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Question

Difficulty: HardNecessary Assumption

Biologist: The African emerald cuckoo deposits its eggs exclusively in the nests of other bird species, leaving its offspring to be reared entirely by host parents. Adult emerald cuckoos consistently produce an identical, complex territorial vocalization across geographically isolated regions, despite never interacting with their biological parents during development. Because avian vocalizations that develop in the absence of social learning are genetically predetermined, the emerald cuckoo's territorial call must be genetically encoded rather than acquired through acoustic imitation.

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

  1. A
    Any bird species reared by foster parents of a different species will fail to acquire the vocalizations of those foster parents.
  2. Juvenile emerald cuckoos do not acquire their territorial call by hearing and imitating unrelated adult emerald cuckoos.Answer
  3. C
    If an avian vocalization is genetically encoded, it will exhibit identical acoustic features across all geographically isolated populations of that species.
  4. D
    Genetic factors play a greater role than environmental exposure in determining all complex behavioral repertoires of brood-parasitic birds.
  5. E
    Host parent birds do not attempt to actively teach their own species-specific calls to emerald cuckoo nestlings.

Answer

The argument depends on the assumption that juvenile emerald cuckoos do not acquire their territorial call by hearing and imitating unrelated adult emerald cuckoos.
The conclusion asserts that the cuckoo's call must be genetically encoded rather than acquired through acoustic imitation because the birds have no contact with their biological parents. This inference assumes there is no other source of acoustic imitation available. If juvenile cuckoos learn the call by imitating unrelated adult cuckoos in their habitat, the conclusion that the call must be genetically encoded is invalidated. Thus, ruling out imitation of unrelated adults is strictly necessary.

Step-by-Step Solution

1
Isolate the premises and the main conclusion of the argument.
Premises: Emerald cuckoos are raised by foster species, never interact with biological parents, yet produce identical territorial calls across regions; calls developing without social learning are genetically predetermined. Conclusion: The territorial call must be genetically encoded rather than acquired through acoustic imitation.
Establishing the core reasoning structure isolates the exact leap between the evidence and the claim.
2
Identify the logical gap between the premises and the conclusion.
The author equates 'not interacting with biological parents' with 'the complete absence of acoustic imitation or social learning.'
A defender assumption is needed to eliminate potential alternative pathways of social learning (e.g., imitating unrelated conspecific adults).
3
Apply the Negation Test to candidate assumptions.
Negating the statement yields: 'Juvenile emerald cuckoos DO acquire their territorial call by hearing and imitating unrelated adult emerald cuckoos.' This directly refutes the claim that the call must be genetically encoded rather than acoustically imitated.
A necessary assumption must fatally undermine the conclusion when logically negated.

Key Concept

Defender Assumption and the Negation Test
Estimated Time:1m 30s
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Topics

Necessary Assumption

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