Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that foraging causes increased brain size in bees. This is based on the fact that older bees tend to have larger brains than do younger bees, and older bees are more likely to forage than are younger bees. In addition, foraging requires greater cognitive ability than what younger bees do.
Notable Assumptions
The author assumes that the correlation between foraging and larger brains is not explained by something else besides foraging causing larger brains. This overlooks the possibility that bees’ brains naturally get larger as they get older, and since older bees are the ones that forage, we see a correlation between foraging and larger brains.
A
Bees that have foraged for a long time do not have significantly larger brains than do bees that have foraged for a shorter time.
The author never suggested that the length of time one forages will cause significant differences in brain size. The hypothesis is simply that engaging in foraging increases brain size. The effects might occur immediately rather than over time; the author never says otherwise.
B
The brains of older bees that stop foraging to take on other responsibilities do not become smaller after they stop foraging.
The author never suggested that the causal impact of foraging on brain size is only temporary. The hypothesis is that foraging increases brain size; that increased brain size might remain even if foraging stops.
C
Those bees that travel a long distance to find food do not have significantly larger brains than do bees that locate food nearer the hive.
The author never suggested that foraging distance will impact brain size. The hypothesis is simply that foraging increases brain size; the kind of foraging or the distances traveled might not matter.
D
In some species of bees, the brains of older bees are only marginally larger than those of younger bees.
This still indicates that the brains of older bees are larger than the brains of younger bees. The author never suggested that foraging had to create a significant difference in brain size.
E
The brains of older bees that never learn to forage are the same size as those of their foraging counterparts of the same age.
This provides evidence that the true cause of larger brains in the older bees is not foraging, but might be age. If foraging were the cause, we’d expect foragers to have larger brains than non-foragers. But (E) shows this isn’t the case.
Note: This video deals with Passage A only. In this video, J.Y. uses the split approach for comparrative passages. This means he reads through Passage A and then makes a first pass through the questions, answering them to the extent possible based solely on the information in Passage A. For an explanation of Passage B and the remaining unsolved questions, head to the next video (shift + → on your keyboard).
Note: This is video #2 in a two-part explanation using the split approach for comparative passages. In the previous video, J.Y. already tackled whatever questions he could based solely on a readthrough of Passage A. In this video, he picks up with Passage B and then cleans up the remaining questions. So, if you don't see a full explanation for a given question in this video, it's because J.Y. tackled that question in the previous video. (Press shift + ← to head to the previous video.)
Summarize Argument
The author concludes that it probably wouldn’t be prohibitively expensive to reduce carbon dioxide emissions from fossil fuels enough to halt global warming. This is because the chemical industry had claimed something similar about CFCs, only to eventually replace them with substitutes at a profit.
Notable Assumptions
The author assumes that fossil fuel industries would be able replace fossil fuels with substitutes in the same way the chemical industry replaced CFCs with substitutes. And in order for the shift from carbon dioxide-producing fossil fuels not to be “prohibitively expensive,” the author also assumes that the fossil fuel industry is financially similar to the chemical industry in all relevant aspects.
A
In the time since the chemical industry phased out CFCs, the destruction of the ozone layer by CFCs has virtually halted, but the levels of carbon dioxide emitted by the use of fossil fuels have continued to increase.
We already know there’ve been no equivalent changes in the fossil fuel industry. We’re trying to strengthen similarities between the fossil fuel industry and the chemical industry.
B
In some countries, the amount of carbon dioxide emitted by the use of fossil fuels has already been reduced without prohibitive expense, but at some cost in convenience to the users of such fuels.
We care about reducing carbon dioxide emissions to levels low enough to halt global warming. We have no idea how much these emissions have been reduced.
C
The use of CFCs never contributed as greatly to the destruction of the ozone layer as the carbon dioxide emitted by the use of fossil fuels currently contributes to global warming.
We don’t care which is worse for the environment. This just tells us the fossil fuel industry will have to make a huge effort to change.
D
There are ways of reducing carbon dioxide emissions that could halt global warming without hurting profits of fossil-fuel producers significantly more than phasing out CFCs hurt those of the chemical industry.
This tells us that fossil-fuel producers can do what the chemical industry did. Thus, it probably wouldn’t be prohibitively expensive to reduce carbon dioxide emissions to levels low enough to halt global warming.
E
If international agreements forced fossil-fuel producers to find ways to reduce carbon dioxide emissions enough to halt global warming, the fossil-fuel producers could find substitutes for fossil fuels.
We’re not talking about finding alternatives to fossil fuels. We’re talking about reducing carbon dioxide emissions from fossil fuels.