Capuchin monkeys in Venezuela often rub a certain type of millipede in

Premise:
Capuchin monkeys in Venezuela often rub a certain type of millepede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins.

Premise:
The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak.

Conclusion:
Therefore monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.

We are looking for information to help us evaluate the conclusion. So we need information that can help up determine WHY the monkey rub millipedes into their fur.

A. Whether the chemicals provide protection for the millipedes is irrelevant. We are only concerned with why the monkey rub the millipedes into their fur.

B. Again out of scope, we are only concerned with these monkeys in Venezuela.

C. Also out of scope, only concerened with monkeys

D. Correct. One of the premises is that the monkeys only rub them into their skin during the rainy season when the mosquito population is highest. They use this premise to arrive at the conclusion that this is only done to protect against mosquites. But adding this additional information that millipedes are only available during the rainy season cast doubt on this logic. It could now be that the only reason they rub them into their skin during the rainy season is because this is the only season they're available. It may just be a coincidence that the millipedes are availabe only during the rainy season when their needed and the monkeys might do the same if millipedes were available in non rainy season.

E. Out of scope, we are only concerned with monkeys and millipedes.

After a really fun time with dengue fever in Venezuela and Brazil... well, so I'd happily rub millipedes all over myself if I thought it would help get rid of the little turds. I wish that capuchin monkeys had taught me this trick back in the day.

Anyway, let's start with the conclusion, which is that "monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes." How does the author arrive at this conclusion?

• We know that capuchin monkeys often rub a certain type of millipede into their fur.
• We also know that this rubbing behavior is rare except during the rainy season. So even though they do this OFTEN, it is uncommon outside of rainy season.
• Rainy season is also when mosquito populations are at their peak.
• The millipedes secrete two chemicals that are potent mosquito repellents.
• Mosquitoes carry parasites that debilitate the monkeys. So the monkeys would have an incentive to use the mosquito repellent, if possible.

The author reasons that since the monkeys only rub the millipedes into their fur during the rainy season when mosquitoes are at their worst, it is likely that the monkeys are only doing this for mosquito protection. If there were OTHER reasons for rubbing the millipedes into their furs, then the monkeys would probably do it all year round.

For example, if the millipede secretions were also good for the monkeys' skin and fur, then the rubbing behavior would probably continue regardless of whether mosquito populations were high or low. But, according to the author, since the monkeys only do this during peak mosquito season, the mosquitoes are probably the only motivation for the rubbing.

Which of the following choices would help us evaluate the author's argument and conclusion? (And if you prefer your explanations in video form, check out this YouTube CR webinar.)


How the millipedes use those chemicals is irrelevant. We only care to explain why the MONKEYS might have an interest in those chemicals. Why do they rub the millipedes and why do they only do so during the rainy season? Choice (A) does not help us answer either of those questions, so it can be eliminated.


We are only concerned with explaining the rubbing behavior of the capuchin monkeys in Venezuela. Regardless of whether the millipedes are found in other parts of the world, why do these monkeys only exhibit the rubbing behavior during the rainy season? Choice (B) is irrelevant and can be eliminated.


Again, we are trying to explain why the capuchins only rub mosquitoes into their furs during the rainy season. The rubbing behavior of other animals is irrelevant, so (C) can also be eliminated.


We know that the rubbing is rare outside of rainy season. The author explains this by suggesting that the rubbing is not needed when the mosquitoes aren't so bad. But what if there is another explanation? What if the monkeys would LIKE to rub the millipedes into their furs outside of peak mosquito season but simply cannot do so because the millipedes are not readily available? If that were the case, it would suggest that the monkeys have OTHER reasons for wanting to continue the rubbing behavior. Wanting to repel mosquitoes during the rainy season would probably not be the ONLY reason. This would contradict the author's argument and conclusion. Thus, choice (D) would be useful to determine in order to evaluate the argument.


We are told that the rubbing behavior is rare outside of rainy season, and we can infer that the monkeys often rub the millipedes into their fur during the rainy season. Sure, they might be doing the same thing with some other insects, but why is the rubbing behavior rare outside of rainy season? The author provides one explanation, and choice (E) does not provide an alternative. Choice (E) has no impact on the author's argument and can be eliminated.

Choice (D) is the best answer.
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I think the key here is to focus on the logical structure of the argument (and this is true for almost ALL CR questions). Think of it as a puzzle/riddle that a friend is telling you. The writer of CR problems includes pieces of information (like in a puzzle) and we should ensure we understand the role of each piece of information. I've found it helpful to practice this exercise for CR questions (i.e. make sure you totally understand the argument). Note that you can practice this virtually with the argument without looking at answer choices (i.e. even on repeat questions) - it's good practice

The process I follow is (largely in line with Manhattan GMAT with some edits - I think pre-thinking (which e-gmat advocates) is a very useful step but MGMAT doesn't stress it too much - i.e. it's good to have not a must have)
1. ID what type of CR question this is
2. read each statement, paraphrase to myself / visualize the sentence. Do the same for sentence 2 and see link to statement 1. Repeat for following statements. THEN synthesize the argument so you have a grasp on the CONCLUSION (if relevant) and the premises (and how they relate to the conclusion)
3. Then attack the question stem - make sure you know exactly what you need to do
4. Prethink an answer - 5-10 seconds tops. If you can't think of an answer. Just say to yourself, "ok i'm looking for answers that does XX (be specific)"
5. Eliminate definite NOs (if you arent sure, let it sit); On the second round you should ideally have 2 choices remaining. Again, eliminate the MORE wrong answer until you are left with one. Pick it and move on!

This might seem like a lot of work but if you practice this process meticulously I'm sure your accuracy will go up and (in time) so will your speed.

For ex. this question
STEP 1 - Ok, so this is an evaluate question - there will be a conclusion here and I need to figure out what question I need to ask to evaluate this argument. (i.e. binary y/n answers will either weaken or strengthen the argument)

STEP 2
Logical Structure
1. Cap monkeys in Ven often rub milipedes into their fur. "hmm ok this is a fact/context. probably setting me up for the meat of the argument"
2. Secretions..debilitate the capuchins. "hmm interesting set of facts - the milis have 2 chemicals that repel mosquitoes and these mosquitoes have parasites that can cause serious harm. Ok i see that he's building a case to explain why monkeys are doing this"
3. The rubbing behavior is rare except during the rainy season, when mosquitoes are at their peak - "hmm, ok this is a peculiar observation and i kinda see what he's suggesting. he's trying to attribute this behavior during rainy season to something"
4. CONCLUSION - monkeys rub milis to protect themselves against milis -"aha i see what he's getting at - the behavior during monsoons is the nail in the coffin and that's why he's concluding this'
5. Synthesize - "ok concluding X because of Y and Z"

STEP 3
GOAL: what's most useful to evaluate the argument

STEP 4: PRETHINK
Hmm ok what questions would i ask the author - some thoughts that popped to me 1. ok, what if the rain makes the monkeys itchy and that's what makes them use milis to scratch? 2. what if there is anything else about the rain / the milis that make monkey use them to scratch? (i.e. it has nothing to do with mosquitoes)

STEP 5: Process of elimination

A. Ok we dont care about the milipedes here. We need to figure out why the monkeys are using them to rub
B. Irrelevant - so what if it's found in other parts of the world. We are focused on Venezuela
C. Again - we care about Venezuelan capuchins
D. HMM..ok this is a good one. If mosquitoes are only available during the rainy season then maybe it has nothing to do with the fact that rainy season has peak mosquito population. Monkeys just rub milis when they can find them and they only find them in the rainy season. This isnt a perfect question but let's keep it.
E. uh ok, we dont care about other insects. The author says monkeys use milis and he's making a conclusion as to why they use milis to rub themselves. I dont care if they CAN use other insects. Let's try variance here - YES other insects are available - ok, great but they could also use milis too. Right? NO other insects are not available - ok, great but then WHY are they using milis? (there could be a thousand other ways the monkeys can repel mosquitoes - the crux of the argument is discussing the validity of one possible cause - i.e. rubbing milis) - eliminate this

Therefore D. I took 1:45 seconds to answer this (even though the explanation makes it look like it took me 5 minutes).

This process works well for me. Let me know your thoughts.

Hi,

I took this argument in a causative fashion, where conclusion says , Rubbing of Milipeds leads to Protection against Mosquitoes, So X leads to Y . Cant a alternate cause could be possible answer to this question,which is mention in option E.

Please correct me where I'm wrong?

Thanks

Hi Nitin,

If you thought that the argument here is "X leads to Y", then you shouldn't have marked an alternate cause as a weakener.

Please visit this article to understand where an alternate cause is a weakener and where it is not

alternate-cause-a-weakener-or-not-155034.html#p1240789

Thanks,
Chiranjeev
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Hi ,

One thing more i need to clarify here is i'm not able to apply the variance test in option D.

D. Whether the only time millipedes are readily available to capuchins is during rainy season
Saying Yes ,means due to readily availablity of milipeds during rainy season would strengthen the argument as they are rubbing to protech from mosiquotoes.

And Saying No, means they are available all the time ,so this would weaken the argument as Monkey rubbing could be for some other purpose or this would weaken the argument as Monkey can rub the millipeds not especially rainy time.

So my confusion is while saying no to option D, how does it weaken the argument.

Thanks

Hi Nitin,

Here is my bit on this:

Your idea of applying variance test seems good i.e. you seem to know that the variance test when applied to the correct choice here will yield two answers: Yes and No. One of these answers will increase your belief in the conclusion and the other will decrease the same. However, your application of the test isn't correct. In fact, you've interpreted the effect of the variance test in an opposite manner here. To understand the same, please consider the following:

The conclusion is drawn regarding the rubbing behavior of these monkeys in a specific season. The author says that they do so because it helps protect these monkeys against the mosquitoes since this behaviour is rare except in the rainy season when the mosquito populations are at their peak. Our job in this question is to find one answer choice that will yield information helpful in evaluating the proposed argument. Accordingly, let's look at option D

D. Whether the only time millipedes are readily available to capuchins is during rainy season

If yes- Rainy season is the only time millipedes are readily available.

As you have rightly pointed out, this choice talks about the availability of millipedes. If the answer to this question is Yes, the only time millipedes are readily available to capuchins is during rainy season then our belief in the argument is decreased. If millipedes are available to these monkeys only in the rainy season, then they can't rub them in other seasons. In other words, the non-availability of millipedes in other seasons may limit the rubbing behaviour of monkeys to only rainy season. This information suggests that they don't have a 'choice'. Hence, in this case, rubbing behavior may not be linked with the increase in the mosquito population during the rainy season Thus, a “yes” to the question posed in choice D weakens the conclusion that protection against mosquitoes is the only reason for rubbing behavior in rainy season.



If No- Rainy season is NOT the only time millipedes are readily available.

Now, we move on to the other end of the spectrum. This time we answer the question by saying No rainy season is not the only time when the millipedes are readily available to these monkeys. Together with the information given in the passage, we know that even though the millipedes are easily available in other seasons, the rubbing behaviour of these monkeys is rare except in rainy season when mosquito population is at peak. This information suggests that the monkeys choose to rub millipedes during a specific time period, increasing our belief in the conclusion that monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.

In all, when we apply the Variance test to choice D, a 'yes' weakens the argument and a ‘no’ strengthens the same.

Does this help?

Dolly.
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For me, the key to solve CR questions is to put myself in the argument. And, it doesn't harm to think of myself as Capuchin monkey to get the answer right

The argument concludes that CM rubs millepedes into its fur to protect against mosquitos. This behavior of rubbing is rare in seasons other than rainy season, when mosquitos are at the peak.

A) Whether the two chemicals provide any protection for millipedes against their own repellents. We are looking for an option that shows weather CM rubs millepedes to protect against mosquitos.
B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world. It does'nt matter
C) Whether animals other than capuchins rub insects of any kind into their fur. We are concerned about CM
D) Whether the only time millipedes are readily available to capuchins is during rainy season. We got it! what if millepedes are available readily only during rainy season. Then CM gets to rub millipedes frequently during rainy season only. Availability can be the reason that CM rubs millipedes and not the mosquito presence. Or it could be to repel mosquito
E) Whether secretions of any other insects accessible to capuchins contain chemicals that repel the mosquitoes. Not concerned about other insects.
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Capuchins rub millipedes that secrete mosquito repellants.
Rubbing happens in rainy season when mosquitos are high in number

Conclusion: Hence rubbing is done to protect against mosquitos.
We need to evaluate this conclusion.

Of the given options, only D talks about an alternate reason of rubbing of millipedes.
Option E talks about some other way in which the capuchins can ward of insects. Great, now they have two ways. But this does not hinder the capuchins from using millipedes as well. Hence this is out of scope.

Correct Option: D

Capuchin monkeys in Venezuela often rub a certain type of millepede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins. The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak. Therefore monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.
Which of the following would be most useful to determine in order to evaluate the argument.

A) Whether the two chemicals provide any protection for millipedes against their own repellents. -Argument is about monekys
B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world. -We are not worried about the various places where we can find them
C) Whether animals other than capuchins rub insects of any kind into their fur -We are not worried about other animals
D) Whether the only time millipedes are readily available to capuchins is during rainy season -CORRECT
E) Whether secretions of any other insects accessible to capuchins contain chemicals that repel the mosquitoes We are not worried about other insects

CAUSAL ARGUMENT :

During Rainy Season --> Higher Mosquito Population, More Rubbing Behavior --> CORRELATION
There comes causation --> Therefore monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes. This is even the CONCLUSION of this argument.

Which of the following would be most useful to determine in order to evaluate the argument.

(A) Whether the two chemicals provide any protection for millipedes against their own repellents.
YES -- the two chemicals provide some protection for millipedes against their own repellents. This does NOT affect the conclusion at all. INCORRECT.

(B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world.
YES -- the type of millipede used by capuchin monkeys in Venezuela is found in other parts of the world. This again does NOT affect the conclusion at all. INCORRECT.

(C) Whether animals other than capuchins rub insects of any kind into their fur
YES -- the animals other than capuchins rub insects of some kind into their fur. SO, HOW WILL THAT AFFECT THE RUBBING BEHAVIOR OF CAPUCHINS. Totally, non-sensical.

Thus, we can see options A, B, and C are totally irrelevant.

(D) Whether the only time millipedes are readily available to capuchins is during rainy season
YES- the only time millipedes are readily available to capuchins is during rainy season : THIS BREAKS THE CONCLUSION. If that was the case then what about the other seasons?? How will the capuchins protect themselves against the mosquitos if millipedes are not available to them, when they are using millipedes (ONLY BECAUSE) for rubbing as a protection measure. The CAUSATION is weakened.

NO - the millipedes are readily available to capuchins not only during the rainy season (implies -- the millipedes are available in other seasons as well): THIS SUPPORTS THE CONCLUSION. Capuchins use millipedes ONLY BECAUSE for protection against the mosquitoes. CAUSATION is strengthened.

(E) Whether secretions of any other insects accessible to capuchins contain chemicals that repel the mosquitoes.
YES - the secretions of some other insects are accessible to capuchins contain chemicals that repel the mosquitoes. BUT how does that even matter to our conclusion at hand. It does not affect the CAUSATION at all. The conclusion is exclusively related to the rubbing of millipedes as a protection measure. So, even if some other insects which are accesible to capuchins and contains the mosquito repellant chemicals, would not be useful to evaluate. INCORRECT.

Capuchin monkeys in Venezuela often rub a certain type of millepede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins. The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak. Therefore monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.

Which of the following would be most useful to determine in order to evaluate the argument.

(A) Whether the two chemicals provide any protection for millipedes against their own repellents. has nothing to do with capuchins. Irrelevant

(B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world. So what if the millipede is found in other parts of the world. How would that affect the argument

(C) Whether animals other than capuchins rub insects of any kind into their fur Irrelevant to the argument. Similar to A.

(D) Whether the only time millipedes are readily available to capuchins is during rainy season The author claims that the capuchins must rub millipedes to protect against mosquitoes, and that this behavior is rare except during the rainy season when mosquitoes are abundant. Maybe the behavior is rare for other reasons e.g. millipedes might be available only in the rainy season? If this is true, this undermines the conclusion. If millipedes are available all year round, but capuchins only rub them into their furs only in the rainy season when mosquitoes are abundant, that strengthens the argument

(E) Whether secretions of any other insects accessible to capuchins contain chemicals that repel the mosquitoes Again irrelevant.

Kudos if you like the answer

Its D

If millipedes are available throughout and are not used by monkeys, then the argument conclusion is strengthened

If millipedes are available on in that season, the argument is weakened.

Capuchin monkeys in Venezuela often rub a certain type of millipede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins. The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak. Therefore monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.

Which of the following would be most useful to determine in order to evaluate the argument?

(A) Whether the two chemicals provide any protection for millipedes against their own predators
We need to evaluate the impact on monkeys

(B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world
We are not worried about parts of world

(C) Whether animals other than capuchins rub insects of any kind into their fur
We are not worried about other animals

(D) Whether the only time millipedes are readily available to capuchins is during rainy season
Correct

(E) Whether secretions of any other insects accessible to capuchins contain chemicals that repel the mosquitoes
We are not concerned about the accessibility to other insects. We must evaluate things related to millipedes

Simplifying the argument:
Lots of mosquitoes in rainy season, Monkeys rub millipedes. Therefore, rubbing must protect these monkeys against mosquitoes.

If millipedes are not available at other times then, this does not have anything to do with mosquitoes. best choice to evaluate the argument is D.

Capuchin monkeys in Venezuela often rub a certain type of millipede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins. The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak. Therefore monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.

Which of the following would be most useful to determine in order to evaluate the argument?


(A) Whether the two chemicals provide any protection for millipedes against their own predators

(B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world

(C) Whether animals other than capuchins rub insects of any kind into their fur

(D) Whether the only time millipedes are readily available to capuchins is during rainy season

(E) Whether secretions of any other insects accessible to capuchins contain chemicals that repel the mosquitoes

The premises talk about Capuchin monkeys and the conclusion just says "monkeys." Wouldn't that mean we're taking an observation about Capuchin monkeys and trying to draw a conclusion about all monkeys of all types everywhere? We are taught to be precise about the language - am I being too precise?

I chose B - because if these millipedes are around in other parts of the world then we can evaluate the behaviors of OTHER monkey's besides Capuchin monkeys.

GMATNinja egmat - Hi Experts - below is my variance analysis on option E. Could you please let me know where am I making a mistake please ?

E - If Yes [yes - secretions of other insects accessible to capuchins contain chemicals that repel the mosquitoes]

Yes, weakens the conclusion clearly because if there are other options available to the capuchin monkey for the purposes of repealing mosquitos (he can rub other insects other than millipedes , why is the monkey still rubbing millipedes during the rain in that case (when there are alternatives the monkey can rub on itself for the purposes of repealing mosquitos) ?

He prefers the millipedes over other insects for some reason OTHER than just repealing mosquitos.

This weakens the conclusion obviously

E - If no [No - secretions of other insects accessible to capuchins don't contain chemicals that repel the mosquitoes]

I thought this strengthened the conclusion does it not ? If there is no option available (for the purposes of repealing mosquitos) to the monkey -- and they are using millipedes

This just shows the millipedes are being used for the purposes of repealing mosquitos.

Where am i going wrong

Even if other mosquito-repelling insects are available to the capuchins, the monkeys could still be rubbing the millipedes into their fur to help protect against the mosquitoes. It’s possible that they rub both the millipedes and the other insects into their fur to repel mosquitoes. The fact that other insects are available does not by itself give reason for us to conclude that the monkeys rub millipedes for reasons other than protection against mosquitoes.

Also, even if millipedes are the only mosquito-repelling insects that are available, capuchins could be using the millipedes for other purposes. So, (E) would not help us evaluate the argument, and we can eliminate it.

I hope that helps!
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Hi GMATNinja

I am still confused. (I still go E)

I’m not sure that do I understand correctly.
In (D),

If YES ( millipedes are only available during rainy season), it can be the capuchin rubs only in rainy season either because millipedes are available only in rainy season or because the capuchin uses millipedes for mosquito-repelling purpose. How can we conclude then?

If NO (millipedes are available all or other seasons), but the capuchin uses millipedes only in rainy season. Mosquito populations are at peak during rainy season but they may be still other seasons, right ? Therefore, the capuchin may use millipedes only in rainy season either because of rains or because of tons of mosquitoes. How can we conclude ?

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