#23 - The brains of identical twins are genetically

[Administrator]

Complete Question Explanation

Assumption—CE. The correct answer choice is (B)

The conclusion in the stimulus is that schizophrenia is caused by damage to the physical structure of the brain. This is concluded based on the discovery that people with genetically identical brains showed a physical difference when one of the two had schizophrenia. Since we are looking for an assumption, we need to find an answer that would eliminate something that could severely weaken this argument (in this case, the possibility that the cause and effect are reversed).

Answer choice (A): The argument is not about the overall size of the brain, but only about specific portions and their relationship to schizophrenia.

Answer choice (B): This is the correct answer choice. As mentioned above, this answer eliminates the possibility that the cause (smaller portion of brain) could actually be the result of the effect (schizophrenia).

Answer choice (C): The comparison in the stimulus is between identical twins, so assumptions about their brains relative to the brains of others is irrelevant.

Answer choice (D): Again, the stimulus is discussing the comparison between one twin with schizophrenia and the other without, so both twins having (or not) schizophrenia is not relevant to the argument.

Answer choice (E): Since we are only concerned about the relationship between the size of a specific portion of the brain and schizophrenia, the frequency with which identical twins get schizophrenia is not important to the argument.

[saygracealways]

Hi PowerScore,

The conclusion in the stimulus says "damage to the physical structure of the brain" caused schizophrenia (effect).

Your explanation says that (B) eliminates the possibility that the C and E relationship are reversed (meaning it eliminates the possibility that schizophrenia smaller brain). I'm a bit confused to how this relationship is reversed because the stimulus says "damage to the physical structure of the brain"? Can we assume that "damage to the physical structure of the brain" is synonymous to "smaller brain"?

Thank you

[KelseyWoods]

Hi saygracealways!

The premise in the stimulus tells us that "when only one of a pair of identical twins is schizophrenic, certain areas of the affected twin's brains are smaller than corresponding areas of the unaffected twin." So the stimulus has already equated "smaller brain areas" with "damage to the physical structure of the brain" for us. The argument is concluding that damage to the physical structure of the brain (signified by smaller brain areas) causes schizophrenia.

Hope this helps!

Best,
Kelsey

[tkt25!]

Hello!

During blind review I chose B correctly, however upon my initial attempt at this question I chose A, aside from answer choice A mentioning the overall size of the brain and we're only focused on "certain areas" of the brain, what else makes A wrong? Also I was a bit confused on how to negate answer choice A as well to test how it fails the negation test.

Any help would be appreciated thank you!

[Jeff Wren]

Hi tkt,

First, just to be clear, the fact that Answer A is discussing total brain size while the argument only focuses on "certain "areas" is enough to make this answer incorrect.

Second, remember that Assumption answers are statements that are absolutely necessary for the argument, so they generally state the bare minimum of what is necessary and nothing more. In other words, you should be wary of strongly worded/exaggerated answers in Assumption questions because they are usually stronger than what is required. For example, answers that claim that something is the best, or the worst, or the most important, etc. are likely to be wrong answers in Assumption questions.

Here, Answer A claims that "the brain of person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia" (my emphasis). This is a very extreme claim. For example, what this answer is claiming is that the brain of an adult suffering from schizophrenia is smaller than the brain of a newborn baby who is not suffering from schizophrenia. This extreme claim is absolutely not required for the argument.

The negation of Answer A would be: "the brain of person suffering from schizophrenia is not necessarily smaller than the brain of anyone not suffering from schizophrenia." This in no way weakens the argument because the argument is not comparing the brain sizes of people suffering from schizophrenia in general to the brain sizes of people not suffering from schizophrenia in general. The argument uses generically identical twins because these twins would have identically sized brains if not for the schizophrenia, so the smaller area of the brain in one twin who has schizophrenia shows the difference. How a brain of person suffering from schizophrenia compares in terms of size to a completely genetically different person (with or without schizophrenia) is completely irrelevant to the argument.