Logical Reasoning

PT117 · S2 · Q4 The top 50 centimeters of soil

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The top 50 centimeters of soil on Tiliga Island contain bones from the native birds eaten by the islanders since the first human immigration to the island 3,000 years ago.

Conclusion (Thus)

The arrival of humans dramatically decreased the bird population in terms of both number and diversity on the island.

Evidence

Soil studies show that for the last 3,000 years, since humans arrived, the bird population is less numerous and less diverse compared to the previous 80,000 years.

Evaluate

We can apply the Explain Curious Fact template to this, since we have a conclusion making a causal claim about non-causal evidence.

CURIOUS FACT: How come there was a larger and more diverse population of birds on Tinga before humans arrived?

EXPLANATION: When humans arrived, their activity reduced the number and variety of birds.

To weaken, we either introduce an alternate explanation for the decline in birds or undermine the plausibility of the human causation theory.

Goal

Find an answer choice that provides an alternate cause for the decline in the bird population, or that debunks the story that human arrival is responsible.

4.

Which one of the following statements, if true, most seriously weakens the argument?

  1. The bird species known to

    Strengthens

    This indicates that bird species eaten by humans had few natural predators, implicitly ruling out an alternate explanation for why the birds dwindled in number and variety.

    3% picked this

  2. Many of the bird species

    Strengthens

    This shows that similar birds persisted longer on uninhabited islands, suggesting a correlation between human presence and bird decline, reinforcing the causal link to humans. It's a No Cause, No Effect strengthener --- the islands that DIDN'T have humans arrive, DIDN'T have bird species disappearing.

    3% picked this

  3. Correct

    The arrival of a species

    Why this is right

    This introduces a microbe carried by some birds but deadly to others, which appeared just before humans arrived. It offers an alternate explanation for the bird decline unrelated to human activity, thus weakening the argument.

    Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

    85% picked this

  4. Bones from bird species known

    Unclear Impact

    If anything maybe this strengthens. It seems to be saying that some of the birds we know these islanders eat were on the island before humans arrived (since they show up in the older soil). If islanders are currently eating these birds, then those birds haven't gone extinct yet from the arrival of humans (but maybe they're on their way to going extinct).

    6% picked this

  5. The birds that lived on

    No Impact

    This notes that birds prior to humans didn’t fly well but doesn’t explain their decline or introduce a factor that distinguishes pre-human and post-human periods in the bird population. If anything, this strengthens by making it more plausible that humans would be able to trap and kill these (non-flying) birds.

    2% picked this

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