The Reluctant Mr. Darwin (9 page)

But during the healthy intervals he was a hard, steady worker—nowadays we'd call him a workaholic—grinding along without breaks for vacation or celebration between one project and another. He wasn't a man to uncork a champagne bottle and kick up his heels just because some book had been finished. On that same day he set the geology page proofs aside, October 1, 1846, Darwin turned to his single remaining container of preserved specimens from the
Beagle
. It held about a dozen barnacles of a very odd sort, minuscule creatures that drilled burrows into the shells of certain marine snails; he had collected them eleven years earlier in the Chonos archipelago off the coast of Chile. Now he meant to dissect these little beasties, get a grip on their identity, write a paper.

He started work under a happy delusion that it wouldn't take long. He didn't foresee being swallowed up by barnacle taxonomy for eight years.

14

From 1846 to 1854, he did almost nothing else but. At a low bench near one window of his study, seated on a revolving stool, he dissected barnacles through a microscope. He drew what he saw. He saved the parts of his dissected specimens on carefully sealed slides. He filed the slides in a drawer. He composed intricate technical descriptions, species by species. He read the barnacle literature, muddled and spotty as it was. He made decisions about how to classify the species he described, correcting bad choices of previous classifiers. Barnacles weren't easy. They came in two types, one type (the sessile barnacles) resembling limpets armored in boilerplate, the other type (the stalked barnacles) resembling mussels mounted on golf tees. Confusing things further, their larvae swam around like larval shrimp. Darwin wrote to barnacle experts and barnacle fanciers, cadging the loan of specimens that he would minutely dismantle before returning what was left. He commissioned a new style of dissecting scope from an instrument maker in London and paid £16, half a year's beer money, to get it built. His study must have smelled like a pub, from the evaporation of pickling alcohol off his specimens. His eyes were bleary at the end of a day's work. Emma delivered another daughter and three more sons during the barnacle period, superintending Down House and all its human activities while Charles labored fervidly. There's a story often told about the impression this eight-year effort made on his young children; the second son, George, visiting one day at the house of some playmates, asked them: “Where does your father do his barnacles?”

Barnacle taxonomy was an unplanned detour leading away from, then eventually back toward, transmutation. It started as a modest task, the describing of one species, and gradually became an obsession—something he wanted to do, something he had to do, something that wouldn't be done until it was done completely and right. But the detour wasn't random or accidental. The guiding impetus had shown itself earlier, within an exchange of letters between Darwin and Hooker in 1845, long before Darwin uncorked the Chonos bottle. They were discussing a certain book on the nature of species, by a French botanist named Frédéric Gérard. Evidently the work was slipshod. Hooker, always rigorous on botanical matters, told Darwin: “I am not inclined to take much for granted from any one who treats the subject in his way & who does not know what it is to be a specific Naturalist himself.” Although Hooker meant no slight to his friend, only to Gérard, Darwin was defensive. Having established his credentials in geology but not in systematic biology—that is, he had never studied any single group of animals or plants with the plodding attention and descriptive purposes of a taxonomist—he took Hooker's comment as a personal criticism. Immediately he wrote back: “How painfully (to me) true is your remark that no one has hardly a right to examine the question of species who has not minutely described many.” Thirteen months later, not wanting to seem a hare-brained theorist ungrounded in the details of how one species differs from another—like Gérard, or the author of
Vestiges
—Darwin began describing barnacles.

That first creature he worked on was puzzling in several ways. No bigger than a pinhead, it belonged among the limpetlike type, the sessile barnacles, he thought, but instead of cementing itself onto a rock and secreting a cone-shaped array of body armor, it found shelter by drilling into a snail shell. Darwin recognized that it represented an unknown genus, provisionally named it
Arthrobalanus,
and began mentioning it fondly as “Mr. Arthrobalanus” in his letters to Hooker. After two weeks of dissecting he was charmed, feeling that he might spend another month on it and uncover some beautiful new structural surprise every day. He rigged a couple blocks of wood to support his wrists while he worked, and told Hooker how glad he was, following all the years of geological write-ups, to be using his eyes and fingers in this way again. After a month, having dug deeper, he was perplexed at the sexual peculiarities of Mr. Arthrobalanus. Most barnacles were known to be hermaphroditic, each individual carrying both male and female organs. This one, so far as Darwin could make out, had two penises and no egg sac. That was his first hint of what would emerge as an important finding from the whole study: Some barnacle species are hermaphroditic, some are separated into males and females, and some are frozen in complicated arrangements halfway between. The sex lives of the Cirripedia (the technical name for all barnacles), varying in progressive stages from hermaphroditism to distinct males and females, suggest a trail of transmutation.

In late November 1846, he sent a draft of his
Arthrobalanus
paper to the anatomist Richard Owen, asking for feedback and confessing that he had gotten so intrigued by barnacles that he was now dissecting a half dozen other genera. During the following spring he lost more weeks to bad health, this time including boils. He also interrupted his work with trips to London for the Geological Society and, the following June, to Oxford for the annual conference of the British Association for the Advancement of Science, one of the last of those big meetings he would attend. Most of his networking was now done by mail. He borrowed a sizable hoard of specimens from a rich private collector and made contact with several museum curators to get more. The consensus among experts was that barnacle classification was in disarray, and at least two of these men told Darwin that he was the guy to fix it. By the end of 1847 he had set himself to do a comprehensive monograph on barnacles, describing new species, revising earlier descriptions, bringing systematic order to the entire group.

He persuaded officials at the British Museum to send him their barnacle holdings on a long, trusting loan, and put out calls in every other imaginable direction. He even dropped a note to Sir James Clark Ross, the captain who had commanded Hooker's Antarctic voyage and was now preparing an Arctic expedition in search of Sir John Franklin, a fellow explorer, mortally stuck somewhere amid the frozen straits west of Baffin Island. While you're up there dodging icebergs and looking for Franklin, Darwin asked, would you please get me some northern barnacles? You'll be busy, of course, but it wouldn't take long to scrape a few off the rocks. Preserve them in spirits, he demanded sweetly, and make sure you don't damage their bases. Ross evidently ignored him.

The scientific confusion over barnacles included a disagreement about just where to place them within the animal kingdom. Are they mollusks? They seemed to be, given that they enclose themselves in shells (the adults do, anyway), live sedentary lives, and gargle seawater through their interior cavities. That misconception was corrected in 1830 by a researcher named J. Vaughan Thompson, who had noticed that the larval stages of barnacles, swimming freely, resemble crustaceans. By the time Darwin came along, it was agreed that the barnacles
are
crustaceans, more or less. The name Cirripedia (meaning “hairy-footed”) reflects the fact that within each shelly exterior lurks a strange little being like a misshapen crawfish, with its head glued to the substrate and its wispy legs waving upward to grab food. Darwin's chosen task was to make sense of the Cirripedia, species by species, genus by genus, family by family, and to assign them collectively a rank and a place within the great phylum of joint-legged animals that in those days was called Articulata. Did the Cirripedia constitute a distinct class of articulates, separate from and parallel to the crustaceans, the insects, the arachnids? Or were they merely a minor division within one of the subclasses of Crustacea already known? Based on his close study of barnacle anatomy, making comparisons among species and matching larvae to adults, Darwin eventually called them a subclass unto themselves. Within the subclass he recognized two main families, the sessile barnacles and the stalked barnacles, plus several aberrant forms that fit into neither. One of the aberrant forms was Mr. Arthrobalanus, the starting point of all his barnacle travails.

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.