PrepTest 126

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
1940s study - Parthenogenesis sometimes occurs in mammals
Rebuttal - The study's methods were flawed, and no other studies have successfully shown the conclusion to be true
Conclusion - Parthenogenesis doesn't occur in mammals (something about chromosomes)

Answer Anticipation:
DO NOT get wrapped up in the science here. Chromosomes, parthenogenesis, fertilization—these words are getting thrown around to confuse you. You don't need to know any science to understand this question—or any question on the LSAT, for that matter.

Instead, we should focus on the argument itself and try to identify elements that are flawed. And this one has a common error in reasoning!

Normally, when a study is done, we would start by considering a sampling flaw, and a correlation/causation flaw. However, in this argument, the study mentioned is specifically noted as not leading to a valid conclusion.

In fact, the argument's conclusion reaches the opposite conclusion of the study—that study concluded parthenogenesis does happen in mammals, and the argument concludes that it doesn't. Whenever an argument reaches the opposite conclusion of an opposing point, we should consider an Absence of Evidence flaw.

In this flaw, the argument uses a flaw in an opposing point, or a lack of conclusive evidence for that point, to conclude that the opposing point is wrong. Note that concluding the opposing point might be wrong isn't a flawed conclusion—if a conclusion is based on flawed logic or inconclusive evidence, then it could be wrong. This flaw is present only when that lack of evidence is used to prove the opposite conclusion.

Here, the argument reaches the opposite conclusion of the study based on a flaw in the study and a failure of other studies to reach the same conclusion. That's enough evidence to conclude that parthenogenesis might never happen in mammals, but not that it never does—let alone that it doesn't for some specific reason (chromosomes). However, the argument is flawed in treating this failure to prove parthenogenesis happens in mammals is sufficient to prove that it doesn't. Let's find that absence of evidence flaw answer.

Answer Explanation:
This is the absence of evidence flaw answer, so it's the correct answer. The argument points out a flaw in a study that showed parthenogenesis happens in mammals, and then uses the lack of subsequent studies that reach the same conclusion to support the opposite conclusion (i.e., the conclusion that the initial view is false). There's no evidence that parthenogenesis doesn't happen in mammals—no analysis of what in the chromosomes might prevent it—and so the argument is based on an absence of evidence for the opposing point.

Key Takeaway:
Whenever an argument reaches a conclusion that is the opposite of the opposing point—in other words, that reaches a conclusion that an opposing point is wrong/false—you should consider an absence of evidence flaw. If that conclusion about the falsity of a view is based on an absence of evidence proving without a doubt the opposing point is true, then you've identified the flaw!

Incorrect. The stimulus says that parthenogenesis is known to occur in "a wide variety" of nonmammalian species, so it doesn't assume that it's a characteristic shared by all such species.

Incorrect. It's unclear what phenomenon this answer is referring to, or what the alternative explanation would be. There was some phenomenon that led biologists to conclude rabbits were reproducing through parthenogenesis, but it's never stated what that phenomenon was. Parthenogenesis itself would be the ruled out explanation, so it can't serve as the phenomenon itself. Additionally, there's no alternative explanation for whatever the phenomenon is outside of parthenogenesis, just that that can't be the explanation.

Incorrect. If anything, the argument establishes something that isn't a necessary condition for parthenogenesis when it defines it as being reproduction without an egg.

Incorrect. The argument doesn't assume that the methods are flawed—it establishes those methods as having "been shown to be flawed."