Melanosomes are granules that produce melanin (a type of pigment)

Question

Melanosomes are granules that produce melanin (a type of pigment) in animals and can be found in bird feathers. An ancient fossilized feather contains dark stripes made from preserved carbon structures similar in size and shape to melanosomes in modern feathers. Although skeptics have pointed out that ancient bacteria could leave carbon remains of the same size and shape, a prominent paleontologist argues that the structures in the feather are almost certainly melonosomes.

Which of the following, if true, would most help justify the prominent paleontologist's judgment that the structures are almost certainly melanosomes?

A. Modern bird feathers rarely if ever contain the carbon remains of bacteria.

B. If the structures in the fossilized feather are melanosomes, they originally created stripes of pigmentation in the feather before it was fossilized.

C. Many other fossilized feathers also contain preserved carbon structures similar in size and shape to melanosomes.

D. Ancient bacteria of the size and shape of those carbon structures were commonly found in biological structures other than feathers.

E. Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes.

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Official Answer

E

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achprak97 · Accepted Answer

This is how I approached the question in exam condition simulation (came across the question for the first time in Prep/Mock):

X causes Y --> Trying to establish a correlation between two variables as per the argument.
Here, there are 2 POVs - one of the skeptics, other that of the paleontologist.

Skeptics: (Ancient bacteria could leave carbon remains of the same size and shape) caused (dark stripes made from preserved carbon structures)
Paleontologist: (Melanosomes) caused (dark stripes made from preserved carbon structures)

A. Modern bird feathers rarely if ever contain the carbon remains of bacteria.
* The argument revolves around the structures of fossilized feathers and not those of the modern birds, hence this option is not going to strengthen the paleontologist's position or weaken that of the skeptics.

B. If the structures in the fossilized feather are melanosomes, they originally created stripes of pigmentation in the feather before it was fossilized.
* It is just stating the converse and not providing any evidence or an assumption (2 of the 3 ways to strengthen a position/argument) on why the bacteria/melanosomes can/cannot form the discrete stripes. (Disclaimer: This was my interpretation during the mock - may or may not be right, open to correction)

C. Many other fossilized feathers also contain preserved carbon structures similar in size and shape to melanosomes.
* The term "Many other fossilized feature" would imply moving away from our scope of the ancient fossilized feather in question. While from an evidence/discovery standpoint, it may be a tempting answer option, but it still doesn't tie back to factors mentioned above (bacteria vs melanosomes) in terms of causation of the dark stripes.

Boiled down to D vs E mainly on the scope words relating to bacteria and feathers.

D. Ancient bacteria of the size and shape of those carbon structures were commonly found in biological structures other than feathers.
* (Disclaimer - my interpretation again, during the mock) In saying that bacteria were commonly found in biological structures other than feathers, one could interpret that the presence of bacteria in feathers would not be as common, hence would not result in the causation of the dark stripes - thereby weakening the skeptics' position.

However, upon reviewing the option again, it only implies on the frequency of the bacterial presence in non-feathered biological structures. It is veering away from the main argument of the feathers and the stripes on said feathers and thus cannot strengthen the paleontologist's position nor weaken that of the skeptics. Therefore, D would also be eliminated.

E. Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes.
* In saying that the bacteria are ALMOST ALWAYS (close to 100% of the cases) distributed fairly evenly throughout the feather, we would be weakening the skeptics' position, because it ruled out the possibility of their presence in the form of stripes, thereby supporting the paleontologist's position that it is indeed the melanosomes that are the causing factor for these dark stripes. E would therefore become the answer.

Please give kudos if you found the explanation useful/helpful!

sayan640 · Answer

We need to show that the structures are almost certainly melanosomes and it was NOT bacteria which left carbon remains of this kind.
Option E states that bacteria s are distributed evenly and hence there can't be "DISCREET" stripes. And hence we can say that it was not 
bacteria 's work and the structures are almost certainly melanosomes.

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Jayam12 · Answer

gmatophobia  How do we eliminate option A? Can't we say that if modern birds feathers do not contain carbon remains of bacteria then the fossilized feather would also not contain them right? Hence we can conclude that they are almost certainly melanosomes

Option E also makes a similar assumption in that way because the answer choice just mentions "Bacteria in a feather" and not "Bacteria in the ancient fossilized feather"

Can't we make use of the same assumption in option A and state that feather of modern birds can be used to refer to the fact that feathers of modern birds and ancient birds would be the same

Freddy12 · Answer

GMATNinja   GMATNinja Two

(A) - Modern bird feathers rarely if ever contain the carbon remains of bacteria.
(E) - Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes.

I was bit confused between the two options. We have "rarely if ever" in (A) and "almost always distributed" in (E). So both the options don't give a sure shot guarantee that it is true in 100% of the cases. How do we eliminate (A) here and choose (E).

Freddy12 · Answer

sayan640  How do you eliminate (A) ?

Shezikiro · Answer

how can we eliminate option B. if we can identify the time line of this we can say the option B holds true

anish777 · Answer

this one " Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes. " is the right answer as it's mentioned that the carbon structures are present in the feather in the form of dark stripes. However this option mentions that the bacteria in a feather should be evenly distributed in the entire feather.
I am wondering why option D is wrong ? Is it because "commonly found" does not guarantee this fact that bacteria won't be found in feather ?

DmitryFarberMPrep · Answer

This argument presents us with ambiguous evidence: based on their size and shape, these structures could be melanosomes or bacteria. We want to support the paleontologist's view that they are melanosomes, so we need some new evidence for this view. It might be a reason to suspect that the structures ARE melanosomes, or a reason to think that they are NOT bacteria.

(E) does the latter--it gives us a reason to believe that the structures are not bacteria, so it supports the paleontologist's theory.

(C) and (D) don't do anything to change our situation. (C) just says that there are other feathers with the same kind of structure, but it gives us no further guidance on what the structures are--melanosomes or bacteria--so we're in the same situation as before. (D) supports the idea that such structures *could* be bacteria, but we already knew that. In any case, if this were new information, it would WEAKEN the argument by suggesting that perhaps these structures are also bacteria, not melanosomes.

(A) feels like an attempted strengthen--it's trying to give us a reason to reject the bacteria hypothesis. The problem is that we have no idea whether we can reason from modern feathers to ancient ones. We can't be expected to know whether this is something that has changed with time, or even how long it takes for something to show carbon remains of bacteria.

(B) is just telling us what would happen if the structures were melanosomes. IF they were melanosomes, they'd show the pattern we see. But we already know that either melanosomes or bacteria could show this pattern, so (B) is a lot like (C) and (D). It doesn't get us any further toward knowing which of the two possibilities is correct.

av722 · Answer

A. Modern bird feathers rarely if ever contain the carbon remains of bacteria.
We don't really care about 'modern bird feathers,' conclusion is about whether the structures in the  ancient  feather are melanosomes.

B. If the structures in the fossilized feather are melanosomes, they originally created stripes of pigmentation in the feather before it was fossilized.
Firstly, we're trying to support the argument that the structures  are  melanosomes. This conditional relies on the assumption that the structures are melanosomes, which can't strengthen our argument. 
Secondly, we don't need to know  how  they created the stripes.

C. Many other fossilized feathers also contain preserved carbon structures similar in size and shape to melanosomes.
We're trying to prove that the structures are melanosomes. The passage says 'skeptics have pointed out that ancient bacteria could leave carbon remains of the same size and shape,' so it's possible that these other fossilized feathers could have structures coming from ancient bacteria, not melanosomes. This does nothing to help prove the conclusion.

D. Ancient bacteria of the size and shape of those carbon structures were commonly found in biological structures other than feathers.
I was chosing between D and E. This gives us the idea that ancient bacteria is found in things other than feathers, so it might be that the structures were melanosomes. But the question is asking 'which of the following would  most  help justify the prominent paleontilogist's judgment that the structures are  almost certainly melanosomes ?' This just doesn't seem like its strong enough to be the right answer. It could be that, in the case of this particular ancient feather, ancient bacteria was the cause of the stripes, even though it was uncommon. There's no way of saying for sure.

E. Bacteria in a feather are almost always distributed fairly evenly throughout the feather, rather than in discrete stripes. 
This gives us the most reason to believe that the structures are melanosomes. If bacteria are  almost always  distributed fairly evenly rather than in discrete stripes throughout the feather, and this ancient fossilized feather contains dark stripes, it gives us must more reason to believe that melanosomes are the cause. E is correct.

GMAT1034 · Answer

couldnt eliminate option B, if striped were there before fossilised, then doesnt it strenghten somehow that fossilization didnt play any role, overall strenghtning the argument?  GMATNinja  
 MartyMurray   sajjad

DmitryFarberMPrep · Answer

We're not concerned about whether fossilization played a role. The objection that skeptics are making is that these same structures could have been caused by bacteria rather than melanosomes. (Either way, we're looking at fossil remains, and we don't have any indication that it matters whether the structures formed before or after fossilization.) So we need a reason to believe that these marks are more likely to have come from melanosomes than from bacteria.

(A) says we don't see bacteria in  modern  bird feathers, but what about ancient ones? Similarly, (D) says we  do  find bacteria in other places than feathers. Okay, cool, but what about feathers? And how do we tell if these are bacteria or M's?

(B) tells us what must have happened  if  these are M's, but we don't know whether this  did  actually happen or not, so it doesn't help us. It's like saying "If X was the killer, he would have done Y first," without telling us whether Y occurred.

(C) says that we can find many other samples like this. Great, but are we seeing bacteria or melanosomes? We still don't have an answer.

(E) gives us a reason to suspect that these marks are  not  from bacteria. We know the structures formed stripes, and apparently bacteria wouldn't do that. There's our suppport!

Melanosomes are granules that produce melanin (a type of pigment)

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Melanosomes are granules that produce melanin (a type of pigment)

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