LSAT 149 | Section 4 | Logical Reasoning: Q2

LR Question 2 Explanation

QUESTION TEXT: When the ancient fossils of a primitive land mammal…

QUESTION TYPE: Weaken

CONCLUSION: The discovery of a primitive land mammal in New Zealand (NZ) disproves the idea that NZ birds flourished due to a lack of mammals.

REASONING: Until the discovery, there were no known land mammals in New Zealand. Now we’ve discovered NZ once had at least one native land mammal.

ANALYSIS: This is a subtle question. You have to read carefully to see what the opposing theory is:

“New Zealand birds did well because they did not face competition from land mammals”

To disprove the theory, we’d have to show there was competition from mammals. This argument hasn’t done that. It’s just shown that one mammal used to exist in New Zealand. It’s possible the animal didn’t provide competition.

___________

1. This strengthens the argument. The more land mammals existed in New Zealand, the more likely they were to compete with birds.
2. CORRECT. This ruins the argument. If the land mammal was extinct before birds arrived in NZ, then the mammal couldn’t have competed with birds.
3. This answer is irrelevant. Introducing reptiles doesn’t help show that birds faced no competition from mammals. We don’t even know if this discovery is significant – maybe scientists already knew New Zealand had reptiles and insects.
4. This was a tempting answer – it seems to show that mammals do destroy bird populations. But notice that it’s talking about countries with a “rich and varied” mammal population. We only have evidence that New Zealand had one mammal. That’s hardly rich and varied. This answer doesn’t fit with our evidence. 
5. This answer slightly strengthens the argument by showing it’s possible we were mistaken about New Zealand’s lack of mammals.