LSAT 16 – Section 3 – Question 14

Target time: 1:38

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PT16 S3 Q14
+LR
Necessary assumption +NA
A
0%
B
20%
164
C
10%
161
D
6%
164
E
64%
169
144
159
174
+Harder 0 +SubsectionMedium

This is a necessary assumption question, though the question stem is quite abrupt and may present some challenges. It’s asking for an assumption, but there is no explicit indication of whether it wants a sufficient or necessary assumption. We have to really understand the nature of our assumptions to see this is necessary rather than sufficient. While it may sound obvious, sufficient assumptions are not necessary: Just because an assumption would be sufficient to validate the argument does not mean that the argument is definitely making that assumption. Necessary assumptions, on the other hard, are necessary. The argument is bound to them and cannot hold without them. Because this question stem is asking for an assumption the argument is definitely and actually making, that is how we know we are looking for a necessary assumption rather than a sufficient.

The stimulus: Well that’s interesting. Caffeine can kill certain insects, or at least their larvae. Now it looks like we have an experiment which is looking into this phenomenon. We see a certain insect die when it ingests some substance which contains caffeine, among other things. We should be drawn to the phrase “in part” because it tells us that there’s other components to whatever we’re feeding these worms. We should immediately question how we know that caffeine, and not some other component of the substance, is responsible. If this argument goes on to draw a conclusion about the effects of caffeine, it’s going to be in trouble.

And that’s exactly what it does in the last line of the sentence, which is our conclusion. The grammar is really convoluted, though, so let’s break it down to determine exactly what the conclusion is. The main body of the sentence is just “This result is evidence for the hypothesis . . .” Which hypothesis? Well, the rest of the sentence specifies which one. But the main part of the sentence is our conclusion: The result is evidence for this hypothesis.

So this doesn’t go as far as it might have. It does not say, “Therefore, caffeine totally evolved as a defense against pests.” That would have been easy to discredit. Rather, it merely says that this experiment is evidence for such a hypothesis. Is it? Well, maybe. What is evidence? Evidence doesn’t have to be conclusive. It only needs to make a proposition more likely to be true. Because there are so many other things they’re feeding to these worms, this is really weak evidence, but despite its weakness, it may nevertheless qualify as evidence. It’s hard to say for sure though. Either way, this opens up a nice big gap with lots of assumptions.

The other observation we might make from this final sentence is the reference to “non-negligible quantities.” Do tea leaves contain non-negligible quantities of caffeine? This argument does not give us an answer. And even if we assume they do, was there enough tea powder in this concoction to deliver a non-negligible dose? Maybe, maybe not. We don’t know. This new term also introduces room for assumptions.

There is a lot going on in this stimulus, and we likely have not have identified every gap. We want to proceed with a POE approach on this one and see what the answer choices might offer up for us to consider.

Answer Choice (A) Sure, maybe. This strengthens the proposition that these plants have insecticidal qualities, but what we care about is caffeine and this does not narrow down which substance in these plants is actually doing the insecticide-ing. Maybe caffeine, maybe something else. Moreover, the hypothesis is addressing caffeine as an evolutionary function, which this does not seem to touch.

Answer Choice (B) This is an interesting suggestion, but it has a problem. Does it have to be “roughly equal” to the amount in the concoction fed to the worms in the experiment? I don’t think so. It could be way higher and we would expect that to do the job.

Answer Choice (C) I can see why this might be attractive. It establishes some link between caffeine producing plants and the pests, and that does appear important to a conclusion about caffeine as an evolutionary response. What if this were not true? What if caffeine producing plants simply don’t grow wherever these pests pose a risk? “Wherever” should give us pause, though. This is a more universal statement than I’m comfortable with here. I think a 99% match would still be pretty compelling. So this gets at something close, but it misses the mark.

Answer Choice (D) Okay. So the specific worm in our experiment is a tobacco pest. What if the tobacco plant doesn’t produce caffeine? That seems like it could be a problem. How can we say caffeine evolved as a defense against these pests if these pests feed off a plant that doesn’t produce caffeine? That might seem seem to break the relevancy of the experiment with any claim about caffeine as an evolutionary mechanism. But does it? It still establishes a sensitivity to caffeine among plant pests. The fact that tobacco may not have evolved that specific defense doesn’t necessarily mean that this can’t support a hypothesis that only relies on the fact that caffeine is an effective pesticide. If D were not true, it would certainly weaken the argument. But I do not think it would destroy it.

Correct Answer Choice (E) This has to be true. No evolutionary pressure; no evolutionary response. If caffeine producing plants have literally never been preyed upon by pests which are sensitive to caffeine, there’s no way this is an evolutionary response. We do need to be a little careful though. Remember, the conclusion is very precise. We are not concluding that these plants evolved caffeine as an evolutionary defense against pests. We are concluding that the experiment with the tobacco worm is evidence that they might have. While this answer needs to be true for this to actually have been an evolutionary response, does it have to be true for this experiment to lend the hypothesis support? Yes. If the hypothesis is disproven, then there is no observation which we would say qualifies as evidence to support it. The hypothesis must remain possible for this experiment to qualify as evidence.

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