LSAT 149 | Section 3 | Logical Reasoning: Q8

LR Question 8 Explanation

QUESTION TEXT: Over the last thousand years, plant species native to islands…

QUESTION TYPE: Strengthen

CONCLUSION: Island plants are going extinct faster than other plants because these island plants haven’t adapted defences against being eaten by large land mammals.

REASONING: Large land mammals normally only arrive on islands after humans do.

ANALYSIS: This argument sounds like it has made a correlation between human arrival on islands and plants extinction. But actually….it didn’t say if extinctions increase after humans arrive!

So to strengthen the argument, we must show that the proposed cause (humans + their mammals) happens right before the proposed effect (island plant extinctions).

___________

1. At best, this answer merely supports the idea that island plants are going extinct. But we already knew that.
    
   (I’m not even sure the answer supports that though: we would reasonable expect there are more species on mainlands: mainland areas are most of the earth’s landmass)
2. This shouldn’t be surprising. If native plants on islands go extinct, we would expect them to be replaced by something else. The problem is this answer doesn’t explain why the island plants went extinct in the first place.
    
   If anything this answer might weaken the mammal argument by suggesting an alternate cause: maybe invasive mainland species killed off the island plants.
3. This weakens the argument by showing an alternate explanation for island plant extinction: commercial development.
4. CORRECT. See the analysis above. This actually places the cause (humans + large mammals) occurring before the effect (island plant extinction). Without this answer we don’t even have a correlation.
    
   (You know from the stimulus that the arrive of humans is a necessary condition for the arrival of large mammals)
5. This weakens the argument slightly. It shows large land mammals tend not to eat island plant species if they can avoid it.
    
   You might have thought that this answer means humans cut down native plants to plant mainland crops for their animals, but that’s a stretch. You have to go by what the answer actually says, not what it could potentially imply.

Recap: The question begins with “Over the last thousand years, plant species native to islands”. It is a Strengthen question. Learn more about LSAT Strengthen questions in our guide to LSAT Logical Reasoning question types.