Logical reasoning PrepTest 131 · Section 1 · Question 15

Incorrect. If a theory is wrong in a key way, then it doesn't matter if it's correct in others—it's an incorrect theory.

Incorrect. The argument does establish an inability to interbreed as a sufficient condition for species distinction, but it doesn't then treat it as necessary.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
Typological theory - Species are grouped based on physical characteristics
Shortcoming - There are species that are physically identical but can't interbreed
Mainstream theory - Animals that can't interbreed are different species
Conclusion - Typological theory is wrong

Answer Anticipation:
Any of these science passages can be difficult to follow, so it's usually a good idea to do two things. First, keep the theories straight. Second, work backwards from the conclusion.

So first, the theories. There are two here—the Typological Theory, and the Mainstream Theory. The Typological Theory is featured in the conclusion, and it's stated to be wrong.

Why? Because it can't account for "sibling species"—species that are physically identical but can't interbreed. Why are they a problem for the Typological Theory? Because the Mainstream Theory says that species that can't interbreed are separate species, but the Typological Theory would classify these as the same species.

But wait—the author is throwing out a theory because it contradicts another theory. There's no evidence that the Mainstream Theory is correct, however! It's not established that species that can't interbreed are separate species—just that the Mainstream Theory states that.

This answer is similar to question #14 in this section in that it assumes one theory is right over a contradictory theory. However, without presenting information supporting the Mainstream Theory's definition of a species over the Typological Theory's, this argument is flawed.

Answer Explanation:
The argument assumes that the Mainstream Theory's belief that species that can't interbreed are separate species is correct, and thus the Typological Theory must be "unacceptable" because it can't account for that. However, that assumes the truth of the Mainstream Theory without providing reason to believe it, and so the argument is flawed in the manner suggested by this answer choice.

Key Takeaway:
Whenever there are competing theories or experts, see if the author gives a reason to believe one over the other. Often, the author will prioritize one without explaining why.

Incorrect. This answer doesn't highlight a flaw—pointing out an error in a theory is enough to show the theory is false.

Incorrect. It doesn't matter why they can't interbreed, just whether that means they're not the same species.