Chimpanzee Vocal Signaling Points to a Multimodal Origin of Human Language

Abstract

The evolutionary origin of human language and its neurobiological foundations has long been the object of intense scientific debate. Although a number of theories have been proposed, one particularly contentious model suggests that human language evolved from a manual gestural communication system in a common ape-human ancestor. Consistent with a gestural origins theory are data indicating that chimpanzees intentionally and referentially communicate via manual gestures, and the production of manual gestures, in conjunction with vocalizations, activates the chimpanzee Broca’s area homologue – a region in the human brain that is critical for the planning and execution of language. However, it is not known if this activity observed in the chimpanzee Broca’s area is the result of the chimpanzees producing manual communicative gestures, communicative sounds, or both. This information is critical for evaluating the theory that human language evolved from a strictly manual gestural system. To this end, we used positron emission tomography (PET) to examine the neural metabolic activity in the chimpanzee brain. We collected PET data in 4 subjects, all of whom produced manual communicative gestures. However, 2 of these subjects also produced so-called attention-getting vocalizations directed towards a human experimenter. Interestingly, only the two subjects that produced these attention-getting sounds showed greater mean metabolic activity in the Broca’s area homologue as compared to a baseline scan. The two subjects that did not produce attention-getting sounds did not. These data contradict an exclusive “gestural origins” theory for they suggest that it is vocal signaling that selectively activates the Broca’s area homologue in chimpanzees. In other words, the activity observed in the Broca’s area homologue reflects the production of vocal signals by the chimpanzees, suggesting thast this critical human language region was involved in vocal signaling in the common ancestor of both modern humans and chimpanzees.

The human socio-cognitive niche and its evolutionary origins

“…A newer view is that apes use both gestures and vocalization in combination and there is evidence that they are more successful when they do so. PET scans of the brains of chimpanzees showed heightened metabolic activity in Broca's area (specialized for language in the human case) in individuals who both vocalized and gestured, as opposed to those who gestured only [78].…”

A comparative neurological approach to emotional expressions in primate vocalizations

“…The use of noninvasive neuroimaging techniques in great apes allowed Taglialatela et al (2008Taglialatela et al ( , 2011 to show activations of the inferior frontal gyrus (IFG) in communicative situations involving both vocal and gestural communication, particularly in the context of producing attention-getting sounds. Liebal et al (2014) interpret these results as suggesting that cortical structures are directly involved in the production of some vocalizations in chimpanzees.…”

Learned vocal and breathing behavior in an enculturated gorilla

“…As evidence suggests that multiple modalities function together interdependently in modern language, a plausible hypothesis for its evolution is that multiple modalities also evolved together interdependently (Kendon 2009;McNeill 2012). Some ape gesture researchers are similarly coming to the conclusion that the evolution of language is best understood from a multimodal perspective (Hopkins et al 2007;Leavens 2003;Taglialatela et al 2011;Waller et al 2013). For example, Leavens (2003) proposed that, ''Because visual and vocal communication seem to be functionally linked in extant apes, language may have been multimodal from its inception'' (p. 233).…”