Chapter 1: A Case Study for Evolutionary Thinking: Understanding HIV

1.	AIDS is primarily a disease of young adults. How does a disease like this affect the size, age distribution, and growth rate of human populations over time? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
2.	In the early 1990's, researchers began to find AZT-resistant strains of HIV-1 in recently infected patients who had never received AZT. How can this be? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
3.	The idea behind multiple drug therapy for HIV is to incrase the number of mutations required for resistance, and therefore reduce the amount of genetic variation in the viral population for survival in the presence of drugs. Could we achieve the same effect by using antiretroviral drugs in sequence instead of simultaneously? 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.
4.	Some physicians have advocated drug holidays as a way of helping HIV patients cope with the side effects of multiple-drug therapy. Under this plan, every so often the patient would stop taking drugs for a while. From an evolutionary perspsective, does this seem like a good idea or a bad idea? Justify your answer. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
5.	In this chapter, we discussed two different types of selection: selection of different virus strains within one host, and selection of those virus strains that are able to transmit themselves from host to host. Suppose an HIV counselor is talking to a patient who is worried that he or she might have a virulent strain of HIV. "Don't worry," the counselor says. "Even if you have a virulent strain now, as long as you remain monogamous the virulent strain will die out." How has the counselor misinterpreted the transmission rate hypothesis? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
6.	An alternative to the transmission rate hypothesis, traditionally championed by biomedical researchers, is that disease-causing agents "naturally" evolve into more benign forms as the immune systems of their hosts evolve more efficient responses to them. What pedictions does this "coevolution hypothesis" make about evolution of HIV virulence in the United States vs. Africa vs. South Asia? What data would help you decide whether the transmission rate hypothesis or coevolution hypothesis is correct? Do the hypotheses suggest different ways to spend the limited budget for HIV research and education? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
7.	Respond to the following quote, from the character named Mr. Spock in "Star Trek": "A truly successful parasite is commensal, living in amity with its host, or even giving it positive advantages, as, for instance, the protozoans who live in the digestive s ystem of your termites and digest for them the wood they eat. A parasite that regularly and inevitabl kills its host cannot survive long, in the evolutionary sense, unless it multiplies with tremendous rapidity . . . it is not pro-survival." [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
8.	The text claims that human populations will evolve in response to the AIDS epidemic, because alleles that ocnfer resistance ot HIV infection shoud increase in frequency in the population over time. Do you agree with this prediction? How would you design a study capable of testing it? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
9.	Suppose that HIV was the ancestor of the SIVs, instead of the other way around. If immunodeficiency viruses were originally transmitted from humans to monkeys and chimpanzees, make a sketch (in your text or lecture notebook) of what Figure 1.13a would look like. [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.