The Reluctant Mr. Darwin

by David Quammen

  From the ashes of Wallace’s misfortune on the Helen arose one squawking phoenix of good news: His agent, the reliable Samuel Stevens, had insured those collections for £200. Maybe Stevens was prescient, or had once been a sailor himself, or had recently seen The Merchant of Venice. Anyway, that money accounts for how Alfred Wallace could now live as a man-about-London for more than a year, taking a role in the city’s scientific societies, writing papers and books, rather than being forced back to surveying rail lines across the Welsh countryside.

  Wallace attended meetings of the Entomological Society, including one just after his landfall, when he could barely walk. He went not as a member (there was still class bias against commercial collectors), but as a visitor sponsored by Stevens, who was an officer of the bug-lovers’ club. Stevens had already made him famous to this group by excerpting his letters for publication and showing his shipped specimens, as John Henslow had done for Darwin fifteen years earlier. Darwin himself was a member of the Entomological Society but, hidden away at Downe, rarely attended its meetings. Those who did attend had seen Wallace’s black-and-yellow swallow-tail butterfly, Papilio columbus, and they may have read his report on the umbrella bird, as published in the Annals and Magazine of Natural History. Stevens also got him entree to the Zoological Society, where on December 14, 1852, he delivered a paper, “On the Monkeys of the Amazon.”

  This paper contained Wallace’s first real statement on biogeography. Having sighted twenty-one different species of monkey along the Amazon and Rio Negro, he had noticed something remarkable. The species on one side of each big stem of river differed from the species on the other side. What he termed “closely allied species,” such as two species of marmoset belonging to the same genus, were in some cases localized on opposite banks. The rivers themselves—the mainstem Amazon and its largest branches, the Negro and the Madeira, which form a vast chicken-foot pattern across the entire basin—seemed to constitute nearly impassable boundaries of distribution. North of the Amazon and east of the Negro lay one biogeographical district, which Wallace labeled the Guiana. Westward of the Negro lay the Ecuador district. South of the Amazon, the Rio Madeira delineated two more districts, called by Wallace the Peru and the Brazil. So far as monkeys were concerned, those four major districts of Amazonia, divided by wide stretches of moving water, might as well have been islands.

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  Islands: Maybe they could tell him something more. Biogeography: Maybe he should pay keener attention. Closely allied species: What did the patterns of their geographical distribution suggest? Wallace planned his next field journey with these considerations in mind. He worked his contacts at the various scientific societies, including the Royal Geographical, to get more letters of introduction and free passage on an outbound boat. After just a year and a half back in England, during which he published two unspectacular books (a small volume on palm trees and A Narrative of Travels on the Amazon and Rio Negro, which suffered lack of concrete detail because of the lost journals), he was set to go. This time, east. Early in 1854 he left on a Peninsular & Oriental steamship, making connections that put him in Singapore by late April.

  Singapore, a bustling international port with just a small patch of forest nearby, only suited him briefly. It was sited on an island, which might have been good, but this island wasn’t a remote and unexplored refuge harboring an abundance of wondrous, unknown species. It was a cosmopolitan crossroads. Also, Chinese woodcutters were whacking away at what forest remained, harvesting timber and planting vegetable gardens on the raw land. Using the woodcutters’ trails, Wallace found plenty of nifty insects, especially among the beetles, but few birds or mammals. He tried basing himself at Malacca, a town farther north, on the Malay Peninsula, but after two months and another spell of fever he wanted to move again. He considered going up to Cambodia with a missionary he’d met, a congenial French Jesuit who spoke four languages. When the Jesuit delayed, Wallace turned instead to the great, beckoning constellation of small and large islands that stretched eastward for almost two thousand miles between Singapore and New Guinea. This region, corresponding roughly to what nowadays is Indonesia, was known then as the Malay Archipelago.

  The biggest of the islands was Borneo, directly east, with Java just south of it; beyond those two lay Bali, Lombok, Celebes, Ambon, Flores, Timor, Komodo, Ceram, and thousands of others, including a little cluster at the eastern extreme, Aru, famous for its bird-of-paradise populations. Wallace had started learning the Malay language, which made remote travel throughout the archipelago more feasible. He was aware, from Darwin’s Journal among other sources, that islands could be extraordinarily rich in endemic species. If they were rich in species, and bounded every which way by saltwater barriers to dispersal, they would also exhibit striking biogeographical patterns—that is, a richness of suggestive information. Wallace caught a boat to Borneo, where he could expect to be welcomed—thanks to a chance encounter—at the highest official level.

  Along the north coast of Borneo stretched a strange private kingdom known as Sarawak, ruled by a buccaneering Englishman named James Brooke, the so-called White Rajah. Brooke had crossed paths with Wallace back in England, evidently liked him, and offered him hospitality if he ever got to Sarawak. Wallace turned up and, with Brooke’s blessing, settled himself in a small house near the mouth of the Sarawak River. Brooke’s own compound was farther upstream, so Wallace was alone again, except for a Malay cook. By this time it was early 1855, well into the wet season, with daily rains that made collecting bad or impossible. When monsoonal downpours wash a tropical forest, the butterflies and the birds hunker invisibly, the beetles crawl somewhere snug, and a person can barely see, let alone walk a trail, wave a net, or place a delicate creature into a dry jar. Wallace sat in his house, thwarted from doing fieldwork, and took the occasion to write another paper. This one was more ambitious than his account of Amazon monkeys, let alone any of the descriptive little reports he’d published on insects and fishes. He titled it “On the Law Which Has Regulated the Introduction of New Species.”

  He was groping toward a theory of transmutation. But he wasn’t quite clear in his own mind as to how far his thinking had gotten him. There’s evidence that he had already begun making notes for a book on the subject, which he planned to call On the Organic Law of Change. The book project was premature, and Wallace seems to have realized that much, or at least intuited it, confining himself for the meantime to producing this brief paper, which he would later refer to as “only the announcement of the theory.” In truth, it wasn’t even an announcement, because he didn’t yet have a theory to announce. More accurately, the Sarawak paper was a hint about the existence of a phenomenon, transmutation, for which an explanatory theory would be necessary. The theory itself still eluded him. Unlike Darwin, Wallace was eager to put his exciting ideas into print, even if they were still amorphous.

  Compounding the confusion, he chose some blurry terminology, which would eventually cause certain readers (including Darwin) to mistake his meaning. In the paper’s title, for starters, his reference to the “introduction” of new species was deceptively bland and ambiguous. It seemed to imply a divine introducer. He also wrote about the “creation” of new species as modifications of earlier types. He used the term “antitype” for those precursors, suggesting a contrast or opposition (anti-), though what he probably meant was merely ante- type, a type that preceded. The “law” he had formulated was really just a generalized descriptive statement. It specified no mechanism of cause and effect.

  Wallace nevertheless made big claims for this law. The puzzling patterns of biogeography, as well as the record of extinct species in geological strata, “are all explained and illustrated by it,” he bragged. Casting light on biogeography was a valuable service, he noted, because so many odd facts had piled up since the time of Linnaeus, and no one had rationally accounted for them. For instance: “Such phenomena as are exhibited by the Galapagos Islands, which contain little groups of plants
and animals peculiar to themselves, but most nearly allied to those of South America, have not hitherto received any, even a conjectural explanation.” That was a gentle poke at Darwin, the most famous of Galápagos travelers, whose Journal had offered observations but no theory. Unaware that Darwin had held anything back, oblivious that Darwin’s explanation was in progress but long overdue, Wallace couldn’t have guessed that he was jabbing such a sensitive spot.

  Wallace’s law also solved—according to Wallace, anyway—the problem of systematic classification, by supplying a natural basis for grouping species into categories. It integrated Charles Lyell’s vision of gradual geological changes into an understanding of trends in the fossil record. And it made sense of rudimentary organs. In politely phrased sentences, the young man was crowing loudly, an upstart naturalist on the far side of the world presuming to deliver a major revelation on the history of life to his better-educated, better-connected elders. He stated his law twice, once near the paper’s start, again near the end, both times in italics so it couldn’t be missed: “Every species has come into existence coincident both in space and time with a pre-existing closely allied species.”

  What exactly did he mean by “come into existence”? What was implied by that coy word “coincident”? Should a “closely allied species” be understood as a genealogically related species? Wallace didn’t say. When species do come into existence, is it by materialistic transmutation or divine creation? The answer to that question, clear in Wallace’s head, was less clear on the page. If he did mean transmutation, what’s the mechanism? He didn’t yet know.

  Never mind. It was a start. He mailed the new manuscript to Samuel Stevens, who would pass it along to an editor at the Annals and Magazine of Natural History, the same journal that had been hospitable to his Amazon field reports. Then he went back to other work. On a good day Wallace could collect, and in the evening there would be beetles and butterflies to pin. On a bad day he could read and think. In northern Borneo, the rain was still coming down.

  22

  Wallace knew Mr. Darwin, at this point, only from a distance. If they had met at all, it was passingly, at the British Museum, in the months before Wallace sailed for Singapore, an encounter that hadn’t seemed important to either of them. So far as Darwin was concerned, Wallace was just another callow young traveler and commercial collector; his Narrative of Travels was too weak on factual detail to impress serious naturalists in Darwin’s circle. So far as Wallace was concerned, Darwin was merely the author of that fine Beagle journal, a robust but conventional book of natural history and exploration. He had no reason to suspect that Darwin was a transmutationist, like himself, and he wasn’t interested in barnacle taxonomy. Having made his own four-year expedition into remote areas of tropical wilderness, under circumstances more difficult than anything Darwin had endured, he may have lost his sense of awe toward the man he had once put in a class with Alexander von Humboldt. Nothing came of the encounter…for a while.

  Darwin’s seemingly endless work on barnacles finally did end, in early autumn of 1854, about the time Wallace decided to leave Singapore for Borneo. Darwin noted in his diary, with a groan of frustration, that the project had cost him nearly eight years. The last of his four Cirripedia volumes wouldn’t be published until weeks later, but on September 9 he finished packing up his specimens. He’d had enough of the squinty dissecting, the laborious sketching, the microscopic penises and fluttery legs. He was eager to move on. That very day, according to another diary note, he “began sorting notes for Species Theory.”

  It was back at the center of his desk. He’d had sixteen years to think about the transmutation of species, to refine his idea of natural selection, to mine the biological literature for relevant facts, to ponder his own data on variation and adaptation in the wild, to hone the arguments he had outlined in 1842 and drafted in 1844. Meantime he had also fathered nine children, buried two of them, and sent his oldest son off to boarding school. He had published eight books (not counting the edited volumes of Beagle zoology), seven of them technical and one a popular travel narrative. He had made himself an expert on the classification of a difficult group of animals, and his expertise had been certified by a major award. No one had a right, he had once worried, “to examine the question of species who hasn’t minutely described many,” and now he had earned that right. So was it time to publish his theory? No, not yet. He still wasn’t ready.

  Instead he launched a further program of empirical research to fill some of the gaps in his trove of evidence. He became an experimentalist, cluttering his house and grounds with simple but astute science projects that often smelled bad but supplied useful data. He worked his network of far-flung contacts for answers to obscure questions. He started keeping pigeons. Throughout the next two years he concerned himself largely with the anatomy and development of domestic animals, plant hybridization, plant fertilization, patterns of species diversity reflected in plant classification, and the capacity of plants for transoceanic travel.

  How long, Darwin wondered, can a cabbage seed be soaked in salt water and still germinate? How long for a radish seed? A carrot seed? A kidney bean? A pea? He was curious about what he called “accidental means” of plant species dispersal, which might entail a seed, a pod, or a seed-bearing stem floating passively across a wide stretch of sea. So he tested the salt-resistant viability of a whole list of vegetables and other plants: rhubarb, asparagus, celery, cress, capsicum, furze, barley, and more. He mixed up a salt solution resembling sea water, poured it into bottles, dropped in seeds as though they had fallen on the ocean, and left them to ride the brine, or to sink and marinate, for measured stretches of days. From this set of experiments he learned several things. He learned that asparagus could float for twenty-three days if it were green and succulent, or as much as eighty-five days if dried first, and that the seeds would remain viable. He learned that cabbage and radish seeds became putrid and stinky “in a quite extraordinary degree,” but that the radishes would still germinate after forty-two days of soaking, while the cabbages wouldn’t. He found that cress seeds put out “a wonderful quantity of mucus,” but that they too would sprout after forty-two days’ immersion. Given the average rate of ocean currents, Darwin calculated, forty-two days was long enough for a floating seed or a pod to travel 1,300 miles. Most of the other species he tested were able to produce at least some germinations after twenty-eight days. The conclusion that Darwin drew from these experiments involved biogeography: Plants were certainly capable of crossing oceans. It didn’t take an ancient land bridge that had sunk beneath the sea (as some of his colleagues imagined), and it didn’t take an act of God, to explain how vegetation might appear on a new volcanic island.

  Floating seeds weren’t the only means for a plant to colonize across water. There were winged seeds, and tiny seeds with parachute rigging like those of a dandelion, which could travel on the wind. Another possibility was transport by a bird—a living bird, or even a dead one. Seeds might stick to the muddy legs of a heron or an egret and be rinsed off in a new location. His young son Francis, now eight years old, made a boy’s gory-minded suggestion about dead birds—such as those that fall victim to a hawk, or to lightning, or maybe to apoplexy—and Darwin pounced on it. He floated a dead pigeon in salt water for thirty days. Seeds from the pigeon’s crop germinated nicely.

  Another bird-related experiment went to the question whether small animals, such as snails, might hitchhike from one place to another. Darwin cut off a pair of duck’s feet and suspended them in an aquarium full of freshwater snails. If a duck was asleep on the water’s surface, dangle-footed and oblivious, how many snails might climb aboard? Would they cling tightly when the duck flew away? Darwin waved his duck feet through the air. How long would the snails stay alive out of water? He let the snails languish overnight. His results suggested that freshwater snails could catch and survive a ride of six hundred miles.

  He wondered too about lizard eggs. Would they float on se
awater? For how long? Having floated for a month or so, would they still hatch? He offered to pay schoolboys a shilling for every half-dozen lizard eggs they could find; snake eggs welcome, too. He’d float them in his cellar. It was all relevant, just as the seed-brining experiments were relevant, because transmutation implied the necessity of natural dispersal. If there was no special creation, there was no special delivery. Biogeography, from a transmutationist perspective, reflected the fact that species had arisen one from another, adapted, and traveled. Darwin needed to prove, among other things, how well plants and animals could get around.

  He also wanted measurements of different varieties of domestic animal, especially fetuses and juveniles, in order to see how their differentiation in form during growth and development might echo evolutionary divergence from common ancestors. He asked friends to keep his morbid interests in mind when any of their pets or livestock died. In one letter, to W. D. Fox, he begged for a week-old chicken and a nestling pigeon, from which he meant to make skeletons. He mentioned passingly to Fox that he’d already begun comparing wild and tame ducks. When he got live birds, he killed them with chloroform or ether, boiled the carcasses to soften them, and then stripped off the flesh, a smelly process that often made him vomit—and not just him, with his delicate stomach, but also Parlsow, the all-purpose butler. So he outsourced that phase of the work. About mammals, he reported cheerily: “I have puppies of Bull-dogs & Greyhound in salt.” And he had commissioned someone to make careful measurements of young colts, both racehorses and cart horses. Whenever possible he wanted data from standard-aged juvenile forms, so that comparisons were valid; for birds, he tried to get them seven days after hatching. But juveniles of some species and some breeds weren’t always easy to find. Did anyone know, he asked, how to lay hands on a seven-day-old wild duck?