LSAT 141 | Section 2 | Logical Reasoning: Q8

LR Question 8 Explanation

QUESTION TEXT: Biologist: Marine animals known as box jellyfish have…

QUESTION TYPE: Necessary Assumption

CONCLUSION: Eyes are only adapted to an animal’s needs.

REASONING: The box jellyfish has eyes with powerful lenses, but can’t use them due to poor retinas. This only lets box jellyfish see the prominent features but not the fine detail of objects.

ANALYSIS: On necessary assumption questions, you should look for a shift in terms, or a concept used in the conclusion that wasn’t used in the argument.

The conclusion talks about eyes being adapted to needs. Yet the argument doesn’t tell us what a box jellyfish needs. Maybe box jellyfish actually do need eyes that can focus on fine detail!

___________

1. It doesn’t matter what other jellyfish can do.
   Negation: One other type of jellyfish can’t focus clearly.
2. CORRECT. The conclusion talked about needs, but the argument never said what a box jellyfish needs! This answer bridges that gap.
   Negation: Box jellyfish need to detect the fine details of objects.
3. This assumption would weaken the argument. The author was implying that box jellyfish didn’t need better vision, which explains their oddly useful yet useless eyes.
   Note: The negation of this answer appears to strengthen the argument. But negations are supposed to destroy the argument, not strengthen it!
   Negation: Box jellyfish wouldn’t benefit from better vision.
4. This answer just makes the situation confusing. If the ancestor jellyfish used to have better eyes, then why did the box jellyfish lose this ability?
   There’s a difference between not developing a better feature and intentionally losing a better feature because you don’t need it.
5. It doesn’t matter if box jellyfish have other means of detection. The core of this argument is whether box jellyfish need better vision, for whatever reason.