PrepTest 107, Section 3, Question 22
Biologist: Some speculate that the unusually high frequency(75 more words not shown)
The biologist's view, if true,(10 more words not shown)
- AThe evolutionary pressure(20 more words not shown)
- BThe unusual frequency(22 more words not shown)
- CContrary to what(16 more words not shown)
- DThe evolutionary pressure(21 more words not shown)
- EA diverse gene(17 more words not shown)
Reading the argument
Why are these goats small? There could be several stories. Perhaps small goats can reach food tucked into narrow spaces. Perhaps they can hide from predators more easily. Those are guesses, but they remind us that an observed trait does not identify its own cause.
The proposed explanation is different: smaller goats let the island support more goats, which helps preserve a diverse gene pool. The biologist objects that this skips the step that would actually spread the trait. According to the passage, a trait becomes more common through reproductive success. Small goats would need to reproduce more successfully than large goats.
A benefit to the population is not, by itself, an explanation of that reproductive advantage. We still need to know why small goats leave more offspring. A food or hiding advantage might help explain that, but the biologist does not establish either possibility.
What we’re looking for
The question asks what the biologist's view most supports. I would expect a rejection of the proposed gene-pool explanation. We can reject that explanation without knowing the actual reason these goats are small. Keep the claim tied to the biologist's account rather than trying to settle every possible question about evolution.
Working the answers
- A
This endorses the explanation the biologist challenges. It says pressure to preserve genetic diversity could make the small-size gene more common. The biologist instead requires an advantage in reproductive success and rejects the population-level benefit as the explanation.
- B
The biologist does not rule out greater reproductive success as the reason small goats are common. That is the mechanism the biologist says is needed. B adds limited space and then denies that mechanism explains the observation. Nothing in the passage supports that denial.
- C
This gives the reproductive advantage to large goats. The biologist says a reduction in average size requires small goats to reproduce more successfully than their larger cousins. C points in the opposite direction. The passage also does not establish a general rule about how large goats do whenever space is limited.
- DCorrect
This rejects the proposed explanation: pressure to ensure a diverse gene pool does not explain an increase in the small-size gene. That follows the biologist's contrast between a supposed benefit to the whole population and the reproductive advantage needed to spread a trait. D does not identify the true cause, and it does not need to.
- E
Why would genetic diversity require smaller goats? A population could contain many genetically different large goats. The passage considers one proposed explanation for small size; it never establishes that reducing size is the only way a goat population can have a diverse gene pool.
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