The finches of the Galapagos Islands provide a classic example of adaptive radiation—the evolutionary process through which a single lineage gives rise to species occupying diverse environmental niches. In one model of how species form, geographical separation leads to evolutionary divergence. Recent evidence permits refinement of this model. For one thing, the relationships among Darwin's finches have become clearer through studies of DNA sequence variation. Also, it is now clear that the Galapagos Islands have changed radically over the 3 million years during which the finches have evolved; changes in the character of the archipelago have helped drive the radiation of species. The birds? physical appearance and song appear to act as cues that help isolate populations when mating. Though it is not yet possible to thoroughly recount how Darwin's finches have evolved, an increasingly dynamic view of adaptation offers an improved explanation.