Logical Reasoning

PT131 · S3 · Q20 The peppered moth avoids

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The peppered moth avoids predators by blending into its background, typically the bark of trees.

Conclusion

The darkest peppered moths were the least likely to be seen and eaten.

Evidence

Peppered moths avoid predators by blending into backgrounds, typically tree bark. In the late 19th century, the lightest moths had the most contrast with their backgrounds, so they were the most likely to be seen and eaten.

Evaluation

If the lightest ones were the most likely to be seen, do we have to make the author's assumption, that the darkest ones were the least likely to be seen?

Not necessarily, we would only accept the idea that if we knew that they were trying to blend into something at least as dark as the darkest moth.

Picture a tree bark that is sort of a medium gray. A moth that is too light will show up against that background, but a moth that it is too dark will also show up against that background. The hardest moths to see would be medium dark, so that they best match the medium-dark of the tree bark.

Goal

Look for an answer saying that or saying .

20.

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

  1. The argument overlooks the possibility

    Strengthens

    If this is true, it only helps the author's notion that the darkest moths were less likely to be eaten.

    9% picked this

  2. The argument takes for granted

    Out of Scope: "control their blend"

    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.

    2% picked this

  3. The argument presumes, without providing

    Too Strong

    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.

    10% picked this

  4. Correct

    The argument overlooks the possibility

    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.

    66% picked this

  5. The argument presumes, without providing

    Too Strong: "the only defense mechanism"

    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% picked this

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