KEY CONCEPT Evidence of common ancestry among species comes from many sources.

Evidence for evolution in Darwin’s time came from several (four) sources. 1. Fossils provide evidence of evolution. Fossils in older layers are more primitive (older) than those in the upper layers. By comparing fossils from older rocks with fossils from younger layers, one could see life on Earth has changed over time.

2. The study of biogeography provides evidence of evolution 2. The study of biogeography provides evidence of evolution. It studies the distribution of organisms around the world. island species most closely resemble nearest mainland species populations can show variation from one island to another

- similar embryos, diverse organisms 3. Embryology provides evidence of evolution. Embryology is the study of ontogeny (the process of development of an embryo). - similar embryos, diverse organisms Larva Adult barnacle Adult crab Fig. Although adult crabs and barnacles look and behave very differently, they can look identical as larvae. This suggested to Darwin that they share a common ancestor.

Comparative embryology

4. The study of anatomy provides evidence of evolution. Homologous structures are similar in structure but different in function. Homologous structures are evidence of a common ancestor. Human hand Bat wing Mole foot Fig. Notice that each of these homologous structures uses the same bones in relation to each other. What body part of a dolphin is homologous to the structures shown above?

Homologous structures

The study of anatomy provides evidence of evolution. Analogous structures have a similar function. Human hand Bat wing Mole foot Fly wing Analogous structures are not evidence of a common ancestor. Fig. Analogous structures evolved separately and are not evidence of a common ancestor. A bat’s wing has bones whereas insect wings do not.

Structural patterns are clues to the history of a species. Vestigial structures are remnants of organs or structures that had a function in an early ancestor. Ostrich wings are examples of vestigial structures. Their wings are used for balance but not to fly.

Vestigial structures Many modern whale species have vestigial pelvic and leg bones. They also have vestigial nerves for the sense of smell, and small muscles devoted to external ears that no longer exist. Other vestigial structures: Human appendix Wisdom teeth Blind cave organisms Snake legs