The peppered moth avoids

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsFlaw

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Stimulus

The peppered moth avoids predators by blending into its background, typically the bark of trees. In the late nineteenth century, those peppered moths with the lightest pigmentation had the greatest contrast with their backgrounds, and therefore were the most likely to be seen and eaten by predators. were the least likely to be seen and eaten.

What this question is testing

Flaw

Your task

Describe the reasoning error the argument actually commits.

Common trap

Answers that name a real logical flaw the argument doesn't actually make.

Winning move

Articulate the gap in the reasoning yourself, then match it to the choice that describes that gap.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question

20.

Which one of the following most accurately describes a flaw in the reasoning

Answer choices

Strengthens10% picked this
The argument overlooks the possibility that light peppered moths had more predators than
If this is true, it only helps the author's notion that the darkest moths were less likely to be eaten.
10%
Out of Scope: "control their blend"3% picked this
The argument takes for granted that peppered moths are able to control the degree to which they
If anything, the author is not assuming they can control their color. He thinks that the lightest moths were screwed because of their contrast with the tree bark. If the moths had control over their blending, then they would darken themselves up to blend in better.
3%
Too Strong9% picked this
The argument presumes, without providing justification, that all peppered moths with the same coloring had the same likelihood of being seen
Too Strong: "all moths with same color = same likelihood" The author's argument makes a soft, generalized comparison. The darkest moths were on average least likely to be seen and eaten, but the author can still permit that individual moths might have had attributes that made them harder / easier to spot.
9%
Correct65% picked this
The argument overlooks the possibility that there were peppered moths of intermediate color that contrasted less with their backgrounds than
Why this is right
Yes, this gets to the "what if the backgrounds are medium gray" objection. In that case, the lightest and the darkest moths would have the most contrast, and the medium-dark moths would be the least likely to be seen.
Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.
65%
Too Strong: "the only defense mechanism"13% picked this
The argument presumes, without providing justification, that the only defense mechanism available to peppered moths was to
Even if the author is assuming that blending into backgrounds is their only defense mechanism, this assumption wouldn't be our problem with the reasoning. We're objecting to the reasoning because the author "presumes, without providing justification, that the darkest colored moths had the least contrast with their backgrounds".
13%

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