Swamp sparrows live in a variety of wetland habitats. Unlike most swam

Question

Swamp sparrows live in a variety of wetland habitats. Unlike most swamp sparrows, which live in freshwater habitats, the coastal-plain subspecies lives in tidal wetlands, where freshwater and seawater mix and the mud is gray rather than brown. Coastal-plain swamp sparrows differ from all other populations of swamp sparrows in having plumage that is gray brown rather than rusty brown. DNA analysis indicates several important genetic differences between swamp sparrows that inhabit tidal marshes and other subspecies of swamp sparrows. Therefore there must have been genetic-selection pressure on swamp sparrows in tidal marshes to become darker and grayer.

Select Strengthen for the statement that would, if true, most strengthen the argument, and select Weaken for the statement that would, if true, most weaken the argument. Make only two seletions, one in each column.

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ID: 100355

Select  Strengthen  for the statement that would, if true, most strengthen the argument, and select  Weaken  for the statement that would, if true, most weaken the argument. Make only two seletions, one in each column.

ID: 100355

ozhan · Accepted Answer

Hi,

Information:
Coastal-plain swamp sparrows are gray brown whereas others are rusty brown.
There are a lot of genetic differences between the coastal-plain swamp sparrows and the others.
Conclusion: 
Genetic differences must be the reason of of the difference in color.

The gap is that we do not know whether the difference is caused by internal(i.e. genetics) or external (i.e. climate, food etc.) reasons.

Taking these into consideration 
A) weakens the argument, because it clearly states that there is no genetic difference between coastal-plain swamp sparrows and freshwater swamp sparrows that affects plumage color, thus the reason of difference in plumage color should be external (for example food)
E) strengthens the argument, because it shows that under same external conditions(“identical diet and controlled conditions”) the birds grew plumage similar in color to that of their respective parents. This shows that external factors have no affect, thus the reason should be genetic.

Hope this helps

Hosai · Answer

Option C states :  SOME  species of birds do not have grey plumage. 
The passage states : there must have been genetic-selection pressure on  swamp sparrows . 
The passage exclusively talks about swamp sparrows, whereas the option C talks about other species ( can be any species - of any bird), which is irrelevant. Maybe parrots did not have the genetic pressure to grow grey plumage - this does not impact the conclusion stated that is exclusive to swamp sparrows.
This is a typical GMAT trap where the option goes from specific to general. Hope this helped

ds1710 · Answer

The strengthen section should remove any ambiguity in the passage to strengthen the conclusion. The facts mentioned about the color of mud can be interpreted as something that doesn’t have a supporting fact. So any strengthen choice should directly help resolve this. The only one that does is answer choice E

The weaken question should directly impact the conclusion. The conclusion is that genetic selection is responsible for the color. The answer choice C correctly weakens by suggesting there are no genetic difference that impact the plumage color.

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Victz · Answer

Why can't B weaken the conclusion? B/c it offers an alternative cause for color difference?

sagarsangani123 · Answer

The conclusion: there must have been genetic-selection pressure on swamp sparrows in tidal marshes to become darker and grayer.

The author's point is mainly regarding the cause of swamp sparrows's plumage color. Option (B) speaks about the color of the mud. It tells us why the color of mud in tidal marshes is gray and freshwater mud brown. When you suggest that the sparrow's plumage color could be due to the mud's color, that does not automatically rule out the cause that author said 'there must have been genetic-selection pressure on swamp sparrows in tidal marshes to become darker and grayer'. I believe you are making an assumption by saying that by proposing an alternate cause alone, the original cause is nullified and the conclusion must be weakened.

This indeed is a tempting choice.

Sajjad1994 · Answer

Official Explanation

The argument is essentially that since coastal-plain swamp sparrows have grayish plumage and live in wetlands with gray mud, whereas other swamp sparrows have browner plumage and live in areas with brown mud, and since genetic differences between the coastal-plain swamp sparrows and other swamp-sparrow subspecies have been identified, genetic selection pressure to match the local mud color must have made the coastal-plain swamp sparrows grayer than the other subspecies. This reasoning implicitly assumes that genetic differences between the subspecies account for the different plumage colors. Evidence supporting that assumption will strengthen the argument, whereas evidence casting doubt on the assumption will weaken the argument.

If none of the genetic differences identified between coastal-plain swamp sparrows and other subspecies affect plumage color, then the argument’s premise about identified genetic differences supports neither the implicit assumption nor the argument’s conclusion. Thus, the first option weakens the argument rather than strengthening it.

The information provided gives no reason to believe that chemical causes of the differences in mud color are relevant to whether the differences in the sparrow subspecies’ plumage colors are genetic, so the second option neither strengthens nor weakens the argument.

The observation that some other bird species in tidal marshes do not have gray plumage is irrelevant to the question of why coastal-plain swamp sparrows do. Whether genetic or environmental factors make the coastal-plain swamp sparrows’ plumage grey, those factors may differ for other species in the same marshes. Therefore, the third option neither strengthens nor weakens the argument.

The observation that all swamp sparrows’ diets can vary seasonally is also irrelevant to the question of why their plumage colors differ. Different seasonally variable diets might have different long-term effects on plumage color. And even if they don’t, other environmental factors might. Thus, the fourth option neither strengthens nor weakens the argument.

If birds of the different subspecies still maintain their distinct plumage colors even after having been raised in similar conditions, it is more likely that genetic rather than environmental factors account for the difference in plumage colors. So the fifth option strengthens the argument.

The correct answer is Baby birds of the coastal-plain subspecies and baby birds of a freshwater swamp subspecies, all raised on an identical diet under controlled conditions, grew plumage similar in color to that of their respective parents.

As discussed in the explanation above, the first option weakens the argument, the fifth option strengthens it, and the second, third, and fourth options do neither.

The correct answer is None of the genetic differences that have been identified in the genomes of coastal-plain swamp sparrows and freshwater swamp sparrows affect plumage color.

ChiranjeevSingh · Answer

Understanding the Passage  
 
 Swamp sparrows live in a variety of wetland habitats.  - These sparrows live in different wetland habitats. (At this stage, I’ll notice that the text says “variety of wetland habitats” rather than “variety of habitats.”)

Unlike most swamp sparrows, which live in freshwater habitats, the coastal-plain subspecies lives in tidal wetlands, where freshwater and seawater mix and the mud is gray rather than brown.

This sentence gives several pieces of information:
 
 Most swamp sparrows live in freshwater habitats 
 A subspecies of swamp sparrows lives in tidal wetlands. (In my mind, there are sparrows. Within them, there are swamp sparrows. Within them, a coastal plain swamp sparrows) 
 Okay. So, this particular species is different from most (but not necessarily all other) swamp sparrows in terms of where it lives. 
 In tidal weltands, freshwater and seawater mix and the mud is gray rather than brown (when I read this, I connect this piece of information with the info about most swamp sparrows. Most swamp sparrows live in freshwater, whereas this subspecies lives in a place where freshwater and seawater mix. I now better understand the difference. Then, the sentence says “the mud is gray rather than brown” - I understand that in tidal wetlands, the mud is gray. But why does the sentence say “rather than brown”? Perhaps, the mud is brown in areas where most sparrows live. So, I understand that the mud is brown in freshwater habitats)

Coastal-plain swamp sparrows differ from all other populations of swamp sparrows in having plumage that is gray brown rather than rusty brown. 
(When I read this sentence, I’ll look back at the previous sentence to confirm that we’re discussing the same subspecies.)

Our subspecies (the one we’re talking about) is unique among swamp sparrows in terms of its plumage (feathers). (Here, I notice that this sentence is comparing our subspecies with ‘all’ other populations of swamp sparrows, whereas the previous sentence compared our subspecies with ‘most’ swamp sparrows.)

Our subspecies’ plumage is gray brown rather than rusty brown. (When I read this, I connect it back to the color of the mud of the area in which this subspecies lives. The mud is gray rather than brown. This is aligned with the color of the plumage. The plumage is gray brown rather than rusty brown. So, the ‘grayness’ of the mud shows up in its plumage)

DNA analysis indicates several important genetic differences between swamp sparrows that inhabit tidal marshes and other subspecies of swamp sparrows. 
There are many important ‘genetic’ differences between our subspecies and other subspecies. (So far, I knew the differences in terms of areas in which they live and the color of their plumage. Now, I get to know that there are ‘genetic’ differences as well.)

Therefore, there must have been genetic-selection pressure on swamp sparrows in tidal marshes to become darker and grayer. 
‘Therefore’ indicates that the author is drawing a conclusion. The conclusion is that the different color of our subspecies is at least partly due to genetic-selection pressure.

(How can we arrive at this conclusion from the information above? I know that our subspecies is grayer than the other subspecies and lives in mud that is gray rather than brown. So, I understand that our species is darker and grayer. But how can we say that there was some genetic pressure on the subspecies to become so? This seems to be a big jump in the author’s logic. The subspecies may have become grayer for the simple reason that it was exposed to that kind of mud. There may not be any genetic pressure. I think these thoughts before moving on to the question.)
   Understanding the Question Stem  
 
 Select Strengthen for the statement that would, if true, most strengthen the argument, and select Weaken for the statement that would, if true, most weaken the argument. Make only two seletions, one in each column.

The question stem is pretty straightforward. We’re looking for one strengthener and one weakener in the options. 
  Evaluating the Options   
I evaluate the impact of each option on the argument, one by one. I’m looking for a strengthener and a weakener. I can reject the options having no impact.

A.  None of the genetic differences that have been identified in the genomes of coastal-plain swamp sparrows and freshwater swamp sparrows affect plumage color. 
No identified genetic differences between our subspecies and other subspecies (in which most swamp sparrows fall) affect plumage color.

This option indicates that genetic differences are not the reason for different plumage colors.

If so, it doesn’t make sense to argue that there was some genetic pressure to have a different plumage color (darker and grayer).

Thus, this option weakens the argument.

B.  Mud in tidal marshes tends to be grayish because of the presence of iron sulfide, whereas freshwater mud is browner because of the presence of iron oxide. 
This option gives us reasons for the different colors of the two muds. However, the reasons (the presence of iron sulfide or iron oxide) are not connected with any aspect of the argument. Thus, this option has no impact on the argument.

C.  Some species of birds that live in tidal marshes do not have gray plumage. 
Some may think that this option weakens the argument. Since some species of birds in the same areas do not have gray plumage, there was perhaps no genetic pressure on our subspecies to become grayer.

The problem with this reasoning is that the question remains as to why our subspecies became grayer. You may say that there was some reason other than genetic pressure. But then, why did that reason not apply to those non-gray-plumage species?

The line of reasoning that seems to weaken the argument is flawed.

If we get to know that some species are not gray, do we get to know any information about why gray species are gray?

I don’t think so.

Thus, this option has no impact.

D.  The diets of both coastal-plain and freshwater swamp sparrows can change significantly from season to season. 
If the option had said that the diets of these two subspecies are different from each other’s, then this option would have created doubt on the conclusion by providing an alternate reason for the difference in plumage colors.

However, this option says that the diets change from season to season.

But their colors don’t change from season to season.

So, this option doesn’t have impact on the conclusion.

E.  Baby birds of coastal-plain subspecies and baby birds of a freshwater swamp subspecies, all raised on an identical diet under controlled conditions, grew plumage similar in color to that of their respective parents. 
(This is a little complex statement to understand. So, naturally, one needs to spend extra time just to understand the statement. Then comes the evaluation. However, I have seen that many people rush to evaluate without understanding. As a result, they go wrong.)

This option talks about babies of our subspecies and babies of freshwater subspecies.

It says that when they are given a controlled environment and identical diet, they still have differently colored plumages.

Thus, this option indicates that the difference in plumage color is not because of diet.

By eliminating this case, the option strengthens the cause advocated in the conclusion. The belief in the conclusion that genetic selection pressure is the cause of the difference in plumage color goes up.

Thus, this option strengthens the argument.

Anooj1705 · Answer

what if the  genetic differences have not been found yet ? Doesn't mean there can not be genetic differences that can be found in the future that can cause the color difference.

Gemmie · Answer

The argument claims that genetic selection pressure caused coastal-plain swamp sparrows to develop gray-brown plumage as an adaptation to their tidal marsh environment.

Strengthening the Argument:    Baby birds of coastal-plain subspecies and baby birds of a freshwater swamp subspecies, all raised on an identical diet under controlled conditions, grew plumage similar in color to that of their respective parents.

This option directly supports the idea that plumage color is genetically determined and not influenced by environmental factors like diet.

Weakening the Argument:    None of the genetic differences that have been identified in the genomes of coastal-plain swamp sparrows and freshwater swamp sparrows affect plumage color.

This directly contradicts the argument's premise that genetic differences led to the development of different plumage colors

Analyzing the Incorrect Options

Mud in tidal marshes tends to be graysih because of the presence of iron sulfide, whereas freshwater mud is browner because of the presence of iron oxide. 
This information is irrelevant to the argument. While it explains why the mud is different colors, it doesn't address the cause of the plumage color difference.

Some species of birds that live in tidal marshes do not have gray plumage. 
This information is also irrelevant. The argument focuses on swamp sparrows, not other bird species.

The diets of both coastal-plain and freshwater swamp sparrows can change significantly from season to season. 
This information is potentially distracting. While diet can influence certain aspects of an organism's physiology, the argument specifically focuses on genetic factors for plumage color.

PA0037 · Answer

ChiranjeevSingh  what if the genetic differences have not been found yet ? Doesn't mean there can not be genetic differences that can be found in the future that can cause the colour difference.

In fact doesn't option B weaken it by suggesting another reason than genetics.- certain chemicals whose presence effects colours  Sajjad1994

zaberfire · Answer

i dont really understand this question.

it seems like the answer is saying that we are looking for statements that strengthens or weakens the link between genes and the gene expression of plumage color which does not make sense at all.

is this link not a given? if the two birds have different colors - naturally their DNA is different, no?

What is the point of the controlled experiment? Of course if you take the birds from these two different species and have them grow up they will look different. If you take a black kid and a white kid, even if you don't raise them the same and feed them the same, it's a given that their skin color isn't going to change as a result of this?

Why would environment or diet change the genes you're born with?

I thought the question was about if there was survival pressure or natural selection reasons on why the differences occur and was looking for answers in that vein. Why would you question if genes decide skin color?

justdivyanshii · Answer

isn't this option for weaken, challenging the fact "  None of the genetic differences that have been identified in the genomes of coastal-plain swamp sparrows and freshwater swamp sparrows affect plumage color."

justdivyanshii · Answer

isn't this option for weaken, challenging the fact "  None of the genetic differences that have been identified in the genomes of coastal-plain swamp sparrows and freshwater swamp sparrows affect plumage color."

Joe258 · Answer

The argument of the passage lies in the last sentence of the passage which, essentially, claims that being a coastal swamp sparrow, the bird's gene must have been altered from the gene of other sparrows; and the plumage color is reflective of the difference.
Remember that DNA analysis has already told you that the genes are different (important!!).

Here is my reasoning for A and E:
Option A explicitly falsifies this claim because coastal genetic selection (A) that created the genetic difference (B), the difference (B) is not reflective of the plumage color (C). (if A then B, but if B then NOT C, therefore if A then NOT C).
Option E implies that the claim is accurate for 2 reasons. First, when baby sparrows take genes from their parents through birth, they must retain the difference between the genes. Second, if the babies ALSO retain the difference in plumage color, given the same diets, habits, whatever, this means that the gene difference must be the cause.

Hope this helps!^^

Swamp sparrows live in a variety of wetland habitats. Unlike most swam

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Strengthen	Weaken
		None of the genetic differences that have been identified in the genomes of coastal-plain swamp sparrows and freshwater swamp sparrows affect plumage color.
		Mud in tidal marshes tends to be graysih because of the presence of iron sulfide, whereas freshwater mud is browner because of the presence of iron oxide.
		Some species of birds that live in tidal marshes do not have gray plumage.
		The diets of both coastal-plain and freshwater swamp sparrows can change significantly from season to season.
		Baby birds of coastal-plain subspecies and baby birds of a freshwater swamp subspecies, all raised on an identical diet under controlled conditions, grew plumage similar in color to that of their respective parents.

GMAT Two-part Analysis (TPA) Questions

Swamp sparrows live in a variety of wetland habitats. Unlike most swam

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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My Rewards