Logical reasoning PrepTest 157 · Section 3 · Question 11

Flawed

Identify the conclusion Identify the premise Determine the role played by the statement from the question stem. For example...

Premise Main conclusion Premise/conclusion

Find the answer choice that correctly expresses the role

On an Argument Structure question, an experienced test taker will first thoroughly deconstruct and understand the entire argument in the passage. Even though our job is to understand the role of the statement in the question stem, the benefits of understanding the whole argument are twofold. First, trying to figure out the role of the statement-in-question too early and without considering the entire argument can sometimes bias us and lead to an incorrect determination. Second, many answer choices will require us to know the roles of multiple propositions. (For instance, if the statement-in-question is a premise/conclusion, we'll probably also need to know which premise supports the premise/conclusion and which conclusion the premise/conclusion supports.) So, let's break down the biologists's entire argument, starting with the conclusion. The last sentence, which uses the structural phrase "It follows that," is the main conclusion. So, the conclusion asserts that the only reason reproduction through sex became the norm for plants and animals is that it helped some species survive over others. What are the other claims doing in this biologist's argument? It's a little difficult to unpack, as the first and second sentences seem like they're at odds. The first sentence establishes that reproduction through sex promotes genetic diversity, which is advantageous for the entire species. That definitely supports the conclusion's assertion that reproduction through sex became the norm for plants and animals because it helped some species survive over others. If reproduction through sex makes it easier for some species to survive, it makes sense that species that reproduced through sex survived over others that didn't reproduce through sex, making reproduction through sex the norm. But what about the second sentence? That establishes that genetic diversity doesn't help individuals survive. How does that figure into the argument? To see that, it can help to consider counterarguments to the conclusion. The phrase "the sole reason" in the conclusion suggests that biologist believes they just refuted a potential counterargument. So, we can consider what alternative conclusions could be drawn in the absence of the second sentence. Pretend like the second sentence wasn't in the argument. In that case, reproduction through sex could promote genetic diversity among individuals of a species, making those individuals more likely to survive. If that were true, it's possible that within a species, some individuals could reproduce through sex and others without sex. If the individuals who reproduced through sex were more likely to survive than the individuals who reproduced without sex, the percentage of sexual reproductive individuals within the species could increase until the entire species was composed solely of sexually reproductive individuals. Rather than one sexually reproductive species surviving over another species that wasn't sexually reproductive, a species could have gradually become sexually reproductive. The second premise, however, eliminates that alternative conclusion. If genetic diversity doesn't make individuals more likely to survive, then the above hypothetical couldn't occur. That supports the biologist's conclusion that the only reason reproduction through sex became the norm is that it helped some sexually reproductive species survive over other species that weren't sexually reproductive. In other words, the second sentence is also a premise that supports the argument's main conclusion. And wouldn't you know it, the question stem asks us about the role of the second sentence, which was the hardest role to figure out. That's just like you, the LSAT. Anyway, we did the hard work and figured out that it's a premise, and now we can look for that in the answer choices.