LSAT 156 | Section 4 | Logical Reasoning: Q12

LR Question 12 Explanation

QUESTION TEXT: Ecologist: El Niño, a global weather phenomenon that …

QUESTION TYPE: Weaken

CONCLUSION: Average rodent populations in region T will likely increase in coming decades.

REASONING: El Niño will become more frequent, El Niño brings heavy winter rainfall to region T, and rodent populations usually increase during long periods of sustained rain.

ANALYSIS: The key thing to notice is that the argument needs to connect El Niño rainfall in region T to the kind of rain that helps rodents. But the ecologist quietly shifts from “heavy winter rainfall” to “long periods of sustained rain.”

Those are not necessarily the same thing. You can have a lot of rain overall without having the kind of long, sustained rainy periods that the premise talks about.

So the best weakening answer will show that in region T, high-rainfall winters usually do not involve long periods of sustained rain. If that’s true, then more El Niño does not necessarily mean the kind of conditions that make rodent populations rise.

___________

1. This just tells us summer is drier than winter. That seems perfectly compatible with the argument and doesn’t really affect the reasoning.
2. This actually supports the argument a bit. If rodents diminish when there are no heavy rains, that makes rain sound even more important to their population size.
3. This is tempting, but it’s pretty indirect. Other regions could differ from region T in lots of ways, so this doesn’t strongly undercut the argument.
4. CORRECT. This goes straight at the gap. If rainy winters in region T usually do not involve long sustained rain, then the ecologist’s key link is much weaker.
5. This just says there are other effects that could matter too. That doesn’t show the ecologist’s reasoning is wrong.