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Hi Experts,
VeritasKarishma GMATNinja GMATNinjaTwo
Why C & D are incorrect?
(C) Some species become extinct because of accumulated gradual changes in their local environments.
- Some species were affected by changes in local environment. May be different species in the same local environment get affected by the changes in their local environment.
Also why can't we assume that some species could be different species.
I don't agree with the explanation that because "some species" was mentioned and not multiple species. Some species means at least one. So it could be 1 or 100.
(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.
- Human intervention has changed the pattern from "random" to "definite". This statement could be the reason for change in pattern. The statement gives partial explanation of the event.
How does "no fossil record" affect the reasoning in D?
Can you please help to understand the reasons for rejecting C, D and E.
Thanks!
krittapat wrote:
GMATNinja VeritasKarishma Could you help explain why option D is incorrect?
I thought that it should be a great explanation for the patterned extinction.
Or it's because of the portion "for which there is no fossil record" that makes D wrong?
The question is asking which of the answer choices forms the "best basis" for a "partial explanation of the patterned extinctions in the fossil record." The stem says this "definite pattern" consists of
"many species vanishing at the same time." So in other words, the definite pattern we are trying to explain is "many species vanishing at the same time."
Let's consider a few of the answer choices:
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(C) Some species become extinct because of accumulated gradual changes in their local environments.
Notice that (C) explains why a species in a certain local environment would go extinct. Depending on how we interpret the word "some," it
could explain why a certain number species in a local environment go extinct, but it's
unclear how many. So this doesn't provide great support for the idea of "many species vanishing at the same time."
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(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.
The question is specifically asking for an explanation of the "patterned extinctions in the
fossil record." Since the effects of human intervention won't be seen in the fossil record, (D) is out.
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(E) Species that are widely dispersed are the least likely to become extinct.
Again, we are trying to explain why
many species would vanish at the same time. While (E) would possibly lead to some kind of extinction pattern, it wouldn't explain the specific pattern we're looking for, so (E) is also out.
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(A) Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.
A "widespread environmental disturbance" that affects "numerous different species" could explain a pattern of "many species vanishing at the same time." Keep in mind, we're just trying find the "basis for a partial explanation" of the pattern. Since (A) does the
best job of that, it's correct.
I hope that helps!