Further Thought

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Further Thought

Use the questions at the end of the chapter to explore concepts and connections in greater depth through application and synthesis.

1. Some biologists regard our bodies as small ecosystems that exert selective pressure for the evolution of invasive metastatic cancer. If this is true, why don't we all get cancer? (Hint: Consider the speed of evolution vs. human life span.) However, these same biologists believe that humans have certain genes that have evolved specifically to prevent cancer. How is it possible to have both strong selection for cancer and strong selection for anticancer genes? (Hint: Consider evolution within one person's body vs. evolution within a population of many people.) [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

2. We have seen how the genetic diversity within a tumor can be used to estimate the tumor's age (see Figure 13.14 on page 522 in your textbook). This analysis depends on mutation rate per cell division being constant. If a cancerous tumor has evolved a high mutation rate, how will this bias the results? Do the genetic markers we use to estimate a tumor's age need to be selectively neutral? Why or why not? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

3. Pathogens require a minimum population size of potential hosts. If the host population is too small, in a short time the entire population has either been killed by the pathogen, or has survived the initial infection and become immune. If this occurs, the pathogen dies out. What evolutionary changes in a pathogen might increase its ability to survive in a smaller population? For example, measles requires a host population of about 500,000 humans, while diphtheria can get by with only about 50,000 humans. Develop some hypotheses for why diphtheria can survive with just one-tenth the number of hosts. For example, how might these two diseases differ from each other in transmission rate, virulence, latency to infection, or mutation rate? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

4. In the experiment illustrated in Figure 13.19b (page 529 in your textbook), why was it important to give one group of lizards a saline injection? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

5. Suppose that your two-year-old child is ill and has a dangerously high fever of 106°F (about 41°C). You and your doctor decide to put your child on an antifever medication. Would you want your child's temperature to return all the way to normal or to stabilize at a "mild fever" level (say, 101°F, or about 38.5°C)? If you feel that you don't have enough information to make this important decision, what further information would you want? (That is, what further studies should be done?) [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

6. Review the studies on fever that were presented in this chapter. Do you agree with Kluger that several of the studies did not really test the adaptive fever hypothesis? If so, can you design an experiment that will truly test the hypothesis? Is your experiment ethical? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

7. The male reed buntings in Dixon et al.'s study (Figure 13.22 on page 536 in your textbook) seem to be consciously aware of genetic relationships and "trying" to increase their reproductive success. Can evolution cause reed buntings (and other animals) to behave as if they are aware of the evolutionary consequences of their actions, without actually being aware of those consequences? Do you think the same could be true of some human behaviors? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

8. Daly and Wilson's data on infanticide risks might be explained by stepfathers having, on average, more violent personalities than biological fathers. Could this "violent personality" explanation also apply to Flinn's data from the Trinidad village? Why or why not? Daly and Wilson's study involved general data about a large number of families, whereas Flinn's study involved detailed data on a small number of families. What are the advantages and disadvantages of each kind of study? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

9. An evolutionary biologist once hypothesized that if evolution has affected human social behavior, then a mother's brothers should take a particular interest in her children—more so than the father's brothers, and perhaps even more so than the father himself. Why did he hypothesize this? (As it turns out, there are many cultures in which men do, in fact, direct parental care primarily toward their sisters' children.) [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

10. In 1999, a mysterious outbreak of human encephalitis occurred in the northeastern United States. The cause was tentatively identified as St. Louis encephalitis virus. At the same time, an unusual number of dead birds were noticed along the northeastern Atlantic coast. Figure 13.27 (page 543 in your textbook) shows genetic relationships of three known encephalitis viruses (St. Louis, Japanese, and West Nile), with viruses isolated from the birds, from two human patients that died, from one dead horse, and from mosquitoes. (Data compiled from Anderson et al. 1999 and Lanciotti et al. 1999.)

Were the birds, the horse, and the humans all suffering from the same disease?

Do you think the outbreak was caused by St. Louis encephalitis virus?

Does this cladogram suggest how the disease might be spread? [Hint]
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.




1.	Some biologists regard our bodies as small ecosystems that exert selective pressure for the evolution of invasive metastatic cancer. If this is true, why don't we all get cancer? (Hint: Consider the speed of evolution vs. human life span.) However, these same biologists believe that humans have certain genes that have evolved specifically to prevent cancer. How is it possible to have both strong selection for cancer and strong selection for anticancer genes? (Hint: Consider evolution within one person's body vs. evolution within a population of many people.) [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



2.	We have seen how the genetic diversity within a tumor can be used to estimate the tumor's age (see Figure 13.14 on page 522 in your textbook). This analysis depends on mutation rate per cell division being constant. If a cancerous tumor has evolved a high mutation rate, how will this bias the results? Do the genetic markers we use to estimate a tumor's age need to be selectively neutral? Why or why not? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



3.	Pathogens require a minimum population size of potential hosts. If the host population is too small, in a short time the entire population has either been killed by the pathogen, or has survived the initial infection and become immune. If this occurs, the pathogen dies out. What evolutionary changes in a pathogen might increase its ability to survive in a smaller population? For example, measles requires a host population of about 500,000 humans, while diphtheria can get by with only about 50,000 humans. Develop some hypotheses for why diphtheria can survive with just one-tenth the number of hosts. For example, how might these two diseases differ from each other in transmission rate, virulence, latency to infection, or mutation rate? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



4.	In the experiment illustrated in Figure 13.19b (page 529 in your textbook), why was it important to give one group of lizards a saline injection? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



5.	Suppose that your two-year-old child is ill and has a dangerously high fever of 106°F (about 41°C). You and your doctor decide to put your child on an antifever medication. Would you want your child's temperature to return all the way to normal or to stabilize at a "mild fever" level (say, 101°F, or about 38.5°C)? If you feel that you don't have enough information to make this important decision, what further information would you want? (That is, what further studies should be done?) [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



6.	Review the studies on fever that were presented in this chapter. Do you agree with Kluger that several of the studies did not really test the adaptive fever hypothesis? If so, can you design an experiment that will truly test the hypothesis? Is your experiment ethical? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



7.	The male reed buntings in Dixon et al.'s study (Figure 13.22 on page 536 in your textbook) seem to be consciously aware of genetic relationships and "trying" to increase their reproductive success. Can evolution cause reed buntings (and other animals) to behave as if they are aware of the evolutionary consequences of their actions, without actually being aware of those consequences? Do you think the same could be true of some human behaviors? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



8.	Daly and Wilson's data on infanticide risks might be explained by stepfathers having, on average, more violent personalities than biological fathers. Could this "violent personality" explanation also apply to Flinn's data from the Trinidad village? Why or why not? Daly and Wilson's study involved general data about a large number of families, whereas Flinn's study involved detailed data on a small number of families. What are the advantages and disadvantages of each kind of study? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



9.	An evolutionary biologist once hypothesized that if evolution has affected human social behavior, then a mother's brothers should take a particular interest in her children—more so than the father's brothers, and perhaps even more so than the father himself. Why did he hypothesize this? (As it turns out, there are many cultures in which men do, in fact, direct parental care primarily toward their sisters' children.) [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



10.	In 1999, a mysterious outbreak of human encephalitis occurred in the northeastern United States. The cause was tentatively identified as St. Louis encephalitis virus. At the same time, an unusual number of dead birds were noticed along the northeastern Atlantic coast. Figure 13.27 (page 543 in your textbook) shows genetic relationships of three known encephalitis viruses (St. Louis, Japanese, and West Nile), with viruses isolated from the birds, from two human patients that died, from one dead horse, and from mosquitoes. (Data compiled from Anderson et al. 1999 and Lanciotti et al. 1999.) Were the birds, the horse, and the humans all suffering from the same disease? Do you think the outbreak was caused by St. Louis encephalitis virus? Does this cladogram suggest how the disease might be spread? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

Chapter 13: Darwinian Medicine

Further Thought