A study found that a field of genetically engineered corn had spread its genes into neighboring wild grasses, raising fears...
GMAT Critical Reasoning : (CR) Questions
A study found that a field of genetically engineered corn had spread its genes into neighboring wild grasses, raising fears that these genes could alter wild grass species throughout the region. However, when the genetically engineered corn was removed, a follow-up study two years later could not find any trace of engineered corn genes in local grasses.
Which of the following, if true, most helps to explain the discrepancy between the two studies?
Passage Analysis:
| Text from Passage | Analysis |
| A study found that a field of genetically engineered corn had spread its genes into neighboring wild grasses, raising fears that these genes could alter wild grass species throughout the region. |
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| However, when the genetically engineered corn was removed, a follow-up study two years later could not find any trace of engineered corn genes in local grasses. |
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Argument Flow:
We have two conflicting scientific studies presented as facts. The first study shows gene transfer occurred, while the second study shows no trace of those genes. This creates a puzzle that needs explaining.
Main Conclusion:
There's actually no main conclusion here - this passage presents a discrepancy between two studies without resolving it. The question asks us to explain this contradiction.
Logical Structure:
This isn't a traditional argument structure. Instead, it's presenting a scientific mystery: Study 1 found gene transfer, Study 2 found no genes after removal. We're asked to find what could explain why these results differ so dramatically.
Prethinking:
Question type:
Paradox - We need to explain why two studies about the same thing produced completely opposite results. The first study found engineered genes in wild grasses, but the second study found zero traces of those same genes.
Precision of Claims
The claims are very specific about timing (2 years later), detection (genes found vs. no traces found), and location (same local grasses). We need to respect that both studies are factually accurate but seemingly contradictory.
Strategy
For paradox questions, we need to find a reasonable explanation that makes both conflicting results make sense. We're looking for a factor that could cause engineered genes to disappear from wild grasses over time, or something that explains why the detection methods or conditions differed between the studies.
This perfectly explains our paradox. If grasses without the engineered genes had better survival and reproduction rates, then natural selection would work against the modified grasses over time. During the two-year period after corn removal, the unmodified grasses would gradually outcompete the modified ones, eventually eliminating the engineered genes from the population. This explains why the first study found the genes (right after transfer) but the second study found none (after natural selection had time to work). This choice makes both study results completely logical and consistent.
This doesn't resolve our paradox at all. If the follow-up study was more thorough, we'd expect it to be MORE likely to find engineered genes, not less likely. A more sensitive detection method should find traces that a less thorough study missed. This choice actually makes the discrepancy harder to explain, not easier.
This choice misses the point entirely. The timing of gene spread isn't what we need to explain - we already know from the first study that gene transfer occurred. The mystery is why those genes disappeared by the time of the second study. Whether the spread took less than two years or longer doesn't help us understand why the genes vanished.
Like choice C, this focuses on gene transfer rather than gene disappearance. We already know the genes spread successfully (the first study proved that). The puzzle is why they completely disappeared later. Even if genes spread easily among many species, this doesn't explain why they would vanish from all species within two years.
This choice contradicts the first study's findings. If most grass species weren't susceptible to alteration, then the initial study shouldn't have found widespread gene transfer in the first place. This choice tries to deny that the first study's results were valid, rather than explaining how both studies can be accurate.