Darwin's finches on the Galápagos Islands are particularly suitable for asking evolutionary questions about adaptation and the multiplication of species: how these processes happen and how to interpret them. All 14 species of Darwin's finches are closely related, having been derived from a common ancestor 2 million to 3 million years ago. They live in the environment in which they evolved, and none has become extinct as a result of human activity. Key factors in their evolutionary diversification are environmental change, natural selection, and cultural evolution. A long-term study of finch populations on the island of Daphne Major has revealed that evolution occurs by natural selection when the finches' food supply changes during droughts. Extending this finding to the past, we discuss how environmental change has influenced the opportunities for speciation and diversification of finches throughout their history: The number of islands has increased, the climate has cooled, and the vegetation and food supply have changed.