Chimpanzees produce diverse vocal sequences with ordered and recombinatorial properties

Area of Science:

• Evolutionary science
• Primatology
• Bioacoustics

Background:

• The origins of human language and its unique combinatorial capacity remain a key question in evolutionary science.
• Animal vocal sequences are often limited, restricting their potential for generating diverse meanings.
• Previous research has rarely quantified the flexibility and structure of vocal sequence production across an entire repertoire.

Purpose of the Study:

• To examine the structure of vocal sequences in chimpanzees, a species known to combine calls into longer sequences.
• To quantify the flexibility and combinatorial potential within chimpanzee vocalizations.

Main Methods:

• Analysis of 4826 vocal recordings from 46 wild adult chimpanzees in Taï National Park.
• Quantification of vocal unit combinations, focusing on bigrams (two-unit sequences) and trigrams (three-unit sequences).
• Examination of positional and transitional regularities within vocal sequences.

Main Results:

• Chimpanzees produced 390 unique vocal sequences.
• Most single vocal units were incorporated into bigrams, which were subsequently embedded into trigrams.
• Significant positional and transitional regularities were observed in bigrams within trigrams, indicating predictable patterns.

Conclusions:

• Chimpanzee vocal sequences exhibit a structured, hierarchical organization from single units to multi-unit sequences.
• This structural flexibility in vocal sequence production potentially supports expansive meaning generation.
• Further research is needed to determine the extent to which these structural sequences convey predictable meanings in chimpanzees.