Logical Reasoning

PT148 · S4 · Q7 Although some animals exhibit

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Although some animals exhibit a mild skin reaction to urushiol, an oil produced by plants such as poison oak and poison ivy, it appears that only humans develop painful rashes from touching it.

Conclusion (Therefore)

Urushiol probably did not evolve in plants like poison oak as a chemical defense.

Evidence

Only humans seem to get a painful rash from touching it. Wood rats even use branches from the poison oak plant to build nests.

Evaluate

Since we want to support the idea that urushiol didn't evolve for reason X, we can strengthen two different ways:

- show a different reason, reason Y, why plants evolved urushiol - add another fact that makes reason X seem implausible

Goal

Let's look for an answer giving us a different reason why these plants evolved urushiol:

Or let's look for more evidence that urushiol isn't a chemical defense mechanism: animals take baths in the stuff.

Which one of the following, if true, adds the most support for the conclusion of the argument?

Wood rats build their nests
Weakens, if anything
The author was saying, "You can tell that urushiol isn't meant to be a turn-off to animals, because wood rats build their nests out of it. Clearly, they aren't turned-off by it." But if we learn that the nests are build from dead branches of the plants, it's possible that the chemical irritant isn't there anymore. Thus, the animal might well be turn-off by the chemical, which goes against the argument.
3% picked this
Correct
A number of different animals
Why this is right
This adds plausibility to the idea that urushiol is not meant to be offensive to other animals: - only humans are bothered by it - wood rats use it to build their nests - a bunch of animals straight up eat the stuff!
Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.
84% picked this
It is common for plants
Weakens, if anything
Saying that lots of plants defend themselves with chemical substances goes the wrong way from this author, who is saying "these plants are not using their chemical substance to defend themselves".
5% picked this
In approximately 85 percent of
No Impact
We have no interest in any more information about what urushiol does to humans. We already know that humans are affected. The mystery of the argument resides in whether urushiol is used to turn-off any other animals.
1% picked this
Poison oak and poison ivy
No Impact
Learning that these plants happen to grow well in certain ecosystems that humans have altered doesn't tell us anything about why they evolved urushiol. Traits take thousands of years to evolve, so the evolutionary cause of urushiol has nothing to do with anything humans have done in the past few centuries.
6% picked this

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