12 Jul 2014

Meaning of chimpanzee gestures

Jolie stroking Jo's mouth, possibly requesting food

This week, my second supervisor, Dr Catherine Hobaiter, received a lot of media attention for her article on the meaning of chimpanzee gestures (Full article: the news: , It’s great news for her, and convenient for me because it’s a good way of explaining my research. I will basically be doing the same thing, except for wild bonobos.
In her study, Cat filmed wild chimpanzees at Budongo research site in Uganda. She filmed all social interactions, and afterwards coded the video, looking for instances of gestural communication. She only coded intentional gestures. We can tell that gestures are intentional if they are directed towards another individual who is paying attention to the gesturer, and the gesturer persists or elaborates if they don’t get a satisfactory reaction. If an individual were not intentionally communicating (if gestures were just an automatic response) then we would expect the gesturer to produce them regardless of whether or not anyone is paying attention. It’s now well established that great apes gesture intentionally, so Cat analysed cases where the gestures met those criteria. This gave her 4531 gestures to work with.
Past studies have described the gestural repertoire of different species by seeing in which context gesture types occur. Perhaps, for example, the reach gesture occurs in the contexts ‘travelling’, ‘feeding’, and ‘playing’.  But how do we determine the specific meaning for each gesture type? What was the goal of the gesturer? Cat’s study is the first to look at such specific meanings. We can’t simply ask animals what their gestures mean; if we could then we’d probably be more concerned with studying their language than their gestures! It’s important to establish the meaning of gestures, or the goal of the animal, in a scientifically rigorous way. It comes back to what we know about intentional communication; we can define the meaning of a gesture by seeing which response satisfies the gesturer. For example, if the gesturer strokes the mouth of another individual, receives food from that individual, and subsequently stops gesturing, we can see that the gesturer is satisfied with the outcome and can say that the meaning of the mouth stroke gesture is “acquire food”. This definition of gesture meanings is the Apparently Satisfactory Outcome (ASO) – the meaning of a gesture is the outcome that satisfies the gesturer.
In an earlier paper, Cat identified 66 gesture types for chimpanzees. In this new paper, she identified 19 ASOs for 36 gesture types, used outside of play. Most of the gestures were to start interactions or to develop interactions, but two were used to stop interactions. One of the shortcomings of this method of assigning meaning is that we can only discover gestures with imperative meanings – telling others to do something – but not declarative meanings. A gesture for “look at that funny looking person with a camera” would not be definable because there is no observable response from the recipient. Still, it’s pretty incredible to be able to look specifically at gesture meanings. With this new way of assigning gesture meanings, we can look at how the meanings differ between individuals, age, sex, and rank; how meaning of the same gesture type differs between contexts; whether different individuals or even species use the same gestures to mean different things.
Finding semantic meanings of intentional communication by great apes brings us another step closer to understanding the evolution of language. I am excited to see how my findings for the bonobo gestural repertoire and gesture meanings compare to those for chimpanzees. 


  1. I find this an interesting blog post, I did read the BBC news article when it came out, and my original question came from the fact that I find the way the media explain things to the general public quite intriguing -- but i was wondering how accurate and how true to the facts the BBC report (and the media reports in general) where, there are often areas they change and blur reports (recently, relating to antibiotics) for ease of publication which make much of the statements in the reports somewhat superfluous. Do you think the news reports of Cat make as much sense when published as the raw copy sent to the news media?

    But reading the above blog, I find myself curious if the 4531 gestures is an expected amount, or larger or less than what you'd expect? And over what time scale is this? Is there any comparable figure from other species of Ape? Do these Chimpanzees generally Gesture throughout their day and interactions or do the gestures peak around certain times of day, possibly meal times, for example ?

    Finally, I also find myself quite intrigued as to - as you've mentioned - gestures are different between species of Chimpanzee and if different species or even different locations of Chimpanzee use differing gestures for the same thing, rather like human language (English/ Chinese, etc)

    All interesting stuff I know little about :(

    1. It is really interesting to see how popular news portrays academic articles, and I think that in this case the BBC did a really good job. They granted adequate importance to the fact that Cat was able to determine specific meanings for gesture types, while also saying that, yes, some of the gesture types had more ambiguous meanings. In the paper, any gesture used for one meaning over 70% of the time was said to have a "tight meaning", 50-70% "loose meaning" and <50% "ambiguous meaning". So of the gesture types that had enough data for analysis, it was quite an even spread; she found 13 with tight meanings, 11 loose meanings, and 12 ambiguous. Actually, at the end of the BBC article Shultz (who really appreciated the article, just had this minor criticism) said that it's "a little disappointing" that many of the meanings are ambiguous - but Cat totally acknowledges that different gesture types can mean different things in different contexts. Which is pretty interesting, because it means that chimps may be considering the contextual information while attending to gestural communication. Or maybe they're using modifiers to change the meaning of their gestures, but that's a whole new research question.

      Which ties nicely to the next point about 4531 gestures - that's the total number of gestures, the number of instances that she observed gesturing. Maybe I should make a clarification about gesture types. Cat found 66 gesture types, gestures categorized by sharing the same physical form, so within the 4531 instances, these 66 types would be used many times. The journal article just says 3 field seasons, but I think that Cat spent 18 months there total. Given long enough, it should be possible to collect a comparable number of gesture instances from all species of great apes, and that many instances is necessary for statistical analysis. If you're comparing the meaning of each gesture type for each individual also by age sex and rank, all of those layers break your data into smaller and smaller chunks for comparison, so it's necessary to start with a really large dataset, e.g. 4531 instances. If you then want to look at whether gesture meaning is modified syntactically (by affixes, series order, paralinguistic features like size and direction), then the number of instances available are usually too few for meaningful statistical analysis. We need a lot of data.

    2. Chimps and other great apes gesture throughout the day, but then their daily activity varies. As far as my experience with bonobos, sometimes in the mornings they would travel non-stop, other times they groom for over an hour, and sometimes they feed in the same tree all morning. To make sure that we catch their gesturing, we film when two individuals come within 5 metres of each other, a reasonable range for a form of communication that requires visual attention or body contact. Gesturing is a short-distance form of communication used during social interactions, whereas vocalizations communicate non-discriminatorily; anyone can hear them and extract information. Gesturing's a bit more subtle; it's directed.

      Hopefully with my bonobo data, we'll be able to compare gesture types and meanings between bonobos and chimpanzees. So far, it seems that the chimpanzee repertoire is species-typical, with all members of the species both wild and captive using the same gesture types. However, we know from ape language studies (Kanzi, Washoe, Koko, Nim etc.) that great apes can learn new gestures/symbols, so it's definitely possible that individuals or groups could have their own unique gestures. Learning is just a more costly way of acquiring gestures, and the simplest explanation for all chimps having largely the same gestural repertoire is that they are species-typical, though a few might be learned. In another paper, Cat found that of her 66 chimp gesture types, 60% were shared with gorillas, and 80% with orangutans. That's just gesture types, not meanings, so the next big paper is going to be comparing gesture types and their meanings across all great ape species!