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# Biologists suspect that feathers are modified scales.

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Biologists suspect that feathers are modified scales. [#permalink]

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22 May 2011, 11:57
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Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

The argument above relies on which of the following assumptions?

A. A characteristic developed for a particular ability does not remain after that ability is lost.
B. Some animals that are able to fly lack feathers.
C. Feathered dinosaurs that were able to fly also used their feathers to regulate body temperature.
D. Today’s flightless birds are direct descendants of feathered reptiles.
E. Without the ability to regulate their body temperature, flightless birds will go extinct.

I thought the answer is D. Can anyone help me understand why A also fits the bill?
[Reveal] Spoiler: OA

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Re: Ancient reptile(Question from TMH's verbal guide): Need help [#permalink]

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22 May 2011, 12:40
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Explanation given in the book:

Answer: A. This is an assumption question. Its conclusion and premises are:
Premises: (1) Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. (2) Many of these early feathered reptiles were unable to fly.

Conclusion: Today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

This argument uses the fact that many early feathered reptiles were unable to fly to conclude that flightless birds developed their feathers for the same reason. But it must be assuming that the feathers did not develop for some other reason. Perhaps the feathers developed first for flight, but the birds eventually lost that ability. Choice A correctly states the assumption of the argument because it indicates that the flightless birds did not develop the feathers for an ability that they now no longer have. Choice B does not address the link between the feathers of flightless birds and the feathers of reptiles. Choice C doesn’t deal with flightless birds at all, so it cannot be correct. Choice D may be true, but it is not an assumption of the argument. The argument is only concluding why the flightless birds developed their feathers, not where they came from. Choice E is new information and not part of the argument.

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Re: Ancient reptile(Question from TMH's verbal guide): Need help [#permalink]

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02 Nov 2011, 08:58
IMO-A,

Conclusion is- today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

Premise- Ancient reptiles developed feathers as a way to insulate their bodies and many of these early feathered reptiles were unable to fly.

Option A clearly explains why Biologists suspect that feathers are modified scales
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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20 Sep 2013, 08:32
Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

The argument above relies on which of the following assumptions?

A. A characteristic developed for a particular ability does not remain after that ability is lost.
B. Some animals that are able to fly lack feathers.
C. Feathered dinosaurs that were able to fly also used their feathers to regulate body temperature.
D. Today’s flightless birds are direct descendants of feathered reptiles.
E. Without the ability to regulate their body temperature, flightless birds will go extinct.

Premises: Ancient reptiles with feathers for holding body temperatures.
Conclusion: flightless birds' feathers as a way to manage body temperatures.
Assumption: MUST BE TRUE that a developed characteristic holds its purpose, otherwise will disappear. Flightless birds' feathers are for holding body temperatures, not for flying.
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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30 Jun 2014, 01:29
One can easily get to the correct option by POE.

Option B - Some animals that are able to fly lack feathers. -- Not relevent to the argument
Option C - Feathered dinosaurs that were able to fly also used their feathers to regulate body temperature. - Irrelevant
Option D - Today’s flightless birds are direct descendants of feathered reptiles. - way to Extreme statement
Option E - Without the ability to regulate their body temperature, flightless birds will go extinct. -Irrelevant-

Hence Option A is correct
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Biologists suspect that feathers are modified scales. [#permalink]

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08 Jul 2015, 18:12

My justification for (A) over (D) is different from other members on here, and I argue that others' justification for (A) is incorrect. Here's why:

A. A characteristic developed for a particular ability does not remain after that ability is lost.
vs.
D. Today’s flightless birds are direct descendants of feathered reptiles.

In the end, both work, but I'd argue that "flight" is too much to assume and is not necessary for the statement to hold true. There are four strong cases for this:

1. Red herring: Sentence (A) and the passage never refer to flight anywhere, hence the find the assumption question. However, it never refers to birds in general (both flying and flightless birds) for the assumption of flying birds to be relevant. E.g., if we compare hairy ancient reptiles to today's hairy apes, and say that these two very different species share hair because it has to do with body temp regulation, then does that having anything to do with today's humans who have only a little bit of hair for a different reason, perhaps to keep water, dirt, etc. from entering our eyes and other orifices? Bringing in the outside info of humans benefiting from hair in a different way is unnecessary. Similarly, today's flying, feathered birds are unnecessary. Assuming the combination of flight and feathered birds is a red herring, no pun intended.

2. Begs the question: if body temp is the main reason for feathers, then why are feathers necessary for flying, which is a completely different, mutually exclusive trait; then why didn't flightless birds lose their feathers if they lost the ability to fly? Because feathers came from ancient flightless reptiles to control body temp? Then why do flying birds still have feathers if its purpose of body temp regulation may have been lost, and feathers somehow remained over millions of years in a state of uselessness until the benefit of flight happened to come along? If flying birds also use feathers for body temp in a dual purpose sense, then the body temp benefit is never lost, but then why do flightless birds still have wings if that's for flight?

3. Contradiction: You don't know that flightless birds are directly descended from today's feathered flying birds. The strong language of "direct" is precisely why we didn't choose (D). So, why should be apply the same language between the relationship of today's flying and flightless birds? It's equally unjustified, which is why the genesis theory of flightless birds' feathers is made in the first place.

4. If-then transposition rule: Note that if A then B = if not B, then not A. If we would have chosen (D) save for its strong language, and if (A) says the exact same thing as (D) by way of if-then logic (again, minus the use of "direct"), then (A) must be chosen for the same reason as (D).

______________________________________________________________________________________________

More details...

For (A), I can see the argument that flightless birds will lose their feathers if they lose their ability to fly, since there's no use for them. But, who says that the biologist is necessarily assuming that? What if the biologist believes that the flightless birds were a different branch of evolution from the ancestors of birds? So, say scaled flying birds developed into two distinct groups: flying feathered birds and flightless feathered birds. Both develop feathers independently, which is a possibility.

(D) can be read as "If today's flightless birds have feathers, then ancient reptiles are directly related because they have feathers, too." I see option D as making too strong of a claim, that today's featherless birds are direct descendants of feathered reptiles, which cannot be inferred (for instance, ancient reptiles and today's flightless birds may share a common ancestor that had feathers, but the two may only be related indirectly by way of the ancestor (= evolutionary fork in the road). And, the language of the passage seems to reinforce that today's flightless birds are very different from ancient feathered reptiles.

Option A is sort of saying D by negating it. So, negative of (D) is, "If not for the feathers on ancient reptiles, then no feathers on today's flightless birds." Notice I dropped the strong word, direct.

There is a transposition rule of logic that comes in handy here: If X, then Y = If not Y, then not X.

So, A reads as: "If not feathers on ancient reptiles (-Y), then trait is lost and not feathers on today's flightless birds (-X). Feathers do exist on today's flightless birds and trait is not lost (+x), then it must have come from ancient reptiles." A is exactly the same as D but differs in that it doesn't use as strong a language.

So, our justifications for (A) differ by placing a higher priority on the following assumptions:

- Mine: Animals are more likely to carry the same traits as very different species through direct or indirect genetic inheritance, and not as likely to develop the same trait for the same purpose independently.

vs.

- Others: Birds can have a dual purpose for feathers (flight and body temp regulation), whether both are primary, one is secondary, or body temp regulation became a sort of unintended benefit for flightless birds so they found a use after losing their ability to fly.
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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26 Feb 2016, 06:40
retro wrote:
Explanation given in the book:

Answer: A. This is an assumption question. Its conclusion and premises are:
Premises: (1) Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. (2) Many of these early feathered reptiles were unable to fly.

Conclusion: Today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

This argument uses the fact that many early feathered reptiles were unable to fly to conclude that flightless birds developed their feathers for the same reason. But it must be assuming that the feathers did not develop for some other reason. Perhaps the feathers developed first for flight, but the birds eventually lost that ability. Choice A correctly states the assumption of the argument because it indicates that the flightless birds did not develop the feathers for an ability that they now no longer have. Choice B does not address the link between the feathers of flightless birds and the feathers of reptiles. Choice C doesn’t deal with flightless birds at all, so it cannot be correct. Choice D may be true, but it is not an assumption of the argument. The argument is only concluding why the flightless birds developed their feathers, not where they came from. Choice E is new information and not part of the argument.

Rgds
Rahul

Still struggling to understand why the early reptiles morphed their feathers to scales ? Weren't the feathers supposed to stay in these reptiles as per choice A ?
Those reptiles would still need way to insulate their bodies from the cold and regulate their body temperatures - and feathers were doing that...
So how can one justify the assumption : A. A characteristic developed for a particular ability does not remain after that ability is lost.? Reptiles would still insulate their bodies from the cold and regulate their body temperatures...
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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16 Jun 2016, 10:58
retro wrote:
Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

The argument above relies on which of the following assumptions?

A. A characteristic developed for a particular ability does not remain after that ability is lost.
B. Some animals that are able to fly lack feathers.
C. Feathered dinosaurs that were able to fly also used their feathers to regulate body temperature.
D. Today’s flightless birds are direct descendants of feathered reptiles.
E. Without the ability to regulate their body temperature, flightless birds will go extinct.

I thought the answer is D. Can anyone help me understand why A also fits the bill?

A says characteristic (feathers) does not remain after ability (flying) is lost.
But the argument says feathers are retained in flightless birds though the ability is lost
How can it be an assumption
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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15 Aug 2016, 15:04
The premise talks about reptiles and conclusion says about birds, so only assumption that joins both is Option D.

Option A is far way assumption which requires more other assumptions not striaght away related to the argument.

Will you please let us know the source of it, because still not able to get convinced or clear why Option A is better than Option D.
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Biologists suspect that feathers are modified scales. [#permalink]

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25 Aug 2016, 01:33
Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

Scope of the question stem : flightless birds
We have to prove :

today’s flightless birds didn't developed their feathers as a way to manage their body temperatures.

However, many of these early feathered reptiles were unable to fly. - I didn't consider this to arrive at my assumption. The ability - Managing their body temperature.

The argument above relies on which of the following assumptions?

A. Negate A :- A characteristic developed for a particular ability does remain after that ability is lost.

so feathers remained even after managing body temperatures ability is lost. so can't tie the fact that today’s flightless birds did develop their feathers to manage their temperature ability. It cast doubt on - today’s flightless birds probably developed their feathers as a way to manage their body temperatures

D. Today’s flightless birds are direct descendants of feathered reptiles.
Today’s flightless birds are direct descendants of feathered reptiles. :- Ok so what. even if they are not - today’s flightless birds probably developed their feathers as a way to manage their body temperatures. It's not necessary to be direct descendants to have feathers that manage their body temperatures.
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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25 Aug 2016, 07:21
Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

Scope of the question stem : flightless birds
We have to prove :

today’s flightless birds didn't developed their feathers as a way to manage their body temperatures.

However, many of these early feathered reptiles were unable to fly. - I didn't consider this to arrive at my assumption. The ability - Managing their body temperature.

The argument above relies on which of the following assumptions?

A. Negate A :- A characteristic developed for a particular ability does remain after that ability is lost.

so feathers remained even after managing body temperatures ability is lost. so can't tie the fact that today’s flightless birds did develop their feathers to manage their temperature ability. It cast doubt on - today’s flightless birds probably developed their feathers as a way to manage their body temperatures

D. Today’s flightless birds are direct descendants of feathered reptiles.
Today’s flightless birds are direct descendants of feathered reptiles. :- Ok so what. even if they are not - today’s flightless birds probably developed their feathers as a way to manage their body temperatures. It's not necessary to be direct descendants to have feathers that manage their body temperatures.

its saying many of the earlier birds were not able to fly so that doesn't mean feather have any linkage with flying.

And since it has concluded that since they donot fly so they must be using it for regulating body temp. he has assumed that if they would not have the issue of body temperature they should not have the feather. hence, A
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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27 Aug 2016, 06:45
Top Contributor
sa18 wrote:
retro wrote:
Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

The argument above relies on which of the following assumptions?

A. A characteristic developed for a particular ability does not remain after that ability is lost.
B. Some animals that are able to fly lack feathers.
C. Feathered dinosaurs that were able to fly also used their feathers to regulate body temperature.
D. Today’s flightless birds are direct descendants of feathered reptiles.
E. Without the ability to regulate their body temperature, flightless birds will go extinct.

I thought the answer is D. Can anyone help me understand why A also fits the bill?

A says characteristic (feathers) does not remain after ability (flying) is lost.
But the argument says feathers are retained in flightless birds though the ability is lost
How can it be an assumption

IMO,
A says characteristic (flying) does not remain after ability (ability to flying) is lost.
premise:Reptiles developed their feathers to manage body temperature.
Conclusion:Flightless birds developed their feathers to manage body temperature

As Assumption,Answer Choice A actually positively correlate characteristic of reptiles with birds correctly

Please let me know ,if I missed anything.
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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14 Oct 2016, 06:43
AndyNeedsGMAT wrote:
retro wrote:
Explanation given in the book:

Answer: A. This is an assumption question. Its conclusion and premises are:
Premises: (1) Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. (2) Many of these early feathered reptiles were unable to fly.

Conclusion: Today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

This argument uses the fact that many early feathered reptiles were unable to fly to conclude that flightless birds developed their feathers for the same reason. But it must be assuming that the feathers did not develop for some other reason. Perhaps the feathers developed first for flight, but the birds eventually lost that ability. Choice A correctly states the assumption of the argument because it indicates that the flightless birds did not develop the feathers for an ability that they now no longer have. Choice B does not address the link between the feathers of flightless birds and the feathers of reptiles. Choice C doesn’t deal with flightless birds at all, so it cannot be correct. Choice D may be true, but it is not an assumption of the argument. The argument is only concluding why the flightless birds developed their feathers, not where they came from. Choice E is new information and not part of the argument.

Rgds
Rahul

Still struggling to understand why the early reptiles morphed their feathers to scales ? Weren't the feathers supposed to stay in these reptiles as per choice A ?
Those reptiles would still need way to insulate their bodies from the cold and regulate their body temperatures - and feathers were doing that...
So how can one justify the assumption : A. A characteristic developed for a particular ability does not remain after that ability is lost.? Reptiles would still insulate their bodies from the cold and regulate their body temperatures...

This might be too late an ans for you:

A: A characteristic developed for a particular ability does not remain after that ability is lost.
These reptiles/birds still have these feathers and for sure they cannot fly......then why do they still have it? Because they developed feathers not for flying, but to regulate their body temp.
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Biologists suspect that feathers are modified scales. [#permalink]

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14 Mar 2017, 06:55
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This is the way I approach this question. Hope it helps.

Premise: flightless reptiles - feathers regulate body temperatures
Conclusion: flightless birds - feathers regulate body temperatures TOO!

The author draws conclusion based on the feature of reptiles.
Prethinking: This reveals the weakener that although those birds are unable to fly as reptiles are, their feathers still do not function as assumed, but as a means to flying, for example. Maybe they used to be able to fly but now they're not. We need to eliminate this weakener!

That's why A is the right answer.

p/s: The way I weaken the conclusion is similar to the way I deny the statement that A -> B by pointing out that, in another place, A -> not B (or, not A -> B).
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Re: Biologists suspect that feathers are modified scales. [#permalink]

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14 Mar 2017, 07:24
if we focus on the line 'However, many of these early feathered reptiles were unable to fly". then we get to know that not all the reptiles were unable to fly there must have some reptiles who used to fly . now if we look option D it says that today feathered birds,which can't fly, are the direct decedents of the feathered reptiles , so there are some birds who can fly too then how these birds can be direct decedents of the reptiles. and also this line 'Biologists suspect that feathers are modified scales, make sure that A is the answer .

please correct me if i am wrong , i will appreciate your guidance

thank you
Re: Biologists suspect that feathers are modified scales.   [#permalink] 14 Mar 2017, 07:24
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