Networks of blood vessels in bats’ wings serve only to disperse heat

Question

The Official Guide for GMAT Review, 11th Edition, 2005

Practice Question  
Question No.: CR 88
Page: 493 
Networks of blood vessels in bats’ wings serve only to disperse heat generated in ﬂight. This heat is generated only because bats ﬂap their wings. Thus paleontologists’ recent discovery that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings provides evidence for the hypothesis that Sandactylus ﬂew by ﬂapping its wings, not just by gliding.

Which of the following, if true, most seriously weakens the argument in the passage?

(A) Sandactylus’ wings were far more similar to the wings of bats than to the wings of birds.

(B) Paleontologists do not know whether winged dinosaurs other than Sandactylus had similar networks of blood vessels in the skin of their wings.

(C) The mechanism used by bats for dispersing heat in ﬂight could, in principle, work for much larger ﬂying creatures, such as Sandactylus.

(D) Not all the bats that use the mechanism described in the passage for dispersing heat in ﬂight live in climates similar to the climate in which Sandactylus lived.

(E) Other winged dinosaurs that ﬂew only by gliding had networks of blood vessels in the skin of their wings similar to those that Sandactylus had.

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GMATNinja · Accepted Answer

adkikani , thanks for the question and for explaining your thought process in detail! Let's start with the hypothesis : "Sandactylus ﬂew by ﬂapping its wings, not just by gliding." Did Sandactylus fly ONLY by gliding? According to this hypothesis, no. The "not just by gliding" part means that Sandactylus certainly may have incorporated gliding in its flight patterns. But, if this hypothesis is correct, then Sandactylus MUST have incorporated wing-flapping in its flight patterns. This hypothesis does not exclude gliding. However, the hypothesis specifies that gliding would not have been the ONLY means of flying. According to this hypothesis, Sandactylus definitely flapped its wings while flying, but it's okay if there was some gliding in there too. In other words, the hypothesis does NOT say that Sandactylus never used gliding. But it does say that Sandactylus used wing-flapping. Whether the wing-flapping was supplemented by gliding makes no difference to this hypothesis. Now what are we trying to weaken here? The hypothesis? Not quite... The author's conclusion is not simply, "Sandactylus ﬂew by ﬂapping its wings, not just by gliding." That's the hypothesis . The conclusion is that the "paleontologists' recent discovery that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings provides evidence for the hypothesis." So the author's argument is not simply focused on how the Sandactylus flew. Instead, the author is trying to make the case that the recent discovery provides evidence for the hypothesis described above. See the difference? It's very subtle, but extremely important. This is exactly what we are talking about in the "Improving your CR reading precision" section of the CR Guide for Beginners , which you're probably already very tired of reading.

Are we trying to weaken the hypothesis ? Not quite. Instead, we are trying to weaken the author's specific argument: Bats have networks of blood vessels in their wings, and those blood vessels disperse heat generated in flight. "This heat is generated only because bats ﬂap their wings." - This implies that if the bats did NOT flap their wings, then they would not generate the heat and thus would not need the blood vessels in their wings to disperse that heat. Paleontologists' have recently discovered that Sandactylus had similar networks of blood vessels in their wings. According to the author, that discovery provides evidence for the hypothesis described above. Bats only need the blood vessels because they flap their wings. But does that necessarily mean that similar blood vessels are evidence of wing-flapping? THAT is the argument we are trying to weaken. Give that some thought, and see if it helps with your POE!

Kurtosis · Answer

Question Type: Weaken

Argument: Sandactylus ﬂew by ﬂapping its wings, not just by gliding

(A) Sandactylus’ wings were far more similar to the wings of bats than to the wings of birds. - Opposite.

(B) Paleontologists do not know whether winged dinosaurs other than Sandactylus had similar networks of blood vessels in the skin of their wings. - We are not worried about winged dinos other than Sandactylus.

(C) The mechanism used by bats for dispersing heat in ﬂight could, in principle, work for much larger ﬂying creatures, such as Sandactylus. - Opposite.

(D) Not all the bats that use the mechanism described in the passage for dispersing heat in ﬂight live in climates similar to the climate in which Sandactylus lived. - Even if some bats use the mechanism live in climates similar to Sandactylus then it strengthens the argument.

(E) Other winged dinosaurs that ﬂew only by gliding had networks of blood vessels in the skin of their wings similar to those that Sandactylus had. - Correct.

Answer: E

sumit9125 · Answer

E
Assumptions - network of blood vessels is necessarily for heat dispersion during flapping. E attacks this point

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adkikani · Answer

GMATNinjaTwo   VeritasPrepKarishma   GMATNinja 
 generis

I can not understand PoE for A and C since in explanations, in OE it says that these two options strengthen the conclusion.

Since this is a weaken question, I first begin with what do I have to weaken:
I have to weaken the hypothesis that Sandactyus flew by using two mechanisms:
A. By flapping its wings
B. By gliding.
My correct weakener should try to claim: Sandactylus ﬂew ONLY by ﬂapping its wing OR ONLY by gliding. (1)
Or my correct weakener shall cast doubt on: Sandactylus does flyies by using either of two mechanisms. (2)
Does (1) and (2) mean the same?

How does author arrive at this hypothesis?
He believes on the results of the discovery of paleontologists that there are SIMILAR networks of blood vessels in skin of wings between Sandactyus and bats. How does similarity helps in arriving at conclusion?
Because network of blood vessels in wings of bat perform ONLY one function - to disperse heat that is generated when they fly. There is no other cause (bats flapping wings) that lead to effect (generation of heat)

So basically author tries to use evidence of similar networks of blood vessels in bats and Sandactyus to conclude that Sandactyus flew by flapping its wings apart from gliding used to fly.

Similarity of wings between birds and bats is not concern for me. As per argument, I am concerned with similar network of blood vessels between Sandactyus and bats. 
This option is out.

Knowledge of paleontologists is outside the scope of argument.

Mechanisms - I am not sure what is the mechanism here and how will affect the conclusion of flying by flapping wings or by gliding.
 Totally irrelevent to the argument. The argument talks about bats and Sandactyus , not different types of bats and Sandactyus

I am concerned with mechanism used by Sandactyus (flapping wings or gliding) for performing action of flying, not how OTHER WINGED DINOSAURS fly.

gmatexam439 · Answer

Networks of blood vessels in bats’ wings serve only to disperse heat generated in ﬂight. This heat is generated only because bats ﬂap their wings. Thus paleontologists’ recent discovery that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings provides evidence for the hypothesis that Sandactylus ﬂew by ﬂapping its wings, not just by gliding.

Which of the following, if true, most seriously weakens the argument in the passage?

(A) Sandactylus’ wings were far more similar to the wings of bats than to the wings of birds. -- Both birds and bats fly by flapping their wings. This doesn't weaken the argument

(B) Paleontologists do not know whether winged dinosaurs other than Sandactylus had similar networks of blood vessels in the skin of their wings. -- Other dinosaurs are out of scope

(C) The mechanism used by bats for dispersing heat in ﬂight could, in principle, work for much larger ﬂying creatures, such as Sandactylus. -- This would strengthen the argument that Sandactylus flew by flapping their wings

(D) Not all the bats that use the mechanism described in the passage for dispersing heat in ﬂight live in climates similar to the climate in which Sandactylus lived. -- Climate is out of scope

(E) Other winged dinosaurs that ﬂew only by gliding had networks of blood vessels in the skin of their wings similar to those that Sandactylus had. -- Correct. If their other dinosaurs that had similar blood vessels and that glided then this option would weaken the argument

AkshdeepS · Answer

(A) Sandactylus’ wings were far more similar to the wings of bats than to the  wings of birds.  Out of scope.

(B) Paleontologists do not know whether winged  dinosaurs other than Sandactylus  had similar networks of blood vessels in the skin of their wings.   Out of scope

(C) The mechanism used by bats for dispersing heat in ﬂight could, in principle, work for much larger ﬂying creatures, such as Sandactylus.   Strengthener. Out

(D) Not all the bats that use the mechanism described in the passage for dispersing heat in ﬂight  live in climates similar  to the climate in which Sandactylus lived.  Out of scope

(E) Other winged dinosaurs that ﬂew only by gliding had networks of blood vessels in the skin of their wings similar to those that Sandactylus had.  Correct. Weakens the conclusion.

VerbalBot · Answer

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Networks of blood vessels in bats’ wings serve only to disperse heat

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