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

Question

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.

The argument in the passage relies on which of the following assumptions?

(A) Sandactylus would not have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.

(B) All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.

(C) Winged dinosaurs that flapped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.

(D) If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.

(E) Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.

Similar Question  :  LINK 1   LINK 2

GMATNinja · Answer

It doesn't matter whether  all  creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings. The author is simply arguing that the discovery " provides evidence  for the hypothesis that Sandactylus flew by flapping its wings." For example, not EVERYONE who has a fancy car has a lot of money. However, having a fancy sports car can still be  evidence  that someone has a lot of money.

If choice (D) were not true, we would have: "If Sandactylus flew by flapping its wings, then paleontologists  might  be able to find some evidence that it did so." The author argues that the discovery provides evidence for the hypothesis that Sandactylus flew by flapping its wings. This argument does not require that, if Sandactylus did in fact fly by flapping its wings, paleontologists would DEFINITELY find evidence that it did so. (D) is not a required assumption.

I hope this helps!

zoezhuyan · Answer

Hi  mikemcgarry ,  GMATNinjaTwo ,  GMATNinja ,  MagooshExpert  Carolyn,  sayantanc2 , VeritasPrepKarishma 
it took me many hours to review this question.

First , i have no idea where is my reasoning wrong?
(E) Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.

E is bit complex, i simplify E, 
flapping generats heat, and the heat CANNOT be dispersed without blood vessels.
in other word, no blood vessel , no dispersed heat.
it meants blood vessel is necessary to dispersed heat generated by Sandactylus in flapping.
because Sandactylus has blood vessel, so it can disperse heat generated in flapping, then provide the evidence that sandactylus flew by flapping its wings,not just by gliding.

second 
if negate E,
(E) Heat generated by Sandactylus in flapping its wings in flight  could not   COULD  have been dispersed by anything other than the blood vessels in its wings.
then negative (E) means there are other ways to disperse the heat generated by flapping.
so whether sandactylus has blood vessels does not provide evidence for the hypothesis, 
Does it weaken ? 
I think it does weaken.

BUT E is incorrect.

I think i must be wrong, but i have no idea where.
Please point out.

mostly, Assumption questions cost me lots of time and energy and i barely get right choice.

Genuinely your help.

Have a nice day
>_~

KarishmaB · Answer

Not sure if you have seen my previous post which discusses exactly why (E) is not the answer. Let me give it again here:

let's try to understand how the argument is structured. I will use variables to make it easier:

Networks of blood vessels in wings - A 
heat generated in flight by flapping wings - B

Given Argument:
Bats have A. Bats have B. A's only job is to get rid of B. 
Dinos had A too. Hence, Dinos had B too.

What is the assumption? That A must have had a purpose in Dinos too (getting rid of B). You cannot have A without having a job for it. Just because Dinos had A, we are concluding that they must have had B too. We are assuming that A must have had a purpose. This is option (A) and is the answer.

Are we assuming that we cannot get rid of B without A? No. (This is what option (E) says)
When would this be the assumption?
If the argument were a little different: Dinos had B. Hence, Dinos had A too. 
In this argument, we are assuming that presence of B implies presence of A to get rid of B. The assumption is that we cannot get rid of B without A.
But given the original argument, this is not the assumption. Hence, answer is not (E).

Does this help?

zoezhuyan · Answer

Hi  mikemcgarry ,  GMATNinjaTwo ,  GMATNinja ,  MagooshExpert  Carolyn, @sayantanc2,@VeritasPrepKarishma
i think i got one of my reasoning problems , but new question came up , genuinely need you help to confirm.

here is my incorrect reasoning 
because Sandactylus has blood vessel, so it can disperse heat generated in flapping, then provide the evidence that sandactylus flew by flapping its wings,not just by gliding.-- is  incorrect.
 
 Please check following 
 (E) Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.

up to there, i hold my reasoning

here, i think my reasoning --because Sandactylus has blood vessel, so it can disperse heat generated in flapping, then provide the evidence that sandactylus flew by flapping its wings,not just by gliding.-- is incorrect.
 i reviewed the following

so i think E is a  necesary assumption , in other words, blood vessel is necessary assumption to dispersed heated generated by flapping
if sandactylus has blood vessels, it maybe dispered heated generated by flapping, maybe not.

So my rasoning is incorrect.

Wait a minute, a new problem, 
according the stimulus,  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. 
 Can i  then get that  Sandaytlus can disperse heat generated in flapping, then provide the evidence that sandactylus flew by flapping its wings, not just by gliding ?

Further confused  between assumption, necessary assumption.
Is necessary assumption a branch of assumption?
An assumption is unstated something that the author must believe to be true in order to draw a certain conclusion
Does it mean if the assumption happens, it can lead to the conclusion?
A is necessary for B, if A doesn't happen, then B would not happen. 
 necessary assumption is a branch of assumption?

i am still confused the following :

All, please help,

Thank in advance 
Have a nice day
>_~

KarishmaB · Answer

We are on the same page - they did first discover blood vessels in wings. This discovery led to hypothesis - "they must be flying by flapping wings". 
Think why? Just because they know that bats have blood vessels and the only purpose of those is to disperse heat generated by flapping wings in flight.
So they assumed that blood vessels in wings must have a purpose. They also assumed that the purpose must be the same as that in bats.

Did they have to assume that heat generated could not have been dispersed by any other way? No. That would have been your assumption had they found out that heat is generated by flapping and then tried to conclude that they MUST have had blood vessels. Here the assumption is that there is no other way to disperse heat.

By negating (E), you are discussing what happens when you KNOW that they generate heat by flapping wings. But we don't know that so it is irrelevant. Don't get lost in it.

See what happens when you negate (A) - Blood vessels may not have had a purpose. Then the whole conclusion falls apart.

Hence (A) is the answer.

duybachhpvn · Answer

Hi,

Could you help with my reasoning on negating option B? I'm not sure which of the below negation is correct

"NOT ALL creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings" --> If I negate like this, then the conclusion does not fall apart as some creatures that can fly by flapping their wings may still have the blood vessels, and thus B is not the answer

However, if the negation is :"All creatures that fly by flapping their wings DO NOT have networks of blood vessels in the skin of their wings", then this mean that if the Dinos have blood vessels in the skin of their wings, they CANNOT fly by flapping their wings, and therefore the Conclusion is no longer true --> B is the assumption needed

What is wrong with my negation reasoning here?

MartyTargetTestPrep · Answer

Interesting question.

I think the emphasis of a sentence that begins with "all" is on the fact that all members of a set have the characteristic. So, the most logical negation of the sentence is the one with "NOT all."

So, your first negation makes more sense.

Another thing to consider here is that the passage states as fact that bats have networks of blood vessels in their wings and flap their wings. So, your second negation conflicts with the facts presented and, therefore, cannot be true within parameters of this scenario.

Overall, while the negation test can be useful, your best bet is to combine the use of the negation test with the use of some general analysis of the logical relationship of an answer choice with the argument presented in the passage. By doing so you gain a holistic perspective of that logical relationship and, thus, are more likely to avoid choosing an incorrect choice.

Pankaj0901 · Answer

AndrewN  - Can you please help answer my above question? Thank you in advance.

AndrewN · Answer

Funny,  Pankaj0901 . You must be the third person in about as many days to ask me to comment on the negation of an answer choice, when I myself do not employ this technique. If I were negating answer choice (E), however, I would alter it slightly from what you have turned it into above:

(E) Heat generated by Sandactylus in flapping its wings in flight could  not  have been dispersed by  something  other than the blood vessels in its wings.

You have to keep in mind, the argument is not based on proving or supporting the hypothesis itself. Such a concern goes beyond the scope of the argument. Rather, it is saying that  networks of blood vessels in the skin of its wings provides  evidence  for the hypothesis . In other words, the very presence of the networks of blood vessels in the skin of the wings of this dinosaur is good enough for the speaker/writer of the content of the passage. Besides, even if some other mechanism existed to disperse heat, the hypothesis could hold (maybe the blood vessels were the primary means of dispersing heat, or perhaps they helped provide support to a main system to disperse even more heat). In short, answer choice (E) addresses the wrong part of the argument, a detail, when we are looking for a necessary link from the premise to the broader argument.

Thank you for thinking to ask. When I looked at the question last November, I apparently answered correctly in 1:10; this time I probably looked at the options for three minutes before I went with (A). (Go figure.)

- Andrew

Nina1987 · Answer

KarishmaB ,  GMATNinja ,  GMATNinjaTwo ,  IanStewart ,  MartyTargetTestPrep ,  MarkSullivan ,  AjiteshArun ,  EMPOWERgmatRichC ,  mikemcgarry ,  DmitryFarber ,  chetan2u ,  sayantanc2k ,  TommyWallach

So essentially option E - Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings  is, what we call in LSAT parlance, a mistaken reversal of the first sentence in the passage,  "Networks of blood vessels in bats' wings serve only to disperse heat generated in flight"  
So, we know that E i.e. a mistaken reversal can never be an inference drawn from an argument. But can we also conclude that a mistaken reversal or a false inference can never be an assumption? Thanks

KarishmaB · Answer

I would suggest you to not use LSAT terminology in GMAT. GMAT questions are far simpler and predominantly based on logic. 
Note here that we are not given the 'If A, then B' structure here. We have assumed it. Option (E) is a case of mistaken reversal, but of our conclusion.

What we are given:

Networks of blood vessels in wings - A 
heat generated in flight by flapping wings - B

Premise: Bats have A. Bats have B. A's only job is to get rid of B. 
Assumption: If one has A, then one has B (If one has A, it must have a function and that would be B)
Conclusion: Dinos have A so dinos have B.

Option (A): If one has A, it must have a function
Option (E): Dinos have B so dinos have A. This is neither implied, nor our assumption. For our argument, 'what happens if you have B' is out of scope.

chetan2u · Answer

StandardizedNerd

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.

Argument: Networks of blood vessel ->  ONLY to disperse heat  ->  Heat is ONLY because of flapping of wings 
Same networks found in Sandactylus wing, so  hypothesis - Sandactylus flew by flapping its wings-  is strengthened.

The argument in the passage relies on which of the following assumptions?

A) Sandactylus would not have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.
 After going through all options, I would stick to this option as all other are way off the mark. 
This assumption would have been more appealing if somewhere in the argument, it could have mentioned that the purpose of these networks is ONLY to dissipate heat. The argument does stress on ONLY but only in case of the bats. We have to stretch that to Sandactylus too. 
Nevertheless, there is no other better option.
 
B) All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.
 We are looking for the opposite .
'All creatures that have networks of blood vessels in the skin of their wings fly by flapping their wings' would be a perfect assumption.

C) Winged dinosaurs that flapped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.
 Effectiveness  - we are not comparing the efficiency of flights.

D) If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.
 The paleontologists are doing a great job . But how is it connected to  network of blood vessels  pointing towards  flapping wings .

E) Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.
 This would surely help incase argument was about proving that Sandactylus had blood vessels in its wings.  But here WHAT(Heat generated by Sandactylus in flapping its wings) we are using to prove something else is exactly what we require to prove.

Although A leaves room for a bit of error, there is no better choice than A.

abhinavbohra · Answer

KarishmaB 
I am confused between A and D

A) The problem with this answer option is that it does not talk about flapping. It says if blood vessels exist, then they must be of some use. But that 'use' can be anything, right? The option does not state that they are used for 'flapping'

D) On negating this answer option, we get - If P then Q, where 
P = Sandactylus flew by flapping its wings
Q= paleontologists would NOT be able to find some evidence that it did so.
But we know that they have found some evidence, i.e. ~Q is true. This implies that P is not true, which breaks the argument that Sandactylus can fly by flapping wings.

KarishmaB · Answer

The blood vessels exist in the wings. If they must be of some use, that use must have something to do with how the wings are used.

The assumption is that the blood vessels cannot exist without any use.

Negate (A): S could have blood vessels in wings without any use. 
Then can we say that S flew by flapping wings? No. We are relying on the info that there are these blood vessels in the wings to say that they must have flapped their wings. But what if the blood vessels can just exist without any use. Then we cannot say that they must have existed because S flapped their wings. 
Negation of (A) breaks our conclusion and hence is the answer.

(D) doesn't have much relevance. 
If says that if S were flapping their wings, then paleontologists would find some evidence that they did so.
Negate it: if S were flapping their wings, paleontologists may not find some evidence that they did so.

The negation of 'would find' is 'may not find.'
It is like 'I am certain' vs 'I am not certain'

Option (D) doesn't have any impact on our conclusion.

ifyouknowyouknow · Answer

Hey experts. I am really torn between A and B. Upon negating option B we get "no creatures that fly by flapping their wings have network of blood vessels in the skin of their wings". I think this fails the argument. The only reason I think its wrong because it also counters premise in the argument that "bats have blood vessels to dissipate heat". Is there something I am missing?

Thank you.

Thank you.

KarishmaB · Answer

I have discussed this question in this video: https://youtu.be/ZQnhC4d5ODU Also note that option (B) does not counter any premise but it is not correct. Argument: Bats have blood vessels... because they are needed to disperse heat ... because bats fly by flapping wings Dinos have blood vessels... Now we are concluding that dinos must have flapped their wings too. So we are assuming that their blood vessels were needed to disperse heat and that heat was created by flapping wings. In a way we are assuming that anyone who has blood vessels in wings must fly by flapping wings. Option (B) says that we are assuming that anyone who flies by flapping wings has blood vessels. Note that this is not our assumption. It is the reverse. Also, negation of 'all' is 'not all.' It is not 'none' All will come. Negation: Not all will come. means there will be some who will not come.

siddharth_ · Answer

Gave this as a prompt to ChatGPT and even it marked E as the correct answer. I told it that the OG answer was A, so it gave me another explanation as to why A is correct and E is incorrect. On further pointing out that it was contradicting itself, it gave the following explanation. Might be useful for folks juggling between A and E.

Adit_ · Answer

Its all a game of pre thinking, you can save a lot of time if you get it right!
The stem's entire point is Blood vessels-->responsible for heat-->happens ONLY when u flap wings
Conclusion: This creature-->flaps its wings and not glides
This means when it flaps the blood vessels disperses heat so hmm, the conclusion says the it is for sure flapping which means you are assuming that it is for sure dispersing heat as well 
which thus means if it was there, the creature is using it for sure, if it does not use it then u cant really say that its ONLY flapping.

Hence  option A

I more or less predicted the direction of the stem so as soon as I saw option A I knew it was perfect and chose it as it lined directly with my pre thinking.

Bunuel  is that a right approach in such assumption situations where there cant be too many straightforward assumptions, that we can go with our pre thinking and save time?

rutikaoqw · Answer

I was confused between A and B. I am now clear why A is the one.
I have a question to link my understanding to why B I was finally able to eliminate, but I need to check if that understanding is correct:
The passage says: Because there were nerves, there was flapping.
Option B says: All flappings have nerves
If option B would have said, all creatures with nerves under wings, flap, then it would have been correct ?
Am i thinking in the right direction ? Please let me know.  KarishmaB   MartyMurray

guddo · Answer

Yes, you’re thinking in the right direction.

The argument needs:  if Sandactylus has those vessels, then  that points to flapping .  So a statement like “all creatures with those vessels flap” would make the inference much stronger.

Option B is the reverse: “all flappers have those vessels.” That does  not  let you conclude flapping from vessels, because the vessels could also show up in non flappers.

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

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

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