Extinction is a process that can depend on a variety of ecological

Question

Extinction is a process that can depend on a variety of ecological, geographical, and physiological variables. These variables affect different species of organisms in different ways, and should, therefore, yield a random pattern of extinctions. However, the fossil record shows that extinction occurs in a surprisingly definite pattern, with many species vanishing at the same time.

Which of the following, if true, forms the best basis for at least a partial explanation of the patterned extinctions revealed by the fossil record?

(A) Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.

(B) Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species.

(C) Some species become extinct because of accumulated gradual changes in their local environments.

(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.

(E) Species that are widely dispersed are the least likely to become extinct.

EMPOWERgmatAllenT · Accepted Answer

Extinction is a process that can depend on a variety of ecological, geographical, and physiological variables. These variables affect different species of organisms in different ways, and should, therefore, yield a random pattern of extinctions. However, the fossil record shows that extinction occurs in a surprisingly definite pattern, with many species vanishing at the same time.

Which of the following, if true, forms the best basis for at least a partial explanation of the patterned extinctions revealed by the fossil record?

QUESTION TYPE:   
Explain – We need to find an answer that resolves the mystery.

FACTS:   
1) Extinctions should be random because various factors should affect species randomly
2) Extinctions are NOT random---they happen in clusters, wiping out many species at once

GOAL:   
Find an answer that explains how despite random factors, many species are wiped out in big clusters at once

A. Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.
 Yes! Think asteroid, or mega-volcano. There’s some sort event that takes down swathes of species.

B. Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species.
 This contradicts the second fact. Don’t we know that many species are wiped out at once? So this answer that species with particular characteristics are selectively wiped out would intensify the mystery.

C. Some species become extinct because of accumulated gradual changes in their local environments.
 This answer only addresses specific single species extinctions, AND that they happen gradually over time. That makes this answer wrong for two reasons. A gradual extinction affecting some species is not the type of extinction the question deals with.

D. In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.
 This answer flat out announces that it addresses circumstances separate from those in the prompt. Boot it.

E. Species that are widely dispersed are the least likely to become extinct
 This is an interesting fact, but it’s completely off-topic. Does the fact that species that are widely dispersed are least likely to become extinct at all reconcile how species go extinct in clusters? No. Its gone too.
 
  A is our answer.

KarishmaB · Answer

There is a paradox here: Extinction depends on lots of factors that are different for different species (their geography, their physiology etc). Still we see many species vanishing at the same time. Why?

(A) Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.

Major widespread environmental disturbances (environmental issues covering many geographies) affect many different species at the same time. Hence this could explain why many species become extinct together. So say an Earth wide warming could affect many species and cause their extinction within a few years. Hence, this is the answer.

(B) Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species.

This tells us that effect is selective on organisms based on their unique characteristics. It does not explain why many organisms get affected together. They should not if the effect is selective.

(C) Some species become extinct because of accumulated gradual changes in their local environments.

This talks about "some species" and their "local environment". Hence it does not explain widespread effect to many species

(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.

This tells us that we have changed the pattern of extinctions. The argument questions why there is a pattern of extinctions to begin with. Whether it is changing and how and because of whom are all irrelevant discussions. 
Our point is - why does a widespread pattern of extinction exist? Many species have been getting affected simultaneously for millions of years (as per fossil records). Why do these species get affected at the same time? 
For recent times, we don't even have fossil records and our argument is not discussing these times. We are discussing the times for which we have fossil records. Hence (D) is out of scope.

(E) Species that are widely dispersed are the least likely to become extinct.

This tells us what kind of species would be least likely to get affected simultaneously. It doesn't provide us the explanation we are seeking.

Answer (A)

kripalkavi · Answer

Easy A! 

D, E - they are clearly out of scope
B - too narrow in scope. It talks only about 'certain extinctions'.
C - Ok. we know why 'Some species' became extince. What about the others? Again, too narrow in scope.

whamberto · Answer

The answer should be A:

A. This answer choice gives us a reason that explains how extinction can occur suddenly with many species going extinct.

B. This answer choice gives an explanation for the extinction of a few species.

C. This answer choice explain only how "some species" become extinct.

D. We are only concerned about the times that have "fossil records."

E. We are not concerned about how species are least likely to become extinct.

chimom · Answer

Excuse me for digging again this thread. I understand all the explanation above and also agree with you guys that A is the best answer here. However, I'm still wondering that A just covers 1 point that extinction occurs simultaneously. What's about the part "definite pattern"? Considering this factor, I think the answer A cannot satisfy it.

igotthis · Answer

I think because the question asks: Which of the following, if true, forms the best basis for  at least a partial explanation  of the patterned extinctions revealed by the fossil record?

sasha40612 · Answer

Can any one give a power-score cr bible explanation for this paradox question ?

Extinction is a process that can depend on a variety of ecological, geographical, and
physiological variables. These variables affect different species of organisms in different
ways, and should, therefore, yield a random pattern of extinctions. However, the fossil
record shows that extinction occurs in a surprisingly definite pattern, with many species
vanishing at the same time.
Which of the following, if true, forms the best basis for at least a partial explanation of the
patterned extinctions revealed by the fossil record?

A. Major episodes of extinction can result from widespread environmental disturbances thataffect numerous different species.

B. Certain extinction episodes selectively affect organisms with particular sets ofcharacteristics unique to their species.

C. Some species become extinct because of accumulated gradual changes in their localenvironments.

D. In geologically recent times, for which there is no fossil record, human intervention haschanged the pattern of extinctions.

E. Species that are widely dispersed are the least likely to become extinct

aditya8062 · Answer

the answer has to be A  :   Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.

reason : the question stem ask us :  best basis for at least a partial explanation of the
patterned extinctions revealed by the fossil record

now if u reason out A then u will notice that if major episode of extinctions are the result of widespread environmental disturbance that affect numerous species in one go then there is a reason for us to believe that all the fossils that we might get will show a definite pattern. consider for an instance that one particular flood destroys a particular village X ,then the fossils of all animal and people, who might have died, will show death by water as the cause and hence we can conclude that all fossils reveal the same pattern

does it help?

anairamitch1804 · Answer

Argument Construction

Situation The fossil record reveals that species become extinct in a surprisingly definite pattern, with multiple species vanishing simultaneously.
Reasoning Which point provides a basis for explaining the pattern? The passage states that the process of extinction depends on so many variables—in the ecology and geography of the environment and in the physiology of the species—that the expected outcome would be a random pattern of extinctions. Yet a definite pattern is found instead. What could explain the disappearance of multiple species at the same time? If there were significant widespread changes in the environment, multiple species could be affected simultaneously, causing their extinction.

A Correct. This statement properly identifies a basis for explaining the pattern of many species becoming
extinct simultaneously.

B This explanation of selective extinction does not explain how many species become extinct at the same
time.

C This explanation addresses only some species, not many species.

D The passage is based on what the fossil record suggests; more recent times, having no fossil record, are outside the consideration of the passage.

E Indicating which species are least likely to become extinct does not explain a pattern of simultaneous extinction of many species.

The correct answer is A.

Sneha2021 · Answer

Hi Experts,
 VeritasKarishma   GMATNinja   GMATNinja Two

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 · Answer

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?

GMATNinja · Answer

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:

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."

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.

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.

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!

VerbalBot · Answer

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Extinction is a process that can depend on a variety of ecological

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