Reading Comprehension

PT101 · S4 · P3 · Q15 Species Gradient

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

When the same habitat types (forests, oceans, grasslands, etc.) in regions of different latitudes are compared, it becomes apparent that the overall number of species increases from pole to equator.

Topic

The increase in species diversity from poles to equator: why there are more species in the tropics than at higher latitudes.

Framework

Answer / Explain

Main Point

The passage explores several hypotheses to explain why there are more species near the equator than near the poles but favors the idea that higher speciation (and not higher extinction) in the tropics best explains this pattern. (Most valuable sentence: Last sentence of P5: )

P1: The Pattern—Latitudinal Diversity Gradient

Scientists have noticed that as you move from the poles toward the equator, the number of species in similar habitats increases, with the effect likely being even bigger than currently known.

P2: The Time Theory Hypothesis

One idea ("time theory") says tropical regions have more species simply because they've had more time without disruptive ice ages for new species to evolve, but this doesn't fully account for differences among various regions.

P3: The Species-Energy Hypothesis

Another hypothesis suggests that more sunlight in the tropics means higher growth and reproduction rates, which could lead to more biomass and thus more species, but the supposed chain of cause-and-effect has several weak links and is unproven.

15.

Which one of the following most accurately expresses the main idea of the passage?

  1. At present, no single hypothesis

    Opposite, if anything

    This flies in the face of 'A fourth and most plausible hypothesis" at the beginning of the 2nd to last paragraph. Granted, plausibility is not the same as how widely something is accepted. But the passage never really discusses how widely accepted any of these theories are.

    5% picked this

  2. The tropical climate is more

    Wrong Emphasis

    This is just asserting the Puzzling Fact that sets the stage for the passage. It's essentially saying, "There is a latitudinal gradient". But the main point of the passage is the author's attempt to explain why the tropical latitude is more conducive to higher numbers of species.

    6% picked this

  3. Correct

    Several explanations have been suggested

    Why this is right

    This nicely captures the purpose of the passage (considering possible Explanations for the Puzzling Fact of the latitudinal gradient, which is a global pattern in species distribution). And it conveys the fact that the author "picks a winner" when she reaches the fourth hypothesis, which focuses on speciation.

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

    83% picked this

  4. Despite their differences, the various

    Out of Scope

    Out of Scope: concur / predict increase Wrong Emphasis The author never says that all these hypotheses make a common prediction that the latitudinal gradient will increase. And this answer would just be missing the mark of delivering the author's big payoff idea, if it doesn't put a big spotlight on the author's preferred answer to this causal mystery: the fourth hypothesis about speciation.

    5% picked this

  5. In distinguishing among the current

    Too Strong: most important Wrong Emphasis

    Again, we have an answer that isn't conveying anything resembling the big payoff idea, "X is the most promising explanation for the puzzling fact we've been discussing". This answer is saying, "As we consider various explanations for the puzzling fact, the most important criterion to keep in mind is Y." Not only is that kind of language not supported anywhere, but it would be pretty strange for any author's main point to be, "As we survey several options, the most important criterion is Y." It's much more likely that an author's main point would be, "Since the most important criterion is Y, that makes Z the best of the available options."

    1% 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