LSAT 101, Section 4, RC Passage 3, Latitudinal Gradient

RC Passage 3 Explanation

Paragraph Summaries

1. The closer you get to the equator, the more species you’ll find (within the same type of habitat).
2. One theory is that species had more time to evolve in the tropics, since they were unaffected by ice ages.
3. A second theory is that there is more energy in the tropics, and this produces more life.
4. A third theory says that the tropics are more stable, and reliably provide resources.
5. A fourth theory is more likely to be correct. It says that the rate of new species formation is higher in areas closer to the equator.
6. New species develop because sub-groups break off and survive. It’s easier for isolated sub-groups to survive in the tropics.

Analysis

There is a lot of information in the passage. You do not need to memorize it.

Instead, when a specific theory is mentioned, you need to quickly reread the paragraph that mentions that theory. Success on this passage depends on mastering the details of each theory, when you’re asked to do so.

You do need to understand a few key terms. Longitudinal gradient refers to the idea that within each type of habitat, there are more species in areas closer to the equator.

So a northern forest will have fewer species than a southern forest. But a northern forest could have more species than a southern desert.

The author discusses four theories. He disagrees with the first three, and then agrees with the final theory.

An unusually large proportion of the wrong answers for this passage are nonsense. On science passages, it’s common for the test writers to string together random terms from the passage to create plausible sounding answers that mean nothing.

The solution? Reread relevant sections for each question, and make sure you know what’s going on. You’ll more than make up for the time you spend understanding, because you’ll get through the wrong answers twice as fast. It’s easy to eliminate nonsense answers if you understand the concepts.