LSAT 117 – Section 2 – Question 04

LSAT 117 - Section 2 - Question 04

October 2004

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT117 S2 Q04
+LR
Weaken +Weak
Causal Reasoning +CausR
A
1%
153
B
1%
153
C
94%
162
D
3%
154
E
1%
151
127
136
145
 +Easier 146.765 +SubsectionMedium

The top 50 centimeters of soil on Tiliga Island contain bones from the native birds eaten by the islanders since the first human immigration to the island 3,000 years ago. A comparison of this top layer with the underlying 150 centimeters of soil—accumulated over 80,000 years—reveals that before humans arrived on Tiliga, a much larger and more diverse population of birds lived there. Thus, the arrival of humans dramatically decreased the population and diversity of birds on Tiliga.

Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that the arrival of humans on Tiliga caused a decrease in the population and diversity of the island’s bird population. As support for this hypothesis, the author compares the top 50 cm of soil (which was accumulated over the 3,000 years since humans arrived) with the lower 150 cm of soil (which was accumulated over the previous 80,000 years). This comparison showed that before humans arrived, there was a larger and more diverse bird population.

Notable Assumptions
The author assumes that it was the arrival of the humans, not something else, that caused the decline in the population and diversity of birds. It could be that some thing else led to both the arrival of the humans and the decline in the bird population. We have a correlation between the arrival of humans and decline of birds, and the author is assuming a causal connection.

A
The bird species known to have been eaten by the islanders had few natural predators on Tiliga.
This reduces the strength of an alternate hypothesis (the alternate hypothesis being that predators may have been responsible for the declining bird population). Reducing the strength of alternate hypotheses is a way to strengthen arguments, so this does not weaken the argument.
B
Many of the bird species that disappeared from Tiliga did not disappear from other, similar, uninhabited islands until much later.
(B) says that birds disappeared much more slowly without humans. “Many” is too vague to make any strong inferences here, but this does give some reason to believe that the presence of humans is related to faster disappearance of birds, which is consistent with the argument.
C
The arrival of a species of microbe, carried by some birds but deadly to many others, immediately preceded the first human immigration to Tiliga.
This weakens the argument because it introduces an alternate hypothesis. (C) suggests that a microbe that arrived at the same time as humans could be responsible for the disappearance of the birds.
D
Bones from bird species known to have been eaten by the islanders were found in the underlying 150 centimeters of soil.
The birds that humans ate would have already existed (and died) on the island so it makes sense that their bones were found in the lower 150 cm of soil. This is consistent with the argument and doesn’t weaken the claim that humans caused a decrease in the bird population.
E
The birds that lived on Tiliga prior to the first human immigration generally did not fly well.
Information about birds’ abilities to fly is completely irrelevant to the argument.

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LSAT PrepTest 117 Explanations

Section 1 - Reading Comprehension

Section 2 - Logical Reasoning

Section 3 - Logical Reasoning

Section 4 - Logical Reasoning

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