Darwin's Backyard

by James T. Costa

  Sedgwick arrived at The Mount on August 2nd, and geologized locally for a couple of days. While at Shrewsbury one episode is recorded that gives some insight into the development of Darwin’s thinking as a scientist-in-training, a revelation about science as a process. Darwin related to Sedgwick that a quarryman had shown him the shell of a tropical volute gastropod he had found in a local gravel pit, thinking the professor would be amazed. He was shocked when Sedgwick dismissed the notion that the shell naturally occurred in the gravel pit, concluding it was surely discarded there by someone. “I was then utterly astonished at Sedgwick not being delighted at so wonderful a fact as a tropical shell being found near the surface in the middle of England,” he wrote in his autobiography. Significantly, he continued: “nothing before had ever made me thoroughly realise, though I had read various scientific books, that science consists in grouping facts so that general laws or conclusions may be drawn from them.”21 This episode surely resonated with the philosophy of John Herschel, and put the zealous researches of Humboldt and others into a new light. Darwin’s many subsequent investigations—including his flair for experimentation—were always aimed at “grinding general laws out of large collections of facts,” as he wrote in his autobiography.22

  Darwin and Sedgwick headed off for Wales and Darwin’s extended “Geology 101” lesson on August 5th. One of the main objects of the excursion was locating and mapping outcroppings of Old Red Sandstone, a sedimentary formation that Sedgwick had identified as Devonian (he had in fact coined that name for the geological period), dated by modern technology at about 419 to 359 million years old. The two were unsuccessful in locating the Old Red, but Darwin learned a great deal of practical field geology. On the last leg of the excursion they separated to cover more ground. Darwin made his way south to Barmouth to see friends, stopping briefly at the breathtakingly beautiful Cwm Idwal hanging valley in the Glyderau Mountains of Snowdonia, with its crystal-clear lake backed by the imposing wall of Devil’s Kitchen and dotted with massive erratic boulders. He made some observations—once again reversing several compass readings—and dutifully reported them to Sedgwick by letter. Sedgwick wrote back correcting some of what he took to be Darwin’s misinterpretations of certain geological formations, but all in all he performed admirably as a geological trainee (though when he returned to Cwm Idwal ten years later he realized how much he missed, as we will see). Then, after seeing his friends he headed home, where a letter from Henslow awaited him. The trip to the Canaries was cancelled. Instead, it offered him a much more extraordinary adventure: to serve as a gentleman-naturalist on a voyage around the world.

  Darwin Abroad

  In some ways it made little sense that Darwin should be invited to take such a post. He was barely out of college, and not a seasoned naturalist. Indeed, he wasn’t the first to be approached: Henslow had been the one initially invited and was tempted. But he had a family and growing responsibilities to the university and his parish. The invitation next went to Leonard Jenyns, Henslow’s brother-in-law and a good naturalist, but he was a newly minted priest just appointed to a parish. Jenyns thought about it for a day and reluctantly turned it down. They both then thought of Darwin. Once the objections of Darwin’s father and the initial misgivings of the captain, Robert Fitzroy, were overcome, Darwin took his place aboard the HMS Beagle as gentleman companion to the captain and informal naturalist on a Royal Navy surveying mission. They departed Plymouth on December 27, 1831, not to return for almost 5 years.

  I will not give an overview of all Darwin did on the Beagle voyage here—that’s beyond our scope.23 For this book’s purposes, we’ll explore how the Beagle voyage led to Darwin’s later experimentation. Darwin, like any scientist undertaking a research program, whether experimental or observational, proceeded to form questions in the context of the theory he had learned. As a college student Darwin was only just aware of the big outstanding questions of natural science—the nature and age of the earth and its formations, the patterns of the geological record, the diversity and distribution of life, and (not least) that “mystery of mysteries,” as John Herschel put it, the origin of species and varieties. At the time and through most of the Beagle’s voyage Darwin was pondering those questions and their possible solutions within the framework of natural theology. What released the inner experimenter in Darwin after the Beagle voyage was seeing the world through a new lens, permitting him to ask fresh questions that only arose in contemplating his observations in a new light.

  The process of seeing the world anew that began with Grant and his zoophytes and was amplified in the inspired company of Henslow, Sedgwick, and others late in his Cambridge career was now helped mightily along on the Beagle voyage, in particular owing to the watershed Principles of Geology by Scottish geologist Charles Lyell (1797–1875), the first volume of which was published in 1830. Encouraging his soon-to-be-companion’s geological education, Captain Fitzroy made a present of Lyell’s book—a book which, Darwin recalled later, Henslow had recommended that he acquire and study, “but on no account to accept the views therein advocated.” That seems like an odd recommendation, perhaps, to read a book but not believe it, but this may reflect the fact that Lyell’s new model of earth processes and history were being hotly debated in the learned societies at the time. Lyell, who trained as a lawyer and knew how to argue, championed the vision of fellow Scot James Hutton, who saw the history of the world as one of ceaselessly acting natural forces that slowly but surely shape the earth’s surface in an endless cyclical process. No miraculous interpositions, no divine catastrophes, just the incessant mundane forces exerted by water, volcanism, ice, and other natural processes combined with the inexorable forces of the uplift and subsidence of land. So it ever was, in Hutton and Lyell’s view, and so it ever shall be. Hence the subtitle of Lyell’s book: “An attempt to explain the former changes of the earth’s surface by reference to causes now in operation.”

  Darwin probably dipped into Lyell’s Principles in fits and starts. The Beagle didn’t make it out of Plymouth Harbor before he was overcome with seasickness. His shipmates likely told him that he’d get his sea legs soon enough, but sadly he was some shade of green throughout the voyage—which in retrospect may have been a good thing from the viewpoint of the history of science, as it encouraged Darwin to go ashore at every opportunity. (In fact, of the nearly 5 years of the voyage, Darwin was actually on board the ship just a year and a half altogether.) Thus he was surely doubly excited at the prospect of landing at Tenerife—relief from vomiting, and at long last an opportunity to see sights so rapturously expressed by Humboldt. And there it was, looming over the port of Santa Cruz. Alas, the Beagle crew were prevented from landing owing to a cholera outbreak back in England. The local authorities insisted on a 12-day quarantine for the English ship, but, impatient, Fitzroy didn’t want to lose time and so hoisted anchor immediately. The captain noted in his memoir of the voyage: “This was a great disappointment to Mr. Darwin, who had cherished a hope of visiting the Peak. To see it—to anchor and be on the point of landing, yet be obliged to turn away without the slightest prospect of beholding Teneriffe again—was indeed to him a real calamity.”24 But the concern at Santa Cruz was well-founded: through the nineteenth century epidemic after cholera epidemic raged in different parts of the world, killing tens of millions of people.

  Still, Darwin didn’t have to wait much longer to experience his first tropical isles: the ship called at the Cape Verde Islands in mid-January, and it was there, at St. Jago, that he noticed something remarkable: a horizontal white band of shells embedded 45 feet above sea level within a cliff face. He now saw this with Lyellian eyes: the sea shells must have gradually risen, as an abrupt, violent movement surely would have broken up the nearly horizontal layer. This was consistent with Lyell’s theory of slow change over great periods of time. Darwin wrote to Henslow: “The geology [of St. Jago] was preeminently interesting & I believe quite new: there are some facts on a large scale of upraised coast (
which is an excellent epoch for all the Volcanic rocks to [be] dated from) that would interest Mr. Lyell.”25

  It was a moment he never forgot: the very first locality he examined showed him “the wonderful superiority of Lyell’s manner of treating geology, compared with that of any other author, whose works I had with me or ever afterwards read.”26 For the rest of the voyage he pointedly examined local geology with Lyell’s Principles as his guide. He answered Lyell’s call, understanding, as Lyell admitted, that the insights and generalizations of the new science may be limited as yet, but “they who follow may be expected to reap the most valuable fruits of our labour. Meanwhile the charm of first discovery is our own . . . as we explore this magnificent field of inquiry.”27

  With characteristic enthusiasm Darwin threw himself into geology, making the rocks ring with his eagerly wielded hammer and getting more and more excited about reading landscapes and formations new to him. What wasn’t to love about this new science?—it dealt with grand, awe-inspiring questions about origins and antiquity, scientific sleuthing that required diligent fieldwork and close observation, representing Hershelian induction at its best. He filled notebook after notebook with observations, musings, and interpretations, and his admiration for Humboldt only grew. On seeing a tropical forest for the first time he rhapsodized to Henslow: “I never experienced such intense delight—I formerly admired Humboldt, I now almost adore him; he alone gives any notion, of the feelings which are raised in the mind on first entering the Tropics.”28

  While Darwin increasingly saw himself as a geologist, that’s not to say he was less diligent in other departments of natural history. Those mysterious marine invertebrates that he first saw in Edinburgh captivated him yet and were always a dip net away. When Darwin wasn’t prostrated with seasickness on those long stretches of open ocean between anchorages he often deployed a plankton net of his own making to see what marine life he could find—just the second recorded instance of the use of one, which means he likely learned to make one from Robert Grant. He pulled in an astonishing menagerie of minute marine organisms—“Many of these creatures so low in the scale of nature are most exquisite in their forms & rich colours,” he wrote in his diary. And then a perhaps unexpected reflection: “It creates a feeling of wonder that so much beauty should be apparently created for such little purpose.”29

  Those tiny marine organisms had outsized significance in Darwin’s thinking. His zoological notes contain page after page of drawings and observations made with the aid of his microscope, foremost among them the “zoophytes,” now recognized to be a grab bag of groups now separated into Cnidaria (several orders, including solitary and colonial corals), Bryozoa (the “moss-animals”), sponges (Porifera), and corallines (Rhodophyta, red algae that secrete a hard calcareous casing). In one significant notebook entry from June 1834 he recorded detailed observations of a curious species of Flustra (a bryozoan), related to the one he studied in Edinburgh, that was coating the sinuous fronds of kelp growing in dense undersea “forests” near Port Famine, in the Strait of Magellan. “I examined the Polypus of this very simple Flustra,” he noted, “so that I might [correct] at some future day, my imperfect notions concerning the organization of the whole family of Dr Grant’s Paper.”30 The paper referred to is a translation Grant published of an 1826 work by the German naturalist August Friedrich Scheweigger, arguing that corallines are plants, not animals, which was the common view in the mid-1830s. Darwin took up the study of these organisms to see if he could find any evidence of animality—microscopic sensitive polyps, perhaps, or the production of “ova” like those he found in Flustra. In a letter to his sister Catherine, written aboard ship “a hundred miles south of Valparaiso,” he commented that “Amongst animals, on principle I have lately determined to work chiefly amongst the Zoophites or Coralls: it is an enormous branch of the organized world; very little known or arranged & abounding with the most curious, yet simple, forms of structures.”31 Writing to Henslow from Valparaiso, he reported that he examined some corallines that had “quite startled” him. He was sure that the classification given by Lamarck, Cuvier, and others was incorrect. “Having seen something of the manner of propagation, in that most ambiguous family, the Corallinas: I feel pretty well convinced if they are not Plants, they are not Zoophites.”32 What were they then?

  Over the course of the voyage his thinking on this, well, evolved. It was all very confusing; some true corals like the Caryophyllia he collected in the Galápagos seemed to reproduce like encrusting Flustra, a zoophyte, while others like the scleractinian reef coral Madrepora (now Acropora) that he found in the Cocos Islands were more like coralline algae. So for that matter was the puzzling Millepora, a hydrocoral (“I cannot help suspecting that their nature is allied to Corallina rather than to Polypiferous corals”), while a so-called nullipore coralline alga that Darwin found in Tasmania seemed awfully plant-like, reproducing via bud-like segmentation. In his zoology notes he commented that this novel method of growth in corallines “calls to mind the propagation of trees.” Reproduction by budding or creeping runners was a decidedly plant-like thing to do. Now coralline algae seemed to do it, and, more remarkably, so did some zoophytes and actual corals: “There is an analogy between the Corall-forming Polypi & turf-forming plants,” he mused—“turf-forming plants” that propagate by runners or stolons. A few lines later he reiterated: “I think there is much analogy between zoophites & plants, the polypi being buds, the gemmules the inflorescence which forms a bud & young plant.”33 These entries say more than they seem; the distinction between the plant and animal worlds was beginning to blur in Darwin’s mind. These simplest of animals and proto-plants (if that’s what coralline algae were) shared some fundamental similarities in structure and mode of reproduction, a captivating idea that just a few years later would dovetail beautifully with his nascent transmutationism. We’ll see in later chapters how Darwin eventually sought evidence for not only common ancestry of plants and animals but all life, and also the idea of an ancestral unisexual state that gave rise to separate sexes. Those were not ideas he held while on the Beagle voyage, but clearly the seeds—or buds?—were planted.

  No, Darwin was no transmutationist during the voyage—not even, as legend would have it, upon stepping ashore in the Galápagos Islands. In fact, judging from his notes and comments, he was struggling to make sense of the structure, adaptations, distribution, and relationships of organisms within the familiar framework of natural theology. Yet we continually see Darwin pondering the significance of what he’s seeing during the voyage. Thus in Australia we find him musing over the significance of finding ant lions, those diminutive but ferocious insect larvae that create pitfall traps to prey upon unwary crawling insects. Here they were on a sunny bank in New South Wales, so similar to the ones at home yet here they were amidst the otherwise exotic animal life of Oz. Did Australian zoology represent a wholly separate creation? Oddities like kangaroos and platypuses suggested maybe so, and the possibility of single versus multiple “centres of creation,” in the jargon of the day, was a topic of serious debate. The close similarity of Australian and European ant lions suggested to him a link between these widely separate faunas. Australia did not represent a separate creation, however odd its mammals: about the ant lions, “what would the Disbeliever say to this? Would any two workmen ever hit on so beautiful, so simple & yet so artificial a contrivance? It cannot be thought so—The one hand has surely worked throughout the universe.”34 But toward the end of the voyage we also see him pondering the relationships of Galápagos mockingbirds, seemingly different from island to island yet as a group rather different too from the common mainland species: Are they mere varieties of the mainland species? Sister species? Why so similar yet distinct, and what is it about islands anyway that makes them so productive of novel forms? “If there is the slightest foundation for these remarks the Zoology of Archipelagoes will be well worth examining: for such facts would undermine the stability of species.”35

/>   HMS Beagle Entering Rio de Janeiro Harbor on April 3, 1832. © 2007 by Jay Matternes. Photo by Richard Milner. Courtesy of Jay Matternes and Richard Milner.

  As a voyage of exploration there was, of course, plenty of hands-on collecting and observing on the Beagle voyage. In Darwin’s Journal of Researches (1839) the words “observation” or “observe” appear 73 times, “examine” another 48. Experiment? Just 4. But there is evidence of a questioning Darwin who wonders if such-and-such is true and devises an experiment on the fly to find out. Thus, for example, we find him confirming that terrestrial flatworms cut in half lengthwise can regenerate into two new individuals (“In the course of twenty-five days from the operation, the more perfect half could not have been distinguished from any other specimen. . . . Although so well-known an experiment, it was interesting to watch the gradual production of every essential organ, out of the simple extremity of another animal”).36 He also tested whether carrion-feeding condors find their food by sight or smell: “I tried . . . the following experiment: the condors were tied, each by a rope, in a long row at the bottom of a wall; and having folded up a piece of meat in white paper, I walked backwards and forwards, carrying it in my hand at the distance of about three yards from them, but no notice whatever was taken.” He pushed the package closer and closer until it practically touched the condor’s beak, whereupon the bird immediately tore into it. “Under the same circumstances, it would have been quite impossible to have deceived a dog,” he wrote in his notebook, but reviewing similar experiments by Audubon and others he had to admit that “the evidence in favour of and against the acute smelling powers of carrion-vultures is singularly balanced.”37 Another experiment was aimed at the nature of corallines: undertaken at Bahia, Brazil, in August 1836 on the last leg of the journey home, he placed a number of them in sunlight to determine if they emitted gas like photosynthesizing plants. “On several occasions having kept vigorous tufts of articulated Nulliporae in sea-water in sun-light, it appeared as if a good deal of gas was exhaled; it would be curious to ascertain what this is.”38 This was reminiscent of experiments done in the 1770s by Joseph Priestley and Jan Ingen-Housz showing that oxygen bubbles were produced by plants under similar conditions. In other cases his experiments bordered on the goofy, as when in the Galápagos Islands he tossed a marine iguana “several times as far as I could, into a deep pool left by the retiring tide,” to see if it would persist in returning to the spot where he picked it up. (The imperturbable iguana invariably did so, we learn, and a giant tortoise was similarly unimpressed when Darwin unsteadily rode it, in what must have been a spectacle recalling Albert Way’s cartoon of a beetle-riding Darwin.)39