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Bergman, T. J., Beehner, J. C., Cheney, D. L., & Seyfarth, R. M. (2003). Hierarchical classification by rank and kinship in baboons. Science, 302(5648), 1234–1236.
Abstract: Humans routinely classify others according to both their individual attributes, such as social status or wealth, and membership in higher order groups, such as families or castes. They also recognize that people's individual attributes may be influenced and regulated by their group affiliations. It is not known whether such rule-governed, hierarchical classifications are specific to humans or might also occur in nonlinguistic species. Here we show that baboons recognize that a dominance hierarchy can be subdivided into family groups. In playback experiments, baboons respond more strongly to call sequences mimicking dominance rank reversals between families than within families, indicating that they classify others simultaneously according to both individual rank and kinship. The selective pressures imposed by complex societies may therefore have favored cognitive skills that constitute an evolutionary precursor to some components of human cognition.
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Rendall, D., Cheney, D. L., & Seyfarth, R. M. (2000). Proximate factors mediating “contact” calls in adult female baboons (Papio cynocephalus ursinus) and their infants. J Comp Psychol, 114(1), 36–46.
Abstract: “Contact” calls are widespread in social mammals and birds, but the proximate factors that motivate call production and mediate their contact function remain poorly specified. Field study of chacma baboons (Papio cynocephalus ursinus) revealed that contact barks in adult females were motivated by separation both from the group at large and from their dependent infants. A variety of social and ecological factors affect the probability of separation from either one or both. Results of simultaneous observations and a playback experiment indicate that the contact function of calling between mothers and infants was mediated by occasional maternal retrieval rather than coordinated call exchange. Mothers recognized the contact barks of their own infants and often were strongly motivated to locate them. However, mothers did not produce contact barks in reply unless they themselves were at risk of becoming separated from the group.
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