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

by Jonathan Weiner

  In short, Darwin was not yet an evolutionist; he was still partly a Creationist. He was on his way home to become a country parson. That was the career for which he had trained at Christ’s College, Cambridge, where he studied Scripture and collected beetles. He was more interested in beetles than Scripture, but in those days a passion for nature was considered the perfect hobby for a parson.

  Darwin in the Galápagos did not have Darwin’s shoulders to stand on. He had to stand on the shoulders of the giants before him. A century before, the Swedish botanist Karl von Linné had tried, as a monumental act of religious devotion, to work out the relationships of all the living forms on earth. By doing so, Linné had hoped to glimpse the plan of the Creator, the meaning of life, much as saints and scholars looked for cosmic lessons in the relationships of all the verses, chapters, and books of the Hebrew and Greek Bibles.

  Linné, who wrote under the Latin name Carolus Linnaeus, divided life on earth into kingdoms, kingdoms into classes, classes into orders, orders into genera, and genera into species. It was a system so beautiful and so convenient that all Western naturalists adopted it, although as they discovered more and more species they had to add categories. (Today the major headings are kingdom, phylum, class, order, family, genus, and species.)

  Linnaeus’s system is often drawn as a tree of life. The trunk of the tree divides near its base to form kingdoms, and each great trunk divides again and again into ever-finer branches and twigs: into species, subspecies, races, varieties, and, at last, like leaves on the twigs, individuals. We depict the order of life, in other words, as a family tree, a genealogy, in which the branches trace back to a common trunk. Every living thing is related, whether distantly or nearly, and every animal and plant shares the same ancestors at the root.

  We have grown so accustomed to this view of life (since Darwin) that a diagram of the Galápagos finches on their evolutionary tree suggests to us instantly a family history, with a single ancestral finch multiplying and changing generation by generation so that there are now, for the moment, thirteen branches.

  But that is not how Linnaeus himself saw his system. To him, and to other pious naturalists of his generation, the myriad relationships and family resemblances that Linnaeus used to bring order to nature did not represent anything like a genealogy of descent. Rather they represented the plan of God, who created the species in a single week, as described in the first pages of the Hebrew Bible: “And God created great whales … and every winged fowl after his kind: and God saw that it was good.”

  Darwin could read the story in his copy of Paradise Lost, which he carried with him on all his inland travels. Every kind of living thing was created in that one momentous week. It is a magnificent vision, as if the great tree of life had sprouted in an instant, breaking the ground and reaching with every branch to the creating sky; or as if all finches, lions, tigers, and oak trees were born pell-mell from the cornucopian womb of the earth, as Milton paints it:

  Innumerous living creatures, perfect forms

  Limb’d and full grown.…

  And all these perfect forms, being perfect, had changed little or not at all since Creation day.

  In Linnaeus’s vast botanical collections he did notice many examples of local plant varieties, variations on a theme. But in his system these varieties were not half as significant as true species. Local varieties were merely instances in which one of the Lord’s created species had come to be adapted to its particular neighborhood. By definition, this divergence from the original type had occurred since the moment of Creation. Thus varieties belonged to time and to our mortal earth, whereas species were incarnations of the holy thoughts in the mind of God during the act of Creation.

  In his later years Linnaeus wondered about this metaphysical gulf between varieties and species. A few species of plants in his collections, including certain South African geraniums, seemed to have arisen by crossing—by hybridization. Other species seemed to have been bent and changed by the influence of a changing environment into something more distinctive than local varieties: they were so novel that they clearly deserved in his scheme to be called species. Linnaeus did not take this problem much further than hints in his diary and in the later editions of his folios. But he began to wonder if not only varieties but also these species were, as he put it, “daughters of time.”

  While Linnaeus himself wondered about the permanence of varieties and species, his own life’s work, by virtue of its very neatness, seemed to confirm it in the minds of others. To his contemporaries, Linnaeus had brought order to the riotous diversity of the natural world. He had done for life on earth what Newton had done for the stars, planets, moons, and comets in the heavens. (“God created,” they said; “Linnaeus arranged.”) The living things in Linnaeus’s folio volumes of natural history seemed to the naturalists who came after him to be fixtures in the universe, as the stars once seemed to astronomers: never growing or changing, never aging or dying, but shining in place as they had since the day of Creation.

  Not everyone subscribed to this orthodox view of life. Darwin’s own grandfather Erasmus argued the contrary view that life changes from generation to generation, and that the marvelous living intricacies and adaptations we see around us were built up bit by bit, rather than minted all at once. Another who argued for what we now call evolution was the great French naturalist Lamarck. A more obscure heretic was one of Darwin’s teachers, Robert E. Grant. (“No relative that I know of,” says Peter.) Grant was more or less thrown out of scientific society for his belief that living forms change down through the generations.

  Arguments like these were in the air during Darwin’s student days at Edinburgh and Cambridge. Nevertheless, the orthodox view was so well accepted that most naturalists in Darwin’s day, including Darwin, collected type specimens essentially two by two, one male and one female. The type was supposed to be the average, the representative, the typical, a specimen of God’s thought at the moment of Creation. Every detail of every beetle had a sacred message if we could learn to read it; even the type of the lowliest worm had begun as a thought in the mind of God. The most glorious type of all, of course, was our own, as written in the book of Genesis: “God created man in his own image, in the image of God created he him.”

  When Darwin collected finches, mockingbirds, and tortoises in the Galápagos, it was the type he was after: the theme, not the variations. He gathered plants and animals for the Beagle by the same principle that Noah collected them for the ark, two by two. Darwin in the Galápagos was still half in Milton’s universe.

  Besides Paradise Lost, Darwin brought along on the voyage the first volume of Charles Lyell’s Principles of Geology, and although his teachers in Cambridge had warned him to take the new book with a grain of salt, Darwin had devoured it. Lyell argued that although animals and plants on this planet had indeed been created by God in an instant, and never changed since, the planet itself had been changing restlessly beneath them. Earth’s crust had been rising and falling, building up and eroding everywhere since its creation. At the Beagle’s very first stop, at St. lago, in the Cape Verde Islands of the Atlantic, Darwin had studied the layers of coral that are exposed in the side of the island, and seen such strong evidence of gradual, geological change that he concluded more or less on the spot that Lyell was right. Thereafter everything Darwin saw in his voyage around the coast of South America confirmed and reconfirmed the then-heretical view that the earth’s surface is continually created and destroyed.

  To Darwin the idea that the sculpting of the earth’s surface is still going on seemed new and outrageous. He was fascinated by the thought that in this sphere, small changes can accumulate with big effect. Lyell showed him that the creation and destruction of the earth’s crust is measured not in days but in ages, and that the operation continues today at the same grand, slow pace as ever.

  Mountains moved, rivers moved, oceans moved, but the species of life stayed ever the same. In the second volume of the Princip
les (which Darwin received by mail at a port in South America), Lyell savages Lamarck for suggesting the contrary. “It is idle to dispute about the abstract possibility of the conversion of one species into another,” Lyell writes, “when there are known causes, so much more active in their nature, which must always intervene and prevent the actual accomplishment of such conversions.” Just what those barriers are, Lyell does not say, but he is convinced they exist. “There are fixed limits beyond which the descendants from common parents can never deviate from a certain type.”

  That is why Darwin dropped the finches from two Galápagos islands into one bag. Like Linnaeus he was well aware that different local conditions can carve a species into local varieties. He and FitzRoy had already seen evidence of that in the foxes of the Falkland Islands, and Darwin thought he saw the same thing in Galápagos rats. But Darwin did not imagine that a species would split into different varieties under the near identical conditions and skies of neighboring islands; even if they had, Darwin did not imagine that such varieties would mean anything all that important.

  Nine months later, the Beagle was on a zigzag course across the Pacific and back to England. Darwin was working on a catalogue of his ornithological specimens, including his Galápagos finches and mockingbirds, which all rode home with him in a very cramped cabin under the forecastle. A new thought struck him, and he jotted himself a note. At that moment he was working (alas for legend) on the mockingbirds.

  “I have specimens from four of the larger Islands,” he wrote. The mockingbirds from San Cristóbal and Isabela looked about the same to him, but the specimens from Floreana and Santiago seemed different, and each kind was found exclusively on its own island. “When I recollect, the fact that from the form of the body, shape of scales & general size, the Spaniards can at once pronounce, from which Island any Tortoise may have been brought. When I see these Islands in sight of each other, & possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties.”

  Only varieties. If so, they would fit comfortably within the orthodox view of life. But what if they were something more than varieties? What if the mockingbirds had been blown to the Galápagos from the coast of South America and then diverged from their ancestors, generation by generation? What if there were no limits to their divergence? What if they had diverged first into varieties, and then gone right on diverging into species, new species, each marooned on its own island?

  “—If there is the slightest foundation for these remarks,” Darwin wrote, “the zoology of Archipelagoes—will be well worth examining; for such facts undermine the stability of Species.” Then, in a scribble that foreshadowed two decades of agonized caution, Darwin inserted a word: “would undermine the stability of Species.”

  DARWIN’S COLLECTIONS WERE being talked about even before he got off the boat, because he sent home letters and crates of specimens during the voyage. The Beagle docked in Falmouth in October 1836, and (with a little diplomatic prodding from Darwin, who was not the only explorer bearing plants and animals from the far corners of the earth) some of the world’s most learned naturalists began poring over his finds, classifying them according to the system of Linnaeus.

  On January 4, Darwin donated all of his Galápagos bird skins (and other trophies) to the Zoological Society of London. Within a week, specialists at the society began talking about this new treasure trove. At the very next scheduled meeting, according to the Proceedings of the Zoological Society, the ornithologist John Gould announced that he was particularly excited about “a series of Ground Finches, so peculiar in form that he was induced to regard them as constituting an entirely new group containing 14 species, and appearing to be strictly confined to the Galápagos Islands.” Gould’s description of Darwin’s finches made the next morning’s newspapers. The London Daily Herald mentioned “11 species of the birds brought back by Mr. Darwin from the Gallapagos [sic] Islands, all of which were new forms, none being previously known in this country.”

  Soon after that, Darwin took an apartment in London: he wanted to be near Gould and the other specialists who were working through his collections. In mid-March he visited Gould at the Zoological Society and asked about his Galápagos specimens. The sheet of paper on which Darwin jotted his notes at this meeting is preserved at the Cambridge University Library. Both sides of the paper are full of racing scribbles, which are themselves covered over on each side with one large scrawled word, Galápagos.

  Gould summarized what he had learned so far about the Galápagos specimens. Almost all of the land birds were new, Gould said; they had never been described before, and apparently they lived only in the Galápagos. Three of the mockingbirds were not just local varieties, in Gould’s opinion. No, as Gould had already informed the members of the Zoological Society, they were separate species. This was the verdict that Darwin had conjectured “would undermine the stability of Species.”

  What is more, the tame little birds that Darwin had found hopping around beneath the bushes were unique too. They were not relatives of blackbirds, warblers, wrens, and finches, as Darwin had thought when he bagged them. They were all finches, a strangely diverse group of finches, and they were all unique to the islands. Darwin squeezed in Gould’s names for them on the back of his notepaper, down at the very bottom.

  That was the fabulous moment—not out on the islands but indoors in a cluttered office in London. Or rather that was one in a swift series of moments, of intellectual shocks, that set Darwin reeling as expert naturalists told him more and more about his finds. The giant tortoises are unique to the Galápagos as well. So are the marine iguanas, Darwin’s “imps of darkness.” So are the very bushes and the cactus trees. Species after species in the Galápagos bears a family resemblance to relatives on the mainland of South America but are clearly distinct from anything ever found there. Year after year these revelations fanned the ember of Darwin’s secret thought. To Darwin all these species, marooned in their lonely archipelago, had diverged from their ancestral stocks and then gone right on diverging. They had broken the species barrier.

  Darwin’s fossils from South America turned out to be exciting too, although while he was digging them up and crating them he had wondered if old bones were worth the work. Many of them proved to be extinct relatives of living forms. The continent of South America is the home of the armadillo, the llama, and the capybara, which is a rodent the size of a hog. Among the fossils that Darwin had found were a giant armadillo, a giant llama, and a rodent the size of a rhinoceros. These fossils helped to confirm what Lyell and other geologists had already guessed from finds in Australia. There is a “law of succession” that links the living to the dead, the same law that links the fossils of one stratum of rock to the fossils in the strata below.

  If the giants he had found in the earth were ancestors of the animals he had watched on top of it, then Darwin could read in them the same thrilling story he read in the Galápagos. Whether he followed his finds horizontally, tracing the spread of animals and plants across the surface of the earth, or vertically, tracing them down into the abyss of time, the same secret stared back at him.

  “It was evident that such facts as these, as well as many others, could be explained on the supposition that species gradually become modified,” Darwin wrote long afterward; “and the subject haunted me.” That spring he made his first jottings about evolution in a red notebook he had started on the Beagle. And that summer he opened his first notebook on “Transmutation of Species.”

  In the memoir that he worked up from his diary, the Journal of Researches (better known as The Voyage of the Beagle), he writes at some length about the birds of the Galápagos, especially the finches, “the most singular of any in the archipelago.” He notes in a famous passage that “in the thirteen species of ground-finches, a nearly perfect gradation may be traced, from a beak extraordinarily thick, to one so fine, that it may be compared to
that of a warbler. I very much suspect, that certain members of the series are confined to different islands.…”

  What follows next is the first published hint of his secret theory: “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that, from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”

  Then he breaks off: “But there is not space in this work, to enter on this curious subject.”

  Of the Galápagos as a whole, he concludes his memoir with this tantalizing and magnificent line: “Hence, both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this earth.”

  Two years after the voyage, Darwin married, and he and his wife, Emma, took a house in London. He fell ill. His stomach was seldom “right” for a whole twenty-four hours. He suffered from anxiety, boils, dizziness, eczema, flatulence, gout, headaches, insomnia, and nausea. He spent the rest of his life pursuing his researches and writings in the bosom of his growing family, first in London, then in the rural privacy of Downe, Kent.

  Only after his electrifying meeting with Gould had he realized how interesting the Galápagos finches might be to him, since they are by far the most numerous and the most diverse land birds in their remarkable archipelago. He had asked permission to look over the finch skins in the collections of Captain FitzRoy and other shipmates, including his own servant on the Beagle, Syms Covington. The captain and the servant had labeled their finches island by island, for the ironic reason that they were not collecting the birds according to a scientific theory—they were just collecting. From their neatly labeled specimens, Darwin tried to figure out where he had caught each of his own finches—and he failed.