LSAT Explanation PT 20, S4, Q22: Wirth: All efforts to identify a

LSAT Question Stem

Which one of the following most accurately expresses Chang's criticism of Wirth's argument? 

Logical Reasoning Question Type

This is a Flaw question. 

Correct Answer

The correct answer to this question is A. 

LSAT Question Complete Explanation

First, let's analyze the argument in the passage. Wirth presents the following argument:

Premise 1: All efforts to identify a gene responsible for predisposing people to manic-depression have failed.

Premise 2: Nearly all researchers now agree that there is no "manic-depression gene."

Conclusion: Any claim that some people are genetically predisposed to manic-depression is simply false.

Chang disagrees with Wirth's conclusion and presents an alternative explanation:

Premise: Many researchers have found evidence that a set of several genes is involved and that complex interactions among these genes produce a predisposition to manic-depression.

The question type is a Flaw question, asking us to identify Chang's criticism of Wirth's argument.

An "Evaluate" question for this argument would be: "Is it possible for a genetic predisposition to manic-depression to be caused by multiple genes interacting rather than a single gene?"

Now let's discuss the answer choices:

a) It presupposes only one possibility where more than one exists.

This is the correct answer. Chang's criticism is that Wirth's argument assumes that a single gene is the only possibility for a genetic predisposition to manic-depression, while Chang presents the alternative possibility of multiple genes interacting to cause the predisposition.

b) It depends on separate pieces of evidence that contradict each other.

This is incorrect because Wirth's argument does not present contradictory evidence. Chang does not dispute the evidence Wirth presents, but rather disputes the conclusion drawn from that evidence.

c) It relies on the opinion of experts in an area outside the experts' field of expertise.

This is incorrect because there is no mention of experts being outside their field of expertise. Both Wirth and Chang are discussing the opinions of researchers in the relevant field.

d) It disallows in principle any evidence that would disconfirm its conclusion.

This is incorrect because Wirth's argument does not disallow any evidence that would disconfirm the conclusion. Chang's criticism is that Wirth's argument does not consider the possibility of multiple genes interacting to cause the predisposition.

e) It treats something that is merely unlikely as though it were impossible.

This is incorrect because the argument does not discuss likelihood or possibility. Chang's criticism is focused on the assumption that only one possibility (a single gene) exists for a genetic predisposition to manic-depression.

In summary, Chang's criticism of Wirth's argument is that it presupposes only one possibility (a single gene) for a genetic predisposition to manic-depression, while Chang presents the alternative possibility of multiple genes interacting to cause the predisposition. The correct answer is A.