For the next few articles, I will be featuring interviews with female researchers in animal behaviour (from students to assistant professors), talking about a recent discovery they made. This week’s interview is with Kirsty Graham.
Kirsty Graham is a PhD student at the University of St Andrews, Scotland, who works on gestural communication of chimpanzees and bonobos in Uganda and DRCongo. I recently asked her some questions about the work that she does and some exciting recent findings of hers about how these animals communicate. You can check out her personal blog here. Credit: Kirsty Graham
How did you become interested in communication, and specifically gestures?
Languages are fascinating – the diversity, the culture, the learning – and during undergrad, I became interested in the origins of our language ability. I went to Quest University Canada (a small liberal arts university) and learned that I could combine my love of languages and animals and being outdoors! Other great apes don’t have language in the way that humans do, but studying different aspects of communication, such as gestures, may reveal how language evolved. Although my interest really started from an interest in languages, once you get so deep into studying other species you become excited about their behaviour for its own sake. In the long run, it would be nice to piece together how language evolved, but for now I’m starting with a very small piece of the puzzle – bonobo gestures.
How do you study gestures in non-human primates?
There are a few different approaches to studying gestures: in the wild or in captivity; through observation or with experiments; studying one gesture in detail or looking at the whole repertoire. I chose to observe wild bonobos and look at their whole repertoire. Since not much is known about bonobo gestural communication, this seemed like a good starting point. During my PhD, I spent 12 months at Wamba (Kyoto University’s research site) in the DRCongo. I filmed the bonobos, anticipating the beginning of social interactions so that I could record the gestures that they use. Then I spent a long time watching the videos, finding gestures, and coding information about the gestures.
What’s it like working out in the field with chimps and bonobos?
Fieldwork is great! It can be pretty lonely sometimes and physically exhausting, but field observation is imperative for figuring out a species’ natural behaviour. Fieldwork and captive experiments complement one another. At Wamba, the bonobos are very well habituated, so we can observe them at a distance of 5-10m when they’re on the ground. I’m now at Kalinzu doing a pilot study on chimpanzees. Sometimes you have excellent days, where the apes are all travelling together, and sit and groom on a log in a clearing while all the infants are playing. Those are great data days. But sometimes you have a day where it rains and the apes spend all morning in their nests! It’s a mixed bag, but overall it’s a pretty fun job.
I think I know what gestures are from when I communicate with people, but how can you decide what counts as a gesture for a non-human animal?
A gesture is a body movement (arms, legs, head, torso) that is performed intentionally in order to communicate something to another individual. Bonobos raise their arms, flap their legs, shake their heads, thrust their hips, just to name a few gestures. There are silent-visual gestures like waving, audible gestures like clapping, and contact gestures like slapping someone on the back. A gesture should be directed towards another individual (no random arm flailing while sitting on your own); the signaller should check that the recipient is paying attention (what’s the point in waving at you if you’re facing the other way?) and select an appropriate gesture (e.g. a tap on the shoulder if the recipient is looking away); and if the recipient doesn’t respond to the gesture, the signaller should persist or elaborate. These criteria show that the signaller has a goal in mind, something that they want to communicate, and are using gestures to achieve that goal.
What kinds of things do chimpanzees and bonobos gesture about? What have you learned from studying them?
Chimpanzees use around seventy gesture types in the wild, and they produce gestures intentionally, aiming to affect the behaviour of the recipient. Chimpanzee gestures are used to request a variety of behaviour, from begging for food to requesting sex. But chimpanzees are not our only closest living relative – the bonobo is equally related to humans. Comparing the two species offers insight into how gesture evolved. My research so far has focused on the bonobo, trying to fill in this gap in our knowledge.
We found that the bonobos at Wamba have a vocabulary of 68 gesture types. The overlap with published data for chimpanzees (at Budongo research site in Uganda) was roughly 90%. Such a large overlap points toward a genetically channelled repertoire of gestures – if the gestures were all individually learned, we would expect more differences between species and even between populations and individuals. The chimpanzee repertoire overlaps around 80% with orangutans and 60% with gorillas, and so it is likely that our last common ancestor used many of these gestures.
Our study was the first to look at each individual’s “understood repertoire”, which is similar to what linguists would call a “receptive vocabulary” – the words that a person can understand, whether or not they ever use them. One can measure the “expressed repertoire” by seeing what gestures an individual deploys, but for the “understood repertoire”, one must see what gesture types the individual receives and responds to in a way that satisfies the signaller. This is also how I figure out what a gesture means – if Bonobo A does an “arm raise” gesture and Bonobo B responds by starting to groom the signaller, and Bonobo A seems satisfied with that response (i.e. they don’t keep gesturing), then the meaning of “arm raise” in this instance was “please groom me”. In that case, “arm raise” would be in Bonobo A’s expressed repertoire and Bonobo B’s understood repertoire.
When we grouped bonobos by age or by sex, then each group had most gestures in their expressed and understood repertoire. For example, both males and females can both express and understand the gesture “Reach”. In fact, of the 47 gesture types that were seen more than three times, forty-two were both used and expressed by males and females, young and adult. Specific gestures are not being produced only by males and received only by females, or only by young and only by old, rather this is a mutually understood communication system in which all individuals have the potential to be both signaller and recipient for almost all gesture types.
Language is also a communication system where any native speaker can have access to the same words as any other native speaker. This mutual understanding of signals is required to communicate about goals that anyone might want and anyone might give. For bonobos and chimpanzees, these activities include play, grooming, feeding, travelling together, and sex. At some point, it became necessary for our human ancestors to communicate about more than these immediate goals, and therein lies the mystery of language evolution.
How similar are the chimpanzee and bonobo gestures to our own? What can your findings tell us about the evolution of human gestures?
Good question! We don’t know exactly how many gestures humans share with chimpanzees and bonobos because we learn a lot of gestures alongside language. By the time infants are old enough to start using gestures, they are also learning words and conventional gestures of the culture that they’re growing up in. Observation of humans is therefore inadequate for seeing which gestures are shared with other apes. Byrne and Cochet wrote a neat paper, “Where have all the (ape) gestures gone?”, suggesting an experiment to test whether naïve human observers could understand other apes’ gestures.
Our findings tell us that given the overlap of all great ape gestures, early humans likely also shared this gestural repertoire. Gestures are an important way for great apes to communicate, they use them to request food, grooming, and sex. But there are other aspects to communication as well, such as vocalisations and facial expressions. New research that looks at how great ape communication works across all of these modalities is necessary before we can start to answer the difficult questions of how language evolved. If these other forms of communication are sufficient for other species of great apes, then why language?
All photos were provided by Kirsty Graham, with permission.