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

Skylar on December 28, 2019

@MACZ, thanks for your question.

Although both (A) and (D) refer to the existence of genetic predisposition, they do so in different ways. (A) refers more to the evidence, whereas (D) refers more to the conclusion.

(A) claims that efforts to identify a gene/gene set responsible for predisposition to manic depression have all failed. Wirth states this with regards to a single gene in his first sentence, so we know he agrees in that context. We also know that Chang agrees with regards to a single gene because he tells Wirth that he does not dispute his evidence. Wirth does not mention anything about a set of several genes, so there cannot be an expressed disagreement about those efforts.

(D) states that current research supports the claim that nobody is predisposed to manic depression. It is likely that Wirth agrees with this, because this is the conclusion he makes in the sentence "any claim that some people are genetically predisposed to manic-depression is simply false." However, it is likely that Chang disagrees with this because he says he takes issue with Wirth's conclusion. Therefore, Chang does not believe that failed research with regards to finding a single gene indicates that there is no genetic predisposition. He offers support to this end by claiming that researchers have found evidence of involvement from a set of genes interacting in a complex manner to produce a predisposition. Since Wirth and Chang disagree here, this is the point at issue,

Does that make sense? Let us know if you have additional questions and best of luck with your studies!