It was those currents and the remoteness of the islands that made the environment unique, because they forced species arriving by air or ocean currents to adapt to the conditions of the various islands of the archipelago, which was formed by volcanoes rising from the sea bed.
As we clambered off our yacht on to pangas - motorised dinghies that sliced through the turquoise brine - we felt less like privileged tourists and more like free-spirited explorers.
The pangas deposited us on the beach of North Seymour Island and I was greeted by a landscape of rust and ash - red lava rock and palo santo trees the colour of bleached bones, twisted and broken like disturbed skeletons.
I picked a path through the espino, cacti and scurrying lava lizards as sea lions padded nonchalantly past. Above us hovered Galapagos doves with their distinctive red feet and blue eyes. I saw my first blue-footed booby, a comical-looking bird famed for its courtship dance, in which it kicks its feet high in the air and spreads its wings while whistling and honking.
A baby sea lion waddled over to a female, who scornfully flicked it into the air. Female sea lions feel affection only for their own babies, so if a mother dies its children are doomed.
We came across a male sea lion howling in pain from two large bite marks on its body.
"This one looks like it's been in a fight with the dominant beach-master sea lion," said Pablo, one of the three naturalists on board our yacht.
"The beach-master can have up to 30 females in his harem and he will chase away younger males because they are a threat."
Despite the exoticism of the animal species in the Galapagos, I found myself comparing the wildlife on the islands with my own species - the male wingless cormorant trying to impress the female by presenting a string of seaweed, only to be spurned until he offered a more substantial clump; the male frigate bird that I watched trying to score with the females by inflating his red throat pouch until it was the size of a balloon.
When he visited the Galapagos, Darwin was surprised by the tameness of the creatures, which did not run from humans because they had not learned to fear them. As our panga skimmed across the glass-splintered sea, the sparkling water looking as though it had been dusted by crushed emeralds, I saw sea lions playfully leaping out of the water as frigate birds fluttered above like flapping origami. On another island, finches landed on branches inches from my face.
The Galapagos do not thrill only with their wildlife - the pink flamingos standing on one leg in the brackish water, the flame-red Sally Lightfoot crabs scuttling on the black rocks, the tropical penguins and the green sea turtles, the dazzling yellow-tailed surgeonfish, sea stars and king angelfish that shimmered in the water under our glass-bottomed boat.
No, it was the landscape of the islands I found enthralling: the red sand beach of Rabida Island, the result of hot lava flowing millions of years ago; pink-smudged sunsets floating above the astonishing whirls and twirls of black molten rock hardened into a lunar landscape on Sullivan Bay; the dun and chalk Kicker Rock, a monumental work of sculpture shaped by wind and sea.
On Santiago Island, the fourth-largest in the archipelago, I saw hundreds of marine iguanas thawing in the sun. The reptiles, which Darwin dubbed "imps of darkness", were so black they melted into the landscape. It was hard to tell rock from reptile except for the shooting white arcs that would explode from their noses - their diets contain excess salt that has to be expelled by sneezing. Their motionlessness made them perfect subjects for photography.
But I didn't want to look through a lens; I wanted to look directly at these prehistoric creatures and wonder what they made of these strange intruders into their world.
What had the forebears of these iguanas made of Alexander Selkirk - Daniel Defoe's inspiration for Robinson Crusoe - who visited the islands in 1708?
What had the turtles thought when they saw HMS Beagle? What did the finches think when they saw gigantic white birds gliding out of the sky and landing on their islands, carrying hundreds of shuffling two-legged strangers?
"Attention! Attention! Killer whale spotted."
The crackling sound from the walkie-talkie shook me out of my reverie. Two killer whales had been sighted off the coast. We leapt into the pangas and raced towards our targets.
Each time we spotted a sliver of black and white in the distance, it had vanished by the time we reached the spot. Having spent the morning feeling like Darwin, I was now Captain Ahab chasing the elusive whale.
It wasn't an idle comparison - Herman Melville passed through here in 1841 gathering material that later wound up in Moby Dick. But unlike Ahab, whose pursuit of Moby Dick became an obsession, our search for the whales lasted less than an hour, after which we returned to our luxury yacht, where waiters served us hot chocolate.
That afternoon, the group gathered in the conference room for a lecture on Darwin and the Galapagos.
Pablo explained how Darwin was only 26 in the autumn of 1835 when he spent five weeks on the archipelago - this "world within itself" as he described it - as part of a five-year voyage aboard the Beagle.
The observations he made in the Galapagos of finches that appeared to be slightly different on each island convinced him it was the conditions of the individual islands that were forcing the finches to adapt and evolve. And so was born a theory that fundamentally altered how people saw nature and life on earth.
The Galapagos Islands are named after its famous tortoises - galapago is Spanish for "saddle", referring to their saddleback shells - and I finally saw them on Santa Cruz Island.
They were grazing quietly, apparently freely, but all suspiciously clumped together in one field. We had been warned not to get too close - advice Darwin had evidently not followed, as he rode the tortoises as if they were horses, getting "on their backs and then giving a few raps on the hinder parts of their shells".
These days riding the tortoises is discouraged, but I did see one giant tortoise clamber on to a female and start having what looked like a good time.
I did wonder about the damage the 160,000 tourists who come to the islands every year are doing. Are they destroying the thing they are coming to see? It was a question I put to Timothy Silcott, who works for the Charles Darwin Foundation, an environmental charity in the Galapagos.
"Tourism is incredibly important to the Galapagos," he told me. "It helps sustain the economy of the islands.
"The regulations for visiting the Galapagos are pretty solid. You can't set foot on the islands without a guide, the itinerary is agreed a year in advance, you can't have a group bigger than 16 and no smoking or eating is allowed inside the national park [which covers 97 per cent of the archipelago]."
So what should an ethically minded traveller do if they want to visit the Galapagos?
"Try to use a tour operator who uses local staff," Silcott suggests, "and one committed to protecting the environment through recycling - and steer clear of hotels and stick to yachts."
Nearly two centuries after Charles Darwin visited the islands, they are still the closest thing to Eden on Earth.
On our last evening we gathered for a final cocktail and Pablo presented a slide show of photographs he had taken during the week. It had been an exhilarating seven days, filled with images and moments I will not easily forget, and yet the most remarkable thing about my time was not what I did see but more what I did not.
Tourists glimpse only a tiny fraction of every island they visit; beyond the trails, the Galapagos remain as they have always been - wild, untamed and mysterious.
CHECKLIST
Getting there: United Travel runs tours through Lindblad Expeditions, which has the National Geographic Endeavour and the National Geographic Islander, cruising the Galapagos.
