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EVIDENCE OF EVOLUTION Key Concepts • What evidence supports the theory of evolution? • How do scientists infer evolutionary relationships among organisms? • How do new species form? Key Terms Homologous Structures – Body parts that are structurally similar in related species. Key Terms Branching tree – A diagram that shows how scientists think different groups of organisms are related. Identifying Supporting Evidence • Identifying supporting evidence helps us understand the relationship between the facts and the hypothesis. • Evidence consists of facts that can be confirmed by testing or observation. Supporting Darwin’s Theory • Fossils show that organisms that lived in the past were very different from organisms alive today. • Patterns of early development show that some different organisms look similar during their early stages. • Similar body structures in different species show that the organisms shared a common ancestor. Interpreting the Evidence • FOSSILS • EARLY DEVELOPMENT • BODY STRUCTURE FOSSILS • The preserved remains or traces of an organism that lived in the past. • Fossils show that organisms that lived in the past were very different than organisms alive today. • Scientists use fossils to infer the structures of ancient organisms. EARLY DEVELOPMENT (embryology) • Scientists compare the early development of different organisms to make inferences about evolutionary relationships. • Similarities in early development among different organisms suggests that they are related and share a common ancestor. BODY STRUCTURE (homologous structures) • Darwin compared body structures of living species when observing the species on the Galapagos Islands. • Body structure is an organism’s body plan, how its bones are arranged. • Similarities in body structure provide evidence that organisms evolved from a common ancestor. Species Relationships • Fossils, early development patterns, and body structure provide evidence that evolution has occurred. • Scientists also have used these kinds of evidence to infer how organisms are related to one another. New Evidence •DNA •Protein Structure Similarities in DNA • Scientists compare the genes of different species to determine how closely related the species are. • The more similar the sequence of bases in the DNA, the more closely related the species are. • The more similar the order of amino acids (codes for proteins) in the DNA, the more closely related the species are. Combining Evidence • The use of DNA and protein structure has confirmed conclusions that scientists had already based on fossils, embryos, and body structure. • The use of DNA and protein structure has also caused scientists to “revise” the branching trees of some species. Branching Trees • Branching trees show common ancestry (phylogeny). • Evolution is about gradualism and phylogeny. How Do New Species Form? (speciation) • A new species can form when a group of individuals remains isolated from the rest of its species long enough to evolve different traits. • Isolation/Separation – River – Volcano – Mountain range Convergent Evolution • The process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. Divergent Evolution (adaptive radiation) • The process by which related species evolve different traits. Gradualism Evolution occurs slowly but steadily.