Chimpanzees produce diverse vocal sequences with ordered and recombinatorial properties
Open paper
https://www.nature.com/articles/s42003-022-03350-8
Abstract
The origins of human language remains a major question in
evolutionary science. Unique to human language is the capacity
to flexibly recombine a limited sound set into words and
hierarchical sequences, generating endlessly new sentences. In
contrast, sequence production of other animals appears
limited, stunting meaning generation potential. However,
studies have rarely quantified flexibility and structure of vocal
sequence production across the whole repertoire. Here, we
used such an approach to examine the structure of vocal
sequences in chimpanzees, known to combine calls used singly
into longer sequences. Focusing on the structure of vocal
sequences, we analysed 4826 recordings of 46 wild adult
chimpanzees from Taï National Park. Chimpanzees produced
390 unique vocal sequences. Most vocal units emitted singly
were also emitted in two-unit sequences (bigrams), which in
turn were embedded into three-unit sequences (trigrams).
Bigrams showed positional and transitional regularities within
trigrams with certain bigrams predictably occurring in either
head or tail positions in trigrams, and predictably co-occurring
with specific other units. From a purely structural perspective,
the capacity to organize single units into structured sequences
offers a versatile system potentially suitable for expansive
meaning generation. Further research must show to what
extent these structural sequences signal predictable meanings.
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