Bonobo and chimpanzee gestures overlap extensively in meaning

Abstract

Cross-species comparison of great ape gesturing has so far been limited to the physical form of gestures in the repertoire, without questioning whether gestures share the same meanings. Researchers have recently catalogued the meanings of chimpanzee gestures, but little is known about the gesture meanings of our other closest living relative, the bonobo. The bonobo gestural repertoire overlaps by approximately 90% with that of the chimpanzee, but such overlap might not extend to meanings. Here, we first determine the meanings of bonobo gestures by analysing the outcomes of gesturing that apparently satisfy the signaller. Around half of bonobo gestures have a single meaning, while half are more ambiguous. Moreover, all but 1 gesture type have distinct meanings, achieving a different distribution of intended meanings to the average distribution for all gesture types. We then employ a randomisation procedure in a novel way to test the likelihood that the observed between-species overlap in the assignment of meanings to gestures would arise by chance under a set of different constraints. We compare a matrix of the meanings of bonobo gestures with a matrix for those of chimpanzees against 10,000 randomised iterations of matrices constrained to the original data at 4 different levels. We find that the similarity between the 2 species is much greater than would be expected by chance. Bonobos and chimpanzees share not only the physical form of the gestures but also many gesture meanings.

The development of gestural communication in great apes

“…For example: gesturing is adjusted to the visual orientation of the target recipient (e.g., Cartmill and Byrne 2007;Leavens et al 2005b;Liebal et al 2004); signallers persist in, and sometimes elaborate, their gesturing until their goal is achieved (e.g. Cartmill and Byrne 2007;Leavens et al 2005b;Hobaiter and Byrne., 2011b;Roberts et al 2014b); and gestures are characterized by a flexible relationship between signal and outcome (means-ends dissociation), implying individual signallers are able to use different signals/gestures to achieve the same outcome/goal, or a single gesture for several outcomes (Graham et al, 2018;Liebal et al 2006;Pika et al 2003;Tomasello et al 1994). (Bard et al 2014a;Liebal et al 2013;Pika and Fröhlich 2018).…”

Gesture Use in Communication between Mothers and Offspring in Wild Orang-Utans (Pongo pygmaeus wurmbii) from the Sabangau Peat-Swamp Forest, Borneo

“…Gestures were employed to achieve eight distinct goals, including six positive requests (Acquire object; Climb on me; Climb on you; Climb over; Play change; Play continue) and two negations (Move away; Stop behavior). As found in chimpanzees and bonobos (Graham et al 2018;Hobaiter and Byrne 2014), gestures were employed flexibly toward multiple goals, but the majority of gesture types were used to achieve at least one play-related goal; thus, flexibility decreased (to an average of two goals per gesture type) when play data were removed. These findings suggest that orang-utans also show means-ends dissociation in their gesturing, with individual gesture types used to achieve several distinct goals and several gestures employed to express an individual goal.…”

“…We did not have sufficient cases of successful gesture use per individual to explore whether specific goals were associated with each gesture type. However, as research has shown that individual signaler identity did not impact signal meaning (Graham et al 2018; Hobaiter and Byrne 2014), we present a preliminary investigation here in which gesture use was combined across signalers. After a gesture was employed, the reaction that caused the signaler to stop signaling was deemed to be the apparently satisfactory outcome, or goal, of the gesture.…”

“…Nonhuman great apes' (hereafter great apes) use of 60-80 gestures in intentional communication remains the only broad system of communication outside of human language in which there is evidence for widespread and flexible use of goal-directed signals to communicate language-like meaning in everyday social interaction (Graham et al 2018;Byrne 2014, 2017;Moore 2014). Great apes employ diverse repertoires of vocal, gestural, and facial signals to communicate a wide range of nuanced information (e.g., bonobos, Pan paniscus: Graham et al 2017;Pika et al 2005; chimpanzees, Pan troglodytes: Bard et al 2017;Fröhlich et al 2016aFröhlich et al , 2016bHobaiter and Byrne 2011a, 2011bPlooij 1978;Roberts et al 2012;Tomasello et al 1985Tomasello et al , 1989; gorillas, Gorilla gorilla: Genty et al 2009;Perlman et al 2012;Pika et al 2003;Tanner and Byrne 1999;orang-utans, Pongo: Liebal et al 2006; crossspecies: Bard and Vauclair 1984;Pollick and de Waal 2007).…”

Understanding Language Evolution: Beyond Pan‐Centrism

“…Findings regarding gestural communication in great apes, including inter-species comparisons, evoke a similar general interpretation. [94][95][96] Altogether, the burgeoning strand of great ape vocal research [28,91,97] shows that traditional ideas about what great apes can and (mostly) cannot do are outdated, too crude or unsubstantiated. The precursor system for (spoken) language evolution will be best understood when zooming out our theoretical and empirical lenses to include the vocal (and gestural) behavior of all great ape genera, including its neural and molecular substrates.…”