PrepTest 102, Section 4, Question 6
The male sage grouse has air sacs that,(50 more words not shown)
Which one of the following,(8 more words not shown)
- ASome female sage(7 more words not shown)
- BWhen diseased male(18 more words not shown)
- CSome healthy male(14 more words not shown)
- DMale sage grouse(14 more words not shown)
- EThe sage grouse(20 more words not shown)
Reading the argument
The male displays its inflated air sacs. Why think that display tells the female whether the male is healthy? We can accept the description of the courtship ritual without accepting the scientists' explanation for it. Perhaps the display signals health. Perhaps the birds perform it for some other reason. Seeing a behavior doesn't by itself establish what function that behavior serves.
I'd like to see females actually choosing mates based on the air-sac display. It would also help to know what information the sacs reveal. If a visible feature distinguishes a healthy male from an unhealthy one, the proposed health-screening role starts to make more sense.
What we’re looking for
That's what I'd look for in a strengthener: connect the display with information about health or with mate selection based on that information. We don't need to prove that every female always picks a perfectly healthy male. We need support for the proposed function of this particular ritual.
Working the answers
- A
Some females choosing unhealthy males doesn't support the idea that the display helps them select healthy mates. It also doesn't by itself disprove the hypothesis; the process might be imperfect or other factors might matter. A gives us no connection between the air-sac display and the choice.
- B
These diseased males received antibiotics and weren't chosen. We don't know whether treatment cured them, whether symptoms remained, or what the females noticed. Their rejection therefore doesn't establish that the sacs revealed poor health. Nor can we conclude that antibiotics themselves caused the rejection. The relevant connection is missing.
- C
Some healthy males don't display their sacs. What happens to those males during mate selection? C doesn't say. They could be overlooked because they don't display, or selected for some other reason. The fact that some healthy males omit the ritual doesn't show that performing it helps females assess health.
- DCorrect
Parasitic infections produce symptoms visible on the air sacs. Now the display can reveal something useful: a female seeing the sacs could see evidence of infection. That gives the ritual a plausible role in distinguishing healthier mates from infected ones. D supplies the connection between the displayed feature and health that we wanted, even without a complete study of every mating decision.
- E
A changing strain of malaria tells us there is a disease affecting these birds. It doesn't tell us whether the infection changes the air sacs in a visible way or whether females use the display to detect it. Compare D, which connects illness directly to the feature being shown.
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