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Publications
The horizontal transmission of cultural knowledge is a powerful mechanism of evolutionary change1. Across taxa, group-specific cultural traditions are expressed in diverse contexts, such as foraging, tool use, self-care and socialization2. These traditions arise when group members converge on specific behavioral phenotypes. When these behavioral phenotypes involve communicative signals, such as gestures, they are termed dialects3. However, gestural dialects are rare in non-humans3. Behavioral phenotypes and traditions can also be lost, a well-documented phenomenon in humans4, but rarely documented in non-human animals5. Here, we find that chimpanzee gestures produced in copulation solicitations show culturally established phenotypes and undergo cultural loss due to human-induced population decline.
Language is a combinatorial communication system able to generate an infinite number of meanings. Nonhuman animals use several combinatorial mechanisms to expand meanings, but maximum one mechanism is reported per species, suggesting an evolutionary leap to human language. We tested whether chimpanzees use several meaning-expanding mechanisms. We recorded 4323 utterances in 53 wild chimpanzees and compared the events in which chimpanzees emitted two-call vocal combinations (bigrams) with those eliciting the component calls. Examining 16 bigrams, we found four combinatorial mechanisms whereby bigram meanings were or were not derived from the meaning of their parts—compositional or noncompositional combinations, respectively. Chimpanzees used each mechanism in several bigrams across a wide range of daily events. This combinatorial system allows encoding many more meanings than there are call types. Such a system in nonhuman animals has never been documented and may be transitional between rudimentary systems and open-ended systems like human language.
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