Columnist: Contrary to what many people believe, the nu1nber

Question Type:
Weaken

Stimulus Breakdown:
Conclusion: The number of species is probably not dwindling.
Evidence: Extinctions are natural. This year we have the same number going extinct as in 1970. But species emergence is also natural. We probably have the same rate of emerging species as we've had for the last several centuries.

Answer Anticipation:
The truth value of the author's conclusion hinges on whether the number of species emerging each year is at least as high as the number of species going extinct each year. We have no precise comment to that effect. Instead, we have two arbitrary benchmarks:
The rate of species going extinct is comparable to 1970's rate.
The rate of species emerging is comparable to that of the last several centuries.

So the author is assuming the rate species have emerged over the last several centuries is at least as great as the rate species went extinct in 1970.

Correct Answer:
A

Answer Choice Analysis:
(A) Ultimately, yes. Since the author uses 1970 as a benchmark year, to make us feel better about the comparative rate of extinction / speciation, this answer weakens by painting an unflattering picture about 1970. In 1970, the number of species on Earth dwindled. So this year provies poor support for an author drawing the opposite conclusion.

(B) Getting specific about regions is out of scope. Our conclusion is about Earth's total number of species.

(C) This doesn't say anything about whether the current rate of losing species is offset by the rate of getting new ones.

(D) "Concern" is out of scope. We need to know the actual numbers.

(E) This shows a difference In detecting endangerment. We need information about the actual number of species going extinct / being created.

Takeaway/Pattern: The conclusion is a very mathematically specific claim, so it behooves us to think about this argument in those terms. Once we pinpoint that we need to quantify how many species we've lost vs. gained, the relevant comparison between 1970 and 'the last few centuries' is clear. However, in the end, the correct answer just attacks one of those benchmarks as sketchy support.