"Surprising" Phenomenon
Why are shrimp at different coral reefs genetically distinct when ocean currents mix up baby shrimp between populations?
Objective
A hypothesis resolving this discrepancy must explain why the intermingling of baby shrimp between reefs is not enough to make those shrimp genetically indistinguishable. It will imply that baby shrimp exchanged between reefs do not breed with each other, or that their interbreeding is not enough to blur the genetic lines between populations.
A
The genetic differences between the shrimp populations are much less significant than those between shrimp and any other marine species.
This does not explain why the shrimp are genetically distinct. If the shrimp have similar genetics, their failure to interbreed is more surprising, not less.
B
The individual shrimp within a given population at any given Indonesian coral reef differ from one another genetically, even though there is widespread interbreeding within any such population.
This deepens the mystery. If the shrimp are capable of interbreeding despite significant genetic differences, then their failure to interbreed between reefs is more surprising.
C
Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched.
This explains why the shrimp populations do not interbreed. Baby shrimp carried to other reefs do not breed until traveling back to their home reefs, so shrimp born at different reefs do not breed with each other.
D
Most shrimp hatched at a given Indonesian coral reef are no longer present at that coral reef upon becoming old enough to breed.
This deepens the mystery. If most shrimp leave their home reef by breeding age, the genetic distinguishability of shrimp between reefs is more surprising.
E
Ocean currents probably carry many of the baby shrimp hatched at a given Indonesian coral reef out into the open ocean rather than to another coral reef.
This does not state that shrimp are rarely exchanged between reefs, only that many do not end up at any reef. It does not explain why the baby shrimp that are exchanged between reefs fail to breed with each other.
Summarize Argument
The author concludes that seawater agriculture should be cost-effective in desert regions near sea level. He supports this by saying that salt-tolerant plants (halophytes) require more water but can be irrigated with seawater, which is much cheaper to pump than freshwater.
Notable Assumptions
The author assumes that seawater agriculture is cost-effective simply because seawater irrigation is cost-effective. He assumes that the benefits of seawater irrigation outweigh any other potential costs of seawater agriculture, like higher fertilizer or equipment costs.
A
A given volume of halophytes is significantly different in nutritional value for animal forage from the same volume of conventional forage crops.
This doesn't tell us if halophytes are more or less nutritious than conventional crops for animal forage. Knowing they have "significantly different" nutritional value doesn't help to establish that halophytes are more cost-effective.
B
Some halophytes not only tolerate seawater but require salt in order to thrive.
The author says that halophytes are salt-tolerant and that they’re more cost-effective because they can be irrigated with seawater. In other words, she already assumes that the plants will be irrigated with salt water. The fact that they require salt is irrelevant.
C
Large research expenditures are needed to develop the strains of halophytes best suited for agricultural purposes.
This weakens the argument by presenting another cost of halophytes. If seawater agriculture requires expensive research, it might not actually be more cost-effective overall.
D
Costs other than the costs of irrigation are different for halophytes grown by means of seawater irrigation than for conventional crops.
The fact that other halophyte costs are “different” from conventional crop costs doesn't tell us if halophytes are more or less expensive overall.
E
Pumping water for irrigation is proportionally one of the largest costs involved in growing, harvesting, and distributing any forage crop for animals.
If irrigation is one of the largest costs in producing forage crops, this suggests that seawater agriculture may indeed be more cost-effective in certain areas, since seawater irrigation is much cheaper.
Summarize Argument
The author concludes that the number of deaths per year would decrease by half if medicine could prevent all iatrogenic disease. This is based on the fact that as many people die of iatrogenic disease (deaths from medical treatments or hospitalization) as die of all other causes combined.
Identify and Describe Flaw
The author overlooks the possibility that if people didn’t die of iatrogenic disease, they might die of other causes (such as the illnesses that required them to be hospitalized or to undergo treatment). So even if we could prevent iatrogenic disease, the number of deaths per year would not go down by half.
A
prevention of noniatrogenic disease will have an effect on the occurrence of iatrogenic disease
The argument concerns what would happen if we could get rid of iatrogenic disease. It’s not clear what impact prevention of noniatrogenic disease has on the reasoning.
B
some medical treatments can be replaced by less invasive or damaging alternatives
The author never assumed that no medical treatment could be replaced by less invasive/damaging alternatives. So pointing out that such replacements are possible doesn’t undermine the reasoning of the argument.
C
people who do not die of one cause may soon die of another cause
This possibility points out that the number of deaths per year would not necessarily decrease by half, even if iatrogenic disease were prevented. People who don’t die from hospitalization might instead die from something else.
D
there is no one way to prevent all cases of death from iatrogenic disease
The conclusion is conditioned on medicine finding ways of preventing iatrogenic disease. The conclusion doesn’t assume that this is possible. It only assumes what would result IF it were possible. So pointing out that prevention is not possible doesn’t undermine the argument.
E
whenever a noniatrogenic disease occurs, there is a risk of iatrogenic disease
We already know that iatrogenic disease results from treatments/hospitalization. So the author would already acknowledge that iatrogenic disease might result from other kinds of diseases. The conclusion doesn’t assume that eliminating iatrogenic disease is actually possible.
Summarize Argument: Counter-Position
Some people argue that negative news reports on the economy can hurt the economy, because those reports hurt people’s confidence in the economy, which can affect their spending.
The author concludes that negative news reports on the economy don’t hurt the economy, because spending trends correlate closely with people’s confidence in their own economic situations.
Identify and Describe Flaw
The author overlooks the possibility that negative news reports on the economy can decrease people’s confidence in their own economic situations; if this occurs, the reports can still lead to lower spending and damage to the economy.
A
one’s level of confidence in one’s own economic situation affects how one perceives reports about the overall state of the economy
This possibility doesn’t indicate how negative news reports can lead to lower spending. With (A), we have no reason to think that the reports affect confidence in one’s own economic situation.
B
news reports about the state of the economy are not always accurate
The accuracy of reports is irrelevant, because we’re concerned with the effects that reports have on confidence levels in the economy. Reports can affect confidence without being accurate.
C
people who pay no attention to economic reports in the media always judge accurately whether their own economic situation is likely to deteriorate or improve
The argument concerns how news reports can affect people generally. There might be some people who don’t pay any attention to reports in the media; news reports may or may not have effects on people overall, regardless of the existence of people who don’t pay attention to media.
D
people who have little confidence in the overall economy generally take a pessimistic view concerning their own immediate economic situations
(D) points out how news reports might still harm the economy by decreasing people’s confidence in their own economic situations through decreasing confidence in the overall economy.
E
an economic slowdown usually has a greater impact on the economic situations of individuals if it takes people by surprise than if people are forewarned
The comparative effects of a surprise slowdown vs. an expected slowdown has no impact on whether news reports can affect the economy.
Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that last year’s mild winter caused this year’s larger-than-usual bird population. This is based on the fact that the mild winter allowed a higher proportion of birds to forage naturally rather than forage at a feeder. In addition, the mild winter also allowed many bird species to avoid having to migrate south during winter, which reduced typical deaths from having to migrate.
Notable Assumptions
The author assumes that there’s no other explanation for why there was a larger-than-usual bird population. The author also assumes that a higher proportion of birds forage naturally rather than by using a feeder is something that is beneficial to bird population.
A
Increases in bird populations sometimes occur following unusual weather patterns.
This doesn’t help establish a causal relationship between a mild winter and the larger bird population. (A) is consistent with a completely coincidental relationship between weather patterns and bird populations.
B
When birds do not migrate south, the mating behaviors they exhibit differ from those they exhibit when they do migrate.
Different mating behaviors have no clear relationship to increased population. In any case, the premises already show how removing the need to migrate south helps increase populations by reducing attrition. We don’t need additional support regarding this aspect of the argument.
C
Birds eating at feeders are more vulnerable to predators than are birds foraging naturally.
This helps establish a causal mechanism between having a lower proportion feeding at bird feeders and a larger population. By allowing a lower proportion to feed at feeders, a mild winter helped protect birds from predators.
D
Birds that remain in their summer range all winter often exhaust that range’s food supply before spring.
If anything, this is something negative about a mild winter. If birds that don’t migrate south often exhaust food supplies before spring, this might suggest a mild winter could make survival more difficult.
E
Birds sometimes visit feeders even when they are able to find sufficient food for survival by foraging naturally.
We know the mild winter allowed a lower proportion to feed at feeders. The fact that some birds might still visit feeders despite not needing to doesn’t change or add to our understanding of the premises and how they relate to the conclusion.
Summarize Argument: Phenomenon-Hypothesis
The number of news stories about small observational studies is larger than the number of news stories about large randomized trials. The author hypothesizes that the reason for this phenomenon is that small observational studies are more likely to have dramatic findings than a large randomized trial. This is based on the fact that newspaper stories tend to report only on studies with dramatic-sounding stories.
Identify and Describe Flaw
The author overlooks alternate explanations for the greater number of stories about small studies. For example, one possibility is that there are simply a greater number of small observational studies than large randomized trials. This is how the overall rate of dramatic findings might be the same between small and large, but we still end up with a greater number of news stories about small studies than large studies.
A
It casts doubt on the reliability of a study by questioning the motives of those reporting it.
The author does not comment on the motives of anyone. Although the author does mention that observational studies are “somewhat unreliable,” he does not suggest that they are unreliable because of the motives of people of people conducting the study or reporting on it.
B
It fails to consider that even if a study’s findings sound dramatic, the scientific evidence for those findings may be strong.
The author’s not concerned with proving whether certain kinds of studies are reliable. So the quality of the evidence is irrelevant. The issue is whether small studies are more likely to have dramatic findings than large ones.
C
It confuses a claim about scientific studies whose findings sound dramatic with a similar claim about small observational studies.
The first sentence claims that newspapers report only on studies with dramatic-sounding results. The second sentence claim stories about small studies are more frequent. These aren’t “similar” claims, but even if they are, the author does not mix up these two claims.
D
It overlooks the possibility that small observational studies are far more common than large randomized trials.
If the small studies are more common than the large ones, that provides an alternate explanation for why there are more news stories about small studies. The greater number of stories doesn’t have to be due to small studies’ having a higher rate of dramatic findings.
E
It fails to rule out the possibility that a study’s having findings that sound dramatic is an effect rather than a cause of the study’s being reported on.
The first line says newspapers tend to report only on studies whose findings sound dramatic. Thus, (E)’s possibility isn’t true. Some studies’ findings sound dramatic. When newspapers choose what to write about, they choose the studies whose findings sound dramatic.