Reading Comprehension

PT157 · S4 · P3 · Q15 Definition of Species

A free, expert breakdown of this official LSAT Reading Comprehension question.

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Political arguments about biodiversity and the preservation of endangered species generally assume we know what a species is.

Topic

The challenge and controversy of defining what counts as a "species," especially in ornithology, and the implications of different definitions.

Framework

Present Debate

Main Point

There is an ongoing debate among scientists about how to define a species, with significant practical and political consequences, especially for conservation. ( — opening sentences, and the summary of practical stakes at the end.)

P1: Debate Over What Constitutes a Species

This paragraph introduces the ongoing debate about what a "species" actually is, focusing on the classic divide between "lumpers" (who group similar populations) and "splitters" (who separate populations into more species). Lumpers use the biological species concept (reproductive isolation), while splitters prefer the phylogenetic species concept (diagnosable populations with unique, genetically traceable traits).

P2: Example of a "Splitter" – Sibley's Contributions

Here we get an example in ornithology: Charles G. Sibley, a splitter, used DNA technology to challenge conventional classifications of bird species, arguing for unexpected relationships among birds (like American vultures being closer to storks than to other vultures).

P3: Pushback and the Limits of Classification

Sibley's ideas faced significant criticism. A critic argues that interpreting genetic differences is arbitrary, and even Sibley concedes that species definitions are inherently slippery because many populations don’t fit our tidy definitions.

15.

Which one of the following most accurately describes the main point of the passage?

  1. Classifying biological populations into different

    Too Strong

    This answer's main clause is "many of [the problems with classifying populations into different species] are closer to resolution thanks to Sibley". This passage was not a puff piece, congratulating Sibley for a job well done. It presented a debate and didn't take a side in terms of who was right. According to this answer, the author is on Sibley's side. But the author offers Sibley's position on the species debate in the 2nd paragraph and then immediately pushes back against it in the 3rd paragraph with "Sibley's work has not been widely accepted".

    1% picked this

  2. Although scientists often disagree on

    Too Narrow

    The main clause of this answer is that "most scientists agree that all species classification systems contain arbitrary elements". There's nothing about ornithologists in here, despite the passage being largely about them. This sounds way too broad about species classification in general, and the passage is ending on a dissonant note, not a note of consensus. The final taste we get is that this debate rages on. The main clause of this answer is saying "they mostly agree".

    4% picked this

  3. Correct

    How biological populations are classified

    Why this is right

    This answer correctly centers itself on an ongoing debate over how to define species. It does leave out the ornithological contour of the passage, but the beginning / ending bookends of the passage were not specifically about ornithological species debates. They were talking about defining species more generally. The answer correctly captures that the author did not pick a side, and it captures why the author finds this debate noteworthy. In other words, we had a Present Debate passage, the author's evaluation or takeaways from that debate are in the final paragraph, and this answer echoes that takeaway. "Political and economic stakes" = practical implications.

    Skill tested: Main Point · how this choice captures the passage's function is the move to repeat next time.

    82% picked this

  4. Traditional methods of classifying biological

    Too Narrow

    This answer's main clause is "the traditional methods of species classification have been called into question by Sibley". While that's true, that wasn't the main idea in the passage. Sibley is already deceased. He's not a newcomer on the scene that the author is profiling. If the author was implicitly on Sibley's side of the debate (like if she gave Sibley the final word in the passage), then this would feel right. But she introduces Sibley's ideas in paragraph 2 only to tell us in paragraph 3 that these have not been widely accepted. Nothing in this answer matches up with the author's wrap-up paragraph.

    7% picked this

  5. Charles G. Sibley developed revolutionary

    Too Narrow

    This answer's main clause is "Sibley developed revolutionary methods, but they haven't been widely accepted". Was the central topic of this passage Sibley's methods? No, it was a debate over "how do we determine how to classify species". Sibley was just a bit player within that debate. The passage begins and ends with the broader topic of "how are we going to figure out which endangered species to preserve if we can't agree on how to define a species". That's the central topic, not Sibley's revolutionary methods.

    6% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free