LSAT 131 – Section 3 – Question 20

LSAT 131 - Section 3 - Question 20

December 2009

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT131 S3 Q20
+LR
Flaw or descriptive weakening +Flaw
Eliminating Options +ElimOpt
A
8%
158
B
2%
155
C
9%
158
D
68%
167
E
13%
159
151
158
165
 +Harder 146.026 +SubsectionMedium

The peppered moth avoids predators by blending into its background, typically the bark of trees. In the late nineteenth century, those peppered moths with the lightest pigmentation had the greatest contrast with their backgrounds, and therefore were the most likely to be seen and eaten by predators. It follows, then, that the darkest peppered moths were the least likely to be seen and eaten.

Summarize Argument
The argument concludes that for peppered moths, which avoid predators by camouflaging themselves against trees, the darkest moths are the least likely to be spotted and eaten by predators. This is backed up with an observation that the lightest moths are the most visible against trees, so are most likely to be eaten.

Identify and Describe Flaw
The argument uses observations about the lightest moths being the most visible to support a conclusion about the darkest moths being the least visible. However, knowing which color is most visible doesn’t actually tell us which color is least visible.
For example, if trees are usually an intermediate shade between dark and light, the darkest moths may be more visible than average-colored moths.

A
The argument overlooks the possibility that light peppered moths had more predators than dark peppered moths.
The number of predators a moth has is irrelevant to the likelihood of a given predator noticing that moth when it tries to blend into its background, so this isn’t something the argument had to account for.
B
The argument takes for granted that peppered moths are able to control the degree to which they blend into their backgrounds.
The argument does not take this for granted—the whole point is that how different moths are colored affects their ability to blend into their backgrounds.
C
The argument presumes, without providing justification, that all peppered moths with the same coloring had the same likelihood of being seen and eaten by a predator.
The argument does not make this presumption. The entire argument is about the overall likelihood of moths being eaten based on their color, not the odds for any individual moth.
D
The argument overlooks the possibility that there were peppered moths of intermediate color that contrasted less with their backgrounds than the darkest peppered moths did.
The argument jumps straight from the lightest moths being the most visible to conclude that the darkest moths are the least visible, without considering that intermediate-colored moths might be even less visible. This means the conclusion relies on a baseless assumption.
E
The argument presumes, without providing justification, that the only defense mechanism available to peppered moths was to blend into their backgrounds.
The argument is focused on how effective the moths’ camouflage is based on color, so any other defense mechanisms they may have are irrelevant.

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LSAT PrepTest 131 Explanations

Section 1 - Logical Reasoning

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Reading Comprehension

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