1. Descent with Modification: A Darwinian View of Life
Chapter 22
Descent with Modification: A Darwinian View of Life
Questions prepared by
Janet Lanza
University of Arkansas at Little Rock
Michael Dini
Texas Tech University

2. Lamarck’s Hypothesis of Evolution
Which of the following statements about Lamarck is/are accurate?
Lamarck thought evolution had occurred.
Lamarck’s proposal that individuals evolve by the principle of use and disuse is well supported by evidence.
Lamarck was wholly wrong.
Lamarck published his ideas only after Darwin published his.
Answer: This question is designed to help students understand the history of evolutionary biology; it can also help give students a better idea of how science moves forward. Lamarck (and others) preceded Charles Darwin in thinking evolution had occurred (thus, option a is correct and option d is incorrect). Lamarck’s idea of use and disuse has not been supported by evidence, so option b is incorrect. 2

3. Lamarck’s Hypothesis of Evolution
Which of the following statements about Lamarck is/are accurate?
Lamarck thought evolution had occurred.
Lamarck’s proposal that individuals evolve by the principle of use and disuse is well supported by evidence.
Lamarck was wholly wrong.
Lamarck published his ideas only after Darwin published his.
Answer: This question is designed to help students understand the history of evolutionary biology; it can also help give students a better idea of how science moves forward. Lamarck (and others) preceded Charles Darwin in thinking evolution had occurred (thus, option a is correct and option d is incorrect). Lamarck’s idea of use and disuse has not been supported by evidence, so option b is incorrect.
Answer: This question is designed to help students understand the history of evolutionary biology; it can also help give students a better idea of how science moves forward. Lamarck (and others) preceded Charles Darwin in thinking evolution had occurred (thus, option a is correct and option d is incorrect). Lamarck’s idea of use and disuse has not been supported by evidence, so option b is incorrect. 3

4. Darwin’s Knowledge
Which of the following statements about Darwin following the voyage of HMS Beagle is incorrect?
Darwin thought individuals varied.
Darwin thought the Earth was a few thousand years old.
Darwin thought fossils in a given area were similar to the animals that were still living there.
Darwin thought organisms produced many offspring.
Darwin thought few offspring of a pair survived.
Answer: This question is designed to make students focus on what information was available to Darwin when he developed his ideas on evolution. Darwin knew species varied (option a), that fossils in a given area were similar to living species in that area (option c), and that many offspring were produced (option d) but few survived (option e). However, from reading Lyell’s Principles of Geology, Darwin realized that Earth cannot be just a few thousand years old. Therefore, the only correct answer is b. 4

5. Darwin’s Knowledge
Darwin thought individuals varied.
Darwin thought the Earth was a few thousand years old.
Darwin thought fossils in a given area were similar to the animals that were still living there.
Darwin thought organisms produced many offspring.
Darwin thought few offspring of a pair survived.
Which of the following statements about Darwin following the voyage of HMS Beagle is incorrect?
Answer: This question is designed to make students focus on what information was available to Darwin when he developed his ideas on evolution. Darwin knew species varied (option a), that fossils in a given area were similar to living species in that area (option c), and that many offspring were produced (option d) but few survived (option e). However, from reading Lyell’s Principles of Geology, Darwin realized that Earth cannot be just a few thousand years old. Therefore, the only correct answer is b.
Answer: This question is designed to make students focus on what information was available to Darwin when he developed his ideas on evolution. Darwin knew species varied (option a), that fossils in a given area were similar to living species in that area (option c), and that many offspring were produced (option d) but few survived (option e). However, from reading Lyell’s Principles of Geology, Darwin realized that Earth cannot be just a few thousand years old. Therefore, the only correct answer is b. 5

6. The Unity and Diversity of Life
Which of the following statements can be associated with the concept of the “unity of life” and which can be associated with the concept of the “diversity of life”?
The amino acid sequences of cytochrome c (an enzyme in mitochondria) differ between humans and chimps by one amino acid.
If the gene for human insulin is inserted into bacteria, the bacteria can make human insulin.
Medium ground finches (Geospiza fortis) have beaks that are similar in shape but smaller than large ground finches (Geospiza magnirostris).
The basic forelimb structure of horses and moles is similar.
Scientists interested in curing human cancer may study cell division in yeasts.
Answer: This question is designed to make students think about the apparent contradiction that evolution can explain both the unity and diversity of life. Options b, d, and e are clearly related to the “unity of life”: these answers all show similarities among different species. Students may disagree on whether option a is associated with “unity” (there is lots of similarity) or “diversity” (there is one difference) and should be able to make good arguments for both. In option c, the similarity in shape would relate to the “unity of life” but the difference in shape would relate to the “diversity of life.” 6

7. The Unity and Diversity of Life
Which of the following statements can be associated with the concept of the “unity of life” and which can be associated with the concept of the “diversity of life”?
The amino acid sequences of cytochrome c (an enzyme in mitochondria) differ between humans and chimps by one amino acid.
If the gene for human insulin is inserted into bacteria, the bacteria can make human insulin.
Medium ground finches (Geospiza fortis) have beaks that are similar in shape but smaller than large ground finches (Geospiza magnirostris).
The basic forelimb structure of horses and moles is similar.
Scientists interested in curing human cancer may study cell division in yeasts.
Answer: This question is designed to make students think about the apparent contradiction that evolution can explain both the unity and diversity of life. Options b, d, and e are clearly related to the “unity of life”: these answers all show similarities among different species. Students may disagree on whether option a is associated with “unity” (there is lots of similarity) or “diversity” (there is one difference) and should be able to make good arguments for both. In option c, the similarity in shape would relate to the “unity of life” but the difference in shape would relate to the “diversity of life.”
Answer: This question is designed to make students think about the apparent contradiction that evolution can explain both the unity and diversity of life. Options b, d, and e are clearly related to the “unity of life”: these answers all show similarities among different species. Students may disagree on whether option a is associated with “unity” (there is lots of similarity) or “diversity” (there is one difference) and should be able to make good arguments for both. In option c, the similarity in shape would relate to the “unity of life” but the difference in shape would relate to the “diversity of life.” 7

8. Adaptation
If an adaptation is defined as a trait that promotes survival or reproduction, which of the following traits would qualify as an adaptation?
Hemoglobin is one color (bright red) when oxygenated and another color (purple-blue) when deoxygenated.
Humans have a “tailbone” (coccyx).
Many desert plants have leaves shaped like needles.
The presence of sickle-cell hemoglobin allele helps the holder survive malaria.
Answer: It is important to realize that not all traits contribute to survival or reproduction. Some traits may have no effect on survival or reproduction (hemoglobin color as in option a; the tailbone in humans as in option b). The ability of hemoglobin to carry oxygen and to release it at low oxygen tensions is an adaptation, but its color is not an adaptation. The tailbone functioned in human ancestors as a support for a tail, which functioned to maintain balance; it is a vestigial trait in humans and does not improve survival or reproductive rates. Option c represents an adaptation. In general, leaves in desert plants are smaller, allowing less water to be lost; and the needle shape discourages many herbivores. Option d is tricky—the sickle cell allele is beneficial in areas where malaria is present but detrimental in areas where malaria does not occur. 8

9. Humans have a “tailbone” (coccyx).
If an adaptation is defined as a trait that promotes survival or reproduction, which of the following traits would qualify as an adaptation?
Hemoglobin is one color (bright red) when oxygenated and another color (purple-blue) when deoxygenated.
Humans have a “tailbone” (coccyx).
Many desert plants have leaves shaped like needles.
The presence of sickle-cell hemoglobin allele helps the holder survive malaria.
Answer: It is important to realize that not all traits contribute to survival or reproduction. Some traits may have no effect on survival or reproduction (hemoglobin color as in option a; the tailbone in humans as in option b). The ability of hemoglobin to carry oxygen and to release it at low oxygen tensions is an adaptation, but its color is not an adaptation. The tailbone functioned in human ancestors as a support for a tail, which functioned to maintain balance; it is a vestigial trait in humans and does not improve survival or reproductive rates. Option c represents an adaptation. In general, leaves in desert plants are smaller, allowing less water to be lost; and the needle shape discourages many herbivores. Option d is tricky—the sickle cell allele is beneficial in areas where malaria is present but detrimental in areas where malaria does not occur.
Answer: It is important to realize that not all traits contribute to survival or reproduction. Some traits may have no effect on survival or reproduction (hemoglobin color as in option a; the tailbone in humans as in option b). The ability of hemoglobin to carry oxygen and to release it at low oxygen tensions is an adaptation, but its color is not an adaptation. The tailbone functioned in human ancestors as a support for a tail, which functioned to maintain balance; it is a vestigial trait in humans and does not improve survival or reproductive rates. Option c represents an adaptation. In general, leaves in desert plants are smaller, allowing less water to be lost; and the needle shape discourages many herbivores. Option d is tricky—the sickle cell allele is beneficial in areas where malaria is present but detrimental in areas where malaria does not occur. 9

10. Descent with Modification
Which of the following conclusions could you correctly draw after studying the figure on the next slide?
a) Barytherium is an ancestor of Platybelodon but not of the manatees and relatives.
b) Loxodonta cylotis is more closely related to Loxodonta africana than to Elephas maximus.
c) Mammut shares a more recent common ancestor with Stegodon than with Elephas maximus.
d) Manatees are more closely related to the living elephant species than hyraxes are.
e) Elephas maximus is an ancestor of both Loxodonta species.
Answer: This question will help students better understand evolutionary trees. Option a attacks a common misconception and creationist “talking point,” that the fossils we see are ancestors of living species. While we may be lucky enough to occasionally get a fossil that is a direct ancestor of a living species, this cannot possibly be common, and a fossil almost always represents a species more closely related to the common ancestor of the fossil and the living species than to the living species. Option e is similar to a. Saying that Elephas maximus is an ancestor of the Loxodonta species is like saying monkeys are human ancestors; neither statement is accurate. Option c is incorrect because the common ancestor of Mammut and Stegodon (living approximately 32 million years ago) is also the common ancestor of Mamut and Elephas maximus. Answer d is incorrect because the diagram does not “resolve” the evolutionary splits of hyraxes, manatees, and the rest of the groups; more information may allow a resolution in the future. Option b is an accurate statement because the common ancestor of the two Loxodonta species is more recent (2 million years) than the common ancestor of Elephas and Loxodonta (5 million years). 10

12. Descent with Modification
Which of the following conclusions could you correctly draw after studying the figure on the next slide?
a) Barytherium is an ancestor of Platybelodon but not of the manatees and relatives.
b) Loxodonta cylotis is more closely related to Loxodonta africana than to Elephas maximus.
c) Mammut shares a more recent common ancestor with Stegodon than with Elephas maximus.
d) Manatees are more closely related to the living elephant species than hyraxes are.
e) Elephas maximus is an ancestor of both Loxodonta species.
Answer: This question will help students better understand evolutionary trees. Option a attacks a common misconception and creationist “talking point,” that the fossils we see are ancestors of living species. While we may be lucky enough to occasionally get a fossil that is a direct ancestor of a living species, this cannot possibly be common, and a fossil almost always represents a species more closely related to the common ancestor of the fossil and the living species than to the living species. Option e is similar to a. Saying that Elephas maximus is an ancestor of the Loxodonta species is like saying monkeys are human ancestors; neither statement is accurate. Option c is incorrect because the common ancestor of Mammut and Stegodon (living approximately 32 million years ago) is also the common ancestor of Mamut and Elephas maximus. Answer d is incorrect because the diagram does not “resolve” the evolutionary splits of hyraxes, manatees, and the rest of the groups; more information may allow a resolution in the future. Option b is an accurate statement because the common ancestor of the two Loxodonta species is more recent (2 million years) than the common ancestor of Elephas and Loxodonta
(5 million years).
Answer: This question will help students better understand evolutionary trees. Option a attacks a common misconception and creationist “talking point,” that the fossils we see are ancestors of living species. While we may be lucky enough to occasionally get a fossil that is a direct ancestor of a living species, this cannot possibly be common, and a fossil almost always represents a species more closely related to the common ancestor of the fossil and the living species than to the living species. Option e is similar to a. Saying that Elephas maximus is an ancestor of the Loxodonta species is like saying monkeys are human ancestors; neither statement is accurate. Option c is incorrect because the common ancestor of Mammut and Stegodon (living approximately 32 million years ago) is also the common ancestor of Mamut and Elephas maximus. Answer d is incorrect because the diagram does not “resolve” the evolutionary splits of hyraxes, manatees, and the rest of the groups; more information may allow a resolution in the future. Option b is an accurate statement because the common ancestor of the two Loxodonta species is more recent (2 million years) than the common ancestor of Elephas and Loxodonta (5 million years). 12

13. Action of Natural Selection
Imagine a species of bird in which females prefer to mate with brightly colored males. However, males with bright backs are more often preyed upon by hawks. Assuming that a wide variety of genetic variation exists in the species, which do you think is the most likely evolutionary outcome?
Males will be selected to be brightly colored.
Females will be selected to choose drab males.
Males will be selected to have bright chests and dull backs.
Females will not mate.
The species will go extinct because the hawks catch all the males.
Answer: This question presents a scenario designed to be analogous to the guppy example in the textbook. You would expect hawks to select against birds with brightly colored backs and females to select for males with bright colors. Option a is likely if only female choice is considered but not with the effect of hawk predation. Option b is a possibility if males contribute parental care (i.e., if males help care for young and they have a high mortality rate, females who mate with drab males may have a higher probability of fledging their offspring). Option c is the most likely scenario (assuming the genetic variation is available) because males with dull backs will not be preyed upon as much by hawks, and females will see and choose males with bright chests. Options d and e are not likely because females will probably mate even if males are rare and hawks are not likely to catch all the males immediately. 13

14. Action of Natural Selection
Imagine a species of bird in which females prefer to mate with brightly colored males. However, males with bright backs are more often preyed upon by hawks. Assuming that a wide variety of genetic variation exists in the species, which do you think is the most likely evolutionary outcome?
Males will be selected to be brightly colored.
Females will be selected to choose drab males.
Males will be selected to have bright chests and dull backs.
Females will not mate.
The species will go extinct because the hawks catch all the males.
Answer: This question presents a scenario designed to be analogous to the guppy example in the textbook. You would expect hawks to select against birds with brightly colored backs and females to select for males with bright colors. Option a is likely if only female choice is considered but not with the effect of hawk predation. Option b is a possibility if males contribute parental care (i.e., if males help care for young and they have a high mortality rate, females who mate with drab males may have a higher probability of fledging their offspring). Option c is the most likely scenario (assuming the genetic variation is available) because males with dull backs will not be preyed upon as much by hawks, and females will see and choose males with bright chests. Options d and e are not likely because females will probably mate even if males are rare and hawks are not likely to catch all the males immediately.
Answer: This question presents a scenario designed to be analogous to the guppy example in the textbook. You would expect hawks to select against birds with brightly colored backs and females to select for males with bright colors. Option a is likely if only female choice is considered but not with the effect of hawk predation. Option b is a possibility if males contribute parental care (i.e., if males help care for young and they have a high mortality rate, females who mate with drab males may have a higher probability of fledging their offspring). Option c is the most likely scenario (assuming the genetic variation is available) because males with dull backs will not be preyed upon as much by hawks, and females will see and choose males with bright chests. Options d and e are not likely because females will probably mate even if males are rare and hawks are not likely to catch all the males immediately. 14

15. Evidence for Evolution
Which of the following statements could challenge the evolutionary view of the history of life on Earth? Be prepared to explain your answer.
New mammal fossils are discovered in the oldest rocks on Earth.
Coal deposits are found in Antarctica.
The mitochondrial DNA of the medium ground finch in the Galápagos is identical to a bird species in Europe.
Both sugar gliders (Australia) and flying squirrels (North America) use flaps of skin to help them glide from one tree to another.
Horse fossils occur in North America even though there were no wild horses in North America in 1492.
Answer: This question is designed to help students understand that there is a massive amount of evidence for evolution and that if evidence arose that contradicted evolution, scientists would revise the theory. Options a and c are very unlikely under evolutionary theory—a because mammals, as a very derived group, would not occur in very old rocks, and c because you would not expect two species to have identical mitochondrial DNA, especially one that is related to American forms (medium ground finch) and one from Europe. Options b, d, and e are all true statements and do not challenge our evolutionary views. Coal deposits in Antarctica occur as a remnant of forests that grew when Antarctica was located farther north before continental drift pushed Antarctica south. Sugar gliders and flying squirrels independently evolved gliding mechanisms and are an example of convergent evolution. Horses evolved in North America but went extinct before Europeans arrived. 15

16. Evidence for Evolution
Which of the following statements could challenge the evolutionary view of the history of life on Earth? Be prepared to explain your answer.
New mammal fossils are discovered in the oldest rocks on Earth.unlikely
Coal deposits are found in Antarctica. true
The mitochondrial DNA of the medium ground finch in the Galápagos is identical to a bird species in Europe.unlikely
Both sugar gliders (Australia) and flying squirrels (North America) use flaps of skin to help them glide from one tree to another. true
Horse fossils occur in North America even though there were no wild horses in North America in true
Answer: This question is designed to help students understand that there is a massive amount of evidence for evolution and that if evidence arose that contradicted evolution, scientists would revise the theory. Options a and c are very unlikely under evolutionary theory—a because mammals, as a very derived group, would not occur in very old rocks, and c because you would not expect two species to have identical mitochondrial DNA, especially one that is related to American forms (medium ground finch) and one from Europe. Options b, d, and e are all true statements and do not challenge our evolutionary views. Coal deposits in Antarctica occur as a remnant of forests that grew when Antarctica was located farther north before continental drift pushed Antarctica south. Sugar gliders and flying squirrels independently evolved gliding mechanisms and are an example of convergent evolution. Horses evolved in North America but went extinct before Europeans arrived.
Answer: This question is designed to help students understand that there is a massive amount of evidence for evolution and that if evidence arose that contradicted evolution, scientists would revise the theory. Options a and c are very unlikely under evolutionary theory—a because mammals, as a very derived group, would not occur in very old rocks, and c because you would not expect two species to have identical mitochondrial DNA, especially one that is related to American forms (medium ground finch) and one from Europe. Options b, d, and e are all true statements and do not challenge our evolutionary views. Coal deposits in Antarctica occur as a remnant of forests that grew when Antarctica was located farther north before continental drift pushed Antarctica south. Sugar gliders and flying squirrels independently evolved gliding mechanisms and are an example of convergent evolution. Horses evolved in North America but went extinct before Europeans arrived. 16

17. Homologies and “Tree Thinking”
Imagine that a phylogeny was developed for a group of mammals based on bone structure. Which of the following statements would be a reasonable prediction about a phylogeny for the same group of species based on similarities and differences in the structure of a particular enzyme?
The same phylogeny would be predicted.
The same phylogeny would be unlikely.
No prediction could be made.
The amino acid sequence would be identical in all species.
The new phylogeny would be different.
Answer: This question is designed to help students understand what phylogenetic trees show. They show evolutionary branching points and indicate how closely related different species are. Furthermore, if you make a phylogeny based on one set of characteristics, you would predict that a phylogeny based on another set of characteristics would yield the same results. Based on this information, the only good answer is a. 17

18. Homologies and “Tree Thinking”
Imagine that a phylogeny was developed for a group of mammals based on bone structure. Which of the following statements would be a reasonable prediction about a phylogeny for the same group of species based on similarities and differences in the structure of a particular enzyme?
The same phylogeny would be predicted.
The same phylogeny would be unlikely.
No prediction could be made.
The amino acid sequence would be identical in all species.
The new phylogeny would be different.
Answer: This question is designed to help students understand what phylogenetic trees show. They show evolutionary branching points and indicate how closely related different species are. Furthermore, if you make a phylogeny based on one set of characteristics, you would predict that a phylogeny based on another set of characteristics would yield the same results. Based on this information, the only good answer is a.
Answer: This question is designed to help students understand what phylogenetic trees show. They show evolutionary branching points and indicate how closely related different species are. Furthermore, if you make a phylogeny based on one set of characteristics, you would predict that a phylogeny based on another set of characteristics would yield the same results. Based on this information, the only good answer is a. 18

19. Homologies and “Tree Thinking”
Imagine two species that are thought to have a recent common ancestor. If this idea is correct, these two species most likely have
no morphological similarities.
few biochemical similarities.
some genes with identical amino acid sequences.
very different habits.
similar embryological development.
Answer: Again, this question is designed to help students understand what phylogenetic trees show. They show evolutionary branching points and indicate how closely related different species are. Furthermore, if you make a phylogeny based on one set of characteristics, you would predict that a phylogeny based on another set of characteristics would yield the same results. Based on this reasoning, you would expect e, similar embryological development, and c for at least some genes should still have identical sequences, but not a lot of differences (as in options a, b, and d). 19

20. Homologies and “Tree Thinking”
Imagine two species that are thought to have a recent common ancestor. If this idea is correct, these two species most likely have
no morphological similarities. (no)
few biochemical similarities. (no)
some genes with identical amino acid sequences .yes
very different habits. (no)
similar embryological development. yes
Answer: Again, this question is designed to help students understand what phylogenetic trees show. They show evolutionary branching points and indicate how closely related different species are. Furthermore, if you make a phylogeny based on one set of characteristics, you would predict that a phylogeny based on another set of characteristics would yield the same results. Based on this reasoning, you would expect e, similar embryological development, and c for at least some genes should still have identical sequences, but not a lot of differences (as in options a, b, and d).
Answer: Again, this question is designed to help students understand what phylogenetic trees show. They show evolutionary branching points and indicate how closely related different species are. Furthermore, if you make a phylogeny based on one set of characteristics, you would predict that a phylogeny based on another set of characteristics would yield the same results. Based on this reasoning, you would expect e, similar embryological development, and c for at least some genes should still have identical sequences, but not a lot of differences (as in options a, b, and d). 20

21. Evolution of Adaptations
Imagine that you have discovered a new lizard that lives in a foggy desert in southwestern South America. As fog rolls in, this lizard stands on its head and lets water condense on its back and roll in grooves to its mouth. Considering the Namibian beetle in the figure below, this trait is an example of which of the following?
convergent evolution
inheritance of acquired characteristics
homology
Answer: This question is designed to make students think about adaptations and how they arise. The imaginary lizard in this question should remind students of the “headstander beetle” in the opening paragraphs of this chapter in the textbook. Lizards and beetles are not closely related and so the water-collecting adaptations must have evolved independently (an example of convergent evolution but not of homology). There is no evidence, either in this question or elsewhere, that organisms evolve by the inheritance of acquired characteristics. The only correct answer is a. 21

22. Evolution of Adaptations
Imagine that you have discovered a new lizard that lives in a foggy desert in southwestern South America. As fog rolls in, this lizard stands on its head and lets water condense on its back and roll in grooves to its mouth. Considering the Namibian beetle in the figure below, this trait is an example of which of the following?
convergent evolution
inheritance of acquired characteristics
homology
Answer: This question is designed to make students think about adaptations and how they arise. The imaginary lizard in this question should remind students of the “headstander beetle” in the opening paragraphs of this chapter in the textbook. Lizards and beetles are not closely related and so the water-collecting adaptations must have evolved independently (an example of convergent evolution but not of homology). There is no evidence, either in this question or elsewhere, that organisms evolve by the inheritance of acquired characteristics. The only correct answer is a.
Answer: This question is designed to make students think about adaptations and how they arise. The imaginary lizard in this question should remind students of the “headstander beetle” in the opening paragraphs of this chapter in the textbook. Lizards and beetles are not closely related and so the water-collecting adaptations must have evolved independently (an example of convergent evolution but not of homology). There is no evidence, either in this question or elsewhere, that organisms evolve by the inheritance of acquired characteristics. The only correct answer is a. 22