Darwin’s youthful “experiments” on the Beagle voyage may have been larks done quickly in some cases, but they also reveal a questioning mind eager to investigate, experience, and learn. The iguana-tossing Darwin is also the Darwin filling notebook after notebook with his finds, thoughts, and observations, alert to anything interesting or unusual. Constantly tossing out his plankton net (easier than capturing iguanas), for example, and marveling over the bounty of his catch, imagine his surprise to one day haul in a bevy of beetles far out at sea. No big deal, one might think, but what were those beetles doing in the open ocean? Later he would come to see this and similar innocuous observations as bearing profoundly on an understanding of geographical distribution (which we take up in Chapter 5). Or again, near Rio de Janeiro Darwin collected a fungus similar to one he knew at home. Musing on how the European species is attractive to beetles, as if on cue a beetle flew in and landed on the fungus in his hand. As with those Australian ant lions, “We here see in two distant countries a similar relation between plants and insects of the same families, though the species of both are different.”40 What did it mean?
Through it all there is Darwin’s sense of wonder—as when he beheld the “aërial voyages of spiders,” when myriad minute spiderlings swarming over the ship’s rigging spun gossamer silk strands to be borne away on the breeze. Or the astonishing evening of “snowing butterflies” off the coast of northern Patagonia, when “vast numbers” of the insects “in bands or flocks of countless myriads, extended as far as the eye could range.” Or the “splendid scene of natural fireworks” witnessed in the south Atlantic, with St. Elmo’s fire on the mast and yard-arms and the sea “so highly luminous, that the tracks of the penguins were marked by a fiery wake.”41 The words “beautiful” and “beauty” appear no less than 105 times in Darwin’s Journal of Researches, and “delight” and “delightful” some 37. And although “sublime” appears just six times, each is expressive of rapturous Humboldtian moments. How inexpressibly gratifying, then, that when Darwin sent with humility (and perhaps some modicum of trepidation) a copy of his newly published Journal of Researches to Humboldt himself with the author’s compliments, he received warm praise and thanks from the great man—along with far-ranging questions and comments on subjects from glacial phenomena to volcanism and climate to sea currents. An elated Darwin replied with enthusiasm, including data on the temperature of the sea in different locations and closing with an expression of his admiration: “That the author of those passages in the Personal Narrative, which I have read over and over again, & have copied out, that they might ever be present in my mind, should have so honoured me, is a gratification of a kind, which can but seldom happen to anyone.”42
A House Burnt by Fire
Darwin returned from the Beagle voyage in October 1836 to find himself something of a celebrity, thanks to Henslow and others giving regular updates to the learned societies on his discoveries and impressive efforts in collecting and observing. Darwin had come a long way by the fall of 1836. His physical journey around the world may have concluded, but his intellectual journey was about to get even more interesting. A month after his return he was elected to the Geological Society of London, and a month after that he rented a small house on Fitzwilliam Street, in Cambridge, to sort out his prodigious collections and equally prodigious plans. He sought out experts to analyze and describe his specimens, and it didn’t take long before papers on his remarkable discoveries were heard. Richard Owen, a few years older than Darwin and a fast-rising star of comparative anatomy, soon began analysis of Darwin’s fossil mammals from South America, declaring before packed meetings of the Geological Society that Darwin had found remarkable new species, gigantic forms of groups even now found on that continent. These fossils supported the Law of Succession, the fundamental link between extinct groups and related ones currently living in an area—findings deemed so important that Lyell, then president of the Society, dedicated his annual presidential address to discussing them in February 1837. (At the same meeting Lyell tapped Darwin for the Society’s Council, another indication of the high regard he was held in.) The ornithologist John Gould was almost as speedy as Owen: in January 1837 he read not one but two papers at the Zoological Society regarding Darwin’s curious South American birds, including one on the enigmatic finches of the Galápagos Islands. In February he followed with another paper on the Galápagos mockingbirds. Meeting with Gould in March—the month he moved from Cambridge to take up residence not far from Lyell in London—Darwin was astonished to learn that in fact nearly all of the Galápagos bird species he collected were unique to those islands, yet bore a close relationship to South American species.
That was just the beginning: 1837 was a watershed year for Darwin. It opened with his first scientific paper on January 4th (“Observations of proofs of recent elevation on the coast of Chili”), and by the year’s end he had read two more papers that were well received, written the third volume of the official multiauthored narrative of the Beagle voyage (produced in a frenzy of writing between January and September 1837; the resulting Journal and Remarks was soon reissued as the stand-alone Journal of Researches), and received a £1,000 grant from the Admiralty to serve as editor for a multivolume treatment of the zoology of the voyage. Little did he know what he was getting himself into with that last project: the volumes duly came out between 1838 and 1843, during which time he experienced all the headaches editors do today: missed deadlines, less-than-careful authors, endless corrections, and illustrators working on their own time. First he lined up the authors: his fish would be treated by Leonard Jenyns, Richard Owen had his fossil mammals, Thomas Bell the reptile and amphibian collection, John Gould agreed to cover the birds, and George Waterhouse took on the living mammals. The insects were too large and diverse a group for any one specialist, so they got farmed out to various entomologists for separate publication, and although kindly Henslow meant well in agreeing to take on the plants, in the end he was much too busy.
Darwin wanted to work up the marine invertebrates himself—another indication of the special status these organisms held in his thinking—but he soon gave up that idea and they never were treated in a dedicated volume. In the meantime he was consumed with writing introductions to the various volumes, adding notes and observations, and supervising the engravings and printing. But as important as those volumes were, they became a backdrop to other, more exciting developments. For the watershed moment in that watershed year came in March, when the insights of Owen (regarding his South American fossils and geological succession) and Gould (regarding his South American and Galápagos birds and their essential geographical relationships) suddenly dovetailed and crystallized for Darwin the heretical idea that species change over time would at once elegantly explain these seemingly unrelated observations, and more.
Darwin’s subsequent work then proceeded along two avenues: geologist and closet transmutationist. Darwin the geologist read paper after paper at the Geological Society, in good Lyellian fashion reporting on areas of elevation and subsidence in the Pacific and Indian Oceans deduced from coral formations, volcanic phenomena associated with earthquakes and a model of mountain chains and volcanoes as effects of continental uplift, and even on the “geological force” exerted by humble earthworms—a subject he was to return to in his very last book some 40 years later (see Chapter 10). He expanded some of his papers into full volumes: coral reefs in 1842, volcanic islands in 1844, and a sweeping geology of South America in 1846. These books were testaments to his industry in those heady years; magnanimous Lyell was delighted that Darwin’s new theory of coral atolls, which suggested an evolution of coral formations from fringing reef to atoll as volcanic islands eroded to sea level, upended his own undersea crater-rim theory.43 Lyell’s Principles of Geology had its controversial aspects, but its overarching theme—explaining “the former changes of the earth’s surface by reference to causes now in operation”—was taking the geological world by storm, and Darwin was
now Lyell’s chief apostle. In 1837 the Principles was already in its fifth edition, just 7 years after the first volume appeared, and Darwin was still as excited by Lyell’s vision as he was when he read that first newly published volume given to him by Fitzroy at the start of the Beagle voyage. By this time the two had become close friends, but Darwin also saw Lyell as a mentor. A comment he made a few years later to Leonard Horner, Lyell’s father-in-law, sums up Lyell’s effect on him nicely: “I always feel as if my books came half out of Lyell’s brains . . . for I have always thought that the great merit of the Principles, was that it altered the whole tone of one’s mind & therefore that when seeing a thing never seen by Lyell, one yet saw it partially through his eyes.”44
Darwin supported Lyell’s view of a dynamic earth characterized by slow and steady uplift and subsidence, a seesaw oscillation of different parts of the crust at different times. It was assumed that continents could not move laterally, but by virtue of the forces below, the comparatively thin and flexible crust could be elevated or depressed as pressure increased or decreased. Volcanism and earthquakes can seem locally catastrophic, but in the grand scheme of things these resulted in incremental changes to the landscape. Over the millennia small changes add up to great ones, Lyell maintained, and so landforms inexorably evolve. Darwin concurred, and when he read papers about Lyellian uplift, volcanism, and earthquakes he spoke with the voice of experience—no armchair naturalist, he had seen Lyell’s theories confirmed for himself, as when he found clear evidence of not only past uplift on the west coast of South America (in the form of high-and-dry marine deposits—strata bearing shells and coral meters above the present level of the sea), but also present uplift. He was at Valdivia, Chile, when an earthquake struck miles away near Concepción in February 1835: “I happened to be on shore, and was lying down in the wood to rest myself. It came on suddenly, and lasted two minutes; but the time appeared much longer. The rocking of the ground was most sensible. . . . There was no difficulty in standing upright, but the motion made me almost giddy.” “A bad earthquake at once destroys the oldest associations,” Darwin mused: “the world, the very emblem of all that is solid, has moved beneath our feet like a crust over a fluid—one second of time has conveyed to the mind a strange idea of insecurity, which hours of reflection would never have created.”45
Nearly 2 weeks later when the Beagle reached Concepción the crew witnessed the terrible devastation. Darwin gathered as much information as he could about the earthquake and ensuing tsunami: “I feel it is quite impossible to convey the mingled feelings with which one beholds such a spectacle,” he wrote. “Several of the officers visited it before me, but their strongest language failed to communicate a just idea of the desolation. It is a bitter and humiliating thing to see works, which have cost men so much time and labour, overthrown in one minute.”46 He noticed, too, the geological aftermath:
The most remarkable effect (or perhaps speaking more correctly, cause) of this earthquake was the permanent elevation of the land. Captain FitzRoy having twice visited the island of Santa Maria, for the purpose of examining every circumstance with extreme accuracy, has brought a mass of evidence in proof of such elevation, far more conclusive than that on which geologists on most other occasions place implicit faith.47
It was clear to Darwin that “the principles laid down by Mr. Lyell” are correct, and we may “fearlessly maintain that the problem of the raised shells . . . is explained.” Periodic earthquakes and their associated uplift would slowly but surely keep raising the newly exposed marine detritus higher and higher, ultimately to become another stratum high in the hills of the Andes but always bearing the unmistakable evidence of its origin beneath the sea. Lyell’s views as laid out in the Principles were as ascendant as these geological formations, and Darwin’s astute Beagle observations made him the first among a new breed of Lyellian geologists.
But, if seeing the world through Lyell’s eyes had its triumphs for Darwin, it’s important to point out that it also had its failures—failures perhaps understandable in the context of the science of the time, and in any case instructive in teaching us something about science as a process, about the difficulty sometimes in seeing things in a light altogether different from what we expect. The old joke about looking for missing keys under a streetlight not because they were lost there but because the light is better contains a truth about science as a human endeavor: we often look for things where we are comfortable looking. Or, put another way, the questions we ask are often shaped by the framework we are used to working in. In important respects Darwin’s ultimate triumph lay in seeing the organic world with new eyes—he became biology’s Lyell, and certainly pursued an idea of nature—including, shockingly, of humans—outside of his society’s comfort zone. But at times he was also guilty of being wed to preconceived ideas, leaping to expected and comfortable conclusions.
Lyell (and Darwin) thought that crustal uplift and subsidence occurred in a balanced way over the earth’s surface, so that elevation in one region was more or less compensated by subsidence in another. Evidence of past uplift went hand in hand with evidence of subsidence, as testified by the thick limestone and sandstone formations often found far inland (think marine fossils in Kansas), indicative of a previous encroachment by the ocean. Flush with the success of his interpretation of South American uplift he decided to try his hand at solving a geological mystery closer to home: the origin of the so-called “parallel roads” of Glen Roy, Scotland. The expansive and green Valley (Glen) Roy, near Lochaber in the west Scottish Highlands, is ringed by three closely spaced parallel white terraces running along the hillsides. Straight as can be, from a distance they look very much like man-made roads, hence the name. The “parallel roads” had puzzled leading geologists of the day, but Darwin saw them as analogous to those strata of marine fossils he had seen high in the Andes. The young Turk made an imaginative leap. In late June 1838, just a few months after his paper on volcanic phenomena, he traveled to Glen Roy and spent 8 days making careful observations. He worked up his analysis in a long paper he read the following February. The “parallel roads,” he declared, were clearly marine in origin. He was sure that the terraces represented ancient marine beaches, formed during a period of subsidence of the land when the sea flooded the wide valley. As the land was raised in fits and starts, he imagined, different “roads” would have been cut at slightly different elevations, the lapping waves leaving their mark on the hillsides as indelibly as a bathtub ring marks the former level of the bathwater. “The whole country has been slowly elevated,” he wrote, “the movements having been interrupted by as many periods of rest as there are shelves.”
A drawing by Darwin’s college friend Albert Way illustrating the “parallel roads” on the hills of Glen Roy, Scotland. From Darwin (1839b), plate II.
Darwin’s theory was elaborate, involving arguments about the fluidity of the earth’s crust, the structure of its interior, and the action of powerful elevational forces. Along the way he considered and dispensed with rival theories positing that the parallel roads were lake, not marine, shorelines. He all but scoffed at this suggestion, arguing that there was no sign whatsoever of the remains of a barrier large enough to dam such an expansive area. A miles-long wall of rock nearly a half-mile high would have been necessary; vestiges should remain as with any blown-out man-made dam. What’s more, his ancillary theory of iceberg transport of boulders reinforced the marine incursion theory. Again following Lyell’s lead Darwin sought to explain so-called erratic boulders—large boulders situated far from the parent material yielding that rock type—as having been dumped by melting rock-strewn icebergs that had floated south from arctic seas. The very year Darwin read his Glen Roy paper he also read a paper to the Geological Society entitled “Note on a rock seen on an iceberg in 61º south latitude”—an observation made on the Beagle voyage and now cited as further support for the idea of an ancient marine incursion. Otherwise, how else could erratics have gotten so far inland?
Darwin's Backyard Page 4