The brains of identical twins are genetically identical. When only one

Question

The brains of identical twins are genetically identical. When only one of a pair of identical twins is a schizophrenic, certain areas of the affected twin‟s brain are smaller than corresponding areas in the brain of the unaffected twin. No such differences are found when neither twin is schizophrenic. Therefore, this discovery provides definitive evidence that schizophrenia is caused by damage to the physical structure of the brain.

Which one of the following is an assumption required by the argument?

(A) The brain of person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia

(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.

(C) The brain of a person with an identical twin is no smaller, on average, than the brain of person who is not twines.

(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size

(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.

daboo343 · Accepted Answer

Here the conclusion is  schizophrenia is caused by damage to the physical structure of the brain.
and is based on the premise that When only one of a pair of identical twins is a schizophrenic, certain areas of the affected twin‟s brain are smaller than corresponding areas in the brain of the unaffected twin 
cause effect
 Physical damage to the structure--------------------------------> Schizophrenia. 
So the point of reasoning is cause leads to the effect
i) No alternate cause leads to the stated effect 
ii) Effect does not leads to the cause
iii) Data used for arriving the result is accurate
iv) when cause happens effect happens
The above four might be the assumption

(A) The brain of person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia.  talks about anyone's brain so out of scope

(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment. 
 Thsi matches with our pre thinking no (ii)
If we negate it what will happen
just check
The relative smallness of certain parts of the brains of schizophrenics is the result of schizophrenia or of medications used in its treatment

See the negated version shatters conclusion

(C) The brain of a person with an identical twin is no smaller, on average, than the brain of person who is not twines. out of scope

(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size  stimulus never talks about this so out of scope

(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.
 irrelevant 
 Hence B

sheolokesh · Answer

Smallness ---> Schizo... B states the assumption that Schizo ---x--> Smallness

B is my take.. OA please..

JarvisR · Answer

Conclusion: 
damage to physical structure -> schizophrenia.

(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.
Negating B would find an alternative cause for Schi..
schizophrenia or of medications used -> smallness of certain parts of the brains of schizophrenics
Weakens the conclusion.
So B is the answer.

sobby · Answer

Typical GMAT question...

Conclusion : A(smallness in brain size/Damage in brain) causes B(schizophrenic) ...

so we need to discard the possibility that B(schizophrenic) causes A(smallness in brain/Damage in brain)

B is doing that perfectly ...........

akshayk · Answer

Physical damage/Relative smallness in the size of the brain causes Schizophrenia.
Assumption - Schizophrenia doesn't cause physical damage to the brain.

A - This is already mentioned in the argument.
B - This looks likely.
C - Irrelevant
D - That's not what were are trying to derive here. Irrelevant
E - Irrelevant.

B is the answer IMO

CrackverbalGMAT · Answer

let us take a look at the main conclusion --

schizophrenia is caused by damage to the physical structure of the brain.

this is a cause and effect statement. We can write this as --

damage to the physical structure of the brain --> schizophrenia

One of the simplest ways to approach an assumption question would be to figure out a flaw in the argument. Negating that flaw would lead us to an assumption made in the argument. 
Commonly found patterns of flaws in causal statements are reverse causation (Effect --> Cause) and alternate cause (Another cause --> effect).

let us take a look at the answer options --

Option A - Incorrect
Not a proper comparison. We are comparing the brains of IDENTICAL TWINS -- from this we are deriving our conclusion that physical damage to the brain causes schizophrenia.

Option B - Incorrect
If the smallness of the brain in the identical schizophrenic twin is due to "medications", this destroys the argument by providing an alternate cause.
If it is due to schizophrenia itself, this tells us that the effect led to the cause (Reverse causation) -- again weakens the argument.
By denying both these flaws, option B states an assumption.

Option C - Incorrect
Not a proper comparison. We are comparing the brains of IDENTICAL TWINS -- this helps us to control for other factors that might impact the brain size. We are not comparing the brain sizes of twins to those of other people.

Option D - Incorrect
this directly contradicts the conclusion -- which says that different size (smaller brain size due to physical damage) is something that causes schizophrenia

Option E - Incorrect
Not relevant to the argument. the argument is concerned with WHAT CAUSES schizophrenia, not HOW LIKELY it is to occur.

unraveled · Answer

Only B and D stand a chance here. D loses out to B since negating it doesn't break the passage apart. After negation D looks like
"When a pair of identical twins both suffer from schizophrenia, their brains are not the same size."
This becomes irrelevant.

B tests the A ---> B or B ---> A principle.

Answer B.

drec108 · Answer

(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.
Thsi matches with our pre thinking no (ii)
If we negate it what will happen
just check
The relative smallness of certain parts of the brains of schizophrenics is the result of schizophrenia or of medications used in its treatment

See the negated version shatters conclusion

(C) The brain of a person with an identical twin is no smaller, on average, than the brain of person who is not twines.out of scope

(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size stimulus never talks about this so out of scope

(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.
irrelevant
Hence B

arpapaar · Answer

This is very well summarized for the typical assumption answers. Thank you so much for this. Very helpful.

kovid231 · Answer

The brains of identical twins are genetically identical. When only one of a pair of identical twins is a schizophrenic, certain areas of the affected twin‟s brain are smaller than corresponding areas in the brain of the unaffected twin. No such differences are found when neither twin is schizophrenic. Therefore, this discovery provides definitive evidence that schizophrenia is caused by damage to the physical structure of the brain.

Which one of the following is an assumption required by the argument?

Let's look at the argument:
When compared, the brain of a twin who is schizophrenic  shows some areas  of the brain smaller in comparison to the non-schizophrenic twin.
If both schizophrenic twins are compared, no difference in the areas of their brains.
 Conclusion:  Schizophrenia is caused by damage to physical structure of brain.

This is a cause and effect question type, in which the damage to physical structure of the brain causes schizophrenia.

Additional point: Note how this is a fact: Brains of identical twins are identical.

We will solve using negation method. idea is to negate the answers and the one that weakens the conclusion, is the central assumption made. Let's go.

(A) The brain of person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia

- Even before we do the negation, this has not been stated anywhere. on the contrary, we are told as a fact that the twins have identical brains. This is a counter to a fact stated, which is not possible in Gmat, you do not negate facts, but only conclusion. Hence, this would be WA.

(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.

Let's use negation:

This will become: The relative smallness of certain parts of the brain of  schizophrenics IS the result of  schizophrenia or of medications used in its treatment.

- This correctly responds to "smallness of certain parts". If this were true, this flips the cause and effect relationship. It says, that it is not the damage that causes schizophrenia. but the reverse is true or could be medication. (B causes A)

(C) The brain of a person with an identical twin is no smaller, on average, than the brain of person who is not twines.

OS: Size of the brain being comparable is not at issue here but parts of the brain smaller in comparison to identical brain is.

(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size

Negation would make that their brains are not of same size. This is again OS. We are not concerned about how their overall size compares.

(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.

OS: Question states, people with identical brains show identical symptoms, not twins are likely to suffer. very bad option.

With this, B should be the answer

The brains of identical twins are genetically identical. When only one

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The brains of identical twins are genetically identical. When only one

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615 to 715 in 15 Days (Ria's Strategies)

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