The Reluctant Mr. Darwin

by David Quammen

  What color are the horses of Jamaica? he wrote to a bureaucrat who’d once owned an estate there. Can you help me with an identification of certain rock specimens? he wrote to a professor of mineralogy at Cambridge. Your ideas about classification are airy and confused, he told George Waterhouse, the Zoological Society curator who had agreed to work on his Beagle mammals, and who subscribed to a system of arranging similar species in neat circles, as though the deity had strung each genus into a closed loop like a pearl necklace. Darwin’s language to Waterhouse was cordial, but his position was firm. The problem with those circles, he explained, was that they meant nothing and went nowhere. Darwin’s own view, a controversial one he’d been keeping discreetly unspoken, was that “classification consists in grouping beings according to their actual relationship, ie their consanguinity, or descent from common stocks.” That is, the underlying principle is transmutation. Saying so to Waterhouse, who wasn’t among his closest friends, reflected Darwin’s impatience to share his secret with someone. And then, in late 1843, he exchanged his first letters with a bright botanist named Joseph Dalton Hooker, just returned from serving as assistant surgeon and naturalist aboard a British ship, the Erebus, on its expedition to Antarctica.

  Darwin had met Hooker passingly back in 1839, before the Erebus sailed, and knew something of this younger man from mutual friends. Hooker knew more about Darwin, having read his Journal, carried it on shipboard for four years, and idolized the scientific traveler who wrote it. Now they connected more personally—though only by mail—in regard to Darwin’s old plant specimens from the Beagle, which had never been properly studied. Despite the chores Hooker faced with his own haul of specimens, he agreed to do it. Darwin asked him to pay special attention to the Galápagos plants, which might bear comparison with the peculiar species of St. Helena, another remote island. That suggestion triggered an outpouring from Hooker about native plants he’d seen on various islands while the Erebus circled the southern oceans, stopping in New Zealand, Tasmania, the Falklands, Hermite Island off Tierra del Fuego, Auckland Island, Campbell Island, Kerguelen, South Shetland, Ascension, and St. Helena itself. Hermite Island, for instance, was rich in mosses. Ascension held eight species of fern, only two of which occurred also on St. Helena, the next island over. Tasmania and New Zealand were unusual in ways of their own. Hooker went on for several pages, his overall message clear: If it’s insular floras you want to talk about, sir, I can oblige you with enthusiasm and data.

  Darwin claimed to be ignorant of botany and waited for Hooker to see the Beagle stuff. Hooker wrote again soon, expressing particular fascination with Darwin’s Galápagos plants, clipped and pressed almost a decade earlier. From having read Darwin’s comments in the Journal, he’d been well prepared to see floral differences among the respective islands, and with the specimens in his hands, that expectation was confirmed. The island-by-island diversity was, in his words, “a most strange fact.” So strange, he volunteered, that it “quite overturns all our preconceived notions of species radiating from a centre.” He meant a center of special creation, presumably on a mainland somewhere. No, the Galápagos plants were flat-out puzzling. Their botanical geography didn’t jibe with the received wisdom of natural theology, and Hooker was willing to say so.

  Darwin perked to that signal. He barely knew Hooker, but suddenly he felt a dawning hope that he had encountered a kindred mind. Hooker was smart and well trained, a conscientious observer; he came from a respectable scientific family (his father was director of the Royal Botanic Gardens at Kew), and had seen as much of the world as Darwin. Yet he was young (only twenty-six) and open to the possibility of junking orthodox tenets if empirical data so dictated. Darwin virtually grabbed him by the lapels. Early in 1844 he wrote again, asking Hooker’s help with “one little fact” about endemic island plants. Then he ended his letter with an impetuous blurt of candor.

  This is a famous moment. It appears in all nine of the Darwin biographies now piled on my desk, plus countless other studies, and it can’t be omitted merely on grounds that the hands of previous writers and scholars have worn it smooth. The letter was undated, but the postmark said January 11, 1844. Darwin confided to Hooker that, besides his interest in southern lands, “I have been now ever since my return engaged in a very presumptuous work,” a work that most people would call downright foolish. He’d been pondering the odd patterns of plant and animal distribution that he had seen in the Galápagos and elsewhere; he’d been reading up on domestic breeding; he’d been collecting every bit of data that seemed relevant to the question of whether species are changeless entities. “At last gleams of light have come,” Darwin wrote, “& I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable.”

  This was a daring admission, cast in sheepish understatement, and contradicting one of the fundamental tenets of British natural theology. Truth be told, he was more than “almost” convinced.

  Less famous is the disclaimer he added immediately: “Heaven forfend me from Lamarck nonsense of a ‘tendency to progression’ ‘adaptations from the slow willing of animals’ &c.” He was trying to distance himself from the discredited ideas of one particular precursor, Jean-Baptiste Lamarck. Darwin knew well that his theory, besides being unsavory, might too easily be confused with other unsavory transmutationist notions that even he considered worthless.

  10

  Historians of biology have found intimations of evolutionary thinking in the works of philosophers and scientists long before Darwin. Books have been written tracking the concept back as far as Aristotle. Some of those early statements referred not to biological transmutation but to loosely parallel matters of cosmology and geology, such as the progressive physical history (from stardust to molten gob to rocky sphere) of planet Earth. Some involved the question of life’s ultimate origin. Some were more closely related to evolution in the modern sense—that is, assertions about the diversity and classification of species, about continuity within that diversity, or about the tricky issue of just what a species is.

  During the eighteenth century in France, for example, Maupertuis tossed forth the idea that vast numbers of living things come into existence by spontaneous generation, of which only a small fraction prove to be well organized enough for survival. Buffon articulated the hypothesis that apes, humans, horses, asses, and all other animals might be related by common descent—and then, having made it sound half-plausible, he backed away from that hypothesis. Diderot published dreamy speculations about living matter, generated in simple form but with a mystical sort of awareness, somehow assembling itself into complex creatures. In Germany, an anthropologist named J. F. Blumenbach studied skulls and suggested that the various races of humans had diversified from common stock in response to local conditions. In England, near the end of the century, Erasmus Darwin published his Zoonomia, with its casual suggestion about “one living filament” from which every sort of warm-blooded animal had arisen. All these bold musings added to an atmosphere of alternate possibility, offering at least some encouragement to anyone inclined toward challenging the rigidly scripture-based dogmas of creation. The likelihood of such challenges also increased with the arrival of new data: specimens and accounts of strange, unexpected species in remote places, sent back from the journeys of exploration and imperial conquest; volumes of biogeographical information, showing that new species and familiar ones are distributed around the planet in curious patterns; more and more fossils unearthed, revealing episodes of extinction and succession over time; the discovery, through microscope lenses, of tiny creatures swimming in every drop of pond water and saliva; the intricate adaptations seen in so many species; and the accumulating evidence of variation within species as well as differences among species. Despite all the restless speculation and all the new data, though, no one had proposed a comprehensive theory of evolution until, at the turn of the century, Lamarck did.

  His full name was Jean-Baptiste
-Pierre-Antoine de Monet, Chevalier de Lamarck, reflecting a family lineage that gave him trappings of nobility but no inheritance. At age seventeen he dropped out of a Jesuit seminary and joined the army. After a taste of war and a try at medicine, in Paris, he made himself a botanist, publishing an excellent three-volume flora of France. The book was well received but didn’t solve Lamarck’s problem of making a living, so he served two years as tutor and traveling companion to Buffon’s son. Then he got himself hired as a botanical assistant, for a measly salary, at the Jardin des Plantes (which was later subsumed within the Musée National d’Histoire Naturelle). Lamarck’s next metamorphosis, the most drastic one, didn’t happen quickly. After twenty-five years as a botanist, he shifted to zoology, taking a museum position as professor of invertebrate animals and managing, throughout the Terror phase of the French Revolution, to keep his head down and away from the guillotine. His job was to lecture on insects, worms, and microscopic animals. Several years later the museum’s mollusk collection fell into Lamarck’s care when the malacologist, a friend of his, died. Studying that material, an assortment of fossils and recent shells, he saw evidence of variation within species and of sequential similarities among species found adjacent to one another in the column of time.

  Abruptly, for whatever reasons, at the age of about fifty-five, Lamarck lost his belief in the immutability of species. Soon afterward, in May 1800, he gave his first lecture with an evolutionary slant. He presented his full theory nine years later in Philosophie zoologique, the book from which it’s mainly known. A refined version appeared still later, in the introduction to his seven-volume natural history of invertebrates. Lamarck outlived four wives, went blind, survived to the age of eighty-five under the care of an unmarried daughter, struggled financially the whole way, and died in 1829, at which point he was more admired by radical British evolutionists (such as those teaching anatomy to medical students in Edinburgh and London) than by his colleagues in France. He was buried cheaply in an unmarked grave, like Mozart.

  Most people, if they know anything about Jean-Baptiste Lamarck, associate him with a single idea: the inheritance of acquired characteristics. There was more, as Darwin’s groaning dismissal of what he considered Lamarckian nonsense (“tendency to progression” “adaptations from the slow willing of animals”) in the letter to Hooker reflects. Lamarck argued that two factors account for evolution. One is, as Darwin noted, an inherent tendency in living creatures to progress from simple forms toward complexity. This tendency is conferred on them, Lamarck thought, by “the supreme author of all things.” The simple forms originate by spontaneous generation. The increasing complexity comes as certain “subtle fluids” somehow open new channels through body tissue to create new and more intricate organs. Lamarck didn’t explain why the progressive tendency exists, or just how those precious bodily fluids do their magic. He treated this factor as a given. It yielded separate lineages, progressing independently toward more complex species—but not to a branching tree of life. That’s an important distinction to keep in mind: Lamarck never proposed that all creatures are descended from common ancestry. The right image for his theory would be prairie grass, with short stalks and long stalks rising parallel from the ground, not a bush or a tree with divergent branches, like the drawing in Darwin’s “B” notebook.

  Lamarck’s second factor, which is more materialistic than his supposition of a God-given tendency to progress, encompasses four elements. First, animals face certain pressures from the external conditions (that is, the environment) within which they live. Second, when external conditions change, animals have new needs (besoins); they respond to those needs by increased use of certain organs or capacities, or by neglecting to use those they’ve been using. Third, increased use tends to enlarge or strengthen an organ or capacity; disuse tends to make it atrophy. Fourth, all such acquired changes are heritable. So here’s the familiar idea, accurately associated with Lamarck but incompletely representing his theory: Offspring inherit the traits that their parents have acquired. The young giraffe is born with a long neck because its mother and father stretched to reach high leaves. The blacksmith’s daughter is gifted with big muscles because her dad developed his over the anvil. Kiwis have useless little winglets because kiwi ancestors neglected to fly.

  Two factors accounting for evolution, four elements within the second factor—and as though that’s not enough, here’s another ingredient of the theoretical stew: Lamarck’s sentiment intérieur. At one point in the Philosophie zoologique, he posited this powerful but obscure sentiment (a sort of “feeling of existence,” he explained, without adding much clarity) in higher animals, supposedly driving their subtle fluids and impelling their bodies toward those uses that produce new strengths and capacities. Maybe sentiment intérieur was just another name for what’s now called consciousness. Or maybe he meant something more. Given the wooziness of the ideas and the losses in translation, it’s not surprising that Lamarck has been often misconstrued. One misconstrual was that he claimed animals have an inherent power to enlarge organs or capacities in response to their wants (a misreading of the French besoins). A giraffe wants a longer neck so it can browse on acacias—and desire plus effort makes it so. That seems to have been Darwin’s impression when he ridiculed Lamarck for suggesting that adaptations derive from “the slow willing of animals.”

  Darwin had gotten his first sniff of Lamarckism back in Edinburgh, as a teenager, during the period when he was discovering that natural history engaged him much more than the grisly and boring demands of medical training. He read old Erasmus’s Zoonomia and, in an uncritical way, admired it. (He wasn’t yet the tough judge of theory and supporting data that he would be later, and it was nice knowing that his own grandfather had written a notorious book.) He also read Lamarck’s technical work on invertebrate classification and, more important, heard talk about Lamarckian evolutionism from a dazzling young instructor who had befriended him, Robert Grant.

  Grant was crusty and formal on the outside but daringly unconventional in his thinking; a prickly and complicated man. Trained as a doctor, he taught invertebrate anatomy in Edinburgh and spent his free hours doing research on marine animals, especially sponges, or taking part in small scientific clubs such as the Plinian Society. He had a habit of making himself the mentor of select students, and in 1827 he picked Darwin. Probably the fact that this gawky youth was the grandson of Erasmus Darwin, whom Grant venerated as an evolutionary pioneer, helped settle his attentions on Charles. Together they took hikes to the seashore, waded in tide pools collecting wormy and mossy creatures, dissected them with the aid of the microscope at Grant’s house, and eventually shared a strong interest in one particular organism, the “seamat” (but it was an animal, not an alga or a throw rug) known as Flustra foliacea.

  One day while they were walking, Grant launched into a panegyric on Lamarck and his evolutionary theory, taking the younger man by surprise. At that point, after all, Charles was a dutiful middle-class kid from Shrewsbury who, despite the surname, wasn’t inclined toward radical ideas, especially those imported from France. “I listened in silent astonishment,” Darwin recalled years later, “and as far as I can judge, without any effect on my mind.” He hadn’t bought transmutation as peddled wholesale by his own grandfather, and he didn’t buy it now as retailed in Grant’s riff on Lamarck. Another reason for his resistance may have been that he’d already seen a dark, mean side of Robert Grant, when the older man pirated some of Darwin’s neophyte observations on the life history of that sea-mat, Flustra foliacea, and incorporated them into a paper. There was no acknowledgment to Charles Darwin, as data contributor or for anything else, in the published version. On the verge of his own first real contribution to science, Darwin had learned a hard lesson about credit and competition. He never forgot.

  He met Lamarckism again during the Beagle voyage, when the second volume of Lyell’s Principles of Geology reached him by mail in Montevideo. He had already read the first volume, which
presented Lyell’s critique of old-fashioned geological thinking, with its dependence on ancient catastrophes such as Noah’s Flood. Lyell made the case for a new vision (adopted and modified from James Hutton’s work, forty years earlier) of geological processes that were more continuous, more gradual, more uniform. That vision, in contrast to catastrophism, would become known as uniformitarianism. Lyell’s point was that geological change tends to be slowly cumulative, not catastrophic, and caused by familiar forces that operate in the present as they did in the past. This seemed brilliantly persuasive to Darwin, and his own geologizing during the voyage was informed by it.

  The second volume of Lyell’s Principles was different. Although it carried the same subtitle, announcing An Attempt to Explain the Former Changes of the Earth’s Surface, by Reference to Causes Now in Operation, this one looked at flux and transition among the animal and plant kingdoms. How were fossils formed? How did peat grow? What went into the formation of coral reefs? Before tackling any of these questions, Lyell addressed a more controversial one: Do species themselves change? His first two chapters were devoted to Lamarck, giving a thorough exposition of the Frenchman’s theory, noting that it “has met with some degree of favour from many naturalists,” and then doggedly refuting it. No, species don’t transmutate, Lyell decreed, not by action of Lamarck’s factors nor by any others. Cats buried with Egyptian mummies look the same as our own cats, he argued. Feral cattle in America, living wild in an unfamiliar climate, eating unfamiliar foods, revert to exact likenesses of aboriginal European cattle. Yes, domestic breeding can yield novel strains of livestock, but those only constitute new varieties, never a new species. It just didn’t seem compatible with Lyell’s uniformitarian view—of large geological changes effected incrementally over long stretches of time—to recognize that species might change that way, too.