Context modulates signal meaning in primate communication
Abstract
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.
Footnotes
- ‡To whom correspondence should be addressed. E-mail: jflack{at}santafe.edu
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Dale Purves, Duke University Medical Center, Durham, NC, and approved November 27, 2006
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Author contributions: J.C.F. designed research; J.C.F. performed research; J.C.F. analyzed data; and J.C.F. and F.d.W. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS direct submission.
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↵ ¶ Other signals used by monkeys also appear to have implications beyond the present interaction, but in a qualitatively different way than has been studied here. For example, Cheney and Seyfarth (48) have shown that baboons recognize one another's close associates. They showed this through an experiment in which they played two unrelated females in proximity to one another sequences of calls that mimicked a fight between their relatives. When call sequences involved relatives, subjects looked (in the 20 seconds after presentation of the stimulus) toward the playback speaker longer than when the call sequences involved nonkin. The dominant female “listener” also was (in the 15 minutes after the stimulus) more likely to supplant her subordinate proximity partner (and the subordinate was more likely to avoid the dominant) in the kin condition. Two critical differences between this study and ours are (i) that the females tested were listening to calls made by others and attending to information (e.g., call frequencies and other features identify the caller) in those calls that was specific to the callers regardless of context and, (ii) although the calls emitted by the combatants were shown to affect the behavior of other group members, the calls were not shown to have causal implications for future interactions, either between the combatants or other group members. Rather, what was shown is that the calls affect the behavior of other group members within 15 min, arguably within the same time step as the conflict in which the calls were produced.
- Abbreviation:
- SBT,
- silent bared-teeth display.
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Freely available online through the PNAS open access option.
- © 2007 by The National Academy of Sciences of the USA
