Descent with Modification: A Darwinian View of Life

1. 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 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. Which of the following statements about Lamarck is/are accurate?

3. 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.

4. 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?

5. 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.

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.

7. 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.”

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.

9. 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.

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.

12. 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 Elephasmaximus 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 Elephasmaximus. 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).

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.

14. 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.

15. Imagine two species that are thought to have a recent common ancestor. If this idea is correct, these two species most likely have Homologies and “Tree Thinking” • no morphological similarities. • few biochemical similarities. • some genes with identical amino acid sequences. • very different habits. • similar embryological development.

16. 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).

17. 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

18. 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.