PrepTest 106, Section 2, Question 22
Wirth: All efforts to identify a gene responsible(83 more words not shown)
Which one of the following(8 more words not shown)
- AIt presupposes only(7 more words not shown)
- BIt depends on(8 more words not shown)
- CIt relies on(13 more words not shown)
- DIt disallows in(8 more words not shown)
- EIt treats something(9 more words not shown)
Reading the argument
What if several genes do the job together?
That possibility survives everything Wirth tells us. Researchers have failed to find a single manic-depression gene, and nearly all agree that there isn't one. Even accepting that result, we haven't eliminated every genetic explanation. A combination of genes could produce a predisposition that no one gene produces alone.
Chang makes that point using the researchers Wirth already relies on. Chang isn't accusing them of incompetence or denying their findings. The reply accepts Wirth's evidence and introduces evidence of the possibility Wirth left out: several genes interacting.
What we’re looking for
Now we're asked to describe Chang's criticism. Wirth has acted as though a genetic predisposition would have to come from one gene. Chang's answer is that there is another way for genes to matter. Look for an answer about overlooking that alternative, rather than an answer attacking the evidence Chang explicitly accepts.
Working the answers
- ACorrect
Wirth assumes that a single gene is the only possible source of a genetic predisposition. Chang points to another possibility: an interaction among several genes. If that interaction can produce the predisposition, showing that no single gene does it won't establish Wirth's conclusion. That's the overlooked possibility the answer describes.
- B
The pieces of evidence can both be true: the searches failed, and researchers agree that there is no single gene. Even evidence for several interacting genes can fit with those facts. A contradiction would require claims that cannot both be true, such as saying the same patch of grass is entirely green and entirely blue at the same time. Here the problem is the step beyond the evidence, not incompatible evidence.
- C
These are researchers discussing the genetic research they conducted. Nothing says Wirth has borrowed an opinion from experts in an unrelated field. Chang actually refers to those same researchers for evidence supporting the alternative explanation.
- D
Wirth reaches an unsupported conclusion, but that doesn't show Wirth has a rule forbidding all contrary evidence. We aren't told how Wirth would respond to new findings. Chang identifies a possibility the argument overlooked; Chang doesn't establish that Wirth would refuse to consider it under any circumstances.
- E
Chang doesn't say a single-gene explanation is unlikely but still possible. Chang accepts the evidence against that explanation and points to a different one. The distinction is between one gene and several interacting genes, not between a small chance and no chance.
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