PrepTest 144, Section 3, Question 9
Astronomer: Proponents of the hypothesis that life evolved(103 more words not shown)
The reasoning in the astronomer's(6 more words not shown)
- Aconcludes, simply because(16 more words not shown)
- Bfails to justify(10 more words not shown)
- Creasons that a(16 more words not shown)
- Dattempts to derive(7 more words not shown)
- Egrants the truth(21 more words not shown)
Reading the argument
Life arrived from space? I'd want evidence for that. But failing to prove a theory isn't the same as proving it false.
First, follow the proponents' timing argument. They say meteorites would have destroyed life on Earth 3.8 billion years ago, yet complex life existed here 3.5 billion years ago. Why couldn't life have developed in between? That's 300 million years. A small-looking decimal doesn't tell us whether the interval was too short.
The proponents claim it was too short. Is that established? And would the bombardment really have destroyed all existing life? Those are questions worth asking. If both claims were sound, they would present a serious problem for the account that life evolved here during that interval.
The astronomer makes a fair distinction: arguments against an Earth-based origin are not direct evidence that spores brought life from elsewhere. But then the astronomer treats the lack of positive evidence as a reason to consider the spore theory false.
What we’re looking for
We could remain unconvinced of either account. 'You haven't shown that it happened' leaves open whether it happened. The flaw question asks us to identify the move from an unsupported theory to a supposedly false theory.
Working the answers
- ACorrect
The astronomer points to the absence of positive support for the spore hypothesis and treats that absence as evidence against it. A hypothesis could be true even if its advocates haven't yet supplied evidence establishing it. We need to distinguish withholding belief from concluding that there is good reason to think it false.
- B
The astronomer doesn't argue that the spore hypothesis is inherently implausible. The criticism is that nobody has supplied positive evidence for it. B substitutes a different basis for rejecting the theory instead of identifying the problem with the basis actually offered.
- C
The astronomer never says the two accounts are equally likely. Nor would another account being equally likely establish that this one is false. That would be a different bad argument. Here the stated reason for rejection is a lack of supporting evidence.
- D
The premises don't contradict the conclusion. A theory could lack positive evidence and also be false. The problem is that lacking positive evidence doesn't establish its falsehood. Failure to support a conclusion is different from giving premises that oppose it.
- E
Accepting something an opponent says isn't itself a mistake. We can grant a point while disputing the conclusion drawn from it. Even if the astronomer accepts the timing claims, we still need to examine whether the stated reason for rejecting the spore theory works. E doesn't identify the unjustified move from no positive support to evidence against.
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