Through a slow developmental process driven by learning and neural maturation, humans can flexibly combine a limited number of sounds into words and then into sequences (i.e., ‘combined utterances’), following syntactical rules. This enables the creation of an infinite number of utterances to convey an unlimited range of information. Whether this capacity is unique to humans or evolved from related species remains uncertain. Comparative research with non-human primates (hereafter: primates) is crucial for understanding this. In contrast to humans, the development of primate repertoires appears to be largely innate and fixed from birth. However, there is some evidence of limited vocal plasticity in certain primate species, with developmental changes linked to acoustic variations and usage learning, likely influenced by social dynamics. A recent study has revealed that adult chimpanzees, one of our closest living relatives, possess an unusual complex vocal repertoire with hundreds of non-random vocal utterances. This lead me question: are these hundreds of vocal utterances innate and present from birth or do they develop through ontogeny? If so, what processes underlie this vocal development, and do they mirror those seen in the development of human language? Therefore, this thesis aims to investigate the ontogeny of vocal sequence acquisition and their potential function in chimpanzees, using a full repertoire approach. To this aim, I conducted 9 months of focal animal sampling on 98 wild chimpanzees (0-55 years old), living in Ivory Coast. I analysed 11,397 vocal utterances from 1,807.3 hours of vocal recordings. First, I found that chimpanzees require about 10 years to reach the adult repertoire, which extends beyond the age when single vocal units emerge. The developmental trajectory of vocal sequence acquisition aligned with key developmental social milestones, supporting social complexity as a driver of vocal complexity. Moreover, neuro-muscular maturation also appears to drive vocal development. Second, I found that the combinatorial flexibility, ordering and re-combinatorial patterns are limited at birth but increase with age. Last, I found that vocal sequences may function to routinely convey combined information about juxtaposed daily life events, a crucial step in the evolution of generalised combinatorial communication. This thesis underscores the importance of studying entire vocal repertoires, including sequences, and their development. It enhances our understanding of chimpanzee communication and suggests likely shared origins and functions of complex communication systems, ultimately contributing to our knowledge of the evolution of human language.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:94625 |
| Date | 28 November 2024 |
| Creators | Bortolato, Tatiana |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/acceptedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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