Voyage of the Beagle 1832-1836
Darwin noticed that the birds on the islands shared important characteristics with those in America (as the birds of Cape Verde Islands shared characteristics with their counterparts on the mainland of Africa). He reasoned that they had migrated from the mainland, and had not originated on the islands. The finches of the Galapagos demonstrated to Darwin that those born with natural variations giving them an advantage in their new environment survived and carried on those characteristics. The food available on the islands included a limited amount of seeds and insects. Competition for these foods, which differed from those on the mainland, caused the finches to evolve according to the island’s demands.
Geospiza parvula. (James’ Island, Galapagos Archipelago) from John Gould's The Zoology of the Voyage of H.M.S. Beagle. Part III: Birds. London: Smith, Elder & Co., 1841.
Finches with the larger beaks to open seeds (such as the Geospiza magnirostris), and smaller ones to eat insects (as Geospiza parvula, above), evolved to fill the environmental niches afforded on the islands. Those species without needed variations died out. In South America, he had discovered fossils of extinct animals that differed from living examples; this contributed to his understanding of the process of natural selection.
Darwin: Page 2 of 3.	back   next