In preindustrial England, a certain species of moth was

hi,

in preindustrial England, a certain species of moth was entirely white. Only genetic throwbacks of this species had colored wings. After the industrial revolution and 100 years had passed, researchers noticed that most members of this species of moth had developed gray wings. The white wings had allowed the moths to blend in with the pale rocks and white sand of the coast, but after the industrial revolution, white wings were not as good camouflage as they had been before. The change in wing color must be attributable to the soot of the industrial revolution, which caused the moths’ habitat, the white rocks and sand, to turn gray.

Which of the following is an assumption that the conclusion of the argument depends upon?

(A) Gray moths can fly faster than white moths and are better able to avoid birds.
(B) The soot of the industrial revolution is the only reason why the rocks and sand turned gray.
(C) The rocks and sand were just as gray in preindustrial England as they are today.
(D) Moths that are best able to blend in with their habitats possess an evolutionary advantage.
(E) The presence or absence of factories in England held an implication for the diet of birds that lived on the coast.


CONCLUSION:The change in wing color must be attributable to the soot of the industrial revolution, which caused the moths’ habitat, the white rocks and sand, to turn gray.===>IT MEANS MOTHS HAVE DEVELOPED GRAY WINGS BECAUSE INDUSTRIAL REVOLUTION CAUSED THEIR HABITAT TO TURN IN TO GRAY COLOUR.
(SEE HIGHLITED PORTION IN ARGUMENT)

see in option B: The soot of the industrial revolution is the only reason why the rocks and sand turned gray.===> THIS IS TELLING THAT SANDS AND ROCKS TURNED GRAY BECAUSE OF INDUSTRIAL REVOLUTION'S SOOT===>THIS IS NOT AFFECTING ANYWAY===>DEVELOPEMENT OF WINGS IS NOT DISCUSSED HERE.
even if you negate this: The soot of the industrial revolution is ONE OF THE reasonS why the rocks and sand turned gray==>DOESN'T AFFECTS THE CONCLUSION .
HENCE IT IS NOT CORRECT.

NOW OPTION D: Moths that are best able to blend in with their habitats possess an evolutionary advantage.===>NOW IF WE NEGATE THIS:
Moths that are best able to blend in with their habitats DO NOT possess an evolutionary advantage.(MEANS MOTHS ARE UNABLE TO CHANGE THEIR COLOUR OF THEIR WINGS)===>THIS SHATTERS THE CONCLUSION.
HENCE THIS IS THE ASSUMPTION OF THE ARGUMENT.

HENCE D

KUDOS IF IT HELPED.

Can someone explain why B is not the correct answer?

Gian,

What is the source of this question?

I picked this question from a pdf from the forum, looks a tough one to crack under 2mins

How do you guys find this Q? I think it should be re-tagged as a 700+, though.

+1 for B. Choice B) is defender assumption option.

The conclusion states that "The change in wing color must be attributable to the soot of the industrial revolution for the white rocks and sand to turn gray". Note the use of the word must here, indicating that it was only soot and nothing else that caused the change in colour.

B) If we negate this option, we get "The soot of the industrial revolution is not the only reason why the rocks and sand turned gray." destroys the argument that soot of the industrial revolution was the responsible for this change.

E) If we negate E we get "Moths that are best able to blend in with their habitats donot possess an evolutionary advantage.". This doesnot impact the argument whether "The change in wing color must be attributable to the soot of the industrial revolution".

Thats true, I felt E as a strengthener but B is a better assumption as it stays within the scope. Evolution is not discussed in the passage as such, although it talks about wing color change.

The argument is based on three premises -
1) The moths were originally white ( later it becomes obvious that it is because that color helps them camouflage under the white rocks and sands backdrop.
2) The industrial revolution turned the sands and rocks into grey ( now this can be due to soot or anything else)
3) The moths couldn't have survived had they not changed their wings to the current color of rocks and sands.

Whats the conclusion?
--- That moths have survived 100s of years by changing the color of their wings to grey.
Applying process of elimination A, C and E are gone for they speak about moth's speed, level of grayness in rocks and sand during IR & diets of birds respectively none of which lead to the conclusion stated.
For B, this statement exclusively talks about the reason behind the grey sands and rocks. Whether or not it is due to soot, the conclusion that the wings have turned grey due to evolutionary adaptation to the grey rocks and sands is not affected.
B is a very necessary assumption, without which there wouldn't be any reason why moth would adapt to the grey color of rocks and sands.

Guys -> I think SKM has already given a fine explanation above to prove why B is wrong and why D is right. Hope it helps.

Unable to understand why D is incorrect..???

Also,what is the relevance of this statement in the passage..

"Only genetic throwbacks of this species had colored wings."
Doesnt it say the "only genetical moths can have coloured wings".???


Awaiting experts revert..

Hi jaituteja.

I'm happy to help.

First of all, I think your question is "Why D is correct?" Is that true?. Anyway, I will analyze the question as followings:

ANALYZE THE STIMULUS:

Fact: Before preindustrial England: Moth was entirely white. After the industrial revolution: most members of moth developed gray wings
Fact: white wings helped moths to blend in with the pale rocks and white sand of the coast
Fact: the soot of the industrial revolution caused the white rocks and sand (the moths’ habita) to turn gray.
Conclusion: The change in wing color must be attributable to the soot of the industrial revolution.

To make the stimulus clearly, I use a diagram below:
Before:
A caused B
After:
C changed A to A*
…. changed B change to B*
Conclusion: C must cause B change to B*
Assumption: A* & B must have correlation. This is a bridge to connect C to B*

Apply to this question:
Before:
White rock & sand caused moth's wings were white
After:
The soot changed white rock & sand to gray rock & sand
…………. changed white wings moths to gray wings moths
Conclusion: The soot causes moths’ wings turned gray.
Assumption: the white wings moths MUST have to adapt new environment – Gray rock & sand.


ANALYZE EACH ANSWER:

(A) Gray moths can fly faster than white moths and are better able to avoid birds.
Wrong. Clearly out of scope.

(B) The soot of the industrial revolution is the only reason why the rocks and sand turned gray.
Wrong. SHELL GAME. It’s very tempting. Some of you may think “oh, this is defender assumption, bingo”. But it’s wrong. This question is about “Supporter assumption”. Please see the diagram, even though the soot is the only reason that turned rocks and sand to gray. How does it affect the conclusion “the soot caused moths’ wings turned gray”? This option only shows the link between the soot and the color of rocks and sand, but it does not connect shoot to color of moth's wing.
You can see the diagram: “C caused A to A*”. That’s it. You need “a bridge” – “A* - B” to connect “C also caused B to B*.

(C) The rocks and sand were just as gray in preindustrial England as they are today.
Wrong. It does not help. “as they are today” does not make any point.

(D) Moths that are best able to blend in with their habitats possess an evolutionary advantage.
Correct. This is exactly the bridge you need. D says “moths were able to adapt new environment by changing their wings’ color”.

(E) The presence or absence of factories in England held an implication for the diet of birds that lived on the coast.
Wrong. Out of scope.

Hope it helps.

I see the point why B) is wrong but somehow not convinced with the option D) either.

For instance if we negate E, we get "Moths that are best able to blend in with their habitats might not possess an evolutionary advantage.". Now, this doesn't destroy the conclusion "The change in wing color must be attributable to the soot of the industrial revolution.".

Conclusion: Researcher hypothesized that this color change in wings was to escape from being eaten by their prey.

Now under what circumstance this will fail: lets say white moth had population of 1000 and colored moth(Grey) had population of 100. No what if all white moth were not able to evolve and were eaten. Now after 100 years we will se only grey moths in area. Under this assumption conclusion fails.

Reverse of this is what is written in option D and therefore it is our assumption.

OptionB: Negate this we get: Rocks colour change was because of many other reasons: Does this fails our conclusion ?

Hi Prakhar,

The trick is to identify what is "the real conclusion."
"The change in wing color must be attributable to the soot of the industrial revolution, which caused the moths’ habitat, the white rocks and sand, to turn gray."

Let's look at the conclusion this way- "The change in wing color must be attributable to the XYZZ."
The change in the wing colour is the main conclusion. To confuse us, the arg talks and explains about "XYZ" i.e, "the soot of the industrial revolution had caused the moths’ habitat, the white rocks and sand, to turn gray..BLAH BLAH"
Now when you negate D, this very conclusion is hit and fails completely. Hence, D is better than B.

Did this help?

what is the major difference between assumption and strengthening questions in critical reasoning

This link might help You -

critical-reasoning-shortcuts-and-tips-91280.html#p697742
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Conclusion - The change in the wing color must be attributable to the soot of the Industrial revolution, which caused the moths' habitat, the white rocks and sand, to turn gray.Why?
Premise - Because the species was entirely white before the pre-industrial revolution.
After industrial revolution, their wings' color changed to gray.
Pre-thinking - > So, what happened in industrial revolution that their wing's color changed? One thing we know for sure is that the moths' habitat turned to gray after industrial revolution. How does that affect the moths' wings colors? Maybe they were affected by their habitats' color or maybe not.
Lets see the reasoning of not being affected by the habitats' color then is there any other way they could have changed their color? Does the soot directly affect the moths' wings colors? We have not been given anything of such kind in the reasoning so we have to negate this possibility.
What we have been given though is that maybe the habitats' color affects the moths' wings. If it does, that means that moths who have adapted to their habitats are now ubiquitously present. So, they must have some advantage over other white moths that were evident before.

D fits in with our assumption because if moths were not directly affected by the industrial soot. They must be through their habitats.
Now, lets analyse why B cant be the assumption. It states that "The soot of the industrial revolution is the only reason why the rocks and sand turned gray." Lets do the negation test.
The soot of the industrial revolution is not the only reason why the rocks and sand turned gray. Okay, so their are other reasons because of which the rocks turned gray. But would that absolve soot of being responsible of turning the rocks and sands gray? No, it would not. It is still partly responsible so our conclusion still stays so this cant be the main assumption.

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