Read an Excerpt
CHAPTER 1
Darwin's Opportunity
Nineteenth-century readers were introduced to the idea of a fanciful "amphibious being" by the barrister-turned-geologist Charles Lyell in his Principles of Geology (vol. 1, 1830). He subtitled his treatise An Attempt to Explain the Former Changes of the Earth's Surface by Reference to Causes Now in Operation and intended the book as a methodological object lesson. Lyell wanted to demonstrate that it was possible to provide a convincing historical explanation for the current state of the globe without referring to physical processes of any type or intensity other than those demonstrably acting in the present. The book is remembered as one of the most important in the history of geology primarily for convincing some readers, notably Charles Darwin, that if the history of the earth was long enough, then the types of organic and inorganic processes at work in the modern world, operating at their observed intensities, could eventually produce monumental changes in the earth's landscape and its inhabitants. In Lyell's view there was no necessary direction to these changes. It was clear that some spots on the surface of the globe that had once been dry land had become sea, and that some of those had again become land.
Lyell evoked this cyclical movement of the earth's crust with his volume's striking frontispiece, an engraving of three ancient columns in Pozzuoli, Italy, that had belonged to a building known as the Temple of Serapis (see fig. 3). Though the columns stood upright, each one had been pockmarked in the section now between twelve and twenty-four feet above ground by Lithodomus, a mollusk that still inhabited the nearby Bay of Naples. By 1830 the question of how these columns could have been submerged to a depth of twenty-four feet, subjected to the ravages of stone-eating mussels, then exposed to the air again was already a well-known geological puzzle. Whereas many observers believed that a change in sea level, whether local or global, was the only explanation compatible with the fact that the columns had not been toppled, Lyell drew on analogies with the observed effects of certain recent earthquakes to contend that the level of the land could have oscillated without necessarily disturbing the pillars.
In support of his methodological precept of reasoning from observed causes, Lyell dedicated the bulk of the Principles, which eventually comprised three volumes, to a catalog of physical and organic forces now operating on the globe. This required acknowledging the limitations of human perception, and it led to the passage that seems so noteworthy in retrospect. Lyell explained that as natives of the earth's surface, our inability to dwell underground or in the water had constrained the progress of geology.
"Although the reader may, perhaps, smile at the bare suggestion," he continued, a geologist who could dwell beneath the sea would gain a better understanding of the processes that were shaping, and had shaped, the physical world. This "amphibious being" would, Lyell declared,
more easily arrive at sound theoretical opinions in geology, since he might behold, on the one hand, the decomposition of rocks in the atmosphere, and the transportation of matter by running water; and, on the other, examine the deposition of sediment in the sea, and the imbedding of animal remains in new strata ... and might mark, on the one hand, the growth of a forest, and on the other that of the coral reef.
Over the next few chapters I will explain how a young man named Charles Darwin transformed himself into an amphibious being and, remarkably, fulfilled each element of Lyell's prophecy. Darwin's metamorphosis began just a few months into his voyage on HMS Beagle, when he recognized the scientific opportunity presented by his shipmates' everyday activity of maritime surveying, or hydrography. He gradually came to apply the tools and practices of hydrography to his zoological work and then to his geological work as well. He did so not by emulating Lyell, as might be imagined, but by drawing on practical experiences from his education in Edinburgh and Cambridge and by emulating the fact-gathering approaches of Alexander von Humboldt. It was only much later, when Darwin was back in London, that the full significance of these approaches for Lyell's geological views would be amplified by the personal interactions between Lyell and Darwin.
One of the pleasures of encountering the young Darwin through his notes and letters is witnessing the exuberance with which he studied the natural world during the Beagle voyage. His vigor was fueled by increasingly grand ambitions for what he might achieve in science when the voyage was finished. Over the years as the Beagle proceeded around South America from the Atlantic to the Pacific and eventually onward into the Indian Ocean, Darwin self-assuredly recorded a series of objectives for his future career: he aimed to rewrite the geological history of South America and the natural history of zoophytes and to advance a theory of coral reef formation he had developed at Tahiti. Several questions must be answered in order to comprehend the scope of Darwin's opportunity and his ambitions. Why was the Beagle passing through these oceans in the first place, and what was his role on board? How did he know these were promising topics on which to establish a scientific career? And what was the foundation for the confidence he developed in his own capacities as a geologist and marine zoologist?
In this chapter I examine three major contexts for Darwin's eventual ambitions. The first was the history of previous efforts to explain the origin and shape of reefs. To understand a theory in historical terms, we must uncover the questions to which it offered an answer. In order to grasp the particular features of reefs Darwin would feel most compelled to explain, I trace inquiries during the previous two generations of European imperial activity in the Pacific, culminating in the twin puzzles of reefs' annular shape and their apparent need for a shallow foundation to build on. This lively and ongoing European discourse about reef formation had a significant impact on the stated objectives of the Beagle voyage itself when it was commissioned by the British Admiralty in 1831. Indeed, one of the Admiralty's directions to Robert FitzRoy was to investigate the origin of coral reefs. The larger maritime and imperial purposes intended for the voyage are thus the second context I examine here. The story of how Darwin came to be aboard the Beagle has been told many times; I pay special attention to a little-noticed but elaborate discussion between Darwin, FitzRoy, and the Admiralty before the voyage over whether they would be directed to the "South Sea islands." Finally, I examine the intellectual and practical knowledge Darwin brought to the voyage. Here I call attention to his previous experience alongside experts in the sciences of marine zoology and terrestrial geology and to his early exposure to the work of Alexander von Humboldt. These three factors shaped his interpretation of (and original attention to) several of the key phenomena that proved relevant to the theories he eventually developed.
Coral Reefs as Objects of Fascination and Terror
The theory of reef formation that Darwin developed during and after the Beagle voyage offered an elegant new answer to a vexing and surprisingly widely asked question. Given that corals can live only in shallow water, how do they build reefs in the deepest parts of the ocean? The mystery was intensified by mid-ocean reefs' strange and distinctive shapes. They were narrow, and curved to form rings surrounding placid lagoons of shallow water. By the time Darwin first witnessed one in 1835, Europeans had been trying to explain the origin of such reefs for more than sixty years, dating back to the late-eighteenth-century wave of Pacific exploration that made household names of Cook and Bougainville, of William Bligh and Fletcher Christian.
The issue of coral reef formation became particularly compelling for several kinds of Europeans between about 1770 and 1830. There were those navigators and naval administrators for whom the threat reefs posed to intertropical navigation was a matter of serious practical concern. They were joined by natural philosophers who took a scientific interest in these structures because of the special position they appeared to hold in the so-called economy of nature. The idea (first proposed in the late eighteenth century) that reefs had been created by living organisms was a prominent topic of discussion among those who sought to catalog and explain the physical and organic causes of change in the natural world. Finally, writers and theologians who drew on the accounts of navigators and voyaging naturalists helped turn corals and reefs into powerful cultural symbols as they explored the contradiction between reefs' own vitality and the threat they posed to seafaring humans.
Among the marvels of the Pacific and Indian Oceans, none inspired a greater combination of fear and puzzlement in European navigators than those ring-shaped reefs we now call atolls. For the French circumnavigator Louis-Antoine de Bougainville, the vast expanse of these reefs east of Tahiti was a seascape of contradictions. He called the group l'Archipel Dangereux, not out of concern for the inhabitants of "[reef-top] strips of land that a hurricane could bury at any moment beneath the water," but because those inconspicuous shoals posed a terrific threat to any unsuspecting ship that might be skimming across the Pacific in low light or poor weather. Yet the reefs and their inhabitants seemed so vulnerable too. Bougainville, who would return home reporting that the permissive Tahitians had escaped the fall of man on their mountainous Eden, wondered of the "almost drowned" low islands nearby, "Is this extraordinary land being born, or is it in ruins?"
On 11 June 1770 a coral reef nearly claimed the man who was to become the most famous Pacific explorer before he had finished his first voyage to the South Sea. At a few minutes before 11:00 pm, as James Cook's ship Endeavour sailed northward off the eastern shore of the land he had dubbed New South Wales, the crewman who was taking soundings with a plumb line called out a depth of 17 fathoms, or 102 feet. "Before the Man at the [sounding] lead could heave another cast," Cook reported, "the Ship Struck and stuck fast ... upon the SE edge of a reef of Coral rocks." They had become the first Europeans to encounter the Great Barrier Reef, a labyrinth from which the Endeavour's crew needed two months to sail clear.
Cook and Bougainville returned from their Pacific voyages at the dawn of the 1770s with tales and charts of these tropical mysteries, fueling the imagination of philosophers and the terror of fellow navigators and the public. Corals sat atop submarine walls springing from depths that were often literally unfathomable with the lengths of rope carried by eighteenth-century explorers. Their submarine slope was always steepest on the windward side, as if the reefs had been specially designed to deprive mariners who rode the winds and currents of even the slightest warning of a shoaling sea.
The first person to propose that these terrifying structures had been created by the growth of corals was Johann Reinhold Forster, the naturalist who along with his son Georg zigzagged the Pacific on Cook's second voyage (1772–75). Forster created a taxonomy of tropical islands, distinguishing ring-shaped "low islands" from the high islands like Tahiti and others whose origin he attributed to the volcanic agency of "subterraneous fire." In explaining the origin of the low isles, Forster offered the then novel claim that corals built the entire structure of what we now call "coral" reefs. While Europeans had long been familiar with fossil corals in geological formations, and though there had been debates through the eighteenth century about whether coral organisms, which produced small stony forms in the Mediterranean and elsewhere, were plants or animals, nobody had previously suggested that they could build massive structures such as those in the Pacific and Indian Oceans. Forster proclaimed that the ringlike shape of low islands was entirely due to the "instinct" of the "animalcules forming these reefs." Corals grew upward and outward from a small base on the seafloor in order to "secure in their middle a calm and sheltered place" where the "impetuosity of the winds, and the power and rage of the ocean" could not encroach. The communal structure therefore emulated the radial shape of an individual polyp. The British navigator Matthew Flinders finished surveying the Australian coast in 1803 full of support for Forster's views, explaining in new detail how "future races of these animalcules erect their habitations upon the rising bank, and die in their turn, to ... elevate, this monument of their wonderful labours." Meanwhile, thanks to the specimens and illustrations produced on the 1800–1803 French expedition under Nicolas Baudin, Pacific corals also began to colonize the pages of taxonomic works being produced by land-bound naturalists such as the Frenchman J. V. F. Lamouroux.
Forster's explanation held tantalizing geological implications, for it suggested that corals were among the few agents with the capacity to remodel the surface of the globe on a large scale. Lamouroux pointed out that "reefs ... may eventually block communication between the temperate zones of the two hemispheres." As the sovereigns of Europe raced to master the Southern Ocean, these concerns stimulated navigators and their philosophically minded shipmates into a wider range of reef studies. Johann Friedrich Eschscholtz, a physician who sailed across the northern Pacific on Otto von Kotzebue's Russian-sponsored voyage (1815–18), challenged Forster with an argument based on the distribution of coral islands. They were entirely absent across tracts of tropical sea that, by Forster's theory, would have offered ideal conditions for reef-building corals. Just like high islands, they were usually found in "rows ... and large groups," suggesting they had a common underlying cause. Therefore, Eschscholtz argued, "the corals have founded their buildings on shoals in the sea; or to speak more correctly, on the tops of mountains lying under water." His views were widely noticed but, because they were published in an unsigned appendix to the "Remarks and Opinions of the Naturalist of the Expedition," they were widely attributed to the voyage's botanist, Adelbert von Chamisso.
By the time the Beagle voyage was being conceived, there was a new explanation for the formation of ring-shaped reefs that superseded the coral theories of Forster, Eschscholtz, and Chamisso. It was originally generated as something of an afterthought by the French naturalists Jean René Constant Quoy and Joseph Paul Gaimard, the naval surgeons on Louis-Claude de Freycinet's 1817–20 voyage of exploration. Quoy and Gaimard had a specific zoological argument—that stony corals could live only in shallow water—that had broader geological implications. Through close attention to the coral fragments brought up by anchors and sounding leads during the voyage, they determined that the robust reef-building species "do not begin to build at depths greater than twenty-five or thirty feet." Their larger argument was that that reefs could not therefore have been built up by corals from the deep seafloor, or even from deeply submerged mountains. The Frenchmen charged Forster with vastly exaggerating the geological significance of coral reefs, arguing that what he had believed were great coral formations were simply thin veneers of coral growing atop "the same minerals that form islands and all the known continents."
This led, in an inconspicuous footnote, to what would become an influential new explanation for ring-shaped reefs. "Couldn't this [circular] arrangement be due," Quoy and Gaimard reasoned, "to submarine craters, on whose rims the lithophytes have built?" Thus, whereas Eschscholtz and Forster had both believed that reefs' annular shape was due to some general property of coral growth, Quoy and Gaimard were suggesting that a ring-shaped reef was evidence of nothing more than the existence of a ring-shaped submarine mountaintop. The question, then, was whether such submarine volcanoes existed, with enormous craters up to thirty miles in diameter sitting within a few feet of sea level.
(Continues…)
Excerpted from "Darwin's Evolving Identity"
by .
Copyright © 2018 The University of Chicago.
Excerpted by permission of The University of Chicago Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
