Logical reasoning PrepTest 137 · Section 4 · Question 6

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
The rate of extinction hasn't changed since the 70s, and it's likely that the rate of new species emerging hasn't changed in centuries, so Earth's total number of species probably isn't decreasing.

Answer Anticipation:
This argument reaches a conclusion that the total number of species on Earth probably isn't decreasing. What's that based on? There are a number of species going extinct, sure, but the number of new species forming is probably balancing that out.

Why does the author believe that this is balancing out? Because these numbers probably haven't changed much—the extinction rate since the 70s, the new species rate in centuries. However, that's assuming that the numbers in the 70s balanced out! If we've been losing species for a few decades, then the argument falls apart. Let's look for any answer highlighting that the declines from the 70s were higher than that rate of speciation.

Answer Explanation:
This answer establishes that in 1970—the baseline year used by the Columnist—there were more extinctions than new species emerging. This undercuts her argument by showing that the baseline she established actually leads to the opposite conclusion that she draws.

Key Takeaway:
When an argument relies on things not changing in order to reach its conclusion, make sure that the baseline supports that conclusion!

Incorrect. The argument is over the total number of species on Earth, so looking at any specific area is out of scope/not broad enough to affect the conclusion.

Incorrect. The rate of extinction balanced against the rate of speciation is relevant, not the overall number of extinct species.

Incorrect. Concern doesn't impact reality—this answer jumps between a subjective consideration and an objective one.

Incorrect. The argument is about the actual extinction rate, not awareness of it ahead of time, so this answer is out of scope.