Q20 - The peppered moth avoids

[avironstyl]

I chose C and am curious as to the reasoning behind the correct answer of D?

[dtangie23]

This is nasty. I was going between (C) and (E) and went with (E). I didn't even consider (D).

Let me see if I can make sense of this in retrospect.

lightest moths = greatest contrast = most likely to be eaten by predators

So, it follows that...

darkest moths = ______________ = least likely to be eaten

The argument never fills in the above blank.

Do the darkest moths have the least amount of contrast? Well we don't know. We can't assume that just because the lightest moths have the greatest contrast that the darkest moths have the least amount of contrast.

Choice (D) identifies this flaw in reasoning. Suppose there were moths of intermediate color. Now, suppose these intermediate moths actually contrasted less with their backgrounds than the darkest moths. The darker moths then, according to the logical connection between the above two statements, could not be the least likely to be eaten.

[ManhattanPrepLSAT1]

Great work dtangle23! And if you'd like to see another question that has similar flawed reasoning, check out:

PT40, S3, Q12 - Novelist: Any author who thinks

There more you can you see how these questions are really testing the same thing, the easier time you'll have spotting the flaw next time. Whenever you do a question, ask yourself, have I seen this (or something similar to this) before.

[clarafok]

hello,

is E wrong because the argument doesn't assume that blending in is the ONLY defense mechanism? i always choose the wrong answer whenever one of the choices say it's overlooking something as the only way.

if the argument said "the peppered moths can only avoid predators by blending" instead, then would E be right? but aren't we supposed to assume everything in the argument is true?

thanks in advance!

[ManhattanPrepLSAT1]

if the argument said "the peppered moths can only avoid predators by blending" instead, then would E be right?

If the argument said this, then the argument wouldn't have really assumed it. Remember an assumption is always unstated, and premises are always assumed to be true. The first sentence of the stimulus tells us that peppered moths blend into the background to avoid predators. This doesn't exclude other defense mechanisms nor does the argument rely on an assumption that peppered moths are not using any other defense mechanisms.

I know what you mean by the strong language. But that doesn't mean that you should stop picking such strong answers. The language in this answer choice could have easily been correct had the argument been different.

For example, I've seen arguments where the flaw is a simple reversal, such as

A ---> B
-----------
B ---> A

and the answer is strongly worded like this one:

"The argument fails to establish that a condition under which a phenomenon occurs is the only condition under which that phenomenon occurs"

Take a look at the following example if you're interested.

PT13, S2, Q26

So be careful. Don't just rule out strongly worded answers! Hope that helps.

[jamiejames]

Can someone explain some more why D is correct?

[timmydoeslsat]

It really is a matter of forgetting about the middle ground.

We are told that in the late 19th century, the lighest pigment moths contrasted the most with their backgrounds. This made them the most likely to be eaten.

The arguer concludes that the darkest pigment moths were the least likely to be eaten.

Now, we do know that these darkest pigment moths would be less likely to be eaten than the lighest pigment moths. But would the darkest pigment moths be the least likely to be eaten?

We have not established that a color between the lighest and the darkest wasn't best suited to blend in with the tree bark. Overlooking this possibility is a flaw in the argument.

[jamiejames]

It really is a matter of forgetting about the middle ground.

We are told that in the late 19th century, the lighest pigment moths contrasted the most with their backgrounds. This made them the most likely to be eaten.

The arguer concludes that the darkest pigment moths were the least likely to be eaten.

Now, we do know that these darkest pigment moths would be less likely to be eaten than the lighest pigment moths. But would the darkest pigment moths be the least likely to be eaten?

We have not established that a color between the lighest and the darkest wasn't best suited to blend in with the tree bark. Overlooking this possibility is a flaw in the argument.

Got it, thanks.

[esultana]

This question was a tough one.

When I came across it on my recent timed test I remembered actually learning about this phenomenon freshman year of college in an Victorian English literature class. Wikipedia explains it here: http://en.wikipedia.org/wiki/Peppered_moth_evolution

Of course, randomly remembering it didn't help me answer the question. But alas - I just love how the LSAT writers actually write about true things.

Just to round out why all the answers are wrong - can someone check my reasoning?
A) is wrong because it just re-states part of the argument.
B) is wrong because it is out of scope.

[sumukh09]

This question was a tough one.

When I came across it on my recent timed test I remembered actually learning about this phenomenon freshman year of college in an Victorian English literature class. Wikipedia explains it here: http://en.wikipedia.org/wiki/Peppered_moth_evolution

Of course, randomly remembering it didn't help me answer the question. But alas - I just love how the LSAT writers actually write about true things.

Just to round out why all the answers are wrong - can someone check my reasoning?
A) is wrong because it just re-states part of the argument.
B) is wrong because it is out of scope.

A) doesn't restate part of the argument because we only know that they were "more likely" to be seen, but that doesn't imply that they had more predators than moths with different pigmentations. Also, if we assume A to be true, is this a flaw in the argument? No, because if they had more predators then that does nothing to address the faulty reasoning that they would be more likely to be eaten than the darkest coloured moths - it only strengthens it.

B) is out of scope like you said; the argument doesn't assume that they can control the degree to which they blend into their backgrounds

[dmt137]

Can someone explain why C is incorrect?

[christine.defenbaugh]

Great discussion going on here! I'm going to break the question down from the top.

As this is a Flaw question, the first thing on our agenda is distilling the core:

Premise: Lightest pigmentation moths ~ greatest contrast ~ most likely eaten.
Conclusion: Darkest pigmentation moths ~ least likely to be eaten.

dtangie23 is spot on in noting that the conclusion completely leaves out the idea of contrast. Just because the lightest group has the greatest contrast, does that mean the darkest group has the least contrast? What if the background color is a medium gray? Then all the moths who are lighter or darker than that would have contrast. The most camouflaged would be *medium gray* moths, not the darkest ones!

(D) gets right on that. If the medium color moths contrast the least, both darkest and lightest moths would contrast more!

Bonus points: There's actually another assumption here. Just because the most contrasted were the most likely to be eaten does not necessarily mean that the least contrasted are the least likely to be eaten! There could be a world where the darkest moths are the least contrasted, and yet they are more likely to be eaten than the medium moths for some completely separate reason!



Not the Problem
(A) Even if the light moths had more predators than the dark moths, this wouldn't hurt the argument. It might actually strengthen it - fewer predators for the dark moths might decrease their chances of being seen (and then eaten).

(B) There's nothing in the argument about, or implying that the moths could control their blending. And if they could or they couldn't, this wouldn't hurt or help the conclusion!

(C) We don't need this to be true for the argument to potentially work. Two equally dark moths might have slightly different likelihoods of being seen and eaten (because one hides and the other taunts predators, perhaps?). Even if that were the case, darkest moths as a group could still be the least likely to be seen and eaten. And the taunting dark moth might be more likely to be seen and eaten than the hiding dark moth, but still be less likely to be seen and eaten than any moths lighter than both of them.

Note the extremeness of this answer. For an 'all' statement to be assumed, that means any deviation from the 'all' statement, however small, would destroy the argument. That's not the case here.

(E) The argument does not assume this. The moths might have myriad defense mechanisms available to them, but for whatever reason it ends up that the lightest among them are the most likely to be seen and eaten.

Be careful of the word 'therefore' here. It is not functioning as a conclusion keyword in this instance. The statement that the lightest moths were the most likely to be seen and eaten is a premise, not a conclusion. The 'therefore' serves the same purpose as the phrase 'as a result' - the author is still reporting known facts. (E) might be tempting if you didn't realize this was a premise.


Remember that for Flaw questions, just like any assumption family question, we have to start with the core! The answers will generally come in the form of "The argument assumes that [assumption]" and "The argument overlooks that [the assumption might not be true]."

I hope this helps make this question a bit more clear!

[513852276]

What if choice A says "the argument overlooks the possibility that light peppered moths has less predators than dark peppered months." Is this just "weaken" stimulus rather than "undermine" stimulus? Could we call a "weakening" to be a flaw?

[christine.defenbaugh]

What if choice A says "the argument overlooks the possibility that light peppered moths has less predators than dark peppered months." Is this just "weaken" stimulus rather than "undermine" stimulus? Could we call a "weakening" to be a flaw?

Thanks for asking 513852276!

I'm not entirely sure that I understand your question, but I'll try to address what I think you're asking!

There is no difference between a "weaken" stimulus and a "flaw" stimulus. All argument stimuli are essentially the same: they have a premise and a conclusion, and we're interested in the gap between. For a weaken question, we would want an answer choice that, as it stands, weakens the argument (makes it less likely). For a flaw question, we need an answer that correctly states a problem that the argument has.

Now, flaws tend to come in a few flavors:

1) The argument assumes that [the assumption]
2) The argument overlooks the possibility that [the assumption isn't true]
3) State the flaw type.

In (A), because the answer choice begins with "the argument overlooks the possibility that", I know that whatever comes after that should be an argument destroyer (super-weakener).

If (A) had said "the argument overlooks the possibility that light peppered moths had fewer predators than dark peppered moths", I would be cautious. This wouldn't be an awesome answer choice, as having more predators is not a sure-fire argument destroyer, as there is a bit of ambiguity in the term 'more predators" (does that mean more species of predators or more creatures that are predators, regardless of category?).

The point of noticing whether it seems to strengthen or weaken is to realize that, at best, (A) would go the wrong direction entirely.

Does that answer your question?

[jenoh82223]

I think why most people did not pick (D) is because they assumed that the color of the bark is more close to the darkest peppered moths rather than intermediate color moths.
The color of the bark does not necessarily have to be close to the darkest moths.

[MollyO658]

Could A also be wrong because the answer refers to "light" and "dark" moths, whereas the stimulus refers to the "lightest" and "darkest" moths?

Thanks!

[ohthatpatrick]

It's definitely a meaningful distinction!

LSAT has before drawn a distinction between talking about the outliers "lightest / darkest" and talking about other things with some degree of that quality.

For example, try this problem and think about how LSAT is playing off the distinction between the superlative outliers and the other data points not necessarily that far from center.
https://www.manhattanprep.com/lsat/foru ... -t707.html

But overall, I wouldn't find that an automatic dealbreaker, whereas the fact that the answer strengthens definitely is.

Hope this helps.