LSAT Explanation PT 44, S2, Q4: The top 50 centimeters of soil

LSAT Question Stem

Which one of the following statements, if true, most seriously weakens the argument? 

Logical Reasoning Question Type

This is a Weaken question. 

Correct Answer

The correct answer to this question is C. 

LSAT Question Complete Explanation

The question type for this problem is Weaken, which means we are looking for an answer choice that undermines the conclusion or the relationship between the premises and the conclusion.

Let's summarize and analyze the argument in the passage:

Premise 1: The top 50 cm of soil on Tiliga Island contains bones from native birds eaten by islanders since the first human immigration to the island 3,000 years ago.

Premise 2: A comparison of this top layer with the underlying 150 cm 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.

Conclusion: The arrival of humans dramatically decreased the population and diversity of birds on Tiliga.

Now let's consider an "Evaluate" question for this argument: "Is there any other factor that could have caused the decrease in population and diversity of birds on Tiliga?"

Now let's discuss each answer choice:

a) The bird species known to have been eaten by the islanders had few natural predators on Tiliga.

- This answer choice actually strengthens the argument because if there were no other natural predators, it seems more likely that the decrease in bird population and diversity was attributable to the human presence on the island.

b) Many of the bird species that disappeared from Tiliga did not disappear from other, similar, uninhabited islands until much later.

- This choice also strengthens the argument by pointing out that when humans were not present, species did not disappear as quickly.

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 is the correct answer choice. A deadly microbe could serve as an alternate cause for the bird extinctions, thus weakening the causal argument in the passage.

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 the islanders ate likely lived on the island before the islanders' arrival, so evidence of the birds' earlier existence has no effect on the causal argument. This response does not weaken the author's argument.

e) The birds that lived on Tiliga prior to the first human immigration generally did not fly well.

- The inability to fly would likely make these birds an easier target for their new human predators, so this answer choice would seem to strengthen the argument in the passage. This choice does not weaken the argument and is therefore incorrect.