LSAT 142 – Section 4 – Question 22

LSAT 142 - Section 4 - Question 22

December 2014

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT142 S4 Q22
+LR
Flaw or descriptive weakening +Flaw
Conditional Reasoning +CondR
A
3%
154
B
10%
160
C
74%
165
D
9%
159
E
4%
161
145
154
163
 +Harder 147.564 +SubsectionMedium

Fish with teeth specialized for scraping algae occur in both Flower Lake and Blue Lake. Some biologists argue that because such specialized characteristics are rare, fish species that have them should be expected to be closely related. If they are closely related, then the algae-scraping specialization evolved only once. But genetic tests show that the two algae-scraping species, although possibly related, are not closely related. Thus, the algae-scraping specialization evolved more than once.

Summarize Argument: Counter-Position
The author concludes that the algae-scraping specialization of certain fish species in Flower Lake and Blue lake evolved more than once. This is based on the fact that if the fish in these lakes are closely related, then the algae-scraping specialization evolved only once. But the fish in these lakes are not closely related.

Identify and Describe Flaw
The author confuses a sufficient condition for a necessary condition. The fish being closely related is sufficient for the algae-scraping specialization to have evolved only once. But this doesn’t mean the fish being closely related is necessary. So even if the fish aren’t closely related, it’s still possible the specialization evolved only once.

A
infers a cause merely from a correlation
The argument’s reasoning is based on an attempted application of a conditional rule. There is not conclusion or assumption of a causal relationship from a correlation.
B
infers that just because the evidence for a particular claim has not yet been confirmed, that claim is false
The author doesn’t argue, “We haven’t confirmed the specialization evolved only once, so it must have evolved more than once.”
C
takes a sufficient condition as a necessary one
The author takes a sufficient condition (fish being closely related) for the specialization being evolved only once as a necessary condition. This is flawed because even if the fish are not closely related, the specialization still could have evolved only once.
D
infers merely because something was likely to occur that it did occur
The author doesn’t argue, “The specialization is likely to have evolved more than once. So it must have evolved more than once.”
E
appeals to the authority of biologists who may not be representative of all biologists with expertise in the relevant area
The author’s reasoning doesn’t rely on the authority of biologists. It relies on the attempted application of a conditional statement.

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LSAT PrepTest 142 Explanations

Section 1 - Logical Reasoning

Section 2 - Logical Reasoning

Section 3 - Reading Comprehension

Section 4 - Logical Reasoning

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