What does all this mean for us? That was the instant thought of the Origin’s readers in 1859. For answers they looked backward. They thought in terms of the past, of history, of ancestry, of lines of descent, as Darwin does in his book. All of Darwin’s books are primarily about history, even where they address the present. That is the program of inquiry established by Lyell: the present is the key to the past. Lyell places that emphasis in the title of his masterwork, Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth’s Surface, by Reference to Causes Now in Operation.
Darwin’s readers were shocked by what they glimpsed of our past condition in the Origin, and later The Descent of Man (also titles that look backward). But today, when we consider Darwin’s process in action, we can see that our condition in the present is shocking too. We have barely begun to digest the Darwinian implications of the present moment; we have barely begun to glimpse the degree to which we are all involved in the action and reaction of evolution right now. In this sense the revolution that Darwin began in 1859 is not yet completed.
In the Origin, Darwin describes the record in the rocks, the virtually endless series of vanished and evaporated vistas, all those long lost ages of unexamined life, as “a history of the world imperfectly kept,” of which we possess only one volume. “Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.”
But we see little of the present as well. The studies of the evolution watchers are like a few scattered chapters and lines of a vast story that is now taking place all around us. Here once again Darwin’s finches can serve us as symbols, heralds, and standard-bearers of events that are taking place everywhere we look and everywhere we have not yet looked. Once again the islands are showing us what is going on in our own backyards.
The changes now in progress make the whole planet and all that lives on it a single colossal demonstration of the power of Darwin’s process, the kind of demonstration we think of as the domain of Darwin’s islands. Many lines of life on Earth, including our own, are now living through days as charged with change as the days when the last dinosaurs died, or the first finches alighted in the Galápagos.
These changes are being driven by the rise of our own kind. As the dominant species on the planet, we are both an effect and a cause of evolution—masters and slaves of Darwin’s process. We almost dread to contemplate this relationship, just as Darwin’s contemporaries feared to look into the relationships his theory unfolds in the human past. But that is what the work of the evolution watchers, from the very earliest to the very latest studies, is urging us to see. The action in the present is a manifold and all-embracing evolutionary event, and the finches in their last precarious solitudes, their islands’ islands, are in a peculiar position to illuminate what it means for us.
All times seem special to those who live in them. But it is neither parochial pride nor shortsighted despair to say that our time is more special than others. According to the fossil record, only five times in the past six hundred million years has there been such abrupt havoc in the biosphere. Only five times have so many twigs and branches been lopped from the tree of life at once. It happened at the end of the Ordovician period, at the end of the Devonian and the Permian, at the end of the Triassic and the Cretaceous; and now it is happening again. We are altering the terms of the struggle for existence: changing the conditions of life for every species that is coeval with our own.
Never before was such havoc caused by the expansion of a single species. Never before was the leading actor aware of the action, concerned about the consequences, conscious of guilt. For better and for worse, this may be one of the most dramatic moments to observe evolution in action since evolution began.
Chapter 20
The Metaphysical Crossbeak
How astonishing are the freaks and fancies of nature! To what purpose, we say, is a bird placed in the forest of South Cayenne, with a bill a yard long, making a noise like a puppy dog, and laying eggs in hollow trees? The toucan, to be sure, might retort—to what purpose were gentlemen in Bond Street created? … There is no end to such questions. So we will not enter into the metaphysics of the toucan.
—SYDNEY SMITH, 1825
Metaphysics must flourish.
—CHARLES DARWIN, 1838
We stand among the other animals on this planet with a strange feeling of kinship and difference. We see so much farther and wider than they can that the eyes of Darwin’s finches, in the famous engravings from his voyage, stir us to pity. They do not know where they come from, they do not know what they are, and they do not see where they are going, though birds’ eyes are as sharp as our own, and though they have the advantage of their wings.
From the beginning we have tried to understand what makes us so alike and unalike: to explain so unequal a distribution of powers. In the caves of Lascaux there is a painting of a man with a beak. In the tombs of the Pharaohs there are bas-reliefs of more bird-man hybrids, the gods Osiris, Horus, and Thoth. Walking and talking in the Athenian Academy one day, Plato defined humankind as the two-legged animal without feathers. The next day, they say, Diogenes dropped by the Academy with a plucked chicken.
We are a species that has become aware of itself—which is not really, when you stop to think about it, such a very grand claim. Students of human evolution are still debating what led to this departure. Sometimes a species is carried into new territory by a journey, like Darwin’s finches, borne to their volcanoes by a long flight over the sea. Sometimes it is not a journey but an invention, a novel adaptation, that opens the new world. The invention of jaws in the Ordovician period, five hundred million years ago, may have given polychaete worms the advantage over priapulid worms. Hinged jaws were a turning point for armored fish, cartilaginous fish, and bony fish in the seas of the Paleozoic, and for the whole vertebrate evolution that followed, from amphibians to reptiles, birds, and mammals.
A modest shift in the position of a few teeth, a matter of millimeters, may have led to spectacular adaptive radiations in certain lines of carnivores. In the beaks of birds, the addition of one extra hinge or flange may have led to the radiation of almost one hundred species of blackbirds, from Alaska to the tip of Argentina.
With crossbills, the elegant experiments at the University of British Columbia have shown how the first slight twist of the mandibles could have made all the difference. That mutant twist was manifest destiny. It allowed the bird to get at seeds no other bird in the forest could eat. It opened vast lands for conquest and set off a cascade of secondary adaptations. The hinge of the jaw grew specialized to allow it to move from side to side, as well as pivot up and down like normal beaks, the British ornithologist Ian Newton notes in his book Finches. The jaw muscles became asymmetrical to help tug the mandibles from side to side. The feet grew bigger and stronger, which helps the bird hold on to a cone while wresting the cone scales open with its beak. The crossbill also evolved new instincts, elaborate routines, and subroutines, as Newton explains:
A bird first wrenches off a cone in its bill, carries it to some firm, horizontal branch, and clamps it between one of its feet and the perch. It then works the tip of its beak behind one of the scales, while the cone is held so that it points forwards and slightly to one side. A bird with the lower mandible deflected to the right holds the cone in its right foot, and vice-versa.… The lower mandible then moves sideways toward the body of the cone, so that the scale is raised by the tip of the upper one. The seed, once released, is scooped out by the protrusible tongue.
Often the crossbill does all this work, straining and heaving, while hanging upside down in the tree.
According to present thinking, the departure of our own line began six or seven million years ago in the African savanna, when our ancestors switched from what is known in the jargon as brachiation—swinging from tree branch to tree branch—to walking on the ground. That change led to a cascade of adaptations, as with the cro
ssbills. One of the first was the trick of rearing up and walking on our hind legs, which the evolutionist Richard Leakey calls “one of the most striking shifts in anatomy you can see in evolutionary biology.”
We walked upright for millions of years before the next great evolutionary change, the expansion of the brain and the skull. This expansion, which began to take off about two million years ago, represents, like the shift onto hind legs, one of the most dramatic evolutionary changes in the fossil record. Since the days of Lucy in Hadar, the human brain has tripled in size. Meanwhile we also evolved an opposable thumb, which is the chief mechanical difference between our hands and the hands of our nearest living relatives, the orangutans, gorillas, and chimpanzees. We modified the hyoid bone, which gave us the gift of full-throated speech. There were other more cosmetic changes too, including the shortening of the muzzle, the shrinking of the jaw and the teeth, and the sculpting of the nose.
Somewhere in this sequence of adaptations (perhaps at the very start of the brain’s expansion), there occurred the heightening of consciousness that we ourselves as members of the species consider distinctively human: the character that Diogenes was wordlessly pointing out to Plato. It is this character, more than the thumb, the voice, the hind-legged stance, or the human face, that we feel sets us apart from other living things on the planet. To us, a man or woman who has lost hands, legs, voice, or even face is still a human being, but a body that has lost consciousness forever has dropped from the human experience.
Some of this evolutionary action took place at the same time that Darwin’s finches were radiating in the Galápagos. It also happened at about the same rate, and—despite the prejudices of human pride and power—it carried our line, in physical terms, no further from our neighbors than the finches have diverged from one another. As a sop to pride, taxonomists have placed us in a separate family from the other primates. But anatomically, chimpanzees, orangutans, gorillas, and humans are as closely related as Darwin’s finches, or the two dozen species of crossbills, or many other young adaptive radiations. Chimpanzees appear to be our closest living relatives: by current estimates, ninety-nine out of every hundred genes are identical. In other words, we are as close to chimpanzees as a ground finch is to a tree finch.
“Man in his arrogance thinks himself a great work, worthy the interposition of a deity,” Darwin scribbled in one of his first secret notebooks, when he had become convinced of the fact of evolution. Darwin felt it was “more humble & I believe true to consider him created from animals.” Our gift of consciousness is a mystery, one of the greatest remaining mysteries in biology—but it is no more of a miracle than a beak, a feather, or a wing, and it is made by the modeling and molding of the same living clay, through the same process, Darwin’s. Why should we assume that consciousness is unique to our kind in anything but degree? “It is our arrogance,” Darwin wrote in his notebook, “it is our admiration of ourselves.”
Someday neurobiologists hope to close in on the origin of consciousness in the brain. They will find some twist in the neural networks of the frontal lobes or the cerebral cortex that leads, as it grows, to a kind of infinite recursion, rather the way mirrors tilted at the proper angle will begin to reflect each other. The discovery of the physical basis of this secret may still be far away, or it may be nearer than we think. But as with the crossbill, it will probably turn out to be a twist in equipment that we otherwise share with many other species: a twist that heightens the trick of recursion and enables us to do tricks with our awareness of the world that other animals cannot do, to pick things up that no other species can handle.
Perhaps when biologists have sequenced the whole of the human genome, and deciphered many of its messages, some slight difference between our genes and the chimps’ may throw more light on this mystery and help us understand the cerebral kink that has made us the metaphysical crossbeak.
One of the gifts of our heightened consciousness is the ability to make new tools. We can build our own adaptations and evolve, in effect, within our own lifetimes. We once imagined this gift, like consciousness, to be uniquely human; Benjamin Franklin called our kind Homo faber, Man the Toolmaker. But Bonobo chimps make and use tools too, and so does the woodpecker finch of the Galápagos, which picks and chooses cactus spines to augment the beak it is born with. Here again we differ from other species only in degree. The difference began to widen thirty or forty thousand years ago, long after our brains and skulls had expanded to their present volume. Suddenly, in southern France and northern Spain, we began carving bone and knapping flints so cleverly that the tool kit of even a single hunter surpassed the beaks of all Darwin’s finches: bone awls sharper than a sharp beak’s, stone chisels bigger than a big beak’s. By now, of course, in our own moment in the evolutionary play, the competitive advantages of our toolmaking are on display all over the planet, even in the Galápagos, where members of our species propel themselves on webbed feet beneath the parrot fish; fly higher and faster than the boobies and frigatebirds; skim the sea faster than the dolphins; and go to sleep each night far out on the water, where the lights of yachts now shine in the eyes of birds along the cliffs like newly risen stars.
With our heightened consciousness we have been able to carve out more adaptive niches more rapidly than any other species on the planet, radiating out of Africa to every continent and both poles. We can do this because our suite of adaptations—the big conscious brain, full-throated speech, and opposable thumbs—allows us to invent new ways of living, not only new tools but new foods, clothes, and shelters, and to pass them on to others with unprecedented speed. Once again the difference is one of degree, as the biologist John Tyler Bonner argues in his recent books The Evolution of Culture in Animals and Life Cycles. In Great Britain, blue tits have learned to peck through the aluminum caps of milk bottles on doorsteps and get the cream. People actually saw the trick spread from house to house and block to block as blue tits across the country learned from watching one another. For a while the blue tits had an easier life than Darwin’s finches wrestling with Tribulus, or crossbills with green pinecones. But soon the milk companies, like the plants, will start putting out their treasures with tougher caps, if they have not done so already.
A famous young macaque monkey named Imo, on an island off the coast of Japan, learned to wash sweet potatoes in the sea before eating them. She also learned to separate wheat kernels from sand by cupping them in her hands and dipping them in the water. The other macaques on the island picked up both these tricks by copying Imo.
Recently investigators in Italy allowed an octopus in a tank to watch through a window as another, trained octopus performed a trick, choosing a red ball or a white ball. If the trained octopus chose the correct ball, it found a small piece of fish behind it; if it chose the wrong ball, it got an electric shock. The experimenters videotaped the untrained octopus. It was watching closely, following the action with its head and eyes, time after time. Afterward, when it was given the same choice, more often than not, it chose the correct ball.
In a social species like ours the benefits of learning from one another are so great that they may have helped to drive the modification of the hyoid bone, toward better and better vocalization, leading at last toward speech; and the expansion of the brain may have been driven in part by the increasing benefits of and demands of language. Language became a tool that allowed us to teach not only each other but even ourselves, after we found a new use for the opposable thumb and fingers. “When you write,” says Annie Dillard, in The Writing Life, “you lay out a line of words. The line of words is a miner’s pick, a woodcarver’s gouge, a surgeon’s probe. You wield it, and it digs a path you follow. Soon you find yourself deep in new territory.”
The ability to learn new tricks from one another is called cultural evolution, and clearly it is not unique to our kind. Perhaps the most haunting glimpse of cultural evolution in another species comes, once again, from Darwin’s finches—but from a species that Darwin neve
r saw.
There is a solitary finch species that lives outside the Galápagos. Its home is on the speck of land that lies nearest the archipelago, 630 kilometers (almost 400 miles) northeast, a little place called Cocos Island.
Like the Galápagos, Cocos is volcanic. The island has virtually no coast: it is walled by steep cliffs as much as 180 meters high, almost all the way around. No human beings have ever tried to raise families there, and it is unlikely that anyone will ever try, because the place is almost as offputting in its way as Daphne Major. Unlike Daphne, however, it is drenched with rain almost every day. The island receives an astonishing 7 or 8 meters of rain a year, and lush rain forest grows from the summit to the very edge of the cliffs.
The Beak of the Finch Page 33