Toxodon, with giant squirrel teeth—that had once roamed the plains. “I have been wonderfully lucky,” he wrote. “Some of the mammals were gigantic, and many of them are quite new.” He collected fragments from a pig-size guinea pig, armor plates from a tanklike armadillo, more elephantine bones from elephantine sloths, and crated and shipped them to England.
The Beagle rounded the sharp jaw-bend of Tierra del Fuego and climbed the western coast of South America. In 1835, the ship left Lima, on the coast of Peru, and headed toward a lonely spray of charred volcanic islands west of Ecuador—the Galápagos. The archipelago was “black, dismal-looking heaps . . . of broken lava, forming a shore fit for pandemonium,” the captain wrote. It was a Garden of Eden of a hellish sort: isolated, untouched, parched, and rocky—turds of congealed lava overrun by “hideous iguanas,” tortoises, and birds. The ship wandered from island to island—there were about eighteen in all—and Darwin ventured ashore, scrambling through the pumice, collecting birds, plants, and lizards. The crew survived on a steady diet of tortoise meat, with every island yielding a seemingly unique variety of tortoise. Over five weeks, Darwin collected carcasses of finches, mockingbirds, blackbirds, grosbeaks, wrens, albatrosses, iguanas, and an array of sea and land plants. The captain grimaced and shook his head.
On October 20, Darwin returned to sea, headed toward Tahiti. Back in his room aboard the Beagle, he began to systematically analyze the corpses of the birds that he had collected. The mockingbirds, in particular, surprised him. There were two or three varieties, but each subtype was markedly distinct, and each was endemic to one particular island. Offhandedly, he scribbled one of the most important scientific sentences that he would ever write: “Each variety is constant in its own Island.” Was the same pattern true of other animals—of the tortoises, say? Did each island have a unique tortoise type? He tried, belatedly, to establish the same pattern for the turtles—but it was too late. He and the crew had eaten the evidence for lunch.
When Darwin returned to England after five years at sea, he was already a minor celebrity among natural historians. His vast fossil loot from South America was being unpacked, preserved, cataloged, and organized; whole museums could be built around it. The taxidermist and bird painter John Gould had taken over the classification of the birds. Lyell himself displayed Darwin’s specimens during his presidential address to the Geological Society. Richard Owen, the paleontologist who hovered over England’s natural historians like a patrician falcon, descended from the Royal College of Surgeons, to verify and catalog Darwin’s fossil skeletons.
But while Owen, Gould, and Lyell named and classified the South American treasures, Darwin turned his mind to other problems. He was not a splitter, but a lumper, a seeker of deeper anatomy. Taxonomy and nomenclature were, for him, merely means to an end. His instinctive genius lay in unearthing patterns—systems of organization—that lay behind the specimens; not in Kingdoms and Orders, but in kingdoms of order that ran through the biological world. The same question that would frustrate Mendel in his teaching examination in Vienna—why on earth were living things organized in this manner?—became Darwin’s preoccupation in 1836.
Two facts stood out that year. First, as Owen and Lyell pored through the fossils, they found an underlying pattern in the specimens. They were typically skeletons of colossal, extinct versions of animals that were still in existence at the very same locations where the fossils had been discovered. Giant-plated armadillos once roamed in the very valley where small armadillos were now moving through the brush. Gargantuan sloths had foraged where smaller sloths now resided. The huge femoral bones that Darwin had extracted from the soil belonged to a vast, elephant-size llama; its smaller current version was unique to South America.
The second bizarre fact came from Gould. In the early spring of 1837, Gould told Darwin that the assorted varieties of wrens, warblers, blackbirds, and “Gross-beaks” that Darwin had sent him were not assorted or various at all. Darwin had misclassified them: they were all finches—an astonishing thirteen species. Their beaks, claws, and plumage were so distinct that only a trained eye could have discerned the unity lurking beneath. The thin-throated, wrenlike warbler and the ham-necked, pincer-beaked blackbirds were anatomical cousins—variants of the same species. The warbler likely fed on fruit and insects (hence that flutelike beak). The spanner-beaked finch was a seed-cracking ground forager (hence its nutcracker-like bill). And the mockingbirds that were endemic to each