Necessary AssumptionDiff: Hardest
Logic Breakdown
Passage Summary: Hairless dogs appeared in both Mexico and Peru long ago. Because it's unlikely they evolved that way in both places independently and they couldn't have walked through the thick jungles, they must have been carried by boat.
Conclusion: Hairless dogs must have been moved between Mexico and Peru via maritime trade routes.
Reasoning: The trait is too rare to have evolved twice, the dogs are not wild animals, and the land route between the two regions was too difficult to traverse centuries ago.
Analysis: The author uses a process of elimination to reach the 'boat' conclusion, ruling out independent evolution and land travel. For this logic to be airtight, the author must assume there are no other possibilities, such as the dogs originating in a third location and being brought to both Mexico and Peru separately. It's a classic 'A or B' argument where the author tries to prove B by debunking A. You should look for an assumption that bridges the gap between 'they didn't walk' and 'they must have been boated,' specifically ruling out other migration methods or origins.
Conclusion: Hairless dogs must have been moved between Mexico and Peru via maritime trade routes.
Reasoning: The trait is too rare to have evolved twice, the dogs are not wild animals, and the land route between the two regions was too difficult to traverse centuries ago.
Analysis: The author uses a process of elimination to reach the 'boat' conclusion, ruling out independent evolution and land travel. For this logic to be airtight, the author must assume there are no other possibilities, such as the dogs originating in a third location and being brought to both Mexico and Peru separately. It's a classic 'A or B' argument where the author tries to prove B by debunking A. You should look for an assumption that bridges the gap between 'they didn't walk' and 'they must have been boated,' specifically ruling out other migration methods or origins.
Passage Stimulus
Passage Redacted
Unlock Full Passage18.Which one of the following is an assumption that the argument requires?
Correct Answer
E
E is required: if centuries ago it was not easier to travel by boat than overland, then we could not conclude the dogs “must have been” transported by boat. Negation test: If boat travel was not easier, the argument’s inference that boat transport was the necessary method collapses, so E is necessary.
Upgrade Your Prep
Ready to go beyond free explanations?
LSAT Perfection is the #1 modern LSAT prep platform, trusted by thousands of students for comprehensive test strategies, advanced drilling, and full analytics on every PrepTest.
Detailed explanations for 59 PrepTests
Advanced drillset builder
Personalized analytics
Built-in Wrong Answer Journal