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

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

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.

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.

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!

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 ?

Posted from my mobile device

The author thinks that the monkeys uses millipedes only to repel mosquitos. To support this argument, he/she points out that the monkeys usually only rub the millipedes in their fur when the mosquitos are present -- in the rainy season. If there were some other reason to rub the millipedes into their fur (they just enjoy the smell, for example), then the monkeys would probably do so all year round, right?

Here, we see that the author's reasoning depends on the connection between the season and the monkeys' behavior. Because the behavior only happens during the rainy season, the author believes that the monkeys' goal is just to repel mosquitos. In other words, the monkeys generally choose to rub the millipedes into their fur when mosquitos are a big problem, and choose not to rub the mosquitos into their fur when the mosquitos aren't a big problem.

Here's (D) again:

If the millipedes are only available during the rainy season, that would blow a huge hole in the author's reasoning. Again, the author uses the seasons to show that the monkeys make a choice to rub in the millipedes during the rainy season, and to not bother when it's not rainy season.

But if the millipedes aren't available outside of the rainy season, then the monkeys don't have a choice at all. In this case, the author's reasoning doesn't stand up -- maybe the monkeys DO just enjoy the smell of the millipedes (or have some other reason to use them). There's simply no evidence that the monkeys use the millipedes only as a mosquito repellent.

You're right that the answer to (D) wouldn't 100% prove why the monkeys rub the millipedes into their fur. However, the answer to (D) would certainly help us evaluate the strength of the author's argument -- either the author's line of reasoning is greatly weakened, or it is not. That's enough to make (D) very useful in evaluating the argument.

I hope that helps!

GMATNinja

I chose C for the following reason.

The conclusion of the passage says that "Monkeys" rub millipedes into their fur. However, the information given to support the conclusion is specifically about "Capuchin monkeys", not monkey in general.

In order to confirm that the conclusion is true, wouldn't we have to know if other types of monkeys (animals other than Capuchins) do similar things?

For a complete discussion of this question, check out our earlier analysis here. But in case it helps, here are a few additional thoughts on why (C) is wrong.

You're correct that the stem provides information about "capuchin monkeys," whereas the conclusion is about "monkeys." However, we can't assume that the answer will hinge on this issue.

Additionally, we are not trying to "confirm that the conclusion is true," but only to determine which of the answers would be "most useful to evaluate the argument." So the right answer doesn't need to prove the argument, it just needs to be helpful for evaluating it.

To analyze (C), let's review the argument we are trying to evaluate: "monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes." In other words, the argument is about why monkeys rub millipedes into their fur.

So knowing if other animals rub insects into their fur wouldn't tell us anything about why they do it. Is it to repel mosquitoes, or for some other reason? We just don't know. That's why we can get rid of (C).

I hope that helps!

Thank you for the wonderful explanation. However, I am still struggling to get past my pre-thinking analysis on Option D and E -

D - Lets assume millipedes are not available 12 months but only during rainy season. So yes this justifies the rubbing only during this time, thus strenghtening the conclusion.
But if we assume that the millipedes are available all around the year, then there is no impact on the conclusion. How do we know if they would rub into their fur any other given season?

E - Assuming Yes to the Option - if that is the case then we can conclude that the monkeys are rubbing the millipedes not only for repelling mosquitoes but for other reasons because if they wanted to, they could choose those other creatures that perform ONLY 1 function.
Assuming No - we can conclude that millipedes are rubbed only for one reason.

Where am I going wrong and how do I refute these thoughts? The rainy season point doesn't sit because essentially there are 2 points in the given argument and the rainy season is just one of them.

Do help, thank you.

For a more in-depth analysis of (D), check out this post.

A few thoughts on your analysis on (D): the conclusion isn't just that the monkeys DO a certain action -- it's about WHY they do that action. If the bugs are only available during the rainy season, it really messes up that "WHY" aspect of the conclusion (see that linked post for more detail).

Take another look at the exact wording of (E):
(E) wouldn't tell us that the ONLY reason to rub in these other bugs is to repel mosquitos. There could be some other reason to rub in these other bugs -- we just know that they DO contain mosquito-repelling chemicals, not that they DON'T offer any other attractive qualities for the monkeys.

Also, (E) doesn't add in another reason for monkeys to rub in the millipedes, as you've suggested. Whether other bugs contain the chemicals doesn't give us any insight into the millipedes themselves. The monkeys COULD have access to other mosquito-repelling bugs, and could STILL rub the millipedes in only to repel mosquitos. Or vice versa! You just can't infer anything about the millipedes, or the monkeys' motivations for using the millipedes, from the question raised in (E).

As far as how to get away from these initial thoughts, and in particular the "rainy season" issue: sure, the rainy season is "only one" point from the passage. But it's an absolutely crucial element in the overall structure of the argument. The author uses the link between the rainy season and the rubbing behavior to reach a conclusion about the motivation of the monkeys. The question raised in (D) could completely mess up this overall argument, even though it only focuses on the rainy season.

So, you can't dismiss an answer choice just because it only speaks to one part of the passage -- you have to carefully think through the implications of each option.

I hope that helps!

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

I understand the logic behind answer choice D, but wouldn't answer choice A also make sense? I'm hung up on the "only because doing so helps protect them against mosquitos" portion. I'm interpreting this as the monkeys are rubbing the millipedes for the sole purpose of repelling ONLY mosquitos.

Let's say the millipedes predators include ticks and fleas. Wouldn't the conclusion be weakened if the monkeys were rubbing the millipedes to repel against ticks and fleas (the chemicals provide protection to the millipedes so it should also protect the monkeys) rather than mosquitoes? Therefore, it is important to know whether the monkeys are rubbing to repel mosquitos or other insects such as the millipede's predators?

­

Context:
Capuchin monkeys in Venezuela often rub a certain type of millipede into their fur.

Premises:
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.

Conclusion:
Monkeys probably rub millipedes into their fur only because doing so helps protect them against mosquitoes.
The use of “only” in a conclusion should raise a flag – Can there be any other objective of rubbing millipedes into the fur too?

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

The argument deals with the advantage the monkeys gain from rubbing millipedes on their fur. The advantage to millipedes from their own chemicals is out of scope.

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

Other parts of the world are out of scope.

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

Animals other than monkeys are out of scope.

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

A premise of our argument says that they rub millipedes only during rainy season when mosquitoes are most rampant. It would be interesting for us to find out whether millipedes are available at other times too.

If we answer
“Yes” – If they are available at other times too, then it seems that there is a reason why monkeys rub them in rainy season only. Then it seems likely that it is solely to repel mosquitoes.
“No” – If they are not available at any other time in the year, then the mosquitoes being the only connection may not be correct. They could be rubbing millipedes in rainy season only not because mosquitoes are plenty at that time but because millipedes are available only during rainy season. This weakens the mosquito connection.

The two answers affect the conclusion differently. Hence, this is the correct option.

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

The point is why the mosquitoes rub millipedes on their fur. Other insects are out of scope.

Answer (D)


Discussion on Useful to Evaluate Questions: https://youtu.be/1JtHjH1lWZc