Argument Part - Answer Choices w/ Assumptions

blndsundoll4mj

In the new version of the core curriculum, the way JY teaches Argument Part questions, he tells us to beware of answer choices that use language like "assumption" or "implies" etc. because if the question states an idea explicitly mentioned in the stimulus, it by definition cannot be an assumption or implicit. This made a lot of sense to me and still does! However, PT39, S2, Q16 makes me struggle a bit. As the right answer calls the explicitly referenced idea "an assumption."

Attractive Wrong Answer: C - "It is offered as evidence for the contention that human beings must be descended from either lungfish or coelacanths."

Correct Answer: D - "It is an assumption that both parties to the dispute use as a starting point for their arguments about human evolution."

The question says "which one of the following most accurately describes the role played in the dispute above by the proposition that frogs are definitely related to the species of fish from which human beings evolved"

The stimulus says "Since biologists agree that frogs are definitely related to the species of fish from which human beings evolved..."

How could that idea possibly play an "assumption" role in the argument if it is explicitly stated?

I know the LSAT makes it pretty hard to hold any absolute truths about the test, but I really thought it would be hard to ever have a correct Argument Part answer choice reference an assumption. Am I totally off-base here? Thanks!

LivinLaVidaLSAT

You're right, that the claim in the question stem is explicitly stated, but who makes this claim? In the stimulus, the claim that "frogs are definitely related to the species of fish from which human beings evolved" is explicitly attributed to biologists, not Stevens/Grover. We don't know if Stevens and Grover are biologists. Neither Stevens nor Grover explicitly connect this claim to their argument but this claim is something that each must believe to be true in order to reach their respective conclusions.

Dr. Stevens- Humans must have evolved from lungfish because there’s a close match between mitochondrial DNA of lungfish and frogs.

Dr. Grover- Mitochondrial DNA is not a reliable indicator of relationships between species over long periods of time (attacks Dr. S argument).
Humans evolved from coelacanths because there’s a close chemical match between coelacanths hemoglobin and tadpoles.

The Answers:
D (correct answer): I think sometimes it helps to think about the more general definition of assumption - something the author believes to be true or something they must be thinking. On the LSAT, assumptions are mostly implied, but be aware it’s possible for an assumption to be explicit.

C (wrong answer): The wording is too extreme. Nothing in the stimulus says humans could have only descended from either lungfish or coelacanths (meaning no other fish are options).