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Tiger Beetles

by fleurdelisse » Sat Mar 28, 2009 5:55 am
Tiger beetles are such fast runners that they can capture virtually any non flying insect . However, when running towards an insect , a tiger beetle will intermittently stop and then, a moment later, resume its attack. Perhaps the beetles cannot maintain their pace and must pause for a moment's rest; but an alternative hypothesis is that while running, tiger beetles are unable to adequately process the resulting rapidly changing visual information and so quickly go blind and stop.

Which of the following, if discovered in experiments using artificially moved prey insects, would support one of the two hypothesis and undermine the other?
  • A. When a prey insect is moved directly towards a beetle that has been chasing it, the beetle immediately stops and runs away without its ususal intermittent stopping.
    B. In pursuing a swerving insect, a beetle alters its course while running and it pauses become more frequent as the chase progresses.
    C. In pursuing a moving insect , a beetle usually responds immediately to changes in the insect's direction, and it pauses equally frequently whether the chase is up or down the incline.
    D. If , when a beetle pauses, it has not gained on the insect it is pursuing, the beetle generally ends its pursuit.
    E. The faster a beetle pursues an insect fleeing directly away from it, the more frequently the beetle stops.

The answer is B because apparently it undermines the theory that the beetle gets tired, and strengthen the second theory about visual information. I agree. But C also strengthen one theory (that of tireness) and weakens the second theory. So why is the answer not C??
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Re: Tiger Beetles

by DanaJ » Sat Mar 28, 2009 9:02 am
fleurdelisse wrote: But C also strengthen one theory (that of tireness) and weakens the second theory. So why is the answer not C??
You are wrong here: the beetle stops EQUALLY frequently whether the chase is up or down the incline, which means that its pauses ARE NOT related to effort. Chasing a but up an incline requires more effort than when chasing a bug down the incline, but the beetle pauses at the same rate, which proves that his pauses are not effort related. This means that the first hypothesis is weakened.

The fact that the beetle changes its course immediately means that it can process the rapidly changing environment really fast, which weakens the second hypothesis too.

This is why C weakens both hypothesis.
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by thought » Thu Apr 02, 2009 7:59 pm
I thought this question was a toughie as it has a lot of moving parts.

First, IMO, Your reasoning is wrong here:
The answer is B because apparently it undermines the theory that the beetle gets tired, and strengthen the second theory about visual information.
The two theories are that the beetle (1) that the beetle gets tired and (2) that the beetle can't see

B: "In pursuing a swerving insect, a beetle alters its course while running" :arrow: undermines (2) and suggests the beetle CAN see.
"Pauses become more frequent as the chase progresses" :arrow: strengthens (1) and suggests the beetle DOES get tired.

As for C:

"In pursuing a moving insect , a beetle usually responds immediately to changes in the insect's direction" :arrow: undermines (2) and suggests the beetle CAN see.
"it pauses equally frequently whether the chase is up or down the incline" :arrow: also undermines (1) and suggests the beetle does NOT get tired.[/b]
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by delhiboy1979 » Thu Apr 02, 2009 11:26 pm
great analysis thought. well done.
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by stormier » Sat Dec 25, 2010 7:08 pm
fleurdelisse wrote:Tiger beetles are such fast runners that they can capture virtually any non flying insect . However, when running towards an insect , a tiger beetle will intermittently stop and then, a moment later, resume its attack. Perhaps the beetles cannot maintain their pace and must pause for a moment's rest; but an alternative hypothesis is that while running, tiger beetles are unable to adequately process the resulting rapidly changing visual information and so quickly go blind and stop.

Which of the following, if discovered in experiments using artificially moved prey insects, would support one of the two hypothesis and undermine the other?
  • A. When a prey insect is moved directly towards a beetle that has been chasing it, the beetle immediately stops and runs away without its ususal intermittent stopping.
    B. In pursuing a swerving insect, a beetle alters its course while running and it pauses become more frequent as the chase progresses.
    C. In pursuing a moving insect , a beetle usually responds immediately to changes in the insect's direction, and it pauses equally frequently whether the chase is up or down the incline.
    D. If , when a beetle pauses, it has not gained on the insect it is pursuing, the beetle generally ends its pursuit.
    E. The faster a beetle pursues an insect fleeing directly away from it, the more frequently the beetle stops.

The answer is B because apparently it undermines the theory that the beetle gets tired, and strengthen the second theory about visual information. I agree. But C also strengthen one theory (that of tireness) and weakens the second theory. So why is the answer not C??

I agree that B is a correct choice.

Please help me explain what's the fallacy in my reasoning in support of choice A-

A - As a prey insect is directly brought towards the beetle (which i also read as change in visual information) it stops. This supports the second hypothesis.

And it runs away without stopping (which i read as - it can maintain pace without stopping for rest). This undermines the first hypothesis.


and I will stress - visual information does change either when something is brought towards ones eyes or when someone moves towards that something !
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by fitzgerald23 » Sat Dec 25, 2010 9:13 pm
To answer this question you need to know the two theories:

1. Beetles can not maintain their pace
2. Beetles cant process rapidly changing visuals and go blind

The question wants an answer that helps strengthen one choice and weakens the other

A. Incorrect. I guess you can read this as undermining point 1 because there is no stopping when it runs away, but does it strengthen choice 2? No. This tells us that if the insect decides to move into an attack position the beetle runs away. It doesnt mean that they can process changing visuals and it specifically states that the direction here is straight.

B. Correct. When the insect swerves so does the beetle, which weakens theory 2. As the chase progresses it pauses more frequently agrees with theory 1 that the beetle can not keep its pace. So you have both a strengthen and weaken statement.

C. Incorrect. Again this weakens choice 2, but does it do anything to make number 1 valid? No. If pauses are equal during the chase both up and down an incline it cant be due to tiring. It should be far more tiring to go up an incline than down one. If you are confused on this one just go back to B and see the subtle difference. B tells you that pauses become more frequent as the chase goes on longer and longer. That is clearly related to tiring.

D. Incorrect. Doesnt have anything to do with either theory.

E. Incorrect. Has nothing to do with rapidly changing visuals.
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by stormier » Sun Dec 26, 2010 5:06 am
fitzgerald23 wrote:To answer this question you need to know the two theories:

1. Beetles can not maintain their pace
2. Beetles cant process rapidly changing visuals and go blind

The question wants an answer that helps strengthen one choice and weakens the other

A. Incorrect. I guess you can read this as undermining point 1 because there is no stopping when it runs away, but does it strengthen choice 2? No. This tells us that if the insect decides to move into an attack position the beetle runs away. It doesnt mean that they can process changing visuals and it specifically states that the direction here is straight.
If prey is brought towards a beetle, it is changing visual information that the beetle perceives. If it stops, one can deduce that it could not process the changing visual information, goes blind and thus stops.

What you are assuming in your argument is that only change in direction changes visual information, and that something moving in front of one's eyes in a straight line does not. I do not think this is true. Try brining your hand straight towards your eyes!

If someone argues that in statement A, when the prey is brought towards the beetle the rate of approach is not specified - rapid, or slow - and thus the information could not be changing rapidly enough for it to stop. However, that makes these choices just too sutble.
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by GMATGuruNY » Sun Dec 26, 2010 6:16 pm
Tiger beetles are such fast runners that they can capture virtually any non flying insect . However, when running towards an insect , a tiger beetle will intermittently stop and then, a moment later, resume its attack. Perhaps the beetles cannot maintain their pace and must pause for a moment's rest; but an alternative hypothesis is that while running, tiger beetles are unable to adequately process the resulting rapidly changing visual information and so quickly go blind and stop.

Which of the following, if discovered in experiments using artificially moved prey insects, would support one of the two hypothesis and undermine the other?
I received a PM asking me to comment.

A. When a prey insect is moved directly towards a beetle that has been chasing it, the beetle immediately stops and runs away without its usual intermittent stopping. Outside the scope: the argument is not about why the beetle stops and flees when an insect is brought toward the beetle but about why the beetle stops intermittently when it chases an insect.

B. In pursuing a swerving insect, a beetle alters its course while running [Weakens the hypothesis that the beetle stops intermittently because it cannot process visual information] and it pauses become more frequent as the chase progresses [Strengthens the hypothesis that the beetle stops because it gets tired: as the chase continues and the beetle grows wearier, the stops become more frequent.] Correct.

C. In pursuing a moving insect , a beetle usually responds immediately to changes in the insect's direction,[Weakens the hypothesis that the beetle stops because it cannot process visual information] and it pauses equally frequently whether the chase is up or down the incline. [Weakens the hypothesis that the beetle stops because it gets tired: moving up an incline would make the beetle more tired, yet the stops become no more frequent]. Incorrect because it weakens both hypotheses.

D. If , when a beetle pauses, it has not gained on the insect it is pursuing, the beetle generally ends its pursuit. Outside the scope. The argument is not about why the beetle ends its pursuit but about why the beetle stops intermittently during a pursuit.

E. The faster a beetle pursues an insect fleeing directly away from it, the more frequently the beetle stops. Doesn't weaken the hypothesis that the beetle cannot process visual information.

Only answer choice B strengthens one hypothesis and weakens the other. The correct answer is B.

Hope this helps!
Last edited by GMATGuruNY on Sun Jan 12, 2014 4:26 am, edited 1 time in total.
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by teal » Fri Feb 03, 2012 2:52 pm
I still don't understand how B undermines the visual hypothesis? Please explain.
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by akashkumar1987 » Wed Oct 17, 2012 8:40 pm
@GMAT GutuNy

B. and it pauses become more frequent as the chase progresses [Strengthens the hypothesis that the beetle stops because it gets tired: as the chase continues and the beetle grows wearier, the stops become more frequent.] Correct. - Can you please elaborate it more.

C. and it pauses equally frequently whether the chase is up or down the incline. [Weakens the hypothesis that the beetle stops because it gets tired: moving up an incline would make the beetle more tired, yet the stops become no more frequent]. Incorrect because it weakens both hypotheses. - - Can you please elaborate it more.
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by GMATGuruNY » Thu Oct 18, 2012 3:59 am
akashkumar1987 wrote:@GMAT GutuNy

B. and it pauses become more frequent as the chase progresses [Strengthens the hypothesis that the beetle stops because it gets tired: as the chase continues and the beetle grows wearier, the stops become more frequent.] Correct. - Can you please elaborate it more.

C. and it pauses equally frequently whether the chase is up or down the incline. [Weakens the hypothesis that the beetle stops because it gets tired: moving up an incline would make the beetle more tired, yet the stops become no more frequent]. Incorrect because it weakens both hypotheses. - - Can you please elaborate it more.
Hypothesis 1: Perhaps the beetles cannot maintain their pace and must pause for a moment's rest.
Hypothesis 2: While running, tiger beetles are unable to adequately process the resulting rapidly changing visual information and so quickly go blind and stop.

The correct answer choice must SUPPORT one hypothesis while WEAKENING the other.

B: In pursuing a swerving insect, a beetle alters its course while running and it pauses become more frequent as the chase progresses.
The longer the beetle chases, the more frequent the pauses, SUPPORTING hypothesis 1 (that the beetle needs to REST).
Since the beetle can ALTER ITS COURSE, hypothesis 2 (that the beetle GOES BLIND) is WEAKENED.
Correct: One hypothesis is SUPPORTED, while the other is WEAKENED.

C: In pursuing a moving insect, a beetle usually responds immediately to changes in the insect's direction, and it pauses equally frequently whether the chase is up or down the incline.
Since the beetle can respond to changes in direction, hypothesis 2 (that the beetle GOES BLIND) is WEAKENED.
Since chasing UP AN INCLINE does NOT cause the beetle TO PAUSE MORE FREQUENTLY, the contention that the beetle is pausing in order TO REST (hypothesis 1) is WEAKENED.
Since both hypotheses are WEAKENED, eliminate C.
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by Srimanoj » Sat Jan 11, 2014 1:31 pm
A. When a prey insect is moved directly towards a beetle that has been chasing it, the beetle immediately stops and runs away without its usual intermittent stopping. Outside the scope: the argument not about why the beetle stops and flees when an insect is brought toward the beetle but about why the beetle stops intermittently when it chases an insect.

Hi,
I have a clarification on GMATGuruNY's highlighted part above and appreciate any explanation.

I'm little unsure why we are tagging this as out of scope completely. When an insect is brought towards the beetle and if the beetle stops, it could be because the beetle is unable to process information (that's rapidly changing since they are approaching one another), goes blind and stops. So this kinda supports one hypothesis. Doesn't it?

and if the beetle runs away without its usual intermittent stopping - agree this is one out of scope or doesn't weaken the other hypothesis that talks about stopping when chasing an insect (not when approached by an insect)
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by Sankeerthana » Sat Jan 11, 2014 3:29 pm
At first, I was confused between B & C, but if you really analyse it, the answer becomes apparent.

2 potential reasons for beetle's intermittent stops:
1. Cannot process visual information rapidly
2. Fatigue

B. In pursuing a swerving insect, a beetle alters its course while running and its pauses become more frequent as the chase progresses. -> If the beetle is able to alter its course as the chase progresses, it means that the beetle is able to rapidly process visual information to effectively change its course, which directly implies that it does not have visual problems. (Here it is safe to assume that the visual information to be processed does not get more complex/ simpler as the chase progresses-->not really our concern). Therefore, the pauses as the beetle is deeper into the chase can be attributed to its fatigue. 1 is undermined and 2 is strengthened.

C. Equally is a very important word here. Naturally, we are all aware that climbing up an incline is atleast 1.5 times more tiring than going down one. The GMAT is asking us to apply common sense from daily occurrences in our lives. Additionally the fact that the beetle responds immediately to changes in the insect's direction implies that it can process visual info to incorporate that info into its chase by altering its course. Therefore both 1 & 2 are undermined. Incorrect.
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by GMATGuruNY » Sun Jan 12, 2014 4:41 am
Srimanoj wrote:A. When a prey insect is moved directly towards a beetle that has been chasing it, the beetle immediately stops and runs away without its usual intermittent stopping. Outside the scope: the argument not about why the beetle stops and flees when an insect is brought toward the beetle but about why the beetle stops intermittently when it chases an insect.

I'm little unsure why we are tagging this as out of scope completely. When an insect is brought towards the beetle and if the beetle stops, it could be because the beetle is unable to process information (that's rapidly changing since they are approaching one another), goes blind and stops. So this kinda supports one hypothesis. Doesn't it?
Note the phrase in red.
There could be MANY reasons that -- when a prey insect is moved TOWARD a tiger beetle -- the beetle runs away with no intermittent stopping.
Perhaps the beetle runs away out of fear -- a condition that is unlikely to be present when the beetle is CHASING its prey.
Since answer choice A presents a scenario that is not necessarily analogous to that presented in the passage, eliminate A.
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