Nonhuman primates do declare! A comparison of declarative symbol and gesture use in two children, two bonobos, and a chimpanzee

Abstract

While numerous publications have shown that apes can learn some aspects of human language, one frequently cited difference between humans and apes is the relative infrequency of declaratives (comments and statements) as opposed to imperatives (requests) in ape symbol use. This paper describes the use of declaratives in three language-competent apes and two children. The apes produced a lower proportion of spontaneous declaratives than did the children. However, both groups used declaratives to name objects, to interact and negotiate, and to make comments about other individuals. Both apes and children also made comments about past and future events. However, showing/offering/giving, attention getting, and comments on possession were declarative types made by the children but rarely by the apes.Recent discussions about the evolution of communication have stressed a perceived distinction between humans and our closest evolutionary relatives, the great apes, wherein human nature is described as uniquely cooperative relative to the more competitive great apes (e.g. Moll and Tomasello, 2007;Tomasello, 2007). Some researchers argue that after splitting from the common ancestor, our evolutionary ancestors formed a social environment that supported the desire and drive to communicate and cooperate with others. According to this hypothesis, this socio-communicative environment resulted in a qualitative difference in the cooperative nature of humans relative to the other apes and this cooperative nature drove the evolution of human language and cognition (Moll and Tomasello, 2007). These researchers further suggest that, due to their uncooperative nature, chimpanzees are not fully capable of taking advantage of human social environments that increase cooperative and communicative abilities.

Ontogeny and phylogeny of language

“…Nonhuman primates' communicative capacity is complex, and their ability to learn word-like symbolic units is well documented (16,23). There might be other cognitive systems that differentiate between humans and nonhuman primates (24) and play a role in the development and evolution of language.…”

The communicative functions of five signing chimpanzees (Pan troglodytes)

“…Other language using apes produce a high frequency of responses to caregiver probes as well (Lyn et al 2011;Miles 1975;Patterson, Tanner, and Mayer 1988). The frequent asking of questions, however, can influence the coding of communicative functions.…”

“…Hearing children produced Description in 22.3% of their utterances (Dore, 1977a(Dore, , 1977b, and deaf children produced Description in 28.6% of their utterances (Day 1986). Other language using apes commonly described objects, actions, and events in their surroundings as well (Lyn et al 2011;Miles 1976;Patterson et al 1988). The describing and naming of objects and individuals is a robust aspect of the cross-fostered chimpanzees language use.…”

Social manipulation in nonhuman primates: Cognitive and motivational determinants

“…In line with that, chimpanzees, reliably point to objects when they themselves can benefit from it but not to help humans obtain a reward (Bullinger et al, 2011c). Chimpanzees' pointing gestures, therefore, have been classified as imperative pointing (serving to request objects for themselves) but not as declarative pointing to inform others (with the exception of language trained chimpanzees who, according to some authors, produce declaratives, see Lyn et al, 2011;Rivas, 2005).…”