Language Origins Viewed in Spontaneous and Interactive Vocal Rates of Human and Bonobo Infants

Area of Science:

• Comparative psychology
• Primatology
• Developmental linguistics

Background:

• Human infants produce "protophones" (speech-like sounds) from early life.
• These sounds and their social use are presumed absent or minimal in other apes.
• Quantitative cross-species comparisons are lacking to support these presumptions.

Purpose of the Study:

• To quantitatively compare vocalization rates and patterns in human infants and bonobo infants.
• To investigate the presence and function of protophone-like vocalizations in bonobos.
• To explore the role of vocal interaction in mother-infant dyads as a foundation for language.

Main Methods:

• Quantitative comparison of vocalization data from captive bonobo mother-infant pairs and human infant vocalization data.
• Analysis focused on low- and moderate-arousal vocalizations.
• Acoustic analysis and functional interpretation of vocalizations.

Main Results:

• Both human and bonobo infants produce distress sounds (cries/screams) and laughter.
• Bonobo infants produce protophone-like sounds, acoustically similar to human protophones.
• Human infants produce protophones significantly more frequently than bonobos; human protophones are more associated with vocal play, while bonobo sounds are less frequent and not observed in social vocal interaction.
• Extensive vocal interaction observed in human dyads, but absent in bonobo dyads.

Conclusions:

• Bonobo infants share the capacity for foundational language-like vocalizations with humans.
• Significant quantitative and functional differences exist in protophone production and use between humans and bonobos.
• Flexible vocalization for social interaction and vocal exploration, rather than just distress or excitement, appears crucial for language foundations.