The flipper of a seal is homologous with the _____ of a bird, and both of these are homologous with the _____ of a human. The wing of a bird and the wing of a butterfly are described as _____ structures that arose as a result of _____ evolution. Remnants of structures in animals that have no use for them, such as the small hind leg bones of whales, are described as _____ structures.