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Name ____________________________ Date _________________ Block _________ Evidence of Evolution What Evidence Supports Evolution? Since Darwin’s time, scientists have found a great deal of evidence that supports the theory of evolution. Fossils, patterns of early development, similar body structures, and similarities in DNA and protein structures all provide evidence that organisms have changed over time. Fossils By examining fossils, scientists can infer the structures of ancient organisms. Fossils show that, in many cases, organisms that lived in the past were very different from organisms alive today. The millions of fossils that scientists have collected are called the fossil record. The fossil record provides clues about how and when new species evolved and how organisms are related. Similarities in Early Development Scientists also infer evolutionary relationships by comparing the early development of different organisms. For example, the organism in this picture look similar during the early stages of development. All four organisms have a tail. They also have a row of tiny slits along their throats. The similarities suggest that these vertebrate species are related and share a common ancestor. Discussion questions: 1. What are the 4 types of evidence that supports evolution? 2. What are fossils? 3. How do fossils support the theory of evolution? 4. How do patterns of early development of different organisms support the theory of evolution? Similarities in Body Structure An organism’s body structure is its basic body plan, which in vertebrates includes how bones are arranged. Fishes, amphibians, reptiles, birds, and mammals all have an internal skeleton with a backbone. This similarity provides evidence that these animal groups all evolved from a common ancestor. Similar structures that related species have inherited from a common ancestor are known as homologous structures. In the picture you can see some examples of homologous structures. These include a bird’s wing, a dolphin’s flipper, and a dog’s leg. Some fossils show structures that are homologous with structures in living species. For example, scientists have recently found fossils of ancient whalelike creatures. The fossils show that the ancestors of today’s whales had legs and walked on land. This evidence supports other evidence that whales and other vertebrates share a common ancestor that had a skeleton with a backbone. Discussion questions: 1. How are the homologous structures similar? 2. How are they different? 1 3. Why do you think the homologous structures shown in the diagram evolved differently? Similarities in DNA and Protein Structure Why do some species have similar body structures and development patterns? Scientists infer that the species inherited many of the same genes from a common ancestor. embryos, and body structure. For example, DNA comparisons show that dogs are more similar to wolves than to coyotes. Scientists had already reached this conclusion based on similarities in the structure and development of these three species. Recall that genes are segments of DNA. Scientist’s compare the sequence of nitrogen bases in the DNA of different species to infer how closely related the two species are. The more similar the DNA sequences, the more closely related the species are. The DNA bases along a gene specify what type of protein will be produced. Therefore, scientists can also compare the order of amino acids in a protein to see how closely related two species are. Discussion questions: 1. What does DNA tell you about how similar two species are? In most cases, evidence from DNA and protein structure has confirmed conclusions based on fossils, 2. In addition to studying DNA itself, what else do scientists study to compare the DNA of different organisms? What does this tell scientists about DNA? 2