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Galapagos and Darwin

Darwin and Evolution

In June 1831, the H.M.S. Beagle set sail from England under the command of Commander Robert Fitz Roy on a 4 year surveying mission (Fitz Roy was promoted to Captain during the cruise). Fitz Roy had decided to take along some one who would "profit from the opportunity of visiting different countries yet little known." The person who took up this unpaid position was 22 year-old Charles Darwin. Darwin had begun his studies as a medical student, then became a divinity student at Cambridge. Neither field has excited him, and his father, a physician, considered him something of a disgrace. Darwin had become interested in geology and spent some time studying geology informally with the great Scottish geologist Charles Lyell (geology was not yet a formal field of study). He was an avid beetle collector as well. After three years of surveying the South American coast, the Beagle reached San Cristobal (Chatham) in September 1835. The Beagle spent 5 weeks in the Galapagos carefully charting the archipelago. Fitz Roy's chart was remarkably accurate and remainded in use until the U.S.S. Bowditch recharted the area in 1942.

In the meantime, Darwin made careful observations about both the geology and biology of the islands. Darwin was particularly struck by the"differences between the inhabitants of the different islands":

"The distribution of tenants of this archipelago", he wrote, "would not be nearly so wonderful, if for instance, one island has a mocking-thrush and a second island some other quite distinct species... But it is the circumstance that several of the islands possess their own species of tortoise, mocking-thrush, finches, and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of this archipelago, that strikes me with wonder."

[In some cases, what Darwin considered separate species are now considered races or subspecies.] Darwin landed at only four of the islands (San Cristobal, Floreana, Santiago, and Isabela); his wonder would have been all the greater had he visited other islands, for the same pattern is repeated throughout the archipelago.

 

Upon his return, Darwin continued to ponder this. But he had other work to do as well. The voyage of the Beagle had been a unique scientific opportunity and he made the most of it. In 1845, he published a general account of his observations as The Voyage of the Beagle. He also published books on the Structure and Distribution of Coral ReefsVolcanic Islands visited during the Voyage of the Beagle andGeology of South America, plus Zoology of the Voyage of the Beagle as well as a number of scientific papers. Darwin's best work, however, on this business of species, their distribution, and their place in the "natural economy", was still to come. It took Darwin nearly 25 years to complete it, though he had the most important part worked out in his own mind within four years. This germinating idea was revolutionize the way we think of the world.

Darwin is often credited with the theory of evolution, the idea that complex organisms have developed gradually over geologic time from simpler ones. This is not correct, as he would freely admit. Naturalists had already developed this idea by the end of the eighteenth century. If any single person deserves credit for evolution, it should be the Frenchman Jean Baptiste de Lamarck (1744-1829), who called his theory "transformism" rather than "evolution". Darwin had learned of transformism at Cambridge, though he remained a "creatonist" until after the Beagle returned to England. As he pondered what he had seen in the Galapagos, he realized that many of these observations could be explained the by this heretical idea. What continued to elude Darwin and the other naturalists of the time, was how tranformation occurred. Lamarck, for example, had believed that characteristics acquired during the lifetime of an individual could be passed on to its offspring. There was, however, no evidence to support this idea, and with our modern understanding of genetics and molecular biology, we recognized that this is quite impossible.

Darwin's great contribution to science was that he solved this mystery of how and why evolution occurred. The answer, which he called natural selection, finally occurred to him in 1839. The essence of the idea is that those individuals born with characteristics that make them best suited for their environment are the ones most likely to survive and most likely to successfully produce offspring. It took Darwin another 20 years to develop the evidence he felt he needed to support this idea. Darwin considered factors such as hybridism, instinct, the fossil record, geographical distribution, and embryology and neatly folded them all into his theory. He published a short paper on it in 1858. Alfred Wallace published a paper with the same idea in the same year; indeed, after Wallace wrote to Darwin telling him of his own idea of natural selection, he and Darwin agreed to publish similtaneous papers. Neither paper attracted much attention, but Darwin's book, The Origin of Species, published the next year (1859), caused an immediate sensation. Darwin's concluding paragraph elequently summarized his view of the evolution of life:

Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.

By 1859, Darwin was an emminent scientist, so his ideas about the how of evolution occurred drew attention to the the more fundamental issue of creation versus evolution. His views were given a careful hearing, even when they were not always believed. As with any important new scientific theory, intense debate followed. Though there are those among the general public who still defend creationism today, Darwin had built such a powerful case that, among scientists at least, the issue was largely settled in favor of evolution and natural selection within ten years.