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Difficulty: HardAssumptions in Causal Arguments

A multi-decade study of the Silver-tufted Macaque, a primate species inhabiting both dense rainforests and newly established agricultural plantations, revealed a striking trend: macaques living in the plantation zones exhibit significantly lower levels of the stress hormone cortisol than their rainforest counterparts. The researchers noted that plantation environments lack the large arboreal predators common in the rainforest. Therefore, the reduced presence of these natural predators in the plantations has caused the lower cortisol levels observed in the plantation macaques.

Which one of the following is an assumption upon which the argument depends?

  1. Macaques that are naturally predisposed to lower cortisol levels are not disproportionately more likely than other macaques to migrate from the rainforest into agricultural plantations.Answer
  2. B
    The reduction in natural predators is the sole factor responsible for the lower cortisol levels observed in the plantation macaques.
  3. C
    For any primate species, a decrease in predator presence will inevitably result in a significant decrease in stress hormones.
  4. D
    The dense rainforests inhabited by the macaques contain a higher density of arboreal predators than do most other natural primate habitats.
  5. E
    Agricultural plantations do not introduce new environmental stressors that are entirely absent from the dense rainforest.

Answer

The correct answer is the option stating that macaques predisposed to lower cortisol levels are not disproportionately more likely to migrate to the plantations.
The argument observes a correlation (living in plantations and lower cortisol) and concludes an absolute causal relationship (lack of predators causes lower cortisol). To make this causal leap, the argument implicitly assumes that the cause and effect are not reversed. If macaques with naturally low cortisol were simply the ones choosing to move to the plantations (perhaps because bolder animals explore new habitats), the causal claim would be invalid. Therefore, ruling out this specific selection bias is a necessary assumption for the argument to function.

Step-by-Step Solution

1
Identify the premises and conclusion of the argument.
Premise: Plantation macaques have lower cortisol and fewer predators than rainforest macaques. Conclusion: Fewer predators caused the lower cortisol.
Deconstructing the argument is necessary to spot the logical gap between the evidence and the claim.
2
Analyze the reasoning flaw or gap.
The argument moves from a correlation (fewer predators and lower cortisol) to an absolute causal relationship, failing to account for alternate causes or reverse causation.
Identifying the gap reveals what an unstated necessary assumption must defend against.
3
Evaluate the options using the Negation Test for necessary assumptions.
Negating the correct option reveals that if macaques with naturally low cortisol self-selected into the plantations, the causal conclusion is destroyed.
The Negation Test definitively separates necessary assumptions from sufficient assumptions and irrelevant statements.

Key Concept

Ruling Out Reverse Causation in Causal Arguments
Estimated Time:2m 0s
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Topics

Assumptions in Causal Arguments

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