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Self-directed behaviors, handedness & lateralization in the bonobo (Pan paniscus)

  • Author(s): Everson, Elysa Anne
  • et al.

The bonobo, Pan paniscus, originated from central African chimpanzees (Pan troglodytes) 1-2 million years ago and has been used as a model for the ancestral human condition. This study focuses on the handedness and directional lateralization of a set of behaviors known as self-directed behaviors, which are often used as an index of emotional arousal with regards to the stress response. They arise from unconscious defense mechanisms that are thought to serve as arousal-inhibiting systems within the central nervous system during the stress response. This study was based on the nonintrusive videotaping of a group of 10 captive bonobos living at the San Diego Zoo during two periods about ten years apart. 1,174 self-directed behavior events were identified and micro-analyzed, in nearly 20 hours of recorded observation. The directional laterality and population-level handedness for each self- directed behaviors were calculated, along with individual handedness scores for each bonobo, which were compared to the handedness scores reported previously by others for these same individuals. It was predicted that, on an individual level, there would be a shift away from symmetrical control in the brain of self-directed behaviors. This prediction was confirmed by the observation of several significant individual-level preference determinations in the execution of self- directed behaviors, presumably reflecting a corresponding asymmetrical functional lateralization in the cerebral management of stress. Significant population-level handedness was neither expected nor observed, confirming a lack of population-level bias in this species and supporting the idea that the alignment of lateralization may not be under selective pressure

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