Swamp sparrows live in a variety of wetland habitats. Unlike most swamp sparrows, which live in freshwater habitats, the coastal-plain...

GMAT Two Part Analysis : (TPA) Questions

Source: Official Guide

Two Part Analysis

Verbal - CR

HARD

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Notes

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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.

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.

Solution

Phase 1: Owning the Dataset

First, Create an Argument Analysis Table

Text from Passage	Analysis
"Swamp sparrows live in a variety of wetland habitats"	What it says: Swamp sparrows inhabit different types of wetlands What it does: Background fact setting up the comparison Key connections: Introduces the variety that will be contrasted
"Unlike most swamp sparrows, which live in freshwater habitats, the coastal-plain subspecies lives in tidal wetlands"	What it says: Most live in freshwater, but coastal-plain ones live where fresh and salt water mix What it does: Establishes the key environmental difference Key connections: Sets up the comparison between two populations
"the mud is gray rather than brown"	What it says: Tidal wetland mud = gray; freshwater mud = brown What it does: Provides environmental detail Key connections: Parallels the plumage color difference Visualization: Gray mud ↔ Gray-brown birds
"Coastal-plain swamp sparrows differ...in having plumage that is gray brown rather than rusty brown"	What it says: Coastal birds are gray-brown; others are rusty brown What it does: Key evidence - physical difference matches environment Key connections: Gray environment → Gray birds
"DNA analysis indicates several important genetic differences"	What it says: There are genetic differences between the populations What it does: Scientific evidence of biological distinction Key connections: Links to the conclusion about selection
"Therefore there must have been genetic-selection pressure...to become darker and grayer"	What it says: Natural selection caused the color change What it does: Main conclusion Key connections: Claims genetic differences explain plumage differences

Second, Identify Argument Structure

Main conclusion: Genetic selection pressure caused coastal swamp sparrows to evolve gray-brown plumage
Supporting evidence:
- Environmental difference (gray vs brown mud)
- Physical difference (gray-brown vs rusty-brown plumage)
- Genetic differences between populations
Key assumption: The genetic differences are responsible for the plumage color differences
Logical flow: Different environment → Different appearance + Genetic differences → Therefore, genetic selection caused the appearance change

Phase 2: Question Analysis & Prethinking

First, Understand What Each Part Asks

We need to find:

Part 1 (Strengthen): A statement that makes the genetic selection argument MORE convincing
Part 2 (Weaken): A statement that makes the genetic selection argument LESS convincing

Second, Generate Prethinking Based on Question Type

For strengtheners, we want evidence that:

Links genetics directly to plumage color
Shows the color difference is inherited, not environmental
Demonstrates adaptive advantage of gray plumage in tidal marshes

For weakeners, we want evidence that:

Breaks the link between genetics and plumage
Suggests environmental factors (not genetics) cause the color
Shows the genetic differences are unrelated to appearance

Third, Develop Specific Prethinking for Each Part

For Strengthen:

Example: "Birds raised in laboratories maintain their subspecies' plumage color"
Example: "Gray plumage provides camouflage advantage in gray mud"

For Weaken:

Example: "The genetic differences affect metabolism, not appearance"
Example: "Diet or mud exposure changes plumage color"

Phase 3: Answer Choice Evaluation

Evaluating Each Choice

Choice 1: "None of the genetic differences...affect plumage color"

Simple meaning: The genetic differences don't control color
Strengthen? NO - This directly contradicts the genetic selection argument
Weaken? YES - If genetics don't affect color, genetic selection can't explain the color difference
Strong weakener

Choice 2: "Mud in tidal marshes tends to be grayish because of iron sulfide..."

Simple meaning: Explains why mud colors differ chemically
Strengthen? Slightly - Provides environmental context for selection pressure
Weaken? No - Doesn't challenge the genetic argument
Neither strong

Choice 3: "Some species of birds that live in tidal marshes do not have gray plumage"

Simple meaning: Not all tidal marsh birds are gray
Strengthen? No - Other species are irrelevant
Weaken? Slightly - Suggests environment doesn't force gray color
Weak for both

Choice 4: "The diets of both...can change significantly from season to season"

Simple meaning: Both populations have variable diets
Strengthen? No - Diet variation doesn't support genetic color determination
Weaken? No - Doesn't explain consistent color differences
Irrelevant

Choice 5: "Baby birds...raised on an identical diet under controlled conditions, grew plumage similar...to their respective parents"

Simple meaning: Color is inherited, not caused by environment
Strengthen? YES - Proves genetic (not environmental) control of color
Weaken? No - Actually supports the genetic argument
Strong strengthener

The Correct Answers

For Strengthen: Choice 5 - The controlled experiment proves plumage color is genetically determined, directly supporting the genetic selection argument
For Weaken: Choice 1 - If genetic differences don't affect plumage, the entire argument about genetic selection causing color change collapses

Common Traps to Highlight

Choice 2 (mud chemistry) might seem like a strengthener because it explains the environmental difference, but it doesn't actually support the genetic selection claim - it just provides context.

Choice 3 (other species) might seem relevant, but what happens in other species doesn't tell us about swamp sparrow evolution. Each species faces its own selection pressures.

Choice 4 (diet changes) is a classic distractor - it introduces a potentially relevant factor (diet) but doesn't connect it to the plumage color issue at hand.

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