LSAT Explanation PT 28, S3, Q22: Researcher: The role of chemicals called

LSAT Question Stem

The researcher's argument requires the assumption that 

Logical Reasoning Question Type

This is a Necessary Assumption question. 

Correct Answer

The correct answer to this question is B. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The researcher is discussing the role of pheromones in determining sexual behavior in animals and humans. The argument is structured as follows:

Premise: Involuntary behavior in animals indicates chemical control (pheromones).

Premise: Sexual behavior in humans is voluntary (free will).

Sub-Conclusion: Sexual behavior in humans is a function of psychological factors.

Conclusion: Pheromones are a vestige of our evolutionary past (i.e., they no longer play a role in human sexual behavior).

The question type for this problem is Necessary Assumption, which means we're looking for an assumption that the argument depends on for it to be valid.

Now let's evaluate the answer choices:

A) Whatever does not have a chemical explanation must have a purely psychological one.

This answer choice goes too far. We're only concerned with voluntary behavior, not everything that lacks a chemical explanation. While it might strengthen the argument, it's not a necessary assumption.

B) Voluntary action cannot have a chemical explanation.

This is the correct answer. If voluntary action can have a chemical explanation, then it's not certain that sexual behavior in humans is only a function of psychological factors. Since the negation of this answer choice weakens the conclusion, it's a necessary assumption.

C) Free will can be found only in humans.

This answer choice is not necessary for the argument. Even if free will exists in other species, it doesn't affect the argument about pheromones and human sexual behavior.

D) Voluntary action cannot have an evolutionary explanation.

This answer choice is incorrect because it doesn't weaken the argument if negated. The author isn't arguing that human sexual behavior isn't a result of evolution; they're saying that chemical factors, as vestiges of our evolutionary past, no longer affect such behavior.

E) There is a psychological explanation for the continuing presence of pheromones in humans.

This answer choice is not necessary because the argument doesn't need to explain why pheromones are still present in humans. The focus is on whether these chemicals control or play a role in human voluntary action (sexual behavior).

In summary, the correct answer is B because it's a necessary assumption for the argument to be valid. The other answer choices either go too far, are not necessary, or are irrelevant to the argument.