Prologue

Man without writing cannot long retain his history in his head. His intelligence permits him to grasp some kind of succession of generations; but without writing, the tale of the past rapidly degenerates into fumbling myth and fable. Man’s greatest epic, his four long battles with the advancing ice of the great continental glaciers, has vanished from human memory without a trace. Our illiterate fathers disappeared and with them, in a few scant generations, died one of the great stories of all time.          the anthropologist LOREN EISELEY (1907-1977)

He who calls what has vanished back again into being, enjoys a bliss like that of creating.          the historian BARTHOLD NIEBUHR (1776-1831)

Navajo Reservation
Day 1,
about 2:00 A.M.

WHERE DO WE COME FROM, we humans? Darwin called this "the great subject." Even five-year-old children sometimes ask this question.

          That we ask such a question at all is a testament to human consciousness. I somehow doubt that the desert animals around here, including the two bats cruising overhead, spend much time contemplating their origin and destiny. We humans love to spin "what-if" scenarios stringing together various concepts from our memories. With them, we attempt to explain the past and forecast the future. However, our consciousness can only be as good as the mental images we conjure up. And memories are surprisingly fragile.

          Beginnings, alas, have usually been lost. Though language gives us a great advantage over our fellow apes in putting our thoughts in order, word-of-mouth doesn’t work very well, down through the generations. The Navajo Indians of Arizona, on whose desert reservation I am now nursing a cup of coffee in the moonlight, wandered down here from Alaska and northwestern Canada only 500 years ago, hunting and gathering along the way. They arrived just in time for the sixteenthcentury Spanish explorers to "discover" them. Their grandchildren were undoubtedly entertained with stories of the old country and the journey, just as my grandfather Leebrick told me of coming west in a covered wagon from Virginia to Missouri in 1882. Yet, only 20 generations of grandparents later, the Navajo have now forgotten all about their ancient home in the Yukon.

         The Navajos are not unusual in such forgetfulness. For most people in most times, there has probably been little notion of history: they think that the world has always been pretty much like it is now. Except, of course, for a Creation; unfortunately, there are hundreds of creation myths around the world and there is very little consensus.

          Writing changed that status quo. It gives the societies that possess it a window into the past, though a narrow one. It enabled the Jews to know, 70 generations after their dispersal, that they once constituted an ancient nation in the Middle East. In the part of the world where agriculture first blossomed, historical records go back 200 generations in some places; empires and other plagues can be seen to come and go. Once the idea of a changing world developed, contemporary clues took on new meaning. In the nineteenth century, the notion that there had been an ice age arose when geologists tried to explain boulders that had been transported long distances from their origins, the strange shapes of some valleys and the parallel scrape marks on their bedrock. They endured scathing skepticism when they reluctantly proposed that mile-high sheets of ice had moved down the valleys and covered up much of northern Europe, Asia, and North America. "No common sense," critics complained. But they were right. There may, in fact, have been several dozen ice ages.

          Now we can reconstruct the past in various ways. The French and Spanish cave paintings give us a glimpse of life 1,100 generations ago at the height of the last ice age. The remaining preagricultural societies help give us a picture of what life might have been like 400 generations ago, after the ice melted but before settled agriculture got started. For the present-day Inuits (Eskimos), the last ice age hasn’t ended; their traditional life styles help us imagine how our ancestors might have existed on the ice age frontiers where skillful hunting was necessary to get through the winter.

          Science is now recovering the lost facts about human origins, sketching in dates, places, and anatomical changes via the stones and bones that survive. While only a limited view of prehistoric cultures, it has radically revised our preconceptions. The brain has been rapidly enlarging for about 100,000 generations, 99.6 percent of whom lived a hunting-and-gathering way of life before agriculture, civilization, and science came along. We are today using that brain for things entirely different than the tasks that shaped its evolution.

         We have found that our roots reach back to a world, of which little can be seen today. To understand ourselves — our pleasures, fears, abilities, and consciousness — we must understand what shaped us: our ancestors’ way of life and the challenges they faced.

          Though it might be a coincidence, the human brain has been enlarging ever since some crazy fluctuations in the Earth’s climate started to occur about 2 to 3 million years ago. After many millions of years of a cooling and drying trend, the Earth began to build up ice in its northern latitudes, covering as much as 30 percent of the land surface; this was an unusual development because the earth has been without polar icecaps for 99 percent of its history. About every 100,000 years, some of the accumulated ice melts off; then the drift back to ice resumes. This has been going on for several dozen cycles, each icy period pushing the more highly selected frontier population back into competition with tropical populations, each warm period providing an opportunity for the survivors on the frontiers to gradually enjoy a baby boom, then fading into another squeeze-and-expand cycle.

         During this odd 2 to 3 million year period since the climate began to fluctuate, one species’ brain underwent what was, by the standards of evolutionary biology, an extraordinarily rapid growth. For some reason — and the rapidity suggests that it was a compelling one — our brains more than tripled in size. That’s 3.6 times larger than the brain that sufficed for the other apes during the same time period. Why?

          That’s perhaps the key question, and it has emerged after millennia of humans sitting out at night under the stars, wondering what life is all about, from whence we came. The "great subject" is what stirs my thoughts tonight, sitting here above the Colorado River in the moonlight, perched on a great slab of sandstone in the desert and warming my hands on a coffee cup. The nearly-full moon is about to set in the southwest and, so close to the mountainous horizon, it appears huge and yellow to me, dominating all else.

         Yet a moment or two after touching the mountains, the moon is gone. The stars come out. The hour is late enough on this summer night that some of the winter constellations can be seen rising in the eastern sky.

         Many minds, stimulated by similar sights, have pondered our origins but pure thought cannot make much progress. Modern humans have many more facts and concepts to aid their contemplation, and we better understand the nature of consciousness itself, why and how we think.

         We have arrived at the refined version of the question, "What caused brains to enlarge, to distinguish humans from apes?", only because a few intermediate things happened to aid our thinking, such as writing and science. Writing made possible the accumulation of facts over the generations. A settled life allowed techniques to progress.

         Facts and techniques aid human consciousness in its attempts to make up stories: we take mental images from past and present, string them together with various future possibilities, and wind up with "what if" scenarios. We then "think it over," trying to see what might go wrong with a plan — and so we discard most such plans before ever acting, thanks to our quality judgments. We make choices, and live with them.

         This ability to simulate the real world inside our heads gives us an enormous advantage, both keeping us out of trouble and allowing us insights which lead to new ways of doing things. To call them plans is to emphasize only one of their uses; I just call them scenarios. We imagine doing something, see how it plays. We like to make up stories, see how they sound.

         Science, too, accumulates facts and techniques, but by making consciousness into a group activity, refines it even more. A scientist struggles to comprehend the known facts and ideas about some concept, thinks up a scenario or equation that seems to account for most of the known facts, and publishes this theory for everyone to see, and then we all (originator included) attempt to poke holes in it. In so doing, we evolve a better explanation. This back-and-forth fitting procedure (similar to a carpenter setting a door into a frame), rather than the usual textbook nonsense about precise logical deduction, is what the "scientific method" is all about. Creating a scenario may be best done inside a single head; trying to find exceptions to the scenario is surely best done by many heads.

         Pondering this, I can see that the time is coming — and soon — for a comprehensive biological theory of human origins. Only in this last generation have most of the known facts about human prehistory emerged. During the same 25 years, our knowledge of animal and human brains has also expanded enormously: we understand more about how mental images are formed, more about the fragility of our memories and how they can fool us, more about our feelings, more about how our brains influence the health of the rest of our bodies. We neurophysiologists can now even conceive mental images about the inner workings of the human brain itself — and even construct scenarios for how the brain makes up scenarios. A lot has happened. In very fundamental ways it affects how we think of ourselves — and on an everyday basis, not just when we find ourselves contemplating the moon setting behind mountains on a starlit night, as the moonlight dims and the Milky Way begins to emerge from the darkening sky.

         We still don’t know why those evolutionary changes occurred, but we’re getting close to providing a detailed scenario that would seem to answer that crucial question about brain size — and a few related ones as well. Various experts now know enough to make some educated guesses about how humans happened, to spin some scenarios that fit the facts — if one can get them to talk about it.

Our new [anthropological] origin beliefs are in fact surrogate myths, that are themselves part science, part myth.... People clearly want to be free to choose their evolutionary origin stories. Bear this in mind as you read this and other accounts of human evolution.        the archaeologist GLYNN LLYWELYN ISAAC (1937-1985)

Lee’s Ferry aerial view looking south along Marble Platform as the Colorado River cuts into it, from Leonard Thurman’s Grand Canyon River Running.

Marble Platform Overlook
Day 1, Sunrise

Some distance upriver from the Grand Canyon, the Colorado River begins its descent through the layers of our biological history. This happens in a narrow canyon, somewhere just below where I am now.

Hiking away from the road into the mountainous desert, I felt the fresh breezes of dawn touch my face. As I approached the precipice, the view opened to the north, revealing a majestic horseshoe of cliffs, the cornucopia out of which the flat Marble Platform seems to flow.

I am now sharing the viewpoint with four birds preoccupied with their early morning chatter, quite oblivious of me writing in my river diary. The morning sun is shining on the cliffs across the way. The shadow line of the new day starts to creep across the Marble Platform toward me as the earth slowly rotates, taking me with it.

Morning in the painted desert: the incredible red-orange and blue-gray of the rocks, enhanced by the special warm light of the sunrise, the spotlighting, and the shadows. The best time of day, worth the all-night journey to get here on time.

The Colorado River, which carved the Grand Canyon, is out there somewhere in the middle of the horseshoe, heading down toward its most grandiose achievement to make a few more minor alterations in the Canyon’s sculpture. The Colorado is not a small river but one of the largest in North America. Yet even from this grand viewpoint there is no river to be seen.

Back up the road, I glimpsed the river by moonlight, heading this way. Yet the Marble Platform seems devoid of rivers, as well as of the trees, sheep, cattle, fences, cultivated fields, houses, towns, and everything else that tends to grow up around rivers. If I sit so that the edge of the cliff obscures my view of its lone highway, the Marble Platform and its surroundings look like a scene from a planet unscarred by humans. Were it not for all the cactus and birds near me on this cliff, I’d say that the view was of a planet untouched by life.

I see only natural scars: the surface of the Marble Platform is interrupted by giant, ragged-edged cracks that descend down into the planet. One crack is the Marble Canyon of the Colorado River, predecessor to its Grand Canyon; the others are the side canyons that lead down to the river, carved by the runoffs of the occasional summer thunderstorms. The river is hidden from this vantage point because it has dug itself a very deep trench during the last 30 million years.

The limestone of the Marble Platform was laid down about 250 million years ago, near the end of the Paleozoic era. The land masses and sea floors were then rearranging themselves into just one big continent, Pangaea, surrounded by one big ocean, Panthalassa. The rock underfoot up here on the overlook was formed about 200 million years ago, early in the dinosaur days of the Mesozoic, when Pangaea was beginning to break up into what became our present set of smaller continents, but before they’d yet wandered very far. As I stood up, I accidentally kicked loose a Mesozoic rock, which promptly fell down toward the Paleozoic. I heard it ricochet down through the ages.

Untouched by life? I can now see that the Platform has a scattering of desert scrubs, but even the local bedrock has been made by life itself. Limestone forms at the bottom of the ocean when the little floating animals die and their calcium-containing bodies sink to rest. And even the other half of the calcium carbonate in limestone was largely contributed by life: the carbondioxide, CO2, breathed out by animals may, if not recycled by plants, make its way into forming this nice hard rock. Limestone isn’t so much an inanimate object, like the lava pushed up from the depths of the earth, as it is ex-animate.

The road ahead rises and falls a little as it works its way around some of the minor hills in what, from up atop the cliff, looked like a flat surface. Another misapprehension exposed. I find that looking up from the road is very distracting, since I am surrounded by the horseshoe of cliffs, their layers a pale pastel rainbow of colors dominated by reds and browns. There is no hint of the dramatic in the desert floor. Then, at the bottom of one of those little dips in the roadway, the highway swings to the left around some rocks — and right before me appears an enormous crack in the earth, as wide as a superhighway corridor. There is nothing subtle about the way the Canyon greets its guests.

To the early Spanish explorers coming up from the south, confronting the canyon must have been a tremendous shock, since they were not forewarned by the almost aerial view of the cracks that I glimpsed from atop the cliffs. Some conquistador’s horse probably stopped so suddenly at the sight of this gaping hole that the rider was in danger of pitching forward over the poor animal’s head. Once the riders collected themselves and ventured on foot to the edge, they would have seen that there is water in the midst of this desert; indeed, quite an amazing amount of water: probably the largest river they’d ever seen. But getting down to the water is like descending the outside of the Statue of Liberty from the torch to the waters of New York harbor. Then there is the little problem of getting back up again. Such is an explorer’s life. Fortunately, I know the easy way down to the water. It’s at the base of the horseshoe, a mere 7kilometers upriver from here, at the old nineteenth-century river crossing place called Lee’s Ferry. It is about the only easy way down to the river in the entire state of Arizona. All the long float trips down the river must cast off from that one beach.

Lee’s Ferry: the only beginning. Just as we count time from the beginning of the universe, so is Lee’s Ferry the place from which all distances along the Colorado River are reckoned. Indeed, when they ran out of fancy Spanish, Hindu, and local Indian names for all the subcanyons of the Grand Canyon, they just gave names such as 75 Mile Creek and 220 Mile Canyon, using the distance downriver from Lee’s Ferry to describe the place.

The Old Navajo Bridge, from Leonard Thurman’s Grand Canyon River Running web pages.

The ferryboat was replaced in 1928 by the Navajo Bridge. This two-lane arch bridge looks like an antique. It peaks up in the middle just like the earliest iron arch bridges in England. It is an exaggeration to say that it looks like a pair of hands folded in prayer, meeting above the river, but the hinge in the middle of the span is designed to allow it to rise up higher when the afternoon heat expands the steel.

To the properly observant, the bridge could serve as a giant Texas-sized thermometer: the hotter it gets, the more peaked it looks. One drives slightly uphill to the middle, crosses the peak, and drives down the other side. But I stop, straddling the peak. I turn off the motor. Silence. It’s not my natural perversity that makes me halt, merely the view. The signs prohibit stopping, but I have yet to see another vehicle on the highway at this hour.

It is as if I were the only person on this world, a visitor exploring a strange and beautiful planet, seeing occasional relics of an ancient civilization and its primitive technology, listening to the sounds of its winds and birds, smelling its natural odors without the overlay of civilization’s everyday pollution. There is a breeze flowing upriver, brushing past me as I lean over the old railing. A pleasant breeze, indeed.

Thirty stories below is the Colorado River. The canyon is about as wide as it is high. A box canyon. The precipitous walls seem brown; the river appears a dark mint green in this shadowed light. Along both sides of the river, clumps of greenery grow on the occasional sand beaches.

Rivers rarely flow in a straight line for very far, given their tendencies to meander, but for a kilometer or more in each direction from the bridge, I can see along the crack until the river bends out of sight. The water is flowing much more quickly than I would have guessed. Something splashes near the left shore, and I look carefully for more activity. Beaver? Rocks falling? Fish jumping? But it isn’t repeated.

That’s a different world down there. Many birds fly over the river, undoubtedly collecting insects. Sometimes the swallows (or are they swifts?) ascend halfway up a canyon wall to disappear into a hole, probably to feed a hungry family. Up here on the bridge, one is a spectator, a passer-by in the manner of an airplane passenger examining the terrain below. I’ve come closer to the river than when I was up on the cliff, but I’m still detached. Literally, above it all. Only the breeze, the smells, and the faint sounds of the river below serve to make me feel a part of the river environment.

Such distancing often happens today. Our civilization takes us far away from the elementary sounds and experiences of our hunting and gathering ancestors, leaves us out of touch with our ancient preagricultural roots. Evolution shaped us from prehumans to humans over at least 100,000 generations; the 400 or fewer generations that we’ve spent away from the hunting and gathering life style probably hasn’t changed our gene pool very much. Our deep roots are to ice-age tribes; although we seem extraordinarily flexible and adaptable, our civilized behaviors are inevitably an overlay, a frosting that may sometimes be spread too thin if it is not well anchored in classic ice-age behavior patterns. Getting away to the wilderness occasionally can be a way of watering those roots, firming up the connection to the overlying high culture, preventing dislocations.

The sun has finally peeked over the top of Echo Cliffs. The shadow line has reached the canyon. Scattered clouds tower over the cliffs, backlit by the rising sun. Mountain sunrises and desert sunrises have always been my favorites. And this is mountainous desert. By the time the sun is overhead today, a group of us should be floating down the river beneath this spot. And probably looking up at this bridge. Tourists will wave at us. The Navajo Bridge will be about the last we’ll see of civilization’s monuments for two weeks. There are no roads reaching the river for 225 miles, no fences, no billboards. It’s a wilderness, totally unlike the Grand Canyon glimpsed by millions of tourists from up on top, behind crowded railings.

The best we can do — if we want a journey backward in time, to see the mileposts in the evolution of intelligent beings, to take a voyage to the origins of life itself, if we want to try to piece it all together — is to take ourselves to the bottom of the Grand Canyon. There we will find rocks of great age, we will find fossils, we will find the dwellings of Stone Age peoples. We will find the land much as our ancestors experienced it, during all those untold generations when prehumans were being shaped into humans. The dimly remembered world from which we somehow took flight.

Such a journey requires some time. The best way is to float down the Colorado River, taking several weeks to investigate the rapids by boat, the side canyons on foot, the waterfalls by inundation. With, of course, the right companions.

Day 1

Tell me to what you pay attention and I will tell you who you are.      JOSE ORTEGA Y GASSET

What was left was the incredible view. This is indeed painted desert country. Not for their edibility are the lower rockwalls called the Chocolate Cliffs. The dark red ones above them are the Vermillion Cliffs and, somewhere unseen over the horizon, are Kodachrome Basin and Rainbow Plateau. Reds and oranges and browns occur in various combinations, often streaked with iridescent metallic colors. Different shale layers are colored blue, purple, green, pink, gray, maroon, and brown.

This panorama forms a horseshoe encircling the view back upriver. The river takes such a sharp S-shaped bend just before Lee’s Ferry that one can hardly see its canyon. Looking upriver seems a dead end. The Colorado River thus appears to come out of nowhere, arising fully fledged from the base of the cliffs.

Setting off the red cliffs from the racing green water is a white high-water line bordering the river, much like the lines that delimit other highways. All of this contrasts with the greenery along the Colorado’s shoreline, the super-green of the willows and tamarisk. People who haven’t experienced the grandeur of the canyon often refuse to believe a picture of it — they assume some trick of color photography. You just have to see it for yourself.

The Colorado moves along at a good clip, generating a welcome breeze. We often don’t row but just float along. To keep up with us, someone would have to jog at a good pace along the shoreline. Ashore we were uncomfortable in the hot, still air as we waited for the last of the packing to be done and the last calls to be made from the lone telephone booth with its eavesdropping lizards. Lizards are advanced animals that have the good sense to take shelter from the midday sun.

Now we have the breeze. The windwaves pitter-patter against the bottom of our boat as we pass the confluence with the Paria River. The Paria comes down from Utah, draining the waters of Bryce Canyon into the Colorado.

There were lots of lizards along the banks of the Paria, jerking their tails about, scurrying among the rocks carried down by the Paria in its more forceful moments. Many of the lizards seem to wear collars, a dark ring encircling their necks. Surely they were therefore Black Collared Lizards. But no, I find that they were Yellow-backed Spiny Lizards. So says the river-runner’s blue bible, Larry Stevens’ invaluable waterproof book The Colorado River in Grand Canyon: A Comprehensive Guide to its Natural and Human History. Authors who have been published in hardcover, paperback, and book club versions now have a new ambition: to see a waterproof edition of their works, truly durable.

All of the Colorado boatmen I’ve met are knowledgeable and versatile, but Larry Stevens carries things to extremes: he’s artist, author, publisher, photographer, biologist, boatman all rolled into one. Mr. Renaissance Man. But, what with his Ph.D. thesis research keeping him too busy, he’s not on the river this summer. Happily, another biologist-boatman, Alan Williams, is on this crew — he caught me up on the progress of his thesis research while we were loading the boats. An ecologist, he studies how cottonwood trees wage psychological warfare on attacking aphids. They make 10 percent of their leaves so attractive to aphids that the tiny insects will fight each other to the death for a standing-room-only spot on a tasty leaf, thus minimizing the damage to the other 90 percent of the leaves. And if you think that’s wild, another ecologist showed that an attacked willow tree releases a "war cry" odor that alerts the downwind willows to the invaders so they can mobilize their tasty defenses in advance. And I used to think that plants were stupid. I doubt that even lizards are that socially-minded.

The lizards are doing pushups. They run around, then they stop and do pushups for awhile. Not only does their head bob up and down, but their whole body with it. This happens when two lizards meet. A lizard will blow itself up to look bigger than it really is, then knocks off a snappy set of stiff-body pushups that would make a army drill instructor proud. The second lizard responds with a similar act of its own. The two lizards then go their own ways, back to the serious business of finding food and mates while the sun shines, before darkness (or too much sun) forces them into quiescence.

Lizards are distant cousins of ours. We shared a common ancestor with them about the time the base of the local cliffs was laid down. The earliest reptiles date back to 340 million years ago, offshoots of amphibians like frogs who were less firmly committed to life on land. The mammals started their own act soon afterward.

THIS BOAT is carrying us down through the ages, the rocks on the left bank getting older by the minute. Indeed, by millions of years each minute. Our vehicle is an inflatable descendant of a dory, crossed with a life raft. Racetrack-shaped like the classic life raft, it is the length of a full-size car and has two inflated crosspieces dividing the boat into three compartments. The rubber (actually neoprene) is stressed to elevate the two ends somewhat, a bow being helpful when crashing into waves, two bows being better than one where rapids may spin the boat around. Two passengers sit forward, two aft, and the boatman with his oars takes the elevated perch in the middle. A rectangular aluminum frame outlines the middle compartment, holding the oarlocks. We carry all of our provisions for the 14 day journey. The boatmen are all pros; the rapids of the Colorado River are the premier white water of North America, no place for amateurs to practice.

In back of us is a great natural amphitheater, a panorama of varicolored cliffs. The blue sky is scattered with fluffy white cumulus. Soon we float into the Canyon proper, with walls rising up out of the river to enclose us, first on the left bank and eventually on the right as well. The rocks in the walls are about 245 million years old, Paleozoic limestone left over from an ancient seabed. They contain fossils of fish and reptiles, but they’re a little too ancient to contain evidence of the dinosaurs. The Mesozoic layers from maybe 220 million years ago, which used to sit atop the canyon walls, were eroded away long ago. But the dinosaur layers are still to be found in the Vermillion Cliffs behind Lee’s Ferry. And the birds are somewhere above all that, starting at about 200 million years ago. The fossil birds, that is — the present-day descendants of those Mesozoic birds are flapping all around us, catching insects.

The canyon walls keep rising at a prodigious rate. We were on the river for less than an hour before we saw the peaked bridge spanning the gorge, thirty stories up. It provided a momentary bit of shade in midriver, then we floated clear of its shadow. We didn’t even look back to say goodbye to this last vestige of the familiar.

There is something touching and heroic About the early Mesozoic.          CLARENCE DAY

SURPRISE — in the shallows we saw a great blue heron lumbering along with its swiveling gait. That bird could have served as the artist’s model for the winged dinosaur; it was almost as tall as one of us, standing perched atop a rock. Then it flew away gracefully, in slow motion, not as ungainly as one somehow imagines a pterodactyl to have been. At least the heron has feathers. They do improve flying, judging from the aerial acrobatics of the swifts and swallows that flit around our boats, skimming along the wavetops in search of insects. We spent some time craning our necks to look up high on the canyon walls, trying to spot the swallow nests in little cracks in the rocks.

There are also big, glossy-black ravens perched on some rocks nearby. Unlike the smaller crows, ravens have shaggy throat feathers, similar to the ones on the tips of their wings. They argue with one another, sounding cr-r-ruck in annoyance. Ravens are much larger than crows, more the size of seagulls. The boatman in the neighboring boat has apparently told a raven story, because several of the neurobiologists have started to respond with their own stories about smart birds.

I once heard of a nature-film producer up in Seattle who had observed some of the northwest crows that frequent the beaches practicing an ingenuous form of shell-cracking at a ferry dock. Clams protect themselves against predators by a muscle that holds the half-shells firmly closed. I suppose that one could use a pry bar, but the crows have instead found ways of simply shattering the shells. Before the ferry would arrive, the crows would fly in carrying some clams extracted from the nearby beach at low tide. The Great Clam Airlift! They would then line up the clams on the pavement, right in the path of the cars coming off the ferry. Not surprisingly, the departing cars ran over the clams. After the cars passed, the crows would swoop down to eat the innards. Crows have rather large brains; even though they themselves are about the same body weight as an adult rat, their brains are five times larger.

Gulls are also clever at opening shells: they have been known to carry shells aloft and drop them on a rocky area. In this way, gravity becomes a simple but effective tool. If a shell doesn’t crack when first dropped, the gull will pick it up and carry it aloft again, repeating this dozens of times until getting to the food inside. While it obviously works best if there are rocks below, I’ve also seen gulls repeatedly drop shells on an ordinary sand beach at low tide; the impact on hard, wet sand eventually seems to work, after a few round-trips.

It isn’t just coastal birds that have the shell-cracking idea, either. The Egyptian vulture does it in the African savannas, carrying ostrich eggs aloft and then dropping them. If the egg is too large to carry, the vulture has another scheme: it carries a rock aloft and bombs the egg. This was observed in the middle of the nineteenth century, long before humans re-invented bombing.

Ravens bomb too. Scientists who were inspecting a raven nest halfway up a cliff face were being "mobbed" by the frantic parents. Then some rocks came falling down. The scientists at first wondered if they were just loose rocks, knocked free by the unhappy parents. But, when they retrieved the rocks, they found a telltale ring of organic matter which demonstrated that the ravens must have pried half-buried rocks out of the ground atop the cliff and then dropped them; the bombing was no accident.

We neurobiologists enjoy talking science, especially about our specialty: how brains work. It isn’t a workaday subject, to be left behind on vacation, but more like a hobby in which we continually indulge ourselves. Some of us specialize in humans, others in monkeys, and quite a few study the primitive brains of various invertebrates. Some have medical school backgrounds, others zoological or anthropological or psychological. This mix should help us to understand the foundations on which brains are built, as together we have quite an evolutionary perspective. The Grand Canyon, of course, inundates us with evolution. It’s in the walls surrounding us, layer upon layer. And the layers are still growing, higher and higher.

"Some of Darwin’s finches in the Galapagos Islands use tools, you know," Dan Hartline volunteered. He’s an old friend from Hawaii, another neurobiologist. "The finches down there are all probably the descendants of just one species of finch, blown west from South America. All it takes is one animal blown far out to sea to start colonizing an island chain."

"One animal is going to get pretty lonely — doesn’t it take two animals blown to the same island?", someone asked.

"All it takes is one pregnant female," Dan replied, "and a little incest. Pretty soon, there were lots of the species. And then that first species subdivided into a whole series of new species, each with a different beak shape corresponding to the food they eat. Some have thick beaks for seed-cracking, others have long skinny beaks, handy for poking into cracks in a tree trunk and catching the insects that live down there. As we say in the business, the finches have diversified."

"The Tool-Using Finch doesn’t have a particularly long beak," he continued, "and certainly doesn’t have the long tongue that a woodpecker uses to probe inside the hole. But he still gets the insects. He finds a twig or a cactus spine and holds it in his beak, pokes it down the hole, and the insects start crawling all over the stick. He pulls the stick out and eats the insects. Now I think that’s pretty clever — that’s just like chimpanzees, fishing for termites by poking a stick into a termite nest."

Islands are a great place for seeing evolution in action. Hawaii, for example, is filled with tiny fruit flies. The islands themselves aren’t very old, but in that time the flies have diversified even more massively than Darwin’s finches.

"But aren’t there lots of problems with evolutionary explanations like that?", someone asked from the neighboring boat. "From what I read in the papers, Darwin was wrong."

"It’d be very surprising if he wasn’t wrong about something, considering the massive detail of his writings," I answered. "But Darwin was amazingly correct, considering that no one knew about genes in 1858, and none of population biology had been done yet. What he didn’t guess was the detailed mechanism of how the genes changed to create a new species out of an old one. But you’ve got to distinguish between if evolution has taken place, and the details of how and where and when it took place."

"Evolution is a very straightforward conclusion, drawn from two observations," Dan Hartline explained. "First, every individual has a parent or two. So far as we know, that has always been true — linking us to the past in an unbroken chain. Second, for each and every species, there was a time when it didn’t exist. Together, these two things tell you that evolution has taken place, modifying some ancestors of a different species into the species’ present-day form."

All this was obvious and widely known even before Darwin’s time. There are other "explanations" but they are — literally — unnatural. "For example," I added, "there are birds all around us here on the river. But there are no bird fossils in those walls of the canyon — those rock layers are too old, laid down when the fishes and amphibians were still the dominant forms of animal life and the reptiles were recent inventions. But if you go up north in Utah, where I was yesterday," I said, pointing back upriver, "you’ll find layers of the Earth from much more recent times which haven’t been eroded away yet. And they’ll contain fossils of what look like modified primitive reptiles — birds, as well as dinosaurs. Go further north, up into Montana, and you can even find some bones of the early primates. So, while birds didn’t exist before 200 million years ago, surely the first birds had parents too, dinosaurs that didn’t quite fly."

"Dan, pardon my ignorance," someone volunteered, "but did you say that an individual could have only one parent? I guess that in high school biology, I pretty much thought that it took two."

"Maybe you were fixated on sex at the time," someone else kidded.

"There is a tendency to confuse sex with reproduction," smiled Dan. "But having two sexes happened only in the last third of our biological history. And the old-fashioned ways — such as budding-off and spores — still work in many species."

"You mean clones?"

"That’s still another way, though I dislike the word these days, ever since the popular press got hold of it and created newspaper-selling headlines about how Hitler could have been cloned."

"So who first invented flying?", asked Dan Richard, sitting up front in our boat. We have two Dans. This one’s a lawyer, the legal counsel to the governor of California. "I fly sailplanes, and I’ve always wondered how flying got started. Were the flies the first to fly?"

"Probably," I responded, "though not the usual two-winged flies that you swat. They’re a streamlined version of more traditional four-winged insects, having suppressed the genes that make the second pair of wings just as the chickens have suppressed the genes that make teeth. But flying itself goes a long ways back. It’s been re-invented so many times that it makes you wonder if even the insects were the first. There were flying dinosaurs, such as the pterodactyls, although their reptilian ancestors probably didn’t fly. The birds did it with feathers rather than just skin on their wings. Among the mammals, the bats used skin on their forelimbs to make a wing."

"And all sorts of other mammals can glide between trees," Abby noted, "using folds of loose skin that they stretch out tight by sticking out all four legs, making a kind of parachute."

"Did you know that besides the gliding squirrels and the flying fish, there’s even a gliding snake?", volunteered Dan Richard. "I saw it on television. Down in the tropics there is a snake that eats insects that live up high in a tree. He climbs the tree with the aid of scale-like protrusions on his underside. When he has picked one tree clean, there’s this little problem of backing down to the ground and climbing another tree. So instead he casts off, flattens his body into a ribbon like a boomerang, and glides between trees. There’s even a parachuting spider."

"Jumping between trees is basically a behavioral invention," noted Dan Hartline. "Behavior precedes form, as Konrad Lorenz once said. Only later does anatomy get modified to make the behavior less dangerous and more efficient. So those animals with extra body skin on their legs are able to glide better, suffer fewer injuries, eat more insects, leave behind more flabby-skinned offspring than their competitors. That’s natural selection — there are just lots of variants within a species, and some succeed better than others."

"It seems only common sense to us now," I commented. "But it took many decades after evolution itself was well known for someone to stumble upon this selective survival as a mechanism for evolving new species. Variations, then editing. One of Darwin’s contemporaries said something like ’How extremely stupid not to have thought of that’ before!"

Mile 8
Badger Rapid

THE LONG RUN IS POSSIBLE only if we consistently take care of the short run. And so our talk of evolution ceased in favor of paying attention to a consuming interest downriver.

Sue stepped atop her seat, as lithe and loose as a ballet dancer just finished with her warmup. Captain of the ship, she had just gotten the four of us wedged tight into our corners of the rubber raft. (I couldn’t help but compare her casual manner upon arising with that of a commuter getting up to leave a bus at the next stop. Then I remembered that she was the driver.) She was, I supposed, not planning to abandon us but merely standing up to get a better view down into the boiling white water of the rapid, toward which we were drifting with the current. Sue guided us by an occasional stroke on the oars.

The water of the Colorado River was deceptively calm — the way it always is, upstream from waterfalls. Like a reservoir above a dam. But, I reassured myself, Badger Rapid is not yet a waterfall. One must be quantitative about waterfalls, after all — Badger rates a mere 7 on the Grand Canyon’s scale (10 is a barely navigable monster rapid; I suppose that 11 would therefore rate as a waterfall). Beyond the lip of the rapid, where the flat river seemed simply to end, great eruptions of white water were being thrown into the air, as if the rapid were advertising its virility, like a gorilla thumping its chest.

Strangely, each great splash was soundless — drowned out, I supposed, by the sustained roar of the rest of the rapid. The splashes were just white flashes against the reddish-brown background of the Canyon walls, first here, then there. Like lightning when you’re too far away to hear the thunder. But those splashes are, ahem, close. And getting closer. Were we going through that?

As we drifted toward the rapid, Sue gave us a quick safety lecture. Life-jackets are very nice when you need them, but the major goal is to keep yourself inside the boat. "Crouch down in one corner of your compartment," she said. "As the floor of the boat rises and falls with the waves, pump your legs, just as if you were skiing. Wedge yourself into a corner, and keep your feet under your body. And keep a secure grip on your two handholds. Always two."

Her lecture completed, Sue sat back down again just as causally as she had stood up, routinely fastened her lifejacket a little tighter, and checked her belt knife ("Don’t get entangled with a rope if we flip over," she’d said only minutes before). She pushed on one oar and then the other, rowing us over to the exact spot where she wanted to enter the rapid, never taking her eyes away from the white water ahead. I think she likes running rapids.

Navigable tongue between two holes, from Leonard Thurman’s Grand Canyon River Running.

THE WATER WAS SO CALM that we felt a bit silly, wedged into our corners and hanging on with whitened knuckles. Then we slid over the smooth lip of the rapid and into the first gentle, rolling wave of the tongue. Pleasant, but I’m not fooled. When we finally reached the tip of the tongue, a viciously cold lateral wave splashed over the right side of the boat, eliciting yells from those slapped by it. Even when one expects it, a bucket of cold water is still a bucket of cold water. After that brief introduction, everything happened so quickly that we had no time to think about what we were doing.

The boat bent up in the middle as its bow climbed a wave, exhibiting a flexibility that we hadn’t suspected. Over the crest of the wave and the boat arched its back just as radically the other way. A rubber roller-coaster. Aided by several swift strokes on the oars, Sue slid us sideways around another standing wave that ended in a boiling white "hole." We had successfully cleared the hole when still another small wave appeared out of nowhere and threw several buckets worth of cold river over the stern compartment. Two more big waves followed. Everyone was yelling, involuntarily or with perverse pleasure.

The river spun us around, sending us careening downriver stern first. The rubber floor of the boat seemed to have a life of its own, dropping slack and then popping up into the compartment with some force. As if we were skiing an endless field of moguls, our legs pumped like pistons, keeping us wedged into our chosen corners.

Then the twisting and turning was over, the ups and downs gradually moderated, and we were left with just the cold water dripping off our amazed faces. We saw a swirling back-eddy alongside, where the water was gracefully sweeping back upriver. Pulling hard against the currents, Sue rowed us over into the eddy — whereupon we reversed course and were carried back upriver.

What is she up to now? Is she going to run it again? Not that we had any time to marvel at all this. Per instructions, we were all bent over, bailing buckets of water out of the bilges. We scarcely managed to see the incredible Marble Canyon scenery for a few minutes.

Take care to get what you like or you will be forced to like what you get. Where there is no ventilation, fresh air is declared unwholesome.          GEORGE BERNARD SHAW

SUE SAID that she normally stayed out of the back eddies, but that we had to provide emergency towing and pickup services for the other boats in case they got into trouble. (Ah, but who covered us?) Which was one reason why we had to bail the water out of the bilges as soon as possible. A boat that’s overloaded with water is no fun to row and doesn’t make a particularly swift rescue vehicle. Hint, hint. So we tried to get the last teaspoon of river out of the bilges. Sue runs a tight ship.

From our new vantage point, we got to watch the other six boats come through. We could barely hear their passengers yelling above the roar of the rapid. A boat would disappear into a trough and then surprise us by suddenly reappearing, on a different side of a wave than we had expected. Most boats got a lot wetter than we did. The last boat through hit a wave wrong, briefly lost control, and slid down into a fury of boiling waves. When it finally sped past us, looking somewhat low in the water, all four passengers were bailing furiously. Sue pulled us out of the back-eddy with a series of strong strokes and we finally caught the main current to follow them down the river.

Susan Bassett, our boatman and an ex-Harvard Medical School secretary, is called "Subie" by the other boatmen. She is tall and slender, with large expressive eyes that don’t miss a thing. As we were renewing our acquaintance, I remembered the first river trip I took with her, down the Middle Fork of the Salmon River up in Idaho. At the time she wore a baseball cap with the letters "SUE B." on the front (the first river crew on which she rowed had another Sue). I suspect that the cap is long since deceased, but everyone still calls her Subie. I took my first big course on brains at Harvard Med when she worked in the Dean’s Office there, and I strongly suspect that she was the helpful secretary who somehow found a spare microscope for me to borrow. We meet again in the strangest places.

Abby, upon seeing this, told us about what she’d seen yesterday down at an ancient cliff-dwelling, Betatakin. "We got down in this canyon with the park ranger about nine in the morning, just when the sun was starting to illuminate the cliff-dwellings set back in this enormous alcove in the cliffs. But out in front of Betatakin, circling in the air, must have been three dozen big birds. Probably turkey vultures."

"They were riding a thermal up out of the canyon?", asked Dan Richard.

Abby nodded. "That’s what the ranger said. They just started circling lazily, and soon they were halfway up. A little longer, and they were up out of the canyon. Then they started flapping away with that distance-covering wingbeat of theirs. Pretty soon they were out of sight. By the time we’d hiked further down the canyon to the ruins, they were all up the escalator and gone. Off to work."

Hot air rises. And birds know it. Or at least the birds that can discover it are a lot more efficient, get more babies to grow up, and so populate the world with smarter birds.

Evolution is fact, not theory.... Birds evolve from nonbirds, humans evolve from nonhumans.          the geneticist RICHARD C. LEWONTIN, 1981

Everything is what it is because it got that way.           the biologist D’ARCY THOMPSON, On Growth and Form, 1917

THE ARGUMENT FOR A GRAND DESIGN usually says something to the effect that fancy anatomy is too sophisticated to have arisen by chance, that it goes against common sense to say otherwise. Architecture requires an architect, and so forth.

The argument against design usually substitutes Darwinian natural selection, saying that all our abilities have been shaped by gradual adaptations, such as the loose skin that gliding snakes use. In this adaptationist view, success in one endeavor allows the genes that promote success to produce a relatively larger share of the next generation. Even small differences in survival and reproduction count when compound interest operates over thousands of generations. And so Darwin’s finches arise, a whole family of birds, each specialized for a particular food or two. What can happen in a newly colonized island in only a few millennia may take longer to happen back on the mainland, but the basic process is the same. It’s probably how all species have arisen, including us.

Abby was not convinced by this approach to evolution. "You know, what bothers me about this standard evolutionary story are not the usual things, like the eye — how could such a perfect optical instrument arise by chance, surely it bespeaks the guiding hand of a Creator — because I buy adaptation for useful traits." She took off her big straw hat and brushed back her blond hair. "But there are just too many things around in which our talents seem greatly in excess of anything our environment demands."

She leaned forward, then continued with a sweeping gesture. "Take music, for example. What on earth is the survival advantage of being able to follow, let alone compose, Bach’s Goldberg Variations? Sure, a little love of music might have helped social cohesion, a little dancing to music might have eased social tensions. But I don’t believe for a minute that prehuman primates held rock concerts and that this made them better warriors or more peaceful citizens. And even if they did, how did it select for the fancy musical abilities like harmony? Four-part inventions? Adaptation arguments just won’t work for music."

No, we conceded. Try as we could, we couldn’t think of any reason that our considerable musical abilities — far in excess of the frenzied chimpanzee rain dance — could have aided evolution enough to help a prehuman survive better.

But, we pointed out, some things in evolution are sidesteps in which an anatomical feature turns out to have additional, unexpected uses besides the one for which natural selection shaped it. Maybe music is another sidestep.

"So what was the original talent from which music emerged?", asked Abby, pursuing her point.

A good question. "Maybe language? They are both timed sequences of sounds," answered someone I didn’t know. I liked that answer.

"But don’t abilities such as music," continued Abby, "make you wonder if there isn’t some higher principle shaping life, some goal to evolution?"

No, we biologists replied. That’s not to say we’re sure there isn’t, but our agnosticism is an occupational hazard of our profession. We cannot assume the existence of a guiding principle because it would discourage us from seeking simpler explanations. It would paint us into a corner. We’ll just have to see if we can come up with a scenario for the invention of music via a sidestep from some adaptive improvement in another skill.

"And what about laughter, what is its evolutionary utility?", Abby added. Here we go. "The chimps and monkeys may romp and tickle, but they don’t laugh or seem to have a real sense of humor. And laughter is almost an involuntary reflex, not what you expect for higher cerebral activity. So where did natural selection produce that?"

Sigh. I’ll add it to the list. Explanations needed: Music, humor, and now laughter. We have a whole two weeks in which to think about them.

Subie calls our attention to Ten Mile Rock, a big pillar of rock on the right bank, a few stories high. Once upon a time, it fell off the face of the cliff above. Somehow it didn’t topple over upon crashing into the river bank. Not your usual balancing rock, like the one we saw driving up the road from Navajo Bridge to Lee’s Ferry. Those are formed by erosion, eating away a softer layer that underlies harder stuff.

I liked the way several people responded to Abby’s point about the involvement of "something else" in evolution. They said that doing science is rather like piecing together a jigsaw puzzle, trying to make the big picture emerge from all the little fragments.

So far, the big picture looks like a tree. A single big tree, not a lot of little ones.

Just as there were no birds before 200 million years ago, so there were no large-brained primates until the last several million years. We don’t know if the prehuman fossils we find are direct ancestors of ours or just cousins on a slightly different branch of the tree. But the shape of the rest of the underlying tree is abundantly clear to anyone who examines the facts. And it isn’t a collection of independent creations every now and then.

We’re apes. Apes come off the primate branch. Primates are rooted in the mammals. The mammals and the birds evolved from the reptiles. About the time that the canyon surrounding us was laid down, the reptiles evolved from amphibians. Earlier, the amphibians evolved from fish, which evolved from primitive chordates, which evolved from an invertebrate rather like the sea-squirt. The invertebrates, and all other multicelled organisms, evolved from a single cell type called a eukaryote — or, as I call it, Supercell. Supercells are the main trunk of the evolutionary tree, the one from which several dozen major branches have arisen.

Supercell took a long time to evolve from Simple-cell, the bacterium. Bacteria have been around for about 75 percent of the Earth’s existence, three times as long as Supercell. In fact, Supercell’s constituents such as mitochondria look as if they may have been hitchhikers, independently living organisms that were taken in and put to work. Supercell looks to be a great committee effort, self-organized from bacterial components, coevolving together. The bacterium in its many forms evolved from some ancestor, probably the outcome of some competition in the early oceans between various forms of self-replicating chemical systems using a common genetic code. The bacterium’s machinery for making proteins will even construct human proteins — such as the growth hormone that dwarfs lack — if you snip the genetic instructions for making these proteins out of the DNA of a human cell and insert them into the bacterium, thus neatly demonstrating that we still use the same protein-building system that was around during the Earth’s childhood.

We can even imagine how chemicals floating around in shallow waters self-organized themselves during the Earth’s infancy into primitive bacterial cells that had the amazing ability to make copies of themselves. We can guess how the genetic coding instructions might have evolved, those necklace-like blueprints that tell the cell how to construct another living cell. We know how the carbon-based chemicals that make up living organisms can have arisen before life itself, since we can see them being synthesized in many different laboratory experiments mimicking the conditions that existed on the early Earth. And how carbon and all the other elements heavier than hydrogen and helium were constructed in the dense centers of collapsing stars. And something of how the Big Bang evolved from pure energy to form stars of hydrogen and helium.

The whole chain of events has taken about 15,000-million years, while our peculiarly large brains have only evolved in the last 2 million years. The puzzle has been pieced together, largely by the last few generations of humans, using science to build on the cultural edifice of many thousands of generations. There is no need to postulate a miracle at any stage. It’s just like doing a jigsaw puzzle: whenever you think that there is no piece that will can possibly fill a blank space, you don’t just throw up your hands and insist that only a miracle will solve the problem. You keep looking, and eventually you find something that links together the parts of the puzzle.

Yet the magnificent façade of science is not a completed jigsaw puzzle, not now. Perhaps there will someday be a piece that won’t fit, a space that won’t fill. Still, the critics who now and then cry "unproved" (rather than "unfinished") are shortsighted if they cannot tell that the picture contained in the incomplete puzzle is a single giant tree. One need not have lines connecting every generation with the immediately preceding one to see that the big picture is one big tree, and not a forest of little trees independently created de novo every now and then.

The theory of evolution isn’t like a Euclidian theorem describing geometry that must be "proven" — it’s a historical synthesis that explains major features of the past in an economical way, a way that makes correct predictions. It’s a well-tested theory that ties together the entire edifice of biology, from molecules to humans. But it’s not complete yet, and its implications aren’t always clear.

[Miracles rest simply] upon our perceptions being made finer, so that for a moment our eyes can see and our ears hear what there is about us always.           WILLA CATHER, Death Comes to the Archbishop, 1958

Lacking foresight, evolution is simply opportunistic, retaining those features that were available when opportunity knocked, forming a patchwork of makeshifts. We too are imperfect, products of the unique set of challenges posed during the ice ages after our ancestors got started with a brain the size of a gorilla’s. Somehow, evolution enlarged that brain threefold and created a unique set of inborn skills for making tools, throwing spears, and speaking sentences. It even created the capacity for music and poetry. And humor. Somehow.

We are all sitting at a cosmic poker game in which the house has an infinite supply of chips. Neither we nor our genes can ever really win, since we can never cash in our chips and go home.... There is nothing but the game, and since it has been going on for a long time, only the best players are left. It is an existential game, the only one in town, and all we can do is to stay in as long as possible. We are all playing, so perhaps we may as well enjoy it. Certainly we should understand it.          the sociobiologist DAVID BARASH, The Whisperings Within, 1979

The reptile tracks are in the Coconino sandstone, the Sahara-Desert-like layer that emerged from the river back about where the bridge span the canyon. Here, it’s high above the waterline now. Curiously, no reptile fossils have been found in it, just tracks. I was going to say that maybe the vultures and hawks ate them all, but the only flying animals back 270 million years ago were the insects. The river certainly does focus us on time, immense stretches of time.

Mile 17
House Rock Rapid

THE RIVER HAD BEEN GETTING SLOWER. And wider. Subie was having to row more. And then there was the sound of an airplane roaring somewhere — except that it didn’t disappear into the distance as airplane sounds are wont to do. It just slowly got louder. Subie smiled at our attempts to locate the airplane and said that House Rock was just around the corner. House Rock Rapid, an 8, is an even larger fraction of a waterfall than Badger.

About the time that we started to worry about our cameras getting soaked, Subie told us not to bother stowing them away in our ammo cans yet, because we were first stopping above House Rock Rapid to have a look at the rapid from shore. She beached our boat on a broad sandy beach on the right shore, and we all climbed out.

Subie and the other boatmen all went bounding through the field of boulders to their favorite lookout place. The rest of us, still clad in orange lifejackets, wandered down the beach to it up close. For most of a city block, the river was a series of big waves. There were a few giant crests but mostly smooth ups and downs, many as tall as a person. Here and there, great holes of white water could be seen where the river poured over a steep rock face in the manner of a waterfall, carrying a lot of air underwater with it; this plunging turbulence is what the boatmen call a "hole."

But the big waves stood still, like hills and valleys usually do. Even those of us who understood why found this amazing. In the ocean, waves move forward but the water doesn’t — the energy is just transferred forward, as in a tightly-packed row of billiard balls hitting one another wham-wham-wham, with only the last ball in line actually moving very far. In a rapid, waves are stationary but the water moves. Standing waves, literally, just like Pythagoras discovered 2500 years ago when analyzing musical chords. They do splash around a little, not being completely stationary, just to make things more interesting for the boatmen. And, of course, the amount of water coming down the river makes a big difference in where the waves and holes are located in the rapid.

Unfortunately the water level of the Colorado is now under the control of technicians at the Glen Canyon Dam, Dan Richard explains. And not just seasonally — since about 1980, they have adjusted the water release every hour according to how many air-conditioners are turned on in Los Angeles and Phoenix, engaging in what is called peaking power generation. Without so much as an environmental impact statement (which the government was legally required to file, according to our lawyer), the Colorado is now flooded daily with large artificial tides, rising and falling with the business day. Release twice as much water several hours later and the standing waves are drowned by high water. To the people who built and run the dam, the Canyon is an inconsequential sluiceway. And all those beautiful canyons upriver of Glen Canyon Dam, with names like Music Temple and Tapestry Wall, are now illuminated only by a pale green light. And the reddish brown silt, which for millions of years gave the river its rich color, is now filling the drowned canyons. This is not your usual benign flood-control dam. High-rise hydroelectric dams don’t prevent floods so much as they create them.

Subie’s boat was again to be the first to take on the rapid, and she rowed upriver with a strong backstroke to position our boat in the center of the river channel. She again specified exactly which handholds were safe and which were to be avoided. "Don’t grab the blue line around the outside of the boat, unless you’re swimming for some reason and need something to grab. And you don’t want to get wrapped up with a rope, or get your leg wedged in a crack. If the boat flips over, you want to be thrown clear and not trapped underneath." In the life jacket, Subie explains, "you’ll go bobbing down the river just like an orange cork, getting a unique cork’s-eye view of the white water. And someone’ll row over and pick you up." Reassured, we faced the rapid — visible now only as a lot of splashing water beyond the smooth surface of our backed-up lake.

"Oh yes," Subie added, "if I yell HIGH-SIDE, I want you to throw your weight to the high side of the boat. That’s in case one side of the boat gets submerged in a wave." Just as in sailboats, one high-sides to counterbalance. In a hurry.

Subie, complaining earlier about someone tracking sand into the bottom of the boat, had said "Oh, well, we’re taking her to the boat wash." Running House Rock Rapid was indeed like being in a washing machine, first a wave from one direction, then from another, overlapping the first. Again and again, as if giants were shuffling a deck of watery cards. And when we bailed the boat, out went the sand too.

We got cooled off again. The water temperature is cold, about 9° Celsius (also known as about 48° Fahrenheit in certain insular parts of the world, namely Yemen and the United States, most everyone else having officially gone metric). The river water doesn’t come from the surface of Lake Powell, the dam intakes being well below the surface to avoid sucking in all the floating trash from the boaters, and the sun’s rays don’t warm up the water very much down at those depths.

Feathers are all very nice for flight, but one needs a lot of them before they do any good at all. A few feathers on the limbs of a running dinosaur would hardly induce liftoff, to recall Stephen Jay Gould’s lovely phrase. So how did the reptile develop ever greater numbers of feathers, to build up to the threshold for flight? Evolution has no foresight, in the manner of human consciousness — it cannot just plan ahead for something useful in the future, such as when the unexplained "#" and "*" buttons were included in pushbutton telephones decades ago, anticipating the future expansion of special services (and causing millions of parents to have to admit, when inevitably asked "What’s that for?", that they didn’t know).

Even if we knew that there was another ice age coming, we couldn’t prepare for it by growing more and more body hair with each generation until we became hairy again. Evolution selects useful features, but based on present-day needs. If you don’t have them when they’re needed — well, it’s just someone else’s turn.

Which, of course, suggests that feathers were initially useful for something besides flying. Indeed, feathers are useful for the same reason as body hair: thermal insulation against the cold. I’m sure that someday we will discover a feathered dinosaur; maybe we’ll get lucky while out searching for the footprints of running dinosaurs, and find a place where one of them stumbled and fell. If it left a nice imprint in a hardening mud flat, it might reveal an abundant plumage on an otherwise reptilian body.

The archaeologists studying the prehuman footprints found at Laetoli in Tanzania, where hardening volcanic ash preserved the footprints left by some upright-walking hominids 3.7 million years ago, presumably have the same hope: to find where someone slipped and fell, or sat and rested. Then we could see how much body hair they had, whether they were wearing clothing or perhaps carrying a basket, and the like. The record of the past is terribly biased by the fact that hard evidence (literally hard: bones, stone tools, pottery fragments) survives better than wooden spears, carrying baskets, and characteristic behaviors. Yet the soft evidence would, in the case of humans, tell much more of the story.

There is some driftwood atop the boulder, left there by the great flood of 1957, one of the last big spring runoffs before the dam was built. Since the dam gates were closed in 1963, most of the driftwood has been trapped in Lake Powell. River parties don’t collect driftwood anymore for bonfires, since what is left is the home of birds and rodents.

Nature, of course, is always trying out variations on a good thing. The variants that find a use — such as downy insulation — are likely to be retained by Darwinian natural selection. But someday, such as when there were enough wing feathers, they might become useful for something else — say, for gliding quickly down a hill while chasing prey. Or for jumping up into the air to bat down a passing insect. From such mundane beginnings may have come the graceful flight of birds.

Evolution rarely proceeds in a straight line from A to B, probably because there are no goals to evolution. Evolution is always finding new uses for old things; this innovative use is the primary basis for how animals have become smarter and more versatile. Bootstrapping can happen when we least expect it, a new combination of anatomy and behavioral skills suddenly exhibiting unexpected properties that allow for a quantum leap in capabilities. Was this the route for the invention for music? And laughter? But as a sidestep from what...?

Evolution’s tempo is a lot like the river’s course through the Grand Canyon. There are long, quiet stretches of flat water where nothing much changes. Then there are exciting periods of great turbulence, such as House Rock Rapid, which are followed by an intermediate stretch where currents swirl around, finding a new dynamic equilibrium, becoming quiet again. Most animal species don’t change much for millions of years. When they do change, it is during one of those turbulent periods, when they are tested, when they sink or swim. What emerges is sometimes a new species, retaining those features which were handy. The evolutionary theorists think of this scenario as a punctuated equilibrium. Myself, I think of it as being like my favorite river: the Colorado River going down the Grand Canyon Staircase.

Later, when no amount of bailing could reduce the foot-deep bilgewater, the boatman leaned far over the bow and felt underneath of the boat. He came up muttering "Yep, big triangular hole." Pivoting atop a sharp rock works just like a drill. It’s just a hole in the floor; the boat won’t sink (unlike a rowboat, the flotation comes from the air-filled compartments). At least the front pontoons were spared. There are, in any event, close to a dozen separate compartments for air, and it’s pretty hard to hole more than two at a time. A nice design.

The boatman decided that repairs could wait until we made camp. That boat took a lot more rowing than the rest, hauling along all that water in the bilges. Penance. One passenger was transferred to our boat to lighten the load. So, though we survived Badger and House Rock, the only damage was done by a minor rock in a quiet stretch of river.

Most nonscientists don’t know very many examples of emergence, other than snowflake crystals. And most scientists know only several examples within their own specialty. Without analogies, it is indeed hard to imagine us humans happening without design — and so one is led to suspect some sort of cosmic principle, if not the guiding hand of a Creator, shaping evolution towards complexity.

Evolutionary theorists usually have seen enough examples of emergence to have faith that, as in the case of natural selection shaping the eye, adaptation and emergent "sidestepping" will be sufficient to explain the overall trend of evolution toward intelligent animals. Including ourselves. But as I said before, we can’t be insistent about this expectation in the same way as when we relate the fact of evolution itself — our working hypothesis about emergence is, for us, an occupational hazard of being researchers.

Mile 21
North Canyon
First Campsite

PATCHING THE BOAT turned out to be easier than I thought. But then I had imagined a surgical sewing job of whale-sized proportions. I had forgotten about the nautical equivalent of duct tape. The simple repair procedure? First unpack the boat and remove the tubular frame. Then tilt the boat up on one side, propping it up on the beach in a near-vertical position, using an oar or two stuck in the sand. Next, just as when patching an inner tube, rough up the surface around the tear in the floor. These boats carry a repair kit that consists primarily of odd-sized sheets of neoprene, some sandpaper, and a can of contact cement. I pushed on the inside while Alan smeared on some cement and applied a patch from the outside. Then we traded places and he applied another patch to the inside. And except for repacking, which Alan is saving until morning, that was it — a whole lot easier than fixing a tire. I can see that this is my kind of boat.

As we were resting in camp after our long day’s labors, sampling the contents of the little aluminum cans kept cool in the bilges, the wind came up. The sky clouded over and then it really began to blow. The fine particles of sand (this stuff is sometimes called "blowsand" for just this reason) began to billow in great clouds across the camp and out over the river. There were sand dunes forming before our very eyes, but we were not inclined to watch as the fine sand kept getting into our eyes. Bandanas came out and were draped around the edges of sunglasses, hats were held to shelter faces from the wind, and we all headed uphill. The easterly wind was blowing down out of the side canyon, so we all gathered on the upriver ledges of Supai around the corner, huddled against the force of the sand gusts. Still we were sandblasted. Sandstorms, it is said, do not last forever. Mike Marsteller, one of the other boatmen, said it was one of the two or three worst sandstorms he’d ever experienced in 500 days in the Canyon.

Five layers have arisen around us in only 21 miles of river, and we hear that the Redwall Limestone will start just downriver from here. We also hear the next section of river is named "The Roaring Twenties" and that we should wear our raingear tomorrow morning if we don’t want to get a little cold. There are nine rapids in ten miles.

Cold, with it this hot? But when I go to wash the sand and grime off in the river, I am reminded that the river is beer temperature. My wet bandana comes away from my face coated with fine sand particles; it feels good to get the sand off. I even get a nap before dinner.

The boatmen all started exuberantly to jump and shout, running around trying to get a better view of the rockfall. In all their years in the canyon, some had never witnessed an actual spontaneous incident in the continuing erosion of the Grand Canyon. They cheered on the rocks when they tumbled into sight across the river. And plunged in, with big splashes: "Ker-plunk, ker-plunk." We watched the final trickle of small rocks, trailing along behind the big rocks, with a feeling that we might never see it again. Few of the millions of visitors to the Grand Canyon each year ever get to see it as anything other than a static colossus — a frozen, finished sculpture. Now we, at least, know better.

Erosion made the Grand Canyon. Rocks falling downhill, shattering into smaller rocks along the way, is the most obvious aspect of erosion. What goes up (via lava upwelling and the mountain-building uplifts that occur as sea-floor spreading causes continental plates to come together and push their colliding edges into the sky) must eventually come down. Aiding gravity in this matter are water, wind, and ice. For example, the water that gets into cracks in rocks at higher elevations is likely to freeze in winter, forcing the halves of the rock further apart just as surely as a wedge splits firewood. So watch out in the springtime for a lot of fresh rockfalls.

Then, a half hour after the rockfall, we got another surprise — the river changed color! Chameleons, maybe, but a river? Starting in the middle of the channel, a dark red tongue intruded into the otherwise mint green waters of the Colorado. Then the tongue widened as we watched, soon filling most of the river except for the shallows along the shoreline. (Why a tongue? Water flows faster in midriver because the shorelines slow down the flow.)

Evidently that sandstorm was a side effect of a big rainstorm up north. This red color is, Subie tells us, what the Colorado River used to look like most of the time, before the dam created that big silt trap called Lake Powell. Now the Colorado turns red only when a side canyon floods somewhere within the park. But where? The Paria doesn’t run red, Subie points out, so the water was probably dumped into Soap Creek, Tanner Wash (which created Sheer Wall Rapid), or Rider Canyon (which donated House Rock Rapid), those being the only possible sources of so much red silt. So, thanks to this little bit of detective reasoning, we know that we missed seeing a flash flood in a side canyon by only about a dozen miles or less.

There seem to be no end of unusual events today. At this rate, we’ll see a comet or a supernova tonight.

Like many others, I had been somewhat skeptical about the boatmens’ plea to avoid the use of flashlights on aesthetic grounds (light spots flashing across the canyon walls, as someone turns around, seem inevitable no matter how carefully one tries to restrict a flashlight beam to the path). We thought we’d stumble around our dark camp bumping into rocks and trees. But it actually works, I could see the whole camp; if I’d used a flashlight, I’d have seen only the swath cut by the beam. I also would have lost my dark-adaptation and so would have had difficulty spotting the fainter stars for the next half hour. They were indeed hard to spot, what with the moon shining from behind the western canyon wall. Being at the bottom of a narrow canyon, we see only a narrow swath of sky. It rather focuses the attention.

As I looked up at the sky for clusters of familiar stars, I knew that I was a real amateur compared to our ancestors who carefully studied the night sky. The names of many constellations, such as the Big Bear (latinized as Ursa Major), have come down to us from the time before writing was invented 5,000 years ago. Our ancestors had a good mental image of a bear, and they could fit seven stars to it.

However, they had a rather limited mental image of their family tree — restricted to several generations, mostly people they’d seen sometime in their lives. Passing on information for which there is no reminder in the environment, such as a real bear, is not easy (which is the reason why most of us can’t name our eight great-grandparents, either — and why the Navajo forgot the Yukon). A skill, cultural artifact, or ritual helps carry information along through the generations, but only with the inevitable modifications that eventually change things radically after a dozen generations. As culture changed, the constellation Ursa Major came to be called the "Big Dipper" in some parts of the world, and to anyone who has used a ladle, it’s hard to see a bear there anymore. Most of us, alas, see more punchbowl ladles than bears.

Living in a city, one seldom sees the stars at all. That leads to a certain insular perspective: at night in the Canyon, I realize that I’m sitting on a planet, almost feeling it turning as I see new stars suddenly appear from behind the high canyon wall on the east side of the river. Here we don’t have to struggle to see through all that distorting haze near the horizon; instead, the stars pop out when we study the top of a cliff. The Milky Way spans the top of the canyon walls. Our very own galaxy, seen edge-on. A few-hundred-billion stars, plus our Sun. Plus the black holes and dark matter of sundry sorts. We passed around the birdwatching binoculars in the starlight.

There are two galaxies that circle our own Milky Way, rather like the moon orbiting the Earth. They are close enough to appear too large to be passed off as mere fuzzy stars. From the southern hemisphere, they appear as luminous clouds to the naked eye. The sixteenth-century Spanish explorer Ferninand Magellan was the first to tell Europe of these great fuzzy patches of light and they have been known there as the Magellanic Clouds ever since. There are actually about 20 galaxies in our part of space, known as the Local Group (which is 3 million light years in diameter). Then for almost 50 million light years, space is virtually empty — before arriving at a particularly rich collection of about a thousand galaxies known as the Virgo Cluster. And there are lots more galaxies than just those.

All those galaxies are still fleeing the Big Bang, that cosmic point of origin that marked the beginning of the universe as we know it. The Big Bang occurred 12,000- to 17,000-million years ago. Call it 15 billion years ago for the sake of convenience (at least until they recalibrate the Hubble constant again, that great astrophysical fudge factor that relates redshift to distance).

The world began with what it is now the fashion to call the "Big Bang"... it could not, of course, have been a bang of any sort, with no atmosphere to conduct waves of sound, and no ears. It was something else, occurring in the most absolute silence we can imagine. It was the Great Light.          LEWIS THOMAS, Late Night Thoughts on Listening to Mahler’s Ninth Symphony, 1983

IN THE BEGINNING, there was no matter. Everything was radiation — the stuff that constitutes light and radio waves alike. Radiation comes in packets called photons: radio waves, infrared and ultraviolet light, and X-rays and gamma rays, they’re all photons just as red light is. The only difference is the amount of energy stored in the packet: lots in X-rays but not so much in infrared photons. Red photons are your average sort of photon — around here, during the day.

Out of such packets of radiation, matter was created (just remember E equals mc², which tells how energy and mass are interconvertible). Two photons of light colliding in the dense packing of the early universe (another way of saying it was very hot) can produce protons and neutrons. In the first microsecond of the lifetime of the universe (one-millionth of a second), it was simply too hot for anything else to exist for long. Particles were converted back into photons almost as fast as photons were converted into particles. But by the time that a millisecond (one-thousandth of a second) had gone by, the universe had expanded and cooled enough for lighter-weight elementary particles, such as electrons, to form from light and survive.

Actually, the story should be told in terms of quarks, the building blocks of protons, neutrons, electrons and, in fact, everything in the universe. Quark? When the physicist Murray Gell-Mann postulated these building blocks in 1960, he wanted a neutral term to describe them, with no physical connotations — and so he picked a made-up word from that masterpiece of make-believe, Finnigan’s Wake. It has been noted by literary killjoys that James Joyce was living in German-speaking Zurich at the time he wrote about quarks. And quark, in German, means "cottage cheese." But that’s not a bad analogy: the "quark soup" of the earliest moments of the universe may be conveniently envisaged as slightly lumpy. Mostly light, but with little bits of matter forming within it.

With more expansion and a thinner "soup," photons quit colliding with each other except on rare occasions. And the particles in the infant universe began to cluster together long enough to assume new identities. Between three minutes and a million years of age, the universe’s elementary particles began to form clusters as the electrical attractions between positive protons and negative electrons brought them together. When an electron and a proton stick very close together, the combination is called a neutron. Or an electron might begin to circle a proton at a great distance; this particular combination is called an atom of hydrogen. This looser clustering was an important event because the neutral hydrogen atom is less likely to capture passing photons than a separate electron and a separate proton.

At approximately 3,000° K. (that’s about as hot as a lightbulb filament), as much matter is converted into photons as photons are converted into matter. As the universe expanded further, however, the balance shifted. This happened when the universe was about a thousand times smaller than at present. At that point, some photons escaped absorption and scattering by electrons — indeed, they escaped the fireball forever. We can still see these "fossil" photons. They are cosmic, arriving from every direction in space (except for those blocked by the moon), a fact which suggests that the universe "inflated" at that point rather than scattering as in an explosion. The fossil photons’ wavelength has also changed. They were originally released at a temperature of about 3000° K. but they have been severely red-shifted by gravity; from originally having wavelengths like visible light, they’ve shifted down into microwaves.

Redshifts are the archetype of monetary inflation, shrinking the energy content of the photon and thus shifting its color, just as if when the buying power of a dollar bill shank, its color somehow gradually shifted from green to yellow. These fossil photons are the afterglow of the infancy of the universe, shrinking as their potential energy instead builds up. Should the universe begin to collapse someday, the potential energy will be restored to the photon, shifting its wavelength toward the blue end of the light spectrum. To date, no one has seen any signs of a blue shift.

It’s one thing to travel down a giant crack in the earth and see the remains of ancient life fossilized in the rock. But to see light left over from the early universe, fossilized as microwaves! This escaped radiation, still rattling around the universe, marks the time at which hydrogen atoms were first formed, the fireball of the expanding universe finally became transparent, and light was no longer trapped in it.

One of the neurobiologists on our trip, a former physicist, told us the story of the discovery of the fossil photons. The scientists who detected the 3° K microwave photons coming in from all directions in space were, of course, quite concerned about false readings, particularly as flocks of pigeons had adopted their horn-shaped antenna. Particularly when dealing with signals near the noise level of the receivers and amplifiers, one has to keep in mind that perhaps the "signals" are nothing but garbage fooling you. The astrophysicists claim that, when contemplating the data, one of the researchers said: "Either we’ve seen a pile of pigeon-shit or the creation of the universe." The former possibility has now been eliminated; the observations have been repeated many times in many places, with even better equipment and fewer birds. You can even see them on a home TV set — just tune to an empty channel and look at the "snow." About 1 percent of the little "snow particles" are generated by cosmic photons left over from the early universe becoming transparent.

Most of the original energy of the universe is now packaged as particles — mass dominates the universe, though it may be converted back into photons whenever some sort of transaction takes place and there are some leftovers. Most of the mass is still in the form of hydrogen atoms. If, however, the binding force between protons and neutrons were only a few percent stronger, hydrogen would be unstable; as the physicist Freeman Dyson once pointed out, that means that stars like our sun couldn’t exist. And there would be no water, a serious matter indeed to river-runners.

Hydrogen, it turns out, is the building block of the universe because of what happens to hydrogen atoms when a lot of them coalesce to form a star. All stars were initially great quantities of hydrogen held together by gravity. Hydrogen has two "heavy" isotopes, deuterium and tritium; their nuclei have a neutron or two in addition to the usual proton of the hydrogen atom. Being neutral in charge, these extra neutrons attract no additional electrons into orbit. But when these heavy hydrogen atoms collide with each other at the 10- to 12-million degree temperatures found in the interiors of stars, their nuclei may fuse, yield a new nucleus with a 2+2 configuration: two neutral neutrons and two positive protons. This doubly-charged nucleus naturally attracts two negative electrons into distant orbit. This "doubled deuterium" is an atom of helium, and the process by which it is formed is called fusion.

Some extra energy — I call it spare change — is given off in the process, because the energy needed to hold together a helium nucleus is slightly less than the sum of that for the heavy hydrogen nuclei (it’s somewhat the same problem as trying to divide up $100 three equal ways— you’re going to need some coins in addition to currency, and it still won’t come out all equal). This excess binding energy appears as photons of light. In fact, photons such as this — after an eight-minute-and-twenty-second trip through space — have inflicted more than one case of sunburn today. And that spare change also heated up the rocks on which we sat to watch the stars.

Twinkle, twinkle little star, I don’t wonder what you are For by spectroscopic ken I know that you are hydrogen.          ANONYMOUS

We have mimicked the fusion furnace of stars here on earth. It is called a thermonuclear reaction (though, in fact, little of the energy released by a hydrogen bomb is from fusion: the great energy release of an H-bomb really occurs because the fusion enables more of the uranium or plutonium of the atomic bomb, which served as the trigger for the hydrogen, to be split). E=mc^2 means that it takes only 1 gram of matter (a small coin weighs about 2 or 3 grams) to release as much energy as there was in one of the atomic bombs dropped in World War II. Someday, controllable fusion (without a "dirty" fission trigger) will become a source of really cheap and clean energy that could make coal and hydroelectric dams obsolete, along with the present nuclear fission plants and their waste disposal problems (instead, we’ll have to worry about thermal pollution!). At least, notes Dan Richard, there will be no Organization of Petroleum Exporting Countries to control their fuel, seawater.

A supernova doesn’t last very long, but for days or weeks it may be so much brighter than an ordinary star that it can be seen in the middle of the day, a bright point of light in the blue sky. Our sun, it is said, can never become a supernova. It isn’t big enough. A supernova is created from a star somewhat larger than our sun. After about 10 percent of its hydrogen has been converted into helium, the star becomes unstable and eventually collapses into a small, dense ball of matter (thus began the cliche, "The bigger they are, the harder they fall"). As the star collapses, particles in it move fast enough (another way of saying that the temperature is hot enough) so that when helium nuclei collide, they can fuse to make carbon, oxygen, and indeed all of the ninety heavier elements. Such fusions, of course, release even more nuclear binding energy than the hydrogen-to-helium conversion, the excess again appearing as light. And so the supernova flashes into existence, lighting up the night sky and soon the daytime sky with the spare change from the pressure cooker that is creating heavy elements in the collapsing star.

It is supernovae that allow matter to evolve, that permit simple atoms to become heavier atoms whose additional electrons in orbit allow the more complex kinds of chemistry needed for life. The evolution of life can occur only after the evolution of heavier matter. Had, however, the Newtonian gravitational force constant been slightly different, all stars would instead become either blue giants or red dwarfs, either too hot or too cool for most scenarios allowing the evolution of life.

Now carbon and oxygen are the stuff on which the chemistry of life depends. And with the exception of a few created here on Earth in bomb tests, every one of the carbon atoms in our bodies and every bit of oxygen we breathe got their start in a supernova. They were flung out into space by the explosive collapse of the star, and later assembled into a planet. And into us. A dramatist would say that stars have died that we might live.

No more than 6,000- to 7,000-million years ago, there was a supernova nearby. Matter flung out from it eventually, under gravitational attraction, began to cluster. Some of the hydrogen collapsed to such a density that the hydrogen-to-helium conversion was ignited and our sun was born. That was about 5,000-million years ago. At roughly the same time, other particles of cosmic dust from "our" supernova and others coalesced into a giant disk of swirling dust, spiraling around the sun. Eddies formed here and there, just as in the river, and an eddy within the spiral disk was probably the focus for the gravitational collapse of some dust into a compact ball. A planet. While some planets developed hot interiors, none ignited. One of these planets, third from the sun in distance, is the Earth; it went into business about 4,600-million years back.

The star of Bethlehem was the supernova of 6 B.C. recorded by the Chinese astronomers (a monk counted incorrectly back in the Middle Ages, when tallying up the elapsed years since the birth of Christ). If we had stayed up long enough for Orion to rise in the eastern sky, we might have seen the nearby Crab Nebula, the galaxy that was the site of a big supernova back in the year 1054. It was so bright that the new star could be seen during the daytime for weeks. But someone estimated that Orion wouldn’t rise until after four in the morning, and that it would be sunrise before it was high enough in the sky to clear the eastern canyon wall.

We gave up before that. No comets, no supernovas, but a half-a-dozen shooting stars as meteors tracked up the night sky. Still, not a bad day.

It took a long time to get to sleep. And then, out of the blue, someone turned the lights on. As suddenly, I thought, as if someone were turning on the bedroom lights in the middle of the night. Surely it wasn’t sunrise yet.

It was the moon, shining into our cave. I’d been in the shadows up until a moment before. It took me several minutes to figure out how to deal with this novel situation. Finally I put my sunglasses on. And tried to get back to sleep. Moonglasses?