PrepTest 137, Section 4, Question 6
Columnist: Contrary to what many people believe, the(67 more words not shown)
Which one of the following,(7 more words not shown)
- AIn 1970 fewer(6 more words not shown)
- BThe regions of(24 more words not shown)
- CThe vast majority(10 more words not shown)
- DThere is no(12 more words not shown)
- EScientists are now(15 more words not shown)
Reading the argument
Why should matching 1970 reassure us?
The columnist says roughly the same number of species will go extinct this year as in 1970. But what if 1970 already had a high number of extinctions? An unchanged rate can still be a troubling rate. Comparing this year with that year doesn't tell us whether species were being lost faster than they were being replaced.
We also get a stable rate of new species emerging. That sounds encouraging, but the question is how the two streams compare: species arriving and species disappearing. Knowing that each has stayed about the same doesn't yet show that the total number of species is holding steady.
What we’re looking for
To weaken the argument, I'd want to expose what the comparison with the past leaves unresolved. The columnist needs the numbers to support 'not dwindling,' not merely 'continuing at about the same rates.'
Working the answers
- ACorrect
In 1970, more species disappeared than emerged. That means the total was declining then. If both the extinction rate and the emergence rate are still about what they were, we have reason to expect that loss to continue.
For example, a steady loss of 100 species alongside a steady gain of 60 would still leave 40 fewer species. Neither rate would need to accelerate. A attacks the balance between gains and losses, which is what determines whether the total dwindles.
- B
Knowing that both processes occur rapidly in the same regions doesn't tell us which is faster. A region could gain more species than it loses or lose more than it gains. The geographical overlap doesn't establish the worldwide balance the conclusion concerns.
- C
This adds up extinctions across the entire history of life. It doesn't tell us how present losses compare with present gains. Most past species could be extinct while the current total was growing, stable, or declining. We need the current direction, not the cumulative history.
- D
People's level of concern doesn't determine the number of species. People could be equally worried in two years while the actual balance between extinctions and new species was quite different. The argument concerns what is happening, not how strongly people react to it.
- E
Better identification of threatened species doesn't itself show that more species disappear than emerge. It concerns our ability to recognize risk. Without a connection to the actual balance of gains and losses, it doesn't challenge the conclusion as A does.
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