From The National Geographic:
The journey of young Charles Darwin aboard His Majesty's Ship Beagle, during the years 1831-36, is one of the best known and most neatly mythologized episodes in the history of science. As the legend goes, Darwin sailed as ship's naturalist on the Beagle, visited the Galápagos archipelago in the eastern Pacific Ocean, and there beheld giant tortoises and finches. The finches, many species of them, were distinguishable by differently shaped beaks, suggesting adaptations to particular diets. The tortoises, island by island, carried differently shaped shells.
These clues from the Galápagos led Darwin (immediately? long afterward? here the mythic story is vague) to conclude that Earth's living diversity has arisen by an organic process of descent with modification—evolution, as it's now known—and that natural selection is the mechanism. He wrote a book called The Origin of Species and persuaded everyone, except the Anglican Church establishment, that it was so.
Well, yes and no.