LSAT (Law School Admission Test)Logical ReasoningMedium
A biologist argues: 'The recent decline in the local frog population is due to increased pesticide use in agricultural areas bordering their habitats. Last year, pesticide application doubled, and the frog population subsequently decreased by 30%.' Which of the following statements, if true, would most weaken the biologist's argument?
- AFrogs are known to be particularly sensitive to environmental changes.
- BOther amphibian species in the same habitats have not experienced a similar decline.
- CThe decline in the frog population began several years before the increase in pesticide use.
- DA new, highly effective predator of frogs was introduced into the area two years ago.
Show answer & explanationAnswer & explanation
Correct answer: D. A new, highly effective predator of frogs was introduced into the area two years ago.
The biologist attributes the decline to pesticides. Option C introduces a strong alternative cause (a new predator) that could easily explain the observed decline, thereby weakening the direct causal link to pesticides.
Why the other options are wrong
- A. This only explains *why* frogs might decline, but doesn't specify the *reason* for this particular decline, nor does it rule out other environmental changes besides pesticides.
- B. This might suggest that the cause isn't a general environmental factor but something specific to frogs, possibly strengthening the idea that pesticides (if frogs are uniquely sensitive) are the cause.
- C. This directly contradicts the timing of the biologist's causal claim, suggesting the decline started *before* the increased pesticide use, thus weakening the argument by challenging the temporal relationship.
Alternative Cause
An alternative cause is a different factor or event that could plausibly explain an observed effect, thereby weakening an argument that attributes the effect to a specific cause.
- Challenges causal arguments.
- Suggests a different explanation for the correlation.
- Does not necessarily disprove the original cause, but makes it less certain.
Memory trick: Don't jump to conclusions, look for other solutions!