Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted definition of...
GMAT Reading Comprehension : (RC) Questions
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Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted definition of the term exists. One approach, called the biological species concept, bases the definition on reproductive compatibility. According to this view, a species is a group of animals that can mate with one another to produce fertile offspring but cannot mate successfully with members of a different group. Yet this idea can be too restrictive. First, mating between groups labeled as different species (hybridization), as often occurs in the canine family, is quite common in nature. Second, sometimes the differences between two populations might not prevent them from interbreeding, even though they are dissimilar in traits unrelated to reproduction; some biologists question whether such disparate groups should be considered a single species. A third problem with the biological species concept is that investigators cannot always determine whether two groups that live in different places are capable of interbreeding.
When the biological species concept is difficult to apply, some investigators use phenotype, an organism's observable characteristics, instead. Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species.
Ques. 1/4
The passage is primarily concerned with
Solution
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| Determining whether a given population of animals constitutes a distinct species can be difficult because no single accepted definition of the term exists. | What it says: Scientists disagree about how to define what makes a "species" What it does: Sets up the central problem the passage will address Source/Type: Factual statement about scientific consensus Connection to Previous Sentences: This is our starting point - no prior context to connect to yet Visualization: Imagine 100 biologists in a room - they don't all agree on one definition of "species" What We Know So Far: Defining species is challenging due to lack of consensus What We Don't Know Yet: What approaches exist, what the problems are with each approach Reading Strategy Insight: This opening sentence tells us the passage structure - it will likely explain different approaches to solving this definitional problem |
| One approach, called the biological species concept, bases the definition on reproductive compatibility. | What it says: Here's one way scientists try to define species - by whether animals can reproduce together What it does: Introduces the first specific approach to the problem mentioned in sentence 1 Source/Type: Factual description of a scientific concept Connection to Previous Sentences: This directly builds on sentence 1's setup. Since there's "no single accepted definition," the author now shows us one attempt at creating a definition. Visualization: Think of it like a matching system: if Animal Group A can reproduce with Animal Group A but not with Animal Group B, then A and B are different species Reading Strategy Insight: The passage is becoming MORE organized, not more complex - we're moving from general problem to specific solution attempt |
| According to this view, a species is a group of animals that can mate with one another to produce fertile offspring but cannot mate successfully with members of a different group. | What it says: This restates the biological species concept in more detail - same species = can reproduce together, different species = cannot reproduce together What it does: Elaborates and clarifies the concept just introduced Source/Type: Detailed explanation of the biological species concept Connection to Previous Sentences: This is NOT new information! Sentence 2 introduced "reproductive compatibility" and now sentence 3 explains exactly what that means. The author is helping us understand by providing more detail. Visualization: • Lions + Lions = fertile cubs ✓ (same species) • Lions + Tigers = sterile ligers ✗ (different species) • Dogs + Dogs = fertile puppies ✓ (same species) Reading Strategy Insight: Feel confident here - this is clarification, not new complexity. The author is making sure we understand the concept before critiquing it. |
| Yet this idea can be too restrictive. | What it says: But there are problems with the biological species concept What it does: Signals a shift to criticizing the approach just explained Source/Type: Author's transition to present problems with the concept Connection to Previous Sentences: This pivots from explanation (sentences 2-3) to criticism. The word "Yet" signals contrast with the previously explained concept. Visualization: Think of this as a "but wait, there's a problem" moment - like realizing a seemingly good plan has flaws What We Know So Far: One approach (biological species concept) defines species by reproductive compatibility What We Don't Know Yet: What specific problems exist with this approach Reading Strategy Insight: The word "restrictive" gives us a preview - the problems will be about this definition being too narrow or limiting |
| First, mating between groups labeled as different species (hybridization), as often occurs in the canine family, is quite common in nature. | What it says: Problem #1: Animals that are supposedly "different species" actually DO mate and reproduce in nature (like different types of dogs/wolves) What it does: Provides the first specific criticism with a concrete example Source/Type: Factual observation about nature, with canine family as example Connection to Previous Sentences: This directly supports sentence 4's claim that the biological concept is "too restrictive." If the concept says different species can't interbreed, but they actually do in nature, then the concept has a flaw. Visualization: • Wolves + Dogs = fertile offspring (this happens in nature) • Coyotes + Dogs = fertile offspring (this also happens) • According to biological species concept = same species • But scientists call them different species • Contradiction! Reading Strategy Insight: The concrete example (canine family) makes the abstract criticism easy to understand. This is the author helping us, not adding complexity. |
| Second, sometimes the differences between two populations might not prevent them from interbreeding, even though they are dissimilar in traits unrelated to reproduction; some biologists question whether such disparate groups should be considered a single species. | What it says: Problem #2: Two animal groups might be able to reproduce together, but they're so different in other ways that it seems wrong to call them the same species What it does: Provides the second specific criticism of the biological species concept Source/Type: Description of another flaw, citing some biologists' concerns Connection to Previous Sentences: This continues the pattern established - sentence 4 said there are problems, sentence 5 gave "First" problem, now sentence 6 gives "Second" problem. This is organized, predictable structure. Visualization: Imagine two groups of animals: • Group 1: Small, brown, eats insects, lives in trees • Group 2: Large, black, eats meat, lives on ground • But they can still reproduce together • Biological concept = same species • Common sense = they seem very different Reading Strategy Insight: The numbered structure ("First... Second...") makes this easy to follow. We're not lost in complexity - we're following a clear list of problems. |
| A third problem with the biological species concept is that investigators cannot always determine whether two groups that live in different places are capable of interbreeding. | What it says: Problem #3: Sometimes scientists can't even test whether animals can reproduce together because they live too far apart What it does: Completes the list of criticisms with a practical limitation Source/Type: Factual statement about research limitations Connection to Previous Sentences: This continues and completes the organized list: "First... Second... A third problem." This reinforces that the biological species concept has multiple serious flaws. Visualization: • Penguin Group A: Lives in Antarctica • Penguin Group B: Lives in Arctic • Question: Are they the same species? • Problem: Can't bring them together to test reproduction • Biological species concept: Can't be applied What We Know So Far: Biological species concept has three major problems: hybridization occurs, similar reproduction doesn't mean similar traits, and geographic separation prevents testing What We Don't Know Yet: What alternative approaches exist Reading Strategy Insight: We've now thoroughly understood why the first approach fails. The passage is building a complete case, not jumping randomly between ideas. |
| When the biological species concept is difficult to apply, some investigators use phenotype, an organism's observable characteristics, instead. | What it says: So scientists have a backup plan - when the reproduction method doesn't work, they look at physical characteristics instead What it does: Introduces the second approach as an alternative to the problematic first approach Source/Type: Factual description of alternative scientific method Connection to Previous Sentences: This directly follows from the three problems just outlined. The word "When" connects to those specific difficulties mentioned in sentences 5-7. This is the logical next step - if approach 1 has problems, here's approach 2. Visualization: Think of this as a backup plan: • Plan A (reproduction test): Often doesn't work • Plan B (physical appearance): Look at what you can actually observe and measure Reading Strategy Insight: This transition feels natural and logical - not confusing. The passage structure is: Problem → Alternative Solution. |
| Two groups that have evolved separately are likely to display measurable differences in many of their traits, such as skull size or width of teeth. | What it says: This explains the logic behind the phenotype approach - if animals evolved separately, they'll look different in measurable ways What it does: Provides the reasoning behind the phenotype approach with concrete examples Source/Type: Explanation of scientific reasoning with specific trait examples Connection to Previous Sentences: This elaborates on sentence 8's introduction of phenotype. Just like sentences 2-3 explained the biological concept in detail, now sentences 8-9 explain the phenotype concept in detail. Same pattern! Visualization: Species Group 1: Skull length 15cm, tooth width 3mm Species Group 2: Skull length 22cm, tooth width 7mm Measurable differences suggest separate evolution = different species Reading Strategy Insight: Notice the parallel structure: both approaches get introduced, then explained in detail. This makes the passage predictable and easier to follow. |
| If the distribution of measurements from one group does not overlap with those of another, the two groups might reasonably be considered distinct species. | What it says: Final explanation: If the physical measurements are completely different between two groups (no overlap), they're probably different species What it does: Completes the explanation of the phenotype approach by stating the decision rule Source/Type: Scientific methodology explanation Connection to Previous Sentences: This concludes the phenotype explanation that began in sentence 8. We now have a complete understanding of approach 2, just as we had complete understanding of approach 1. Visualization: Group 1 measurements: 12cm, 13cm, 14cm, 15cm, 16cm Group 2 measurements: 22cm, 23cm, 24cm, 25cm, 26cm No overlap between 16cm and 22cm = distinct species What We Know So Far: Two approaches to defining species: reproductive compatibility (has problems) and physical characteristics (used as alternative) What We Don't Know Yet: Nothing major - the passage has given us a complete overview Reading Strategy Insight: This ending gives us a complete, organized understanding. We're not confused - we clearly understand both approaches and when each is used. |
2. Passage Summary:
Author's Purpose:
To explain the challenges scientists face when trying to define what makes a species and to describe the different approaches they use to solve this problem.
Summary of Passage Structure:
In this passage, the author walks us through a scientific problem and the methods used to address it:
- First, the author identifies the central problem - scientists don't agree on how to define a species
- Next, the author explains one popular approach called the biological species concept, which uses reproductive compatibility as the test
- Then, the author systematically presents three major problems with this reproductive approach, showing why it often doesn't work in practice
- Finally, the author introduces an alternative approach that uses physical characteristics instead, explaining how scientists measure observable traits when the reproductive method fails
Main Point:
Defining species is complicated because the most common method (checking if animals can reproduce together) has serious limitations, so scientists often have to rely on comparing physical differences instead.
Answer Choices Explained
A
describing the development of the biological species concept
Why It's Wrong:
- The passage doesn't trace the historical development or evolution of the biological species concept
- It focuses on current applications and problems, not how the concept developed over time
- The passage actually spends significant time critiquing this concept rather than describing its development
Common Student Mistakes:
- Did I confuse "describing how it works" with "describing how it developed"?
→ The passage explains what the concept is and how it functions, but doesn't discuss its historical origins or evolution - Am I focusing too narrowly on just the biological species concept?
→ Remember that the passage covers two approaches, not just one
B
responding to a critique of reproductive compatibility as a criterion for defining a species
Why It's Wrong:
- The passage isn't responding to external criticism - it's presenting the author's own analysis of problems
- The structure shows the author introducing the concept first, then critiquing it, rather than defending it against existing critiques
- The passage moves beyond just responding to criticism by offering an alternative approach
Common Student Mistakes:
- Am I mistaking the author's presentation of problems for a response to outside critics?
→ The author is systematically analyzing limitations, not defending against attacks - Did I miss that the passage goes beyond just reproductive compatibility?
→ The second half introduces phenotype as a completely different approach
C
considering two different approaches to identifying biological species
Why It's Right:
- The passage explicitly presents "one approach, called the biological species concept" followed by an alternative where "some investigators use phenotype"
- It systematically explains both approaches: first reproductive compatibility, then physical characteristics
- The structure moves from explaining one method to identifying its problems to presenting the alternative method
- Both approaches are given substantial explanation and analysis
Key Evidence: "One approach, called the biological species concept, bases the definition on reproductive compatibility" followed by "When the biological species concept is difficult to apply, some investigators use phenotype, an organism's observable characteristics, instead."
D
pointing out the advantage of one method of distinguishing related species
Why It's Wrong:
- The passage doesn't advocate for either method over the other - it presents both as having their place
- It actually points out significant problems with the first method rather than highlighting advantages
- The phenotype approach is presented as an alternative when the first approach "is difficult to apply," not as superior overall
Common Student Mistakes:
- Am I assuming the second method is being promoted as better?
→ It's presented as a practical alternative, not as superior - Did I focus only on the problems with the biological concept and miss the balanced presentation?
→ Both approaches are presented matter-of-factly with their applications and limitations
E
identifying an obstacle to the classification of biological species
Why It's Wrong:
- While the passage mentions definitional challenges, this is just the setup for discussing solutions
- The bulk of the passage focuses on explaining two specific approaches rather than dwelling on obstacles
- The passage is more solution-oriented than problem-oriented in its overall structure
Common Student Mistakes:
- Am I focusing too much on the opening sentence about definitional difficulties?
→ That's the setup, but most of the passage explains how scientists address this challenge - Did I get distracted by the problems listed for the biological species concept?
→ Those problems lead to the alternative approach - they're part of explaining the two-method structure
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