Descent with Modification: A Darwinian View of Life Chapter 22 Descent with Modification: A Darwinian View of Life Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Lamarck’s Hypothesis of Evolution Which of the following statements about Lamarck are accurate? Lamarck thought evolution had occurred. Lamarck proposed a mechanism for evolution. Lamarck thought organisms became more complex because of an inner drive for complexity. 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 e is incorrect). Option b is also correct: Lamarck proposed a mechanism (use and disuse, and inheritance of acquired characteristics). However, Lamarck’s idea of a drive toward complexity has not been supported, so option c is incorrect. Related to material on textbook page 454. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Darwin’s Knowledge Which of the following statements about Darwin 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 most 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, textbook page 458), that fossils in a given area were similar to living species in that area (option c, textbook page 456), and that many offspring were produced (option d, textbook page 458) but few survived (option e, textbook page 458). However, from reading Lyell’s Principles of Geology, Darwin realized that Earth cannot be just a few thousand years old (textbook page 456). Therefore, the only correct answer is b. Related to material on textbook pages 455-456 and page 458. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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.” Related to material on textbook pages 455-460. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Adaptation If an adaptation is defined as a trait that promotes survival or reproduction, which of the following traits would qualify as adaptations? Hemoglobin is one color (bright red) when oxygenated and another color (purple-blue) when unoxygenated. Humans have a “tailbone” (coccyx). Young oak trees, growing in shade, have large leaves compared to older plants, growing in sun, that have smaller leaves. Male elephant seals are enormous and have ferocious battles over the opportunity to mate with females. 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. Options c and d both represent adaptations. In general, leaves in sun are smaller, allowing light to pass by to lower leaves and preventing heat build up. The largest elephant seals win most of the battles and have the most opportunity to mate with females. Option e is tricky—the sickle cell allele is beneficial in areas where malaria is present but detrimental in areas where malaria does not occur. Related to material on textbook pages 456-459. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Descent with Modification Which of the following conclusions could you correctly draw after studying Figure 22.8 in the textbook? Barytherium is an ancestor of Platybelodon but not of the manatees and relatives. Loxodonta cylotis is more closely related to Loxodonta africana than to Elephas maximus. Mammut shares a more recent common ancestor with Stegodon than with Elephas maximus. Manatees are more closely related to the living elephant species than hyraxes are. 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). Related to material on textbook page 457. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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 on textbook page 460. 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. Related to material on textbook pages 460-461. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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 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. Related to material on textbook pages 460-465. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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. Related to material on textbook page 464. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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. 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, but not a lot of differences (as in options a, b, and d). Because species diverge over time, you would not expect identical amino acid sequences (option c). Related to material on textbook page 464. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

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. 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 (page 452). Lizards and beetles are not closely related and so the water-collecting adaptations must have evolved independently (an example of convergent evolution, pages 464-465, but not of homology, page 464). There is no evidence, either in this question or elsewhere, that organisms evolve by the inheritance of acquired characteristics (page 454). The only correct answer is a. Related to material on textbook pages 464-465. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.