LSAT Explanation PT 28, S3, Q25: The interstitial nucleus, a subregion of

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 E. 

LSAT Question Complete Explanation

Let's first analyze the argument in the passage. The argument states that the interstitial nucleus, a subregion of the brain's hypothalamus, is typically smaller for male cats than for female cats. A neurobiologist performed autopsies on male cats who died from disease X and found that these male cats had interstitial nuclei that were as large as those generally found in female cats. The conclusion of the argument is that the size of the interstitial nucleus determines whether or not male cats can contract disease X.

In simpler terms, imagine a group of people where those with a specific characteristic (e.g., wearing glasses) are more likely to catch a cold. The argument is suggesting that having this characteristic (wearing glasses) determines whether someone can catch a cold or not.

An "Evaluate" question for this argument could be: "Are there any other factors that could influence whether male cats contract disease X?"

Now let's discuss the answer choices for the Weaken question type. The correct answer is E, but let's analyze each answer choice:

a) No female cats have been known to contract disease X, which is a subtype of disease Y.

- This answer choice doesn't directly weaken the argument as it is about female cats, and the argument is about male cats. The relationship between the interstitial nucleus size and disease X in female cats doesn't necessarily affect the relationship in male cats.

b) Many male cats who contract disease X also contract disease Z, the cause of which is unknown.

- This answer choice doesn't necessarily weaken the argument because it doesn't provide an alternative cause for disease X. Disease Z could be an additional effect of the enlarged interstitial nucleus, or it could be unrelated to the size of the interstitial nucleus. This answer choice doesn't provide enough information to undermine the conclusion.

c) The interstitial nuclei of female cats who contract disease X are larger than those of female cats who do not contract disease X.

- This answer choice is also about female cats, making it less relevant to the argument about male cats. Even if it were about male cats, it would actually support the argument rather than weaken it.

d) Of 1,000 autopsies on male cats who did not contract disease X, 5 revealed interstitial nuclei larger than those of the average male cat.

- This answer choice doesn't significantly weaken the argument because it only provides a small sample of male cats with larger interstitial nuclei who did not contract disease X. Additionally, the interstitial nuclei are only larger than the average male cat, not necessarily as large as those found in female cats.

e) The hypothalamus is known not to be causally linked to disease Y, and disease X is a subtype of disease Y.

- This answer choice directly weakens the argument because it severs the link between the hypothalamus and disease Y (and thus disease X). If the hypothalamus is not causally linked to disease Y, it is unlikely that the size of the interstitial nucleus, a subregion of the hypothalamus, determines whether male cats can contract disease X, a subtype of disease Y.

In conclusion, answer choice E is the correct answer because it most effectively weakens the argument by undermining the causal relationship between the size of the interstitial nucleus and the contraction of disease X in male cats.