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

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.

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)
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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.

fossil record shows definite pattern, with many species vanishing at the same time so there might be other variable/factor other than the mentioned ones that affects all species uniformly

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.

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.

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?

Ah, now I see it. My mistake to not read the Question stem carefully. Thank you a lot!!

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

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?

The assumption here is that the "variety of ecological, geographical, and physiological variables" are not the cause for the pattern.

A - give us exactly that what we need (strengthen the assumption).
B - This is focuses on specific species, and hence is not generalize enough to reference to a "group" of species.
C - Some could be 2, and hence not representative for a large population with a specific phenomenoa.
D - recent times are not relevant - Out of scope
E - out of scope

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.

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


Option A provides a reason that covers a wide variety of species that extincted over a relative period of time and is therefore correct.

As this is a CR question, let’s begin by reading the Question Stem: this question is EXPLAIN THE ARGUMENT question


Premise:
1. Extinction  Depends  ecological, geographical and physiological variables
2. Variables affect different species  different ways  Hence, should yield random pattern of extinctions
3. However  Fossil record shows  extinction occurs in a surprisingly definite pattern  MANY species vanishing at the same time

We need to look for option which can provide us with a reason where one or multiple variables impact multiple species at the same time.

(A) Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.
- This looks the correct answer, it is telling us that widespread environmental disturbances have affected different species (One variable impacting multiple species). Lets read other options as well. (A is the CORRECT answer)

(B) Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species.
- Problem with this is it is referring to a specific species and not multiple, hence this does not explain what we are looking for

(C) Some species become extinct because of accumulated gradual changes in their local environments.
- Again referring to some species not necessarily multiple species

(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions.
- We are not talking about any recent times in this passage neither specifically about human interventions

(E) Species that are widely dispersed are the least likely to become extinct
- This goes against of what we are looking for

It's an easy one. A.
The idea is to look for an answer that explains disappearance of collective species.

All other options except A talk about individual species.

Posted from my mobile device

Imo A
We have to look for some reason which caused definite extinction pattern of different species .
Option A provides that some natural calamity can affect several species simultaneously.

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.
Correct

(B) Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species. X
This reinforces one fact in the paradox: These variables affect different species of organisms in different ways, and should, therefore, yield a random pattern of extinctions. However, this choice fails to account for fact #2.

(C) Some species become extinct because of accumulated gradual changes in their local environments. X
We are not looking to explain WHY species become extinct, but HOW multiple species become extinct simultaneously.

(D) In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinctions. X
Does not address the question

(E) Species that are widely dispersed are the least likely to become extinct. X
We care about those species that are becoming extinct...not the ones that don't...
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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!

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?