Tonkean macaques communicate with their right hand.

Area of Science:

• Primate behavior
• Evolutionary linguistics
• Neuroscience

Background:

• The origins of human language are debated, with vocal and gestural theories presenting conflicting hypotheses.
• Gestural origin theory posits language evolved from manual gestures, with left-hemispheric control extending to vocalizations.
• Understanding primate communication offers insights into the evolutionary roots of language.

Purpose of the Study:

• To investigate functional hemispheric specialization in Tonkean macaques regarding manual gestures.
• To contribute empirical data to the debate on the gestural versus vocal origins of language.
• To examine handedness patterns in manual gestures for communicative purposes in Tonkean macaques.

Main Methods:

• Quantitative analysis of hand biases during object grasping and manual gesturing in Tonkean macaques.
• First-time study of handedness in Tonkean macaques.
• Comparison of macaque handedness patterns with those of baboons and human infants.

Main Results:

• Tonkean macaques exhibit significant right-hand preference for manual communicative gestures.
• Handedness patterns in Tonkean macaques show convergence with baboons and human infants.
• This study provides the first quantitative data on Tonkean macaque handedness.

Conclusions:

• Findings support the gestural origin theory of language.
• Left hemispheric lateralization for language likely evolved from an ancestral gestural communication system.
• The common ancestor of macaques, baboons, and humans may have possessed a gestural communication system.