Here’s a short new paper from Proc. Nat. Acad. Sci. that, in fact, reports just a single gesture of one chimpanzee towards another. Was that worth a whole paper? Well, it appears to document the first example of “referential gesturing” in any animal other than humans.
What is a “referential gesture”? It’s a gesture that one individual could make to call attention of another individual to something, usually involving an object, an action, or a third party. (This is how humans use such gestures.) Pointing is one of these actions (you all know that when you point at something to a dog or cat, they look at your hand, not what you’re pointing at!).
In this case, one chimp held out a leaf to another chimp, and when the second chimp didn’t respond, the leaf-holder moved it towards the other’s face to call more attention to it. Click on the screenshot below to see the paper, which has free access, and you can find the pdf here.
The behavior is connected with the way chimps groom themselves to get rid of parasites and keep themselves clean. Sometimes they also appear to groom leaves—for reasons unknown. I’ll reproduce the report of the one gesture involving a chimp who was grooming a leaf.
We recorded an instance of a referential showing gesture between conspecifics in the context of leaf grooming in the Ngogo chimpanzee community, Kibale National Park, Uganda that seems to be produced declaratively. During self-grooming or social grooming, groomers occasionally pluck leaves that they manipulate with their fingers and mouths as if grooming them while also peering closely at them. They may be inspecting ectoparasites (e.g., ticks) they have placed on the leaves, but the function of leaf grooming remains unexplored in this community. The event described here involved a mother/adult daughter dyad. Adult female Fiona was sitting next to her mother Sutherland, whom she had been grooming. Fiona plucked a leaf from a small sapling and started leaf grooming. Sutherland’s attention was focused elsewhere while Fiona did this (Fig. 1 and Video S1), and after grooming the leaf for several seconds, Fiona held it out toward Sutherland. She repositioned her arm when the initial holdout did not elicit a response (Fig. 1). Once Sutherland attended to the leaf by fully orienting her eyes and head toward it, Fiona retracted it and continued leaf grooming.
It’s already known that chimps (and other species) use gestures to indicate what they want from others, like food or grooming, and here’s a video of such gestures:
But these aren’t referential gestures showing something to another chimp just to get its attention. As we’ll see shortly, Fiona apparently wasn’t offering the leaf to her mother to say, “here’s something for you to eat” or “here’s something we can eat”, but, according to the authors, the gesture was meant to get Sutherland’s attention, meaning roughly, “Have a look at this.” Fortunately, the gesture was filmed by the researchers, and here it is. Note how Fiona moves the leaf around until the object has Sutherland’s full attention.
The authors dissect this gesture to show that it’s truly referential:
The movements of this behavior are in line with the definition of showing or “holdouts” in human infant literature. Using the operational definitions of the most recent research on infant showing and giving, this gesture would be coded at least as an incipient show and potentially, as a fully formed conventional show. Incipient gestures are those that are plausibly part of the developmental trajectory toward the emergence of the conventional gesture form. Moreover, Fiona showed persistence with her gesturing (indicative of intentional signaling) (12), moving the leaf closer to Sutherland and more into her line of sight until Sutherland clearly adjusted her head to follow the movement of the leaf. Although Sutherland dropped her gaze to the leaf when Fiona first extended her arm, this may not have been clear from Fiona’s perspective, and head direction could have been a more reliable indicator for her. Once Sutherland had clearly seen the leaf, Fiona ceased gesturing, suggesting that the goal of Fiona’s gesturing behavior was simply to get Sutherland to attend to the leaf.
However, there are two alternative explanations for the gesture, all of which the authors find implausible (my paraphrasing):
1). Fiona was trying to share the leaf (and/or any parasites on it) with her mother as food. This seems unlikely because Fiona did not surrender the leaf to her mother. Further, chimps at Ngogo don’t eat this species of leaf. In sixty-six other observations of chimps grooming leaves near other chimps, there were no cases in which the nearby chimp took or ate any part of the leaf.
2.) Fiona’s leaf play was meant to induce some other “dyadic social activity” like grooming or playing. But chimps already show, as we see in the first video, different gestures to initiate these activities, and Fiona’s display gesture was different from these. And in 58 other observations of leaf grooming involving 30 chimps, only 5 such behavior—none showing “declarative referential gesturing”—produced immediate social grooming or play. This is the case even though three quarters of all leaf grooming events got the attention of other chimps (this was absent in the one above, making Fiona produce the referential gesture). The authors conclude:
Overall, there were no consistent differences between the leaf groomer’s behavior before and after leaf grooming, with social behaviors (social grooming, play) being more frequent before than after. This indicates that leaf grooming is not reliably used imperatively to elicit grooming or play from a partner, making it unlikely that Fiona gestured to request such an outcome.
The upshot: In my view, Fiona was indeed calling attention to the leaf (as the author say, Fiona was “sharing attention for sharing’s sake”), though we don’t know why. The fact that this is the first time such a gesture has been observed despite chimps being observed for decades AG (“after Goodall”) also suggests that referential gesturing is not common in this species. Perhaps it occurs only under very special and specific conditions, but we’ll need a lot more observations to reach this conclusion.
However, if we do find that referential gesturing in chimps is part of their behavioral repertoire, it leads to one inference, an inference that was the subject of Darwin’s book The Expression of the Emotions in Man and Animals (1872). Darwin found (or thought he found) similarities in how humans and other species express emotions, leading him to conclude, as part of his Big Game Plan, that our emotional expressions evolve from precursors present in our common ancestors with other species, and that other living species have inherited expressions resembling ours from those ancestors.
In this case, it’s not really the expression of an emotion that Fiona shared with humans, but a referential gesture. But the implication is the same. As the authors say, the analogy to human behavior is critical here:
Several aspects of the Fiona–Sutherland interaction provide hints as to where such future research may find further examples of showing and other protodeclarative gestures in one of our closest living relatives. . . Additionally, Fiona was interacting with her mother, with whom she shared a close social bond. Our observation suggests that in highly specific social conditions, wild chimpanzees, like humans, may be motivated to communicate cooperatively and share interest and attention simply for the sake of sharing. If so, this raises the question of whether differences between humans and chimpanzees in the ability to engage in cooperative communication are quantitative rather than qualitative, with ramifications for our understanding of the evolution of human social cognition.
I presume, though, that animals like cats and dogs could be trained to respond to referential gestures. (They’re already trained to make them to humans, like pointer dogs assuming a stance pointing to human prey.) Has anybody trained of observed their pets respond to a referential gesture, like looking at something you’re pointing at rather than at your hand?