The Beak of the Finch Read online

  What Darwin developed, as a living demonstration of his theory, was an analogy. He studied the power of breeders. People had been shaping and molding animals and plants since before the time of the shepherds in the land of Israel. There are allusions to the practice in Genesis. There are treatises on animal husbandry in ancient Chinese encyclopedias. Breeders in England in Darwin’s own time were spectacularly active, making new breeds of sheep and cattle, new varieties of strawberries and roses. The best of the new breeds were exported all over the world. British racehorses and bulldogs with fine pedigrees fetched high prices.

  Darwin knew that breeders could shape not only animals’ bodies but their very instincts. In the Origin he notes that “a cross with a bulldog has affected for many generations the courage and obstinacy of greyhounds; and a cross with a greyhound has given to a whole family of shepherd-dogs a tendency to hunt hares.” Darwin tells of one dog “whose great-grandfather was a wolf, and this dog showed a trace of his wild parentage only in one way, by not coming in a straight line to his master, when called.”

  There were some who thought that God created each kind of domestic animal and plant separately; they argued “for every variety being an aboriginal creation.” But Darwin knew from reading the breeders’ treatises that the power lay with the breeders themselves. They called their secret the power of “picking,” or “selection.” Picking the most prolific hen in the chicken coop, the fleetest horse in the field, or the best rose in the garden, over and over again, according to one treatise that Darwin read, “enables the agriculturalist, not only to modify the character of his flock, but to change it altogether. It is the magician’s wand, by means of which he may summon into life whatever form and mould he pleases.” The results were like Creation itself. One British lord, praising the work that breeders had done with sheep, wrote, “It would seem as if they had chalked out upon a wall a form perfect in itself, and then had given it existence.”

  Since breeders called the art of choosing “selection,” they called any changes in a breed that did not take place because of their conscious efforts—all of the casual, frustrating, and inexplicable changes in their flocks and herds behind their backs—“natural selection.”

  To see the selection process firsthand, Darwin took up the breeding of pigeons. In 1855, twenty years after his visit to the Galápagos Islands, Darwin began collecting pigeons in a coop in back of Down House. Though he now loathed travel, Darwin went into London to the Freemason’s Tavern to meet with gentleman pigeon fanciers of the Philoperisteron Society. He went to pigeon shows and poultry shows. He asked the secretary of the Philoperisteron Society, William Tegetmeier, to buy pigeons and their skeletons for him at Covent Garden.

  English pouter and English fantail. From Charles Darwin, The Variation of Animals and Plants under Domestication. The Smithsonian Institution

  “Very many & sincere thanks for keeping me in mind about Pigeons,” he wrote to Tegetmeier on New Year’s Day, 1856, and two weeks later he wrote apologetically to a neighbor, “I had meant to have sent you a line on Sunday, but quite forgot it myself. —Indeed we are all sick & miserable, & I hardly care even for Pigeons, so you may guess what a condition I am in!”

  In April 1856 Darwin stood in front of his pigeon coop with the geologist Charles Lyell. By now Darwin had fifteen breeds in his coop, including tumblers, trumpeters, laughers, fantails, pouters, polands, runts, dragons, and scandaroons. These birds were so very different from one to the next, as Darwin explained to Lyell, that if they had been found in the wild they would have been classified by biologists as belonging to separate species, or even as separate genera—distinct groups of species. Yet all these breeds had been created by nothing more mysterious than selection. If selection could do this much with pigeons in the short space of human history, how much more could the same power do in nature in the course of millions and millions of years, in the spans of time that move mountains?

  An English carrier. From Charles Darwin, The Variation of Animals and Plants under Domestication.

  The Smithsonian Institution

  Lyell was not converted by Darwin’s pigeons, but he was impressed. He urged Darwin to publish something fast, to establish priority for his ideas about evolution and natural selection. On Lyell’s urging, then, Darwin began the great writing project that resulted at last in his Origin of Species. He called it his “Big Book.” His working title was Natural Selection.

  Darwin knew better than to hang this book on the finches he had collected so haphazardly as a young man in faraway islands. He describes the finches in Natural Selection, the long first draft of his manuscript, but he does not even mention them in the final draft. Instead Darwin begins the Origin with his pigeons, including the English carrier (“greatly elongated eyelids … a wide gape of mouth”), the short-faced tumbler (“with a beak in outline almost like that of a finch”), and the common tumbler (“has the singular and strictly inherited habit of flying at a great height in a compact flock, and tumbling in the air head over heels”).

  The rock pigeon, parent-form of all Darwin’s fancy pouters, laughers, fantails, and scandaroons. From Charles Darwin, The Variation of Animals and Plants under Domestication.

  The Smithsonian Institution

  Generations of readers have wondered (behind drooping lids) why Darwin goes on so long about pigeons when his true theme is so much more exciting. Why talk about change in pigeon coops and hothouses when Darwin’s subject is turbulence in the natural world? But farms and nurseries were the only place where Darwin had seen it happen, and the only place he thought human beings could see it.

  “In Darwin’s treatment of the subject, no proof is adduced that a selective process has ever been detected in nature,” wrote the British evolutionists Guy C. Robson and Owain W. Richards in their influential book The Variation of Animals in Nature, published in 1936. “Throughout the work such a process is suggested and assumed: its actual occurrence is nowhere demonstrated. Stated briefly, the argument is as follows: selection has plainly ‘worked’ in domesticated races, analogous results and appropriate processes and conditions are found in nature, therefore we may assume that selection works in nature. In short, the proof is based on circumstantial rather than direct evidence, and the mainstay of the case is the analogy between Artificial and Natural Selection.”

  Robson and Richards add, “It is a very unsatisfactory state of affairs for biological science that a first-class theory should still dominate the field of inquiry though largely held on faith or rejected on account of prejudice.”

  THE FABLE THAT HAS GROWN up around Darwin and his finches is a Hollywood version of the romance of the mind. It simplifies the story by putting all those pigeons and mockingbirds in the background (Get those birds off the set!), and it speeds up the action by making it love at first sight, an Archimedean eureka. Darwin is so impressed by the finches and their beaks that his theory of evolution leaps straight into his head. He sails away dizzy with impious visions, as if he has just tasted an apple from the Tree of Knowledge.

  In one popular account the young man sits down by one of the giant tortoises’ drinking holes and stares at the gray domes of the tortoises, rather the way the young Hamlet sits in a Danish graveyard and ponders a skull. “If there are differences in the beaks of the finches and the shells of the tortoises, I must exercise extreme care to label each island’s collection quite scrupulously,” Darwin muses. “… That could be the most important discovery of my journey. What causes these differences? ‘Aye, there’s the rub.’ ”

  Another popular account asks us to imagine Darwin arguing his finch theory with Captain FitzRoy in their narrow cabin, “or, if you like, out on the poop deck on a calm night as they sailed away from the Galápagos, putting forth their ideas with all the force of young men who passionately want to persuade one another and to get to the absolute truth.” FitzRoy dismisses Darwin’s ideas as “blasphemous rubbish,” but Darwin hurls his notions back “against the blank wall of FitzRo
y’s uncompromising faith,” as if “battering down the Church itself.”

  Millions of students have been taught this fable, and thousands are still taught it every year. “It has become, in fact, one of the most widely circulated legends in the history of the life sciences,” writes the historian Frank J. Sulloway, “ranking with the famous stories of Newton and the apple and of Galileo’s experiments at the Leaning Tower of Pisa, as a classic textbook account of the origins of modern science.” Sulloway tried to break the spell on the hundredth anniversary of Darwin’s death. He published not just one but a series of brilliant papers on Darwin’s conversion and on the evolution of the legend. Yet the legend is still in wide circulation.

  ALTHOUGH DARWIN HIMSELF never went back to the Galápagos, many of the naturalists who sailed there in his wake collected finches. In 1868, 460 specimens. In 1891, about 1,100 specimens. In 1897, 3,075 specimens. In the ambitious expedition of the California Academy of Sciences in 1905–6, 8,691 specimens. By then Darwin’s finches had become one of the best-known tribes of birds on the planet.

  Just by looking at these birds, three generations of biologists felt as if they could almost see evolution in action—once Darwin had opened their eyes to the process. But the Grants are the first scientists equipped with enough patience, stubbornness, ground support and sea support, enough computer power, airplane power, and staying power, to watch the process actually happen.

  Chapter 3

  Infinite Variety

  … where, if we may use the expression, the manufactory of species has been active, we ought generally to find the manufactory still in action.…

  —CHARLES DARWIN,

  On the Origin of Species

  Peter Grant began to wonder about the variation of animals and plants during his undergraduate days at Cambridge University, the university where Charles Darwin was a fair-to-middling divinity student. After graduating, Grant went on brooding about variation while studying goldfinches and cardinals on the Tres Marías Islands of Mexico, nuthatches in Turkey and Iran, chaffinches in the Canaries and the Azores, mice and voles around McGill University in Canada.

  Rosemary came to the subject even younger. She grew up in a village in the Lake District, where she lived very much outside, and she remembers trailing after the old family gardener when she was four years old, asking him why individual plants, birds, and people are different one from the next. A row of vegetables, and no two were exactly alike. Birds: you could tell them apart. It was true of all the trees roundabout, beeches, birches, oaks, and ash; and all the common birds, tits, robins, blackbirds, finches.

  “What applies to one animal will apply throughout time to all animals—that is, if they vary—for otherwise natural selection can do nothing,” Darwin says in the Origin. Slight variations, in Darwin’s view, are what the process of natural selection is daily and hourly scrutinizing. Variations are the cornerstones of natural selection, the beginning of the beginning of evolution. And as Darwin shows in the first two chapters of the Origin with wild-duck bones, cow and goat udders, cats with blue eyes, hairless dogs, pigeons with short beaks, and brachiopod shells, variations are everywhere.

  Darwin studied the variation problem most deeply not in birds but in barnacles. In October 1846 he began trying to classify a single curious barnacle specimen that he had found on the southern coast of Chile. It was the very last of his Beagle specimens, an “illformed little monster,” the smallest barnacle in the world. To classify that barnacle he had to compare it with others. Soon the working surfaces of his study were littered with barnacles from all the shores of the planet.

  The classic barnacle is an animal with the body plan of a volcano: a cone with a crater at the top. It colonizes rocks, docks, and ships’ hulls. Every day when the tide rolls in, each barnacle pokes out of its crater a long foot like a feather duster and gathers food. When the tide goes out, each barnacle pulls in the feather duster and clamps its crater closed with an operculum—a shelly lid. To mate, a barnacle sticks a long penis out of its crater and thrusts it down the crater of a neighbor. Since every barnacle in the colony is both male and female, this is not as chancy as it sounds.

  What could be more of a sameness than a colony of barnacles? But Darwin, staring through a simple microscope, found himself descending into a world of finely turned and infinitely variable details. He wrote to Captain FitzRoy: “for the last half-month daily hard at work in dissecting a little animal about the size of a pin’s head … and I could spend another month, and daily see more beautiful structure.”

  A few of Darwin’s barnacles. From Charles Darwin, A Monograph on the Sub-class Cirripedia, volume 2.

  The Smithsonian Institution

  In every barnacle genus he found astonishing variations. In one genus, “the opercular valves (usually very constant) differ wonderfully in the different species.” Elsewhere he found variations in the form of “curious ear-like appendages,” “horn-like projections,” and, in one strange species, “the most beautiful, curved, prehensile teeth.”

  Everywhere he looked, individual differences graded into subspecies, subspecies shaded into varieties, varieties slid into species. Which specimens were the true species? Where should he draw the line? “After describing a set of forms as distinct species, tearing up my MS., and making them one species, tearing that up and making them separate, and then making them one again (which has happened to me), I have gnashed my teeth, cursed species, and asked what sin I had committed to be so punished.”

  (Darwin’s friends knew just how he felt. The botanist Joseph Hooker wrote Darwin across the top of one letter, “I quite understand and sympathize with your Barnacles, they must be just like Ferns!”)

  This profusion and confusion of barnacles helped confirm for Darwin that one species can shade one into another: that there is no species barrier. In many cases Darwin discovered one barnacle subspecies, variety, or race (he did not know which to call them) on rocks at the southern edge of a species’ range, and another subspecies, variety, or race at the northern edge of its range. In Natural Selection, his sprawling first draft of the Origin of Species, he notes that in many of these cases, “natural selection probably has come into play & according to my views is in the act of making two species.”

  Of course Darwin assumed that the split, the act of creation, would be much too slow to observe any motion in his lifetime, because evolution proceeds at a barnacles pace. Darwin proceeded at a like pace through his barnacles. “I am at work at the second volume of the Cirripedia, of which creatures I am wonderfully tired,” he wrote in 1852, when he had been plowing through barnacles for six years, and still had one more year to go. “I hate a Barnacle as no man ever did before, not even a sailor in a slow-sailing ship.”

  Variation is both universal and mysterious, one of the deepest problems in nature, and for Darwin it was for a long time completely bewildering. He wondered why, if his thinking was right, we see any species at all. Why not a continuous spectrum from tiny individual variations right on up the scale to kingdoms? Why for instance do we find a vampire finch and a vegetarian finch? (An example that Darwin might have liked, if he had known about the vampires.) Why not a whole smooth series of omnivores between the two, with a perfect series of intermediate beaks? Why not a blur, a chaos, an infinite web or Japanese fan of continuous variations?

  In the sixth and final edition of the Origin of Species, in his chapter “Difficulties of the Theory,” Darwin puts this objection at the very top of the list: “First, why, if species have descended from other species by fine gradations, do we not everywhere see innumerable transitional forms? Why is not all nature in confusion, instead of the species being, as we see them, well defined?”

  Very briefly, Darwin’s explanation is that the same process that makes varieties also destroys them. In the struggle for existence, some variants do better than others. When we look around us in the Galápagos or in Jersey or in New Jersey, the species of animals and plants we see are survivors. Varie
ties in between them have died off and disappeared, so that, after the long lapse of ages, we see only the victors and not the intermediate forms; we see the spines but not the webbing of the Japanese fan. “Thus,” Darwin says in the Origin, “extinction and natural selection go hand in hand.”

  By this reasoning, if we were present at the creation of new species, if we could locate a point of origin, a place where the tree of life is growing new branches right now, we would see something less distinct and more chaotic. We would see a blur of variations shading from the individual up to the level of the species, or even up to the level of the genus. Wherever naturalists find such a blur they should suspect that here is a place where evolution is in fast action, where species are in the act of being born. Of course, Darwin thought even this fast action would be too slow to watch. We would know that we stood at the point of origin of new forms not by seeing turbulent motion, but only by seeing a sort of frozen foam from which we could infer the waterfall, “an inextricable chaos of varying and intermediate links.”

  The thirteen Galápagos finches are just such an inextricable chaos of varying links. Darwin never knew how many links there really are, the chaotic and almost continuous variation in his Galápagos finches, because he brought back only thirty-one specimens, but he got an inkling of the problem when he watched the experts struggle with them. At first the ornithologist John Gould named one finch Geospiza incerta, meaning “ground finch, I guess.” Later Gould changed his mind and lumped that specimen with another. The fact that Gould ended up with the same total number of species of Galápagos finches as taxonomists currently do is a coincidence, because Gould’s thirteen were not the modern thirteen.