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

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

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.

 
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:

1. Most swamp sparrows live in freshwater habitats
2. 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)
3. Okay. So, this particular species is different from most (but not necessarily all other) swamp sparrows in terms of where it lives.
4. 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.)

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.
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.­­­­

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.

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.