Chimpanzees’ use of gesture was described in the first detailed field study [], and natural use of specific gestures has been analyzed []. However, it was systematic work with captive groups that revealed compelling evidence that chimpanzees use gestures to communicate in a flexible, goal-oriented, and intentional fashion [], replicated across all great ape species in captivity [] and chimpanzees in the wild []. All of these aspects overlap with human language but are apparently missing in most animal communication systems, including great ape vocalization, where extensive study has produced meager evidence for intentional use ([], but see []). Findings about great ape gestures spurred interest in a potential common ancestral origin with components of human language []. Of particular interest, given the relevance to language origins, is the question of what chimpanzees intend their gestures to mean; surprisingly, the matter of what the intentional signals are used to achieve has been largely neglected. Here we present the first systematic study of meaning in chimpanzee gestural communication. Individual gestures have specific meanings, independently of signaler identity, and we provide a partial “lexicon”; flexibility is predominantly in the use of multiple gestures for a specific meaning. We distinguish a range of meanings, from simple requests associated with just a few gestures to broader social negotiation associated with a wider range of gesture types. Access to a range of alternatives may increase communicative subtlety during important social negotiations.

Thirty-six gestures were associated with 13 nonplay ASOs as either a primary or secondary outcome ( Tables 2 and S3 ). We recorded how many times a particular ASO was recorded as being the primary, secondary, or tertiary meaning of a gesture type. ASOs varied in the number of gestures for which they were a primary outcome, between 0 and 9 gestures, and for which they were a primary or secondary outcome, between 0 and 16 gestures. In rank ordering, the pattern is the same, whether primary alone or both primary and secondary meanings were assessed ( Table 2 ). The number of gesture types associated with an ASO might be an effect of sample size, i.e., rarely observed outcomes are recorded less often and have fewer gesture types associated with them; however, that was not the case here. Neither the number of gestures associated with an ASO as their primary outcome (Pearson’s correlation: r = 0.38, n = 15, p = 0.16) nor primary and secondary outcomes combined (Pearson’s correlation: r = 0.34, n = 15, p = 0.22) were correlated with the number of cases of that ASO.

The apparently satisfactory outcome (ASO, as defined in Table S1 ; see Table S3 for data) listed in order of the number of gesture types (N) to which they are associated as the primary, then secondary, or tertiary ASO for each gesture type.

These two ASOs were recorded only as the tertiary or even less frequent outcome of a gesture type, as used by the community as a whole. However, their use was necessarily limited to young infant signalers; evidently they would be more prominently represented in a study of infant gesturing.

a These two ASOs were recorded only as the tertiary or even less frequent outcome of a gesture type, as used by the community as a whole. However, their use was necessarily limited to young infant signalers; evidently they would be more prominently represented in a study of infant gesturing.

These two ASOs were recorded only as the tertiary or even less frequent outcome of a gesture type, as used by the community as a whole. However, their use was necessarily limited to young infant signalers; evidently they would be more prominently represented in a study of infant gesturing.

a These two ASOs were recorded only as the tertiary or even less frequent outcome of a gesture type, as used by the community as a whole. However, their use was necessarily limited to young infant signalers; evidently they would be more prominently represented in a study of infant gesturing.

As almost all gestures (32 of 36) were used toward more than one ASO, we sought a convenient way of describing their level of ambiguity in meaning. Following Cartmill and Byrne [], we took gestures used toward a single ASO 70% or more of the time to have “tight meanings,” while gestures used toward a single ASO 50%–70% of the time were considered to have “loose meaning.” All other cases were considered to be ambiguous. On this basis, 13 gesture types had tight meaning, 11 had loose meaning, and 12 were ambiguous.

Having shown that gestures are employed for specific outcomes by all individuals, we next examined gesture meanings. Thirty-six gestures were suitable for the analysis of their ASO distributions in contexts other than play; the gestures associated with each ASO as both a primary outcome and a secondary outcome are listed in Table 1 . In 35 of 36 cases, there was a significant association between gesture type and ASO distribution ( Table S3 ; see Supplemental Experimental Procedures for details of analysis).

“Real-world” meanings are defined and listed with the gestures with which they are associated, as either a primary or a secondary outcome (see Table S3 where data comes from all individuals, with raw scores converted to proportions). Meanings are consistent across individuals ( Figure S1 Table S2 ). Meanings are ordered in declining order of the number of gestures used to effect them; note that negation (“stop that” and “move away”) can be achieved with the largest variety of gestures, and that more alternatives are available for social negotiation than for simple requests.

We found a statistical effect of individual identity in only two of the 15 gesture types, hand on and touch other ( Table S2 ), with a borderline effect (p = 0.058) in slap object. Both hand on and touch other have a clear primary function shared across individuals (“stop that” and “acquire object,” respectively); however, their secondary functions varied between individuals, although with common themes of social interaction or negotiation (“move closer,” “move away,” “climb on me,” “climb on you”). Thus, although some gestures have ambiguous meaning, the majority do not, and gestures used for specific meanings are primarily used in the same way across individuals.

In two gestures, leaf clipping and present climb on, all usage by all individuals tested was exclusively for their primary ASO ( Table S2 ). In a further three gestures, big loud scratch, hand fling, and present groom, the primary ASO was recorded significantly more often than all other (14) ASOs combined, indicating a close association with the primary ASO. In one gesture, mouth stroke, all usage by all individuals was exclusively for the primary and secondary ASOs combined. In a further three gestures, directed push, present sexual, and reach, the primary and secondary ASOs were recorded significantly more often than all other ASOs combined. In three gestures, embrace, object move, and object shake, the combined frequency with which the primary, secondary, and tertiary ASOs were recorded across individuals was significantly greater than all other ASOs combined. Thus, in 12 of a possible 15 cases, there was statistical evidence of an association across individuals with particular outcomes.

The appearance of multiple meanings for a single gesture might be the result of variation among signalers in the ways in which they employ their gestural repertoire. We therefore examined whether meaning varied with signaler identity. Fifteen gesture types met the conditions for inclusion in the detailed analysis ( Supplemental Experimental Procedures ), and 46 individuals contributed data. The possible effect of individual identity was examined in two ways, graphical and statistical. For each gesture type, we plotted the deviation from normal distribution of the ASO distribution (as used in the ANOVAs above), per individual signaler. ASOs with similar meanings were plotted adjacent to one another, allowing us to distinguish visually between gestures with multiple meanings that are unambiguously different (e.g., big loud scratch: “groom me” and “travel with me”) and those that are more ambiguous, with several similar meanings (e.g., object shake: “sexual attention to male,” “follow me,” “travel with me,” “move away,” etc.). These plots gave a graphical indication of whether individual signalers used the same gesture in the same way ( Figure S1 ). An additional 21 gestures were used regularly outside of play but were not recorded with sufficient frequency from sufficient individuals for parametric analysis; for these gestures, similar plots, indicating whether or not signalers employed these gestures toward the same distribution of ASOs, are provided ( Figure S1 ).

We examined whether different gestures were associated with a specific pattern of outcomes, differing from the general distribution of ASOs in gestural communication. Fifteen gesture types met the conditions for inclusion in the initial analysis ( Supplemental Experimental Procedures ), and 46 individuals contributed data. We found a significant effect of gesture type on distribution of ASOs (gesture: f = 2.30, df = 14,101, p = 0.009; two-way ANOVA). Thus, the frequency with which gesture types are used, outside of play, toward particular ASOs varies between gesture types, suggesting that gestures have specific meanings.

Although we identified 19 ASOs and chimpanzees have a repertoire of at least 66 gesture types [], some gestures may have more than one meaning. In fact, only 10 of the 66 gestures were used for only a single ASO, and of these, seven were recorded on three or fewer occasions. The majority of the repertoire was used for multiple ASOs (number of ASOs per gesture type: mean = 4.6 ± 3.0, mode = 2, range 1–12). The extent of this multiplicity or ambiguity of meaning is likely underestimated, since the number of recorded instances of a gesture type correlated positively with the number of ASOs with which it was associated (gestures recorded on three or more instances, Pearson’s correlation: r = 0.75, n = 43, p < 0.0001). However, some of these ASOs occurred at very low frequencies, raising the possibility that, rather than implying genuine ambiguity, they might stem from observer error or misunderstandings by the recipient uncorrected in further communication by the signaler. Eliminating those ASOs with less than three instances per gesture type across the population as potential errors, the majority of the gestural repertoire was associated with two or three meanings (mean 2.8 ASOs per gesture). Moreover, in most cases (57 of 66 gestures), at least one ASO was play-related, e.g., “start play”. The generality with which play-related meanings occurred indicates that there may be something special about play signals. Play is the most common context for gestural communication [], but in play, gestures are not necessarily used with their normal meaning and the outcome may not reliably signal the gesture’s meaning in other contexts. In subsequent analyses, we therefore excluded data from play bouts to avoid masking the “real-world” meaning of gestures. (An analysis including play data is provided in the Supplemental Information .)

We observed 4,531 gestures within 3,419 bouts of intentional communication; 3,175 bouts (4,247 gestures) apparently satisfied the signaler (communication ceased following the audience’s response; Table S1 ). We used ASOs to indicate the signalers’ intended meanings; recorded ASOs were of 19 different kinds. Most ASOs (17) encouraged interactions to start (e.g., “groom me”) or to develop (“move closer,” “change play”); however, two that discouraged further social interaction (“stop that” and “move away”) were used broadly across contexts to negate a wide range of behavior.

In animal communication, signal meanings have generally been identified with the information exchanged between individuals []; in previous studies, only the characteristic effect of a signal on recipients has been assessed. For example, monkey alarm calls function as if they referred to specific predators; recipients act appropriately upon hearing the calls []. Whether callers intend to influence a specific audience is unknown but is suspected not to be the case []. In human communication, however, meaning has been treated quite differently because signals—linguistic utterances—are produced intentionally []. Indeed, the signaler’s intentions are paramount, and cognitively demanding flexibility is often necessary to interpret meaning []. Ape gesturing is the only nonhuman communication system with substantial evidence for intentional use [], providing a unique opportunity to examine the intended meanings, analogous to human linguistic meanings, of nonhuman signals. Ape gestures show at least first-order intentionality: they are produced with the purpose of changing the recipient’s behavior []. We present here a systematic analysis of meaning for the gestures employed by a wild chimpanzee community. To date, the widely described flexibility of gestures has been reported in terms of the variety of contexts in which a gesture is observed []. Although this method avoids potential pitfalls of attempting to interpret mental states of another species, it risks exaggerating flexibility where gestures with a single meaning are employed across multiple contexts. One previous study examined the effect on recipients of four hand gestures, concluding that responses were not dependent on situational context and were “primarily used for directing a recipient’s movement or attention” []. Here we investigated communication in a natural group across the full range of chimpanzee behavior, and we are able for the first time to distinguish “real-world” usage from the play-based communication that predominates in captivity. We examined what each gesture is for: if a gesture is used to alter the behavior of a recipient toward a specific goal, what was that goal? To find out, we adopted a holistic approach to the study of meaning that uses the behavior of both signaler and recipient [], first piloted with captive groups []. We therefore focus on whether a recipient’s reaction satisfied the signaler, so indicating their intended meaning. An outcome that resulted in the cessation of communication and that represented a plausible desire on the part of the signaler (e.g., not an aversive experience) was taken to have satisfied the signaler and was termed an apparently satisfactory outcome (ASO; see Supplemental Experimental Procedures available online).

Discussion

32 Grice H.P. Studies in the Way of Words. Chimpanzees use their gestures in purposeful communication with other chimpanzees; as such, they can be considered meaningful []. In our present study of wild chimpanzees, living under conditions that permit the complete expression of their natural behavior, we analyzed the meanings of 36 gestures and found them to be used intentionally to achieve 15 purposes, other than in play. There was considerable similarity of use across individuals, indicating that meanings are inherent to gestures, as opposed to idiosyncratic to particular individuals or subgroups of individuals.

10 Genty E.

Breuer T.

Hobaiter C.

Byrne R.W. Gestural communication of the gorilla (Gorilla gorilla): repertoire, intentionality and possible origins. 14 Cartmill E.A.

Byrne R.W. Semantics of primate gestures: intentional meanings of orangutan gestures. Similar indications of specific meaning have been found in studies of captive orangutan and gorilla gesturing []. However, in those studies, no analysis of individual differences was possible, and gestures used in play were included in analyses (a necessarily consequence of the limited range of behavior expressed in captive groups). Any analysis of meaning from data sets including play should be interpreted with caution. Although playful usage should not be confounded with “real-world” usage in the analysis of meaning, play may serve as an important learning environment for communication. Play allows younger individuals a safe testing ground for their exploratory use of gesture, toward potentially risky goals such as sexual solicitation or social negotiation. Our method of deciding intended meaning works well in nonplay contexts, whereas if data from play are included, the overwhelming dominance of play within the overall data set can obscure any real statistical association between gesture and (nonplay) meaning.

28 Seyfarth R.M.

Cheney D.L.

Marler P. Vervet monkey alarm calls: semantic communication in a free-ranging primate. Setting aside playful uses greatly reduces the apparent ambiguity of gesture meanings: 35 of the 36 gestures have specific individual patterns of meaning used toward one to three of the 15 intended outcomes. The degree of ambiguity remaining is not uniform across the repertoire. Some gestures are unambiguous, employed consistently toward a single meaning: for example, leaf clipping is used only to acquire sexual attention. Others appear ambiguous: for example, grab is used for “stop that,” “climb on me,” and “move away,” etc. ( Figure S1 ). Appearance of ambiguity may arise in part from the difficulty for human observers in discerning subtle variations in the nature of the contact. It is evident to a human recipient whether or not a gentle touch is intended to reposition us or to prevent us from moving; however, those distinctions are very difficult to distinguish visually. Finally, gestures can be employed toward two or three outcomes of a very similar nature: for example, push is used for both “move away” and “stop that.” This last category is perhaps most similar to the type of broad semantic class of information expressed in primate vocalizations, where an alarm call rarely indicates (for example) a leopard specifically but rather is used toward a range of similar ground-based threats [].

We found considerable variation in whether an intended meaning was signaled by a single gesture type or several gestures of apparently equivalent meaning. Intriguingly, the degree of this redundancy appeared to covary with the need for context to fine-tune intended meaning. Our method necessarily restricts analysis to that of imperative demands (declarative communication requires no overt change in recipient behavior to satisfy the signaler). However, among these imperative demands we could distinguish different types of meaning, covarying with the number of gestures used to express them.

Where we found that an intended meaning was conveyed by several different gestures, the desired outcome was often apparently one that required some negotiation or persuasion. For example, a request to give affiliative contact (embrace, rump rub, shake hands, bite) does not have a canonical form of response that is always appropriate: exactly what the signaler wants by giving the gesture may often become clear only after some further interaction. In contrast, meanings typically conveyed by a single gesture were often well defined and unitary, for example “initiate grooming” (big loud scratch).

The subtle regulation of individual social relationships is critical to chimpanzee reproductive strategy, in which strong alliances are formed with related or unrelated individuals of both sexes. These relationships can impact mating success, contributing toward individual fitness. Interpretation will be aided by the integration of contextual cues, some of which may be quite subtle (an individual starting to move in a certain direction, or prior experiences of interacting with a particular signaler). We suggest that, in addition, the availability of multiple gestures for meanings involved in social negotiation allows for equally subtle distinctions, allowing for room to maneuver in negotiation of outcomes. The majority of nonplay use of the gesture types generally employed in play was in social negotiation meanings, such as “follow me” or “move away.” It may be that play is used to explore socially delicate communications: even though gesture meanings are basically species typical, a young ape may have much to learn about the appropriateness of using gestures in particular social contexts.