My panguero was a lean, cool Ecuadorian in sunglasses and baseball cap. Part cowboy, part gondolier, he drove standing up, one hand on the outboard throttle of the panga, a pontoon dinghy for ferrying tourists in and out of the small harbors of the Galápagos Islands. He didn't say much; he left the talking to our naturalist guide Dora, but he knew what we'd come to see. The Venecia Islets are something to behold, scattered lava formations off the coast of Cerro Dragon on Santa Cruz, central island of the Galápagos, made when the islands were spat from the Pacific in fiery chunks a few million years ago. Some of the islets are purely rock while others bristle with shrubs and candelabra cactus. Mangroves fringe the lagoons. This is a place of eerie beauty -- but on the first day of a weeklong cruise in the archipelago, we were, like most visitors to the Galápagos, intent on something else. We were there to see creatures.

You have to be careful with names in the Galápagos. Don't call the land tortoises turtles or the sea lions seals -- and I suppose you shouldn't call the animals creatures if you believe in evolution, which I do, although why I couch it in those terms, as a question of faith, I can't explain. It sounds as odd as saying I believe in calculus. At any rate, we were there to see them, the famously tame ones who'll let you walk right up to them and take their picture. Such was our understanding of the Galápagos, that first day. Our cameras were ready.

It was late afternoon. A low bank of clouds lay along the horizon except in one distant spot, where a columnar rainstorm towered. The panguero cut the motor and we drifted. Quiet fell, an unfamiliar species of silence. No ocean roar, no bird cry. The water was green and cold and clear. It occurred to me that I had come to the end of the world.

And then a giant ray swam by in underwater flight, followed by a green sea turtle, slow and shadowy under the panga; a squadron of six spotted eagle rays; and a big parrotfish. In the upper cove a nest of white-tipped reef sharks hung motionless, eight of them together. Sea lions woke from napping on the rocks, their pelts black as oil when wet, tawny and plush as they dried.

We moved in for close-ups. I snapped my first shot, and something went haywire. The lens retracted and jammed. I had two seconds of panic, but I couldn't afford more, there was too much to see. Black marine iguanas by the dozen lay clumped on the lava, basking and digesting their meals of algae; and at the top of a small cliff one bright golden land iguana raised its head. Strange birds appeared, noddies and blue-footed boobies and frigate birds with red, ballooning throat pouches. Clinging to the lava at water's edge were spidery orange-and-blue Sally Lightfoot crabs, supposedly named by a sailor lovesick for his dance-hall girl. Up on Cerro Dragon I knew there were flamingos, and more to come on the island of Floreana, as well as other islands and other animals -- flightless cormorants, tropical penguins, lava lizards, bottlenose dolphins -- fabulous animals, I took to calling them, for they could have been the work of a fabulist, a yarn spinner with a wild imagination and a sense of humor.

Belief in evolution doesn't stop me from keeping an eye out for a little something else, a trace of the fabulist or glimpse of the design, some symbols or mysteries.

The light faded, and we headed back to our mother ship, the Polaris, waiting at anchor. My camera was a goner; I would have to see the archipelago through my own eyes, and rely on memory to call up its mysteries. Slowly, an amazing equatorial night descended, thickly dark at the surface with a star-packed sky high above.

There are some 60 named islands in this archipelago 600 miles off the coast of Ecuador, and each of the largest 13 has at least two names, one Spanish and one English, and sometimes another or even a fourth. The archipelago itself has been known as the Encantadas, or Enchanted Islands (not enchanted in a good way, but bewitched, hard to find and dangerous); Las Huérfanas (orphans, perhaps because no country wanted them until Ecuador made a claim in 1832); and the Galápagos (for the tortoises that resemble saddles). Its official name is one I've never heard anyone use, the Archipiélago de Colón (though Columbus was never there).

The inconsistency of names reflects the checkered past of the namers, a history both bizarre and scanty. No human beings inhabited the Galápagos until the 19th century. In ancient times Incas knew of the place but didn't establish settlements. In 1535 a lost bishop from Panama happened upon the islands, and the word spread. Two waves of marauders followed, pirates and then whalers, who came and plundered and went. Fur seals were hunted, and the great land tortoises were taken by the thousands, because they could be stacked alive in a ship's hold for months without food or water, providing fresh meat throughout a long voyage.

The islands eventually attracted a trickle of 20th-century European settlers seekinga Pacific utopia -- but I hesitate to recite the history of these people because it's so outlandish it probably ought to be forgotten. One Floreana settler in the 1930's was a German dentist whose preparations for living in paradise included removing all his teeth and buying a set of steel dentures, which he shared with his equally toothless mistress. They gardened in the nude and were written up in The Atlantic Monthly as a modern-day Adam and Eve. Another settler was a whip-toting, self-styled ''baroness'' who brought along two lovers but was on the prowl for more. Most of these people, evidently, ended up killing one another.

Their strange history is important precisely because it is so pitiful. Man in the Galápagos has pretty much been a fool -- a discouraging record, particularly now when what's required is not folly but heroism. Only human intervention and intelligence can undo the damage that's been done by man and his entourage: his pigs, goats, donkeys, dogs, plants and bugs, all of which disturb the evolved ecology and displace endemic species. On Floreana I was trekking to the flamingo pond when a bunch of aggressive wasps blocked my path. They arrived on a boat some years ago, I was told, and have swarmed over the island. These days, additional threats come from the fishing industry and the tourism business, one depleting the population of sea cucumbers and sharks, the other increasing the human population by attracting people in search of jobs. On Santa Cruz, the little village of Puerto Ayora grew from 1,200 to 12,000 in 10 years. Sixty thousand tourists visited the Galápagos last year.

Often the trade-off isn't even reasonable. Sharks are taken for their fins, to make gourmet soups. As for the sea cucumbers, their organs are dried or pickled to make aphrodisiacs.

The Polaris is one of the larger vessels licensed to tour the Galápagos, and it's comfortably old-fashioned in style. We had about 70 passengers on board, including grandparents, teenagers, singles, couples, retirees, teachers, lawyers, a hairdresser, an artist, a restaurant manager and one big C.E.O. A woman from New York was making her 15th voyage with Lindblad, the tour company that owns the ship, and I could understand why. Our journey to the end of the world was as easy as pie. We were provided with informative lectures, gorgeous local food, snorkeling equipment, a well-stocked library and, I think, an honest assessment of the problems that tourists, even ecotourists, can cause. Yet I had the feeling there were at least a few matters left unspoken. Even if we all made donations to the Charles Darwin Foundation, which runs the Charles Darwin Research Station on Santa Cruz, where tortoises are raised for eventual reintroduction, and to the Galápagos National Park and to various scholarship funds, still, there was no getting around the fact that we were part of the problem. We could only hope to be a bigger part of the solution.

''As I touched land a curious feeling of hopelessness came over me,'' wrote William Beebe of his arrival in the Galápagos in 1923. His curious despair was the kind brought on by hope. In a jungle, Beebe explained, there's no chance of studying everything, but on an island, discovery seems within reason. Everything is visible, circumscribed and isolated. So if there is any spot of earth we can save from ourselves, it would seem to be the Galápagos. I was full of hope at every stop we made, and still at every stop I sensed, like Beebe, ''the possibility of an opportunity slipping past forever.''

At Punta Suárez on Española, I met up with a blue-footed booby standing smack in the middle of the footpath. It made no offer to step aside and let me pass. Looking into its birdy eye, I saw . . . nothing at all. No fear, but also no aggression. No anxiety, affection, hope, recognition. Its indifference was profound, as if I were invisible, although I'd been told that if I did step too close it might jab at me with its beak. This strange fearlessness can't be explained by any local history of kindness on the part of man. Even Darwin killed birds and ate tortoises. The blue-footed booby wasn't afraid of me, but the name for this is not tameness. It's genetic innocence. Since the animals evolved in the absence of man, their innocence exists at a molecular level. I saw it again in the eye of an albatross just before it turned to begin its mating dance; I saw it in the stare of a sea lion nursing her pup on the beach. The animals felt nothing for people one way or the other, yet all around them were people, including me, in love with the animals.

And why did we fall for them? Because they made us feel innocent. Because we could believe, for a short while, that we were not dangerous, plundering, marauding fools. But all the same, encountering that blue-footed bird, I was seized by a major doubt as to which was the innocent and which the booby.

At night, we slept while the Polaris cruised to the next island; we visited eight in all. Among my favorites were Bartolomé, for its red cragginess and incongruous staircase to the summit; Santiago, where Darwin spent part of his crucial five weeks; and the extraordinary Genovesa, its harbor a collapsed volcanic crater into which the sea has poured, forming a bay partially ringed by cliffs. Then there was the cave at Punta Vicente Roca on Isabela, as beautiful a spot as I've ever seen, mysterious as Delphi, where we rode an ocean swell into the very mouth of the cave. In the interior of Santa Cruz we drove up to the green highlands, and the tortoise reserve at El Chato, where I decided that those ancient, stolid animals, heavy as boulders, were the ones I loved most -- until I saw their opposite alight on a nearby branch, a red splash of feathers in the greenery, the tiny vermilion flycatcher.

One evening, we anchored off the coast of Floreana for a barbecue supper on the rear deck. There was a full moon, a dome of unfamiliar stars and not a single airplane. Crew members took their cell phones to the top deck and called home. Schools of fish gathered in a pool of light at the stern, and every now and then a lone gull swooped in the shadows like a bat, skirting the light. ''Ghost gulls,'' the panguero said.

By day, I walked the islands or lay in a hammock reading ''The Voyage of the Beagle'' or, when we came to a place that was, as Dora said, ''snorkable,'' I snorkeled. The first time my body slipped from the panga into that cold water, my heart nearly quit -- and it didn't help that just then someone shouted, ''Hammerhead!'' It turned out that the cry was not a warning, it was an exclamation of joy. Everyone but me was eager to snorkel with sharks. I was happier with the sea lions, who were less scary than sharks and less aloof than boobies. A young sea lion would torpedo toward me at full speed until its nose seemed only inches from my mask, and then it would dive, skimming along the length of my outstretched body without touching it. They don't like to touch or be touched, Dora explained to me.

And now I'll tell the very kind of animal story I usually dislike, the kind that proves animals do love us. My snorkeling partner one afternoon was an energetic Tennessee woman in her 70's. We'd both been in the water a long time, and we were the last to return to the panga, cold and tired. I got in first, but Paula had some trouble swimming against the current. She was falling behind, and a flash of anxiety crossed her face. I called to the panguero: we needed to get her in. Then, without warning, four sea lions popped up alongside her. One rose exactly under her hand, and lifted it; and while they didn't boost her into the boat, they certainly boosted her spirits. Once she made it to the stern ladder, they slipped under the sea again.

Back in Puerto Ayora, I found the town lively with vendors and artists, children and lovers, scientists and scuba divers. Along the waterfront people were selling fish and trinkets, playing volleyball, strolling. A varied flotilla of blue-and-yellow boats, water taxis, fishing vessels and excursion yachts filled Academy Bay. Despite the bleaker side streets, Puerto Ayora looked like a good enough town, one I could imagine might actually, against all odds and expectations, raise its children to be the heroes it will need.

Re-entry into mainland culture was harder. Guayaquil, the largest city in Ecuador, is almost beautiful, with a colonial-era center and a new waterfront promenade. By the time I got to the heart of old Guayaquil, I was longing for the quiet deep calm and subtly changing colors of the Galápagos waters, the volcanic hills, the night skies -- and I was missing the creatures. In the city's Bolívar Park, land iguanas roam free and are fed daily. They laze overhead in the branches of trees or amble along the paths and the lawn, growing fat and, it seems, contented. I saw one big one watching a man eat an apple. Suddenly the iguana, at least two feet long, leapt onto the man's pants leg at thigh level, gobbled the apple and disappeared up a tree.

Everyone human was delighted. I tried to make something of it, symbolically speaking -- garden, reptile, animal, man -- something to do with wildness triumphant. But in the end I only looked up, and met the gaze of a dark eye through the leaves, looking down.

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