What can the socio-communicative behavior of chimpanzees and bonobos tell us about the origins of human spoken language?

Jared P. Taglialatela, Kennesaw State University and Ape Cognition and Conservation Initiative

A fundamental characteristic of human language is multimodality.  In other words, humans use multiple signaling channels concurrently when communicating with one another.  For example, people frequently produce manual gestures while speaking, and the words a person perceives are impacted by visual information.  However, humans also have the ability to rely exclusively on speech, allowing complex communication with individuals that are not in direct view or physical proximity.  This level of vocal control and flexibility is unique among primates – and indeed exceedingly rare among mammals.  It is unclear what selection pressures led to this phylogenetically unprecedented capacity for autonomous speech.  Given that speech and the soft-tissue that supports it do not leave well-preserved marks in the fossil record, the study of variation in communicative behavior in extant nonhuman primates – particularly chimpanzees and bonobos - is critical for understanding the evolutionary origins of human sociality and communication.

Despite being closely related – diverging from a common ancestor only approximately 1 million years ago - bonobos and chimpanzees exhibit some notable behavioral differences.  One of the most striking, but least studied, differences between these species are their vocal repertoires.  We hypothesize that differences between the Pan species’ feeding ecology may have favored bonobos to become increasingly reliant on vocalizations, as opposed to other modalities, to communicate with conspecifics and mediate social interactions.  Consequently, subsequent selection for increased vocal control and flexibility occurred in bonobos as compared to chimpanzees – a situation that may have been similar to the selection pressures faced by early hominins.

For this talk, I will review species differences in the socio-communicative behaviors of chimpanzees and bonobos and discuss the neurobiological and genetic foundations for these complex social, cognitive, and communicative behaviors.