Rutgers University

There are shared properties of communication systems currently observeable in extant species including humans and other primates that offer a window into communciation systems of common ancestors and suggest a mechanism for the emergence of systematic vocal communication. A 1996 study of the transition to reference in human infants (aged 9-16 months, McCune, et al., 1996) demonstrated that referential language was first observed in the month following first communicative use of grunt vocalizations. The autonomic grunt is an involvuntary vocalization resulting from a sequence of physiological events attendant upon metabolic demand for oxygen following effort, thermoregulation, and possibly other events. Briefly, reduced oxygen blood level sets in motion reflexive activation of the intercostal muscles and laryngeal closure, mediated by the vagus, the tenth cranial nerve. When respiratory rhythm demands inhalation, a sudden burst of air at the larynx leads to the grunt vocalization.

Communicative use of grunts in human infants demonstrated a voluntary non-autonomic production of this vocalization. Examination of developmentally earlier contexts of grunt use revealed that the infants first grunted under conditions of physiological effort, then during bouts of focussed attention, and finally in communicative contexts. Review of primate literature revealed that many species of nonhuman primates include communicative grunts in their repertoire, and some like vervet monkeys (Cheyney & Seyfarth, 1982), and chimpanzees (Goodall, 1986) use grunts with consistent acoustic properties in specific contexts. Developmental examination of the literature reveals that in both of these species grunts of effort have been observed prior to communicative grunt use, and that use of communicative grunts precedes appropriate use of other calls in the species vocal repertoire (Plooij, 1984; Seyfarth & Cheney, 1986).

Based on these observations I propose that infant primates’ experience of their own autonomic grunts in conjunction with internal states of effort prompts their attention to this juxtaposition of an interior "mental" state and a vocalization. Following Tinbergen (1952) I suggest that the grunt vocalization, initially integrated with effortful activity, becomes a displacement activity associated with internally effortful or focussed states. Given the common occurrence of this vocalization among conspecifics, the induction of a matchng internal state in the communicative partner is likely and would facilitate joint understanding. Such matching internal states can then form a bridge to induction of the young into the existing adult communicative repertoire. In humans this is attested by the shift into referential language learning at the point when communicative grunts are observed, and by the child’s subsequent request for names for a variety of objects encountered. McCune (1999) presents an analysis of comparative data in support of this thesis.

This developmental analysis exhibits the Darwinian (1872/1965) proposition regarding the derivation of purely expressive acts from those originally serving some basic function for the animal. He first suggested that a "useful" behavior accompanying a particular internal state might later recur under similar internal states, in which although in the later cases the behavior may serve no direct use, it nonetheless expresses information about the internal state of the animal. With respect to evolution of communication I propose that this developmental mechanism has operated across millennia as a gateway for new members of each primate species into the vocal communicative repertoire of that species, regardless of the simplicity or complexity of that repertoire. Thus the cradle of meaning is attributed always to infancy, to initial mother/infant communication. As adults of a community broaden or strengthen that repertoire, the development of laryngeal control in service of communication would continue to unlock the initial rungs of the communicative ladder for each new member. The continued use of communicative grunts by adult humans across cultures (e.g., "mm" and "uh huh" in English; Schlegoff, 1972) provides a comparison point with adult vervets and chimpanzees who rely upon such vocalizations for regulating much of their social life. I attach Figures 1-3 to demonstrate comparative steps in three primate species to their quite diverse repertoired, including the developmental timing of occurrenceof grunts.

Table 1: Steps Toward Language In Human Infants

Table 2: Steps Toward Adult Communication in Vervet Infants

Table 3: Steps Toward Adult Communication in Chimpanzee Infants

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