Logical Reasoning

PT148 · S1 · Q5 During its caterpillar stage

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During its caterpillar stage, the leopard magpie moth feeds on a plant called the Natal grass cycad and by so doing laces its body with macrozamin, a toxin that makes the moth highly unpalatable to would-be predators.

Conclusion

The leopard magpie moth is danger of extinction.

Evidence (since)

During its caterpillar stage, the leopard magpie moth feeds on a plant called the Natal grass cycad, which laces its body with a toxin that is a deterrent to predators.

The Natal grass cycad is now endangered and facing extinction.

Evaluate

Since the argument feels more like Comparison / Causal real-world science talk (and less like abstract rules and language math), we should probably think about coming up with an Objection, rather than solving for a Missing Link.

Given that ... the LM moth uses the cycad to coat itself in a way that turns off predators, and that ... the cycad is endangered, How can we argue .. the LM moth isn't endangered?

Maybe it doesn't have as many predators to worry about any more. Some evolutionary adaptations outlive the selection pressure that gave rise to them. Maybe the moths still put the cycad slime on their bodies, even though there are very few predators around to even be deterred. This argument, then, must be assuming that .

Similarly, somewhat, maybe the LM moth wouldn't be endangered even if it loses its ability to coat itself in cycad slime because there are simply too many LM moths for any loss to predation to bring the LM moth species to the endangered status. In other words, it's possible that the loss of the cycad species will definitely mean that more LM moths die from predators, but the moth population might be starting at such a populous high number that the lessening effect from increased predation wouldn't ever reduce the moth population to endangered levels.

Goal

There are a lot of different directions this answer could go. It could be very literal in its Linking: .

It could sound like it's ruling out an Objection: or and so on.

Which one of the following is an assumption required by the argument?

Correct
Feeding on the Natal grass
Why this is right
"The only" is strong, and thus a red flag, but also conditional, and thus something we should examine by looking at it conditionally (as well as its contrapositive). "The only" is a sufficient, Left-side indicator word. (only and only if are necessary, Right-side indicator words) So the idea following "the only", a means of making itself unpalatable to predators, would go on the Left of the arrow. a way to make itself feeding on highly unpalatable → the Natal to predators grass cycad When correct answers are conditional, they're usually written in contrapositive form (to be sneaky, to disguise their potential appeal). When we contrapose this one, we get: can't feed on the no means to make Natal grass cycad → itself highly yucky to predators Did the author's argument make that move? Sure. Not explicitly, but that's definitely the intended meaning of how the author goes from thinking, "Oh, no, the plant that gives them their anti-predator toxin is endangered. Thus they are endangered." He must be thinking that without this plant, the moth loses this defense mechanism, and thus the predators will be able to gobble them up to the point where their species will be in danger of surviving. This answer choice is just calling out that first thought, that "without this plant, the moth will lose the defense mechanism of making itself taste yucky." If we negate this answer and say, "the cycad isn't the only way the moth can make itself unpalatable. There is at least one other way to make itself unpalatable", then that would badly weaken the argument, since it would make it seem like the moths aren't so vulnerable to predators all of a sudden.
Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.
85% picked this
The leopard magpie moth does
Too Strong: any
The argument does need to assume that the moth can't just outrun all its predators (and probably even needs to assume it can't outrun most of its predators). But it doesn't need to assume the extreme idea that it can't outrun a single one of its potential predators. This answer looks tempting because it has the "ruling out" word not, which is very common in correct Necessary Assumption answers. If we negate this, it's saying "the moth does have the speed or agility to escape from at least one of its potential predators". That definitely weakens somewhat! It helps us argue that the moth won't be in that bad a situation when it comes to predators, once it loses its ability to lace its body with cycad toxins. But it doesn't weaken as much as the negation of (A), which makes it sound like the moth's situation isn't going to get any worse at all. The negation of (A) makes it sound like when the cycad goes extinct, the moth won't actually be losing its ability to make itself highly unpalatable.
7% picked this
Potential predators of the leopard
Weakens, if anything
This has the lovable ruling-out language "cannot", no let's negate it and see if it weakens: Predators can determine from appearance alone whether a moth's body is laced with the toxin. No, that would actually strengthen. When they cycad runs out, and the moth is now flying around toxin-free, it wouldn't have the temporary protection of its predators assuming that it still tastes nasty like they've always known it to. Instead, this negation is saying they would visually see that the moth wasn't wearing its "yuck suit" anymore, so it would be open season on hunting the moths.
2% picked this
Leopard magpie moths are not
Too Strong: abundant
This conditional answer would look like this: cycad plants are → moths can't locate not abundant cycad plants Did our author's thinking make that move? No, not really. It made a move that looked more like this: cycad plants are → moths can't reliably endangered/extinct use toxin-defense
5% picked this
None of the potential predators
Too Strong: none
It wouldn't hurt the author's argument at all if we negated this and said, "at least one of the potential predators has already developed a tolerance for the macrozamin defense mechanism". The author definitely needs to assume that some or even most predators aren't immune to this defense mechanism. After all, if all the predators were already immune to this defense mechanism, then it wouldn't be a functional defense mechanism. So losing it when the cycad goes extinct wouldn't actually change anything in terms of threat from predators. But it's too strong to say the argument needs to assume that not a single one of the potential predators has developed a tolerance for it.
1% picked this

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