Logical reasoning PrepTest 131 · Section 2 · Question 21

Incorrect. This answer provides indirect means for disease to lead to animal deaths and extinction, so it aligns with the argument instead of weakening it.

Incorrect. One way to counter the argument in the stimulus is to raise counterexamples—organisms that were exposed to the disease-causing microorganisms but didn't go extinct, such as humans. This answer choice explains why humans aren't a counterexample to the argument, thus removing a potential weakener.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Many species went extinct within a few thousand years of humans coming to North America, but it's implausible that hunting caused the extinction, so it was probably disease carried with humans.

Answer Anticipation:
The conclusion is about the "crucial factor" that led to animal extinctions—causal language. Is this relationship based on a correlation? It sure is—humans arrived, and animals were dead within 2,000 years.

The argument then rules out one way humans could have caused the extinction (hunting) before settling on another—disease caused by microorganisms.

As with any argument that jumps from correlation to causation, the correct answer can weaken this argument in some common ways—identify an alternative cause; bring up counterexamples; provide evidence the relationship is reversed. The last doesn't make sense here—animals going extinct won't cause disease-causing microorganisms to travel with humans. However, alternative causes and counterexamples are definitely in play, so let's head to the answers with those in mind.

Answer Explanation:
An interesting answer that provides evidence for an alternative cause—hunting (we'll circle back to that premise). If very few animals that weren't hunted went extinct, then that provides evidence it was hunting and not disease that caused the extinctions. But what about that premise—which we have to accept as true—that "ruled out" hunting? We need to look at it again—it doesn't say that it's impossible hunting led to extinction, just that it's "implausible." Implausibility is a subjective statement about what the speaker believes is possible, so hunting as the true cause of the extinctions isn't truly ruled out by the stimulus.

Key Takeaway:
File this "implausible" takeaway under Unlikely to Repeat on the exam—in general, premises are premises and you can't call them into question.

The bigger takeaway here is that arguments that ask you to weaken correlation/causation arguments will frequently have correct answers that highlight an alternative cause, and that's particularly true when an alternative cause is raised in the argument itself. Here, in raising hunting as an alternative cause of the extinctions, the stimulus was previewing the correct answer.

Incorrect. In speaking about "individual" humans and animals instead of the species as a whole, and not getting into how prevalent this type of immunity is within the species, this answer choice just doesn't have enough weight to impact the argument. Even if it did, it would provide an explanation for how humans could carry these diseases without going extinct.

Incorrect. Without knowing if these species were among those that the new arrivals (humans) encountered, this answer doesn't necessarily have an impact on the argument.