The brains of identical twins are genetically identical. When only one of a pair of identical twins is a schizophreni...

shunhe May 30, 2020

Hi @Shirnel,

Thanks for the question! So let’s take a look at what this stimulus is telling us. We’re told that the brains of identical twins are genetically identical. When one pair of twins is a schizophrenic, certain areas of the twin’s brain are smaller than its twin’s brain’s corresponding parts. No differences found when neither twin is schizophrenic. And so the argument concludes that this discovery shows that schizophrenia is caused by damage to the physical structure of the brain.

Now we’re asked for an assumption that the argument requires. Oftentimes, on these kinds of causation questions, we want to keep in mind if the possibility for reverse causation is there. Sometimes, people will think Y caused X, when really, it’s the case that X caused Y. Here, that is a potential assumption of the argument: that damage to the physical structure of the brain is what caused schizophrenia, and not the other way around, that schizophrenia caused damage to the physical structure of the brain. So this is one such assumption the argument requires that we can anticipate and take with us as we look into the answer choices, and we see that this is what (B) tells us. The argument assumes that the reason that some brain parts are smaller in schizophrenics isn’t the result of schizophrenia or of medications used in treatment; it assumes that the smaller brain parts are the cause of schizophrenia. So you might have read the conclusion a bit too quickly.

Hope this helps! Feel free to ask any other questions that you might have.