Applying biological markets theory to a captive group of brown capuchin monkeys (Cebus apella) - CII/ISPA/PI-05-010 (2005 to 2006)

Research Team:

António Santos (Project Leader)
João Daniel
Mónica Guimarães


Project's Summary:

Operational definition of relationships in animals can be all to easy to confuse with the human concept of relationships, leading to the implicit assumptions that they are, in fact, equivalent (Barrett & Henzi 2002). This, in turn, may lead to an overestimate of specie’s cognitive abilities.

Proofs of non-human primates’ planning ability are not congruent, therefore suggesting that the formation of long-term relationships is not the result of strategic planning taking place within the head of an individual monkey. However this is not to say that animals’ decisions do not have long-term consequences, nor rules out the possibility that long-term affiliation does occur between certain individuals (e.g. kin) (Barrett & Henzi 2002).

Non-human primate’s social responses may thus take place on a more short-term basis than is usually supposed and frequent partner changes may be the norm, rather than the exception. Increasing attention to the likely short-term benefits of individual action may therefore pay dividends when trying to explain the apparent goals of non-human primates sociality (Barrett & Henzi 2002).

The theories of reciprocal altruism and the iterated prisioner’s dilemma (IPD) have received widespread attention as explanations for the occurrence of altruism between unrelated individuals. Despite the theoretical value of these ideas, they have proved difficult to test in real biological systems. This is a consequence of the problems involved in quantifying precisely the costs and benefits of particular actions, especially when these are in different currencies (Barrett et al. 2000).

The biological markets (Noe & Hammerstein 1994, 1995) approach to the analysis of social dynamics represents a potentially valuable alternative to models based on reciprocal altruism (Henzi & Barrett 2002). This theory conceives grooming as a tradable commodity, and individuals within a primate group as traders that compete with each other in the marketplace exchanging grooming for itself (reciprocal traders) or for other goods (interchange traders). An understanding of market forces as determinants of social interactions thus allows more precise predictions to be made and tested. Such market model assumes that when grooming is exchanged for itself, females will use immediate reciprocation (time matching) in order to avoid being cheated and to obtain equivalent value for their services. However some authors state that reciprocation within bouts may not be necessary if females reciprocate grooming over longer time spans (Manson et al. 2004; Schino et al. 2003).

Another alternative tack to circumvent practical problems of reciprocal altruism and IPD is Roberts & Sherratt (1998) ‘raise the stakes’ (RTS) strategy. This model allows individuals to ‘test the water’ before embarking on a full-blown cooperative relationship as a means of avoiding defection and exploitation. In this view, cooperation needs not take place in an all-or-none fashion, but can build up gradually over the course of a series of interactions, allowing individuals to gain ‘confidence’ or ‘trust’ in their partners. An individual playing RTS will increase is investment in a cooperative interaction if its partner matches or betters the individual’s own last move. The essential nature of Roberts-Sherratt argument nevertheless can be sited within the conception of biological markets (Barrett et al. 2000). In the case of primate’s, infrequent groomers can be expected to show a higher level of uncertainty about their partners than frequent groomers- such individuals may use RTS to reduce the risk of being cheated by an unfamiliar partner.

Although biological markets theory appears to be a promising avenue for the study of animal cooperation, its application to low cost behaviours such as primate’s grooming needs further investigation. In this sense, we think that evaluating some of the specific predictions of biological markets, in a captive group of brown capuchin monkeys (Cebus apella) will enable us to test the applicability of the model to this specie (and in a wider sense to New World monkeys), allowing us to examine whether previous findings on Old World species can be replicated.

In New World primates the function of grooming is not yet so well understood. Work done on brown capuchin monkeys (di Bitetti 1997; Parr et al. 1997) showed that they share some common features with Old World species, although the way they distribute grooming is different (grooming is rank related but performed mainly by higher ranking animals), suggesting a need for re-evaluation of current theories regarding the social function of grooming.

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