We do this using linguistic rules for calls and sentence structure. "A dog eats" tells us one thing while "a big dog" means another while "you're such a dog" from a friend at the bar means something else completely.
Humans have mastered syntax.
How did that evolve? The comparative approach, comparing the vocal production of other primates, with that of humans, provides some answers. Other primates typically use a single call type while some species combine calls, it is mostly as an alarm. All those known are too limited to be a precursor to the complex, open-ended combinatorial system that is human language.
Unless we just don't know hidden linguistic capacities of our closest living relatives. Researchers recorded thousands of vocalizations from three groups of wild chimpanzees in the Taï National Park in Ivory Coast. They examined how the meanings of 12 different chimpanzee calls changed when they were combined into two-call combinations.
Credit: ©Liran Samuni, Taï Chimpanzee Project
They describe four ways in which chimpanzees alter meanings when combining single calls into 16 different two-call combinations, analogous to the key linguistic principles in human language. Chimpanzees used compositional combinations that added meaning (e.g., A = feeding, B = resting, AB = feeding + resting) and clarified meaning (e.g., A = feeding or travelling, B = aggression, AB = travelling). They also used non-compositional idiomatic combinations that created entirely new meanings (e.g., A = resting, B = affiliation, AB = nesting).
They believe they have evidence of a highly generative vocal communication system, which echoes recent findings in bonobos suggesting that complex combinatorial capacities were already present in the common ancestor of humans and these two great ape species.
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