Reef Madness: Charles Darwin, Alexander Agassiz, and the Meaning of Coral - David Dobbs (2005)

Part II

Chapter 9. The Pleasure of Gambling

Darwin in the late 1830s, soon after his return from the Beagle voyage

I

ALEXANDER HAD been preceded in the Andes by both his father and Charles Darwin. Louis had visited just two years before Alex did, taking inland forays from a failed marine-research trip. His mission, underwritten by his old friend Benjamin Peirce, who had become director of the U.S. Coast Survey, had rounded South America in the Hassler, an experimental ship designed to dredge at depths never before reached. Louis hoped the Hassler would pull up early, primitive life-forms that would shed unflattering light on the theory of evolution. But the boat and its equipment malfunctioned so often that Louis did little dredging, and the rigors of the trip taxed his health. He did disembark a few times and rode high enough into the Andes to find evidence of glaciers there; these, wrote Liz Cary in the trip’s sole publication (an Atlantic Monthly article) confirmed Louis’s earlier assertions about an ice sheet covering South America.

Darwin’s visit, almost forty years earlier, had been longer and more productive. The Beagle, having spent much of the preceding few months in dismal weather off Patagonia and Tierra del Fuego, reached the sunny Chilean port of Valparaiso on July 23,1834. “After Tierra del Fuego,” wrote Darwin, the dry, clear climate “felt delicious.” He was entranced with the sight of the mountains, some as high as 23,000 feet, dozens of miles away. Securing horses and a guide, he rode into the foothills. His interest rose with the landscape. As Alex would later, Darwin found fascinating the uplift suggested by the steep terrain. “Who can avoid wondering at the force which has upheaved these mountains, and even more so at the countless ages which it must have required to have broken through, removed, and leveled whole masses of them?” he wrote in the Voyage of the “Beagle.”

In his first trip he headed north along the coast to Quintero “to see the beds of shells, which stand some yards above the level of the sea.” These were almost certainly the same shells, blanketing sea side terraces several hundred yards high, that Alex would examine four decades later. To both men these beaches spoke of remarkable, repeated rises in the land. For Alex, it was these “ancient Sea beaches,” along with coral he found several thousand feet up in the Andes, that made him “wish I could have time to remain here to study the uprising of the land; there is a good deal to do and quite interesting work. … I believe however Darwin has already done something in this line.”

Darwin indeed had, for he spent the sort of extended time in the Andes that Alex didn’t allow himself. For much of 1834 and 1835, while the Beagle mapped the coasts of Chile and Peru, Darwin climbed and rode up peaks and cut across valleys, “geologizing,” as he called it, to his heart’s content. These landlocked months in the Andes contributed as much to his coral reef theory as the Galápagos visit did to his evolutionary theory. In fact they probably shaped his scientific approach as much as anything on the voyage. For it was here, studying uplift, that he began to indulge the broad-scale, speculative theorizing that characterized both his stunning successes, like the theory of evolution, and his embarrassing mistakes, such as at Glen Roy.

The young man who hammered rock in the Andes is unrecognisable as the sedentary, dyspeptic thinker who dominates our popular historical picture of Darwin. He was a healthy, insatiably curious man of twenty-five, younger by more than a decade than Alex was when he rode through the Andes and, during this time of his life, just as rugged, if more innocent. The man who from his mid-thirties on would rarely travel (and then usually only to take a “water cure” or some other palliative for his gastric torments) was at this point strong and lithe, quick to travel amid real dangers posed by bandits, rebels, and deadly weather. While no Thoreau (he was less rowdy and irreverent; indeed, he hated rocking the boat), he was hardly untouched by the age’s Romantic vision of wild nature as a transformative place. He took a Wordsworthian pleasure in his rambles. “I cannot tell you how I enjoyed some of these views,” he wrote his Cambridge mentor John Henslow. “It is worth coming from England once to feel such intense delight. At an elevation from 10-12000 ft. there is a transparency in the air & a confusion of distances & a sort of stillness which gives the sensation of being in another world.” He also found exciting his own growing comfort in these distant heights, so remote and rarefied that even most animals forsook them. “We unsaddled our horses near the spring,” he wrote of one excursion he took into the mountains with two cowhands as guides,

and prepared to pass the night. The setting of the sun was glorious, the valleys being black whilst the snowy peaks of the Andes yet retained a ruby tint. When it was dark, we made a fire beneath a little arbour of bamboos, fried our charqui (or dried slips of beef), took our matte and were quite comfort able. There is an inexpressible charm in thus living in the open air. The evening was so calm and still; the shrill noise of the mountain bizcacha & the faint cry of the goatsucker were only occasionally to be heard. Besides these, few birds or even insects frequent these dry parched up mountains.

Though wilderness was new to him, Darwin was no stranger to the outdoors. He had long been an avid bird hunter and walker. Born in Shrewsbury in 1809, he was the fifth of six children. He lost his mother when he was eight. His father, Robert Darwin, a doctor successful and rich, was a mercurial and sometimes harsh man. Yet he indulged a certain idleness in his youngest boy, whose namesake, the doctor’s older brother, had died at twenty, devastating his entire family. The second Charles also had another, more reliably benevolent patriarch in his uncle Josiah Wedgwood, brother to Charles’s dead mother and founder of the Wedgwood china dynasty. Josiah lived thirty miles from the Darwins on a huge estate called Maer, where Charles was always welcome. There Charles spent much time hunting, riding, walking, and, in the waning light after a day out doors, happily conversing with his uncle, aunt, cousins, and their friends.

He especially loved to hunt. Under the tutelage of his uncle, his own older brother, and Maer’s gamekeepers, he became a crack shot. He soon outhunted everyone. For weeks each fall he exercised a “zeal … so great,” he recalled in his charming, disarming Autobiography, that “I would place my shooting-boots open by my bedside so as not to lose a half-minute putting them on in the morning.” He was obsessed. In off-seasons he refined his upland bird technique by practicing his gun raising before a mirror and shooting out the flames of moving candles with an airgun. In season, he carefully tallied each bird he shot. The seriousness with which he took this head count led two hunting friends to conspire one day to claim, every time he downed a bird, to have fired also, faking a reload of their guns and asking him not to count that last one, as they had shot at the same moment and it might have been one of them who had downed the bird. After some hours, he recalled later (almost fifty years later, actually, and still with some pique), “they told me the joke, but it was no joke to me, for I had shot a large number of birds, but did not know how many, and could not add them to my list, which I used to do by making a knot in a piece of string tied to a button-hole. This my wicked friends had perceived.”

Shooting gripped him far more than school did. The man who would later eclipse Louis Agassiz (who, one year younger, was already energetically pursuing his career plan in Germany and Paris) was in his youth a decided underachiever, as distractible as Louis was focused. He had originally planned to follow his father’s profession, but when he showed no stomach for it while studying medicine at Edinburgh (witnessing his first surgery sickened him), his father pressed him to enroll at Cambridge so that he could become a country parson. Though Charles did not care for the dogma of the Church of England (he was raised a Unitarian), he went along gamely, for he recognized that otherwise he indeed might, as his father feared, “[turn] into an idle sporting man, which then seemed my probable destination.” “How I did enjoy shooting!” he con fessed in his Autobiography.“But I think that I must have been half-consciously ashamed of my zeal, for I tried to persuade myself that shooting was almost an intellectual employment; it required so much skill to judge where to find most game and to hunt the dogs well.”

Cambridge did not immediately reverse this. When he arrived he had to take remedial Greek and Latin, for he found that he had forgotten almost every word he’d supposedly learned in earlier schooling. Almost immediately he fell into a “sporting set … [of] dissipated low-minded young men” with whom he “sadly wasted” much time-though apparently not too sadly. “We used often to dine together in the evening,” he recalled in the Autobiography,“and we sometimes drank too much, with jolly singing and playing at cards afterwards. I know that I ought to feel ashamed of days and evenings thus spent, but as some of my friends were very pleasant, and we were all in the highest spirits, I cannot help looking back to these times with much pleasure.

Such was his later regret about his student indifference. He found boring almost every subject but geometry, so beautiful in its deductions, and chemistry. The one new thing that excited him as much as shooting and cards-the one new thing that engaged this bright young man surrounded by his culture’s greatest minds and libraries-was hunting beetles. By his own account, this beetle gathering was “a mere passion for collecting,” with no real scientific discipline. It was certainly a passion. Once, having caught a rare beetle in each hand and seeing a third, he popped one of the handheld beetles into his mouth so he could grab the new one. (The one beetle ejected a liquid so foul that he spat it out, losing it and the latest specimen as well.) But he said later that there was no rigor to it; it was mere accumulation, not study. He had no real curiosity about beetles’ function in the natural order.

However, chasing beetles did nudge Darwin nearer his final vocation, steering his outdoorsmanship more toward biology. He moved closer yet when he began attending public lectures given by the Reverend John Henslow, the Cambridge professor and leading naturalist who became his primary mentor. Darwin so admired the clarity of Henslow’s thinking and the beauty of his illustrations that he began going on the weekly natural history walks Henslow led. Henslow was intrigued by some combination of energy and intelligence in this young underachiever. He took in Darwin much as Cuvier would take in Agassiz a year later. Almost daily they went on long walks during which the lecture-leery but quick-eyed Darwin absorbed a field education in botany, entomology, and geology. Henslow also invited Darwin to weekly gatherings at his home, and frequently to dinner. The two spent so much time together in Dar win’s last year at Cambridge that the dons took to calling Darwin “the man who walks with Henslow.” Through Henslow, Darwin came to know many of Britain’s most prominent scientists, most notably the scientist-philosopher William Whewell, whose empiricist principles were then beginning to exert immense influence on British science, and Charles Lyell, whose work in geology Darwin would soon find so inspiring.

Henslow also introduced Darwin to a work that “stirred up in me a burning zeal to add even the most humble contribution to the noble structure of Natural Science.” It was Alexander von Hum-boldt’s 1819 Personal Narrative, a six-volume account of his five years exploring South America. Darwin’s encounter with this book marked his birth as a serious student and scientist. He read it several times in his last year at Cambridge, relishing this tale of geologizing and collecting in the Andes and the South American rainforest. He fantasized endlessly about taking such a trip. Humboldt profoundly influenced Darwin even as he directly mentored Louis Agassiz 250 miles south in Paris.

Darwin had fantasies but no expectations of following Hum boldt. He tried to organize a trip that summer to the Canary Islands, but it fell through for lack of funds and companions. Otherwise he had nothing going. Henslow and Humboldt had fired his enthusiasm for natural science, but the flame was hardly concentrated. As he neared graduation Darwin was still noodling over whether to join the clergy. A quiet country parsonage, he rationalized, would allow him to do the sort of natural history that pastor-naturalist Gilbert White had described in yet another favorite book, Natural History and Antiquities of Selborne.Beyond that, he had no agenda other than paying off his school debts and enjoying the opening day of partridge season September 1.

Yet if Darwin lacked the drive of Humboldt’s more direct protégé, he shared Louis’s luck with mentors. Just before graduating in spring 1831, he was invited by one of Henslow’s friends and fellow reverend-professors, Adam Sedgwick, to go geologizing in Wales that August. He accepted and joined Sedgwick after idling away most of the summer. The two walked for miles hunting fossils and mapping strata, having some fair luck and a good time-though they missed the glacial scarring that would leap into view for Darwin a decade later when he had learned of Louis Agassiz’s ice age theory. Yet the three weeks of geologizing did not exactly clarify Darwin’s calling. When he finished the trip with no other real plans, he could find direction only in the most literal way: “I left Sedgwick and went in a straight line by compass and map across the mountains to Badmouth [where he visited some old Cambridge friends], never following any track unless it coincided with my course. I thus came on some strange wild places, and enjoyed much this manner of traveling.” Then he headed home to collect his guns and hunting togs and go to his uncle’s estate. It was two days short of September 1. And “at that time I should have thought myself mad to give up the first days of partridge-shooting for geology or any other science.”

Yet he would, quite soon. At home he found a letter from Henslow informing him that Henslow had recommended him for a berth as naturalist on the round-the-world voyage of the HMS Beagle, a trip projected to take two to three years. To claim the spot he had only to favourably impress the captain, Robert Fitzroy who at twenty-six was only four years older than Darwin.

Had Darwin never read Humboldt’s Personal Narratives, he might have blanched at such a lengthy commitment. But coming on the heels of Humboldt and his own aborted Canary Island plans, the invitation inflamed his tropical travel lust. He told his father he would very much like to go.

His father forbade it. He feared the trip would stop forever his son’s halting walk toward the clergy. The son, disappointed but nonetheless happy enough to resume his shooting plans, wrote Henslow his regrets the day after receiving the invitation. The next morning he rode to his uncle’s, where he told Wedgwood of the vetoed invitation. Uncle Jos was not happy with this turn of events. He immediately wrote Dr. Darwin, answering each of the doctor’s objections and appealing his decision, and the next day, doubly deter mined that his nephew not miss such an opportunity, Wedgwood stopped Charles as he was heading off to the shooting fields, put him in a carriage, and rode with him the thirty miles to Dr. Darwin’s house. They arrived to find the doctor already convinced by Wedg wood’s letter. After all, he allowed, he had told Charles he would agree to the trip if he could find even one sensible man who thought it a good idea, and he could hardly call Wedgwood otherwise.

Thus Darwin, shoved into an about-face by his uncle, decided to claim the job of naturalist on the Beagle. To console his still doubting father, Charles told him that at least aboard the Beagle he would not be able to overspend his allowance, as he had so consistently at Cam bridge, “unless I was deuced clever.”

His father responded, “But they tell me you are very clever.”

2

The Beagle trip made Darwin, forming his mind and giving him the material for most of his major works. He later called the journey (which took five years rather than two) “by far the most important event in my life. … I owe to the voyage [my] first real training or education” as well as the “habit of energetic industry and … concentrated attention.” He began the trip an easily distracted idler and finished it a hard worker and penetrating theorist.

His wistful recollections of the journey also suggest that he later saw this period as the time he was most completely alive-still physically adventurous even as he first experienced the exaltation of deep intellectual engagement. His physical and mental exertions were linked more seamlessly than they ever would be again, for his field-work sparked an ongoing interplay of observation and abstraction. “Everything about which I thought or read,” he said of that time, “was made to bear directly on what I had seen or was likely to see.” This sentence describes precisely the loop of thought, observation, speculation, and reshaped thought that marks Darwin’s mature method. The method puts thought first-ideation inspiring examination rather than vice versa-and weighs reasonable conjecture (“what I … was likely to see”) as heavily as actual observation (“what I had seen”). Every outing both shaped and was shaped by the theoretical framework taking shape in his head.

Darwin was introduced to this approach early in the Beagle voyage by another book that changed his life and thinking, Charles Yell’s Principles of Geology. Reading the freshly published first volume (of an eventual three) in his first days at sea, he thrilled to find an intellectual world opening in his head even as a new, corresponding physical world opened beyond the ship’s rail. “The Principles,” Dar win would write a decade later, “altered the whole tone of one’s mind and thence when seeing a thing never seen by Lyell, one yet saw it partially through his eyes.” The influence was so great, said Darwin, that “I always feel as if my books came half out of Lyell’s brain.”

This first volume of the Principles was a gift from Captain Fitzroy Fitzroy later regretted it intensely. The captain was so conservative that he had almost rejected Darwin for the naturalist post when he heard he was a Whig. He was also an evangelical Christian, and he was so appalled when Darwin published his evolutionary theory in 1859 that he became a vociferous and prominent critic. The tension from maintaining this public opposition to his old friend helped drive him mad; in 1865 he killed himself by slitting his throat.

Darwin probably sensed that Lyell’s Principles was seditious. Henslow, while recommending the book to him as interesting, had warned him not to believe it. Darwin not only believed but reveled in it. “The very first place which I examined,” he wrote in the Voyage of the “Beagle,”“namely St. Jago in the Cape de Verde islands, showed me clearly the wonderful superiority of Lyell’s manner of treating geology.”

It wasn’t only Lyell’s geology that Darwin considered superior; he loved Lyell’s imaginative approach to making sense of nature. Lyell rejected the prevailing catastrophist explanations of the earths features as well as the contemporary inductivist prohibitions against speculation. He insisted, in short, on both sticking to the facts and using them as springboards for bold conjecture. In doing so he at once confirmed and pushed ahead of the empirical tenets of his fellow British scientists, alarming some while thrilling others.

Lyell’s break from catastrophist theory was sharp and explicit, and it liberated geology as thoroughly as Darwin’s evolutionary theory later liberated biology. Doubtless that explains some of its attraction to the young Darwin. The catastrophist geology taught during Darwin’s college days left him cold, for despite its visions of flying rock, lava, water, and ice, catastrophist geology offered a static view of nature. It saw the earth as essentially nondynamic, with a stable order occasionally disrupted by huge, presumably divine catclysms- global floods, immense volcanic eruptions, disturbances from passing comets-that had shaped its crust. The outbursts were exciting. But as the order was God’s, the forces driving these spasms needed little further explanation.

Lyell rejected that as no science at all. He insisted on explaining geologic history not by reference to divine act but by means of natural causes presently in effect. This uniformitarianism, as Whewell would later term it, was really both a geologic theory and a wider scientific principle. Principles main geologic argument was that the earth’s features were formed over long periods by forces still in operation; it followed that one should explain geological phenomena by referring to causes demonstrably at work. As geology, this uniformitarianism, or gradualism, would eventually be considered overkill; a twentieth-century “actualism” would reconcile it with a more natural catastrophism to allow for occasional events we’ve never directly witnessed but for which ample evidence exists, such as tectonic collisions, ice ages, and meteor strikes. As a working principle, how ever, Lyell’s uniformitarianism cleared the way for science’s advance in profound and badly needed ways. For while the insistence that every theory use verifiable existing causes sometimes left science short of explanations for complicated or elusive phenomena, it fostered more certain progress by preventing science from accepting idealist or catastrophist explanations. It forced empiricism. It was not enough to say that an apple falls because God tossed it down; you had to define and calibrate the natural force that makes the apple drop. You were required, in the schoolteacher’s term, to show your work. Of course, much of the most lasting science had always been done in this manner. But the indulgence of catastrophism allowed such empirical thinking to be set aside, and science to stagnate, whenever a natural cause proved too elusive or threatening. Uniformitarianism meant always seeking a natural explanation- even if it meant not finding one.

Lyell did not invent uniformitarianism. The British geologist James Hutton had first proposed it in his 1795 Theory of the Earth. But neither Hutton’s leaden prose nor a clearer 1802 explication by his friend John Play air could unseat the catastrophist geology then being elaborated by Cuvier. Lyell had better luck. Cuvier died soon after Lyell’s first volume came out, for one thing. More important, in the quarter century since Hutton and Play air, British science had grown increasingly confident in its empiricist principles. Finally Lyell simply made a better case for uniformitarianism than Hutton had, demonstrating repeatedly over three volumes how it was not just possible but necessary, as his book’s subtitle put it, to “explain the former changes of the Earth’s surface by reference to causes now in operation.”

Principles similarly pressed another Lyell innovation: It rejected inductivist taboos regarding speculation. This innovation posed more of a challenge to many of his British colleagues than did his uniformitarianism, for at the time, a cautious, gradual method of theory building was de rigueur among British scientists. This strict inductive model-the insistence on moving slowly and carefully from the specific to the general-had originated in 1620 with Francis Bacon, who forged it to liberate science from the bonds of church, state, and errors of logic. Bacon outlined an elaborate process of inductive inference to replace the deductive approach that had been established by Aristotle two thousand years earlier. Aristotle’s deductive model called for juxtaposing two or more known truths to reach a third, as in the classic syllogism “Gods are immortal; humans are mortal; therefore, humans are not gods.”* Aristotelian deduction worked splendidly as long as you used sound premises. But it begged error and abuse. Obviously you could err if you used a false premise-if, say you had somehow overlooked some mortal gods-for one false premise could produce many others that would in turn produce yet more mistakes. The method’s susceptibility to abuse had proven even more serious: If someone could dictate which premises were to be considered true, the syllogistic method generated stasis. Thus astronomy was inhibited (to put it mildly) by the Catholic church’s insistence that the earth was the center of the universe, and geology and biology had long been hampered by Christian dicta about the earth’s age and humanity’s origin. You would only get so far in astronomy, for example, if you had to use as a premise “The universe orbits the earth.”

To free science from these dangers, Bacon offered his slow, incremental intuitivism. Here was a way to peg theory to observable fact. It’s no coincidence that he worked in the wake of Martin Luther, who in the early 1500s had launched Protestantism by insisting that religious truth lay not in the church’s authority but in the evidence of Scripture. Bacon, also hoping to supplant authority with evidence, tried to design a scientific method that left nothing to leaps of faith, unsupported assertion, or unfounded supposition. Rather than work from untested premises or move from a few observations to an “illicit and hasty generalization,” the scientist would use observed particulars to slowly build a pyramid of “gradual generalizations” leading to broader theories or laws.

Bacon’s method quickly won great standing in Britain. By the early 1800s it had been bolstered by the empiricist philosophies of Locke and Hume and the accomplishments, held to be reached in Bacon Ian fashion, of Keller, Newton, and other scientific giants. The tension between British intuitivism and Germany’s idealist Naturphilosophie only deepened British allegiance to Bacon’s method. By the time of Lyell and Darwin, intuitivism had become the rule of the day in the British scientific establishment; to deny you practiced it was to risk your credibility.

In 1830, however, the Englishman John Herschel, a respected member of the British scientific establishment because of his careful mathematics and astronomy, argued in his Preliminary Discourse on

the Study of Natural Philosophy that too strict an intuitivism needlessly hampered progress. In a lucid discussion of how scientific theories are formed and tested, Herschel held that it mattered little how you came up with a hypothesis-it could be an educated inference, a wild guess, or a dream-as long as you tested it rigorously against observation. We shouldn’t hold a theory’s creation to the same standards as its proof. Since a hypothesis was just a provisional explanation that required testing to become a legitimate theory, why should its genesis be relevant? Why couldn’t you leap to the top of the pyramid and then build the understructure, revising as needed? If a child joked that the sun was at the center of the solar system, wasn’t this as useful a hypothesis (assuming you tested it against observation afterward) as a conjecture based on years of telescope work? The real test of either lay in measured observation; origin hardly mattered.

Herschel’s proposal stirred a long, uneasy controversy, for he had articulated a fundamental tension in the accelerating push toward empiricism. Did a primacy of the observable require that knowledge move from the particular to the general? Everyone agreed that a theory must not merely fit a few facts but stand in accord with virtually all available relevant observations and experiments. But must it rise directly from observations and experiment? Or need it merely agree with them once conceived? This debate would run for another century, expressed as much in people’s work as in their talk. Both Darwin and Alex Agassiz would find themselves enmeshed in its labyrinthine difficulties.

Most of the published response came soon after Herschel’s Preliminary Discourse appeared in 1830. The eminent empiricist William Whewell, for instance, objected sharply in his review, insisting that while scientists must use inference to form a hypothesis, those inferences should be incremental and rise from sober consideration of significant evidence. They could not be large deductions or flights of imagination. The path from fact to theory must be one of many steps, not a jump over a gap that you fill in later.

As Whewell was a man of immense intelligence, accomplish ment, and influence, his review, as well as his arguments in conversation in London and at Oxford and Cambridge, did much to discourage acceptance of his friend Herschel’s argument. A decade after Herschel published his Preliminary Discourse, Whewell authoritatively elaborated his inductivist caution in his monumental, two-volume Philosophy of the Inductive Sciences of 1840, which built on his equally weighty History of the Inductive Sciences of three years before. In the History Whewell had described how key scientific advances had been made; in the Philosophy he drew on that history to update and elaborate Bacon’s inductive method. He wrote-and at Hens-low’s and other Cambridge gatherings, talked-all during the 1830s and 1840s on these ideas, which were given extra credibility by his brilliance, his voluminous reading, and his experience in mathematics, mineralogy, and tides.

Coming atop almost two centuries of inductivist tradition, Whe-well’s deeply learned advocacy won the day and even the century. Throughout the 1800s, his neo-Baconian approach remained the standard prescription for inductive method, especially among the British. Scientists might privately admit that they sometimes yanked ideas from the blue. But publicly they sided with Whewell rather than Herschel. Thus in his Autobiography Darwin, though he named Herschel’s book (along with Humboldt’s) as one of the two that most influenced him, would claim that in forming his evolutionary theory he worked on “true Baconian principles.”

Lyell preferred Herschel’s model. In Principles he put it to work with unprecedented boldness, freely jumping to hypotheses about the earth’s crust and openly justifying the need to speculate. In a way he was simply making virtue of necessity, as replacing catastrophism’s miracles with natural forces sometimes required conjecture. But he did so unapologetically He was happy to value observations not merely as facts to be accumulated incrementally but as the basis for imaginative conjecture. Once he had leapt to a new idea, he would amass robust evidence to support his position. But he was not shy about having leapt to get there.

Lyell was also willing to argue through relevant analogy as well as direct evidence, another Herschellian idea that defied Bacon. This greater use of speculation and analogy made many of his colleagues queasy. Yet he used this method so productively and backed his assertions with so many observations that even those wary of his speculation agreed that he had greatly advanced geology.

For the young Darwin, as for many others, the effect was breath taking. Lyell changed geology from an enumerative task to a quest engaging eyes, legs, intellect, and imagination; one saw both the earth and the possibilities of science in a new light. Geologizing before and after reading Lyell was something like the difference between simply hunting beetles and studying them with their evolutionary arc in mind. To be a pre-Darwinian beetle collector, as Dar win had been, was to gather bugs and fit them, unquestioning, in a stable, divinely designed system. Like finding and piecing together the lenses of a stained-glass window, it gave a certain pleasure but ultimately only confirmed a prescribed order. In that sense, as Dar win wrote Henslow early in the Beagle voyage, “in collecting, I can not go wrong.” Yet for Darwin, such work created no excitement beyond the hunt. He cared less for completing a prescribed vision than for sketching a new one. Thus thinking about beetle collecting bored him, as did geology before Lyell.

Geology after Lyell was another story. Nothing, said Darwin, now matched the pleasure of hammering rock and pondering its meaning. “The pleasure of the first day’s partridge shooting or first day’s hunting,” he wrote his sister from Tierra del Fuego, “cannot be compared to finding a fine group of fossil bones, which tell their story of former times with almost a living tongue.” Geology had eclipsed even shooting. Looking over his time geologizing in South America, he wrote in his Autobiography,

I can now perceive how my love of science gradually preponderated over every other taste. During the first two years my old passion for shooting survived in nearly full force, and I shot myself all the birds and animals for my collection; but gradually I gave up my gun more and more, and finally altogether, to my servant, as shooting interfered with my work, more especially with making out the geological structure of a country. I discovered, though unconsciously and insensibly, that the pleasure of observing and reasoning was a much higher one than that of skill and sport.

It comes as a jolt, reading Voyage and Darwin’s letters from the trip, to realize that history’s most famous biologist began his career far more entranced with geology. His zoological and botanical collecting on the Beagle trip, he said later, were at the time valuable mainly for sharpening his powers of observation; only when he was back in England did he see the evolutionary patterns in his zoological data. During the trip, he still saw zoology as just collecting. In contrast, “the investigation of the geology of all the places visited … was far more important, as reasoning here comes into play.”

His Beagle field notes show clearly his enthusiasms: He took just four hundred pages on zoological topics and some fourteen hundred on geology. Of the five books he wrote soon after he returned, the three most technical and scientifically substantive concerned geology, as did a portion of a fourth. In 1839, meeting part of his obligation to the voyage, he wrote a section of the official account, the Narrative of the Surveying Voyages of Her Majesty’s Ships “Adventure” and “Beagle” and also published the Journal of Researches into the Natural History and Geology of the Countries Visited During the Voyage Round the World of H.M.S. “Beagle” which soon became a best-seller known as The Voyage of the “Beagle.” Much of Voyage concerned geology, and his next three books focused on it exclusively: his coral reef book in 1842, a volume on volcanic islands in 1844, and one on the geology of South America in 1846. Nothing excited him as much as geology did. Nothing so engaged his suddenly curious mind. The task of discerning the earths evolution gave a thrill, he wrote a cousin, “like the pleasure of gambling.”

3

Darwin’s delight in geology peaked in the Andes, where he found his investigations so enthralling, he wrote his sister, that he “could hardly sleep at night for thinking over my days’ work.” Through much of 1834 and most of 1835, he took long horseback expeditions all over the still-rising Cordillera and its flanking ranges. Ignoring the ocean almost completely and leaving most zoological collecting to his assistant, he paused in his travels only when he had to reboard the Beagle to sail up the coast or, twice, when gastrointestinal torments laid him out. (Though these illnesses were apparently gen- uine, probably due to intestinal parasites, they seem to have planted the mental seed for the psychosomatic gastric distresses of his later life.)

Roaming the Andes in clear light, he found they beautifully demonstrated Lyell’s long, incremental view of the earths construction. “The stratification in all the mountains is beautifully distinct and from a variety in the colour can be seen at great distances,” he wrote Henslow; they lay like the page edges of a book. “I cannot imagine any part of the world presenting a more extraordinary scene of the breaking up of the crust of the globe.”

He had not been there long before he witnessed this breaking up directly. On February 20,1835, he was camping in the dense forest of southern Chile when a massive earthquake struck. Though Darwin was some twenty miles from the epicenter, the quake rearranged his visceral sense of the earth as thoroughly as Lyell had rearranged his theoretical conception of it: “An earthquake like this at once destroys the oldest associations; the world, the very emblem of all that is solid, moves beneath our feet like a crust over a fluid; a second of time conveys to the mind a strange idea of insecurity, which hours of reflection would never create.” He told Henslow that the sensation underfoot was “like that of skating over very thin ice; that is distinct undulations were perceptible.” The unsettling feeling was rein forced when he visited Concepción, a port city of several thousand people that stood (briefly) at the quake’s center. He found the town “nothing more than piles and lines of bricks, tiles, and timbers,” he wrote his sister Caroline. “It is the most awful spectacle I ever beheld,” he went on. “The force of the shock must have been immense. The ground is traversed by rents, the solid rocks are shivered, [the cathedral’s] solid buttresses 6-10 feet thick are broken in to fragments like so much biscuit.” Seventy villages in the nearby countryside were similarly destroyed. Only the animals seemed to have sensed it coming. Gulls were seen heading inland two hours before the quake, and Concepción’s dogs, which typically howled “as if hearing military music” during low-grade tremors common in the area, quietly left about an hour before the shock; they were standing on the surrounding hills when the quake hit and came slinking back afterward. The earth’s undulations threw cattle and horses to the ground, from which they rose “exceedingly terrified, running about as if mad, with their tails in the air.” Cows on one steep slope rolled into the sea. Trees slammed against one another. Jets of lava burst from the water near the beach.

After the earth stopped moving, huge swells appeared on the Pacific horizon; a quarter hour later, waves twenty-five feet tall slammed ashore and smashed several hundred feet inland, dumping schooners into the middle of town and carrying away anything that floated. Afterward “the coast was strewed over with timber and furniture as if a thousand great ships had been wrecked. Besides chairs, tables, bookshelves in great numbers, there were several roofs of cottages almost entire, Store houses had been burst open, and in all parts great bags of cotton, Yerba [maté], and other valuable merchandise were scattered about.” It was one of the most violent quakes ever to strike South America.

Though several hundred people died in Concepción, the quake would have killed many more had it struck at night. Thousands survived because they were working outdoors or, if indoors, had “the constanthabit,” as Darwin noted, “of running out of their houses instantly on perceiving the first trembling… The inhabitants scarcely passed their thresholds before the houses fell in.” The English consul, for instance, scrambled outside at the first motion; he had just reached the courtyard

when one side of his house came thundering down; he retained presence of mind to remember that if he once got on the top of that part which had already fallen, he should be safe; not being able, from the motion of the ground, to stand on his legs he crawled up on his hands & knees; no sooner had he ascended this little eminence, than the other side of the house fell in; the great beams sweeping close in front of his head.

For the rest of his life, Darwin often called this earthquake the most fascinating spectacle he’d ever seen and said that he considered earthquakes “one of the greatest phenomena to which this world is subject.” Their possible cause intrigued him. Humboldt, in the six-volume work Darwin read so many times, had offered that quakes were caused by the same subterranean pressures that drove volcanoes and argued that they helped lift the Andes. Lyell had expanded on this quake-volcano connection in the first volume of Principles, speculating that quakes were essentially repressed volcanoes-would-be eruptions that couldn’t escape and so lifted the earth instead. Now Darwin, privileged to be on hand at a major quake, was thrilled to see that much of the land had indeed risen. The bay around Concep-ción jumped three feet, as shown by the rim of mollusks, barnacles, and other sea-edge life now a yard up out of the water. The island of Santa María, thirty miles offshore, rumbled upward eight feet. Other spots along the coast rose up to a dozen feet. Darwin was giddy. Having come to ponder what built the Andes, he had seen them grow several feet. He also talked to locals who told of harbor shores that over the previous two decades had risen four feet in unnoticeable increments (as evidenced by the rise of dock anchors and other things they knew were formerly at the surface); it seemed that along with moving in jumps of a few feet, the earth also rose steadily and less violently, en masse, at rates almost too slow to measure.

In the weeks after the earthquake, wandering the barren heights and canyons of the Andes, Darwin found yet more evidence of such gradual elevation. Canyon walls showed layers tilted upward by some uprising force. The “strata of the highest pinnacles,” he wrote his sister Caroline, were “tossed about like the crust of a broken pie.” These upsurges had clearly occurred in stages, not the one-rip, mountain-building spasms the catastrophists proposed. He found seashells and coral at numerous heights-at shoreline; at elevations of a few dozen, a few score, and a few hundred feet; at thirteen hundred and three thousand feet; and finally, at twelve thousand feet. Only a series of rises over time could explain this.

Consolidating bits from Lyell, Humboldt, and a few others, Darwin formed a theory of mountain building that saw volcanoes and earthquakes as part of a dynamic that could either slowly lift land, rend it, or suddenly raise it several feet. Driving these movements was a layer of molten rock, varying in thickness and pressure, beneath the earths crust. Lyell, Humboldt, and many others had written of cavities of such molten or gaseous material underlying volcanic regions, but Darwin was one of the first to propose that a layer of such material wrapped the entire globe and that it was either more active or closer to the surface in some areas than in others. In a theory that anticipated plate tectonics, he proposed that most or all of South America floated atop this layer of molten rock and lava, the pressure from which gradually raised most of the continent through long periods and occasionally caused volcanoes or earthquakes or pushed the range sharply up via “angular displacement” caused by the injection of lava beneath.

Finally, if he was to believe what he saw, the land did not merely rise; it often dropped. Amid the volcanically formed layers of the Andes he found layers of sedimentary rock-earth laid down through millennia of deposition and compression. Some of these layers held marine fossils, making it clear they had formed underwater. The most spectacular find, which he stumbled across at around seven thousand feet, was a grove of large, pale, smooth, ancient trees pre served in sandstone holding seashells; clearly the trees had grown hundreds of years on land, then ridden a subsiding landmass down below sea level, where eons’ worth of sediment-now sandstone- accumulated around them before the Andes rose again to lift them high. This was only one of many arresting finds. By the time Darwin was done, he had found evidence of two or three cycles of uplift and subsidence that had carried South America several thousand feet above sea level and at least two thousand feet below.

The earths crust, then, bobbed up and down almost constantly. The relation any expanse of crust bore to sea level depended on timing, the pressures beneath it, and, no doubt, some factors that no one yet understood. Like Lyell before him, Darwin stressed that, given the difficulty of knowing what happened underground, any theory regarding earthquakes, elevation, or subsidence entailed speculation. Yet some things seemed clear. It seemed obvious, for instance, that some areas tended to move more up than down, or vice versa, which is why the Andes’ up-and-down cycles left them ever higher. The same would apply to sunken areas. Lyell had speculated that falling land or seafloors subsided when underlying cavities collapsed after their pressurized lava, steam, or gas escaped or condensed. But Dar win, happily insomnious with his vision of South America rising on swelling magma, regarded this notion of collapsed lakes as small thinking. The crust’s movements might be slow, but they were large.

And as Lyell had suggested, a rise in one place tended to be balanced by a drop somewhere else. If the molten layer beneath the crust could lift whole continents, then perhaps the floors of entire oceans were also dropping en masse.

Which invited a question: How did all these rising and subsiding forces operate in the huge bowl of water to his west? What did one make of the vast basin of the Pacific and its coralline archipelagoes?

4

Even as he was composing his Chile notes, Darwin was turning his mind west. The Beagle, having finished its laborious survey of the South American coast, was making ready to sail. Examining charts of the route ahead, Darwin contemplated the oddity that is the Pacific: a broad pan, immensely deep, with arcs and ovals and doglegs of coral isles rising, as he put it, from its “profoundest parts.” Several of these archipelagoes-the Galápagos, the Tuamotus, French Polynesia, the Fijis, and the Friendlys-lay along the Beagle’s route. In the sixty years since Captain James Cook had mapped them, these islands had commanded much interest among geologists and naturalists. They were intrigued by the great depths from which they rose; their volcanic nature; their ordered but irregular arrangements, like pearl necklaces tossed to the floor; and the islands’ distinctive annularity

Someone excited sleepless by geology wasn’t likely to resist such shapes. Darwin’s Andean wanderings and ruminations had whetted what would prove an insatiable appetite for discovering patterns spanning space and time. These ringed islands presented precisely such a pattern.

The puzzle seemed ripe for solution. Though coral islands and reefs had intrigued Europe’s scientists and public for almost a century (an interest greatly boosted by the descriptions Cook brought back of the South Pacific archipelagoes in the 1770s), no one had plausibly explained how they came to be. They were initially appreciated mainly for the sheer wonder of their existence, apparently climbing from the sea’s depths to create new landscapes. In the eighteenth-century fascination with the idea of a Great Chain of Being, corals held a special place for seeming to bridge the gap between plant and animal, and, after Jean-André Peyssonnel showed them to be animals in 1753, for creating with their calcified skeletons the huge structures that joined the organic and the inorganic worlds as well as sea and land. In the early nineteenth century, some saw in coral reefs a welcome antidote to the erosion that, according to Huttonian geology was erasing humankind’s terrestrial platform. “Whatever destroying tendencies … exist on the earth,” wrote one prominent geologist in 1818, “these renovating powers compensate for them.”

Such speculations rose naturally when geology was so young, the reefs so many, and scientific visits to them so few and brief. Naturalists on the Cook and other expeditions of the late 1700s, however, began to fill in the blanks. They established that the reefs were formed by the accumulating skeletons of huge colonies of tiny, tube-shaped animals known as coral polyps. These polyps, which would later be found to be hard-bodied cousins of sea anemones, were also variously referred to as insects, “molluscus worms,” or even “animalcules.” They seemed to live only in warm tropical waters, generally no further than twenty-five or thirty degrees from the equator. The polyps apparently built their great works extremely slowly. No one who lived in coral regions described discernible growth, and while nineteenth-century European visitors who compared the reefs to descriptions and charts from the previous century discovered that some reef areas had apparently been torn up by storms, they could not find measurable expansion. At first it was thought that the reefs might build themselves up from sea bottom as deep as several hundred or even several thousand feet. But by 1820 scientists knew that corals grew only in water no more than one hundred or two hundred feet deep.

These observations presented two critical mysteries. One was how shallow-water animals came to grow on platforms that rose from the Pacific’s greatest depths. Did they just happen to find these plateaus, or did they somehow build them? The other puzzle was the distinctive annularity of reefs surrounding islands, of many coral islands themselves, and even of the vast coral atolls, or groups of smaller islands, that were strung around the Pacific. The reefs encircling islands followed their contours, often ringing them with a calm lagoon between reef and shore. Other reefs surrounded lagoons only, with no island in the lagoon’s center. And the Pacific’s many atolls tended to be ringlike or looplike themselves. With so many reefs and atolls taking circular and ovoid forms, it seemed unlikely that reefs just happened to grow on convenient platforms. Some dynamic relationship between the reefs and their foundations seemed to shape them.

The first coral reef theories, offered in the late 1700s and early 1800s, gave fairly simplistic or teleological answers to these questions. For instance, J. R. Forster, the naturalist on Cook’s second voyage in the mid-i770s, proposed that corals simply knew they needed to build a circular structure to give themselves a sheltered environment. Another early theory, that of the naturalist and vulcanist Christian Leopold von Buch (1774-1853), had coral reefs growing on the rims of “elevation craters” that had formed when huge, gaseous blisters (quite distinct from volcanoes) raised the sea bottom and then popped and collapsed. This theory, which ignored the fact that every major known reef lay in a volcanic area, was a strange one coming from Buch, for he was a noted vulcanist, having firmly established, early in the 1800s, that lava formed new rock. Buchs discovery of the volcanic nature of rock greatly advanced uniformitarianism, for cata-strophist theory had maintained that all the earths rocks and land had long before precipitated from a primordial ocean. Yet this pioneering vulcanist overlooked the seemingly obvious connection between coral reefs and volcanoes. A few other reef scientists, citing what seemed plain in Caribbean and Atlantic reefs, which emerged from shallower depths, offered that most reef platforms consist of sediment deposited by current.

The first theory to get wide acceptance was that of Johann Esch-scholtz, who visited the Marshall Islands on an 1815-1818 Russian voyage led by Otto von Kotzebue. Eschscholtz hypothesized that corals, responding to the influx of oxygen and food as they rise on existing platforms, slowly create a bulwark that grows faster on its sea-facing side. Reefs grow from the center outward, in other words. This, he said, creates a tendency toward annularity that, along with the shape of the platforms they grow on, accounts for typical reef forms. Though Eschscholtz overextended this idea to unlikely deeps because the depth limit of coral growth wasn’t established until just after he offered his theory, his hypothesis seemed to cover many reef forms and helped to explain lagoons.

Eschscholtz experienced mixed luck with this theory. While his reef-building model exerted immense influence, it was incorrectly attributed for seventy-five years (fifty years beyond Eschscholtz’s death) to his colleague on Kotzebue’s voyage, a poet-naturalist named Adelbert von Chamisso. In any event, the Chamisso-Eschscholtz hypothesis, especially its assertion that coral reefs grow faster to sea ward, shaped thinking about reefs for a century, generating further theories.

Foremost among these other theories, and the one that came closest to enjoying a consensus in the early 1800s, was what might be called an elevated-volcano theory. This held that most of the world’s coral reefs grew on volcanic mountaintops that had risen close to the sea’s surface, presumably lifted by mountain-building forces similar to those on land, and then expired, leaving only the round ring of the volcano’s mouth. The round shape of many islands and atolls sup ported this idea, as did the existence of old coral on some islands jut ting well out of the water. For how would those corals have reached terrestrial mountaintops if the mountains hadn’t been pushed from below?

This raised-volcano hypothesis, as it happens, was the one backed by Lyell and presented in Principles of Geology as the most authoritative explanation. This theory held weaknesses too, however, and Darwin, pondering the charts in Chile, found them damning. Yes, he recognized, many isles had risen well above the surface, suggesting elevation. But the charts showed that those taller islands were vastly outnumbered by the thousands of coral isles and atolls, including archipelagoes hundreds of miles long, that barely cleared the water. The above-water portions of these low structures were clearly created by coral debris and sand being tossed atop subsurface reefs. Were we to accept that the foundations of all these isles had conveniently risen to within a couple hundred feet of waterline and then stopped growing so that coral could complete the trip? Hardly. As he put it in the Voyage of the “Beagle”

It is [highly] improbable that the elevatory forces should have uplifted throughout… vast areas, innumerable great rocky banks within 20 to 30 fathoms … of the surface of the sea, and not one single point above that level; for where on the whole surface of the globe can we find a single chain of mountains, even a few hundred miles in length, with their many summits rising within a few feet of a given level, and not one pinnacle above it?

Besides, he noted, the vast spans of many atolls, some of them rough circles dozens of miles in diameter, others oblongs thirty miles by six, or fifty by twenty, could hardly mark the rims of volcanoes, for where had there ever been volcanic craters so large or oddly shaped?

He didn’t care either for the second-most popular hypothesis then around, which was that reef platforms accumulated through sedimentation. “It is improbable in the highest degree,” he noted, “that broad, lofty, isolated steep-sided banks of sediment, arranged in groups and lines hundreds of leagues in length, could have been deposited in the central and profoundest parts of the Pacific and Indian Oceans, at an immense distance from any continent, and where the water is perfectly limpid.

But what could explain these huge chains and rings of coral? Some of these island groups stretched hundreds of miles. At least one pair of Pacific archipelagoes, the Low and the Radack, together had hundreds of low coral isles spread along a line over four thousand miles long, and a similar formation fifteen hundred miles long curved across the Indian Ocean. All of these isles grew atop shallow platforms that fell away steeply to immense depths. What could have created such long curves and circles of shallow platforms rising from deep water?

Darwin, having for weeks mulled over the image of South America rising next to a falling Pacific, saw what now seemed to him obvious: The Pacific’s coral islands did not form on rising mountains; they formed on islands and the high points of large landmasses- possibly even continents-that were slowly sinking.

The thought, he said later, came to him in a flash while he was still on the coast poring over charts. Indeed, his notes and correspondence show that he first saw the Pacific reefs not so much as some thing to be explained but as evidence of a Pacific subsidence that balanced the rise of the Andes. In his Autobiography(not too many pages before claiming that he developed his evolutionary theory through “strict Baconian methods”), he confesses of the coral reef theory that “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 South America, before I had seen a true coral reef

This was enough to make a Baconian inductivist quake. Yet Dar win could hardly reject his notion of falling islands, for it seemed to explain everything about reefs. In particular, the man who would later study variations in finch beaks found it especially compelling that this idea explained why coral islands, reefs, and atolls appeared in ringlike or looping forms. The different reef and atoll shapes reflected different stages in the subsidence of the islands on which they took root.

Take a volcanic island, proposed Darwin. Corals would naturally form on the shallows surrounding it. At first this reef, which he called a “fringing reef,” would be thin and lie directly against the island’s shores. But if the island slowly dropped, these corals growing in its surrounding shallows would slowly grow upward, ever thickening but never breaking the surface, to provide a platform for yet more coral. The fringing reef would thicken and broaden, reaching further out to sea.

The fringing reef would soon change, however. If, as Chamisso held, corals grow more quickly toward the open ocean than toward protected water, the reef would grow faster toward the sea than it would toward the sinking island, and as the shore sank, a lagoon would form between the reef and the land. The fringing reef would now be a barrier reef-that is, a reef with a lagoon or channel between it and the land it grew around. As time took the island further down, the reef would continue to thicken to stay near the surface, and it would continue to grow outward toward the sea. Eventually the island would sink beneath the water. Then the barrier reef would become an atoll-a ring of coral matching the former outlines of the island but now surrounding only a calm lagoon. In the meantime or soon after, the waves might throw enough coral debris and sand atop the reefs to create some of the narrow, strip-shaped islands so common to the Pacific’s coral archipelagoes.

To Darwin, this theory not only explained all three types of reefs-fringing, barrier, and atoll-it seemed to be the only theory that satisfactorily explained barrier reefs and atolls at all. Fringing reefs could be explained simply by the fact that corals grew in shallow water. But barrier and atoll reefs required some other theory, and no other theory accounted for both of them. Even if you bought that circular atolls had grown on submerged volcanic rims, that idea didn’t cover barrier reefs or more oddly shaped or huge atolls, and it asked you to believe that in some areas, thousands of these dead volcanoes came within one hundred fathoms of the surface while none reached above. The other explanations either ignored common reef forms and features or asked you to believe the unbelievable. It was absurd to assert that thousands of mountains all came close to the surface without breaking it; only subsidence could explain these strings of low islands. And only subsidence could plausibly explain barrier reefs and atolls. The logical link was so strong, Darwin thought, that the barrier reefs and atolls in turn provided evidence of subsidence.

rain’s subsidence theory saw reef formation as a continuous process that transformed the fringing reef surrounding a slowly sinking island (A) to first a barrier reef separated from the island by a lagoon (B) and finally a ring-shaped atoll (C).

This was all from the west coast of South America. When he hop scotched across the Pacific and finally visited atolls and barrier reefs in Tahiti and at the Indian Ocean’s Cocos (or Keeling) Islands, the sight of the formations-particularly the Tahitian island of Moorea, which sat surrounded by its lagoon and barrier reef like an engraving by its mat and frame, as he put it-confirmed for Darwin the accuracy of his vision. “I glad we have visited these islands,” he wrote in his diary, for the coral reefs “rank high amongst the wonderful objects in the world… [They are] a wonder which does not at first strike the eye of the body, but, after reflection, the eye of reason.” As lovely as the reefs were in aesthetic terms (and Darwin keenly appreciated their beauty), they provided for him the even deeper thrill of embodying a deep, time-based pattern apparent only to the imaginative intellect.

This subsidence theory was an audacious idea for a twenty-six-year-old. Conceptually ambitious and blatantly deductive, it begged trouble from all quarters. While challenging the coral-formation theory favored by the new leader of British geology, Lyell, it also aggressively pushed Lyell’s controversial gradualism and speculative method into new territory. As the Beagle rounded Africa and made for En gland in early 1836, Darwin worried how the senior colleagues he admired, particularly Henslow and Lyell, would receive his theory.

He was elated when, on his return in fall 1836, the scientists most important to him, starting with Lyell, found it as thrilling as he did. When he told Lyell of the theory at a lunch at Lyell’s house soon after returning, his host became so excited he leapt around the room shouting and laughing, and he immediately dropped his own idea that reefs grew atop mountains that had risen. Darwin’s idea, he agreed, was far more powerful and beautifully concise. Reefs were not caps atop mountains that had fallen short. They were, as Lyell put it in a letter to Herschel, “the last efforts of drowning continents to lift their heads above water.”

Lyell immediately arranged to have Darwin read an abstract of the theory at the Geological Society. He warned Darwin that others might not share his own excitement. “Do not flatter yourself that you will be believed till you are growing bald like me, with hard work and vexation at the incredulity of the world.” Yet to Darwin’s delight, he was believed almost immediately. The positive reception began as soon as he read his paper before the Geological Society, in May 1837. Herschel liked it and Whewell did too, despite its non-Baconian birth, for the thing worked. Darwin soon won over a wider circle with his presentation of the theory in Voyage in 1839 and more fully in the 1842 Structure and Distribution of Coral Reefs. Meanwhile, Lyell incorporated Darwin’s subsidence theory into his 1840 edition of Principles, making it the textbook explanation. Pacific investigations in the 1840s by the British researcher J. B. Jukes and a young James Dwight Dana seemed to confirm the theory. Jukes, having looked extensively at Pacific reefs, said Darwin’s explanation “rises beyond a mere hypothesis into the true theory of coral-reefs.”

Doubters lurked. Some geologists found it difficult to envisage the tectonic movements of which Darwin said subsidence was part. One reviewer called the idea of such movements “bold and startling … even to the most hardy of our geologists.” Another scientific reviewer hoped “to find the boldness of [Darwin’s] theories a little modified; and … resting upon a more solid foundation than the supposed undulations of subterranean fluid.” A few people considered these objections quite damning. John Cluines-Ross, the owner of Cocos Islands, where Darwin saw the atolls that confirmed for him his theory, called it “palaver” and dismissed it out of hand.

These arguments worried Darwin only slightly, for he recognized that they came from people who simply didn’t buy the Herschel-Lyell need to speculate. They were fair objections regarding rightly debatable conceptual issues. Of more concern was the way the existing empirical evidence often contradicted his theory and offered it little direct support. As skeptics noted, most of the coral isles studied so far showed much evidence of elevation and no sign of subsidence. Explorers had found corals and other marine fossils atop the taller islands, for instance, but no corresponding terrestrial fossils or structures beneath the surface. And though many (including Dar win) had observed contemporary elevation in action, no one had observed ongoing subsidence. Darwin’s defense-that the recent elevations were cycles amid an overall pattern of marine subsidence, the evidence for which had not been observed because it was hidden underwater-couldn’t be backed by anything tangible.

Even more troubling to Darwin was that in the world’s expanding catalog of examined strata, no one had discovered any deep thickness of continuous coral. Geologists had found many thick layers of marine sandstone and sedimentary limestone above ground; why no great thicknesses of coral? When he and Lyell couldn’t resolve this one despite extensive discussion, Darwin had to admit it was a “weighty and perplexing” objection.

These and other objections, however, scarcely slowed the theory’s acceptance. By 1850 Darwin’s theory, backed by Lyell and his own expanding base of supporters, became the single-most widely accepted theory of coral reef formation. Meanwhile he moved on from it and other geology to work on barnacles and, quietly in the background, his transmutation theory. Even as he did so, the reef theory consolidated its hold. By the time he wrote his Autobiography, in 1876, he could accurately say of The Structure and Distribution of Coral Reefs that it was “thought highly of by scientific men, and the theory therein given is, I think, now well established.” He still got a kick out of its simple power and success; he said it gave him more pleasure than any other theory he’d ever come up with.

For good reason. It’s hard to overstate how vital Darwin’s coral reef theory was in developing his career and thinking. It paved the way, conceptually and methodologically, for everything to come, particularly his transmutation theory. The likenesses startle. Like the transmutation theory, the coral reef theory described how small, virtually unnoticeable changes could create differences of essential type in seemingly immutable forms-and in doing so, account for broad patterns of development and difference.

Thematically formally, and even psychologically, then, Darwin’s coral reef theory served almost as direct progenitor of his species theory. As perhaps nothing else could have, it prepared him for the conceptually similar but more difficult work on evolution and natural selection. He seems to have needed this dry run-a theoretical foray into the relatively tame territory of rocks and reefs-before pursuing a similar argument on the more perilous species question. He barely thought about the species issue, in fact, until he had finished developing his coral concept. Though the raw zoological data and specimens he collected on the Beagle proved key to his evolution work, they did so only later. His expedition notebooks contain no real contemplation of evolution or variation until he was in Australia, well after his Galápagos visit, when he had just finished recording in his notebook, on the sail from Tahiti to Sydney, the first full abstract of his reef theory. In Australia, with the abstract sketched out, he made a few brief notes on species variation, then resumed expanding his reef abstract on the Indian Ocean leg. Returning to London six months later, he told and wrote not of species variation but of coral reef variation. It was only the following summer that Darwin, who always started a new, subject-specific notebook when he began thinking in earnest on some problem, dedicated his first notebook to “transmutation of species.” That was in July 1837, a few weeks after he successfully presented his coral reef paper to the Geological Society and began drafting its full explication in The Structure and Distribution of Coral Reefs. The one theory seemed almost to spring from the other.

The coral reef theory’s subsequent success doubtless helped sustain Darwin during the two decades that he agonized over his trans mutation theory. But as he surely recognized (and probably would have liked to forget), another early theory of his also shared the reef theory’s conceptual hallmarks: Glen Roy. His botched explanation of that valley’s parallel roads, published two years after his initial coral reef presentation, also sought to solve a geologic mystery by proposing a series of changes over long periods. It too sprang from a vision of rising and falling landmasses. Yet in the decade after he published it, his Glen Roy theory fell to Louis Agassiz and became Darwin’s most painful humiliation. (“Eheu! Eheu!”) If the success of his reef theory buoyed him in his evolution work, the Glen Roy debacle served as a sober warning. Indeed, that reversal gave him ample reason to doubt his coral reef theory. He had erred at Glen Roy both by overlooking contradictory evidence (the streams that he missed but Agassiz found) and by downplaying the lack of direct confirming evidence, such as the missing marine fossils, as a type of evidence that was simply unlikely to be found. In his coral reef theory he chose to overlook the common signs of elevation and dismiss the absence of direct evidence of subsidence. Might these errors prove as fatal as those he made at Glen Roy? Darwin seemed to set aside such questions as the decades passed. But they were right there for anyone else to pick up.

*As Aristotle put it, “A deduction is speech … in which, certain things having been sup posed, something different from those supposed results of necessity because of their being so.” Aristotle’s Prior Analytics 1.2, 24-bi8-20.