Time-space-displaced responses in the orangutan vocal system

Area of Science:

• Primate communication
• Evolution of language
• Animal cognition

Background:

• Displaced reference, the ability to communicate about absent or non-immediate events, is a hallmark of human language.
• Its evolutionary origins and precursors in non-human primates remain poorly understood.

Purpose of the Study:

• To investigate vocal behavior in Sumatran orangutans (Pongo abelii) for potential precursors to displaced reference.
• To explore the cognitive mechanisms underlying vocal control in response to perceived threats.

Main Methods:

• Observational study of wild Sumatran orangutan mothers' vocal responses to predator models.
• Analysis of alarm call suppression duration in relation to perceived danger (self and infant).
• Testing predictions related to stress-based versus higher-order cognitive mechanisms.

Main Results:

• Orangutan mothers suppressed alarm calls for up to 20 minutes when predator models were visible.
• Vocal delay was correlated with perceived danger to the infant, not solely self-perceived danger.
• Stress-related explanations for vocal suppression were not supported.

Conclusions:

• Observed vocal suppression in orangutans shows remarkable parallels with displaced reference.
• This behavior suggests that cognitive abilities underlying displaced reference may have roots in ancestral hominids.
• Findings provide insights into the evolutionary pathway of a key component of human language.