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1. In Darwin’s finches— a. occurrence of wet and dry years preserves genetic variation for beak size b. increasing beak size over time proves that beak size is inherited c. large beak size is always favored d. all of the above The correct answer is a—occurrence of wet and dry years preserves genetic variation for beak size A. Answer a is correct. Selection in different years favors different phenotypes. Assuming that there is a genetic basis to variation in beak size, this oscillating selection will maintain variation through time. The correct answer is a— B. Answer b is incorrect. By itself, change in beak size over time cannot establish that the trait is inherited. In Darwin’s finches the comparison between parent’s and offspring’s beak size, especially in years when the environment of the parent is different from that of the offspring, would be expected to be similar if the trait was genetically based. The correct answer is a— C. Answer c is incorrect. In wet years small seeds are abundant enough that birds with small beaks survive very well. Notice that beak size decreases in wet years. The correct answer is a— D. Answer d is incorrect. Only answer a is correct. 2. In the case of peppered moths, a parallel case in the United States— a. is best considered as a coincidence b. adds support to the industrial melanism hypothesis c. demonstrates that birds don’t eat moths d. none of these The correct answer is b— A. Answer a is incorrect. So many of the patterns between the two systems are the same that it would be unlikely to represent a mere coincidence. In evolutionary biology, this is frequently a means for establishing the strength of a particular hypothesis The correct answer is b—adds support to the industrial melanism hypothesis B. Answer b is correct. So many of the details agree between two geographically isolated systems that an alternative explanation would be hard to provide. For example, in both regions the frequency of melanistic individuals increases with increasing pollution, and then declines as pollution subsides. The correct answer is b— C. Answer c is incorrect. The parallel increase and decrease in frequency of melanistic individuals in parallel with levels of pollution does not indicate why this has occurred. Kettlewell’s hypothesis that predation by birds is responsible is still being investigated. The correct answer is b— D. Answer d is incorrect. A correct answer is provided. 3. Artificial selection is different from natural selection because— a. artificial selection is not capable of producing large changes b. artificial selection does not require genetic variation c. natural selection cannot produce new species d. breeders (people) choose which individuals reproduce based on desirability of traits The correct answer is d— A. Answer a is incorrect. As can be seen in the case of domesticated dogs, artificial selection can produce very large differences that are often greater than the differences seen between species in nature. The correct answer is d— B. Answer b is incorrect. Both natural selection and artificial selection require variation among individuals that is genetically based. Otherwise, the traits of organisms selected for breeding would not be expected in the offspring. The correct answer is d— C. Answer c is incorrect. Natural selection, working over very long periods of time (generations), is capable of producing changes that eventually lead to the generation of new species. The correct answer is d—breeders (people) choose which individuals reproduce based on desirability of traits D. Answer d is correct. The only difference between artificial and natural selection is that people replace the “environment” as the source of variation in survival and reproduction. 4. Gaps in the fossil record— a. demonstrate our inability to date geological sediments b. are expected since the probability that any organism will fossilize is extremely low c. have not been filled in as new fossils have been discovered d. weaken the theory of evolution The correct answer is b— A. Answer a is incorrect. Geological sediments can be aged both relatively (position) and absolutely (by radioactive decay). The correct answer is b—are expected since the probability that any organism will fossilize is very low B. Answer b is correct. Circumstances leading to the creation of a fossil are rare. Most organisms that die decompose or are destroyed by scavengers. Moreover, organisms without hard parts (for example, bone and an exoskeleton) are even less likely to become fossilized. The correct answer is b— C. Answer c is incorrect. As more fossils are discovered, more and more “gaps” are getting filled in. The best examples include modern birds and whales. The correct answer is b— D. Answer d is incorrect. Gaps do not threaten the theory of evolution; they are expected, given the great diversity of extant species and what we know about the process of fossilization. The study of work by biologists and paleontologists in closing famous “gaps” is an excellent illustration of both the scientific process and how robust the theory of evolution is. 5. Intermediate fossils illustrating the evolution of whales from their hoofed ancestors include— a. Pakicetus b. Archaeopteryx c. Equus d. all of these The correct answer is a—Pakicetus A. Answer a is correct. The fossil of Pakicetus showed that it was a four-legged mammal that may have lived on land, also spending time in the sea, but had already evolved a whale-like skull. The correct answer is a— B. Answer b is incorrect. Archaeopteryx is an intermediate form between dinosaurs and birds. The correct answer is a— C. Answer c is incorrect. Although Equus is a four-legged animal, it is the genus of current and ancestral species of horses, not an ancestor of the whale. The correct answer is a— D. Answer d is incorrect. Only one answer is correct, answer a. Neither Archaeopteryx nor Equus are ancestors of the whale. Archaeopteryx is believed to be an intermediate form between dinosaurs and birds, not an ancestor of the whale. Although Equus is a four-legged animal, it is the genus of current and ancestral species of horses, not an ancestor of the whale. Hint: Paleontologists continue to fill in the gaps in the fossil record. Although many gaps interrupted the fossil record in Darwin's era, even then, scientists knew of the Archaeopteryx fossil was transitional between dinosaurs and bird. Today the fossil record is far more complete. For example, recently a four-legged aquatic mammal, Pakicetus, was discovered that provides important insights concerning the evolution of whales and dolphins from land-living, hoofed ancestors. 6). The evolution of modern horses (Equus) is best described as— a. the constant change and replacement of one species by another over time b. a complex history of lineages that changed over time, with many going extinct c. a simple history of lineages that have always resembled extant horses d. none of these The correct answer is b— A. Answer a is incorrect. Even though species ancestral to horses were small and lacked many characters of modern horses (for example, hooves), branches of the horse evolutionary tree showed a mosaic of changes. For example, some lineages had evolved specialized hoofs and teeth without necessarily showing large increases in body size, and size actually decreased in some lineages. The correct answer is b—a complex history of lineages that changed over time, with many going extinct B. Answer b is correct. The original view of a gradual change with species replacement stemmed from the lack of a rich fossil collection for horses. As paleontologists discovered more fossils, our view of the history of horses changed. Horse evolution illustrates the evolutionary change is branching and diversifying, and does not follow a linear path. This example shows both the importance of fossils as a source of data, as well as how evolutionary hypotheses are always subject to modification in light of new data. The correct answer is b— C. Answer c is incorrect. Horses have changed drastically over the last 50–30 million years. The correct answer is b— D. Answer d is incorrect. Answer a is the correct answer. 7. Homologous structures— a. are structures in two or more species that originate as the same structure in a common ancestor b. are structures that look the same in different species c. cannot serve different functions in different species d. must serve different functions in different species The correct answer is a—are structures in two or more species that originate as the same structure in a common ancestor A. Answer a is correct. Homology is not necessarily a statement about function or structure, although both properties can help identify homology, they do not define it. The most important characteristic of homology is the idea that the same characteristic can be identified in a common ancestor of the species in question. The correct answer is a— B. Answer b is incorrect. Structures that look the same are not necessarily homologous. For example, the wing of a bat and a bird look similar—they are both wings, after all. But wings were not present in the ancestor common to bats and birds. The correct answer is a— C. Answer c is incorrect. The wing of a bird does not perform the same function as the forelimb of a rat. In the first case (flight) the structure has a quite different function from the second case (walking). The correct answer is a— D. Answer d is incorrect. As described in c, homologous structures may perform similar or dissimilar functions. The forelimbs of bats and dogs are homologous and perform the same function. 8. Convergent evolution a. involves species that are closely related evolutionarily b. depends on natural selection to produce similar phenotypic responses in unrelated lineages c. occurs only on islands d. is expected when different lineages are exposed to vastly different selective environments The correct answer is b— A. Answer a is incorrect. Convergence may and does occur among taxa that are not closely related to one another. That is, the similarity does not come from descent from a common ancestor with similar characteristics. The correct answer is b—depends upon natural selection to produce similar phenotypic responses in unrelated lineages B. Answer b is correct. Only natural selection can make it likely that totally unrelated organisms will come to resemble one another so closely. The effects of natural selection come from the fact that the convergent taxa are exposed to very similar environmental pressures. The correct answer is b— C. Answer c is incorrect. Although some of the most striking examples of convergence come from island fauna and flora, it is not restricted to such habitats. The correct answer is b— D. Answer d is incorrect. The evolution of convergence must come from similarity of the selective environment. 9. Convergent evolution— a. occurs when natural selection produces similar characteristics in unrelated species b. is a weakness in evolutionary theory c. is the best explanation for why there are gaps in the fossil record d. always involves homologous characteristics The correct answer is a—occurs when natural selection produces similar characteristics in unrelated species A. Answer a is correct. Convergent evolution by definition is unrelated species adapting to a similar environments in comparable ways. For example, fastswimming marine organisms as diverse as sharks, tuna, and dolphins have all evolved the same streamlined body form. Presumably, this results from natural selection favoring a restricted set of “solutions” to common environmental problems. The correct answer is a— B. Answer b is incorrect. Convergent evolution is consistent with evolutionary theory. Indeed, one might expect convergence given that biological materials and the laws of chemistry and physics apply constraints to the directions in which evolution can act. The correct answer is a— C. Answer c is incorrect. Convergence has nothing to do with gaps in the fossil record. The correct answer is a— D. Answer d is incorrect. Convergence may occur with characteristics that do not have an origin in a common ancestor. 10. Which of the following represents valid criticism that weakens the theory of evolution? a. evolution violates the second law of thermodynamics b. there are no fossil intermediates. c. irreducible complexity of biological structures. d. all of the above e. none of the above The correct answer is e— A. Answer a is incorrect. The Second Law of Thermodynamics applies to closed systems, which the Earth is not. The Earth is an open system that receives continuous input of energy from the Sun. Biological systems use that energy to create and maintain order. The correct answer is e— B. Answer b is incorrect. Since Darwin, many intermediates have been found in a wide variety of taxa. Today, many well-studied transition species are known that had not been discovered in Darwin’s time but which vastly strengthen his theory of evolution. The correct answer is e— C. Answer c is incorrect. In every case where a biological character has been claimed to be “irreducibly complex,” subsequent analysis has shown that to be false. Lack of a detailed explanation of structure and function for every single complex biological structure that exists does not mean that irreducibly complex structures exist. Moreover, natural selection can lead to the evolution of characters that today appear irreducibly complex because structures that previously were not crucial to the functioning of the character can over time evolve to become necessary. The correct answer is e— D. Answer d is incorrect. None of the previous answers are correct. The correct answer is e—none of the above E. Answer e is correct. None of the answers are correct. 11. Darwin’s finches are a noteworthy case study of evolution by natural selection because evidence suggests— a. they are descendants of many different species that colonized the Galápagos b. they radiated from a single species that colonized the Galápagos c. they are more closely related to mainland species than to one another d. none of the above The correct answer is b— A. Answer a is incorrect. Although they resemble many different species that can be found on the mainland, such as woodpeckers, tree finches, ground finches, and so on, they diverged from a common finch ancestor that colonized the island. The correct answer is b—they radiated from a single species that colonized the Galápagos B. Answer b is correct. The finch species and morphological divinity provides a clear and powerful example of the strength of natural selection in producing morphological diversity that can take advantage of various ecological opportunities. The correct answer is b— C. Answer c is incorrect. Both molecular and genetic evidence argue the contrary. The correct answer is b— D. Answer d is incorrect. Answer b is the correct answer. 12. Vestigial structures— a. are difficult to explain given evolutionary theory b. always provide evidence of convergent evolution c. can help establish patterns of common ancestry d. must always severely affect negative survivorship or reproduction The correct answer is c— A. Answer a is incorrect. Vestigial structures usually have no effect (good or bad) on an individual’s fitness; that is, they are inconsequential structures. As such, they are not incompatible at all with evolutionary theory or the theory of natural selection. The correct answer is c— B. Answer b is incorrect. The utility of structures is central to hypotheses of convergent evolution. Vestigial structures, by definition, have lost their utility and as such are unlikely to support hypotheses about evolutionary convergence. The correct answer is c—can establish patterns of common ancestry C. Answer c is correct because vestigial structures can often be identified as the remnants of homologous features that can be used to infer evolutionary relationships. For example, the vestiges of the hind limb bones and pelvic girdles in some transitional species allowed biologists to more completely trace the history of animals related to modern whales back to the early origins within hoofed mammal ancestors. The correct answer is c— D. Answer d is incorrect. Vestigial structures persist due to their lack of function. 13. An example of convergent evolution is— a. Australian marsupials and placental mammals b. the flippers in fish, penguins, and dolphins c. the wings in birds, bats, and insects d. all of these The correct answer is d— A. Answer a is incorrect. Although the evolution of similar characteristics in Australian marsupials and placental mammals provides many examples of convergent evolution, this is not the only example provided. The correct answer is d— B. Answer b is incorrect. Although the development of flippers in fish, penguins, and dolphins is an example of convergent evolution, this is not the only example provided. The correct answer is d— C. Answer c is incorrect. Although the development of wings in birds, bats, and insects is an example of convergent evolution, this is not the only example provided. The correct answer is d—all of these D. Answer d is correct. Convergent evolution can be viewed as two different species adapting to similar environments in similar ways. All of the examples listed exhibit parallel evolutionary adaptations in similar environments. Hint: Different geographical areas sometimes exhibit groups of plants and animals of strikingly similar appearance, even though the organisms may be only distantly related. It is difficult to explain so many similarities as the result of coincidence. Instead, natural selection appears to have favored parallel evolutionary adaptations in similar environments. Because selection in these instances has tended to favor change that made the two groups more alike, their phenotypes have converged. This form of evolutionary change is referred to as convergent evolution. 14. Archaeopteryx— a. is an intermediate form between extinct and extant horses b. is an intermediate form between extinct and extant whales c. is an intermediate form between dinosaurs and birds that is intermediate in all its characteristics d. shows a common pattern for intermediate forms of mixtures of some traits resembling descendants and some traits resembling ancestors The correct answer is d— A. Answer a is incorrect. Archaeopteryx is not related to horses. The correct answer is d— B. Answer b is incorrect. Archaeopteryx is not related to whales. The correct answer is d— C. Answer c is incorrect. Archaeopteryx is not intermediate in all respects. Rather, it is a mosaic, with some traits nearly identical to those of its dinosaur ancestors, and others very similar to those of birds. The correct answer is d—shows a common pattern for intermediate forms of mixtures of some traits resembling descendants and some traits resembling ancestors D. Answer d is correct. Like many fossil “intermediates,” Archaeopteryx is a mosaic of ancestral and modern traits. Evolution does not proceed with all traits evolving at the same rate, and so it is unreasonable to expect real organisms to appear as smooth transitions between forms in all aspects of their characteristics. 15. The shape of the beaks of Darwin's finches, industrial melanism, and the changes in horse teeth are all examples of— a. artificial selection b. natural selection c. sympatric speciation d. stabilizing selection The correct answer is b— A. Answer a is incorrect. Artificial selection is the process whereby humans impose selection on plants and animals through selective mating to enhance characteristics desirable for human uses. Artificial selection has produced substantial change in the phenotypes of organisms throughout human history. The changes, which occurred in Darwin’s finches, moths, and horse teeth, were not controlled by human intervention, rather by natural alterations of their environments. The correct answer is b—natural selection B. Answer b is correct. Natural selection is the selection of specific traits in organisms over time based on the contributions of those traits to survival. If those traits have a genetic basis, then evolutionary change will occur. The shape of the beaks of Darwin's finches, the coloration of moths in industrialized areas, and the changes in horse teeth were all traits selected for by changes in the organism's environment. The correct answer is b— C. Answer c is incorrect. Sympatric speciation is the process by which one ancestral species diverges into two species in sympatry. The role of sympatric speciation is still debated, and no strong evidence suggests that it occurs in horses or Darwin’s finches. Moreover, industrial melanism refers to change within a species. The correct answer is b— D. Answer d is incorrect. Stabilizing selection refers to the situation in which natural selection favors the intermediate phenotype in a population. Evolutionary change in horses, Darwin’s finches, and peppered moths was the result of directional selection that favors individuals with extreme phenotypes. Challenge Questions 1. What are the conditions necessary for evolution by natural selection? Answer—Briefly, they are: A. There must be variation among individuals within a population. B. Variation among individuals must be related to differences among individuals in their success in producing offspring over their lifetime. C. Variation related to lifetime reproductive success must have a genetic (heritable) basis. Refer to Figure 21.2 for the following two questions. 2. Explain how data shown in Figure 21.2a and b relate to the conditions identified by you in question 1. Answer—Figure 21.2a shows in an indirect way that beak depth varies from year to year. Presumably this is a function of variation among individuals in beak size. However, the most important point of 21.2a is that it shows the result of selection. That is, if the three conditions hold, we might expect to see average beak depth change accordingly as precipitation varies from year to year. Figure 21.2b is more directly relevant to the conditions noted for natural selection to occur. The figure shows that beak size varies among individuals, and that it tends to be inherited. 3. On Figure 21.2b, draw the relationship between offspring beak depth and parent beak depth, assuming that there is no genetic basis to beak depth in the medium ground finch. Answer—The relationship would be given by a cloud of points with no obvious linear trend in any direction different from a zero slope. In other words, it would be a horizontal line through an approximately circular cloud of points. Such data would suggest that whether a parent(s) has a large or small beak has no bearing on the beak size of its offspring. 4. Refer to Figure 21.5, artificial selection in the laboratory. In this experiment, one population of Drosophila was selected for low numbers of bristles and the other for high numbers. Note that not only did the means of the populations change greatly in 35 generations, but also all individuals in both experimental populations lie outside the range of the initial population. What would happen if, within a population, both small and large individuals were allowed to breed, but middle-sized ones were not? Answer—Assuming that small and large individuals would breed with each other, then middle-sized offspring would still be born (the result of matings between small and large flies). Nonetheless, there would also be many small and large individuals (the result of small x small and large x large matings). Thus, the frequency distribution of body sizes would be much broader than the distributions in the figures. In some experiments, reproductive isolation evolves in which small and large individuals evolve mating preferences that prevent them from interbreeding, leading to the production of two different-sized species. This would be a laboratory example of sympatric speciation. Most studies, however, have failed to produce such reproductive isolation; rather, a single population remains through time with great variation.