Descent with Modification: A Darwinian View 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 chimpanzees 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.”

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. 3

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. 4

Imagine two species that are thought to have a recent common ancestor 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. several homologous structures. similar embryological development. Both C and D are correct. Answer: e, because the more homologous structures and similarity in development organisms have, the more likely it is that they are closely related. 5

Imagine two species that are thought to have a recent common ancestor 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. several homologous structures. similar embryological development. Both C and D are correct. 6

You find a section of sedimentary rock in which the strata and some fossils have been exposed. You notice that a clam fossil is in deeper strata than a fish fossil you can see. Using relative dating, which fossil is most likely older? clam fish not enough data to answer Answer: The answer technically should be A, but students could argue that C or even B is correct, since tectonic activity could have altered these strata. 7

You find a section of sedimentary rock in which the strata and some fossils have been exposed. You notice that a clam fossil is in deeper strata than a fish fossil you can see. Using relative dating, which fossil is most likely older? clam fish not enough data to answer 8

You discover fish living in a cave with no natural light You discover fish living in a cave with no natural light. The fish have no eyes, but they do have eye sockets. Using a Lamarckian thought process, which of the following would be the reason for this? The fish were in a dark environment, and therefore didn’t need eyes. Over time, they used their developmental energy for other more useful features, so because they didn’t use them, they lost them. The fish never had eyes but are slowly evolving to have them because they will need them someday. Originally, some fish in the population had eyes and could see, but those without eyes had more acute other senses, allowing them to eat, avoid being eaten, and find a mate more easily. Eventually, those with eyes died before they could pass on their genes, and the population changed to those without eyes. Answer: a, because Lamarck believed in the concept of Use and Disuse. 9

You discover fish living in a cave with no natural light You discover fish living in a cave with no natural light. The fish have no eyes, but they do have eye sockets. Using a Lamarckian thought process, which of the following would be the reason for this? The fish were in a dark environment, and therefore didn’t need eyes. Over time, they used their developmental energy for other more useful features, so because they didn’t use them, they lost them. The fish never had eyes but are slowly evolving to have them because they will need them someday. Originally, some fish in the population had eyes and could see, but those without eyes had more acute other senses, allowing them to eat, avoid being eaten, and find a mate more easily. Eventually, those with eyes died before they could pass on their genes, and the population changed to those without eyes. 10

You discover fish living in a cave with no natural light You discover fish living in a cave with no natural light. The fish have no eyes, but they do have eye sockets. Using a Darwinian thought process, which of the following would be the reason for this? The fish were in a dark environment and therefore didn’t need eyes. Over time, they used their developmental energy for other more useful features, so because they didn’t use them, they lost them. The fish never had eyes but are slowly evolving to have them because they might need them in the future. Originally, some fish in the population had eyes and could see, but those without eyes had more acute other senses, allowing them to eat, avoid being eaten, and find a mate more easily. Eventually, those with eyes died before they could pass on their genes, and the population changed to those without eyes. Answer: c, because this illustrates that selection was occurring, and that it was occurring at a population level. 11

You discover fish living in a cave with no natural light You discover fish living in a cave with no natural light. The fish have no eyes, but they do have eye sockets. Using a Darwinian thought process, which of the following would be the reason for this? The fish were in a dark environment and therefore didn’t need eyes. Over time, they used their developmental energy for other more useful features, so because they didn’t use them, they lost them. The fish never had eyes but are slowly evolving to have them because they might need them in the future. Originally, some fish in the population had eyes and could see, but those without eyes had more acute other senses, allowing them to eat, avoid being eaten, and find a mate more easily. Eventually, those with eyes died before they could pass on their genes, and the population changed to those without eyes. 12

Using the Galápagos finches example from the book, which of the following best explains the Darwinian reason why the insect-eating finch has such a long, narrow beak? Variation existed in the finch population. Those that naturally had longer, narrower beaks could reach their food more easily, allowing finches with these features to survive and reproduce more often than those that did not. Every day, finches who needed to eat insects would squeeze their beaks into tiny holes to reach insects, eventually changing the shape of their beaks, which then got passed on to future generations. Those with longer, narrower beaks carried the dominant gene for that, which is how they evolved. Answer: a, because those with the best fit to the environment, which was the long, narrow beak, were able to eat and survive, and therefore had a greater chance of passing on their genes. 13

Using the Galápagos finches example from the book, which of the following best explains the Darwinian reason why the insect-eating finch has such a long, narrow beak? Variation existed in the finch population. Those that naturally had longer, narrower beaks could reach their food more easily, allowing finches with these features to survive and reproduce more often than those that did not. Every day, finches who needed to eat insects would squeeze their beaks into tiny holes to reach insects, eventually changing the shape of their beaks, which then got passed on to future generations. Those with longer, narrower beaks carried the dominant gene for that, which is how they evolved. 14

MRSA infections are occurring at alarming rates MRSA infections are occurring at alarming rates. One reason for this could be that people do not finish their antibiotics. Which of the following is the most likely reason that this could lead to something like MRSA? Antibiotics take awhile to start working, giving the bacteria time to mount defenses against the antibiotics over a few days. Because antibiotics are often taken when there is no bacterial infection, the antibiotics aren’t using their medicinal/antibacterial properties and are losing them. The first few days of antibiotics kill off the weak bacteria, making people feel better. Then, when people stop taking the antibiotics, the strong bacteria that survived have been selected, breed with one another, and create a stronger population. Answer: c, because the antibiotics originally selected out and killed the weaker bacteria, leaving only the strong ones to breed with one another, changing the population into a more antibiotic-resistant group. 15

MRSA infections are occurring at alarming rates MRSA infections are occurring at alarming rates. One reason for this could be that people do not finish their antibiotics. Which of the following is the most likely reason that this could lead to something like MRSA? Antibiotics take awhile to start working, giving the bacteria time to mount defenses against the antibiotics over a few days. Because antibiotics are often taken when there is no bacterial infection, the antibiotics aren’t using their medicinal/antibacterial properties and are losing them. The first few days of antibiotics kill off the weak bacteria, making people feel better. Then, when people stop taking the antibiotics, the strong bacteria that survived have been selected, breed with one another, and create a stronger population. 16

Plants in “Mediterranean” ecosystems have similar adaptations for surviving hot dry summers and fire. Given that these ecosystems are presently found in southern Europe, California, Chile, South Africa, and southern Australia, which of the following best explains the origin of these adaptations? These adaptations likely arose in a common ancestor on Pangea, and continental drift later moved these drought- and fire-adapted plants to their present locations. These plants likely share a recent common ancestor and have been subjected to the same selective pressures. Although these plants likely do not share a recent common ancestor, they have been subjected to the same selective pressures. Answer: c, because these regions are widely spaced apart around the Earth making it unlikely the plants are all descended from the same recent common ancestors. It is more likely that the common environmental factors (drought and fire) selected for the same types of adaptations (making this a case of evolutionary convergence). 17

Plants in “Mediterranean” ecosystems have similar adaptations for surviving hot dry summers and fire. Given that these ecosystems are presently found in southern Europe, California, Chile, South Africa, and southern Australia, which of the following best explains the origin of these adaptations? These adaptations likely arose in a common ancestor on Pangea, and continental drift later moved these drought- and fire-adapted plants to their present locations. These plants likely share a recent common ancestor and have been subjected to the same selective pressures. Although these plants likely do not share a recent common ancestor, they have been subjected to the same selective pressures. 18

A number of scientists influenced Darwin’s thinking about evolution A number of scientists influenced Darwin’s thinking about evolution. Which of the following scientists had proposed that the geological processes of the past (e.g., rivers forming valleys over time) were still in operation? Cuvier Lyell Linnaeus Malthus Wallace Answer: b, because it was Lyell’s book “Principles of Geology,” which Darwin read while on his voyage aboard the Beagle. 19

A number of scientists influenced Darwin’s thinking about evolution A number of scientists influenced Darwin’s thinking about evolution. Which of the following scientists had proposed that the geological processes of the past (e.g., rivers forming valleys over time) were still in operation? Cuvier Lyell Linnaeus Malthus Wallace 20