#8 - Biologist: Marine animals known as box jellyfish have

[Administrator]

Complete Question Explanation

Assumption. The correct answer choice is (B)

In this stimulus, the biologist tells us how a box jellyfish sees. Although the lenses of the jellyfish’s eyes are well-formed and so could produce “sharp images that reveal fine detail,” the far-forward placement of the animal’s retinas prevent such sharp vision. Instead, the jellyfish is able “to receive only a blurry image that reveals prominent features of objects but not fine detail.” Based on this information, the biologist reaches a broad conclusion, that instead of being adapted to “some abstract sense of how a good eye would be designed,” eyes are adapted “only to an animal’s needs.”

We know from the question stem that this is an Assumption question. Since there is information that appears for the first time in the conclusion, i.e., “eyes are adapted only to an animal’s needs,” we classify this as a Supporter Assumption question. The correct answer choice will link this new information to the premises.

It is apparent from the stimulus that the biologist does not consider the box jellyfish’s eyes to be well-designed, since the potential of its lenses are defeated by the placement of its retinas. If the biologist concludes from this example that eyes are adapted to an animal’s needs, and the box jellyfish can see “the prominent features of objects but not fine detail,” then it must be the case that the biologist thinks the box jellyfish needs to see “the prominent features of objects but not the fine detail.” Our prephrase is that the correct answer choice will describe this need of the box jellyfish.

Answer choice (A): The argument’s conclusion was general, describing how an animal’s eyes are adapted. Whether the box jellyfish is the only kind of jellyfish with retinas that do not focus clearly does not tell us anything about how an animal’s eyes are adapted to need. This answer choice is not required for the conclusion to be valid, nor is it even relevant to the conclusion.

Answer choice (B): This is the correct answer choice because it addresses the visual need of the box jellyfish, consistent with the biologist’s conclusion that the jellyfish’s eyes developed by means of adaptation to that need. If it were not the case that box jellyfish needed to detect prominent features but not fine details, then the conclusion would be proven invalid.

Answer choice (C): Since the biologist’s argument had to do with the jellyfish’s need rather than what would benefit the animal, this answer choice is irrelevant to the conclusion and is incorrect.

Answer choice (D): This answer choice could strengthen the conclusion, but is not required for it to be valid. First, it is not required, because we do not need to know the retinal capacity of the box jellyfish’s evolutionary predecessor to reach the conclusion that the animal’s current retinal structure emerged in response to the animal’s need. At the same time, it could strengthen the conclusion by indicating that although the animal at one time had a better constructed retina, that biological feature disappeared because it was no longer needed.

Answer choice (E): Here, the answer choice could be tempting because it indicates that box jellyfish rely on their vision to detect prey. However, that reliance is not necessary for the conclusion regarding adaptation, because it does not tell us that in detecting their prey the box jellyfish need to see prominent features of objects but not fine detail.

[LSAT1802017]

Is there a causal assumption in the argument as well?

[Eric Ockert]

Hi!

Potentially, yes, there could be some causal assumptions here as well. Remember, most arguments make multiple assumptions, and when dealing with an Assumption question, the correct answer only has to touch on one of these assumptions.

In the case of causal assumptions, typically these fall on the Defender Assumption side of things. Since the principal flaw in most causal arguments on this test is that the author fails to consider some alternate explanation for the relationship observed, that means these authors must assume that any other possible explanation does not exist. Often, this is exactly the kind of correct answer you see on Assumption questions with a causal argument in the stimulus. But it doesn't have to be. It's good to be aware of this common pattern, but don't the pattern will always be present.

Hope that helps!

[teddykim100]

Hi!

I understand the other answer choice explanations, however I am confused as to why D COULD potentially strengthen the conclusion.

is it because developing a retina that receives less clear images from its previous ancestors implies that an evolutionary advantage has occurred? and therefore that is why it might be seen as a "need"? If that makes any sense. . .

basically, I do not see how choice D could strengthen the argument's missing link, which is that box jellyfish have a need of seeing prominent features, but not fine details.

thank you!

[Robert Carroll]

teddykim,

Our explanation that answer choice (D) "could strengthen" the conclusion is not intended to identify anything good about the answer, but instead to indicate that, at best, this answer strengthens without being an assumption necessary, so at best, it's still wrong. The interpretation involves the assumption that adaptations will continue to better serve species' needs, so if the box jellyfish adapted away from receiving clear images, that adaptation is presumed to better fit its needs. Because that itself involves a questionable assumption, we certainly wouldn't want to pick this answer for an Assumption question, and the issue of whether the answer strengthens is irrelevant. So don't worry too much about it.

Robert Carroll