LSAT Explanation PT 39, S2, Q16: Biologists agree that human beings evolved

LSAT Question Stem

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? 

Logical Reasoning Question Type

This is an Argument Part question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

In this LSAT problem, we have a passage discussing the disagreement between biologists about which species of fish human beings evolved from. Dr. Stevens-Hoyt claims that humans evolved from lungfish due to the close match between the mitochondrial DNA of lungfish and frogs, while Dr. Grover contends that humans evolved from coelacanths, citing the close chemical match between the hemoglobin of coelacanths and tadpoles. The passage also states that biologists agree that frogs are definitely related to the species of fish from which human beings evolved.

The question type is Argument Part, and we are asked to identify the role played in the dispute by the proposition that frogs are definitely related to the species of fish from which human beings evolved.

Let's analyze each answer choice:

a) This answer choice is incorrect because the proposition does not imply that human beings are not descended from lungfish. Instead, it serves as a starting point for both Dr. Stevens-Hoyt's and Dr. Grover's arguments.

b) Similar to answer choice (a), this answer choice is incorrect because the proposition does not imply that human beings are not descended from coelacanths. The proposition is a common starting point for both arguments, not evidence against either claim.

c) This answer choice is incorrect because it presents a false dichotomy. The proposition itself does not contend that human beings must be descended from either lungfish or coelacanths. While both doctors argue for one of these options, the proposition is not offered as evidence for this contention.

d) This is the correct answer choice. The proposition serves as an assumption that both Dr. Stevens-Hoyt and Dr. Grover use as a starting point for their arguments about human evolution. Although the proposition is explicitly stated, it is a belief that both parties accept without providing further evidence, making it an assumption in this context.

e) This answer choice is incorrect because the proposition does not imply that a match of mitochondrial DNA or hemoglobin between lungfish and coelacanths would show that human beings evolved from one of these two species. The proposition only states that frogs are related to the species of fish from which humans evolved, not specifying which type of match would be sufficient to determine the ancestor species.

In summary, the correct answer is (d) because the proposition serves as a common starting point or assumption for both Dr. Stevens-Hoyt's and Dr. Grover's arguments about human evolution.