|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: http://www.cell.com/current-biology/abstract/S0960-9822(14)00667-8 . In the news: http://www.bbc.co.uk/news/science-environment-28023630 , http://www.telegraph.co.uk/science/10945811/The-66-gestures-which-show-how-chimpanzees-communicate.html). 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.