$"!We investigated the unimanual actions of a biological family group of twelve western lowland $#! gorillas (Gorilla gorilla gorilla) using a methodological approach designed to assess behavior

Our objective was to demonstrate that human right-handedness, is not species specific, precipitated from language areas in the brain, but rather is context specific and inherited from a behavior common to both humans and great apes. In general, previous methods of assessing human handedness have neglected to consider the context of action or employed methods suitable for direct comparison across species. We employed a bottom-up, context-sensitive method to quantitatively assess manual actions in right-handed, typically developing children during naturalistic behavior. By classifying the target to which participants directed their manual action, as animate (social partner, self) and inanimate (non-living functional objects), we found that children demonstrated a significant right-hand bias for manual actions directed towards inanimate targets, but not for manual actions directed towards animate targets. This pattern was Comparisons of handedness patters support the view that human handedness, and its origin in cerebral lateralization is not a new or human-unique characteristic. Additionally these data are consistent with the theory that human population-level right-handedness is a trait developed through tool use that was inherited from an ancestor common to both humans and great apes.

29We assessed the unimanual actions to animate and inanimate targets during naturalistic behaviorof a group 30 of nine captive, zoo-housed chimpanzees (Pan troglodytes). The main aim of this study was to expand on 31 our previous study on gorillas (Gorilla gorilla gorilla), which demonstrated a right-hand unimanual bias to

The influence of the social environment on lateralized behaviors has now been investigated across a wide variety of animal species. New evidence suggests that the social environment can modulate behavior. Currently, there is a paucity of data relating to how primates navigate their environmental space, and investigations that consider the naturalistic context of the individual are few and fragmented. Moreover, there are competing theories about whether only the right or rather both cerebral hemispheres are involved in the processing of social stimuli, especially in emotion processing. Here we provide the first report of lateralized social behaviors elicited by great apes. We employed a continuous focal animal sampling method to record the spontaneous interactions of a captive zoo-living colony of chimpanzees (Pan troglodytes) and a biological family group of peer-reared western lowland gorillas (Gorilla gorilla gorilla). We specifically focused on which side of the body (i.e., front, rear, left, right) the focal individual preferred to keep conspecifics. Utilizing a newly developed quantitative corpus-coding scheme, analysis revealed both chimpanzees and gorillas demonstrated a significant group-level preference for focal individuals to keep conspecifics positioned to the front of them compared with behind them. More interestingly, both groups also manifested a population-level bias to keep conspecifics on their left side compared with their right side. Our findings suggest a social processing dominance of the right hemisphere for context-specific social environments. Results are discussed in light of the evolutionary adaptive value of social stimulus as a triggering factor for the manifestation of group-level lateralized behaviors.