Logical Reasoning

PT147 · S1 · Q23 Zoologist: Plants preferentially absorb

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Zoologist: Plants preferentially absorb heavy nitrogen from rainwater.

Conclusion (Thus)

The prehistoric European cave bears were not exclusively herbivores.

Evidence

Animals that are not exclusively herbivores (they eat meat) have higher concentrations of heavy nitrogen in their bodily tissues than do animals that are exclusively herbivores.

The level of heavy nitrogen in the bones of these prehistoric European cave bears was identical to the levels of heavy nitrogen present in the blood of present-day bears who eat meat.

Evaluate

The author is interpreting the significance of nitrogen levels in these prehistoric cave bears' bones, so we can use our Explain Curious Fact mindset.

Curious Fact ... why does the level of nitrogen in prehistoric cave bears' bone samples match the level of nitrogen in modern meat-eating bears' blood samples?

Author's Explanation ... because they were both meat eaters, and eating meat gives you higher concentrations of nitrogen.

Goal

Because this is Strengthen, a correct answer could,

1. rule out an Alternate Explanation for why their nitrogen levels match. maybe these prehistoric European cave bears were strictly herbivores, but there's some other reason why they have as much nitrogen in their bones as modern meat-eating bears have in their blood. an answer that rules-out such a thing makes the author's hypothesis more likely.

2. increase the plausibility of the Author's Explanation. does any answer give us more reason to think that these prehistoric European cave bears ate meat?

23.

Which one of the following, if true, would most strengthen the zoologist's argument?

Plants can also absorb heavy
No Impact
This is focused on a background claim that isn't even part of the core argument. We don't care whether plants have other sources of heavy nitrogen. None of that will change the premise that animals that eat meat have higher concentrations of heavy nitrogen than do animals that strictly eat plants.
1% picked this
The rate at which heavy
No Impact
The author thinks these prehistoric European cave bears were not herbivores, so it's unclear why we'd care to hear anything about prehistoric herbivores. Furthermore, do we care about the rate at which heavy nitrogen accumulated in their blood? It seems like the argument only cares about final level of heavy nitrogen present in the bone/blood samples. It doesn't care about the rate at which that nitrogen accumulated (i.e. did it accumulate at a rate of 2 mg/month or 5 mg/month?)
18% picked this
The same number of samples
Very Weak Impact
Do we care whether the number of bone samples was precisely equal to the number of blood samples? Not really. I mean, if they were in crazy imbalance then maybe we could say, "Hey --- how trustworthy is your data? You took 100 samples of modern bears but only 3 samples of prehistoric bears." But we wouldn't bat an eye if it was 100 samples vs. 80 samples or anything like that. So knowing that the number of samples was exactly the same mildly strengthens the trustworthiness of the data by ruling out the possibility that we have compared a very uneven number of samples, but it's not doing much.
3% picked this
Correct
Bone samples from present-day bears
Why this is right
This answer is sneaky for most of us. It doesn't sound that much more interesting than the "same" presented in choice (C), but we should ask ourselves, "Do we care whether bone samples from modern bears would have the same nitrogen content as their blood samples?" Hopefully this causes us to look back at the argument and notice a detail that most of us don't see on our initial read: the evidence is comparing the bone samples of prehistoric bears to the blood samples of modern bears Are those fair to compare? If you compared the amount of calcium in my brother's bones to the amount of calcium in my blood, would that be a good basis for judging which of us drinks the most milk? Not necessarily! If calcium collects more in bones than in blood, then you wouldn't look at my brother's higher calcium level (from his bone sample), compare it to my lower calcium level (from my blood sample), and say, "You need to drink more milk, dude!" Similarly, if nitrogen collects at different levels in bones vs. blood, then comparing prehistoric bear bones to modern bear blood could be an Apples vs. Oranges comparison. This answer strengthens the argument by reassuring us that these two things are fair to compare. In a sense, this answer is just a Necessary Assumption. If it weren't true, it would badly weaken the argument. The fact that it is true mildly strengthens, but that's the best option we've got. A lot of correct answers on really hard Strengthen questions just supply a Necessary Assumption.
Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.
65% picked this
The level of heavy nitrogen
Weaker Impact
Just like (C), this answer makes the evidence a little more safe and secure. And like (C), if we were to negate this, it wouldn't be as big an objection as it would be if we negated (D). This answer rules out an objection that "modern bears who are fed meat-enriched diets are not fair representatives of how much nitrogen a meat-eating bear would have in its bones". But the author's argument doesn't hinge on these present-day bears perfectly representing all meat-eating bears. His argument just cares that these modern bears being fed meat have nitrogen levels that match those of prehistoric bears, and he thus takes that as a sign that the prehistoric bears also had meat in their system.
13% picked this

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