The communicative flexibility reported in this paradigm32,33,34,35 goes far beyond that reported in previous studies, where apes were faced with an unresponsive experimenter6,31 or where conspecific social interactions did not require face to face behavioural coordination from a distance though intentional gestural signals to achieve the desired goal20,22,23,26,27,28,29,30. Here both chimpanzees dynamically and flexibly modified their intentional gestures in relation to the naive experimenter’s 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 primates10,11,14. 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 the behaviour of the experimenter, allowing him to regulate the search for hidden food, while they communicated, regardless of the experimenter’s search25. In this case, success of chimpanzees in the current task would be due to the experimenter’s ability to read and interpret the chimpanzee’s behaviour, rather than chimpanzees’ skill at communicating. However, the success rate of the inexperienced experimenter was high, and there was no significant difference in trial duration between the experienced and inexperienced experimenters. 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. Furthermore, great care was taken to fully conceal the hiding place and, in previous experiments, uncued control objects (that are not shown to the chimpanzees) were very rarely found32. It is therefore clear that the search behaviour of the experimenters, and their success in finding the hidden food, was shaped by communication with the chimpanzees.

Moreover, if chimpanzees simply learned the appropriate individual behaviours to get the food without perceiving the role of the experimenter in finding it, they should simply continue repeating the same movement sequences and communicative strategy, rather than modifying their behaviour in relation to the experimenter’s behaviour towards the food25. However, both chimpanzees used communicative means that referred to the role of the experimenter. That is, Panzee and Sherman used manual shaking and bobbing to signal that the experimenter was close to the food. Panzee also pointed higher to indicate when the experimenter’s pointing was too close or pointed lower to indicate that experimenter’s pointing was too far. This ability to make distinctions such as ‘near’ and ‘far’ is similar to some human pointing gestures37, and reveals 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 in finding the hidden food.

The communicative strategies employed by the chimpanzees could have been shaped by the experimenter in repeated sessions of this task, or on similar tasks, ritualizing the interactions38. In captivity, chimpanzees can point to food locations outside their reach39,40,41, 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 experience40. However, communicative persistence more broadly is also evident in wild20,22,23 and captive26,27,28,29 chimpanzee gestural communication, indicating that the capacity is not unique to enculturated individuals. Nonetheless, in this experiment the interactive aspect of Panzee's pointing was more elaborate, producing tactics that resemble those evident in human communication37. By raising her arm higher when the experimenter incorrectly pointed lower, and lowering her arm when experimenter incorrectly pointed higher, Panzee may have associated her own behaviour with the experimenter’s change in pointing height. As Panzee modified her pointing in relation to changes in the height of the experimenter’s pointing relative to location of the food, and not the experimenter’s pointing height itself, the specific communicative tactics used indicate considerable flexibility in intentional communication in chimpanzees42.

The specific and individual strategies employed in response to the experimenter’s search behaviour differed between Panzee and Sherman. Sherman’s understanding of how to use manual gestures to guide the experimenter’s search actions was more limited than Panzee's. After orienting his body toward the hidden object, he primarily responded to increases in the overall proximity of the experimenter to the target location with manual shaking and bobbing. Sherman displayed a lower frequency of points than Panzee did, and did not use or modify the morphology (height) of his pointing to indicate the location of the food. Thus, Sherman did not exploit the communicative potential of pointing as fully as Panzee did to guide the experimenter’s understanding in this task. While Sherman’s behaviour indicates that he was sensitive to the experimenter’s behaviour in relation to the food location, Panzee appears to have understood the experimenter’s comprehension of her communicative gestures about the location of the hidden food. By tailoring her communicative signals to accommodate the experimenter’s 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 behaviour13. Both Panzee and Sherman responded to the experimenter’s overall proximity to the target location. Panzee also responded to the experimenter’s understanding of her gestures, by confirming accurate searches and correcting inaccurate searches. When the experimenter pointed to different referents in the environment, Panzee agreed or disagreed with the experimenter’s interpretation and was able to retrieve the food items more efficiently than Sherman, showing that intentional communication can increase the efficiency of attaining goals.

The capacity for chimpanzees to intentionally coordinate to obtain desired goals appears to be more sophisticated than previously demonstrated, and this level of skilled communication probably would have been present in early humans. It is likely to be a component of the general cognitive and communicative capacities that underpinned the evolution of language. In one scenario for the evolution of language, selection for enhanced communication took place in the context of coordinating social foraging3,43,44,45. 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 the absence of language, gesturing (with arm, hand, head, or whole body) to different referents in the environment may have acted as a translation of another’s intentions into communicative signals, facilitating the mapping between communicative signals and real world events.

The use of nonverbal signals such as hand signals to coordinate joint activities in hunter–gatherer groups can potentially provide insights into this process, as the hunter–gatherer lifestyle was dominant during the majority of human evolution46. When hunting, many different hunter–gatherer groups use an extensive range of hand signals to coordinate joint activity—these include Congo Pygmies47, Aboriginal Australians48 and two Kalahari Khoe-speaking groups49. Further, a cross-cultural comparison of hunter–gatherer groups demonstrated that hand signals occur more frequently in societies that have a higher dependence on hunting for subsistence50. The use of hand signals thus appears to be important in coordinating joint activities across groups of hunter–gatherers.

The context of joint activity may have provided an arena for the acquisition of linguistically based communication from learnt, ritualized signals in our hominin ancestors3. The intentionality in gestural communication might indicate that language evolution occurred partially in the gestural domain9. Gestures frequently co-occur with vocalizations; however, whereas gestures can intentionally convey meaning to recipients, vocalizations seem to be unintentional from the signaller’s perspective5,20,21,22,23. The scaffolding of vocalizations by intentional gestures may have enabled the attribution of meaning to vocalizations and a gradual move towards intentional communication in the vocal domain21,51,52. Although whether such a gestural stage was necessary is a matter of debate27,53, studying processes of vocal and gestural intentional communication in both humans and non-human primates in the context of coordinating joint activity may provide important insights into language evolution26,27,28.