The Beak of the Finch: A Story of Evolution in Our Time

by Jonathan Weiner

  Once they have pitched camp, however, the world of the Galápagos settles around them. They can sit on the cliff edge at sunset and watch the nearer islands turn golden. They can watch Galápagos sharks patrol the Landing, and great manta rays leaping from the water, schools of dolphins, and sometimes breaching whales. Lava lizards skitter across the rocks. Owls emerge from crooks in the rocks, and so do scorpions. Some of the finch watchers hang their boots from bamboo poles to keep scorpions from crawling into the toes.

  After dark, they can sit on thrones made of relics of several shipwrecks apiece and lashed together with bits of string, and read the Origin by candlelight. And a single black male finch sits at the top of a cactus tree giving out long, repeated whistles, very lonely and melancholy. Before going to bed they sometimes look up and see great frigatebirds like black angels silhouetted against the moon.

  The limits of the island make it almost like the frame of a work of tragic art in which someone has tried to put everything of life and death in a single place, in a single piece, in a single play. The place speaks of bare necessities, these white rocks and pale rocks and streaked lava rocks all in a pile beneath a dark gray sky and climbing out from the dark blue sea, with the long scar of the trail to the crater rim. It is an island’s island, with just one half-safe place to land, one dented place to camp.

  The Grants and their team live and work there like those cartoon castaways who squat on a single lump not much larger than a Galápagos tortoise, with one palm tree growing from the center. Only here, there is not even a palm tree, and the castaways are all business and vigor and eagerness, with not much time to talk.

  The whole island is a diagram of limits. If a castle describes the impossibility of assault, an Alcatraz or Devils Island the impossibility of escape, then Daphne Major suggests the near impossibility of life, and the near impossibility of its study by human beings. Yet both have triumphed. The bizarre flora and fauna hang on here drought after drought, deluge after deluge. And these biologists, all of them, team after team, year after year after year, are coming away with gold, so that the prison has become a treasure-house.

  “LET’S GET ON with the measuring, darling, because this bird is a breeder too,” says Peter Grant.

  The beak of the bird in the second trap is as black as the first, but slightly larger. It is 15.8 millimeters long, 9.7 millimeters deep, and 9 millimeters wide. This finch is also heavier than the first, by 2.2 grams. “Probably had lots of banana,” Rosemary jokes.

  She and Peter band the bird’s left leg with orange over black (“It’s a Princeton bird, isn’t it?” Rosemary says), and they band his right leg with white over metal.

  The last four years on the island have been the kind that highlight Darwin’s “struggle for existence.” With virtually no rain, there has been virtually no breeding—so there are virtually no naive birds to catch. Despite the Grants’ nets and traps, their young assistants, and their almost unlimited interest, they have never been able to catch these two birds. Rosemary succeeded this morning only after a large investment of time. She has been coming to this spot all week. On Monday she did nothing here but watch her quarry. On Tuesday she brought up two traps and baited them, but left the doors open. On Wednesday and Thursday she kept the doors wide open, changing the bananas each morning. Now it is Friday, and she has them.

  Her shorts and her pink shirt are torn, and speckled by the brown sap of the Croton trees, which have decorated the clothes of virtually every scientist in the Galápagos since Darwin. Her hair is so light that it would be hard to say if it is blond or gray, and her cheeks, despite years beneath the equatorial sun, have the kind of rosiness that is prized on islands halfway across the planet, the British Isles, where she was born and raised.

  Peter’s shirt too is splotched by the sap of the Croton trees. He is tall, fit, wiry, with a memorable beard. In his mid-fifties, he has just started wearing glasses. He grew up on the southern edge of London, one hour’s drive from Darwin’s old homestead, and as the tip of his beard turns white his resemblance to Darwin is growing almost uncanny. Of course, Darwin by this age was an invalid. (His health may have been destroyed by a tropical disease, or by his own theory, which he worked on more or less in secret for twenty years after the voyage of the Beagle, the daily anxiety almost killing him.) Peter strides up the volcano at a pace that would be brisk on a level in England, or New England. His bare brown legs are as well toned as the legs of an athlete of twenty. He wears a set of small black binoculars around his neck with which he can identify a bird—read its I.D.—from a dozen steps away, and he whips them up often as he walks.

  Rosemary swabs the finch’s wing tip with an alcohol pad to clean the skin beneath its feathers. While she swabs, she chats, rather as a doctor might while preparing a patient for an injection. Just a quick prick—the bird doesn’t even seem to notice. She blots the drop of blood with the same filter paper that nurses use in hospitals with newborn babies, and presses the alcohol pad to the feathers for a moment.

  When the Grants leave the island, this drop of blood and the morning’s numbers will travel back with them to their other lives in Princeton, New Jersey, for analysis. There too, Rosemary and Peter work side by side. They have adjoining offices at Princeton University. Rosemary is a lecturer in the Department of Ecology and Evolution; Peter is, this year, the chairman of the department.

  Their tools on Daphne are low-tech; tools have to be simple to work reliably, month after month, on a desert island that Robinson Crusoe would have laughed at. But the instruments that are trained on their results in Princeton and elsewhere are among the most sophisticated in the armamentarium of science: computers, of course, to store and analyze the decades of marching numbers; and equally powerful but more exotic machines to read the coded messages that are inscribed, as if on myriad twisted and spiraling scrolls, in every drop of bird blood. Between the numbers in the notebooks, and the sentences in the blood, the Grants and others are now reading the story of life from the outside in and from the inside out. They are watching evolution in the flesh, and evolution in the blood.

  “In the distant future I see open fields for far more important researches,” Darwin writes in the last pages of the Origin. “… Light will be thrown on the origin of man and his history.” The study of evolution in action throws light on our origin and our history, on the silent bones of Olduvai Gorge and Koobi Fora. It also casts a new light on our tumultuous present and our destiny: for the processes that are illuminated by these studies, the processes that got us here, are in turmoil. With the conditions of life on this planet changing everywhere faster and faster, the pressures of natural selection are everywhere increasing in intensity, daily and hourly, even on islands as remote as the Galápagos. Whether or not we choose to watch, evolution is shaping us all.

  This is the view of life that is opening now, for those who stand on Darwin’s shoulders. They can see farther than Darwin ever dreamed, and much lies in the offing, or beyond the offing.

  Chapter 2

  What Darwin Saw

  Steeped in fable, steeped in fate …

  —HERMAN MELVILLE,

  “The Coming Storm”

  There are thirteen species of finches in the Galápagos. Some of them look so much alike that during the mating season they find it hard to tell themselves apart. Yet they are also spectacularly and peculiarly diverse.

  The black cocks that Rosemary trapped this morning are cactus finches. Cactus finches do more with cactus than Plains Indians did with buffalo. They nest in cactus; they sleep in cactus; they often copulate in cactus; they drink cactus nectar; they eat cactus flowers, cactus pollen, and cactus seeds. In return they pollinate the cactus, like bees.

  Two other species of Darwin’s finches use tools. They pick up a twig, a cactus spine, or a leafstalk, and they trim it into shape with their beaks. Then they poke it into the bark of dead branches and pry out grubs.

  One finch eats green leaves, which birds are not supposed
to do. Another, the vampire finch, found chiefly on the rough, remote, cliff-walled islands of Wolf and Darwin, perches on the backs of boobies, pecks at their wings and tails, draws their blood, and drinks it. Vampires also smash boobies’ eggs against rocks and drink the yolk. They even drink the blood of their own dead.

  There is a vegetarian species that knows how to strip the bark off twigs into long curling ribbons like Geppetto’s shavings, to get at the cambium and phloem. There are also species that perch on the backs of iguanas and rid them of ticks. The iguana invites a finch to perch by assuming a posture that makes it look like a cat that wants to be petted.

  Four of Darwin’s finches, from his Journal of Researches.

  1) Large ground finch. 2) Medium ground finch. 3) Small tree finch. 4) warbler finch.

  The Smithsonian Institution

  The whole family tree of Darwin’s finches is marked by this kind of eccentric specialization, and each species has a beak to go with it. Robert Bowman, an evolutionist who studied the finches before the Grants, once drew a chart comparing the birds’ beaks to different kinds of pliers. Cactus finches carry a heavy-duty lineman’s pliers. Other species carry analogues of the high-leverage diagonal pliers, the long chain-nose pliers, the parrot-head gripping pliers, the curved needle-nose pliers, and the straight needle-nose pliers.

  That is how they are often displayed in the textbooks, as an array of thirteen beaks, the most famous tool kit in the natural world. Sometimes the birds are also painted in a full-length group portrait, as thirteen pairs—male and female, black and brown—perched in the branches of their family tree. In either style of family portrait, they represent the mystery of mysteries in miniature, a microcosm of the astonishing diversity of life on earth.

  The Grants are little known outside their field, but inside it their work on these famous birds made them celebrities years ago. “The Grants are the gurus of Darwin’s finches,” says William Provine, a historian of science at Cornell University. “There’s no question about that. Good grief! They are known everywhere in evolutionary biology, in every country on earth where people are working on the problems of evolution.”

  “The history of research in the Galápagos is in itself an interesting topic,” says another historian of science, Frank J. Sulloway, who has made an extensive study of it. “You are talking about one set of organisms and also, to a large extent, one set of problems. We’re not talking here about the problems of physiology or endocrinology: we’re talking about the problems of evolutionary biology. And as you look at the studies that have been done from generation to generation, you can see that the research has gotten incredibly more sophisticated as time goes on. The Grants are doing things that people like Swarth or Lack would only have dreamed of doing,” he says, naming authors of classic finch studies that were published in the first half of this century.

  “It’s like the difference between an adding machine and a personal computer,” Sulloway says. “You couldn’t make those calculations in the twenties and thirties. You couldn’t conceive of those calculations in the twenties and thirties. The Grants’ studies have raised this whole area to a whole new level of excellence. It’s really quite extraordinary.”

  “Peter Grants service to biology has been extreme,” says William Hamilton, an evolutionist at Oxford University “He has shown that the most important and pervasive theory that biology has really does work, and that almost all of the varied and fine details of evolution that he has found occurring are understandable by this theory, and, so far, seem to need no other.… I think it can be claimed that the [Grant group’s] work as a whole gives the most detailed unified support to the Neo-Darwinian view of evolution that the theory has yet received.”

  “The problem with Daphne is, it’s going to destroy bird studies forever,” says David Anderson, one of the Grants’ former field assistants, in the tone of a young Russian novelist lamenting War and Peace. “No one is ever going to live up to it. Yet everyone is going to try, because they’ve read the Daphne study. In a sense, it’s a disaster for ornithology. The island is small enough for the Grants to know all the birds, but large enough for them to get good numbers. And they’ve been doing it continuously since 1973! No one’s ever going to do anything like it.”

  Season after season, Darwin’s finches keep showing the Grants more. The next view is always wider than the one behind them. They look, talk, and move like people who have discovered a fountain of youth. And if their spirits ever sag for an hour, or they begin to feel almost old for an evening, alone on their lump of rock, they are carried along by the thought of where they are.

  Views of the Galápagos. From Robert Fitzroy’s

  Narrative of the Surveying Voyages of His Majesty’s Ships

  Adventure and Beagle.

  The Smithsonian Institution

  THE PLACE WHERE DARWIN first rowed ashore is one day’s short sail from Daphne Major, on the island of San Cristóbal, which the English call Chatham. The landing party included Captain FitzRoy, Midshipman Philip Gidley King, and some other Beagle shipmates, according to Darwin’s diary entry of September 17, 1835.

  Darwin had joined the voyage four years before, at the age of twenty-two, as the unpaid gentleman’s companion to the captain, who was very young too and worried about the loneliness of the command, the ship’s previous captain having committed suicide. By the time the Beagle reached the Galápagos, FitzRoy had already fulfilled his chief mission, a survey of the coast of the continent of South America. Now he and his crew had set out from the coast of Peru. They were starting across the Pacific on the long way home to England.

  The men in the landing party hoped to find giant tortoises. They were looking forward to roasted tortoise meat and terrapin soup. But they did not see a single tortoise at the beach on San Cristóbal. In FitzRoy’s memoir of the voyage, he describes “black, dismal-looking heaps of broken lava.… Innumerable crabs and hideous iguanas started in every direction.… This first excursion had no tendency to raise our ideas of the Galápagos Islands.”

  Darwin had studied the sloping black shoulders of the island from the ship, and at that distance he had thought the trees were all dead. But now as he picked his way across the beach he could see that almost every plant was “both in flower & leaf.” He botanized a bit and found ten different flowers, “but such insignificant, ugly little flowers” that they would have seemed more at home in the Arctic than here in the heat of the equator. Beneath the bushes he saw small birds hopping on the lava, hunting for seeds.

  “The birds are Strangers to Man & think him as innocent as their countrymen the huge Tortoises,” Darwin writes in his diary. “Little birds, within 3 or four feet, quietly hopped about the Bushes & were not frightened by stones being thrown at them. Mr King killed one with his hat.…”

  That is the way Darwin’s finches enter Darwin’s diary—under a hat. And for the next five weeks Darwin writes about the birds just as casually. In fact he hardly mentions them. He has too many other adventures to write about. He finds whole herds of giant tortoises, and rides on the back of one. He picks up one of the iguanas (“imps of darkness”) and throws it into the water, over and over; over and over, it swims straight back to him. He yanks the tail of a land iguana that is busily digging a burrow. The lizard backs up to the surface and stares at him as if to say, “What made you pull my tail?”

  As he had done all along the voyage, Darwin collected diligently in the Galápagos: “Fish in Spirits of Wine,” “Reptiles in Spirits of Wine,” “Insects in Spirits of Wine,” and so on. He also shot a total of thirty-one finches, representing nine kinds, from three of the four islands he visited, and he stowed them all away aboard the Beagle. (He had learned how to stuff birds from a freed black American slave, John Edmonstone, who gave cheap taxidermy lessons at the Edinburgh Museum.)

  All this matters so much to the course of human thought that the historian Frank J. Sulloway spent fourteen years figuring out what happened and what did not happen in th
e islands, nailing down the story finch by finch. Thanks to his detective work, the episode is now not only one of the most famous but one of the best-documented turning points in the history of science.

  Contrary to legend, Sulloway has shown, Darwin did not think the finches were very important. He did not even think they were all finches. The cactus finch looked to him like some kind of blackbird;, other finches looked like wrens and warblers. Darwin assumed there were plenty more just like them on some part of the coast of South America where the Beagle had failed to stop. In other words, the very quality that makes the finches so interesting now made them look like nothing special to Darwin. Their diversity disguised their uniqueness.

  Much to his later regret, Darwin stored the finch specimens from his first two islands in the same bag, and he did not bother to label which bird came from where. Since conditions on the islands seemed more or less identical, he assumed the specimens were identical too.

  He did notice that the mockingbirds he shot on his second island were slightly different from the mockingbirds on the first. For that reason he took the trouble to label these specimens, and all of the other mockingbirds he caught, by place of origin. But when the vice-governor of the islands told Darwin that the tortoises varied from island to island as well (claiming he could tell which island a tortoise came from by its shell), Darwin more or less ignored him. “I did not for some time pay sufficient attention to this statement,” he confessed later, “and I had already partially mingled together the collections from two of the islands. I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted.…”