Darwin visited the Galapagos Islands several times. During his trips, he observed some differences in the finches living on each of the islands. He noted that the finches had many traits in common; however, each had a different beak. Some beaks were short, some long. Some beaks looked straight, while others curved. Darwin believed that each species of finch was related but had developed some special beak adaptations. He suggested that the finches had developed these adaptations because there were different food sources on each island. The curved-beaked finches ate berries. The straight-beaked finches burrowed for worms. The short-beaked finch ate only seeds. Each beak was well-suited for the specific food source.

Darwin believed the shape of the finch's beak was related to the food it ate.