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4. Discovery
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[ 26 ] four v Discovery During an exPeDition from Valparaíso to the high Andes in 1834, Darwin located marine deposits that included the remains of a petrified forest. He deduced that this part of the South American continent had once been under the sea and was subsequently uplifted more than 7000 feet. Darwin was on Chiloe Island when he witnessed the volcanic eruption of Chile’s Mt. Osorno on 26 November 1834. He also survived an earthquake in Valdivia which destroyed the city of Concepción on 20 February 1835. These experiences demonstrated Lyell’s geological principles in dramatic fashion and stimulated Darwin’s revolutionary ideas. During an expedition into Argentina, and again in the Andes, Darwin fell seriously ill. He developed a fever, now suspected to have been caused by the bite of the benchuga bug, Triatoma infestans, a frequent carrier of the protozoan parasite Trypanosoma cruzi, which causes Chagas’s disease. Trypanosoma frequently invades cardiac muscle and destroys nerves in the intestines, causing heart and digestive disorders; it also has periods of latency. Today approximately 50,000 people in Latin America die annually from Chagas’s disease, which kills 10 to 20 percent of the people it infects. This disease has been offered as one explanation of Darwin’s lifelong illness, but not all medical detectives are convinced. Others consider his physical problems, although very real, to have been psychosomatically induced, caused by the stress his [ 27 ] ideas produced, and there is a good deal of circumstantial support for this hypothesis. In fact, Darwin’s health improved in the years after the general scientific acceptance of his ideas. His stress-based symptoms might even be considered a form of panic disorder. Still others have speculated that he turned himself into an invalid to avoid social distractions so he could get on with his work. These three explanations are not mutually exclusive. Darwin may very well have had a mild form of Chagas’s disease as well as suffering the ill effects of self-induced stress, and he certainly guarded his time. (See To Be an Invalid by Ralph Colp Jr. for speculation about Darwin’s illness.) Traveling the Andes, which provided Darwin with evidence of the geological forces described by Lyell in his Principles of Geology. (From Darwin’s Journal of Researches) [3.229.122.112] Project MUSE (2024-03-19 09:12 GMT) [ 28 ] The eruption of Antuco volcano. Witnessing volcanic eruptions helped create Darwin the geologist. (From Atlas de la Historia Fisica y Politica de Chile, by C. Gay [1854].) Remains of the cathedral at Concepción, Chile, after the earthquake in 1835, from a drawing by Darwin’s favorite Beagle officer, First Lieutenant John Clements Wickham. Earthquakes, volcanoes, and mountainbuilding completed Darwin’s geological education. (From Narrative of the Surveying Voyages of HMS Adventure and Beagle between the Years 1826 and 1836.) [ 29 ] Triatoma sp., the vector of Chagas’s disease caused by the protozoan parasite Trypanosoma cruzi (inset). These assassin bugs are members of the order Hemiptera, family Reduviidae. (From Missouri Conservationist , June 2003, p. 27; used with permission of the photographer, David Liebman.) After departing from the west coast of South America, the Beagle sailed west about 600 miles (1000 km) to the Galápagos Islands, named for their giant tortoises. The Beagle spent five weeks in the Galápagos in 1835, and Darwin visited four of the sixteen major islands. During a dinner party, the vicegovernor of the Galápagos explained that he could identify which island a tortoise came from by the shape of its shell. (Later, when leaving the Galápagos, the crew took eighteen live tortoises to use as food on the way home.) Likewise, Darwin had noted differences between the mockingbirds (four species of Nesomimus) from various islands. Almost every biology textbook has a pictorial feature about Darwin’s finches and how important they were to Darwin’s idea of natural selection. The truth is that Darwin, while in the Galápagos, did not recognize differences among the finches. In fact, his labels did not include the island from which he collected each finch. Only after the voyage, when ornithologist [3.229.122.112] Project MUSE (2024-03-19 09:12 GMT) [ 30 ] Top, Galápagos giant tortoise, Geochelone elephantopus porteri, from Santa Cruz. Note the dome-shaped shell found on tortoises from islands with rainfall adequate to support lush vegetation. These tortoises tend to be larger and have relatively short legs and necks. These adaptations allow the...