Naturalist Charles Darwin's five-year voyage on the Beagle changed the face of modern science and our understanding of human existence. After stops along the coast of South America, the Beagle explored the Galapagos Islands, an isolated volcanic archipelago straddling the equator. It was there that Darwin noticed that each island contained identical species of finches whose beaks differed in size and structure. From this observation Darwin later extrapolated his theory of natural selection, the evolutionary process by which organisms with certain adaptive characteristics tend to survive and pass on those qualities.