Passage Summary: Just because animals make noises or gestures at one another doesn't mean they have a language; we haven't proven they are actually using those sounds to talk about specific things or concepts.

Conclusion: The fact that animals signal each other does not prove they possess language.

Reasoning: Signaling through sounds and gestures is insufficient proof of language because it doesn't demonstrate the ability to refer to concrete objects or abstract ideas.

Analysis: The zoologist's argument contains a significant logical gap: it assumes that the ability to refer to objects or ideas is a requirement for a communication system to be called 'language.' To find the necessary assumption, we must identify the link the author relies on to dismiss signaling as proof. If language did not require the ability to refer to objects or ideas, the zoologist's evidence would fail to support the conclusion. Therefore, look for an answer choice that establishes this 'referential ability' as a necessary condition for language.