe was rooting for: a visionary in the same mold as Geoffroy, Goethe himself had made fundamental contributions to comparative anatomy, and even advanced a theory of unity of form in botany that paralleled Geoffroy’s work in zoology.

  The Cuvier-Geoffroy debate is directly relevant to Darwin’s development as an experimentiser, though it took time for him to feel the aftershocks of the seismic events of 1830 at the Académie. There is no evidence that he knew about the debate at the time, his letters and diary filled instead with excited talk of beetle collecting, fishing, hunting, and horses. Le trois glorieuses found him preparing for a trip to north Wales. Geoffroy had published an account of the debate in his Principles of Zoology (1830), including his and Cuvier’s papers read at the Acadeémie. Darwin laboriously made his way through Geoffroy’s book in late 1837, filling four notebook pages with comments: “[Geoffroy] states there is but one animal: one set of organs—the other animals created with endless differences,” reads one entry—note the word “created” underscored. He saw the transmutational significance, continuing: “does not say propagated, but must have concluded so.”13 Several passages are marked in Darwin’s copy of the book, the margins littered with exclamation marks, comments, and notes to extract quotations. It is telling which passages got him excited: explaining about the “natural development” of animal bodies (a phrase underlined by Darwin), Geoffroy stated that “man, considered in his embryonic state, in the womb of his mother, passes successively through all the degrees of evolution of the lower animal species: his organization, in its successive phases, approaches the organization of the worm, the fish, the bird.”14

  Geoffroy, familiar with the embryological work of Karl Ernst von Baer, was convinced that modifications at various stages of embryological development were key to his idea of unity of all animal forms—an idea with clear evolutionary implications. Cuvier, dismissive of Geoffroy’s “unity of composition” talk as “contrary to the simplest testimony of the senses,” maintained that the resemblances that Geoffroy pointed to merely reflect how the “agreement of parts” simply follow from their “coordination for the role that the animal has to play in nature.” Form follows function, in Cuvier’s view, not the other way around. Darwin excitedly scored this passage, too. But where Cuvier asserted that “conditions of existence”—adaptation to environment, say—explained resemblances, Darwin disagreed: resemblance may also follow from common ancestry. As for the “unity of composition” that Cuvier so emphatically dismissed, it’s clear from Darwin’s marginal comment that it was a given: “The unity of course due to inheritance.” Common ancestry was common sense to Darwin.

  Darwin’s interest here resonated with his interest in Thompson’s barnacle work. He noted how Geoffroy acknowledged a wide gap between insects and mollusks, but also the variation within each group, certain organ systems being more or less developed in each and forming something of a series. “This explains the large hiatus that has been noticed between the families,” the Frenchman asserted, “especially with regard to the beings at the center of each series, and also the very numerous relations that they exhibit at their extremes.” Referencing this in his notebook that fall of 1837, Darwin noted that barnacles were just such a group at the extreme of the series, and wondered whether Geoffroy thought that such a series was linear or could be branched.

  The Whole Art of Making Varieties

  But in the late 1830s barnacles were filed away in Darwin’s mind—or maybe mentally shelved is more like it, similar to his tagged Beagle specimens shut up in sturdy glass-doored museum cabinets. As we’ll see, he returned to them nearly a decade later, but now he increasingly looked at the puzzle of reproduction, inheritance, and variation through the lens of domestic breeds—a knotty issue that would shed light on the species question. It was knotty because common sense and the prevailing view held that little could be learned from domesticated breeds. If anything they were evidence that species could not change, as Lyell so eloquently expounded in the Principles: domestic varieties were changeable only to a degree, it was claimed, and as soon as they run wild they revert back to their generic form. Patently unnatural, domestic animals couldn’t survive in a state of nature; only a Gary Larson could imagine wild packs of fancy poodles. Darwin’s first hunch was that the environment somehow interacted with individuals to engender variation and species change, and if kept separate from other individuals undergoing their own changes, wholesale transmutation would eventually be achieved.

  Thinking along these lines, his initial interest in domestication had more to do with how people affect variation by controlling the environment of farmed plants and animals. But by summer of 1838 he began to have second thoughts: maybe there was more to domestic breeds than met the eye? Immersing himself in the breeders’ craft, he pressed friends and acquaintances for information and struck up conversations with anyone and everyone having practical experience with one kind of domestic group or another: beekeepers and horticulturists, pigeon fanciers and husbandrymen, poultry aficionados and dog breeders. There was plenty of expertise close at hand, too, between the coachmen and gardeners who worked for his father and Uncle Josiah. And, of course, he pored over the writings of the likes of Bakewell, Yarrell, Youatt, Wilkinson, Sebright, and other pioneering breeders behind Britain’s first agricultural revolution. The problem was that there was often conflicting information on phenomena like hybridization and heritability. Soon their pamphlets yielded an unexpected insight.

  Darwin was primed to appreciate the basic idea of selection applied by people to improve animal breeds months before his reading of Malthus catalyzed his insight into selection in nature. It’s hard to say when he became conscious of the concept, but unmistakably it first appears in entry 17 of transmutation notebook C, dating to February 1838: “The changes in species must be very slow owing to physical changes [being] slow and offspring not picked as man [does] when making varieties,” he wrote in his usual shorthand.15 This is a revealing comparison: believing that physical changes in the environment induce changes in species, and aware that “picking” offspring, selecting those that will or will not be bred, is the way that people create new varieties, he is suggesting here that the rate of species change in nature is slower in part because there’s no one to do the picking and accelerate the process. His thinking along these lines is evident in a number of other entries; he was beginning to appreciate more and more the analogy between domestic breeds and species and varieties in nature. It all had to do with the power of picking.

  “Picking” becomes methodical selection in his thinking through the influence of two agricultural improvement pamphlets: Sir John Saunders Sebright’s The Art of Improving the Breeds of Domestic Animals (1809), and John Wilkinson’s Remarks on the Improvement of Cattle (1820). These works, which Darwin heavily annotated in March 1838, drove home the power of selective breeding. In fact, the word “selection” in this very context is used repeatedly by Sebright and Wilkinson, in passages that Darwin underscored. Consider, for example, Sebright’s assertion that the art of breeding consists “in the selection of males and females, intended to breed together, in reference to each other’s merits and defects,” or that traits like “the fineness of fleece, like every other property in animals of all kinds, may be improved by selection in breeding.” Yes, climate, soil, and other environmental factors have some effect on wool quality, he acknowledged, “but not so much as is generally supposed.”16 Sebright’s use of the word “selection” meant selective breeding, with some individuals chosen for breeding and others for the pot. He shook his head at the widespread misapprehension that improvements are achieved and new varieties made by hybridizing existing breeds: “The alteration which may be made in any breed of animals by selection, can hardly be conceived by those who have not paid some attention to this subject,” he declared. “They attribute every improvement to a cross,” when the actual cause was simple: “it is merely the effect
of judicious selection.”17 The power of selection is what it’s all about, a point underscored by Wilkinson:

  The worst must unquestionably be rejected, while the rest, and especially the best of these, are carefully to be preserved for future stock. . . . By such procedure [i.e., selection], animals have at length been produced, so different from the generality of the stock from whence they were originally taken, that none but such as are well acquainted with these matters, could have an idea, that there existed between them the least affinity. The distinction indeed between some, and their own particular variety, has scarcely been less than the distinction between that variety and the whole species.18

  Darwin gave this passage an excited double score in the margin, as he did another passage where Wilkinson emphasized that such changes “are in general gradual,” proceeding “but slowly through several generations.” This was all electrifying. In his C notebook, he declared, “Sir J Sebright pamphlet most important,” and that the “Whole art of making varieties may be inferred from facts stated.”19 He saw clearly a parallel between domestic and wild animals, and the power of selection to diversify. His ungrammatical notebooks make for difficult reading, but their almost stream-of-consciousness shorthand also conveys a sense of the energy and excitement of discovery Darwin must have been feeling.

  In mid July, he opened a fresh notebook. About 25 percent of the entries pertain to domestication and record his ups and downs in relating what he learned from Sebright, Wilkinson, and others to species and varieties in nature. “The varieties of the domesticated animals must be most complicated,” he lamented at one point. In selective breeding only a few individuals are picked out to reproduce, but how does that happen in nature? And he still sensed that separation played a role in the formation of new breeds by preventing intermixing: “The very many breeds of animals in Britain shows, with the aid of seclusion in breeding how easy races or varieties are made,” he wrote a few pages later (emphasis Darwin’s).20 Always alert to observations or data bearing on species and varieties, he was amazed by the sheer number of rose varieties when he visited the famous botanic garden and arboretum of George Loddiges in Hackney, just north of London: “Loddiges garden 1279 varieties of roses!!! Proof of capability of variation,” he recorded on 23 September 1838.21 Variation enough to permit the cultivation of so many rose varieties suggested an inexhaustible supply—so much for Lyell’s insistence that variation was limited! And unlimited variation meant an unlimited capacity for change.

  That visit to Loddiges’ garden came just a week before Darwin’s re-reading of Malthus provided the spark that led him to natural selection—suddenly grasping nature’s version of the picking and choosing process going on in farmyards and fields for centuries. The key was superfecundity. This was a vision of reproductive output on a staggering scale. Picture each bit of confetti in a ticker-tape parade as so many lottery tickets. There are scant few winners; the vast majority in the confetti blizzard are destined to be swept away. What determines winning or losing in the farmyard is the breeder calling the shots; in nature it is the demands of the immediate environment determining which of those hopeful propagules makes it. Variations—ubiquitous, abundant, small, and (very importantly) random—provide the raw material, with Malthusian population pressure the crucible for selection to act, slowly, inexorably changing species according to the demands of their environment.

  In another notebook Darwin sketched out how he might explain the process to others, an outline for an argument if you will, building on domestication as an analogy. First, he noted to himself, point out that new varieties are made in two ways: one is by environmental change, while the other is by picking offspring and preventing free intercrossing. Next ask: “Has nature any process analogous?—if so she can produce great ends.” Rhetorically asking “But how?” he instructs himself to “make the difficulty apparent by cross-questioning.” Finally, he says, “Here give my theory—excellently true theory.”22 An excellently true theory it was, but there were so many details yet to work out. What causes all that variation? To what extent is it heritable, and how? What role does environment play? How common is hybridization, and what are its effects? Why do parental traits sometimes blend in offspring and sometimes seem unequally expressed? Some of these issues weren’t resolved until the twentieth century, with the revelations of Mendel and the later insights into DNA structure and gene expression. Darwin could only grasp at straws.

  Just as Darwin was entering his own new domestic life—he and Emma were married in the chapel at her home, Maer Hall, in January 1839, and soon happily residing on Upper Gower Street, London—he pondered domestic breeds ever more deeply. He pestered friends, family, and colleagues with questions at every opportunity, and gathered all manner of information bearing on domestic varieties and breeding, even starting a separate notebook on questions and experiments. A slender notebook of about 40 pages, it’s divided into sections that tell us something about his working method between about 1839 and 1844: “Experiments in crossing &c. Plants,” “Questions Regarding Plants,” Questions Regarding Breeding of Animals,” “Experiments in crossing animals,” are some of the general headings for lists of questions directed to botanists and horticulturists like his Cambridge mentor Henslow and the gardeners at Maer and Shrewsbury, medical men like his father and Henry Holland (Darwin’s doctor in London), zoologists and museum men like John Gould and Edward Gray, breeders like William Yarrell, and others.23

  As he wrote in his autobiography, with natural selection he had “at last got a theory by which to work.” But although he was bursting with questions and did manage experiments and other investigations (see especially Chapter 6 for Darwin’s work on crossing and pollination at this juncture), he was able to direct frustratingly little of his efforts to his species theory in the next several years. He was overwhelmed as a new husband, parent, and ambitious young scientist determined to make a name for himself. After William Erasmus (“Doddy,” later Willy) was born in 1840, Emma was in a nearly continuous state of pregnancy for the next decade or more. On the scientific front he was in demand as an active participant in the learned societies, and there was the seemingly unending task of writing up his Beagle material. His output was prodigious, with three volumes on geology (coral reefs in 1842, volcanoes in 1844, and the geology of South America in 1846), plus his travel memoir (first out in 1839), introductions to the Beagle voyage’s zoological volumes (fish, reptiles, birds, and more), and last but not least, various geological and zoological papers.

  With a mysterious illness beginning to manifest itself on top of (maybe because of?) the work load, soon after their second child, Anne Elizabeth, was born in 1841 he resigned from the secretaryship at the Geological Society and stepped down from the council of the Royal Geographical Society. This illness was to worsen and plague him for the rest of his life, with periods of violent gastrointestinal distress and severe headaches that came and went. The precise nature of the malady is still debated today—was it the lingering effects of a parasite picked up on the Beagle voyage? A psychosomatic reaction to the stress and strain of harboring ideas he knew would be fiercely repudiated by society and threaten to estrange his devout wife? Overwork, or an allergy or metabolic condition like lactose or gluten intolerance? Perhaps some inherited disorder? We may never know.24 What is certain is that he responded to what would be considered quack treatments today: the “water cure” (dousing in chill water and lying motionless for hours wrapped in wet towels) together with strict regulation of his exertions, mental and physical. The enforced idleness was maddening to Darwin, but it seemed to have a positive effect, at least for a time.

  Prior to the worst manifestations of his illness the family got away to Maer for a month’s respite each summer, and it was there, in 1842, that he finally managed to gather his thoughts and write out a brief sketch of his theory to date. He opened this brief account with the analogy from domestic breeds, entitling the first section “On variation under domestication, and o
n the principle of selection.” It was a format he stuck with: from the expanded 230-odd page Essay version of this sketch written out 2 years later to his “big species book” manuscript Natural Selection to On the Origin of Species itself, he consistently set up his case for evolution by natural selection with domestication as a strong analogy with variation, selection, and slow, steady change in nature.25 It was a philosophical and rhetorical approach that was likely inspired by the renowned John Herschel, whom we met in Chapter 1. In his Preliminary Discourse on the Study of Natural Philosophy (1830), the much-admired astronomer, mathematician, and philosopher pointed to the power of analogy as one way to gain insight into vera causae—true causes—in nature. This was a book that Darwin studied closely, one of just two cited in his autobiography many years later: the other was Humboldt, and together they fired up his zeal for science. He recalled, “No one or a dozen other books influenced me nearly so much as these two.”26

  By the time Darwin penned his lengthy Essay in 1844 he had a largely complete theory—there were some key details missing yet, as we will see in the next chapter, but in structure and content the Essay very much has the look of a condensed version of the Origin that appeared 15 years later. Darwin thought it was sufficiently complete at that stage that he hired the local schoolteacher to write out a fair copy (his own handwriting anything but fair), sealing it in an envelope with a poignant letter asking Emma to publish the essay without delay in the event of his untimely death. But if it was that complete, and he had that much faith in its essential correctness, why not just go ahead and publish it? That is a question that scholars have debated and discussed for over a century. Some have claimed that Darwin delayed publishing out of fear of the repercussions, or out of respect for the deep religious convictions of his wife. There may be something to the repercussions idea—it may not be coincidental that the scandalous Vestiges of the Natural History of Creation came out that same year, thrusting the idea of transmutation into the limelight in 1844 and provoking venomous condemnation by the leading lights among naturalists—many of them Darwin’s scientific friends, mentors, and professors. But it’s also true that he simply wasn’t ready to publish: he had more work to do, probably more than he realized then—not least a return to barnacles, which Hooker had something to do with.