PrepTest 126, Section 1, Question 20
A study of rabbits in the 1940s convinced(60 more words not shown)
A flaw in the reasoning(7 more words not shown)
- Atakes for granted(18 more words not shown)
- Binfers that a(18 more words not shown)
- Crules out an(19 more words not shown)
- Dconfuses a necessary(9 more words not shown)
- Eassumes that the(24 more words not shown)
Reading the argument
A flawed study isn't proof that the phenomenon is impossible.
The rabbit study apparently persuaded people that reproduction without fertilizing an egg could occur in mammals. I can imagine ways a study like that might go wrong: perhaps a male rabbit was overlooked, or fertilization happened before observations began. Those are guesses. The passage tells us the methods were flawed without telling us exactly how.
So the original evidence is unreliable, and later studies haven't demonstrated the phenomenon either. That leaves us without a successful demonstration. It doesn't by itself show that no mammal could ever reproduce this way.
Then the author takes another step: something about mammalian chromosomes must rule it out. Why chromosomes specifically? Could some other difference, perhaps an environmental condition such as temperature, matter? We haven't been shown that chromosomes are the explanation.
What we’re looking for
For the flaw question, my first thought is that jump to a particular explanation. But keep the earlier step in view too: the author moves from a lack of proof that mammalian parthenogenesis occurs to treating it as impossible. Either unsupported move could matter to the reasoning.
Working the answers
- ACorrect
This targets the earlier problem. The rabbit study is flawed, and no later study has demonstrated mammalian parthenogenesis. The author treats that lack of proof as establishing that mammals cannot do it, then proposes a chromosome-based reason for the supposed impossibility.
My attention went to why chromosomes were singled out. A exposes a problem before we even get there: we haven't established the impossibility that needs explaining. A flaw doesn't have to address the last few words of the conclusion to undermine the argument.
- B
The passage says parthenogenesis occurs in a wide variety of nonmammalian vertebrates, not all of them. The argument doesn't take some examples and conclude that every nonmammalian species shares the characteristic. B describes a claim the author never makes.
- C
The author proposes a chromosome-based explanation. The argument doesn't reject a competing explanation merely because another explanation is available. The concern is that it jumps to a particular explanation for an impossibility it hasn't established, not that it dismisses an identified rival account.
- D
No requirement for parthenogenesis is first stated and then incorrectly treated as enough to guarantee it, or the other way around. The argument instead draws a conclusion about impossibility from unsuccessful evidence. D doesn't describe that inference.
- E
The flawed methods are given as a fact. The author doesn't argue that the methods must have been flawed because rabbit findings cannot be extended to every mammal. We aren't told the basis for judging the methods, so E invents one.
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