Inttranews Special Report: Katie Slocombe

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After spending eight months observing a group of wild chimpanzees in the Budongo forest in Uganda, Katie Slocombe, a PhD student in psychology at St Andrews University in Scotland, has reported that chimpanzee communication is more complex than even research by Jane Goodall, the world's foremost authority on chimpanzee behaviour, seemed to indicate.
So are we even closer to chimpanzees than many would like to think? And what might Ms Slocombe’s research indicate about the evolution of human language?
Inttranews decided to find out more…

Inttranews: Where did your interest in chimpanzees stem from?

Katie Slocombe: I have always been fascinated with animals and chimpanzees are particularly interesting as they are such complex social animals.

Inttranews: Before visiting Uganda, had you worked with chimpanzees a great deal?

KS: No, I spent a month studying the chimpanzees at Edinburgh Zoo before going to Uganda, just to get a basic understanding of their behaviour and communication systems.

Inttranews: What was the main focus for your research on vocal communication among chimpanzees?

KS: The global aim of my research if to investigate whether chimpanzees are able to produce and understand functionally referential calls as part of their natural communication. Functionally referential communication in this sense means using calls to refer to objects and events in the outside world. More specifically the calls need to be discrete acoustic signals, which are reliably produced only in response to a specific external event. These calls then crucially need to been shown to be meaningful to recipients.

Recently I have focussed on the screams chimpanzees give during agonistic interactions. Acoustic analysis has revealed that victims and aggressors give acoustically distinct screams. Agonistic chimpanzee screams could therefore contain information about the role an individual is taking in an interaction. Chimpanzees unable to see the fight may be able to extract this important social information just by listening and use this information to inform decisions about whether to intervene. We have several behavioural observations which support this hypothesis and indicate that the social information encoded in the screams is valuable to listeners, however we need to formally test this with playback experiments.

Inttranews: In relative terms, can you indicate what percentage of communication between chimpanzees is based on body language and on vocalisation?

KS: I have focussed only on vocal communication so far, so making valid comparisons between gestural and vocal communication is difficult. However, it is important to understand that in their native habitat, where visibility can be as low as a few metres and members of a community can be spread over several square kilometres vocal communication seems to be the ideal modality for communication. Gestural communication (including body language) is obviously still very important in mediating interactions between individuals in close proximity to each other, but vocalisations allows important communication with both distant group members and rival neighbouring groups.

Inttranews: What does your research indicate, if anything, about the evolution of animal sounds into human language?

KS: Human language is one of the only behaviours that continues to distinguish humans from the rest of the animal world. Therefore an understanding of how this complex cognitive ability evolved is of enduring interest. Recent genetic evidence has suggested that until quite recently humans did not possess the oro-facial control required for production of the range of sounds that characterise modern human language. This evidence suggests modern human language has had an astonishingly short time period in which to evolve. One reasonable assumption therefore is that many of the key cognitive capacities that language relies on predate the emergence of human language and these capacities have their evolutionary roots deep in the primate lineage. One of the key cognitive capacities for human language is the ability to use words to refer to external objects and events. If there is evidence that other primate vocalisations can function referentially then this supports the notion that human language builds on key capacities which predate the emergence of modern human language.

Currently there is strong evidence that several monkey species have alarm calls which function referentially. However, despite considerable research effort there is no comparable evidence for any of the great ape species. This is very surprising because apes are thought to be more intelligent than monkeys and apes are more closely related to humans. It also poses considerable problems for some theories of language evolution. My work therefore focuses on this anomaly.

I hope my research will help us understand the evolutionary roots of human semantics; a key component of human language.

Inttranews: Did you find any marked differences in communication between chimpanzees raised in zoos and in the wild? If so, what where they?

KS: In my experience there seem to be remarkably few global differences in vocal communication in wild and captive chimpanzees. Call production and usage seems to be fairly consistent across the two populations. Obviously there are differences due the two different environments (i.e. the stimulus for alarm calling tends to be natural predators such as snakes in the wild, whereas captive chimps will produce alarm calls to things such as cement mixers) and other research indicates there are likely to be mild ‘local dialects’ specific to different populations of chimpanzees. However, in general the same types of calls seem to be given in the same behavioural contexts across the two populations, indicating there may only be a limited role for learning in call production.

Inttranews: Experiments are continuing today in the use of sign language with chimpanzees, gorillas and orang-utans, and there is some evidence of the transfer of acquired signs by parents to offspring. Is any research being carried out on this facet of primate communication?

KS: Questions concerning to what extent natural communication has to be learnt in apes and what mechanisms may under lie this learning if it does occur are very interesting. However to date very little work has been completed on the ontogeny of natural vocal communication in apes. Evidence from other primate species indicates vocal production is largely innate with only small amounts of flexibility available in call usage (e.g. young vervet monkeys given eagle alarm calls to most aerial objects to begin with and gradually learn to narrow this so as adults they only give eagle alarm calls to Martial eagles). However, it seems more likely that there is much more flexibility and room for learning in call comprehension.
Whether social learning between family members is a crucial mechanism for learning to associate certain calls with specific events remains unknown.

Inttranews: As Desmond Morris pointed out in "The Naked Ape", and genetic research has confirmed, human beings are much closer to primates than many would like to remember or believe. What does your research indicate?

KS: Although we may be close to finding evidence for functionally referential communication in chimpanzees, there is still a large chasm between the complexity of the communication systems of humans and apes. I believe many aspects of language are unique to humans and will remain so. However if more research effort were put into investigating the vocal communication of apes, we may find more complexity in these systems and therefore more similarities than we currently see. For instance there is no evidence for any syntactic structure in ape communication. However, we are only just beginning to understand what chimpanzees can understand from each other’s vocalisations. In order to examine syntactic structure, which in chimpanzees may entail call sequences that have a different meaning from the sum of the constituent parts, we first have to understand what the individual calls mean. Therefore, at present, we can’t rigorously test whether chimpanzees have basic syntactic structure in their natural vocal communication. With more research, vocal communication in apes may be revealed to be more complicated than we currently realise, however I still believe aspects of human language will continue to set us apart from the rest of the animal world.

Inttranews: What is the focus for your research from now on?

KS: I have focused on collecting observational data from wild chimpanzees to date. This is vital to establish whether chimpanzees produce distinct vocalisations in response to discrete external events. However, in order to establish whether these calls are truly functioning referentially we need to test whether the calls are meaningful to listeners. We will do this by conducting playback experiments with captive chimpanzees. Playback experiments enable vocalisations to be heard by subjects in the absence of the context which normally elicits them. The subject’s consequent behaviour will inform the experimenter whether the listener has been able to extract information from the vocalisations alone and therefore whether they are meaningful to the listener.

References and further reading:
Cheney and Seyfarth (1990) How monkeys see the world, University of Chicago Press, London.
Mitani, J. C., Hasegawa, T., Groslouis, J., Marler, P. & Byrne, R. 1992. Dialects in Wild Chimpanzees? American Journal of Primatology, 27, 233-243.
Seyfarth RM, Cheney DL, Marler P (1980) Vervet monkey alarm calls: Semantic communication in a free-ranging primate. Animal Behaviour 28:1070-1094
Slocombe KE and Zuberbuhler K (2005). Agonistic screams in wild chimpanzees vary as a function of social role, Journal of Comparative Psychology, 119(1), 67-77
Zuberbühler K (2000) Referential labelling in Diana monkeys. Animal Behaviour 59:917-927.

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