PT137.S4.Q6 > Question

SECTION 1 · rc

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PASSAGE 3

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PASSAGE 4

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SECTION 3 · lr

SECTION 4 · lr

The columnist concludes that the number of species on Earth is probably not decreasing. He supports this by saying that the extinction rate this year will likely be similar to 1970, and that new species are probably emerging at the same rate as in past centuries.

In order for the number of species on Earth not to decrease, the columnist must assume that the extinction rate today and in 1970 is equal to or lower than the rate at which new species are emerging. If extinction is happening faster than new species are emerging, the number of species is decreasing.

This weakens the columnist’s conclusion by proving his key assumption is false. If fewer new species emerged than went extinct in 1970, the number of species decreased. So, since extinction and speciation rates are likely the same today, the number of species is decreasing.

It doesn’t matter where these species are emerging and going extinct. (B) doesn’t show that the rate of extinction, regardless of where it is happening, is higher than the rate of speciation, so it doesn’t weaken the columnist’s argument.

While most species that have ever existed are now extinct, new species are still emerging. (C) doesn't give us any reason to believe that new species aren't replacing those that go extinct, so it doesn’t weaken the conclusion that the overall number of species is not decreasing.

People’s concern about extinction is irrelevant to the columnist’s argument. He is only addressing the actual rates of extinction and speciation, regardless of whether people care about it.

Scientists may be more aware of endangered animals now, but this doesn’t change the fact that "about as many species are likely to go extinct this year as... in 1970." (C) doesn’t address the difference between extinction and speciation rates, so it doesn’t weaken the argument.

PrepTest 137 - Section 4 - Question 6

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