Logical Reasoning

PT135 · S4 · Q23 Biologist: Researchers believe

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Biologist: Researchers believe that dogs are the descendants of domesticated wolves that were bred to be better companions for humans.

Conclusion

All dogs descended from domesticated wolves, but some dogs descended from more recently domesticated wolves.

Evidence

Some breeds of dog are more closely related genetically to wolves than to most other breeds of dog.

Evaluate

Since we know that all dogs broke off the evolutionary tree from some domesticated wolf, the author is saying these more recently domesticated wolves must have broken off from the tree more recently.

Presumably she thinks that the longer it's been since you branched off the evolutionary tree and became your own species, the more genetically you would drift away from wolves and towards other breeds of dogs.

We could think of alternate explanations for how these more recently domesticated wolves have DNA that's more like wolves than dogs, but since this is a Principle question, we're probably not ruling out new objections. Principle answers are usually just connecting bridge ideas that get us from Premise language to Conclusion language.

Goal

The premise is that , and the conclusion is .

So a principle could sound like .

23.

Which one of the following principles underlies the biologist's argument?

  1. If one breed of dog

    Reversal

    This says "If conclusion, then premise". We need "if premise, then conclusion".

    28% picked this

  2. Correct

    If one breed of dog

    Why this is right

    This matches the move from Premise to Conclusion. The hardest part is seeing that the Conclusion half is a meaning match. The Premise said that these more recently domesticated wolves are more closely related genetically to wolves than to other breeds of dog. That matches the "if" condition here. The Conclusion said "these dogs are descended from wolves that were domesticated much more recently". Is that the same as "these dogs have more recent undomesticated wolf ancestors"? Yes, basically. The conclusion is talking about one type of wolf that was domesticated more recently than another type of wolf. Let's say Wolf X was domesticated 100,000 years ago, whereas Wolf Y was domesticated only 20,000 years ago. If Breeds A, B, C, D, E all branched off from Wolf X, they have been genetically drifting from Wolf X for 100,000 years and now they are more related to each other than to Wolf X. The more recently domesticated wolves (Breed Z we'll say) in this argument are more like a Wolf than like other breeds of dog. Our author is saying that Breed Z must have branched off Wolf Y. It wouldn't have as much time to genetically drift as other breeds of dog and it wouldn't be related to Wolf X, so that's why Breed Z's DNA looks more like a wolf's than other dogs'. The conclusion said that "Breed Z descended from a wolf that was domesticated more recently", which matches our idea that Breed Z descended from Wolf Y, which was domesticated 20,000 years ago, whereas Breeds A thru D descended from Wolf X, which was domesticated 100,000 years ago. This answer choice says, "Breed Z descended from a wolf that was more recently undomesticated." That's saying the same thing, referring to the same 20,000 years ago time marker. Wolf Y was domesticated 20,000 years ago, so 20,001 years ago it was still undomesticated. Meanwhile, Breeds A thru D came from Wolf X, which was domesticated 100,000 years ago, so the last time Wolf X was undomesticated was 100,001 years ago. The moment in time that your species becomes "domesticated" is the same moment in time that it stops being "undomesticated". So saying "more recently domesticated" = "more recently undomesticated" in an obnoxious way.

    Skill tested: Principle-Conform · how this choice captures the argument's function is the move to repeat next time.

    53% picked this

  3. Any breed of dog descended

    Bad Premise / Conclusion Match

    This tries to make a move from breed descended more closely related from domesticated → to some dogs than wolves to wolves And we're trying to match up with more closely related descended from wolf to wolves than to → that was domesticated most dogs more recently

    2% picked this

  4. If one breed of dog

    Bad Premise/Conclusion Match

    This tries to make a move from breed X more closely breed X more related related to wolves → to wolves than to than breed Y is breed Y And we're trying to match up with breed X more closely breed X's wolf ancestor related to wolves → domesticated more than to breed Y recently than breed Y's

    14% picked this

  5. Any two breeds of dog

    Relative vs. Absolute Illegal Opposite

    This tries to make a move from breed X more breed X and Y related to breed Y → descended from than to wolves wolf domesticated long ago And we're trying to match up with breed X more closely breed X's wolf ancestor related to wolves → domesticated more than to breed Y recently than breed Y's Besides appearing to be basically an illegal negation of the argument core, this answer is using the absolute sense of "long ago". It could be that all of the dogs we're discussing (even the wolfy ones) descended "long ago" from wolves. The language we need is relative -- which wolf ancestor was domesticated more recently.

    3% picked this

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