Summarize Argument
The bottom-up theory claims that ecosystems are determined by how many edible plants they can support. This is because edible plants support herbivores, which in turn support predators. Everything depends on edible plants.
Notable Assumptions
While the bottom-up theory holds that the population of predators has little effect on ecosystems, the theory doesn’t account for the population of herbivores. Given that the bottom-up theory states that edible plants determine the characteristics of an ecosystem, this means the bottom-up theory assumes that an influx of herbivores also wouldn’t cause any changes. Nothing besides the availability of edible plants can have a deterministic effect on ecosystems.
A
In an effort to build up the population of a rare species of monkey on Vahique Island, monkeys were bred in zoos and released into the wild. However, the effort failed because the trees on which the monkeys fed were also nearly extinct.
This seems to support the bottom-up theory: edible plants determine an ecosystem. We need something that challenges the theory.
B
After hunting virtually eliminated predators on Rigu Island, the population of many herbivore species increased more than tenfold, causing the density of plants to be dramatically reduced.
Rather than plants determining how many herbivores an ecosystem can support, the number of herbivores determines the availability of plants. Thus, we have a deterministic factor that isn’t edible plants.
C
After many of the trees on Jaevix Island were cleared, the island’s leaf-cutter ants, which require a forested ecosystem, experienced a substantial decrease in population, as did the island’s anteaters.
Supposing those trees are edible plants, this supports the bottom-up theory. We need something that challenges it.
D
After a new species of fern was introduced to Lisdok Island, native ferns were almost eliminated. However, this did not affect the population of the herbivores that had eaten the native ferns, since they also thrived on a diet of the new fern.
Edible plants are plentiful here. This doesn’t challenge the bottom-up theory.
E
Plants that are a dietary staple of wild pigs on Sedif Island have flourished over the last three decades, and the population of the pigs has not changed much in spite of extensive hunting.
Nothing here challenges the claim that edible plants determine the characteristics of an ecosystem. Not even hunting local herbivores makes a difference.
Summarize Argument
The author concludes that social inertia plays a greater role in human behavior than the desire for comfort or safety. As evidence, he cites the fact that many historical innovations were resisted by people whose lives these innovations would’ve improved.
Notable Assumptions
The author assumes that resisting technological innovation constitutes social inertia. He also assumes that people didn’t resist technological innovation for some reason other than social inertia. Finally, the author assumes that “many examples” of this one phenomenon are enough to draw a claim about the relative power of forces determining human behavior.
A
People correctly believe that technological innovations often cause job loss.
Social inertia wasn’t the reason why people resisted technological innovation. They were rightly concerned about losing their jobs.
B
People are often reluctant to take on new challenges.
That “reluctance” sounds like social inertia. Besides, we have no evidence these technological innovations were “challenges.”
C
Some examples of technological innovation have been embraced by workers.
This points out an exception. The author, however, doesn’t need his very general conclusion to be true in all historical cases. Social inertia may still be more powerful than the desire for comfort—just not always.
D
People tend to adapt easily to gradually implemented technological innovations.
If this is true, then in many cases technological innovations haven’t been implemented gradually. People evidently didn’t adapt easily in those cases, hence the resistance.
E
People correctly believe that technological innovations almost always increase workers’ productivity.
If this is true, why are workers resisting? Inertia would seem to be a totally valid hypothesis. We need something that weakens that hypothesis.
Summarize Argument: Phenomenon-Hypothesis
In a study, joggers who habitually stretch before jogging experienced about the same number of injuries as joggers who didn’t stretch before jogging. The author believes this statistic shows stretching before jogging doesn’t help prevent injuries.
Notable Assumptions
The author assumes that there isn’t another explanation for why joggers who stretch get injuries at the same rate as joggers who don’t stretch. For example, the author’s overlooking the possibility that joggers who stretch start off with a higher chance of injury than joggers who don’t stretch. (Maybe joggers who stretch tend to be older and weaker?)
A
For both groups of joggers compared by the scientists, the rate of jogging injuries during the study was lower than the overall rate of jogging injuries.
Regardless of how the groups compared to the average joggers outside of the study, we still know that, within the study, the stretching group and non-stretching group had the same number of injuries. That still needs to be explained.
B
Among the joggers in the groups compared by the scientists, many of those previously injured while jogging experienced difficulty in their efforts to perform stretches.
We still know the stretching group and non-stretching group had the same number of injuries. Regardless of difficulty during stretching, we still know the stretching group stretched before jogging. (B) doesn’t suggest that the stretching group didn’t actually stretch.
C
Most jogging injuries result from falls, collisions, and other mishaps on which the flexibility resulting from stretching would have little if any effect.
This supports the hypothesis that stretching doesn’t help prevent jogging injuries.
D
The more prone a jogger is to jogging injuries, the more likely he or she is to develop the habit of performing stretches before jogging.
This raises the possibility that stretching might reduce jogging injuries, but the two groups had the same number of injuries because the stretching group began with a higher chance of injury than the non-stretching group.
E
Studies have found that, for certain forms of exercise, stretching beforehand can reduce the severity of injuries resulting from that exercise.
The conclusion is about stretching before jogging, and it’s based on a study about stretching before jogging. Other studies about other kinds of exercise don’t affect how we should interpret the results of the jogging study described by the stimulus.
The author concludes that superconductor development, which will enable more efficient energy transport, will improve industrial productivity. As evidence, the author offers an analogous case where oil replaced coal as the primary fossil fuel and decreased shipping costs in the process.
Identify Argument Part
The referenced text is the argument’s main conclusion. The argument uses an analogy to explain how superconductor development will improve industrial productivity.
A
It is a conclusion for which the claim that shipping costs for fossil fuels are partly a function of the losses of material in transit is offered as partial support.
Shipping costs are partly a function of transit losses, and superconductor development will enable more efficient transit. Thus the conclusion, superconductor develop will improve industrial productivity. The first premise is the “partial support” the answer refers to.
B
It is a generalization for which the claim that superconductor development will enable energy to be transported farther with less energy lost in transit is offered as an illustration.
This isn’t a generalization. Instead, it’s a specific prediction the author attempts to support through an analogy.
C
It is an assumption supporting the conclusion that superconductor development will enable energy to be transported farther with less energy lost in transit.
This is a conclusion that’s supported by the argument, rather than support itself. It’s not assumed—it’s reasoned to be likely.
D
It is a premise offered to support the claim that oil and natural gas have replaced coal as the primary fossil fuels used in North America.
The referenced text isn’t a premise. Instead, it’s a conclusion supported by premises, such as the analogy about oil and natural gas in North America.
E
It is cited as evidence that shipping costs are a function of the distances fossil fuels are shipped and the losses of material in transit.
The referenced text concludes that superconductor development will improve productivity. It doesn’t support the definition of “shipping costs,” which is what this answer refers to.
Summarize Argument
The argument concludes that social theorists who believe that people are only concerned with their self-interest must also believe that democracy is impossible. This is based on two claims: that democracy requires government by consent; and that if people are only concerned with their self-interest, government by consent is impossible.
Identify and Describe Flaw
The argument uses a claimed implication of some theorists’ belief about self-interest to come to a conclusion about what those believe about democracy. This assumes that everyone who has the belief about self-interest must agree with what that implies about democracy. However, it’s still possible that not everyone who has the belief about self-interest will agree that democracy is impossible.
A
infers merely from the fact of someone’s holding a belief that he or she believes an implication of that belief
The argument infers that everyone who believes that people are only concerned with their self-interest will also believe the supposed implication that government by consent is impossible. This inference has no support other than the mere fact of holding the first belief.
B
infers that because something is true of a group of people, it is true of each individual member of the group
The argument doesn’t make any inferences about the properties of individual people based on the properties of the groups they belong to.
C
infers that because something is true of each individual person belonging to a group, it is true of the group as a whole
The argument doesn’t make any inferences about the properties of groups based on the properties of individual people in those groups.
D
attempts to discredit a theory by discrediting those who espouse that theory
The argument isn’t attempting to discredit any theory. It also never tries to discredit supporters of any theory—in fact, there’s no discussion of people’s character at all.
E
fails to consider that, even if an argument’s conclusion is false, some of the assumptions used to justify that conclusion may nonetheless be true
The argument doesn’t attempt to claim that any other argument’s conclusion is false.
This is a pretty tough question. Hopefully, you're well trained by now to always separate premises from conclusions.
This passage makes you work for it. The first sentence is a premise:
selfish --> /gov't by consent
The second sentence contains a conclusion followed by "since" and another premise:
/gov't by consent --> /democracy
Forget the conclusion for now. Let's just piece together the premises.
selfish --> /gov't by consent --> /democracy
What conclusion can you validly draw? This one:
selfish --> /democracy
What conclusion do they draw?
B(selfish) --> B(/democracy)
Sort of. They make a small assumption [/democracy --> futile to aspire to democracy]. Anyway, this is a tiny assumption and reasonable too, so let's concede this point.
Besides, they committed a huge logical error.
If I tell you that Tommy is 3 years old and just formed a new belief that this delicious object he's eating is called "banana". Can you conclude that Tommy believes that this object is a fruit? That's reasonable isn't it since banana --> fruit?
Well, that depends on whether Tommy knows that conditional relationship holds. Tommy just learned "banana". Who knows if he understands that "banana" is a sub-set of this other thing called "fruit".
Now imagine things more complex than "banana" and "fruit" and you'll see that this applies to all of us. We don't know all the logical relationships that exist. X --> Y may be true, but if we are unaware of that truth, our knowing X doesn't imply our knowing Y.
Anyway, this is not the first time that you've seen this exact error on the LSAT. Plenty of questions before this one committed similar errors.