LSAT Question Stem

Which one of the following, if true, most helps explain the puzzling fact cited above? 

Logical Reasoning Question Type

This is a Paradox question. 

Correct Answer

The correct answer to this question is D. 

LSAT Question Complete Explanation

In this passage, we learn that the common ancestors of Australian land- and tree-dwelling kangaroos had prehensile (grasping) tails and long opposable thumbs, which are well-adapted to tree-dwelling but offer kangaroos few advantages on land. It's understandable that land-dwelling kangaroos lost these attributes; however, it's puzzling that modern tree-dwelling kangaroos also lack these attributes. The question type is a Paradox question, which asks us to identify the answer choice that best helps explain the puzzling fact cited in the passage.

Before discussing the answer choices, let's break down the information in the passage. Imagine a family tree where the common ancestor of both land- and tree-dwelling kangaroos had grasping tails and long opposable thumbs. These features are beneficial for tree-dwelling kangaroos, as they would help them climb and move around in trees more efficiently. However, these features are not useful for land-dwelling kangaroos, so it makes sense that they lost these attributes over time. The paradox lies in the fact that modern tree-dwelling kangaroos, which should benefit from these features, also lack them.

Now, let's analyze the answer choices:

a) This answer choice tells us that modern tree-dwelling kangaroos descend trees differently than their common ancestor. However, it doesn't explain why they lost the beneficial attributes of grasping tails and long opposable thumbs in the first place. This choice merely restates the paradox without resolving it.

b) This answer choice provides information about the size of modern tree- and land-dwelling kangaroos compared to their common ancestor, but it doesn't address the loss of the grasping tails and long opposable thumbs in modern tree-dwelling kangaroos.

c) This answer choice tells us that modern tree-dwelling kangaroos' tails cannot grasp branches and are somewhat longer and more flexible than those of modern land-dwelling kangaroos. However, it doesn't explain why they lost the grasping ability, which is the main paradox in the passage.

d) This answer choice explains that modern tree-dwelling kangaroos are descended from land-dwelling kangaroos that had been land-dwellers for many generations before modern tree-dwelling kangaroos started to develop. This resolves the paradox by suggesting that modern tree-dwelling kangaroos lost the grasping tails and long opposable thumbs during their time as land-dwellers, and they haven't yet redeveloped these attributes since returning to tree-dwelling. This is the correct answer.

e) This answer choice discusses the hind legs and land movement speed of modern tree-dwelling kangaroos compared to modern land-dwelling kangaroos. However, it doesn't address the loss of the grasping tails and long opposable thumbs in modern tree-dwelling kangaroos, which is the main paradox in the passage.

In conclusion, the correct answer is choice D, as it resolves the paradox by explaining that modern tree-dwelling kangaroos lost the grasping tails and long opposable thumbs during their time as land-dwellers and haven't yet redeveloped these attributes since returning to tree-dwelling.