Wirth: All efforts to identify a gene responsible for predisposing people to manic–depression have failed. In fact...

shunhe on January 11, 2020

Hi @Samantha-Alexis,

Thanks for the question! Let’s walk through Wirth’s argument and then Chang’s argument. Wirth is telling us that the claim that some people are genetically predisposed to manic-depression is false. Why? Wirth points to evidence suggesting there is no single gene responsible for manic-depression. Chang doesn’t disagree with the evidence about there being no single gene responsible for manic-depression, but does disagree with the conclusion Wirth to which Wirth comes. Chang thinks that there’s a set of genes that interact with each other and produce a predisposition to manic-depression. We need to find the point at issue, and it seems to be whether or not people can be disposed to manic-depression. This is what (D) tells us. Wirth would say yes, current research does support the claim that no one is genetically predisposed to manic-depression. Chang would say no, current research doesn’t support this claim.

(C), on the other hand, is incorrect because Chang isn’t disagreeing with the fact that nearly all researchers now agree that there’s no manic-depression gene. Chang, in fact, explicitly states that he doesn’t agree with Wirth’s evidence, which includes this premise. Instead, Chang is disagreeing with Wirth’s conclusion about genetic predisposition to manic-depression. Hope this helps! Feel free to ask any further questions that you might have.