ࡱ > p s m n o _ bjbj(( ; B8\B8\b4 , T T "
" " " " " " " 8 .# *$ 4 " gu ^$ T ( ( ( ( ) + o, P t t t t t t t $ +x z b t u " , ) ) , , t " " ( ( !u 8 8 8 , " ( " ( o 8 , t 8 8 g l ( PxT 4 i 4 o 7u 0 gu i ( C{ 5 C{ h l l l C{ " Zm p , , 8 , , , , , t t 6 , , , gu , , , , C{ , , , , , , , , , T > ! : Chimpanzees modify intentional gestures to coordinate a search for hidden food
Abstract
Humans routinely communicate to coordinate their activities, persisting and elaborating signals to pursue goals that cannot be accomplished individually. Communicative persistence is associated with uniquely human cognitive skills such as intentionality, because interactants modify their communication in response to anothers understanding of their meaning. Here were show that two language-trained chimpanzees effectively use intentional gestures to coordinate with an experimentally-nave human to retrieve hidden food, providing some of the most compelling evidence to date for the role of communicative flexibility in successful coordination in nonhumans. Both chimpanzees (Panzee and Sherman) increase the rate of non-indicative gestures when the experimenter approaches the location of the hidden food. Panzee also elaborates her gestures in relation to the experimenters pointing, which enables her to find food more effectively than Sherman. Communicative persistence facilitates effective communication during behavioural coordination and is likely to have been important in shaping language evolution.
Introduction
The ability to appreciate that others have comprehension states and that these states can affect their behaviour is hypothesised to underpin the emergence of complex forms of communication in human evolution ADDIN EN.CITE ADDIN EN.CITE.DATA 1-3. In intentional communication, the signaller has a goal and influences the comprehension state of the recipient by flexibly modifying their communication ADDIN EN.CITE ADDIN EN.CITE.DATA 4-6. Communicative persistence is a key indicator of intentionality in humans and other primates and it precedes the transition to linguistically based communication in human infants ADDIN EN.CITE Bates19794724724726Bates, E.Benigni, L.Bretherton, I.Camaioni, L.Volterra, V.The emergence of symbols1979New YorkAcademic Press7. There is growing evidence for intentionality and communicative persistence in great ape gestural signalling defined as voluntary movements of arms, legs or bodily postures ADDIN EN.CITE Hewes197341441441417Hewes, G. W.Primate communication and the gestural origin of languageCurrent Anthropology 5-241419738. Communicative persistence can be evidenced by a signallers repetition or elaboration of signals in relation to different comprehension states of the recipient, until their goal is obtained, or failure is clearly indicated ADDIN EN.CITE ADDIN EN.CITE.DATA 7,9,10. However, understanding communicative persistence in non-verbal animals is not straight-forward; it is difficult to disentangle whether a signaller influences recipients comprehension of the meaning of the signal or influences directly their behaviour (i.e. makes them do something without assessing any comprehension about the goal) ADDIN EN.CITE Seyfarth200310091009100917Seyfarth, R.Cheney, D.Signalers and receivers in animal communicationAnnu Rev PscholAnnu Rev Pschol145-173542003Tomasello19991010105Tomasello, M.Zelazo, P.Olson, D.Astington, J.Having intentions, understanding intentions and understanding communicative intentionsDeveloping theories of intention.1999CambridgeCambridge University Press5,11. Studying episodes of coordination, where individuals communicate with one another in turn-taking sequences to achieve a goal that could not be accomplished individually, enable the nature and complexity of communicative persistence to be determined ADDIN EN.CITE ADDIN EN.CITE.DATA 12-14. Communicative persistence in these contexts requires coordination of attention and communication to a task, goal and to one another, providing evidence that signallers perceive others as entities with comprehension states about the goal ADDIN EN.CITE Ratner197811061106110617Ratner, NancyBruner, JeromeGames, social exchange and the acquisition of languageJournal of Child LanguageJournal of Child Language391-40153197815. For instance, if persistence reflects a particular internal state, contingent upon changes in the availability of the goal itself, then only repetitions of the original signals would be expected to occur. If, on the other hand, senders are aware of the impact that their signals will have on the recipient, then they should elaborate their signalling flexibly, contingent upon recipients comprehension about the goal ADDIN EN.CITE Golinkoff198644244244217Golinkoff, R. M.I beg your pardon - the preverbal negotiation of failed messagesJournal of Child LanguageJournal of Child Language455-47613319860305-0009WOS:A1986E756800001<Go to ISI>://WOS:A1986E756800001Golinkoff199344144144117Golinkoff, R. M.When is communication a meeting of mindsJournal of Child LanguageJournal of Child Language199-20720119930305-0009WOS:A1993KQ86800012<Go to ISI>://WOS:A1993KQ868000129,16.
In examining the ability of signallers to influence recipients, studying gestural communication is particularly useful because gestures are directional ADDIN EN.CITE Roberts201210141014101417Roberts, A.I.Vick, S-J.Roberts, S.G.B.Buchanan-Smith, H.M.Zuberbhler, K.A structure-based repertoire of manual gestures in wild chimpanzees: Statistical analyses of a graded communication systemEvolution and Human BehaviorEvolution and Human Behavior578-5893352012Roberts201310271027102717Roberts, A.I.Roberts, S.G.B.Vick, S-J.The repertoire and intentionality of gestural communication in wild chimpanzeesAnimal CognitionAnimal Cognition201310.1007/s10071-013-0664-517,18, meaningful ADDIN EN.CITE Roberts201397397397317Roberts, A. I.Vick, S-J.Buchanan-Smith, H.Communicative intentions in wild chimpanzees: Persistence and elaboration in gestural signallingAnimal CognitionAnimal Cognition187-1961622013Roberts201297297297217Roberts, A. I.Vick, S-J.Buchanan-Smith, H.Usage and comprehension of manual gestures in wild chimpanzeesAnimal BehaviourAnimal Behaviour459-4708422012http://dx.doi.org/10.1016/j.anbehav.2012.05.02219,20 and can draw attention of the recipient to specific spatial locations in the environment ADDIN EN.CITE Leavens20094944944945Leavens, D.A.Racine, T.P.Hopkins, W.D.Botha, R.Knight, C.The ontogeny and phylogeny of non-verbal deixisThe prehistory of language142-1652009New YorkOxford University Press21. These characteristics of gestural communication allow researchers to determine the signallers goal in gesturing, in particular in relation to the meaning of elaborations, and to identify their role in effectively influencing the recipient. If communicative persistence is an unintentional expression of frustration at the goal itself, then diffuse, uninformative elaboration would be expected to occur ADDIN EN.CITE Golinkoff198644244244217Golinkoff, R. M.I beg your pardon - the preverbal negotiation of failed messagesJournal of Child LanguageJournal of Child Language455-47613319860305-0009WOS:A1986E756800001<Go to ISI>://WOS:A1986E7568000019. If on the other hand, signallers perceive recipients as capable of comprehension about the goal, then they should elaborate by the use of informative signals which refer to the role of the recipient in pursuit of the desired goal, i.e. inform the recipient what they want him to do ADDIN EN.CITE Warneken200610941094109417Warneken, FelixChen, FrancesTomasello, MichaelCooperative activities in young children and chimpanzeesChild DevelopmentChild Development640-66377320061467-862422. For instance, when signallers direct their gestures to the recipient, but fail to achieve the desired response, they may direct the recipients attention to the desired referent in the environment by the use of indicative gestures such as pointing. However, when recipients respond appropriately to the signal, signallers may use non-indicative gestures such as bobbing to affirm the recipients comprehension about the goal.
Results from observational and experimental studies show some evidence for communicative persistence in wild and captive apes. However these are restricted to less complex experimental tasks or conspecific social interactions which did not require face to face behavioural coordination from a distance through gestural signals, as in the present case, to achieve a goal ADDIN EN.CITE ADDIN EN.CITE.DATA 19,20,23-27. For example, when presented with two food items (desirable and undesirable), in close proximity and visible during a fixed delay interval, great apes persisted with gesture production only following the (predetermined) delivery of the undesirable and not the desirable food items ADDIN EN.CITE Leavens200545745745717Leavens, D. A.Russell, J. L.Hopkins, W. D.Intentionality as measured in the persistence and elaboration of communication by chimpanzees (Pan troglodytes)Child DevelopmentChild Development291-30676120050009-3920WOS:000226771500020<Go to ISI>://WOS:000226771500020Cartmill200740740740717Cartmill, E. Byrne, R.Orangutans modify their gestural signaling according to their audience's comprehension Current BiologyCurrent Biology1345-1348171520076,28. However, as the experimenter neither initiated nor responded to the apes communicative efforts prior to the food delivery, it is unclear whether the apes gestures following food delivery were in response to the experimenters behaviour (delivery of the undesirable food) or to the experimenters apparent lack of comprehension of the apes gestures ADDIN EN.CITE Roberts201397397397317Roberts, A. I.Vick, S-J.Buchanan-Smith, H.Communicative intentions in wild chimpanzees: Persistence and elaboration in gestural signallingAnimal CognitionAnimal Cognition187-196162201319. Moreover, recent research demonstrates that when two chimpanzees required help of one another to retrieve a desirable food reward, they relied on a relatively simple leader-follower strategy, rather than using a more elaborated form of communication to coordinate food retrieval ADDIN EN.CITE Bullinger201110221022102217Bullinger, A.F.Wyman, E.Melis, A.P.Tomasello, M.Coordination of chimpanzees (Pan troglodytes) in a Stag hunt gameInternational Journal of PrimatologyInternational Journal of Primatology326201112. Thus, the issue of whether great apes can flexibly persist in communication to intentionally influence recipients remains unresolved ADDIN EN.CITE Tomasello200510231023102317Tomasello, M.Carpenter, M.Call, J.Behne, T.Moll, H.Understanding and sharing intentions: the origins of cultural cognitionBehavioural and Brain SciencesBehavioural and Brain Sciences675-7352820052.
In this study we examined communicative persistence in two language trained chimpanzees, using a spatial memory task that demanded simultaneous coordination between the chimpanzee and a human interactant to find hidden food23,24. Both chimpanzees (Panzee and Sherman) recruited and directed an experimenter to search for a food item, hidden at various distances and locations, with the experimenter unaware of the location of the food. The experimenter searched by repeatedly pointing towards potential target locations, watching the chimpanzee for feedback and, based on this feedback, varying the pointing direction, pointing distance, and his own distance to the target location.
Here we show that both chimpanzees respond to experimenters search efforts towards food by flexibly modifying their intentional gestures. Both increase the rate of non-indicative gestures when the experimenter approaches the location of the hidden food. Panzee also elaborates her gestures in relation to the experimenters pointing and disambiguates the experimenters understanding of her gestures about the location of hidden food. Panzee strategy enables her to find food more effectively than Sherman. Communicative persistence facilitates effective communication and is likely to have underpinned language evolution.
Results
Communicative exchanges
The chimpanzees used intentional gestures to coordinate search efforts with the experimenter (see also accompanying Supplementary Movie 1 of the task), for the food, hidden at various distances and locations (Supplementary Table S1), gesturing only when the experimenter was visually oriented towards them (Fig. 1a). These gestures were informative, goal-directed and either indicative (e.g. manual pointing) or non-indicative (manual shake and bobbing of the head or body) in terms of their ability to draw the recipients attention to specific spatial locations(Supplementary Table S2) ADDIN EN.CITE Leavens200545745745717Leavens, D. A.Russell, J. L.Hopkins, W. D.Intentionality as measured in the persistence and elaboration of communication by chimpanzees (Pan troglodytes)Child DevelopmentChild Development291-30676120050009-3920WOS:000226771500020<Go to ISI>://WOS:0002267715000206. The experimenter and chimpanzee spontaneously influenced and shaped the directionality of each others behavior by taking multiple turns in responding to indications of the location of food. On Panzees trials, the mean (SD) number of turns prior to finding the hidden food per target location was 36.3 (30.57) as compared to 43.5 (30.62) for Sherman. The majority of these turns involved intentional communication by the chimpanzees, the mean (SD) proportion for Panzee and Sherman were 0.76 (0.15) and 0.81 (0.06) respectively (Supplementary Table S1), which was significantly higher than the proportion of turns lacking intentional communication for both Panzee (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031) and Sherman (n = 6, t = 0, p = 0.031). By alternating their communication in this manner, the chimpanzees and the experimenter were able to obtain the hidden food. Although the mean (SD) proportion of turns responded to with incorrect experimenter pointing directions was high for both Panzee: 0.74 (0.18) and Sherman: 0.78 (0.17), most trials were successful (11 out of 12) and the food item was found quickly, within a large area of woodland. The mean (SD) duration of trials was 2.30 (1.8) minutes for Panzee and 3.02 (1.5) minutes for Sherman.
Strategies of chimpanzees to lead experimenter to the food
By modifying their communication in response to changes in the experimenters behaviour, relative to the location of the hidden food, the chimpanzees were able to successfully retrieve hidden food. The common strategy was to modify their non-indicative gestures in relation to the experimenters spatial proximity to the target location. Both Panzee (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031) and Sherman (n = 6, t = 0, p = 0.031) displayed a higher rate of non-indicative gestures when the experimenter was near to the target location (within 0-4m), as compared to far from the target location (over 4m). Gesturing ceased as soon as items were found by the experimenter (Fig. 1b), indicating that gesture production did not simply reflect high arousal in anticipation of food delivery ADDIN EN.CITE Melis201110171017101717Proceedings of the Royal Society B: Biological Sciences1405-14132781710201131. Instead, the chimpanzees produced non-indicative gestures to provide positive feedback to the experimenter as he approached the target location, and ceased once this goal had been met.
In addition to this common strategy, Panzee elaborated her gestural exchanges in relation to the accuracy of the experimenters pointing gestures. Panzee produced a higher rate of non-indicative gestures when the experimenter pointed toward the food rather than elsewhere (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031, Fig. 2). Panzee thus shaped the experimenters understanding of direction by observing his directional points and giving him a push in the right direction, at just the right moment. In contrast, incongruent experimenter responses led to a higher rate of indicative gestures. When the experimenter was far from the target location (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031) or when his pointing was not directed toward the hidden food (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031, Fig. 2), Panzee increased her pointing rate. Further, Panzee would raise her pointing hand high if the experimenter pointed too close (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031), but lower her hand downwards when pointing was at the correct distance or beyond the target location (n = 6, t = 0, p = 0.031, Fig. 3). Panzees pointing gestures were directed towards the hidden object more often than elsewhere (Wilcoxon signed ranks test; n = 6, t = 0, p = 0.031). Panzee thus used pointing to influence the experimenters understanding of what was off track and what was on track, whilst simultaneously indicating the precise location of the hidden food.
In contrast, Sherman only responded to the overall proximity of the experimenter to the target location with manual shaking and bobbing (Table 1) and Panzees method increased the efficacy of the experimenters search on this task ADDIN EN.CITE Sayers201210701070107017Sayers, K.Menzel, C.R.Memory and foraging theory: chimpanzee utilization of optimality heuristics in the rank-order recovery of hidden foodsAnimal BehaviourAnimal Behaviour20120003-347230. There were no significant differences between the chimpanzees in the experimenter or in the chimpanzee distance to the target at the start of the trials, or trial duration (Supplementary Table S1) but the distance covered by the experimenter during their search, corrected for chimpanzee communicative effort (duration of responses), was significantly greater for Panzees than Shermans trials (Mann Whitney test, n = 12, t = 26, p = 0.041). This shows that Panzees skills at communication were more efficient at directing the experimenter to the food and the success of the task was influenced by the ability of chimpanzees to communicate its location ADDIN EN.CITE Sayers201210701070107017Sayers, K.Menzel, C.R.Memory and foraging theory: chimpanzee utilization of optimality heuristics in the rank-order recovery of hidden foodsAnimal BehaviourAnimal Behaviour20120003-347230. Additionally, when comparing performance by experimenters who were familiar and unfamiliar with the chimpanzees behaviour on this particular task, the success rate of the inexperienced experimenter was also high (5/6 trials were successful) and the trial duration did not differ between experimenters across trials matched for distance to hidden food (Mann Whitney test, n = 12, t = 37, p = 0.818; Supplementary Table S3). This indicates that success was not solely determined by the experimenters experience on this particular task, but was instead the result of intentional communication between the chimpanzees and experimenters.
Discussion
The communicative flexibility reported in this paradigm ADDIN EN.CITE ADDIN EN.CITE.DATA 29,30,32,33 goes far beyond that reported in previous studies, where apes were faced with an unresponsive experimenter ADDIN EN.CITE Leavens200545745745717Leavens, D. A.Russell, J. L.Hopkins, W. D.Intentionality as measured in the persistence and elaboration of communication by chimpanzees (Pan troglodytes)Child DevelopmentChild Development291-30676120050009-3920WOS:000226771500020<Go to ISI>://WOS:000226771500020Cartmill200740740740717Cartmill, E. Byrne, R.Orangutans modify their gestural signaling according to their audience's comprehension Current BiologyCurrent Biology1345-1348171520076,28 or where conspecific social interactions did not require face to face behavioural coordination though intentional gestural signals to achieve the desired goal ADDIN EN.CITE ADDIN EN.CITE.DATA 19,20,23-27. Here, chimpanzees dynamically and flexibly modified their intentional gestures in relation to the nave experimenters search efforts towards the hidden food, to successfully guide the experimenter to the food item. Such communicative persistence, particularly in turn-taking episodes of communication where individuals respond communicatively to one another, is a key marker of intentional communication in humans and primates ADDIN EN.CITE Tomasello19991010105Tomasello, M.Zelazo, P.Olson, D.Astington, J.Having intentions, understanding intentions and understanding communicative intentionsDeveloping theories of intention.1999CambridgeCambridge University PressBates19794724724726Bates, E.Benigni, L.Bretherton, I.Camaioni, L.Volterra, V.The emergence of symbols1979New YorkAcademic Press7,11. This study therefore provides some of the clearest evidence to date for such communicative persistence, and thus intentional communication, in chimpanzees.
Both chimpanzees showed communicative persistence, and used intentional gestural communication to guide the experimenter to a hidden food item. One interpretation could be that chimpanzees did not communicate to influence the experimenter to find hidden food, but simply adhered to behaviour of experimenter, allowing him to regulate the search for hidden food, while they communicated, regardless of experimenter search ADDIN EN.CITE Warneken200610941094109417Warneken, FelixChen, FrancesTomasello, MichaelCooperative activities in young children and chimpanzeesChild DevelopmentChild Development640-66377320061467-862422. In this case, success of chimpanzees in the current task would be due to the experimenters ability to read and interpret the chimpanzees behaviour, rather than chimpanzees skill at communicating. However, the success rate of the inexperienced experimenter was high, he found food relatively quickly and there was no significant difference in trial duration between the experienced and inexperienced experimenters. In previous experiments, uncued control objects (that are not shown to the chimpanzees) were very rarely found ADDIN EN.CITE Sayers201210701070107017Sayers, K.Menzel, C.R.Memory and foraging theory: chimpanzee utilization of optimality heuristics in the rank-order recovery of hidden foodsAnimal BehaviourAnimal Behaviour20120003-347230. Further, as both experimenters were naive to the location of the food, hidden in a different location (with a varying angle and distance) on each trial, in the large woodland area and care was taken to fully conceal the hiding place ADDIN EN.CITE Sayers201210701070107017Sayers, K.Menzel, C.R.Memory and foraging theory: chimpanzee utilization of optimality heuristics in the rank-order recovery of hidden foodsAnimal BehaviourAnimal Behaviour20120003-347230, it is clear that the search behaviour of the experimenters, and their success in finding the hidden food, was shaped by communication with the chimpanzees.
Moreover, the chimpanzee reactions to the experimenters behaviour towards the food further clarifies whether chimpanzees communicated with regard for the experimenter. If chimpanzees simply learned the appropriate individual behaviours to get the food without perceiving the role of the experimenter in finding food, they should simply continue repeating the same movement sequences and communicative strategy, rather than modifying their behaviour in relation to experimenters behaviour towards the food ADDIN EN.CITE Warneken200610941094109417Warneken, FelixChen, FrancesTomasello, MichaelCooperative activities in young children and chimpanzeesChild DevelopmentChild Development640-66377320061467-862422. However, chimpanzees used communicative means which referred to the role of the experimenter, i.e. Panzee and Sherman used manual shaking and bobbing to signal that the experimenter was close to the food. Panzee also pointed higher to indicate experimenters pointing was too close or pointed lower to indicate that experimenters pointing was too far. This ability to make distinctions such as near and far, is similar to some human pointing gestures ADDIN EN.CITE Kendon19889619619616Kendon, A.Sign languages of Aboriginal Australia: Cultural, Semiotic and Communicative Perspectives. 1988CambridgeCambridge University Press34, and reveals a sophistication comparable to the usage of some deictic words in human language. These strategies can be seen as evidence that chimpanzees understood their own and the experimenters actions as interdependent of one another to find hidden food.
Additionally, it could be claimed that the communicative strategies employed by the chimpanzees were shaped by the experimenter in repeated sessions of this task, or on similar tasks, ritualising the interactions ADDIN EN.CITE Ross198710951095109517Ross, Hildy SLollis, Susan PCommunication within infant social gamesDevelopmental psychologyDevelopmental psychology241-48232198735. In captivity, chimpanzees can point to food locations outside their reach ADDIN EN.CITE ADDIN EN.CITE.DATA 36-38, and some language-trained apes are more likely to use their index finger than whole hand to point, indicating that gesture use and morphology are influenced by experience ADDIN EN.CITE Leavens199925252517Leavens, D. A. Hopkins, W. D.The whole-hand point: The structure and function of pointing from a comparative perspective.Journal of Comparative PsychologyJournal of Comparative Psychology417-4251134199937. However, communicative persistence more broadly is also evident in wild chimpanzee gestural communication, indicating that the capacity is not unique to enculturated individuals ADDIN EN.CITE ADDIN EN.CITE.DATA 18-20. Nonetheless, in this experiment the pointing by Panzee was more elaborate, producing tactics that resemble those evident in human communication ADDIN EN.CITE Kendon19889619619616Kendon, A.Sign languages of Aboriginal Australia: Cultural, Semiotic and Communicative Perspectives. 1988CambridgeCambridge University Press34. By raising her arm higher when the experimenter incorrectly pointed lower, and lowering her arm when experimenter incorrectly pointed higher, Panzee associated her own behaviour with experimenters change in pointing height. As Panzee modified her pointing in relation to changes of height of experimenters pointing relative to location of the food, and not the experimenters pointing height itself, the specific communicative tactics used indicate considerable flexibility in intentional communication in chimpanzees ADDIN EN.CITE Gillespie-Lynch10981098109817Gillespie-Lynch, KristenFeng, YunpingGreenfield, Patricia MSavage-Rumbaugh, SueLyn, HeidiA cross-species study of gesture and its role in symbolic development: Implications for the gestural theory of language evolutionFrontiers in PsychologyFrontiers in Psychology16041664-107839.
The specific and individual strategies employed in response to the experimenters search behaviour differed between Panzee and Sherman. Shermans understanding of how to use gestures to guide the experimenters search actions was more limited, in that he simply responded to the overall proximity of the experimenter to the target location with manual shaking and bobbing. Sherman displayed a low frequency of points, and did not use or modify morphology (height) of his pointing to indicate the location of the food, suggesting that Sherman did not understand as well as Panzee did the communicative potential of pointing to guide the experimenters understanding in this task. Thus in Shermans case, the search may have been driven mainly by the experimenters interpretation of these non-indicative gestures. In contrast, Panzee clearly used directional pointing to guide the experimenters search behaviour. While Sherman understood the experimenters behaviour in relation to the food location, Panzee appears to have understood the experimenters comprehension of her communicative gestures about the location of the hidden food. By tailoring her communicative signals to accommodate the experimenters level of comprehension, Panzee was significantly more effective than Sherman at directing the experimenter to the food.
The different strategies used by Panzee and Sherman reveal the importance of intentional communication in effectively coordinating behaviour ADDIN EN.CITE Golinkoff198644244244217Golinkoff, R. M.I beg your pardon - the preverbal negotiation of failed messagesJournal of Child LanguageJournal of Child Language455-47613319860305-0009WOS:A1986E756800001<Go to ISI>://WOS:A1986E7568000019. Both Panzee and Sherman responded to the overall proximity of the experimenter to the target location, but also Panzee responded to the experimenters understanding of her gestures by confirming accurate searches and correcting the experimenters inaccurate searches. When the experimenter pointed to different referents in the environment, Panzee agreed or disagreed with experimenters interpretation and was able to achieve the goal of finding food much faster than Sherman, showing that intentional communication can increase the efficiency of attaining goals.
Chimpanzees abilities to intentionally coordinate to obtain desired goals thus appears more sophisticated than previously demonstrated, and this level of skilled communication would have been available in early humans. It potentially could have been involved as a part of the general cognitive and communicative background in the evolution of language. In one scenario for the evolution of language, selection for enhanced communication took place in the context of coordinating social foraging of complex resources such as large game and underground storage organs of plants ADDIN EN.CITE ADDIN EN.CITE.DATA 3,40-42. The communicative strategies employed by chimpanzees in our study suggest that intentionally coordinating to obtain desired goals may have been an important aspect of social behaviour and foraging in early humans. By reformulating the understanding of the location of the resource by communicative signals, and confirming and disconfirming this understanding, two or more interactants would have increased their efficiency in foraging, hunting or other joint activities. In absence of language, gesturing to different referents in environment may have acted as a translation of anothers intent into communicative signals, thus assisting interactants in making the mapping between communicative signals and real world events.
The use of hand signals to coordinate joint activities in hunter-gatherer groups can provide insights into how this process may have worked, as the hunter-gatherer lifestyle was the dominant one for the vast majority of human evolution ADDIN EN.CITE Hewlett11091109110917Hewlett, Barry SFouts, Hillary NBoyette, Adam HHewlett, Bonnie LSoci a l l e a r n i n g a m o n g C o n g o B a s i n h u n t e r g a t h e r e r s <