Key Evidence of Evolution Fossil Records, Homologous Structures, and Molecular Biology Explained

Evidence of Evolution Lesson Objectives Explain how geologic distribution of species relates to their evolutionary history. Explain how fossils and the fossil record document the descent of modern species from ancient ancestors. Describe what homologous structures and embryology suggest about the process of evolutionary change. Explain how molecular evidence can be used to trace the process of evolution. Explain the results of the Grants’ investigation of adaptation in Galápagos finches. Lesson Summary Biogeography Biogeography is the study of where organisms live now and where they and their ancestors lived in the past. Two biogeographical patterns are significant to Darwin’s theory: ▶ The first is a pattern in which closely related species differentiate in slightly different climates. The Galápagos tortoises and finches follow this pattern. ▶ The second is a pattern in which very distantly related species develop similarities in similar environments. The rheas, ostriches, and emus fall into this pattern. The Age of Earth and Fossils ▶ Radioactive dating techniques have confirmed that Earth is ancient—approximately 4.5 billion years old. ▶ Recent fossil finds document intermediate stages in the evolution of many groups including whales, birds, and mammals. Comparing Anatomy and Embryology ▶ Homologous structures are shared by related species and have been inherited from a common ancestor. Similarities and differences among homologous structures help determine how recently two groups shared a common ancestor. • Body parts that share a common function, but neither structure nor common ancestry, are called analogous structures. Analogous structures do not provide any evidence for evolutionary descent. • Homologous structures that are greatly reduced in size or have little to no function are called vestigial structures. • Many homologous structures develop in the same order and in similar patterns during the embryonic, or pre-birth, stages of related groups. These similarities provide further evidence that the animals share common ancestors. Genetics and Molecular Biology At the molecular level, the universal genetic code and homologous molecules such as genes and proteins provide evidence of common descent. Testing Natural Selection Scientists have designed experiments to test natural selection. Observations of Galápagos finches confirm that competition and environmental change drive natural selection. Biogeography For Questions 1–3, complete each statement by writing the correct word or words. 1. Biogeographers study where organisms live now and where they and their ancestors lived in the past. 2. When individuals from a mainland bird population immigrate to various islands, natural selection may result in closely related , but different, island species. 3. Distantly related organisms may be similar if they live in similar environments . 4. What explains the distribution of finch species on the Galápagos Islands? The finch species had descended with modification from a common mainland ancestor. 5. What explains the existence of similar but unrelated species? Such species evolved features in common because they were exposed to similar pressures of natural selection. The Age of Earth and Fossils 6. The illustrations below show organisms whose fossils make up part of the fossil record. The organisms are in order from oldest to most recent. In the boxes, draw an animal that might have been an intermediate form between the shown organisms. Answers will vary. Students’ drawings may show a slightly elongated shell and/or slightly longer tentacles. Answers will vary. Students’ drawings may show a somewhat more coiled shell. Use the illustrations of the marine organisms on the previous page to answer Questions 7–8. 7. Describe a situation in which organism 3 might have had an advantage over organism 2? SAMPLE ANSWER: Having a more compact body may have made it easier for the organism to escape predators. 8. How might these fossils provide evidence for evolution? They show similarities to one another, but they also show changes that have occurred over time. Comparing Anatomy and Embryology 9. Complete the table about types of anatomical structures. Types of Anatomical Structures Structure Type Description Homologous structure Structures that are shared by related species and that have been inherited from a common ancestor Example Mammalian leg and amphibian leg Analogous structure Body parts that share common function, but not structure Wing of a bee and wing of a bird Vestigial structure Body parts in animals that are so reduced in size that they are just vestiges, or traces, of homologous structures in other species Hipbones in dolphins For Questions 10–14, match the structure with the correct type. A structure type may be used more than once. Anatomical Structure Structure Type A 10. bat wing and mouse arm A 11. reptile foot and bird foot B. analogous structure B 12. dolphin fin and fish tail C. vestigial structure C 13. eyes on a blind cave fish B 14. snake tongue and dog nose A. homologous structure Use the illustrated homologous structures to answer Questions 15–17. Humerus Radius/Ulna Carpals (wrist bones) Metacarpals/Phalanges (finger bones) Human forelimb Bat forelimb 15. How are the forelimbs similar? The forelimbs have the same kinds of bones in approximately the same positions. 16. How are the forelimbs different? SAMPLE ANSWER: The bat’s “finger bones” are elongated and form the structure of a wing, while the human phalanges are shorter and form the structure for fingers. 17. How are homologous structures such as forelimbs evidence for common descent? The bones are noticeably similar in structure and arrangement. It is, therefore, reasonable to assume that they are descended from a common ancestral form. 18. How does the pattern of embryological development provide further evidence that organisms have descended from a common ancestor? The early developmental stages of many vertebrates look very similar. Therefore, it is reasonable to assume that vertebrates are descended from a common ancestor. Genetics and Molecular Biology For Questions 19–25, complete each statement by writing the correct word or words. genetics 19. The science of theory. provides molecular evidence that supports evolutionary DNA 20. All living cells use and RNA to code heritable information. 21. The universal genetic code is used by almost all organisms to direct protein synthesis 22. Proteins that are homologous . share extensive structural and chemical similarities. 23. Cytochrome c is a protein used for cellular respiration in almost every living cell. 24. Homologous genes called Hox genes control timing and growth in embryos . 25. Relatively minor changes in an organism’s genome can produce major changes in an organism’s structure . Testing Natural Selection Write the letter of the correct answer on the line at the left. A 26. Which of the following hypotheses did the Grants test? A. Differences in beak size and shape produce differences in fitness. B. For beak size and shape to evolve, the birds must leave the islands. C. For beak size and shape to evolve, the climate must change radically. D. Differences in beak size and shape are not determined by genetic mutations. C 27. The data that the Grants collected proved that there is A. no link between the environment and the shape of finch feet. B. no link between the environment and the shape of finch beaks. C. great variation of heritable traits among Galápagos finches. D. very little variation of heritable traits among Galápagos finches. A 28. The Grants conducted their experiment to test which of the following processes? A. Natural selection B. Genetic mutation C. Artificial selection D. Sexual reproduction 29. The art shows how finch beaks are similar to certain kinds of hand tools. Suppose a finch fed on insects that burrowed into small holes on tree trunks. What type of tool do you think this finch’s beak would resemble? Explain your answer. Tree Finches Ground Finches Pinaroloxias Platyspiza Geospiza Certhidea SAMPLE ANSWER: The finch’s beak might resemble a very thin probe that can reach into a small hole and skewer or grasp the insect. 30. Complete the concept map. Evidence for Evolution includes i l d the geographic distribution of living species the fossil record similarities in anatomical structures and embryological development the universal genetic code and homologous proteins and genes experiments that verify natural selection occurs in nature Chapter Vocabulary Review Match the term with its definition. Term Definition A 1. evolution A. Change over time C 2. fossil G 3. fitness B. Inherited characteristic that increases an organism’s chance of survival B 4. adaptation C. Preserved remains of an ancient organism 5. natural selection F 6. homologous structures E D. The process by which organisms with variations most suited to their environment survive and leave more offspring than others 7. vestigial structures E. Small structures with little or no function D F. Structures that develop from the same embryonic tissues but have different mature forms G. Ability of an individual to survive and reproduce in a specific environment For Questions 8–10, write a definition for the vocabulary term. 8. biogeography the study of where organisms live now and where they and their ancestors lived in the past 9. artificial selection the use of selective breeding to produce organisms with certain desirable traits 10. analogous structures body parts that share common function, but not structure 11. Does the illustration below show analogous or homologous structures? Explain. Turtle Alligator Bird Mammals Homologous structures. These limbs evolved from the front limbs of a common ancestor. If these animals had different origins, they would probably not share so many common structures. “The Chapter Mystery explained how the ’i’iwi and other Hawaiian honeycreeper species evolved adaptations suited to their specific habitats. What happens when species face a loss of their habitats due to urbanization or environmental degradation? SUCH VARIED HONEYCREEPERS Learning Habitat Loss and Endangered Species Scientists report that in the United States, habitat loss is the most widespread cause of species endangerment, affecting approximately 85 percent of imperiled species according to a recent estimate. Designed to combat the problem, the U.S. Endangered Species Act of 1973 is a federal law that protects threatened and endangered species. When a species is listed as endangered, the government enforces more stringent protections on the species’ remaining habitats, especially when those habitats are on federal lands. In addition, the Act allows the government to purchase land containing important habitats and forbids the capture, killing, or sale of an endangered species. In addition, people who violate the Act can be prosecuted. Unfortunately, threats to many species continue. Experts believe that fewer than half the species native to the United States—especially insect, plant, and fungi species—have yet been discovered and catalogued. Therefore, it is impossible to know whether these species are endangered. Another problem, other scientists emphasize, is that the regulations protecting endangered species are not effective enough and are based on an underestimation of the problem. One recent expert analysis suggests that, even within the pool of known species, the number now threatened with extinction may actually be as much as ten times greater than the number currently protected under the U.S. Endangered Species Act. The table below, adapted from data compiled by the nonprofit scientific group NatureServe, assesses the current situation for vertebrate species in the United States. Vertebrate Species Data in the U.S. Group: Imperiled U.S. Vertebrates Total Number of Known Species Number of Species Imperiled or Extinct/ Possibly Extinct Percentage of Species Imperiled or Extinct/ Possibly Extinct Mammals 421 29 7 Birds 783 75 10 Reptiles 295 28 9 Amphibians 258 66 26 Freshwater Fishes 798 179 22 Vertebrate Totals 2555 377 15 Continued on next page ▶ Themes Science and Global Awareness 1. What is believed to be the most widespread cause of species endangerment? Habitat loss is the most widespread cause. 2. According to the table, which group of vertebrates in the United States includes the largest number of imperiled or extinct species? Freshwater fish species, with 179 varieties imperiled or extinct 3. According to the table, which group of vertebrates appears to be most endangered overall? How can you tell? Why do you think this group is most imperiled? Amphibians are the most endangered group because they have the highest percentage of species imperiled or extinct of any of the vertebrate groups. Students may be able to draw a connection between the imperilment of amphibian species and the vulnerability of their wetland ecosystems. 4. What is the U.S. Endangered Species Act? Enacted in 1973, the U.S. Endangered Species Act is a law that designates threatened and endangered species and offers federal protection to the listed species’ habitats. 5. Some experts think that a significant number of species native to the United States have yet to be discovered. Some experts think that the U.S. Endangered Species Act underestimates the number of endangered species. How does the first problem lead to the second? The U.S. Endangered Species Act cannot protect species that have yet to be identified. Meanwhile, habitat destruction and possible extinction of species continue. Species Presentation The skills used in this activity include information and media literacy; critical thinking and systems thinking; and problem identification, formulation, and solution. Visit the Web site of the U.S. Fish and Wildlife Service to learn more about the agency’s efforts to protect endangered species in the United States. Choose one endangered species and investigate the threats it faces. Present the information to the class, including whether you believe the species deserves protection under the Act and, if so, why. Your presentation can be in the form of a video about the species or an illustrated guide. Evaluate students’ presentations by their inclusion of the description of the species and the threats it faces, its habitat range, what is being done to protect the species, and their opinion. Evaluation should also depend on the appropriate use of available media.