Darwin, a naturalist's voyage around the world

STAGE 10

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Le voyage de Darwin

STAGE 10

15 September – 20 October 1835
Galápagos, fauna, flora, samples, adaptation


On September 15, the Galápagos Islands came into view. The explorers were to spend a little over a month discovering this equatorial Pacific group of islands, made up of a dozen volcanic islands covered with thousands of craters.

On the 17th, the Beagle landed at Chatham Island, amid sweltering heat. The ground was made up of a black basalt lava flow, which was rough and in some places peppered with small cones of volcanic origin. At first sight, the only things growing there appeared to be some skimpy stunted shrubs, large odd-shaped cacti, sickly-looking weeds, and a few acacias. But the island was not entirely devoid of animal life. Darwin was intrigued by what appeared to be paths made by some kind of animals as they headed towards sources of water. He quickly found out what had made the paths when he came face to face with two huge tortoises. Present in very large numbers, these animals, which were to become the symbols of Galápagos, could provide up to 100 kg of edible meat. This explained why it sometimes took as many as six to eight men to lift them off the ground. Darwin tried several times to keep his balance on their backs, but with little success.

On the 23rd, the explorers travelled to Charles Island, which had been settled for six years by several hundred people of color, who had been banished from the Republic of Ecuador for political crimes. Like its fellows, the island featured a few shrubs on the coast, which were quickly replaced by greener woodland and then by a lush vegetation of coarse grasses and ferns at the summit. Although pigs and wild goats were scattered throughout the woods, the giant tortoises were the main source of food for the islanders. This much-appreciated fare was accompanied by sweet potatoes and bananas. Darwin met a man who assured him that he could tell which island a tortoise was from just by looking at it. At the time, he didn't pay much attention to what the man had said!
On the 29th, the ship arrived off the coast of Albemarle island, which was covered with solidified lava and populated by large black aquatic lizards. Measuring up to four feet long, these lizards were the only ones in the world able to feed off marine plants. Another odd thing about them was that they were larger on this island than anywhere else. Darwin also studied some very numerous, hideous-looking yellowish-brown lizards, which were very slow-moving and could weigh as much as 15 pounds. This terrestrial species ate berries, acacia leaves and above all cacti.

On October 8, accompanied by several men, Darwin landed on James Island, where he met a small band of Spaniards catching and drying fish. They were also salting tortoises, and during his stay the naturalist ate nothing but the meat of these reptiles. The temperature was in excess of 40° C on the island, which was also home to the yellowish-brown lizards. The holes they made in the ground were so numerous that it was difficult to pitch the tents. On the baking-hot coast, only a few bare shrubs managed to grow. But higher up the air was less suffocating and the vegetation was more welcoming, and there were even a few meadows. As on all the islands of the archipelago, the higher ground, where clouds gather, was wetter and more fertile than the lowlands.

Altogether, in scarcely over a month, Darwin collected no less than 193 species of plants, 26 species of terrestrial bird, 17 species of shellfish, 15 saltwater fish and 11 waders, as well as aquatic birds, reptiles, insects, etc. But behind these impressive figures, there lay an even more astonishing underlying reality: many of these species were quite unique. Even more amazingly, some of them only existed on one of the islands of the archipelago and not on the others. Each island appeared to have engendered species that were specifically adapted to their own environment. The example of the finches was especially revealing. Although the morphology of these birds was strikingly similar, they differed from each other in various details such as the shape and size of their beaks. Darwin realized that the isolation of these birds on their respective islands meant that, from a single species of continental origin, the birds had diverged and now showed variations that were probably related to differences in their way of life and feeding habits. This discovery, and many others, was to contribute to the elaboration of his theory of natural selection and to shed light on the mechanism whereby species evolve by adapting to their environment.
But for now, it was 20 October 1835, and the Beagle set sail, heading for Tahiti.

CNRS    sagascience