Biological Evidence of Evolution

1. Biological Evidence of Evolution

2. How Species are Related • Evolution does not occur in a straight line with one species replacing another in a series of orderly steps. • Living species that are closely related share a common ancestor. • How closely related two species are depends on when they diverged, or split, from their common ancestor.

3. How Species are Related The fossil record indicates that different species of horses often overlapped with each other.

4. How Species are Related One of the main points of debate among biologists today is SPECIATION, the process of one species splitting into multiple species. Phyletic Gradualism Punctuated Equllibrium Many scientists think that natural selection produces new species slowly and steadily. Other scientists think species exist stably for long periods and that change occurs in short bursts.

5. Evidence in Anatomy Comparative anatomy is the study of similarities and differences among structures of living species. • Homologous Structures • Analogous Structures • Vestigial Structures

6. Evidence in Anatomy Homologous structuresare body parts of organisms that are similar in structure and position but different in function. The forelimbs of these species are different sizes, but their placement and structure suggest common ancestry (they are related).

7. Evidence in Anatomy Body parts that perform a similar function but differ in structure are analogous structures. The wings of these species are similar in function but different in structure, which suggests they are NOT closely related.

8. Evidence in Anatomy Vestigial structures are body parts that have lost their original function through evolution.

9. Evidence in Anatomy • The short, stubby wings of flightless birds are an example of vestigial structures.

10. Evidence in Development The science of the development of embryos from fertilization to birth is called embryology. All vertebrate embryos exhibit pharyngeal pouches at a certain stage of their development. These features, which develop into neck and face parts, suggest relatedness.

11. Evidence in Genetics • Molecular biology is the study of gene structure and function. • Differences in DNA are responsible for differences between species. It can tell us how closely or distantly related species are. • Scientists can study relatedness of organisms by comparing genes and proteins among living species.

12. Molecular data indicate that whales and porpoises are more closely related to hippopotamuses than they are to any other living species.

13. The Study of Evolution Today • Since Darwin’s discovery, scientists have confirmed, refined, and extended his theory by examining life through the lens of natural selection. • Genetic research is a very young science. Almost daily, scientists understanding about life and the connections between species are being shaped by new information from DNA. • As new fossils are discovered and added to the fossil record, scientists are able to get a more complete picture and refine their ideas about the origin and evolution of different species.