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Difficulty: HardAssumptions in Causal Arguments

Agronomists observing wild varieties of the montane scrub-oak have discovered that trees growing on the northern slopes of the Oakhaven range produce acorns with significantly thicker shells than those growing on the southern slopes. Over the last century, the northern slopes have experienced a steady increase in the population of the red-crested woodpecker, a bird that occasionally bores into acorns to extract nutrients. Since the red-crested woodpecker population has remained negligible on the southern slopes, the agronomists conclude that the increased presence of these woodpeckers has driven the evolutionary adaptation of thicker acorn shells in the northern scrub-oaks.

Which of the following are assumptions upon which the agronomists' argument depends? (Select all that apply)

  1. The scrub-oaks on the northern slopes did not already produce acorns with significantly thicker shells prior to the steady increase in the red-crested woodpecker population.Answer
  2. The presence of thicker acorn shells on the northern slopes was not the primary factor that caused the red-crested woodpecker population to increase in that area.Answer
  3. C
    Any bird species that occasionally bores into acorns will inevitably trigger an evolutionary adaptation in the oak trees upon which it feeds.
  4. D
    The red-crested woodpeckers strongly prefer consuming the sap and acorns of the montane scrub-oak over those of any other tree species in the Oakhaven range.
  5. E
    The red-crested woodpecker population on the southern slopes will not experience a steady increase comparable to that of the northern slopes in the coming century.

Answer

The correct assumptions are that the scrub-oaks did not already produce thicker shells before the woodpeckers arrived, and that the thicker shells did not cause the woodpeckers to migrate there in the first place.
The argument concludes that the woodpeckers caused the oak trees to evolve thicker shells based on a correlation. For this causal relationship to hold, the argument logically depends on defensive assumptions. First, it assumes the chronological sequence is intact: the thicker shells could not have existed before the woodpeckers arrived. Second, it assumes the causal arrow is not reversed: the thicker shells could not be the reason the woodpeckers populated the northern slopes. Both statements represent necessary assumptions that defend the argument against alternate explanations.

Step-by-Step Solution

1
Identify the premises and the conclusion of the argument.
Premise: Northern oaks have thicker shells, and northern slopes have seen a recent increase in woodpeckers. Conclusion: The increase in woodpeckers caused the adaptation of thicker shells.
Deconstructing the argument structure is essential for exposing the logical gap between the evidence and the conclusion.
2
Analyze the causal claim being made.
The agronomists observe a correlation (woodpeckers and thicker shells co-occurring on the northern slopes) and definitively conclude that one caused the other.
Causal conclusions drawn from correlations inherently carry logical vulnerabilities that require defensive assumptions.
3
Determine the necessary assumptions to bridge the correlation-to-causation gap.
The argument assumes that the supposed effect (thicker shells) did not precede the cause (woodpeckers) and that the causal relationship is not reversed.
If alternate explanations like chronological mismatch or reverse causation were true, the argument's conclusion would collapse.
4
Evaluate the choices using the Negation Test.
Negating the correct statements yields: 'The thicker shells existed prior to the woodpeckers' or 'The thicker shells caused the woodpeckers to increase.' Both negated statements destroy the conclusion.
The Negation Test confirms whether an assumption is strictly necessary for the argument to hold.

Key Concept

Defending Causal Claims (Eliminating Reverse Causality and Timeline Flaws)
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Topics

Assumptions in Causal Arguments

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