Dr Nicholas Newton-Fisher has published a paper on ‘Grooming decisions under structural despotism: the impact of social rank and bystanders among wild male chimpanzees’ in the journal Animal Behaviour.
Understanding the evolution of cooperation remains a central concern in studies of animal behaviour, with fundamental issues being how individuals avoid being cheated, or ‘short-changed’, and how partners are chosen. Economic decisions made during social interactions should depend upon the availability of potential partners nearby, as these bystanders generate temptations to defect from the current partner. The influence of bystanders is highlighted in two theoretical approaches, biological markets theory and parcelling, both economic models of behaviour. Here, Dr Newton-Fisher and his research team tested predictions of these models using the grooming behaviour of wild male chimpanzees, Pan troglodytes, living under strong structural despotism, where grooming is exchanged both for agonistic support and for itself, and so they have provided the first investigation of both presence and value of bystanders on chimpanzees’ grooming decisions.
Dr Newton-Fisher’s research has found that male chimpanzees take into account the relative value (rank) of bystanders compared to that of their current partner, with this more important than bystander numbers. High-ranking bystanders appeared to generate incentives to defect from a potentially cooperative interaction and it has been found that grooming effort was parcelled into discrete episodes, with smaller parcels used when a bystander outranked the current partner. The number of bystanders also generated a temptation to defect, as bidirectional (reciprocated) bouts were more likely to occur with fewer bystanders. Such bouts were more likely with smaller rank distances between groomer and recipient. No influence of grooming relationship on initial investment was found: groomers did not appear to trust that they would receive grooming in return, even from those with whom they had a history of strongly reciprocal grooming. The findings of the research team are consistent with an economic-benefits, markets-based approach, but not a relationship model paradigm. The work highlights the importance of considering the immediate social context (number and quality of bystanders) in studies of cooperation.
The full article is available to read here.