A recent study has provided clues to predator-prey dynamics in the

Question

A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in present-day carnivores with tooth fractures in carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.

In considering possible explanations for this finding, the researchers dismissed demographic bias because older individuals were not over represented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.

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Main idea

This question depends on understanding the passage as a whole. The first paragraph reports the findings of a recent study. The second paragraph examines possible explanations for the findings, ruling out all but one of them. It then suggests some inferences that researchers have drawn based on the findings and the explanation.

(A) Several explanations are entertained, but only to be dismissed; the number of tooth fractures is not presented as a well-known fact.

(B) The passage does not mention alternative methods or a debate.

(C) The likely explanation for the tooth fractures is not shown to be controversial.

(D) The passage does not question the methodology of the study.

(E) Correct. The passage explores possible explanations for a recent research finding and some tentative inferences that it might support.

The correct answer is E.

1. The primary purpose of the passage is to

(A) present several explanations for a well-known fact
(B) suggest alternative methods for resolving a debate
(C) argue in favor of a controversial theory
(D) question the methodology used in a study
(E) discuss the implications of a research finding

2. According to the passage, compared with Pleistocene carnivores in other areas, Pleistocene carnivores in the La Brea area

(A) included the same species, in approximately the same proportions
(B) had a similar frequency of tooth fractures
(C) populated the La Brea area more densely
(D) consumed their prey more thoroughly
(E) found it harder to obtain sufficient prey

3. According to the passage, the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by

(A) the aging process in individual carnivores
(B) contact between the fossils in the pits
(C) poor preservation of the fossils after they were removed from the pits
(D) the impact of carnivores’ teeth against the bones of their prey
(E) the impact of carnivores’ teeth against the bones of other carnivores during fights over kills

4. The researchers’ conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that

(A) the older an individual carnivore is, the more likely it is to have a large number of tooth fractures
(B) the average age at death of a present-day carnivore is greater than was the average age at death of a Pleistocene carnivore
(C) in Pleistocene carnivore species, older individuals consumed carcasses as thoroughly as did younger individuals
(D) the methods used to determine animals’ ages in fossil samples tend to misidentify many older individuals as younger individuals
(E) data concerning the ages of fossil samples cannot provide reliable information about behavioral differences between extinct carnivores and present-day carnivores

5. According to the passage, if the researchers had NOT found that two extinct carnivore species were free of tooth breakage, the researchers would have concluded that

(A) the difference in breakage frequencies could have been the result of damage to the fossil remains in the La Brea pits
(B) the fossils in other Pleistocene sites could have higher breakage frequencies than do the fossils in the La Brea pits
(C) Pleistocene carnivore species probably behaved very similarly to one another with respect to consumption of carcasses
(D) all Pleistocene carnivore species differed behaviorally from present-day carnivore species
(E) predator densities during the Pleistocene era were extremely high

6. The passage suggests that tooth fractures in Pleistocene carnivores probably tended to occur less frequently

(A) during periods in which more prey were available
(B) at sites distant from the La Brea area
(C) in older individual carnivores
(D) in species that were not preserved as fossils
(E) in species that regularly stole carcasses from other species

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JOURNAL ARTICLE
Tough Times at La Brea: Tooth Breakage in Large Carnivores of the Late Pleistocene
Blaire Van Valkenburgh and Fritz Hertel
Science
New Series, Vol. 261, No. 5120 (Jul. 23, 1993), pp. 456-459
Published by: American Association for the Advancement of Science
https://www.jstor.org/stable/2881931
Page Count: 4

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File comment: Tough Times at La Brea: Tooth Breakage in Large Carnivores of the Late Pleistocene

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Show Answer Question #1

Official Answer

E

Show Answer Question #2

Official Answer

B

Show Answer Question #3

Official Answer

D

Show Answer Question #4

Official Answer

D

Show Answer Question #5

Official Answer

A

Show Answer Question #6

Official Answer

A

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GMATNinja · Accepted Answer

Question 1 asks what is the primary purpose of the passage. For (A) to be the correct answer, we would need to see a  well-known fact  in the passage.

The "fact" presented at the end of the first paragraph tells us  "The breakage frequencies in the extinct species were strikingly higher than those in the present-day species."  but we can hardly say this fact is well-known -- it is a result from the  recent study  described at the start of the passage.

Also, the passage does not present several explanations. The researchers "reject", "dismiss", or "rule out" several explanations in the second paragraph, before discussing the ONE explanation for their research finding that is most plausible.

(A) is out.

The start of the second paragraph discusses possible explanations for findings of the recent study before stating: 
 
This part of the paragraph discusses the implications of the research finding given at the end of the first paragraph.

So, overall, in this passage the author:
  Introduces a research finding  
 Rejects a bunch of potential explanations for this finding 
 Discusses a more plausible explanation, and the implications of that explanation

From this breakdown, we can say that the author's purpose in writing the passage was to "discuss the implications of a research finding." (E) is the correct answer to question 1.

I hope that helps!

GMATNinja · Answer

Refer to this portion: "The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular,  more contact between the teeth of predators and the bones  of prey   due to more thorough consumption of carcasses by the extinct species." The passage specifically talks about contact between teeth of predators and the bones OF PREY, not between teeth of predators and the bones OF OTHER CARNIVORES during fights over kills. Thus, (E) should be eliminated, and (D) is the best choice.

As for question 4, refer to this portion: "the researchers dismissed demographic bias because older individuals were not over represented in the fossil samples." We can infer that demographic bias has to do with age differences. More specifically, if all of the fossils were from OLDER individuals, then the high proportion of tooth fractures might simply be a result of the aging process . In other words, in order to accurately compare the fossil teeth to the teeth of present-day predators, we need samples representing all ages in both groups.

With that in mind, let's consider the choices:

Shivikaa · Answer

I got confused between D and E in Q3. Both the statements are mentioned in the paragraph. 
Also, in Q4, I didn't understand why we chose D as an answer. Please explain the meaning of the statement.
Thanks in advance.

gmat1393 · Answer

2. According to the passage, compared with Pleistocene carnivores in other areas, Pleistocene carnivores in the La Brea area

(A) included the same species, in approximately the same proportions
(B) had a similar frequency of tooth fractures
(C) populated the La Brea area more densely
(D) consumed their prey more thoroughly
(E) found it harder to obtain sufficient prey
 B

Hi  GMATNinja

Can you please help in eliminating option D for Q2.

I selected D based on the highlighted part.

The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular, more contact between the teeth of predators and the bones of prey due to  more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low,

GMATNinja · Answer

The piece of the passage that you've highlighted shows a difference between  present day  carnivores and  extinct  carnivores. Take another look at question #2:
 
This is a different comparison than the one in your analysis -- question #2 asks us to compare Pleistocene carnivores in the La Brea area with Pleistocene carnivores in other areas. In other words, we need to compare carnivores that lived in the same time frame, but in different locations.

Here is the relevant piece of the passage to make that comparison:
 
This tells us that Pleistocene carnivores in multiple locations had similar tooth fractures. This aligns nicely with answer choice (B), which states that the carnivores in different locations "had a similar frequency of tooth fractures." (B) is the correct answer for question #2.

Answer choice (D) tells us that Pleistocene carnivores in the La Brea area "consumed their prey more thoroughly" than Pleistocene carnivores in other areas. Because we know from the passage that tooth breakage data were consistent across multiple locations, we cannot conclude that this is true. Eliminate (D).

I hope that helps!

Montyyy95 · Answer

In Q1, I got stuck between option A and E; Could someone clarify why E is correct?

jaisonsunny77 · Answer

1. The primary purpose of the passage is to

In the opening line of the first paragraph, we have "A recent study has provided clues..." the second paragraph then builds on the implications of the new findings. (E) captures this thought perfectly.

(E) discuss the implications of a research finding

Hence,   (E) is the right answer choice.  
  
 2. According to the passage, compared with Pleistocene carnivores in other areas, Pleistocene carnivores in the La Brea area

Towards the middle of the second paragraph, we have "breakage data obtained from other Pleistocene sites were similar to the La Brea data." This would imply that the data from the two sites had to be similar to each other. This thought is captured in (B).

(B) had a similar frequency of tooth fractures

Hence,   (B) is the right answer to this question.

3. According to the passage, the researchers believe that the high frequency of tooth breakage in carnivores found at La Brea was caused primarily by 
 
Towards the end of the second paragraph, we have "more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses". This is what we have in (D).

(D) the impact of carnivores’ teeth against the bones of their prey

Hence,   (D) is the right answer choice.  
 
  4. The researchers’ conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that 
 
In the beginning of the second paragraph, we have "dismissed demographic bias because  older individuals  were   not over represented  in the fossil samples "

(D) the methods used to determine animals’ ages in fossil samples tend to misidentify many older individuals as younger individuals - what (D) tells us is that many ''younger individuals'' were misidentified; In fact, these misidentified younger individuals were actually ''older individuals''. So, this would imply that the fossils did contain a disproportionately larger presence of older individuals than younger ones, thereby weakening the reasoning provided to reject demographic bias. Hence,   (D) is the right answer choice. 
 
  5. According to the passage, if the researchers had NOT found that two extinct carnivore species were free of tooth breakage, the researchers would have concluded that 
 
To answer this question, let us first understand what implications did this ''finding'' have on the research.

The second paragraph is constructed to explain why " The breakage frequencies in the extinct species were strikingly higher than those in the present-day species."

Towards the middle of the second paragraph, we have "They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits". In other words, the researches rule out the possibility of the ''teeth fractures'' appearing as a result of any other process than the teeth-to bone contact.

Now, if these two extinct carnivore species (found in the La Brea tar pits in Los Angeles) did have tooth breakage, then one could presume that the all fossils found in the pits will contain tooth breakage.

Hence, it will be impossible to rule out the possibility that the teeth breakage would be caused by some sort of damage to these fossils while these fossils were preserved in the pits. (In other words, if the entire sample of fossils obtained have teeth breakage, then it becomes that much more difficult to point out a particular reason/source for the teeth breakage observed). This thought is perfectly captured in (A).

(A) the difference in breakage frequencies could have been the result of damage to the fossil remains in the La Brea pits

Hence,   (A) is the right answer choice.  
 
  6. The passage suggests that tooth fractures in Pleistocene carnivores probably tended to occur less frequently 
 
In the second paragraph, it is established that ''thorough consumption'' is what eventually led to higher teeth breakage frequency. If in any case the ''breakage frequency'' is lower than usual, then it must imply that thorough consumption did not take place.

From the passage, we can infer that shortage of prey is what led to thorough consumption. So, it is possible that an abundance of prey could lower the chances of thorough consumption and hence ''teeth breakage frequency''. Therefore, tooth fractures in Pleistocene carnivores probably tended to occur less frequently when there was an abundance of prey. This is what we have in (A).

(A) during periods in which more prey were available

Hence,   (A) is the right answer choice.

HASTOWINGMAT · Answer

I believe for 5th question, option B is the correct the correct answer as it creates a bias.

Please can elaborate more here why B here is rejected and A is accepted.

CrackverbalGMAT · Answer

Hi

Let me try to address your query. Question 5 asks us: ...if the researchers had  NOT found  that two extinct carnivore species were free of tooth breakage, the researchers would have concluded that:

Let us examine the relevant section of the passage that deals with this point. The second sentence of the second paragraph mentions this fact, and states:

They  rejected preservational bias because a total absence of breakage in two extinct species  demonstrated that the fractures were not the result of abrasion within the pits.

Hence, the absence of breakage in these two species helped the researchers to reject "preservational bias". Therefore, "...if the researchers had  NOT found " this, they would have had to allow for "preservational bias".

What exactly preservational bias is is explained in the second half of the same sentence, which states: "...the fractures  were not the result of  abrasion within the pits."

Since this explains the rejection of preservational bias, preservational bias itself would be the complement of this ie; "...the fractures  were the result of  abrasion within the pits."

This fact is well laid out in option (A), which is the correct answer. Option (B) does not deal with breakage within the pits and is incorrect.

Hope this helps.

GMATNinja · Answer

Question 3 
As a whole, the passage:
  Introduces a finding (that extinct species found in the Rancho La Brea tar pits had more tooth-breakage than modern-day species) 
 ELIMINATES a bunch of potential explanations for this finding 
 Discusses a plausible explanation

One of the explanations that is eliminated is "preservational bias":

"They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits."

In other words, the researchers asked, "what if these tar pits just suck at preserving teeth? Maybe the teeth were NOT broken when the animal died, but were damaged while hanging out in the tar pits for thousands of years." This would cause "preservational bias," because the finding about tooth damage would just show that the tar pits did not preserve the teeth very well, rather than giving any insight into the behavior of the animal.

The scientists then found two species in the pit with teeth that were NOT broken at all. If the tar pits were the problem, then the teeth of ALL species would have been equally damaged by their time in the pits. Because two species had undamaged teeth, the researchers ruled out the possibility of preservational bias. Another factor must have caused the broken teeth for certain species.

Question 3 asks us what the researchers would have concluded if they had NOT found these two species without tooth breakage.

Here's (A):
 
The PRESENCE of the species with unbroken teeth allowed the researchers to concluded that the tar pits didn't damage the other species' teeth. So, WITHOUT the two unbroken-teeth-species, the researchers would still be left wondering whether the tooth damage was caused by the pits themselves. (A) is looking good.

The two species with unbroken teeth proved that the La Brea tar pits SPECIFICALLY did not cause the damage in the other species' teeth. In other words, the La Brea tar pits did not cause preservational bias.

(B) brings up a totally DIFFERENT bias -- local bias, which is discussed later in the paragraph.

Because the researchers use the two unbroken-teeth-species to rule out preservational bias, the absence of this specific evidence would call THAT factor into question. This data is NOT used to compare fossils in the tar pits to fossils in other Pleistocene sites, so the absence of the data would not lead the researchers to conclude anything about local bias.

(A) is the correct answer to question 3.

I hope that helps!

mba757 · Answer

4. The researchers’ conclusion concerning the absence of demographic bias would be most seriously undermined if it were found that

“In considering possible explanations for this finding  , the researchers dismissed demographic bias because older individuals were not over represented in the fossil samples.”
 
 (A) the older an individual carnivore is, the more likely it is to have a large number of tooth fractures
 Because older individuals were not over represented in the fossil samples (therefore) the researchers dismissed demographic bias. We’re talking about volume of relatively older carnivores to the volume of relatively younger carnivores. How MUCH older is not pertinent to the argument – this get’s too granular.

(B) the average age at death of a present-day carnivore is greater than was the average age at death of a Pleistocene carnivore
 This removes a possible alternative cause. The Pleistocene Cs were NOT older than present day ones. This supports the conclusion.

(C) in Pleistocene carnivore species, older individuals consumed carcasses as thoroughly as did younger individuals
 this doesn’t affect the conclusion at all. HOW they consumed the carcasses isn’t relevant. We need talk about the volume.

(D) the methods used to determine animals’ ages in fossil samples tend to misidentify many older individuals as younger individuals
  This is it. This hits on the volume, stating that the volume may not be accurate. It could have been misidentified and there MAY actually be more older Cs than younger.

(E) data concerning the ages of fossil samples cannot provide reliable information about behavioral differences between extinct carnivores and present-day carnivores
 Half wrong/half right. We don’t need to know the behavioral differences. The conclusion is that the older individuals were NOT over represented in the fossil samples.

5. According to the passage, if the researchers had NOT found that two extinct carnivore species were free of tooth breakage, the researchers would have concluded that

“They   rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits.”
 
  (A) the difference in breakage frequencies could have been the result of damage to the fossil remains in the La Brea pits
  This is it. The researchers flat out reject this preservational bias BECAUSE of the absence of breakage in two species. If there WERE breaks, then it COULD have been the result of damage to the fossil remains (the main point the researchers were trying to figure out).

(B) the fossils in other Pleistocene sites could have higher breakage frequencies than do the fossils in the La Brea pits
 We know that the researchers are thinking the following: absence of breaks in two species -> fractures didn’t come from abrasion w/i the pits. This could just provide support for how the breakage could be stemming from within the pits – i.e., internal conflicts WITHIN the pits. This extrapolates at least two layers further out – (1) it’s similar within other sites and (2) there are higher breakage frequencies in these other sites.

(C) Pleistocene carnivore species probably behaved very similarly to one another with respect to consumption of carcasses
 Not supported.

(D) all Pleistocene carnivore species differed behaviorally from present-day carnivore species
 This is possible, but the passage doesn’t support this. ALL P. carnivore species? This is too extreme.

(E) predator densities during the Pleistocene era were extremely high
 This is probably/potentially true within the passage BUT this is not relevant to the discussion on hand.

6. The passage suggests that tooth fractures in Pleistocene carnivores probably tended to occur less frequently

(A) during periods in which more prey were available
  “Such thorough carcass consumption   implies to the researchers…that prey availability was low…” so if prey was low = more fractures, but if prey were high = fewer fractures.

(B) at sites distant from the La Brea area
 “They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data.”

(C) in older individual carnivores
 “dismissed demographic bias because older individuals were not over represented in the fossil samples”

(D) in species that were not preserved as fossils
 This one just isn’t supported at all.

(E) in species that regularly stole carcasses from other species
 “Such thorough carcass consumption   implies to the researchers…that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities” This means the opposite.

VerbalBot · Answer

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