A central issue in the evolution of social complexity and the evolution of communication concerns the capacity to communicate about increasingly abstract objects and concepts. Many animals can communicate about immediate behavior, but to date, none have been reported to communicate about behavior during future interactions. In this study, we show that a special, unidirectional, cost-free dominance-related signal used by monkeys (pigtailed macaques: Macaca nemestrina) means submission (immediate behavior) or subordination (pattern of behavior) depending on the context of usage. We hypothesize that to decrease receiver uncertainty that the signal object is subordination, senders shift contextual usage from the conflict context, where the signal evolved, to a peaceful one, in which submission is unwarranted. We predict and find that deceasing receiver uncertainty through peaceful signal exchange facilitates the development of higher quality social relationships: Individuals exchanging the peaceful variant groom and reconcile more frequently and fight less frequently than individuals exchanging signals only in the conflict context or no signals. We rule out alternative hypotheses, including an underlying reciprocity rule, temperament, and proximity effects. Our results suggest that primates can communicate about behavioral patterns when these concern relationship rules. The invention of signals decreasing uncertainty about relationship state is likely to have been critical for the evolution of social complexity and to the emergence of robust power structures that feed down to influence rapidly changing individual behavior.cost-free signal ͉ social complexity ͉ subordination ͉ uncertaintyreduction ͉ innovation

Our understanding of social communication and emotional behavior in nonhuman primates has advanced considerably through research over the past half century. Chimpanzee facial displays have typically been described as highly graded communicative signals, but we propose an additional distinction: blended displays. They appear to be morphologically and acoustically similar to the expressions in ≥2 prototypical/parent categories. We describe the facial and vocal communicative repertoire of chimpanzees and examine how they use graded and blended signals in different social contexts. Data from behavioral observations revealed that they used facial displays differently depending on the social context. Specifically, the variability can be explained by 7 factors representing nervousness and distress, agonism, contact reassurance, excitement, greetings, play, and vigilance. Additionally, the use of blended displays was not simply divided between the contexts that elicited the parent types, nor were they used in totally unique contexts. Instead, the data showed that the contextual use of blended displays is primarily correlated with the social contexts that elicited only one of the parent expressions. Thus, the blended displays appeared to reflect conflicting internal motivational states in the sender, instead of expressing features of the external environment. We proffer several possible explanations for how the blended

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Previous experience affects how young primates respond to challenging social situations. The present retrospective study looked at one aspect of early experience, the quality of the mother-infant relationship, to determine its relationship to young bonnet and pigtail macaques' responses to two social challenges: temporary maternal separation at 5-6 months and permanent transfer to an unfamiliar peer group at 16-17 months. Relationship quality was measured quantitatively on 30 macaque mother-infant pairs with the Relationship Quality Index (RQI), the ratio of relative affiliation to relative agonism as previously applied to capuchin monkeys. Infants with high RQI values had amicable mother-infant relationships and infants with low RQI values had agonistic mother-infant relationships. Young monkeys with amicable and agonistic relationships showed consistent differences in behavior before, during, and after each social challenge, supporting the hypothesis that juveniles from amicable mother-infant relationships based on the RQI coped more effectively with social challenges than did juveniles from agonistic mother-infant relationships. Results suggest 1) characteristic amicability or agonism in early mother-offspring macaque relationships has the potential to influence offspring behavior in tense social contexts and 2) the RQI is useful as one of a coordinated suite of methods for studying the development of social skills.

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