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

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?

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
>_~

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.

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?

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.

VeritasKarishma
can i go by only if A ,then B logic here
can i say
only if dispersion of heat required,then network of blood vessels exists
which means
if dispersion not required ,then no blood vessles

A) says they would not have blood vessels if they are of no use(i.e no dispersion as dispersion is their only use)
is the application only if A ,then B logic here
done correct by me ?

Yes. The only if logic has been used here for another question with the same structure:
https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2012/1 ... tatements/

The correct answer is option (A).

Understanding the passage:

Bats flap their wings in flight -> this causes heat to be generated -> networks of blood vessels in the bat's wings disperse this heat.

The passage states that heat is generated only because bats flap their wings, and this network of blood vessels exist, only for the purpose of heat dissipation. i.e. no other reason for heat generation, and no other reason for existence of blood vessels.

Recent Discovery: Sandactylus (a winged dinosaur) had similar networks of blood vessels in their wings

Hypothesis of the paleontologists (in this case, also the conclusion of this argument): Sandactylus flew by flapping its wings, not just by gliding.

Logic of the hypothesis: Because we have seen that such networks existed only to dissipate heat caused by flapping of the wings during flight in bats, the existence of these networks should mean that Sandactylus too, flew by flapping its wings.

Thought Process:

An assumption is that implicit thought which is not stated, but has to be true for the conclusion to hold true. So, if an assumption is not true (negated), then the conclusion should break. A failsafe way to identify the assumptions is to identify the conditions under which the conclusion would definitely break.

So, let us falsify the conclusion:

In what scenario would Sandactylus not fly, by flapping its wings?

Condition: What if unlike bats, in Sandactylus, the blood vessel networks in the wings did not serve any purpose i.e. they just existed (like a vestigeal entity)? Then, the existence of blood vessel networks is not proof of heat generation, which implies we cannot definitely say that Sandactylus flapped its wings to fly. This condition will actually break down our conclusion.

Hence the Assumption is: It is not possible that Sandactylus had networks of blood vessels in its wings, unless they served some purpose.

Let us look at the option choices.

(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.

This statement uses different words to convey the same meaning as our assumption! This essentially means that the blood vessels served some purpose for Sandactylus. From the passage, we know that the only use blood vessels served was to dissipate heat, which is proof of wing flapping.

We can negate this option to double check - if the blood vessels served no purpose, then we can not say that it was used to dissipate heat generated by flapping of wings. We can not definitely say then Sandactylus flew by flapping their wings. Hence, this assumption is the correct one.

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

Even if this is true, this does not mean that Sandactylus flew by flapping their wings. All A has B, does not imply that All B has A.

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


Irrelevant. Effectiveness of flight has nothing to do with our conclusion.

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

Paleontologists already found some evidence (the blood vessels). This option also, has no real impact on the conclusion.

(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.

Interesting choice. But this is also incorrect.

Let us say Heat generated = A; Blood Vessels = B Any other means of heat dissipation = C.

The assumption is A can be dispersed only by B, not by C.

Negated assumption: A can be dispersed by B and C.

Even if this is true, from the passage, the sole purpose of B is to dissipate A. So, existence of B will imply presence of A. Or in other words, as long as blood vessel networks exist for the sole purpose of heat dissipation, heat dissipation and therefore, flapping of wings for flight can be inferred based on the passage logic. The presence of other heat dissipating means (C) will not make any difference to the conclusion drawn.

Hence, this is not the correct option.

Cheers!

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.


Bats
P1)
function => ONLY to disperse heat

P2)
Cause effect
Only flapping -> heat is generated.

Evidence of similar network in Dino.
Conclusion: Dino flew by flapping

Assumptions: What is relevant for Bats is relevant for Winged Dons.
1) ONLY Flapping produces heat in dinos just as in bats.
2) The network functions ONLY to dissipate heat/not help them fly or any other function.

E) ONLY network can dissipate heat
Wrong
Would be correct if Premises were
[only] Networks of blood vessels in bats' wings serve to

A) IF networks were of no use, dinos would not have them. (In line with 2)
Contra Dinos have them -> networks are of use.
We know that Dinos have them as per evidence.
These networks should have atleast 1 function in line with assumption 2 i.e. to dissipate heat.
Before these networks can have this function as the ONLY function

If networks don’t even have a single function, how can they have an ONLY function

Negate
Dinos have them -> networks are not of use.
Breaks

Took me 10 minutes. I really wanted to understand what the argument was about. And that's key to answering this question. Once you figure that out...you won't be tempted by the devil into choosing E, the main antagonist in this problem.

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.
Correct …suppose the networks were of no use (i.e. they didn’t disperse the heat generated from flight)…then the hypothesis is ruined…

(B) All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.
-we know that the Sandactylus has networks of blood vessels in its wings…
-not the 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.
-this talks about the effectiveness of flight using flapping…strengthens the argument, but not the assumption

(D) If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.
-this is a conditional expressing uncertainty, that if true, would strengthen the hypothesis by providing evidence for the species’ flapping

(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.
-tempting choice…this is just a justification for the presence of networks of blood vessels in the skin

Networks of blood vessels in bats' wings(N) serve only to disperse heat generated in flight. (H)
N---> only H
This heat is generated (H)only because bats flap their wings(F).
H---> only F
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.
Found N--> Its means F

Given: Only F ---> H ---> N + others
Found: Because N--> so must b F

Assumption: It means F leads to H and H must have lead to N.


(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.
N only for F- yes
If no then it must be of no use because N is used only for H
Correct

(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.
H can lead to N , H can also lead to others . Because only network is responsble for H, but H can be bring to N and anything else
Hence incorrect

Thank you KarishmaB for you nice explanation.

Recently i have learnt about Necessary Assumption and sufficient Assumption from one of your posts. Since then I have been trying understand the differences between them and how they work. My understanding is Necessary Assumption is the minimum qualifying assumption that author must made to reach his/her conclusion. It may or may not ensure the authenticity of the conclusion. whereas Sufficient Assumption, validifies the conclusion, sometimes extending to a degree not needed to reach author conclusion. Now my question is whether option B and E fall into the Sufficient Assumption category?

Sorry for my choice of words. Hope you understand my point.
Thanks in advance.

Thanks in advance.

While I understand the logic and rationale behind the correct option A, I have a small doubt with respect to the NEGATION technique as it is very useful to eliminate SUFFICIENT assumptions (trap option choices) in order to arrive at the NECESSARY assumption (correct answer choice). I would just request an expert to VALIDATE if my understanding and interpretations are correct. I have had great learnings from this official question, I just don't want to TAKE AWAY something WRONG.

My question is: What is the correct NEGATION (And, the correct INTERPRETATION of the NEGATED statement) of OPTION E?

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.

NEGATED Option (E):
Heat generated by Sandactylus in flapping its wings in flight COULD have been dispersed by anything other than the blood vessels in its wings.

Now, I am trying to interpret the above negated sentence:

Interpretation 1: Heat generated could be dispersed by anything other than blood vessels INCLUDING blood vessels?
=> Heat generated by flapping of wings could still be dispersed by Blood vessels. And, since the presence of blood vessels STILL implies that dinos fly by flapping wings, the negated statement is NOT completely WEAKENING the conclusion. The Option E is not a NECESSARY Assumption.

Interpretation 2: Heat generated could be dispersed by anything other than blood vessels EXCLUDING blood vessels?
=> The conclusion that "the presence of blood vessels implies flapping of wings" WILL be WEAKENED. Hence, Option E will be a NECESSARY ASSUMPTION.

Since, as per the OA, Option E is not the Assumption, Interpretation 1 is the clear WINNER. Interpretation 2 is Wrong.

Thanks in advance!

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

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

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

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.