1.
The evidence supporting the pattern component of the theory of evolution can be criticized on the grounds that it is indirect. For example, no one has directly observed the formation of a vestigial trait over time. Because of the indirect nature of the evidence, it could be argued that structural and genetic homologies are coincidental, and do not result from common ancestry. Is indirect evidence for a scientific theory legitimate? Are you persuaded that modification with descent is the best explanation available for the data reviewed in section 21.1? Why or why not?
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2.
Some biologists encapsulate Darwinian evolution with the phrase "mutation proposes, selection disposes." Explain how this quip relates to the four postulates listed at the start of section 21.2.
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3.
Review the section on the evolution of drug resistance in Mycobacterium tuberculosis.
In M. tuberculosis, how does heritable variation arise for the trait of drug resistance?
What evidence do researchers have that a drug-resistant strain evolved in the patient analyzed in their study, instead of being transmitted from another infected individual?
If the antibiotic rifampin were banned, would the mutant rpoB gene have lower or higher fitness in the new environment? Would strains carrying the mutation continue to increase in frequency in M. tuberculosis populations?
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4.
Review Box 21.4 on page 424 of your textbook and the section on the evolution of flower size in alpine skypilots (pages 422-425).
To estimate the heritability of flower size, a researcher planted offspring into randomly assigned locations in the environment. Why was this randomization step important?
Consider the experiment that was designed to test whether any differences exist between the flower size of offspring from hand pollination between randomly chosen skypilots and the offspring from pollinations performed by bumblebees. In what sense did the randomly pollinated population serve as an experimental control?
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5.
Darwinism is sometimes criticized because it is "just a theory." In everyday English, the word theory refers to an idea or proposed explanation that is untested. (In the dictionary, some definitions of the word even offer conjecture and speculation as synonyms.) As a scientific term, however, the word theory has a far different meaning. Based on material in this chapter and Chapter 1, give a concise definition of a scientific theory. How has the conflict between the everyday and scientific usage of the word contributed to the controversy over the theory of evolution by natural selection?
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