Logical Reasoning

PT106 · S3 · Q25 The interstitial nucleus, a subregion

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The interstitial nucleus, a subregion of the brain’s hypothalamus, is typically smaller for male cats than for female cats.

Conclusion (Thus)

The size of the interstitial nucleus determines whether or not male cats can contract disease X.

Evidence

A neurologist performed autopsies on male cats who died from X and found that these male cats had interstitial nuclei that were as large as those generally found in female cats.

Evaluate

Since the author is concluding something causal (the size of Y determines whether you can contract X) based off a correlation (male cats with X were more likely to have bigger interstitial nuclei than average male cats), we are in familiar Explain the Curious Fact territory.

Curious Fact ... why did these male cats who died of X have bigger than average interstitial nuclei?

Author's Explanation ... having a big interstitial nucleus makes it possible for a male cat to contract disease X (the ones with regular sized interstitial nuclei cannot contract disease X).

Goal

Since this is Weaken, we would want to either

1. suggest an Alternate Explanation for the Curious Fact why else could it be that the cats who died from X had bigger than average interstitial nuclei? maybe (Reverse Cause) the disease itself causes your interstitial nucleus to enlarge? maybe (Third Factor) there's some genetic condition where a male cat is born with certain female traits, such as the bigger interstitial nucleus, and that genetic condition is ultimately what causes susceptibility to disease X.

or

2. undermine the plausibility of the Author's Explanation what could make it seem less likely that size of interstitial nucleus has any causal bearing on whether male cats can contract X?

25.

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

  1. No female cats have been

    Unclear Impact

    Females have large interstitial nuclei (the same size as the interstitial nucleus of the male cats who got disease X). Since the females don't get X even though they have big interstitial nuclei, it somewhat seems to weaken the plausibility of the author's idea that big interstitial nuclei in male cats is what enables them to get disease X. So, this feels a little like Effect without Cause, because it's giving Big Interstitial + No Disease X. But it's not really giving "big interstitial" because female cats naturally have a larger interstitial nucleus. For the male cats, a nucleus this big was abnormal and thus more likely to be associated with a disease. The text also tells us that disease X is "a disease affecting no more than 0.05% of male cats". It's not clear whether that means it only affects male cats or whether it could affect both sexes of cats.

    7% picked this

  2. Many male cats who contract

    No Impact

    Since we know nothing about disease Z, this fact doesn't help us evaluate anything about whether disease X in male cats is causally connected to the size of their interstitial nucleus.

    7% picked this

  3. The interstitial nuclei of female

    Strengthens

    This adds plausibility to the Author's Causal Explanation, that the bigger interstitial nucleus in these male cats is what caused them to contract disease X.

    9% picked this

  4. Of 1,000 autopsies on male

    Unclear Impact

    This may feel like a Cause without Effect plausibility weakener, since it's talking about male cats who had the bigger nuclei but didn't contract disease X. However, it's not clear how much we should care about this fact. The male cats who died of X had interstitial nuclei that were as large as a female cat's. The male cats in this answer choice had "larger than average" interstitial nuclei, but we don't know if they were as large as those of a female cat. Also, this would only weaken the argument if we thought the author was saying that "male cats with larger nuclei will get disease X". The author is only concluding that "male cats with larger nuclei can get disease X".

    29% picked this

  5. Correct

    The hypothalamus is known not

    Why this is right

    This badly hurts the plausibility of the Author's Explanation. It essentially denies the possibility of a causal mechanism by which the interstitial nucleus could have influence over disease X. But to make this idea harder to understand, the answer refers to higher categories. Hypothalamus is a bigger category that includes the subregion of the interstitial nucleus. Disease Y is a bigger category that includes the subtype of Disease X. If hypothalamus is known not be causally linked to disease Y, then it seems pretty unlikely that the interstitial nucleus has any causal link to disease X.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

    48% picked this

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