humans deploy deictic gestures , such as pointing , to direct a recipient 's attention to a particular object or location , while iconic gestures are deployed to recreate an aspect of the shape or movement of an object or event . both types of signals are referential , in that they either direct attention to a present referent or generate a mental representation of an absent referent . so far , there has been very little evidence for referential signals of these kinds in great apes . this is surprising because language - trained apes have no difficulties communicating referentially with humans . reported that kanzi and mulika made hitting motions toward nuts they wanted a human observer to crack open for them . surprisingly , however , these individuals do not spontaneously use their acquired communication skills to interact with each other . nevertheless , our study suggests that great apes are capable , in principle , of producing iconic and deictic gestures even when interacting with each other , and a main conundrum is why do not take regular advantage of this capacity . ( 1 ) motor constraints iconic gesturing may be rare because it is mechanically easier for an ape to depict a movement in space ( e.g. direction of approach , location of desired grooming ) , than to pantomime other types of activities . however , a few anecdotes suggest that apes sometimes pantomime actions , although typically when interacting with humans . for example , gruber et  al . reported on a bonobo apparently pantomiming drinking from a cup to communicate to her caretaker , indicating that great apes are not fundamentally incapable of pantomiming . also , byrne and byrne have shown that gorillas can produce complex , fine - tuned finger movements to process food , suggesting that apes are not fundamentally constrained in terms of their motor control . ( 2 ) conceptual constraints another hypothesis is that great apes may only have limited capacities to mentally represent the world around them . for example , they may be able to mentally represent the notion of  movement but they may have a concept of  fruit tree or tool. although there is little doubt that primates and other animals can represent their worlds in terms of mental concepts , these concepts may be less clearly delineated compared to what is present in humans . although this is a difficult topic , we interpret the current evidence as consistent with the hypothesis that primates can form mental representations of social categories ( such as genetic relatives ) , or physical objects and their functional properties , such as tools ( gruber et  al . submitted ) , suggesting that apes are not fundamentally constrained in terms of cognitive capacities to mentally represent their world in in conceptual categories . ( 3 ) comprehension constraints human children use deictic gestures from about 10 months when communicate to their caretakers , long before they produce their first words . iconic gestures emerge somewhat later , around 12 months , an important step toward the ability to use symbols . interestingly , however , the comprehension of iconic symbols appears much later , around 26 months , following the acquisition of basic symbolic speech . the comprehension of iconic gestures , in other words , appears to be cognitively more demanding for children than its production or the comprehension of deictic signals , including pointing . in our study , however , subjects appeared to understand the intention behind beckoning , but it was unclear whether this was due to general capacity to comprehend iconicity or some simpler process . here , it would be necessary to explore whether apes can comprehend iconic signals that are novel to them , but depict some natural behavior ( e.g. , climbing , grooming ) or a relevant object ( e.g. tool , fruit tree ) ? ( 4 ) cooperative constraints apes experience personal intentions , and use communication signals to communicate intentions to others , but they appear to be unable to share their intentions with others i.e. they lack a  we - intentionality as it is typical for humans . because of this , the argument goes , great apes will only communicate what is beneficial for them and not what is useful for others . although the hypothesis has intuitive appeal , there are also some contradictory findings , suggesting that , in some conditions , primates communicate intentionally to direct the attention of others to external objects or events relevant to them . this has been found in the contexts of danger , foraging , and during fights . however , although great apes are not fundamentally incapable of sharing information with others they may only show this behavior in very specific situations where their own reproductive success is directly at stake . our findings have shown that great apes can naturally use spatial reference as part of a communicative intention with signallers producing gestures that depict the spatial features of a desired action and recipients responding to such signals appropriately . although this suggests that iconic signaling is part of natural communication in great apes , and as such present in the common ancestor of humans and apes , it is equally puzzling how rare such behavior is in great apes , despite its obvious advantages . we address 4 possible hypotheses on potential shortcomings underlying this human - ape difference : motor control , conceptual organization , comprehension abilities and shared intentional capacities , and find some support for the last one . however , it is also clear that more research is needed to decide what cognitive or psychological shortcomings really are responsible for the apparent underuse of a truly human capacity , the ability to use communication to iconically refer to an absent entity . we thank claudine andr and brian hare for permission to work at the lola ya bonobo sanctuary and the ministry of research and the ministry of the environment of the democratic republic of congo for supporting our research . we are grateful to all of the lola ya bonobo staff for their invaluable assistance , to richard w. byrne and catherine hobaiter for discussions .
we comment on a recent behavioral study in which we describe a human - like beckoning gesture in 2 groups of bonobos , used in combination with sexual solicitation postures . 
 the beckoning gesture fulfils key criteria of deixis and iconicity , in that it communicates to a distant recipient the desired travel path in relation to a specific social intention , i.e. , to have sex at another location . 
 we discuss this finding in light of the fact that , despite the documented great ape capacity and obvious communicative advantage , referential gestures are still surprisingly rare in their natural communication . 
 we address several possibilities for this peculiar underuse and are most compelled by the notion that non - human primates are generally not very motivated to share their experiences of external objects or events with others , which removes most reasons for referential signaling .