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Difficulty: MediumAssumptions in Causal Arguments

A ten-year ecological study of the Silver-tufted Macaque found that troops living in regions with high concentrations of naturally occurring lithium in the water supply exhibit significantly lower rates of aggressive intra-troop conflicts compared to troops living in lithium-poor regions. Based on this observation, the researchers concluded that the consumption of lithium-rich water reduces aggressive behavior among these macaques.

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

  1. A
    Any macaque troop that relocates from a lithium-poor region to a lithium-rich region will immediately exhibit a decrease in aggressive behavior.
  2. B
    Other animal species living in the observed lithium-rich regions also display lower than average levels of aggression compared to their counterparts elsewhere.
  3. Silver-tufted Macaque troops do not establish territories in lithium-rich regions because they already possess an inherently lower propensity for aggression.Answer
  4. D
    The physiological mechanisms by which lithium affects the brain chemistry of Silver-tufted Macaques are identical to the mechanisms observed in other primates.
  5. E
    The researchers documented the aggressive interactions of every single troop of Silver-tufted Macaques living in the specified regions over the ten-year period.

Answer

The option stating that Silver-tufted Macaque troops do not establish territories in lithium-rich regions because they already possess an inherently lower propensity for aggression.
The argument observes a correlation between lithium-rich water and low aggression, then concludes that the lithium causes the lower aggression. For this causal claim to be valid, the author must implicitly assume that reverse causation is not responsible for the correlation. The correct option states exactly this: it assumes that the macaques did not simply settle in the lithium-rich regions as a result of already being inherently peaceful. If we apply the Negation Technique and assume they DID settle there because they were already peaceful, the researchers' conclusion that lithium causes the peace is completely destroyed.

Step-by-Step Solution

1
Identify the premises and the conclusion of the argument.
Premise: Macaques in lithium-rich areas have less intra-troop aggression than those in lithium-poor areas (a correlation). Conclusion: Consuming lithium-rich water causes the reduction in aggressive behavior.
Separating facts from the author's claim is the first step in finding the logical gap.
2
Identify the logical gap (the jump from correlation to causation).
The author assumes that because lithium and low aggression occur together, the lithium must be the cause of the low aggression.
In causal arguments, correlations are vulnerable to alternate causes and reverse causation.
3
Formulate a necessary assumption that defends the causal claim.
The argument must assume that the low aggression did not cause the macaques to live in the lithium-rich areas (ruling out reverse causation).
If reverse causation were true, the conclusion that lithium causes low aggression would fall apart.
4
Apply the Negation Technique to the correct option to verify.
Negating the correct option yields: 'Macaques DO establish territories in lithium-rich regions because they already possess lower aggression.' This destroys the argument's conclusion.
A necessary assumption must destroy the argument when proven false.

Key Concept

Ruling out reverse causation in causal arguments
Estimated Time:1m 30s
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Topics

Assumptions in Causal Arguments

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