LSAT 106 – Section 2 – Question 22

LSAT 106 - Section 2 - Question 22

June 1999

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Question QuickView	Type	Tags	Answer Choices	Curve	Question Difficulty	Psg/Game/S Difficulty	Explanation
PT106 S2 Q22	+LR +Exp	Flaw or descriptive weakening +Flaw Lack of Support v. False Conclusion +LSvFC	A 80% 167 B 6% 158 C 1% 154 D 7% 158 E 6% 159	144 152 161	+Medium	147.566 +SubsectionMedium

Wirth: All efforts to identify a gene responsible for predisposing people to manic-depression have failed. In fact, nearly all researchers now agree that there is no “manic-depression gene.” Therefore, if these researchers are right, any claim that some people are genetically predisposed to manic-depression is simply false.

Chang: I do not dispute your evidence, but I take issue with your conclusion. Many of the researchers you refer to have found evidence that a set of several genes is involved and that complex interactions among these genes produce a predisposition to manic-depression.

Summarize Argument

Wirth concludes that no one is genetically predisposed to manic-depression. He supports this by saying that all attempts to identify a “manic-depression gene” have failed, and most researchers now agree that no such gene exists.

Identify and Describe Flaw

Chang points out that Wirth’s argument is flawed because his evidence doesn’t support his conclusion. Just because there’s no “manic-depression gene” doesn’t mean that people can’t be genetically predisposed to manic-depression. Wirth assumes there’s only one possible cause of genetic predisposition, but other factors, like multiple genes interacting, could also be involved.

It presupposes only one possibility where more than one exists.

Wirth presupposes that there’s only one possible cause of genetic predisposition— a “manic-depression gene.” But Chang points out that other factors, like multiple genes interacting, could cause someone to be genetically predisposed to manic-depression instead.

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

Wirth’s pieces of evidence— efforts that have failed to find a “manic-depression gene” and researchers who agree that no such gene exists— do not contradict each other. Also, Chang doesn’t criticize Wirth on this front; instead, he explicitly accepts Wirth’s evidence.

It relies on the opinion of experts in an area outside the experts’ field of expertise.

Presumably the researchers that Wirth cites aren’t experts in some field other than genetics. But even if they were, Chang doesn’t criticize Wirth’s evidence at all; he accepts it.

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

Chang presents evidence that disconfirms Wirth’s conclusion, but Wirth never claims to disallow such evidence on principle. And even if he did, that doesn’t describe Chang’s criticism of Wirth’s argument.

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

Wirth does treat the existence of a “manic-depression gene” as impossible, but so does Chang and so do the researchers. In other words, it’s not “merely unlikely” that a “manic-depression gene” exists, it actually is impossible. Also, Chang doesn’t criticize him on this front.

LSAT 106 – Section 2 – Question 22

LSAT 106 - Section 2 - Question 22

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LSAT PrepTest 106 Explanations

Section 1 - Logical Reasoning

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Reading Comprehension

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