On a sunny day in October 1835, a 26-year-old Charles Darwin hiked from the parched coast of Santiago Island in the Galápagos archipelago to the island’s green, damp highlands. After a long walk, he sat in the shade and watched the island’s giant tortoises as they ambled along broad roads that had been trodden by their elephant-like feet over countless generations. He timed their gait (faster than he had supposed), measured their carapaces (six and eight feet in circumference) and tried to lift them (tortoises can weigh upwards of five hundred pounds). Finding he could not, he climbed aboard, rapping on their shells and trying not to slip off their backs as they trudged along.

Today, the species of tortoise that inhabits Santiago Island is named for Darwin, following the system of Latin binomials used to classify species since the 18th century. C. darwini is one of 15 different species of Galápagos giant tortoises, each of which inhabits an island or volcano in this Pacific archipelago 600 miles off the coast of Ecuador. Galápagos giant tortoises are, along with the archipelago’s famous finches, exemplary evidence of evolution. The giants diversified because of geographical separation, each species adapting to the conditions of life on a different island in the archipelago. Today, these enormous reptiles are textbook examples of the process of adaptive radiation in what is often called ‘Darwin’s natural laboratory of evolution’.

Yet it was not Darwin who named the species, nor he who revealed the tortoises’ evolutionary significance. When Darwin was in the Galápagos, he was not yet thinking about evolution as we now understand it. Although he made notes about the tortoises’ behaviour, gait, hearing and size, he did not make collections of the animals, as he did with island birds, plants, rocks, lizards and insects. Instead, he ate them.

Today we think of the Galápagos as a wonderland for both nature tourists and biologists, but in the mid 19th century most visitors came not to marvel at unique endemic creatures but to find their dinners. The tortoises were world-renowned for their taste, not their scientific import. Throughout the 18th and 19th centuries, the Galápagos were a popular stopover for ships in the eastern Pacific that carried pirates, buccaneers, and later whalers and sealers. Though the islands offered little fresh water, they were a useful storehouse where sailors could gather timber, fresh fruits and vegetables and, above all, giant tortoises. After months at sea, weary sailors considered the tortoises a sought-after prize. As one British admiralty captain-turned-whaler wrote in 1798, giant tortoise meat ‘in whatever way it was dressed, was considered by all of us as the most delicious food we had ever tasted’. The Beagle men took 45 giant tortoises on board as food, although ships commonly took dozens, if not hundreds, of the animals to fill their hulls. The tortoises are said to have been able to survive for months, even a year or more, without food or water, making them an ideal portable source of fresh meat and fat.

Darwin was less impressed with the animals’ taste than other sailors were. For two days he camped in the highlands of Santiago with tortoise hunters, subsisting on nothing but tortoises. For dinner, the hunters made tortoise carne con cuero in the style of Argentinian gauchos – roasting meat on the breastplate and frying it in tortoise fat. Jotting down his impression of the meal afterward, Darwin deemed it ‘very good’, although he preferred the ‘capital soup’ made of young tortoises.

The tortoise hunters Darwin hired to be his guides on Santiago were not sailors but instead some of the archipelago’s first human inhabitants. They were political exiles from the new state of Ecuador sent to the Galápagos as penal labourers. Throughout the 19th and early 20th centuries, the Galápagos archipelago was not only a field site for scientific endeavour and a stopover for Pacific sailors but also a developing frontier for a new postcolonial state. The islands were a place for Ecuadorian politicians to rid the new nation of undesirables – from political opponents to criminals, debtors, the poor and often indigenous people as well. The Floreana colony was called Asilo de la Paz, Asylum of Peace, but peace was far from its fate. Not long after the Beagle voyage, captive labourers rebelled, and the colony failed. It was the first in a series of ill-fated attempts at island colonisation during the period.

Darwin and Beagle captain Robert FitzRoy visited Floreana several weeks before going to Santiago. The men saw not simmering unrest but a flourishing hacienda of sugarcane, bananas, corn and sweet potatoes where about three hundred colonists lived what Darwin described as a ‘sort of Robinson Crusoe life’. They toured the colony with the acting vice governor, a Norwegian mercenary named Nicholas Lawson. It was Lawson who sent the tortoise hunters to Santiago to supplement the rapidly diminishing population of tortoises on Floreana, which the colonists relied upon for food. It was also Lawson who first told Darwin something that, in retrospect, was a significant clue to the puzzle of evolution that Darwin was beginning to piece together.

As Darwin and Lawson toured the Floreana colony, Lawson remarked that he could ‘with certainty tell from which island any [tortoise] was brought’. Weeks later, the tortoise hunters told Darwin the same thing – that the tortoises differed on each island enough that it was possible to tell them apart. On small, dry islands, the tortoises were smaller, and their shells curved up at the back of their necks, making their carapaces look like saddles (an adaptation to island environments with sparse ground cover that allowed the animals to stretch their necks up to reach leafy trees and juicy cactus pads). On larger, higher islands like Floreana and Santiago, where volcanic calderas are often enshrouded in misty clouds, the tortoises were much larger when full grown and their carapaces were dome-shaped, without the upside-down ‘U’ at the back of their necks. These animals lived in places where the ground was blanketed in greenery year round, giving them a steady food supply. In addition to these two dominant morphotypes, the tortoises also differed slightly in colouring – some were deeper black, others had yellow markings under their chins and throats. Lawson and the tortoise hunters would not have understood differences among the tortoise populations as evolutionary adaptations, but small distinctions in size and morphology were just the kind of significant details that hinted at the diversification of species. Yet while Darwin was in the Galápagos, he failed to see the importance of what Lawson and the Ecuadorians told him. ‘I did not for some time pay sufficient attention to this statement’, Darwin lamented back in England years later. ‘I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted.’

It was thus not until Darwin was back in England that he began considering the evolutionary significance of the giant tortoises and other Galápagos animals. Upon his return, Darwin distributed the many biological specimens he had collected from the Galápagos and other places to expert taxonomists. Ornithologist John Gould, curator of the Zoological Society of London, examined the birds Darwin had collected in the Galápagos and found that what Darwin had thought were three different types of birds were in fact all ground finches with such curiously divergent forms that they represented 12 new species. But when Darwin had labelled these birds, he had not included their islands of origin. So, despite this exciting revelation, the specimens did not make for reliable evidence of evolution. Darwin got better news two months later when Gould told him that the mockingbirds he had collected, and labelled by island, were not just varieties but also differed enough to constitute separate species – related to, but distinct from, South American mockingbirds. Darwin realised the import of this information and filled the sheet of paper he had brought to the meeting with excited scribbles. Back at home, he soon started his first notebook on ‘transmutation’, as evolution was often called at the time.

Darwin realised the news about the finches and mockingbirds was parallel to Lawson’s observation about the tortoises. But he had not made scientific collections of the tortoises – perhaps because at the time naturalists thought the Galápagos tortoises were part of the same species of giants that sailors had long reported finding on islands in the Indian Ocean, which British taxonomist John Gray had named Testudo indica. The remains of the 45 animals the Beagle crew had taken as food had been tossed overboard, or their shells turned into serving bowls and plates. The only tortoises that had made it back to England were four tiny young animals that Darwin, FitzRoy and others had brought home as pets. Yet Darwin was eager to know whether the Galápagos tortoises were distinct species, and so he gathered the four young animals for Gray to analyse. As it turned out, though, they were too small to show significant differentiation, Gray found. Darwin did not have the evidence to confirm his hunch that the Galápagos tortoise, as he wrote in his Journal of Researches (1845), was an ‘aboriginal inhabitant’ of the islands, much less that the tortoises differed by island as the mockingbirds did. It would be nearly 80 years after his Galápagos visit before naturalists proved this hypothesis.

How then did the Galápagos tortoises become evidence of evolution? The answer lies in the story of how C. darwini got its name.

Darwin marvelled about the Galápagos in his popular travel narrative about the Beagle voyage, even writing that the archipelago was the ‘origin … of all my views’. But he scarcely mentioned the islands in his Origin of Species, because he did not have enough evidence. It was not until the decades after Darwin published the Origin in 1859 that the Galápagos became a proving ground for theories of evolution. Giant tortoises became proxies for evolution in the final decades of the 19th century after a naturalist named Albert Günther, who was the keeper of zoology at the British Museum, published a study in 1875 that showed that the Galápagos giants were not part of the T. indica species but were a distinct lineage. Günther thought the Galápagos Islands had five different tortoise species. As original and unique inhabitants, the Galápagos tortoises, Günther demonstrated, were what biologists now call endemic species – not only native to the islands but existing only in one particular place. They were not recent arrivals but had lived in the islands for quite some time. Yet Günther did not comment on the evolutionary significance of the Galápagos tortoises. He was ambivalent about Darwin’s theory of evolution – perhaps because he worked for Darwin’s arch-rival, Richard Owen, who used his position as curator of the British Natural History Museum to vociferously challenge Darwin’s interpretation of what caused evolutionary change.

Günther’s study set off a mania for collecting giant tortoises at the turn of the 20th century, including three expeditions financed by amateur natural historian (and banking family scion) Walter Rothschild, who once housed dozens of giant tortoises on his family’s Tring estate. The most extensive Galápagos expedition of this period, though, was led by the California Academy of Sciences (Cal Academy) in 1905–6. A team of eight natural history collectors set off from San Francisco with the mission of ‘collecting evolution’ – when they returned after spending 366 days in the archipelago, their specimens would provide the basis, as Matthew James has written, for ‘vindicating’ Darwin.¹ Nine months into their stay, in late July 1906, the team caught five tortoises on Santiago, including the animal that would become Specimen 8109. During a previous visit to the island in January, lead collector Rollo Beck had found the remains of the camp once used by tortoise hunters but no live tortoises there, only scattered bones. On this trip, he was determined to find living tortoises and hiked further inland through the harsh, lava-strewn terrain. Deep in the interior of the island, Beck and another collector, Ernest King, found two large male tortoises. Crew members prepared the animal specimens in situ, skinning them by dissecting them and cleaning out their internal organs, scraping meat and fat from their skin and bones. As they skinned, Beck continued searching, eventually finding three more tortoises. The men hauled these five animals back to shore by ‘backing down’ smaller ones on their shoulders or strapping large ones to poles shouldered by two or more men. It was arduous work: these Santiago tortoises, one collector noted, had ‘the heaviest shells and bones of any taken by us’ and were ‘very fat’.

Transporting specimens from far-flung locations like the Galápagos to metropolitan museums was always difficult – damp sea air, mould, bugs and bacteria ate away at organic matter, and there was always risk of simply losing collections in transport. Animals were more difficult to preserve than plants, and thus many collectors predominately saved animals with hard features – a tortoise’s shell was an ideal material because of its durability, if not its size and weight. Many museums’ tortoise specimens were just cleaned shells, the animal’s internal organs, bones and soft tissue having rotted away or been discarded. The specimens the Cal Academy men preserved, though, were more complete – some were fully stuffed in lifelike positions, while others included the animals’ necks and heads, which had been cleaned, stuffed, dried and dusted with arsenic to keep insects away.

When the Cal Academy team returned to San Francisco in November 1906, they delivered their tortoise specimens – 266 in all – to the museum’s herpetologist, John Van Denburgh. It was Van Denburgh who named the Santiago tortoises for Darwin in 1907. Yet the animals Van Denburgh studied were quite different to the living creatures Darwin had watched drinking from muddy pools. The five Santiago tortoises Van Denburgh studied were dead carcasses, sitting on research tables thousands of miles away from their homeland. Of the five, Van Denburgh chose one, Specimen 8109, as the type specimen to represent the species he called Testudo darwini. That animal now sits in a back storeroom of the California Academy of Sciences in San Francisco. Darwin might have ridden on the backs of these tortoises, but T. darwini could no longer move of its own accord – its desiccated head and neck resting on a table, lifeless and only part of the animal that had once existed.

After nearly a decade of close study of the Galápagos tortoises, Van Denburgh published in 1914 the monograph that established that the archipelago had 15 different kinds of tortoise, each on its own island or volcano, as Darwin had supposed. Over the 20th century, despite debates about whether the tortoise populations should be considered species or subspecies and changes in the genus name from Testudo to Geochelone to Chelonoidis, Van Denburgh’s monograph served as the authority on the species. The significance of the Galápagos giant tortoises as a set of species that exemplifies the dynamic evolutionary processes of life had emerged, ironically, only through the study of still life. While the Santiago species bears Darwin’s name, the tale of its incorporation into the annals of evolutionary science reveals another story: one of the contingencies of knowledge production and the role of little known actors rather than the solitary genius of a scientific hero.

FURTHER READING

Colnett, J. (1798) A Voyage to the South Atlantic and round Cape Horn into the Pacific Ocean, for the Purpose of Extending the Spermaceti Whale Fisheries, and Other Objects of Commerce, by Ascertaining the Ports, Bays, Harbours, and Anchoring Births, in Certain Islands and Coasts in Those Seas at Which the Ships of the British Merchants Might Be Refitted: Undertaken and Performed by Captain James Colnett, of the Royal Navy, in the Ship Rattler (London).

Darwin, C. (1845) Journal of Researches into the History and Geology of the Countries Visited During the Voyage of the H.M.S. Beagle Round the World under the Command of Capt. Fitz Roy, R.N. (London: John Murray).

Van Denburgh, J. (1914) ‘Expedition of the California Academy of Sciences to the Galápagos Islands, 1905–1906. X. The gigantic land tortoises of the Galápagos archipelago’, Proceedings of the California Academy of Science, 4.

Hennessy, E. (2019) On the Backs of Tortoises: Darwin, the Galápagos, and the Fate of an Evolutionary Eden (New Haven, CT: Yale University Press).

James, M.J. (2017) Collecting Evolution: The Galápagos Expedition that Vindicated Darwin (New York, NY: Oxford University Press).

Keynes, R.D. (ed.) (2001) Charles Darwin’s Beagle Diary (Cambridge: Cambridge University Press).

Larson, E. (2001) Evolution’s Workshop: God and Science on the Galápagos Islands (New York, NY: Basic Books).

Sulloway, F. (1984) ‘Darwin and the Galápagos’, Biological Journal of the Linnaean Society, vol. 21, 29–59.

¹ M.J. James, Collecting Evolution: The Galápagos Expedition that Vindicated Darwin (New York, NY: Oxford University Press, 2017).