LSAT 152 – Section 4 – Question 12

LSAT 152 - Section 4 - Question 12

November 2018

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Question
QuickView		 Type Tags Answer
Choices		 Curve Question
Difficulty		 Psg/Game/S
Difficulty		 Explanation
PT152 S4 Q12
+LR
Strengthen +Streng
Causal Reasoning +CausR
A
2%
155
B
86%
163
C
8%
154
D
1%
157
E
3%
154
136
145
153
 +Medium 147.181 +SubsectionMedium

The Amazon River flows eastward into the Atlantic Ocean from its source in the western part of South America. The land through which the Amazon flows is now cut off from the Pacific Ocean to the west by the Andes Mountains. Yet certain freshwater fish that inhabit the Amazon are descended from now-extinct saltwater fish known to have inhabited the Pacific Ocean but not the Atlantic. For this reason, some scientists hypothesize that the Amazon River once flowed into the Pacific Ocean.

Summarize Argument: Phenomenon-Hypothesis
Some scientists hypothesize that the Amazon River previously flowed into the Pacific Ocean, not the Atlantic Ocean. Why? Because some freshwater fish in the Amazon are descended from saltwater fish that lived in the Pacific but not the Atlantic, and the Andes Mountains currently separate the Amazon from the Pacific.

Notable Assumptions
The scientists assume some Amazon fish are descended from Pacific Ocean fish because the Amazon used to flow into the Pacific, and not for some other reason. This means assuming ancestors of the freshwater fish entered the Amazon when it flowed into the Pacific. It also means assuming the Andes Mountains prevent any fish from traveling from the Pacific Ocean to the Amazon River on its current route.

A
In many cases, species of freshwater and saltwater fish that share certain characteristics do not in fact share a common ancestor.
Since the Amazon fish are known to have descended from the Pacific-dwelling species, this is irrelevant. It doesn’t provide any new information suggesting the Amazon was once connected to the Pacific.
B
Most of the fossilized remains of the now-extinct saltwater fish from the Pacific Ocean date to a period prior to the formation of the Andes Mountains.
This confirms that the Pacific-dwelling species lived before the Andes separated the Amazon from the Pacific. It rules out the possibility that the Pacific-dwelling fish emerged when the Amazon was already inaccessible from the Pacific because of the Andes Mountains.
C
Many species of fish that inhabit the Atlantic Ocean are related to fish species that are known to inhabit the Pacific Ocean.
If anything, this weakens the argument. It suggests an alternative hypothesis: that an intermediate descendant of the Pacific-dwelling species lived in the Atlantic, and served as an ancestor for the current freshwater species in the Amazon.
D
The Andes Mountains extend from the northernmost to the southernmost extremes of the South American continent.
This is irrelevant. It’s important only that the Andes cut off the Pacific from the Amazon—their precise geographical span doesn’t affect the argument.
E
There are very few fish species that are known to be able to survive in both fresh and salt water.
If anything, this weakens the argument. It suggests it’s unlikely that saltwater fish from the Pacific entered the Amazon directly and descended into the present-day freshwater species.

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LSAT PrepTest 152 Explanations

Section 1 - Logical Reasoning

Section 2 - Logical Reasoning

Section 3 - Reading Comprehension

Section 4 - Logical Reasoning

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