In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging...
GMAT Critical Reasoning : (CR) Questions
In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. Such burrowing discourages barnacles from clinging to their shells. When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow.
Which of the following, if true, most helps to explain the surprising finding?
Passage Analysis:
| Text from Passage | Analysis |
| In order to withstand tidal currents, juvenile horseshoe crabs frequently burrow in the sand. |
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| Such burrowing discourages barnacles from clinging to their shells. |
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| When fully grown, however, the crabs can readily withstand tidal currents without burrowing, and thus they acquire substantial populations of barnacles. |
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| Surprisingly, in areas where tidal currents are very weak, juvenile horseshoe crabs are found not to have significant barnacle populations, even though they seldom burrow. |
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Argument Flow:
The passage sets up a clear pattern about horseshoe crabs and barnacles, then throws us a curveball. We start with juveniles burrowing to survive currents, which keeps barnacles away. Then we see adults who don't burrow and get covered in barnacles. This makes perfect sense so far. But then we get hit with a weird finding that breaks this pattern - in weak current areas, juveniles don't burrow but still don't have many barnacles.
Main Conclusion:
There's no main conclusion here - this is a puzzle piece. The passage presents a surprising finding that doesn't fit the established pattern and asks us to explain it.
Logical Structure:
This isn't a typical argument with premises leading to a conclusion. Instead, it's a 'setup-and-puzzle' structure. The first three statements build a logical cause-and-effect relationship (currents → burrowing → fewer barnacles vs. no currents → no burrowing → more barnacles), and then the final statement presents an anomaly that breaks this pattern, creating a mystery we need to solve.
Prethinking:
Question type:
Paradox - We need to explain why juvenile horseshoe crabs in weak current areas have few barnacles even though they don't burrow much. This contradicts our expectation based on the established pattern.
Precision of Claims
The key claims involve specific relationships: burrowing frequency (frequent vs seldom), barnacle populations (substantial vs not significant), and tidal current strength (strong vs very weak). We need to respect that juveniles in weak currents seldom burrow but still have few barnacles.
Strategy
We need to find alternative explanations for why juvenile crabs in weak current areas have few barnacles despite not burrowing. The current explanation (burrowing prevents barnacles) doesn't work here since they're not burrowing. We should look for other factors that could prevent barnacle attachment specifically for juveniles in weak current environments.