Passage map: Overall the passage describes genetic diversity as another unintended consequence of severed environmental disruptions to Salmon Habitats
P1: to describe the extent of the problem and non-obvious
p2: To argue that large scale disturbances in one locale impact another
p3: To state the potential human cause of straying
Q1 E is correct - quite clear from the 1st - 2nd sentence in P1
A - no conventional explanation therefore incorrect
B - no common misunderstanding therefore incorrect
C - no, not to compare, but to argue that humans can have the same effect
D - no, the argument routinely refers to one environmental effect and humans as one potential cause of this effect
Q2 Inference -refer back and infer.
We are told that some salmon stray to other streams and that this straying is crucial as it provides a source of novel genes and a way by which a location, presumably the disturbed one, can be repopulated if the fish in that disturbed population disappear.
We are then asked to infer what straying provides:
A - it does not state anywhere that pristine streams become polluted by straying populations -incorrect
B - no, we are in fact told the opposite - that dilution occurs.
C - no. We aren't told anything on the population numerical impact
D - Yes. As we are told, VERY INDIRECTLY, "a location can be repopulated".
E - No. We have no basis for this statement.
Q3 Detail - refer back.
We are told of the impact on human activity in the first and last paras. The obvious impact is the numerical effect: decrease in population of polluted environments.
A is incorrect- we are only told that the populace decreases in polluted rivers, nothing of an "increase" in "previously polluted" streams
B is correct - this statement - " the decline in the number of salmon in SOME rivers" (the polluted ones) is the stated effect
C is incorrect because we aren't given a quantitative link between straying and human impact
D is incorrect because we are in fact told the opposite in the last para - "substantial gene flow"
E is incorrect because we are told that humans' increase the vulnerability of salmons by increasing the likelihood of their populace straying
Q5 Which of the following must be true in order for the argument to be true? That's the question.
The argument: A dramatic increase in straying from damaged streams to more pristine streams increases gene flow, lowering the fitness of subsequent generations.
A - This is not required for the argument to be true because humans could SIMPLY cause straying e.g. 1-2% straying rate and the fitness of subsequent generations of the salmon impacted could still be lowered
B - Again, this quantity is not necessarily assumed in arguing that the overall fitness decreases
C must be true because if it weren't true then it wouldn't matter if salmons inter-bred. The argument is that "fitness" (or how good something is) essentially decreases, so if decreasing is bad, what must be true? Keeping genes pure must be true.
D is incorrect - NO - humans are PART of the cause, not ALL of the cause
E is incorrect - no this is the opposite. What's inferred by E is that some of the straying salmon DONT decrease the fitness.
Q6 The potential for humans to impact straying is discussed in P3 by the statement - "although NO ONE has QUANTIFIED changes in the rate of straying as a result of...humans" "there is no reason to believe that the effect would be qualitatively different".
A is not mentioned or supported
B is incorrect because no such studies exist
C is mentioned in the passage, but it is not mentioned in support of the argument that humans increase or cause straying rates. For this reason, C is incorrect.
D is incorrect. Firstly it is the weakness in the view that humans ONLY decrease populations - the whole premise of the passage is that HUMANS DO OTHER THINGS i.e. "increase Straying". Second, "extinction" generally isn't supported. Third, destruction actually INCREASES genetic diversity (mixing).
E is incorrect - The way it is worded can be off-putting. But E essentially states that the "absence" of any "reason (evidence)" does not negate the argument that humans cause straying.
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