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Columnist: Contrary to what many people believe, the nu1nber

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Columnist: Contrary to what many people believe, the nu1nber [#permalink]

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Columnist: Contrary to what many people believe, the number of species on Earth is probably not dwindling. Extinction is a natural process, and about as many species are likely to go extinct this year as went extinct in 1970. But the emergence of new species is also a natural process; there is no reason to doubt that new species are emerging at about the same rate as they have been for the last several centuries.

Which one of the following, if true, most weakens the columnist's argument?

(A) In 1970 fewer new species emerged than went extinct.
(B) The regions of the world where new species tend to emerge at the highest rate are also where species tend to go extinct at the highest rate.
(C) The vast majority of the species that have ever existed are now extinct.
(D) There is no more concern now about extinction of species than there was in 1970.
(E) Scientists are now better able to identify species facing serious risk of extinction than they were in 1970.

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Re: Columnist: Contrary to what many people believe, the nu1nber [#permalink]

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New post 15 Sep 2017, 03:04
Masshole wrote:
Columnist: Contrary to what many people believe, the number of species on Earth is probably not dwindling. Extinction is a natural process, and about as many species are likely to go extinct this year as went extinct in 1970. But the emergence of new species is also a natural process; there is no reason to doubt that new species are emerging at about the same rate as they have been for the last several centuries.

Which one of the following, if true, most weakens the columnist's argument?


Premise 1: The rate of extinction at present is the same as in 1970
Premise 2: The rate of the emergence of new species at present is the same as in the last several centuries.
Conclusion: the number of species on Earth is probably not dwindling

(A) In 1970 fewer new species emerged than went extinct.
Correct. This choice points out the flaw in the argument. If the rate of new species emerged is less than the rate of extinction, the number of species on Earth is dwindling

(B) The regions of the world where new species tend to emerge at the highest rate are also where species tend to go extinct at the highest rate.
This choice provides information that is too general. We can't conclude anything from this one.

(C) The vast majority of the species that have ever existed are now extinct.
We still can't conclude that whether the number of species on Earth is dwindling

(D) There is no more concern now about extinction of species than there was in 1970.
Concern about extinction of species is irrelevant.

(E) Scientists are now better able to identify species facing serious risk of extinction than they were in 1970.
This choice is irrelevant to the argument.
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Re: Columnist: Contrary to what many people believe, the nu1nber [#permalink]

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New post 18 Sep 2017, 10:45
Quote:
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.

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Re: Columnist: Contrary to what many people believe, the nu1nber   [#permalink] 18 Sep 2017, 10:45
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