Evolution 1: Evidence of Evolution LabCh. 16

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1 Evidence of Evolution- Pre-AP Name: Per: COOK Background: Much evidence has been found to indicate that living things have evolved or changed gradually during their natural history. The study of fossils as well as work in embryology, biochemistry, and comparative morphology provides evidence for evolution. Objective: To compare homologous, analogous, and vestigial structures and analyze their significance in evolutionary history. I. Fossils Part I Study the figure at right. 1. Which rock layer is the oldest? 2. Which rock layer is the youngest? 3. Explain what can scientists learn about evolution when comparing different fossils in different rock layers? (Use terms like relatedness, extinction, etc.) You must write at least two complete sentences. Examine the diagrams and descriptions located at the lab station and use the information to answer these questions. I. Fossils Part II 1. Hyracotherium lived in a dense forest area dominated by a rich undergrowth of ferns. What do you think the advantages of small body stature might be in this type of environment? 2. A change in vegetation from ferns to grasslands brought about changes in the shape of the horse s leg. What changes in vegetation could have caused the evolution of the horse? 3. The teeth of the browsers, such as Mesohippus, were covered with a thick layer of enamel. The teeth of the modernday horse, by comparison, have less enamel and appear to be much wider and flatter. Provide reasons for some of the changes in teeth. 4. Why would changes in the environment have caused changes in the horses predators?

2 II. Homologous Structures The idea that ancestral structures have been reused in descendants is called homology. Homology is another major piece of evidence for evolution. Homologous structures are structurally similar although they perform different functions. Evolution is the explanation for the existence of common structures in otherwise unrelated species. 1. Carefully examine the drawings of the bones in Figure 1 below. Look for similarities among the various animals. Color each bone of the human arm a different color. All bones of the wrist (carpals) should be a single color, and the bone groups of the hand (metacarpals and phalanges) should be another color. Then color the corresponding bones (containing the same pattern) in each of the other animals the same color as the human bone (i.e. if you color the humerus blue in the human, it should be blue in all the other animals). 2. Based on the limbs, which two animals do you think are most closely related? Provide evidence for your prediction. 3. a. Pick one bone. b. How has the bone you picked been adapted for new purpose in these vertebrates? Use two examples in your answer. Explain the function of the bone in each animal and how has the bone been modified to help with this function.

3 4. Use pages to describe the differences between homologous structures and analogous structures. Make sure to include an example of each type in your description. 5. How does comparative anatomy provide evidence for evolution? These structures on the following page are formed in similar ways during embryonic development and share like arrangements; however, they have somewhat different forms and functions. They are called homologous structures. b. What does the prefix homo mean? III. Analogous structures 1. Examine the butterfly wing and the bird wing shown in Figure 2. a. What function do these structures share? b. How do the structures differ internally and externally? (Give three examples) c. Do birds and insects share any structural similarities that would suggest they are closely related in the single tree of life that includes all organisms? Explain. d. Some apparently related animals have organs with similar functions, yet are very different in structure and form. These structures are called. IV. Vestigial structures Vestigial organs are remnants of organs that are no longer functioning in the species. Most are reduced (smaller) in size. Humans have many more (more than 100) vestigial organs. Go the following website: (link is also on my website). 1. Name 3 vestigial organs that humans have. Gradual changes have occurred through time that have, in some cases, reduced or removed the function of some body structures and organs. The human appendix that is reduced and no longer digests rough vegetation and pelvic bones of snakes that have no legs are examples of this phenomenon.

4 2. The cave fish and minnow shown in Figure 3 are related, but the cave fish is blind. a. Explain why eyesight is not an important adaptation to life in a cave. b. Do the appearance of the cave fish and minnow suggest common ancestry? Explain. 3. Organs or structures that have lost their function in the organism and have become reduced in size (because of efficiency) are called. Why do snakes have legs? Snakes evolved from four legged animals similar to lizards. Most species of snakes have lost all traces of limbs but snakes in the boa and python family have a tiny pair of hind legs. Unlike whales the python's (or boa's) vestigial legs can actually be seen as a pair of "spurs" that stick out where the body ends and the tail begins. (Admittedly, it is difficult for an untrained person to tell where that is!) 4. Snakes have legs. Do they use them? Do they walk? 5. Explain why snake legs are vestigial. 6. Explain how a vestigial organ is evidence of evolution. V. Embryology 1. Using complete sentences, describe how comparing early development can help scientists learn about the relatedness of species. Page 385 may give you a start. Give an example. a. b. c. d.

5 Look at the diagrams on the previous page. 2. Try to determine what kind of organism will come from each of these embryos; reptile, human, bird or pig. Write your best guess on the line above the picture. 3. Which ones are most closely related? 4. How do you know? VI. Genetic comparisons Biochemistry DNA is the code for making proteins, the closer the DNA, the closer the proteins are. Look at the following data: Amino Acid Sequences Baboon ASN THR THR GLY ASP GLU VAL ASP ASP SER PRO GLY GLY ASN ASN Chimp SER THR ALA GLY ASP GLU VAL GLU ASP THR PRO GLY GLY ALA ASN Lemur ALA THR SER GLY GLU LYS VAL GLU ASP SER PRO GLY SER HIS ASN Gorilla SER THR ALA GLY ASP GLU VAL GLU ASP THR PRO GLY GLY ALA ASN Human SER THR ALA GLY ASP GLU VAL GLU ASP THR PRO GLY GLY ALA ASN 1. For each primate, count the number of amino acids that are different from the human sequence. Record these numbers in the data table below. 2. Calculate the percentage differences by dividing the amino acid differences by 15 and multiplying by 100. Record these numbers in the data table. Baboon Chimpanzee Gorilla Lemur Primate # of Amino Acids Different from Humans Percent Differences Analysis and Interpretations 1. Explain why the homologous structures in Part II are evidence of evolutionary relationships. 2. Explain the evolutionary relationship between the fin of a fish and the flipper of a whale (a mammal). 3. If a scientist states that two species are closely related based on morphology, what would you expect a comparison of their DNA base sequence to reveal? 4. Which of these pieces of evidence for evolution provides the most powerful evidence for common decent? Explain.

6 Evolution I Across 9. different structure, common function 10. ancient organism preserves 11. chromosomes do not divide currently during meiosis 12. change over time in a species 13. inherited characteristic that increases chance of survival Down 1. different function, similar shape 2. organisms best suited for the environment survive and reproduce 3. lost its function and shrinks 4. chart used to trace a genetics trait in a family 5. ability to survive and reproduce in a given environment 6. developed the theory of evolution 7. trait found in every generation that affects both sexes 8. trait that can skip generations and both sexes are carriers 9. nature provides variation and man selects for it

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