First report of “referential gesturing” in any animal other than humans

November 25, 2022 • 9:15 am

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?

22 thoughts on “First report of “referential gesturing” in any animal other than humans

  1. “You all know that when you use your hand to point out something to a dog, it looks at your hand, not what you are pointing to”. Is that so? Lots of people (including me) take it that dogs learn fairly easily to follow a pointing gesture to a treat that has fallen (for example). Or to something worth investigating. Dogs doing referential gesturing would be another matter but I wonder what investigators doing canine cognitive research say.

    1. My dog makes referential gestures all the time, and I didn’t train him to do it. He enjoys going up to strangers and getting them to play “fetch” (He’s a Labra-mutt, so retrieving is his raison d’être). He’ll approach and drop the ball in front of the stranger, which typically elicits a “what the hell?” response; then he’ll point at the ball, as if to say, “I can’t believe you don’t know how this works”. If the stranger is especially slow on the uptake, he’ll bring the ball closer and point at it again, and even bark (“Arf!”) if need be.

      As often as not, the stranger is a pretty girl in a bikini, and it’s occurred to me that these girls may think that I trained him to go up to pretty girls in bikinis, but no, he figured this out all on his own. He also responds to my gesturing with the chuck-it stick for him to “look over there” on those occasions when he’s lost track of the ball.

      In sharp contrast, my cat used to, indeed, look at my fingertip on those occasions when I tried to point something out to him. Pure comedy.

        1. Don’t know if this qualifies but here goes ….

          My German shepherd dog kept repeatedly looking at his bag of Greenies ( a dental treat he adores) and then looking at his water bowl. He did this several times and I thought no you are not getting anymore greenies but perhaps he needs fresh water. I went to his water bowl and to my surprise there was a greenie at the bottom of it. Retrieved the item and gave it to him and off he trotted very happy.

          I guess communication is really a 2 way street

      1. I would distinguish my dog’s behavior from “play solicitation” for the following reason: Sometimes, when he is soliciting a human stranger to throw the ball, another dog will interrupt by grabbing the ball, running some distance away, turning and facing him, with his tail wagging. That is, dog number two makes a bona fide “play solicitation”.

        My dog, because he regards “retrieving” not as play but as his job, ignores the play solicitation. He’s not interested in chasing a dog–because that would be a stupid waste of time. When this happens he tends to look at me as if to say, “can you believe this idiot?” He’ll wait for the other dog to lose interest and drop the ball, at which point he goes back to work.

        So we have to either (1) distinguish between two kinds of play solicitations (like he does), or (2) regard one as play and the other as something else. Either way, he’s gesturing, and it’s all innate, as I’ve never trained him to do any of this.

        If anything, I’d say that he’s training random humans to throw balls. Even when those balls are all drooly and repulsive, he’s able to persuade these hominids them to pick them up and throw them, over and over.

  2. Further: the canine cognition lab at Duke lists other centers of canine cognition research. I believe some of this was inspired by Michael Tomasello’s research on humans and primates.

  3. The most impressive detail is in the younger chimp, who adjusted where her hand was in order to put the hand (and leaf) in the line of sight of her mother That is in the ambit of theory of mind, part of which is that one can realize what another must be seeing (or not seeing) bc of the direction of their gaze. As for the mother chimp, she looked at the leaf but only bc it was in the hand. My dog would do the same. With that part of the event, I would be more impressed if the item of interest was some feet away from where the youngster was pointing. My dog would never look in the direction I’m pointing at first.

  4. Actual information: “Human-like social skills in dogs?”, in Trends in Cognitive Science, by Brian Hare and Michael Tomasello, has a lot of information on the evolutionary significance of the development of cooperative communication between dogs and humans.

  5. Yes to the comment about Frans de Waal–he has an amazing insight into ape-family behavior, though I don’t remember whether he mentions this sort of thing in any of his books I’ve read.

    Most of my cats have just looked at my hand when I pointed, but there have been two who actually understood the concept behind pointing. I’ve tried to teach it to others, but only those two really grasped the idea. Alex, one of my current cat family, sees me point and immediately looks in the direction in which I’m pointing. I’ve practiced with him where I’m making sure not to give accidental clues, such as throwing a treat where he can hear it hit the floor or moving my arm in a way that he can see it. If I throw something on a rug while he is looking elsewhere outside of peripheral vision, then get his attention and point, also using the word “such'” (German for “search”), he immediately heads in that direction. He has an almost 100% success rate. The other cat, from long ago, was equally talented.

  6. It is fairly routine to train retrievers to retrieve multiple dummies. My English cocker spaniel can retrieve 3 dummies which seems to be as many as she can keep track of.
    She retrieves the one I point to and leaves the others alone until I point to them.
    Not sure if this is an example of what you are looking for.

    1. She will also go to an area I point to if she did not see the dummy.
      (I am a recovering hunter in case anyone wonders why I went through the trouble of training)

  7. The Scientific American from last week has a discussion of this research with some comments, including from Tomasello. Not surprisingly, he thinks you would need a larger body of observations. The researchers respond.

  8. Animals training people. People speak of themselves as staff of their cats. I was staff of one dog, who trained me to respond to pointing. He liked lying on an outdoor bed, but the bed needed to be moved as the sun moved in the sky. When the bed needed to be moved, he stood up where I could see him from inside the house, to inform me I needed to come outside. Then he would take up a position and stand there. I would move his bed to the place thus indicated, and he would lie down on the bed in the new position. He was the only dog I ever had that wasn’t a working breed. Working breeds figure out what you want, but this dog’s idea was that you did what he wanted. Do cats train people like this?

  9. I have German Shorthair Pointers that indeed know when I’m pointing at something. Some are “quicker” than others, but they all seem to “get” referential gestures. You can also train pointers to “back” other pointers that are pointing; it’s basically honoring another dog that’s on point so their movement stops and they don’t disturb the prey. I have a male (probably the smartest GSP I’ve had) that understands directional hand signals as well; he also taught himself how to open most doors; cute at first, but I now wish he didn’t know how to do it.

    Thanks for this post, I found the chimp’s referential gesture remarkable.

      1. That’s why I’ve had them for 20 years or so: my parents raise and train them. Mom facilitates the pups, dad trains the “potential winners” and participates in field trials and such. They are a magnificent breed. I don’t hunt or train, but they have such innate instincts, they almost train themselves. I like what Max wrote below. His experiences with his Brittanies is very relatable.

  10. I had always understood this as a difference between domestic dogs and wolves, as well as the bulk of other animals.
    I have a neighbor whose dog is trained to herd cattle. When we are driving the cows from one place to another, the dog keeps an eye on his master, who will occasionally point to a cow that needs to be brought closer in to the herd.
    We have Brittanies, the best of which point birds or other critters without training. Certainly as Mark writes above, other dogs will see the one on point and home into the bird themself.
    My dog is obsessed with balls and frisbies. If I throw one, and he does not see where it went, in surf or high grass as examples, he will look at me to gesture left or right with my arm, and he follows the direction.
    If we are in the house, I say “where is the ball?”, and he goes and finds one. If it is under a chair or some other place he cannot reach, he points at it, and keeps looking between me and the ball until I get up and go get it.

    Monkeys have hands, so their pointing looks a lot like ours. Dogs have their noses, and can emote to some extent. But I have seen a great many examples of dogs correctly interpreting a person’s pointing.

    I just did an experiment. In this room, his bed is in one corner, and there is a golf ball near the chair. When I pointed to the ball, he went and fetched it for me to toss. I pointed at his bed, and he went and laid down. Same gesture, no words, but he picked up on my intent based on what I was pointing at. I did not deliberately teach him to do this. He knows what the ball is for and what the bed is for.

    I have not been around wolves enough to see if it works on them as well. I am unsurprised that simians use such gesturing routinely.

    1. Yes, dogs do understand human gestures like pointing. And I remember reading that wolves don’t do that naturally but I didn’t look too far into it.

  11. Do pointers have to be trained to point?

    My recollection is that it’s a natural element of wolf/dog hunting behavior, which pointers have been bred to specialize in.

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