Direct, Indirect and Generalized Reciprocity of Grooming in Long-Tailed Macaques (Macaca fascicularis)

Reciprocation is a key mechanism favouring the occurrence of altruism among non-relatives. Three types of reciprocity have been proposed: direct, indirect and generalized reciprocity. Although all three types are theoretically possible, examining their relative prevalence in real biological systems is key to understand their role in the evolution of altruism. We tested concurrently the occurrence of direct, indirect and generalized reciprocity by analyzing grooming exchanges in long-tailed macaques. The occurrence and timing of grooming interactions between our study animals were extracted from 5-hr long focal sessions. Our various analyses supported the occurrence of direct reciprocity in macaque grooming exchanges. Conversely, we found no evidence for indirect and generalized reciprocity. Macaques may possess the cognitive skills that are thought to be necessary for direct reciprocity to occur. Alternatively, direct reciprocity may be driven by a system of partner-specific emotional bookkeeping of past social interactions that does not require complex cognitive capacities. We suggest generalized reciprocity becomes marginal or absent when animals are given the choice between generalized and direct reciprocation, wheras indirect reciprocity might be too cognitively demanding for non-human animals.