A closer look at communication among our closest relatives
I am writing this while conducting fieldwork in Zambia, with only very limited access to the internet. Therefore, I could not read already existing posts and the corresponding responses and discussions, and some of the issues I will refer to might have been raised by others already. However, as a researcher interested in the gestural and facial communication of great apes, I want to offer some comments and facts from a comparative perspective on human communication and language evolution.
As a more general comment, I specifically liked the way Thom Scott-Phillips navigates the reader through this book by providing definitions of different terms, particularly of those often causing confusion when being used by scholars of different disciplines, as well as summaries of the most important facts of each chapter together with a brief outlook about what the reader can expect in the following chapter. Furthermore, although I am interested in potential precursors of human language in other primates, thus favoring a continuous approach to language evolution, I agree that researchers interested in language evolution sometimes compare “pears and apples”, since the behaviors of interest are not correctly (or too broadly) defined. Sometimes there is a tendency to focus on similarities between humans and other primates, while at the same time, differences might be neglected. However, I will point out later why I do not agree with some of the conclusions Thom Scott-Phillips draws from comparative research, with special focus on his chapter 4, dedicated to the origins of ostensive communication.
The nature of ostensive signal
Thom Scott-Phillips defines ostensive signals as “signals that express communicative intentions, and hence informative intentions” (p. 9). While the informative intention represents what the signaler wants to communicate, the communicative intention conveys the information that the signaler wants to communicate. He uses the example of tiling a cup (“I want more coffee”) plus establishing eye-contact (“I want to communicate my intention”) and then comments that “typically, both types of intention are expressed in one and the same behavior, such as the tilt of the coffee cup”. Based on this example, I am not sure about the nature of ostensive signals: On the one hand, Thom Scott-Phillips suggests that both intentions are expressed by one behavior (tilting the cup), but then refers to the importance of eye-contact to signal the communicative intention to a specific recipient and to make clear that one intends to communicate. Without this signal, Thom Scott-Phillips continues, the recipient would not realize that “tilting the cup” was directed at him.
Why am I so picky about this? If we are not clear about what exactly ostensive signals are and which forms they can take in humans (visual gestures? facial expressions? eye gaze? tactile communication? body postures/movements? vocalizations?), then it is also not clear what exactly we are looking for in nonhuman great apes (or other primates) and how we should interpret findings from comparative research. To give an example: Chimpanzee males use a “penis offer” to communicate that they want to copulate with a female. To make sure that the female perceives this visual behavior, the males combine it with a “leaf-clipping” behavior, which causes a sound to attract the female’s attention. Thus, while the “penis offer” refers to the “what”, the “leaf-clip” conveys the intention to communicate. One of course could argue that the males only want to change the female’s behavior, but not her mental representations. Furthermore, I am aware that this example only covers the expression, but not the recognition of ostensive-inferential communication (see p. 86), and that particularly in the gestural (in contrast to vocal) modality, we still know very little about great apes’ understanding of others’ communicative (and informative) intentions (in contrast to vocalizations, as highlighted in the book). Still, I think it is important to point out which types of ostensive signals we would expect to observe in other primates. It is also important to define clearly why we would consider some behaviors, but not others as potential ostensive signals, but not others. Gestures, and some vocalizations, are considered, but not facial expressions, which are barely mentioned throughout the book. Facial expressions might not be used intentionally, as are gestures and some vocalizations; however, despite the common notion that facial expressions might merely express internal, affective states and are not intentionally used, this aspect has never been studied systematically by applying the suggested criteria for intentional use to facial communication in nonhuman primates.
Imagine a chimpanzee approaching another one and using an “arm raise” gesture (ritualized from actual hitting), but combining this gesture with a play face to signal that he wants to play and not attack. The gesture is directed at a specific individual to signal his communicative intent, and the play face informs the recipient about the nature of this approach, since the very same gesture is also used in aggressive contexts. Again, one could argue that it is still unclear whether the signaler is meant to change the other’s behavior instead of mental representations, and that facial expressions are merely expressions of affective states instead of intentionally produced signals. Taken together, what I would like to emphasize is that we have to define clearly which forms ostensive signals can take in other species.
Origins of ostensive communication (Chapter 4)
This particular chapter, from my point of view, does not always represent our current knowledge about primate communication and the corresponding socio-cognitive skills in an appropriate way. While reading it, I got the impression that Thom Scott-Phillips postulated a potential fundamental difference between the communication of humans and other primates, which he then confirms by selecting the corresponding (but not always representative) studies, while neglecting others.
Furthermore, what I missed here was a more in-depth discussion of the function of so-called “attention-getting gestures”, which are the tactile and auditory gestures that chimpanzees seem to use to attract the attention of a not-attending recipient. Thus, it could have been of special interest to discuss whether nonhuman primates use attention-getters to manipulate the attentional states (and thus visual perspectives) of others (conspecifics or humans), thus signaling communicative intentions, and whether signalers combine attention-getters with subsequent specific intention movements, particularly since existing studies draw different conclusions. Furthermore, I think the conclusions drawn from section 4.5 on the mindreading skills of nonhuman primates are rather problematic. The conclusion that “there is little evidence that chimpanzees have command of the type and extent of mental metarepresentations that have been identified as cognitive pre-requisites for ostensive communication” is simply premature. Thom Scott-Phillips even acknowledges that it is difficult to develop a paradigm that is appropriate and ecologically valid for nonhuman primates and that such studies might be very difficult to conduct because of methodological reasons. I do not want to argue that the socio-cognitive skills of nonhuman primates are most likely as complex as those of humans and that potential differences are only a matter of quantity, not quality. However— with apologies for this almost trite remark—, “the absence of evidence is not the evidence of absence”. In this context it is also not helpful to refer to the possibility that negative findings have been most likely not published. Currently we have to acknowledge that we still know comparably little about the mindreading skills of nonhuman great apes. The point I want to emphasize here is that we simply don’t know (yet) the mindreading skills of nonhuman primates to the extent they have been studied in humans.