PrepTest 135, Section 4, Question 23
Biologist: Researchers believe that dogs are the descendants(54 more words not shown)
Which one of the following(5 more words not shown)
- AIf one breed(39 more words not shown)
- BIf one breed(31 more words not shown)
- CAny breed of(23 more words not shown)
- DIf one breed(33 more words not shown)
- EAny two breeds(23 more words not shown)
Reading the argument
Genetic closeness isn't automatically a clock.
A breed could retain a close genetic relationship to wolves over a long period, while another breed changes more rapidly. So learning how closely related the breeds are doesn't, by itself, tell us when their wolf ancestors were domesticated. The biologist moves from a genetic comparison to a claim about timing.
Keep the comparison precise. Call the breeds X and Y. The evidence can say X is more closely related to wolves than X is to Y. The conclusion needs to tell us that X's undomesticated wolf ancestors were more recent than Y's. We aren't just deciding which dog looks more like a wolf.
What we’re looking for
The principle needs to take us from the genetic relationship we know to the historical relationship the biologist concludes. A rule beginning with recent domestication and then predicting genetic closeness would run in the wrong direction for this argument.
Working the answers
- A
This starts with more recent domestication and says the breed may be more closely related to wolves. But recent domestication is what the biologist is trying to establish, not a fact already available to trigger the rule. We need genetic closeness to establish recency; A gives recency as a possible explanation of closeness.
- BCorrect
If breed X is more closely related to wolves than to breed Y, X has more recent undomesticated wolf ancestors than Y does. That connects the precise kind of genetic comparison in the evidence to the difference in domestication timing in the conclusion. It supplies the genetic-clock relationship the argument relies on.
- C
This compares a dog's genetic relationship to some other breeds with its relationship to wolves. It never tells us when any wolf ancestors were domesticated. Even if the comparison were true, it wouldn't connect genetic closeness with the timeline we need.
- D
Notice the two different comparisons. The first ranks X and Y by how close each is to wolves. The second compares X's closeness to wolves with X's closeness to Y. Those aren't identical claims, so D isn't merely repeating itself. But both concern genetic relationships; neither establishes anything about the recency of domestication. That missing timeline makes D unhelpful here.
- E
This addresses two breeds that are closer to each other than to wolves and places both ancestries long ago. Our evidence instead identifies breeds closer to wolves than to most other dog breeds, and our conclusion needs a difference in recency between the breeds. E supplies a rule for a different comparison and a shared age description.
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