PrepTest 141, Section 2, Question 8
Biologist: Marine animals known as box jellyfish have(72 more words not shown)
The argument requires assuming which(4 more words not shown)
- ABox jellyfish are(12 more words not shown)
- BBox jellyfish have(12 more words not shown)
- CBox jellyfish would(12 more words not shown)
- DBox jellyfish developed(7 more words not shown)
- EBox jellyfish use(8 more words not shown)
Reading the argument
We know what these jellyfish can see. Do we know what they need to see?
The lenses can produce a sharp image, but the retinas' position means the jellyfish receive a blurry one. I don't need to know the anatomy beyond that. The animal can detect prominent features and can't make out fine details. Then the biologist says this shows eyes are adapted to the animal's needs. Where did we establish those needs?
What we’re looking for
What if fine detail were important to the jellyfish's survival? Then the blurry image wouldn't illustrate an eye doing exactly what the animal needs. To use this example as the biologist does, we have to connect its limited vision with its requirements: detecting prominent features meets a need, while detecting fine detail isn't needed. That's the missing assumption I'd look for.
Working the answers
- A
The argument doesn't need box jellyfish to be the only jellyfish with this feature. Other jellyfish could also have blurry vision, and this example could still support the claim if the box jellyfish's vision matches its needs. Uniqueness doesn't supply the missing information about those needs.
- BCorrect
This matches the animal's needs to the vision described. Box jellyfish need to detect prominent features, which they can detect, and don't need fine details, which they can't detect. Without that connection, an eye with limited vision could be failing the animal's needs rather than illustrating adaptation to them.
- C
Benefiting from sharper vision isn't the same as needing it. Something can be useful without being required. More importantly, the biologist doesn't have to assume that sharper vision would provide a benefit; the argument could work even if it provided none. C doesn't establish that the actual blurry vision matches the animal's needs.
- D
We don't need this particular history of development. The claim concerns how the box jellyfish's current eyes relate to its current needs. Whether its ancestors received clearer images doesn't tell us what it needs now, and the argument doesn't require such ancestors to have existed.
- E
Vision could help the animal in some way without being its main means of detecting prey. Perhaps another sense does most of that work. The argument needs a connection between the vision described and the animal's needs, not a ranking of the methods it uses to find prey.
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