ScienceDaily (Jan. 11, 2010) — The grooming behaviour displayed by primates is due to less rational behaviour than often thought. According to a computer model developed by scientists at the University of Groningen, one basic rule explains all possible grooming patterns: individuals will groom others if they're afraid they'll lose from them in a fight.
Two wild long-tailed macaques in the Sacred Monkey Forest, Ubud, Bali in Indonesia. The grooming behaviour displayed by primates is due to less rational behaviour than often thought. According to a computer model developed by scientists at the University of Groningen, one basic rule explains all possible grooming patterns: individuals will groom others if they're afraid they'll lose from them in a fight. (Credit: iStockphoto/George Clerk)
Primates are assumed to reconcile their conflicts by grooming each other after a fight. They are also supposed to carry out intricate trading of grooming for the receipt of help in fights. Professor and theoretical biologist Charlotte Hemelrijk shows in a computer simulation that many patterns of reconciliation and exchange surprisingly emerge simply from fear of losing a fight with another individual. 'This shows that reconciliation and exchange behaviour are not necessarily conscious behaviour', Hemelrijk -- specialist in self-organization in social systems -- states. 'It's simply a consequence of rank and of which primates are in the vicinity of the primate that wants to groom.' The results of the research conducted by the group that worked with Hemelrijk on the computer model have appeared in late December in the journal PloS Computational Biology.
Intelligence
'Primates are intelligent, but their intelligence is overestimated. The social behaviour of primates is explained on the basis of cognitive considerations by primates that are too sophisticated', Hemelrijk continues. 'Primates are assumed to use their intelligence continually and to be very calculating. They're supposed to reconcile fights and to do so preferably with partners that could mean a lot to them.' This would explain why primates prefer grooming partners higher in rank in order to gain more effective support in fights. Moral considerations would bring them to repay the grooming costs by grooming others.
Such behaviour patterns all presuppose a rational thought process, according to Hemelrijk: 'In order to reconcile, the primates must recall exactly which fight they last had and with whom. They must also be able to gauge the importance of each relationship. And for the reciprocity and repayment, they must keep careful track how often and from whom they have received which grooming or support 'service' in order to be able to repay it sufficiently.'
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Journal Reference:
Puga-Gonzalez et al. Emergent Patterns of Social Affiliation in Primates, a Model. PLoS Computational Biology, 2009; 5 (12)
Emergent Patterns of Social Affiliation in Primates, a Model
Ivan Puga-Gonzalez, Hanno Hildenbrandt, Charlotte K. Hemelrijk*
Theoretical Biology, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands
Abstract
Many patterns of affiliative behaviour have been described for primates, for instance: reciprocation and exchange of grooming, grooming others of similar rank, reconciliation of fights, and preferential reconciliation with more valuable partners. For these patterns several functions and underlying cognitive processes have been suggested. It is, however, difficult to imagine how animals may combine these diverse considerations in their mind. Although the co-variation hypothesis, by limiting the social possibilities an individual has, constrains the number of cognitive considerations an individual has to take, it does not present an integrated theory of affiliative patterns either. In the present paper, after surveying patterns of affiliation in egalitarian and despotic macaques, we use an individual-based model with a high potential for self-organisation as a starting point for such an integrative approach. In our model, called GrooFiWorld, individuals group and, upon meeting each other, may perform a dominance interaction of which the outcomes of winning and losing are self-reinforcing. Besides, if individuals think they will be defeated, they consider grooming others. Here, the greater their anxiety is, the greater their “motivation” to groom others. Our model generates patterns similar to many affiliative patterns of empirical data. By merely increasing the intensity of aggression, affiliative patterns in the model change from those resembling egalitarian macaques to those resembling despotic ones. Our model produces such patterns without assuming in the mind of the individual the specific cognitive processes that are usually thought to underlie these patterns (such as recordkeeping of the acts given and received, a tendency to exchange, memory of the former fight, selective attraction to the former opponent, and estimation of the value of a relationship). Our model can be used as a null model to increase our understanding of affiliative behaviour among primates, in particular macaques.
Author Summary
Individual primates distribute their affiliative behaviour (such as grooming) in complex patterns among their group members. For instance, they reciprocate grooming, direct it more to partners the higher the partner's rank, use it to reconcile fights and do so in particular with partners that are more valuable. For several types of patterns (such as reconciliation and exchange), a separate theory based on specific cognitive processes has been developed (such as individual recordkeeping, a tendency to exchange, selective attraction to the former opponent, and estimation of the value of a relationship). It is difficult to imagine how these separate theories can all be integrated scientifically and how these processes can be combined in the animal's mind. To solve this problem, we first surveyed the empirical patterns and then we developed an individual-based model (called GrooFiWorld) in which individuals group, compete and groom. The grooming rule is based on grooming out of fear of defeat and on the anxiety reducing effects of grooming. We show that in this context this rule alone can explain many of the patterns of affiliation as well as the differences between egalitarian and despotic species. Our model can be used as a null model to increase our understanding of affiliative patterns of primates.
Citation: Puga-Gonzalez I, Hildenbrandt H, Hemelrijk CK (2009) Emergent Patterns of Social Affiliation in Primates, a Model. PLoS Comput Biol 5(12): e1000630. doi:10.1371/journal.pcbi.1000630
Editor: Karl J. Friston, University College London, United Kingdom
Received: May 26, 2009; Accepted: November 30, 2009; Published: December 24, 2009
Copyright: © 2009 Puga-Gonzalez et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded by the NWO Cognition and Behaviour program, grant number 051.07.006 (http://ict.nwo.nl/nwohome.nsf/pages/NWOA_6VALUT_Eng). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: C.K.Hemelrijk@rug.nl
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