Social Complexity and the Evolution of Intelligence: grooming reciprocity in chimpanzees
| Principal Investigator: | Dr Nicholas E. Newton-Fisher |
|---|---|
| Project dates: | 2009 – 2012 |
| Funding: | Leverhulme Foundation |
Aims
The goal of this project is to investigate reciprocity as the driving force behind the evolution of intelligence. Primate/human intelligence is thought to exist to deal with social complexity, but the nature of this complexity is poorly understood and so the selective advantage of intelligence – why it exists – remains unclear. This project examines one particular candidate for social complexity – maintenance of reciprocity in grooming, using a detailed pre-existing dataset from wild chimpanzees to investigate: (1) How is grooming reciprocated? (2) Are different strategies employed to enforce reciprocity? (3) Is grooming reciprocity cognitively demanding? (4) Are reciprocal grooming relationships social ‘safe-havens’? In conjunction with a newly collected dataset, this project will be addressing: (5) Do chimpanzees trade grooming in a biological market & (6) Are there cultural differences in the way grooming bouts are negotiated.
Background
Current evidence suggests that ‘social complexity’ has driven the evolution of primate – including human – intelligence, but despite 20+ years of discussion, little progress has been made in understanding what constitutes this complexity.
To address this deficit, we need to know which social interactions, specifically, are complex and cognitively demanding. This requires detailed studies examining both behavioural strategies that function to solve social problems and the cognitive demands that these impose. Wild chimpanzees are an ideal species with which to conduct such research. They live in large groups, associations between individuals are fluid, and social relationships variable. They show evidence of culture and their intelligence is among the most developed of all non-human primates.
This project will examine the strategies and mechanisms related to one particular social problem – the maintenance of reciprocity in grooming interactions in wild chimpanzees. The aim is to find evidence that this is a behaviourally complex, cognitively demanding, social interaction. Many studies place grooming at the centre of chimpanzee sociality, but surprisingly little attention has been paid to reciprocity in grooming. The nature of grooming reciprocity, strategies used and proximate mechanisms all remain poorly understood.
Objectives
(1) How is grooming reciprocated?
Grooming between chimpanzees appears complex; sometimes one individual grooms without receiving any grooming, individuals can alternate grooming, or both groom simultaneously, and can groom for seconds, or over an hour. It is unclear how much grooming between pairs of individuals is partly or completely reciprocated, or how reciprocity varies across &/or within bouts. To quantify this complexity, we need to know how reciprocity is distributed across different types of grooming.
(2) Are different strategies employed to enforce reciprocity?
My observations suggest that chimpanzees use different behavioural strategies to enforce grooming reciprocation. For example, in some bouts, participants settle to groom without conflict, whereas in others there is a period of ‘negotiation’; initial brief, reciprocated, bursts of grooming followed by either termination or sustained grooming. To understand the behavioural complexity of grooming reciprocity, we need to know the extent to which chimpanzees use these different strategies.
(3) Is grooming reciprocity cognitively demanding?
If reciprocity, as social complexity, is the driving force behind the evolution of primate intelligence, ensuring reciprocity should be particularly demanding cognitively. Reciprocity can arise through three different mechanisms – a by-product of frequent association; a mirroring of social attitudes; or partner-specific mental score-keeping – each increasingly demanding on intelligence. To relate the behaviour to social complexity, we need to know which mechanism is employed and so the extent to which reciprocity in wild chimpanzee grooming is cognitively demanding.
(4) Are reciprocal grooming relationships social ‘safe-havens’?
Some pairs of wild chimpanzees have strongly reciprocal grooming relationships, but the function of these relationships is unknown. My hypothesis is that they represent ‘safe havens’, ensuring access to stress-reducing benefits of grooming that might be otherwise compromised by competition within the group.
(5) Do chimpanzees trade grooming in a biological market?
Chimpanzees groom one another far more than would be necessary for mere hygiene. Traditional explanations for this have posited that grooming functions to build and repair social relationships, but such a view is based largely on untested assumption. An alternative idea is that grooming functions as an exchange of direct benefits, primarily stress reduction, and that it allocated according to market forces. We need to know which of these hypotheses is correct.
(6) Are there cultural differences in the way grooming bouts are negotiated?
Chimpanzees show a variety of behaviours that appear to be socially learnt and certainly vary between communities in ways that are difficult to explain otherwise. Most examples come from material culture, and out knowledge of non-material culture lags behind. Beyond the hand-clasp form, next to nothing is known about cross-community variation in the performance of grooming. Subtle differences in the way an individual grooms, or attempts to negotiate a grooming bout, may well be socially learnt and community specific – we may find good evidence of (non-material) cultural differences between community by examining grooming behaviour, and so we need to know the extent of inter-community variation in the way grooming is performed.
Publications
Newton-Fisher, N. E. & Lee, P.C. (2011). Grooming reciprocity in wild male chimpanzees. Animal Behaviour 81:439-446.