Research directed toward recovering ancient DNA began in 1984, when pieces of DNA were extracted from museum specimens of an...
GMAT Reading Comprehension : (RC) Questions
Research directed toward recovering ancient DNA began in 1984, when pieces of DNA were extracted from museum specimens of an animal extinct for about a century. Most such genetic material recovered from biological relics consists of tiny fragments, rather than the strings of thousands of molecules typically found in living organisms, but these fragments may contain sufficient information to identify a species through comparison with modern DNA from descendant species. However, the need to verify whether particular fragments actually come from ancient organisms or whether they come from modern contaminants, such as the sweat of people who have handled the specimens, is crucial. For example, some scientists claim to have extracted DNA fragments from 17-million-year-old magnolia leaves found in an unusual fossil deposit in Idaho. But other scientists suggest that this DNA is a modern contaminant; they argue that even under the most favorable conditions, the rate of degradation of DNA is such that useful genetic material could not be recovered from fossils that old and that since the leaves were trapped in wet deposits, it is particularly unlikely that any DNA would have survived so long. A solution to this debate lies in the fact that any ancient DNA should differ from that of related modern species. If the DNA extracted from the fossil leaves were actually a modern contaminant, this fact would be apparent from the information contained in the DNA.
The passage is primarily concerned with
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| Research directed toward recovering ancient DNA began in 1984, when pieces of DNA were extracted from museum specimens of an animal extinct for about a century. | What it says: Scientists started trying to get DNA from dead animals in 1984, beginning with an animal that died about 100 years ago. What it does: Introduces the main topic - ancient DNA research - with a concrete starting point Source/Type: Historical fact Connection to Previous Sentences: This is our foundation sentence - establishes the field of study Visualization: Timeline: 1984 → Scientists extract DNA from museum specimen of animal extinct since ~1880s What We Know So Far: Ancient DNA research exists and started in 1984 What We Don't Know Yet: How this research works, what challenges exist, specific examples |
| Most such genetic material recovered from biological relics consists of tiny fragments, rather than the strings of thousands of molecules typically found in living organisms, but these fragments may contain sufficient information to identify a species through comparison with modern DNA from descendant species. | What it says: Ancient DNA comes in small pieces (not long chains like in living things), but these small pieces can still tell us what species we're looking at by comparing to modern relatives. What it does: Explains the basic challenge and potential of ancient DNA research Source/Type: Scientific explanation/fact Connection to Previous Sentences: This builds on sentence 1 by explaining HOW the DNA extraction works and what scientists can do with it. We're getting the "how it works" details. Visualization: • Living organism DNA: Long chain of 10,000+ molecules • Ancient DNA fragments: Small pieces of 50-200 molecules • Process: Compare ancient fragments → modern relative DNA → identify species Reading Strategy Insight: Notice the "but" structure - challenge followed by opportunity. This is a common RC pattern. |
| However, the need to verify whether particular fragments actually come from ancient organisms or whether they come from modern contaminants, such as the sweat of people who have handled the specimens, is crucial. | What it says: Scientists must make sure the DNA they find is really ancient and not from modern sources like human sweat from people who touched the specimens. What it does: Introduces the main problem/challenge in ancient DNA research Source/Type: Scientific methodology concern Connection to Previous Sentences: This builds on sentence 2's explanation by revealing the major obstacle. We learned the potential (sentence 2), now we learn the main challenge. Visualization: • Scenario 1: DNA fragment = truly from 100-year-old specimen ✓ • Scenario 2: DNA fragment = from researcher's sweat in 2023 ✗ • Problem: How to tell which scenario you have? What We Know So Far: Ancient DNA research exists, works with fragments, can identify species, but has contamination issues What We Don't Know Yet: Specific examples, how to solve contamination problem |
| For example, some scientists claim to have extracted DNA fragments from 17-million-year-old magnolia leaves found in an unusual fossil deposit in Idaho. | What it says: Some scientists say they got DNA from extremely old magnolia leaves (17 million years) found in Idaho. What it does: Provides concrete example of the research described in previous sentences Source/Type: Scientists' claim Connection to Previous Sentences: This gives us a specific real-world case of the ancient DNA research we've been learning about. Notice "For example" - this is just illustrating concepts we already know. Visualization: • Timeline: 17 million years ago → magnolia leaves fossilized in Idaho • 2024: Scientists extract DNA fragments from these leaves • Scale: Much older than the century-old animal from sentence 1 Reading Strategy Insight: Feel confident here - this is just an example, not new complexity! |
| But other scientists suggest that this DNA is a modern contaminant; they argue that even under the most favorable conditions, the rate of degradation of DNA is such that useful genetic material could not be recovered from fossils that old and that since the leaves were trapped in wet deposits, it is particularly unlikely that any DNA would have survived so long. | What it says: Other scientists disagree - they think this DNA is modern contamination because DNA breaks down too quickly to survive 17 million years, especially in wet conditions. What it does: Shows the contamination problem in action with the specific Idaho example Source/Type: Scientific counter-argument Connection to Previous Sentences: This is NOT new information! This perfectly illustrates the contamination problem from sentence 3. We're seeing that exact challenge play out with the Idaho magnolia example. Visualization: • Team A: "We found 17-million-year-old DNA!" • Team B: "Impossible - DNA degrades too fast, especially in wet conditions" • Core issue: Same contamination problem from sentence 3 Reading Strategy Insight: This reinforces rather than complicates! The abstract problem (sentence 3) now has a concrete example. |
| A solution to this debate lies in the fact that any ancient DNA should differ from that of related modern species. | What it says: There's a way to solve this argument: real ancient DNA should be different from modern DNA of related species. What it does: Introduces the solution to the contamination problem Source/Type: Scientific principle/solution Connection to Previous Sentences: This directly addresses the contamination problem from sentence 3 and the specific Idaho debate from sentences 4-5. The author is giving us the answer to the challenge. Visualization: • If truly ancient: Magnolia DNA from 17M years ago ≠ Modern magnolia DNA • If contamination: "Ancient" DNA = Modern human/plant DNA (identical to current species) Reading Strategy Insight: Relief moment! We're getting a solution, not more problems. |
| If the DNA extracted from the fossil leaves were actually a modern contaminant, this fact would be apparent from the information contained in the DNA. | What it says: If the Idaho magnolia DNA is really contamination, the DNA itself will reveal this. What it does: Restates and applies the solution to the specific Idaho example Source/Type: Logical conclusion Connection to Previous Sentences: This is NOT new complexity! This simply takes the solution from sentence 6 and applies it back to the Idaho case from sentences 4-5. Complete circle back to reinforce the main point. Visualization: • Test the Idaho DNA against modern magnolia DNA • If identical = contamination confirmed • If different = potentially ancient What We Know Now: Ancient DNA research exists, faces contamination challenges, but has a clear solution through DNA comparison Reading Strategy Insight: This is pure reinforcement! The passage has come full circle - problem identified, example given, solution provided, solution applied. Feel confident you understand the complete argument. |
2. Passage Summary:
Author's Purpose:
To explain how ancient DNA research works and how scientists solve the key problem of distinguishing real ancient DNA from modern contamination.
Summary of Passage Structure:
The author builds their explanation in a logical sequence that moves from basic background to a specific problem and its solution:
- First, the author introduces ancient DNA research by explaining when it started and how it works with small DNA fragments to identify species.
- Next, the author identifies the main challenge facing researchers: figuring out whether DNA fragments are truly ancient or just modern contamination from people handling specimens.
- Then, the author illustrates this contamination problem with a real example involving scientists who disagree about whether DNA from 17-million-year-old magnolia leaves is genuine or contaminated.
- Finally, the author presents the solution to this debate: ancient DNA should be different from modern DNA of related species, so comparing the two will reveal whether the sample is truly ancient or contaminated.
Main Point:
While ancient DNA research faces the serious challenge of contamination from modern sources, scientists can solve this problem by comparing suspected ancient DNA to modern DNA from related species - any real ancient DNA will show clear differences from its modern relatives.
3. Question Analysis:
The question asks us to identify what the passage is "primarily concerned with" - this means we need to find the main purpose or focus that drives the entire passage structure.
Connecting to Our Passage Analysis:
From our passage analysis, we can see the author follows a clear progression:
- Introduces ancient DNA research and its basic methodology
- Identifies the central challenge: distinguishing ancient DNA from modern contamination
- Provides a concrete example of this contamination debate (Idaho magnolia leaves)
- Presents the solution: comparing ancient DNA to modern DNA of related species
The passage analysis shows that the contamination problem is the core issue that drives the entire discussion. The author doesn't just describe ancient DNA research in general - they focus specifically on the critical challenge of verification and how to solve it.
Prethinking:
Based on our analysis, the passage is primarily concerned with identifying and solving the central methodological challenge in ancient DNA research: how to determine whether recovered DNA fragments are genuinely ancient or modern contaminants. The entire passage structure revolves around this verification issue, making it the primary concern.
Why It's Wrong:
- The passage doesn't question whether ancient DNA methodology works - it explains how it works and addresses challenges
- The author presents solutions to problems rather than questioning the entire approach
- The tone is explanatory and problem-solving, not skeptical about the methodology itself
Common Student Mistakes:
- Doesn't the passage show scientists disagreeing about the Idaho magnolia DNA?
→ This disagreement is about whether specific DNA is ancient or contaminated, not about whether the methodology of ancient DNA research is valid - Isn't the author being critical of the research?
→ The author is identifying challenges within the field and providing solutions, not questioning whether the field itself is worthwhile
Why It's Right:
- The passage focuses specifically on the verification challenge - determining if DNA is ancient vs. contaminated
- The entire structure revolves around this dating/verification issue: problem identification, example, and solution
- The contamination problem is fundamentally about correctly determining the age and authenticity of DNA fragments
Key Evidence: "However, the need to verify whether particular fragments actually come from ancient organisms or whether they come from modern contaminants, such as the sweat of people who have handled the specimens, is crucial."
Why It's Wrong:
- The passage doesn't present evidence to undermine a theory about age - it addresses methodology for determining age
- The author doesn't take sides in the Idaho magnolia debate but presents both perspectives
- The focus is on solving verification problems, not undermining age claims
Common Student Mistakes:
- Doesn't the passage show that the 17-million-year-old claim is wrong?
→ The passage presents the debate but doesn't resolve it; instead, it offers a method for resolving such debates - Isn't the author supporting the skeptical scientists?
→ The author remains neutral and focuses on the verification methodology rather than taking a position
Why It's Wrong:
- The passage only describes one method for verification (DNA comparison), not multiple dating methods
- The focus is on contamination detection, not dating techniques specifically
- No comparison of different methodological approaches is presented
Common Student Mistakes:
- Aren't there two approaches mentioned - extraction and comparison?
→ These are steps in the same process, not separate dating methods - Don't the different scientific positions represent different methods?
→ The disagreement is about interpretation of results, not different methodological approaches
Why It's Wrong:
- The passage doesn't focus on why DNA survives but on how to verify its authenticity
- Only one explanation for survival is mentioned (favorable conditions), not multiple explanations
- The emphasis is on contamination detection, not survival mechanisms
Common Student Mistakes:
- Doesn't the passage discuss conditions affecting DNA survival?
→ Survival conditions are mentioned only in context of the contamination debate, not as the main focus - Aren't there different theories about the Idaho magnolia DNA?
→ These are competing explanations for the same sample (ancient vs. contaminated), not multiple survival theories