What are homologous structures? • Structures that are embryologically similar, but have different functions. • Suggests inheritance from a common ancestor • The forelimbs of the penguin, alligator, bat, and human all derive from the same embryological structures. What are Analogous Structures? • Have similar functions, but a different origin Hummingbird moth Hummingbird The wings serve similar functions, but they differ in structure and derive from different embryological structures. What are Vestigial Structures? • Structures that currently have no function, but were once useful to an ancestor. Examples Tailbone in humans Appendix in humans More examples of Vestigial Structures Wings of Ostriches Eye of a Blind Cave Salamander Similarities in Embryology • Similar embryological development among species indicates a common evolutionary history. EXAMPLE Chicken Turtle Rat Evidence from Molecular Biology • Similarity in biomolecules such as RNA, DNA, and proteins indicates a common evolutionary history. The amino acid sequences in human hemoglobin (red blood cell protein) and gorilla hemoglobin differ by one amino acid, while the hemoglobin molecules of humans and frogs differ by 67 amino acids. The more similar the proteins are in different species, the more closely related the species is thought to be.