The Reluctant Mr. Darwin

by David Quammen

  Such decision making about categories and similarities represented the routine, necessary work of taxonomy, into which Darwin had plunged himself. The rationale behind this branch of biology is that the human mind craves order, and taxonomy (describing species, naming species, classifying them within a system of sets and subsets) is what gives comprehensible order to the dizzying multiplicity of living creatures. It’s a very old game. Aristotle sorted animals into the “blooded” and the “bloodless” (insects were bloodless) and proceeded from there. He managed to distinguish whales from fishes, but also mistakenly separated them from mammals, and he included barnacles with mollusks. During the Middle Ages, plant identification and classification became important for medical purposes, and some experts published herbals (plant dictionaries) telling people what was what. Plants were simply listed, by name, in alphabetical order. But as the number of known plant species increased, herbalists found that alphabetization wasn’t the most convenient or useful way to present their information. A man named Caspar Bauhin, offering notes on six thousand different plants in 1623, grouped species into genera according to their similarities of appearance or other physical traits; Joseph Tournefort, sixty years later, clarified the genus concept and placed his genera into classes. These relatively obscure contributors were followed by Carl Linnaeus, the famed Swedish naturalist of the mid-eighteenth century, who founded the modern system of biological classification. Under his rules, every species is known by a two-word Latinate name, announcing also its genus, and is classified within a hierarchy of nested categories. Below the level of kingdom (plant or animal), Linnaeus specified four other levels: class, order, genus, species. Later taxonomists, including Darwin, have parsed the living world more finely, into seven main levels—kingdom, phylum, class, order, family, genus, and species—plus a number of mezzanines (such as suborder, superfamily, subspecies) in between. Defining a hierarchy of categories, though, was only the most obvious part of devising a classification system. Two other questions were trickier: What causal reality (if any) did the categorical arrangement reflect; and how should a taxonomist determine which species to place where?

  Linnaeus divided the animal kingdom into six classes, one of which was Vermes, encompassing not just earthworms and tapeworms and leeches and flukes but also sea cucumbers, slugs, snails, starfish, sea urchins, corals, bryozoans, octopuses, squids, oysters, and all the other mollusks, echinoderms, and crustaceans, including barnacles. It was a big bucket, his Vermes class, overflowing with homely, diverse critters. The next major advance came in 1795, when Georges Cuvier dissented from Linnaeus in a work whose title translates to Memoir on the Classification of the Animals Named Worms. Instead of lumping all those wormy and not-sowormy invertebrates together, Cuvier split them into six new classes. In a later book he organized the various classes of animal into his four great embranchements, or phyla: vertebrates, mollusks, articulates (including those later known as arthropods), and radiates (circular animals such as starfish and sea urchins). He also made the case that each embranchement reflected a fundamental body plan, utterly distinct from the other three. The core of each pattern was the nervous system. All other anatomical attributes were functional modifications, according to Cuvier, suitable for particular conditions (life within a certain environment) and built around one of the four archetypal nervous systems. The existence of four embranchements was something Cuvier took as a given. Furthermore, he believed, the functional interdependence of organs was so intricate that one organ couldn’t change without throwing the others out of whack. In other words, his system incorporated the idea of adaptation (arising from circumstances) and excluded the possibility of transmutation.

  Cuvier’s colleague, sometime friend, and implacable rival on matters of comparative anatomy was Etienne Geoffroy Saint-Hilaire, also working in Paris during the early nineteenth century. In contrast to Cuvier’s functionalism, Geoffroy argued a formalist view. That is, he considered the form of a species to be deep-seated and basic. Diversity among species arose as peripheral and contingent modifications of archetypal forms, not as necessary functional attunements to external conditions. It might sound like only a difference of emphasis, but it was more. Beneath the multiplicity of animal shapes, Geoffroy discerned “unity of plan.” The vertebrate skeleton, for example, was the template of one plan, providing a structural framework common to mammals, birds, reptiles, and fishes. This went well beyond Cuvier’s notion about one sort of nervous system underlying each embranchement, with functional demands accounting for the varied anatomical details. Structure played the major role in dictating function, according to Geoffroy’s view, rather than vice versa. The underlying structural plan was the main determinant of animal anatomy, to which adaptive modifications were secondary. Geoffroy admitted a possibility of some transmutation within lineages, but he didn’t accept the idea of common descent for all creatures. Eventually he proposed an even broader unity, claiming that articulates belong with the vertebral group. An insect, he figured, is just a vertebrate wearing its skeleton on the outside. In 1830 he tried stretching the group still further, to include mollusks as well as articulates, on the evidence of supposed parallels between the anatomy of a cephalopod and of a vertebrate bent back on itself. But Cuvier, in a celebrated debate, shot that octopus out of the sky.

  Another classification scheme that suggests the range of perspectives in those years was the quinarian system, a numerological approach dreamed up by a British entomologist and diplomat named William Sharp MacLeay. MacLeay’s quinarianism was passingly influential. Robert Chambers for one had absorbed it, and he featured it in Vestiges of the Natural History of Creation when the book first appeared in 1844. Richard Owen, as a young lecturer, had drawn heavily from MacLeay. Darwin too had read MacLeay (whom he knew through the Zoological Society) and, after a period of strong interest, reflected in the early notebooks, had rejected his notions. As MacLeay saw the living world, species were ordered by their similarities into circular sets of five. A circle would include five finch species, five iguana species, five whatever. Each species stood adjacent to similar species in a progression of resemblances around the circle, which closed on itself, the fifth species resembling the first. Every other taxonomic level also comprised five groups, again circularly arranged according to their degrees of resemblance. The animal kingdom consisted of five classes, for instance, corresponding to Cuvier’s four embranchements plus another, Acrita (the amorphous ones, such as sponges). The class of vertebrates contained five orders. MacLeay’s head was abuzz with fives. He seemed to believe that God’s head was, too.

  And the circles, the fives—they were just the start of it. MacLeay also saw affinities, parallelisms, analogies, osculations, all interconnecting the whole system like a bowl of magnetic Cheerios. Parallel to the animal kingdom was another circle constituting the plant kingdom, MacLeay asserted, though admitting his total ignorance of botany. Didn’t it stand to reason that, if animals were quinarian, plants would be too? The circles at each level were linked to one another by what he termed aberrant groups or species, intermediates that didn’t fit neatly into one circle or another, and by osculants, wherein two circles kissed. The platypus was an aberrant species somewhere between mammals and birds. But did it belong to both circles, or to neither? Answer: It was osculant. Affinities were the similarities among groups within a given circle. Analogies were the correspondences between groups in parallel circles. The affinity between reptiles and birds showed in hawksbill turtles. Tunicates were osculant between the classes Mollusca and Acrita. Barnacles were intermediates in the limbo connecting radiates and articulates—that is, between sand dollars and lobsters. It might all sound flaky to us but, in its time, quinarianism represented a careful attempt at finding order within biological diversity. In 1839 MacLeay went off to Australia, leaving his system to linger in the thinking of British biologists.

  For Darwin, quinarianism was another source of headache, and he had plenty of those already. What frustrat
ed him about all these systems was that they didn’t consider why species might resemble one another, either in deep structural plan (for instance, all vertebrates) or in external particulars (for instance, two species of barnacle within the same genus). The problem with current taxonomic practice, as he had complained to George Waterhouse back in 1843, “lies in our ignorance of what we are searching after in our natural classifications.” Linnaeus himself had admitted being clueless on that. “Most authors say it is an endeavor to discover the laws according to which the Creator has willed to produce organized beings,” Darwin wrote. But to him those were “empty high-sounding sentences.” He confided to Waterhouse his own wild view, which I quoted earlier, that classification should reflect “consanguinity,” meaning descent from common ancestors. It wasn’t metaphysics. It was genealogy.

  The dull task of describing species, naming them, classifying them into an orderly system, was for Darwin an exercise in applying the idea of transmutation. What better enterprise for a man who wasn’t yet ready to trumpet the idea itself? He’d write a fat monograph on Cirripedia, making it encyclopedic, straight-faced, inoffensive, even soporific, with transmutation as its implicit subtext. And if the result seemed more rational, more persuasive than other systems, then barnacle systematics would constitute an elegantly laconic confirmation of his theory. That was worth some considerable measure of his energy and time, wasn’t it? Yes…though not necessarily eight years.

  15

  His barnacle contact at the British Museum was John Edward Gray, keeper of the zoological collections, who in 1848 gave Darwin a scare. By then Darwin had committed himself to the barnacle project, with encouragement from Gray among others, and invested considerable work in it. Gray had helped persuade the museum trustees to allow Darwin an unusual privilege: borrowing all their barnacle specimens, receiving them batch-by-batch at his home, and snipping some into bits. Though he was intrigued by barnacles himself, Gray had even set aside his own research plans—so it seemed, anyway—in favor of allowing the field to Darwin. Then in March of that year, out of the barnacle blue, Gray presented a couple of short Cirripedia papers at the Zoological Society. Darwin let that much pass; either word didn’t reach him (which is unlikely) about Gray’s new barnacle efforts, or he didn’t care, or he stifled his jealousy. Several months later, he heard a rumor from gossipy friends that Gray “intended to anticipate” Darwin’s work, publishing descriptions of the strangest, most interesting barnacle species before Darwin could get around to them himself. This sounded like a dastardly deed—scientific poaching on his barnacle turf. He confronted Gray in person (which must have entailed a trip to the museum and a curt conversation, exactly the sort of event that often made him sick) and then followed the meeting with a huffy, legalistic letter. He would never have undertaken such a huge, tedious task, Darwin wrote, if he’d known that Gray was likely to swoop in and cherry-pick the juiciest barnacle revelations. Darwin apologized for having to raise the subject, but he didn’t sound apologetic. Gray backed off, leaving barnacles to Darwin, and the museum’s specimens continued to travel.

  It was a small disagreeable moment that passed quietly, and almost wouldn’t be worth mentioning, except that it illuminates a point of character. Did Darwin care about priority? Yes he cared about priority. The tiff with Gray suggests, alongside the earlier contretemps with Robert Grant over Flustra foliacea and a more distressing episode (with Alfred Russel Wallace) to come, that Charles Darwin possessed his reasonable share of human pride, and that he enjoyed not just the pure satisfactions of scientific inquiry and discovery but also the pleasures of publication, credit, renown, and getting there first.

  Another sort of anguish hit him soon afterward, when his elderly father began to fade. Dr. Darwin was eighty-two, gouty and blimpish and confined to a wheelchair at the house in Shrewsbury, where Charles’s unmarried sisters, Susan and Catherine, shared the nursing and fetching chores with two faithful servants. Charles had a complicated relationship with this intimidating man, the only parent he’d known since age eight. Dr. Darwin (or as Charles sometimes called him, “the Governor”) was always generous in paying bills and dispensing pointed advice, but he had mostly delegated, to Charles’s various sisters, the softer tasks of child rearing when Charles was a boy and the letter writing in years since. Charles respected his father’s force of personality, his business acumen, and his powers of character judgment, and felt deep gratitude for his financial beneficence; but there were also a few scars on Charles’s psyche, left by his father’s sometimes bluntly expressed disapproval. He never forgot the remark about being “a disgrace to yourself and all your family” and would quote it (or reconstruct it from sulky memory) in an autobiography written many years later, when he was a codger himself. But in the same passage he would call his father “the kindest man I ever knew” and express loving forgiveness about that hard, unjust comment. Their relationship had improved as Charles became more successful, first as a lionized young naturalist who had capitalized well on his Beagle opportunity, then as a published author and respected scientist. The doctor and he seem to have worked through their difficulties, converting conflict to affection pretty well for a pair of bullheaded and stiff Victorian gentlemen. Also, Dr. Darwin probably thought better of Charles over the years as he saw that his younger son was the achiever in the family, whereas Erasmus had ripened into a full-time professional slacker, never marrying, nor practicing medicine, nor choosing to clutter his social schedule with any other sort of gainful employment. Charles didn’t hold a job either, but he produced books, some of which earned good reviews and money. An additional bond between son and father was Charles’s sense of guilt. Having withdrawn to his reclusive life in Kent, having centered his attention narrowly—on his work, on Emma and their children, on his own state of bad health—Charles knew he’d left his father and two unmarried sisters without as much of his presence and emotional support as they might have expected. The house in Downe represented voluntary solitude, while the house in Shrewsbury was plain lonely. And now, to the exacerbation of all these tangled feelings, Dr. Darwin was dying.

  Charles last saw his father during a visit in October 1848. It was a period when, according to his diary, he himself had been “unusually unwell, with swimming of head” and also “depression, trembling—many bad attacks of sickness.” He went to Shrewsbury anyway. His sisters presumably tended both patients. Back in May, during an earlier visit, there had been cheerful card games with the doctor, but probably not this time. Charles wrote another long letter about barnacles, to a scientist at Harvard, and otherwise occupied himself somehow in the gloomy manor. Then he came home. Three weeks later Catherine, the youngest of the family, wrote to say that Dr. Darwin was worse. We wheel him into the greenhouse, she explained, and he sits gasping for air, unable to speak above a whisper, but placid and ready. He tried to talk about you this morning but was overcome with emotion. Sorry your stomach is still bad, she wrote, reminding Charles of his self-absorption. The next day’s letter from Catherine said: Father died this morning.

  The funeral will be Saturday, she added, which should give you time to be here.

  It did and it didn’t. For one reason or another (he may have been too sick, or waiting for Emma to return from a visit), Darwin let a few days pass before setting out. Finally he went up to London on Friday, traveling alone, leaving his wife behind with their latest newborn and the house full of older children, servants, and barnacles. He stayed that night at Erasmus’s place in the city, though Erasmus himself had already gone to Shrewsbury. During the solitary stopover, grieving for himself as well as for his father, he scribbled a note back to Emma that shows the depth to which his loving dependence on her had grown:

  My own ever dear Mammy.—

  Here I am & have had some tea & toast for luncheon & am feeling very well. My drive did me good & I did not feel exhausted till I got near here & now I am rested again & feel pretty nearly at my average.—

  My own dear wife
, I cannot possibly say how beyond all value your sympathy & affection is to me.—I often fear I must wear you with my unwellness & my complaints.

  Your poor old Husband, C.D.

  The next day he caught a train onward to Shrewsbury, arriving at the family home after the cortège had rolled away toward the church. Rather than chasing it, Charles stayed at the house, along with one married sister, who like him didn’t feel up to enduring the funeral or standing at graveside. Later he rationalized that it was “only a ceremony,” but admitted he felt sad at the “deprivation.” No one will ever know whether he had dawdled on purpose to miss seeing his father buried. But his absenteeism from grim ceremonies and big events was more than accidental. It was a pattern.

  16

  When his health allowed, Darwin was seeing some exciting things among the barnacles: bizarre kinds of intermediate sexuality, homologies with other crustaceans, rudimentary or “abortive” structures, barnacle noses, barnacle ears, a larval stage with no mouth, and cement glands that vent through the antennae to form a point of attachment when an immature barnacle finally settles down to adulthood, gluing itself forevermore onto a rock, a log, or the hull of a ship. Species of the genus Proteolepas, Darwin noticed, have no legs. Species of Alcippe develop only three body segments of the seventeen possessed by an archetypal barnacle, omitting fourteen, and as though that’s not enough, the female has no anus. Species of Ibla include only females—or so it seemed, until he looked closer and found tiny parasitic males, hardly more than sperm capsules, embedded in one female’s flesh like blackheads. All of these oddities were particular to a genus, or to one or more species within a genus. He also found notable differences on another categorical level: within species. Contrary to what he’d believed all along about the rarity of variation in the wild, barnacles turned out to be highly variable. A species wasn’t a Platonic essence or a metaphysical type. A species was a population of differing individuals.