PrepTest 133, Section 2, Question 6
Recently discovered bird fossils are about 20 million(40 more words not shown)
The reasoning in the argument(6 more words not shown)
- Adraws a generalization(10 more words not shown)
- Brejects the consensus(10 more words not shown)
- Cattacks the adherents(13 more words not shown)
- Dfails to consider(7 more words not shown)
- Eignores the possibility(9 more words not shown)
Reading the argument
These birds couldn't have descended from animals that lived later. But how did we get from that timing problem to no bird ever descending from any dinosaur?
The fossils challenge a particular account of ancestry. The bird fossils are older than the fossils of the birdlike dinosaurs they're supposedly descended from. That deserves an explanation. Perhaps older fossils of those dinosaurs haven't been found yet. We shouldn't assume the oldest fossil we've discovered marks the first animal of its kind.
Even setting that possibility aside, the conclusion reaches far beyond these fossils. Could other birds have descended from other dinosaurs? Could a later group of birds have descended from these birdlike dinosaurs? The evidence doesn't rule those possibilities out.
What we’re looking for
For the flaw question, I'd describe that expansion: the author takes a finding about particular birds and dinosaurs and applies it to every bird and every dinosaur. A problem with one proposed line of descent doesn't eliminate every possible line of descent.
Working the answers
- ACorrect
The findings concern the ages of particular fossils. The generalization concerns all birds and all dinosaurs. The fossil dates might undermine the proposed ancestry for these birds, but they don't establish that no bird descended from any dinosaur. That's the specific way the conclusion is broader than the evidence warrants.
- B
The author does offer counterevidence: the newly discovered fossils and their dates. We can think that evidence fails to support the sweeping conclusion without saying no evidence was provided. Disagreeing with experts isn't automatically the problem; the problem is how much the author claims these findings establish.
- C
Nobody attacks the paleontologists personally. The author challenges their account by pointing to fossils, rather than rejecting it because of some supposed defect in the people who believe it. An unsuccessful argument against their view is still different from a personal attack.
- D
This asks about ancestry running in the other direction: birds giving rise to dinosaurs. The conclusion we're evaluating concerns birds descending from dinosaurs. Pointing out that another evolutionary possibility wasn't discussed doesn't show why the fossil evidence fails to establish this conclusion.
- E
A common ancestor is different from one group descending from the other. Learning that two groups share an ancestor wouldn't, by itself, settle which birds descended from which dinosaurs. The relevant gap is that the evidence about these particular fossils doesn't justify a claim about all bird-dinosaur ancestry. E doesn't identify that gap.
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