Darwin's finch refers to a group of about 15 species of small birds found primarily on the Galápagos Islands. These birds are known for their diverse beak shapes and sizes, which have adapted to different food sources available in their environment. This variation in beak morphology is a key example of evolution in action. The finches played a significant role in Charles Darwin's formulation of the theory of natural selection. During his visit to the Galápagos Islands in the 1830s, he observed how these birds adapted to their specific habitats, leading him to understand how species evolve over time based on environmental pressures.