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Difficulty: HardRuling Out Alternate Explanations (Defender)

Wildlife ecologists monitoring the endangered silver-tufted macaque in the Valerius Basin have documented a severe population collapse over the last five years. During this exact same period, the region's population of non-native feral wildcats has nearly tripled. Because feral wildcats are known to hunt small primates in other ecosystems, the ecologists concluded that predation by these wildcats is the primary cause of the macaque population's decline.

Which one of the following is an assumption on which the ecologists' argument depends?

  1. The recent surge in the feral wildcat population was not fueled by scavenging on the remains of macaques that had died from an independent mass mortality event.Answer
  2. B
    Feral wildcats are the only animal species in the Valerius Basin that possesses the physical capability to hunt the silver-tufted macaque.
  3. C
    The diet of the feral wildcats in the Valerius Basin consists almost entirely of silver-tufted macaques.
  4. D
    In other ecosystems similar to the Valerius Basin, introduced feral wildcats have consistently caused the extinction of small primate populations.
  5. E
    The feral wildcats currently residing in the Valerius Basin are not actually a non-native species.

Answer

The assumption that the wildcat population surge was not fueled by scavenging on macaques that died from an independent mass mortality event.
The ecologists observe a correlation (macaques decrease, wildcats increase) and conclude that wildcats hunting the macaques is the cause. However, a glaring alternative explanation exists: an independent event (like a virus) caused the macaques to die, and the wildcats experienced a population boom because they had a massive supply of macaque carcasses to scavenge. For the ecologists' conclusion to be logically sound, they must assume this alternative scenario did not happen. If we negate this correct option and assume the wildcats DID boom due to scavenging macaques killed by something else, the argument that predation caused the decline is completely destroyed.

Step-by-Step Solution

1
Analyze the argument structure.
Premise: Macaque population collapsed at the exact same time the wildcat population tripled. Conclusion: Wildcat predation is the primary cause of the macaque decline.
Identifying the premises and conclusion is the necessary first step to evaluate the logical gap in any argument.
2
Identify the reasoning flaw.
The argument assumes causation based purely on correlation. It assumes A (wildcats) caused B (macaque decline), failing to consider reverse causality or a third variable.
Recognizing the causal flaw reveals what the author must assume (that alternative explanations are false).
3
Anticipate alternative explanations that fit the evidence.
An alternative explanation: A disease killed the macaques, and the wildcats' population tripled because they scavenged the abundant dead bodies.
A 'Defender' assumption works by explicitly ruling out a competing alternative explanation that would weaken the argument.
4
Apply the Negation Technique to the choices.
Negating the correct option reveals that if the wildcats merely scavenged macaques killed by something else, wildcat predation is not the cause of the decline, completely destroying the argument.
The Negation Technique is the definitive test for a Necessary Assumption.

Key Concept

Ruling Out Alternate Explanations (Defender) - Causal Relationships
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Ruling Out Alternate Explanations (Defender)

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