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

by Jonathan Weiner

  Peter dangles the bird in a little weighing cup. “Weight, 22.2 grams.”

  “This bird has lived a long time,” he muses. “Thirteen years.” There are only three others of its generation still alive on the island, and none older. “But I don’t think there’s a single one of his offspring flying around. Not one has made it to the breeding season.” The bird has been a father many times, and never once a grandfather.

  Cactus finches. From Charles Darwin, The Zoology of the Voyage of H.M.S. Beagle.

  The Smithsonian Institution

  Peter puts a gray ring and a brown ring on the bird’s left ankle. He puts a light green ring over a metal one on its right ankle. Bands like these, and an ingenious color code, help the Grant team to keep track of their flocks from dawn to dusk, from the cliffs at the base of the island to this guano-painted rubble at the rim.

  Peter holds the bird in his fist one more time and inspects its beak in profile. In rushing up to join Rosemary at the rim, he has forgotten his camera. Otherwise he would photograph the bird just so, from a distance of 27 centimeters. That is the Grants’ standard mug shot for one of Darwin’s finches.

  THE ORIGIN OF SPECIES SAYS very little about the origin of species. Darwin’s full title is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Yet the book does not document the origin of a single species, or a single case of natural selection, or the preservation of one favored race in the struggle for life.

  Darwin talks about the breeding of pigeons. He talks about Malthus, fossils, patterns in the geographic distribution of the world’s flora and fauna. He marshals an enormous mass of evidence that evolution has happened. Yet Darwin never saw it happen, either in the Galápagos (where he spent only five weeks) or anywhere else.

  “It may metaphorically be said,” he writes in a famous passage, “that natural selection is daily and hourly scrutinising, throughout the world, the slightest variations; rejecting those that are bad, preserving and adding up all that are good; silently and insensibly working, whenever and wherever opportunity offers.… We see nothing of these slow changes in progress, until the hand of time has marked the lapse of ages, and then so imperfect is our view into long-past geological ages, that we see only that the forms of life are now different from what they formerly were.”

  That is Darwinism for Darwin. Life changes, down through the generations. The chief mechanism of change is the process that Darwin called natural selection. This process is at work right now around us, “whenever and wherever opportunity offers,” as Darwin emphasizes with his italics: not confined to a moment of creation in the dim past. It goes on this year as much as last year, now and forever, here and everywhere, like Newton’s laws of motion. But the action and reaction are too slow to watch.

  The invisibility of the process made its demonstration more difficult for Darwin, although the naturalist Thomas Henry Huxley, Darwin’s self-appointed bulldog and griffin (“I am sharpening up my beak and claws in readiness,” he wrote, as the Origin went on sale), met critics head on. “It has been urged, for instance, that in his chapters on the struggle for existence and on natural selection, Mr. Darwin does not so much prove that natural selection does occur, as that it must occur,” Huxley wrote; “but, in fact, no other sort of demonstration is attainable. A race does not attract our attention in Nature until it has, in all probability, existed for a considerable time, and then it is too late to inquire into the conditions of its origin.”

  Huxley gave a public lecture with the title “The Demonstrative Evidence of Evolution.” His evidence was a series of extinct ancestors of the modern horse, beginning with Eohippus, the “dawn horse,” now called Hyracotherium, which lived and died about fifty million years ago. The naturalist Alfred Russel Wallace published “A Demonstration of the Origin of Species by Natural Selection,” which consisted of a brief table divided in two columns. The left-hand column listed the keys to the process of natural selection. (Like Newton’s laws of motion, they are so few and so simple that they can be written on the back of an envelope.) The right-hand column listed the logical consequences of these laws, ending with “changes of organic forms,” or evolution. Wallace headed the items on the left “Proved Facts” and the items on the right “Necessary Consequences (afterwards taken as Proved Facts).”

  Fossils argued that evolution has happened. Logic argued that natural selection can make it happen. But neither bones nor logic could demonstrate the one leading to the other, natural selection causing evolution. In 1893, in an essay entitled “The All-Sufficiency of Natural Selection,” the German biologist August Weismann confessed (in italics) “that it is really very difficult to imagine this process of natural selection in its details; and to this day it is impossible to demonstrate it in any one point.”

  A few biologists did try to demonstrate it at the turn of the century. A Yankee biologist named Hermon Carey Bumpus thought he saw it at work among a flock of sparrows in Providence, Rhode Island. Other investigators reported natural selection in action among crabs in Plymouth Sound, moths in Yorkshire birch trees, mice in sandhills on an island in Dublin Bay, and chicks in a Long Island poultry yard. But most of these sitings were brief and ambiguous (Bumpus’s data base was a single snowstorm). The work tended to be neglected by both sides of the debate.

  Mountains of books and papers, technical and popular, were published about evolutionary theory. Much of this literature approached the level of abstraction of the medieval scholiasts’ angels-on-the-head-of-a-pin. Some of the most learned interpretations of Darwinism were more or less unconstrained by reality. In crucial ways, for all the mountainous literature, the theory of evolution by natural selection was still a proof on the back of an envelope, and the origin of species remained what Darwin called, in his journal of the Beagle voyage, “that mystery of mysteries.”

  “If ever an idea cried and begged” for an experimental research program, a geneticist lamented in 1934, “surely it is this one … but there have been so very, very few of them.” A quarter-century later, in 1960, another geneticist wrote that “the amount of observation or experiment so far carried out upon evolution in wild populations” was still “surprisingly small.” He found this impoverished state of affairs disturbing because “evolution is the fundamental problem of biology while observation and experiment are the fundamental tools of science.” In 1990, in a one-volume Encyclopedia of Evolution, a physical anthropologist wrote that the “complaint of a half-century ago holds good: The number of experimental tests of natural selection is pitiful; the few that have been conducted still do heavy duty as exemplars.”

  This is also the burden of the Creationists’ cry, “Only a theory.” According to a little paperback entitled The Handy-Dandy Evolution Refuter, whose cover bears the gold seal of the Chapel of the Air, in Wheaton, Illinois, “Neither evolution nor creation can be tested as a scientific theory, so believers in evolution or creation must accept either view by faith.” Duane Gish, the most prominent Creationist writer today, declares in his book Evolution? The Fossils Say No!, “By creation we mean the bringing into being by a supernatural Creator of the basic kinds of plants and animals by the process of sudden, or fiat, creation. We do not know how the Creator created, what processes He used, for he used processes which are not now operating anywhere in the natural universe.” (The italics are his.)

  Today more and more evolutionists are doing what Darwin thought impossible. They are studying the evolutionary process not through fossils but directly, in real time, in the wild: evolution in the flesh. “Evolution” comes from the Latin evolutio, an unrolling, unfolding, opening. Biologists are observing year by year and sometimes even day by day or hour by hour details of life’s unrolling and opening, right now.

  So many new studies are coming out that one investigator has published a technical guide for evolution watchers, a detailed and rigorous book entitled Natural Selection in the Wild. The centerpiece of the book i
s a table, “Direct Demonstrations of Natural Selection.” This table begins to supply what Darwin, Huxley, Wallace, and Weismann never could. It lists more than 140 instances in which a piece of the Darwinian process has been documented. Some of these case studies, like Bumpus’s sparrows, are only flashes in the storm, glimpses of the process that is at work around us, but many of the latest studies, like the Grants’, are remarkably, almost panoramically complete.

  Taken together, these new studies suggest that Darwin did not know the strength of his own theory. He vastly underestimated the power of natural selection. Its action is neither rare nor slow. It leads to evolution daily and hourly, all around us, and we can watch.

  The Grants are leaders of this field, and they are among its ideal representatives. Year after year they go back to the most celebrated place in the study of evolution, the place that helped lead the young Darwin to his theory: the Galápagos, the Enchanted Islands. There they observe Darwin’s finches, the birds that Darwin was the first naturalist to collect; the birds whose beaks inspired his first veiled hints about his revolutionary theory; the birds whose portraits in textbooks and encyclopedias have now introduced so many generations to Darwinism that they have become international symbols of the process, totems of evolution, like the overshot brows and cumulous beard of Darwin himself. Now the Grants’ work on Darwin’s finches is entering the textbooks too. This is one of the most intensive and valuable animal studies ever conducted in the wild; zoologists and evolutionists already regard it as a classic. It is the best and most detailed demonstration to date of the power of Darwin’s process.

  TO STUDY THE EVOLUTION of life through many generations you need an isolated population, one that is not going to run away, one that cannot easily mix and mate with others and, by mixing, mingle the changes induced in one place with the changes induced in others. If you detect a change in the wingspan of a bird, the teeth of a bear, the fins of a fish, or the mandibles of an ant, you want to be able to explain why the change occurred. You want to know the action to which the change is a reaction. For this you need something in nature approximating the simplicity and isolation of a laboratory.

  Islands are ideal for this purpose, because it is hard for your subjects to leave them, and it is hard for outside influences to invade. Islands are like castles, communities with moats around them. Evolutionists are now watching life evolve on Gotland, in the Baltic Sea; on Mandarte, in the Georgia Strait of British Columbia; on Trinidad, in the West Indies; on the Big Island of Hawaii, in the center of the Pacific. But of all the islands in the world the nearest approach to paradise for evolutionists is still the Galápagos archipelago.

  There are about a dozen major and a dozen minor islands in the Galápagos. They are the tips of volcanoes that erupted from the floor of the sea. They broke the surface of the Pacific within the last five million years or so, which makes them far younger than most of the rock that composes the continents. In fact a few of these islands are still in their birth throes, among the most fiery volcanoes on the planet. Because they are so young, the creation of new forms from old is still in the early stages in the Galápagos: life is evolving as fast and furiously as the volcanoes. And because much of this life is trapped on separate islands—the summit of each volcano is a prison for most of the creatures that live and die there—and because there was never any bridge to the mainland (South America is a thousand kilometers, or six hundred miles, to the east), the life-forms of this archipelago are following strange paths of their own.

  Daphne Major, where the Grants have spent most of their time, is small and lonely even by the standards of the Galápagos. There is only one way onto the island. The Grants and their team have to go there at low tide, as early in the morning as they can, while the sea is still relatively calm, and sail around the island’s base to a certain point on the south side. They can’t land a boat, because Daphne Major has no shore, nothing at the waterline all the way around but cliffs two and three stories high. Most of these cliffs are steeper than walls, because the waves have cut them inward, so that the profile of the volcano at the waterline is overshot, like Darwin’s brow. The Grants can’t even anchor, because the waters around the island are absurdly deep, one thousand fathoms of sharks to the bottom of the ocean.

  They have to leave their boat’s captain describing figure eights offshore while they search along the south side of the island in a rowboat, which in the Spanish slang of the Galápagos fishermen is called a panga. (The origin of the word is obscure, although a wooden rowboat or dinghy laboring toward black Galápagos cliffs looks frail as a leaf of corn husk, which is also a panga.) They watch for a place where the cliff’s rim stoops toward the water and the angle of the slope becomes slightly more inviting. Just at this spot, there is a wet black ledge near the waterline. An experienced pangero can find it easily. At night this ledge is often haunted by sea lions, octopuses, and night herons, but by day it is guarded only by barnacles.

  Daphne Major, in the center of the Galápagos archipelago.

  Drawing by Thalia Grant.

  The first one off the panga has to leap when a swell lifts the boat to the top of this ledge, which has the surface area of a large welcome mat. Often the panga will be flying up above the welcome mat a few meters, then dropping down below the mat a few meters, or more, depending on the mood of the ocean (“miscalled Pacific,” as Darwin notes in his Beagle diary—for it is not always as calm as it is this morning). From the panga the ledge seems to shoot up as high as a ceiling and then plummet as deep as a basement.

  They leap onto the welcome mat and climb the little cliff, hand over hand, on rock that is dark, wet, and many-formed, much abused by the waves, until they come to an upper ledge they call the Landing. Then they form a human chain and pass up tent canvases, bamboo poles, clothes, crates of tinned soups, all of their food for the next six months, including hefty water barrels called chimbuzos. They cannot land without all these provisions because there is no food or water on Daphne Major. On many days the little island feels like the solar face of Mercury. The black lava gets hot enough to fry an egg (not the proverbial egg, a real one). A jerrycan of water left out in the sun at noon can come so near a boil that it is too hot to sip. Every drop they drink they have to carry up the cliff on their backs in the chimbuzos, and each chimbuzo weighs fifty kilos, or about a hundred pounds.

  Everyone in the Grants’ group detests landing day. “Nobody’s talking science,” Rosemary says.

  “Or talking,” says Peter.

  “It is possible to see some slightly frayed tempers,” says Rosemary, mildly.

  Of course, the Grants chose the island partly for its inconveniences. The whole of the archipelago was discovered by human beings rather late in the heyday of global exploration. The first historical account of them dates from the sixteenth century, when the third bishop of Panama was swept off course on a mission to Peru and almost died there. (The bishop wrote not only the first but the best one-line description of the islands: “It looked as though God had caused it to rain stones.”) In the next century the place became a retreat for buccaneers. By the time of Darwin’s visit there were a few settlers who led “a sort of Robinson Crusoe life” in the islands, hunting the descendants of the wild pigs and goats that the buccaneers had brought there. There was even a penal colony on the island of Floreana.

  But even then, not many soldiers, sailors, jailors, pirates, or whalers would have taken the trouble to climb onto this steep little rock of an island. Those who did would have needed only an hour to walk around the island’s base, and twenty minutes to walk around the rim. It is unlikely that before the arrival of the Grants and their team a single human being ever actually tried to live there, and even though the island is located in the very center of the archipelago it was not even included in some of the earliest maps. (It may be a nameless speck on the chart made by Ambrose Cowley, the buccaneer, in 1684, but it is not on the chart made by Alonzo de Torrés, a captain in the Royal Spanish Armada,
more than a century later.) Nor did Darwin himself see Daphne Major. The Beagle missed it by dozens of kilometers. The island may have been briefly visible during the voyage of HMS Beagle as a homely blip on the horizon. Even today, in spite of its central location, Daphne is a rare and restricted stop for the tourist cruises that now crisscross the Galápagos. The average tourist would probably fall right off the island.

  On landing day, the Grants and their assistants store some of their supplies in caves above the welcome mat. But they have to lug most of their gear almost to the rim of the volcano. This is the only spot on the island where it is flat enough to pitch a tent, aside from the crater floor, which is forbidden ground because it is the nesting place of blue-footed boobies. The trail that slants up from the Landing to the camp is not very steep, but even with the sky cloudy and a wind blowing it is still hot, muggy, and full of glare. Much of the rock, solid or loose (and almost all of it is loose and broken up to some extent), is white or near white, from many long-worn coats of guano. The whitest birds on earth, masked boobies, scream and whistle and honk from their nests along the edges of the trail, or in the middle of the trail, but do not budge. Sometimes it is hard to step around the boobies without falling off the island, for the trail is narrow, the rock is loose, and the boobies are vociferous—long darting necks, long sharp beaks, and angry honks and whistles. (The Beagle’s captain, Robert FitzRoy, when he landed on his first Galápagos island, called it “a shore fit for Pandemonium.”)

  At their campsite, the Grants lash tarpaulins to bamboo poles and prop up the poles with strings tied to piles of stones. These days they use materials that can survive the vertical sun at the equator. In earlier expeditions they used ordinary tarps. The sun and the wind beat down until, according to Trevor Price, a veteran of the finch watch, the tarp was “reduced to a symbolic flag flying from half a bamboo pole. When ‘whiteys’ arrived in camp,” Price remembers wickedly, “they got into all sorts of contortions trying to stay in its shade and prevent pinkness.”