Marine biologists had hypothesized that lobsters

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsNecessary Assumption

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Stimulus

Marine biologists had hypothesized that lobsters kept together in lobster traps eat one another in response to hunger. Periodic checking of lobster traps, however, has revealed instances of lobsters sharing traps together for weeks. Eight lobsters even shared one trap together The marine biologists’ hypothesis, therefore, is clearly wrong.

What this question is testing

Necessary Assumption

Your task

Find the assumption the argument requires in order for its conclusion to hold.

Common trap

Answers that would help the argument but aren't strictly required (sufficient, not necessary).

Winning move

Negate each choice — the right one breaks the argument when negated.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question

14.

The argument against the marine biologists’ hypothesis is based on which one of

Answer choices

Opposite (if anything)3% picked this
Lobsters not caught in lobster traps have been observed eating
Since the author's goal is to show that lobsters don't eat other in traps, it would seemingly hurt her argument if they have been observed eating each other elsewhere. If we negated this and said, "Lobsters outside of traps are never observed eating each other", that would strengthen her case, not weaken.
3%
Too Strong13% picked this
Two months is the longest known period during which eight or more lobsters have
The author doesn't need two months to be the longest period ever! She only needs to believe that two months is long enough of a time period for them to start eating each other, if they were going to ever eat each other.
13%
Irrelevant Quality: unusual3% picked this
It is unusual to find as many as eight lobsters caught together in
Who cares whether 8 lobsters is common or rare? There's no significance to the number eight. The author is just saying, "Check it out -- a bunch of lobsters in a trap for two months and none of them ate each other."
3%
Out of Scope: other species3% picked this
Members of other marine species sometimes eat their own kind when no other food
This argument is about lobsters and makes no assumptions about any other species.
3%
Correct78% picked this
Any food that the eight lobsters in the trap might have obtained was not enough
Why this is right
This answer has the lovable Defender "not", so we negate it and see if it weakens. "The food they lobsters obtained WAS enough to ward off hunger". Yup, that definitely weakens. If they were finding enough food to avoid being hungry, then there's no reason we'd expect them to start eating each other. And thus, this doesn't any longer look like a counterexample to the claim that "lobsters in a trap eat each other in response to hunger". A counterexample would involve hungry lobsters in a trap that didn't eat each other. And the lobsters in this trap weren't hungry, so they don't qualify as a counterexample.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
78%

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