Logical reasoning PrepTest 124 · Section 1 · Question 3

Incorrect. First, without establishing whether this is true in humans, there's a big shortcoming in this answer. Second, even ignoring that, resistance is out of scope as it means that they still have the potential to be infected by the disease, but they also have preventative measures to stop that from happening.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Humans and cats have a lot of DNA in common. Many human diseases are genetic in nature. Therefore, the shared DNA is the reason we have so many diseases in common.

Answer Anticipation:
In Weaken (and Strengthen) questions, correlation/causation flaws are extremely common, so we should be on the lookout for them. And while we're used to seeing purely correlative language ("more likely", "tends to", "associated with"), or conditional language, comparisons are also correlations—two things share a common element.

So while this argument is heavily steeped in comparisons, it also has a causal assumption—that genes are the cause of the diseases we have in common. And that's based on a correlation between our DNA.

"But wait," you might ask, "doesn't the argument say that genes are the cause of these diseases, thus providing a causal premise?" It's correct to say that there's a causal premise, and that genes are cited as a cause of "[m]any" human diseases. However, it doesn't state that the human diseases with a genetic basis are the ones they share with cats.

As such, anything that calls into question that connection will weaken this argument.

Answer Explanation:
If the shared diseases don't have a genetic basis, then the causal relationship between the shared DNA and these diseases is severely weakened. This answer directly attacks that relationship, but it can feel as if it's directly questioning a premise. It's not, however, as we noted in the Anticipation step—since the argument just states that some human diseases have a genetic basis, that doesn't guarantee overlap with the diseases shared with cats.

Key Takeaway:
In order to hide a correlation/causation flaw, the LSAT will sometimes assume a causal relationship instead of explicitly stating one in the conclusion of the argument. Be on the lookout for this in any argument that brings up a correlation, or that seems to be talking about causes. Also, note that comparisons can be viewed as correlations!

Incorrect. All these diseases could have a genetic basis, especially since humans and these primates have so much DNA in common, suggesting the primates and cats do, as well.

Incorrect. They still exist—the argument isn't about how big of a problem this is, just whether the diseases have a certain cause.

Incorrect. The genes they do share with cats could still be the basis for disease.