These data support the hypothesis that both degrees of postural instability and complex manipulation, such as bimanual coordination, may influence the expression of behavioral asymmetries in primates. Both freestanding bipedal posture and coordinated bimanual hand use elicited significantly stronger lateral biases in reaching when compared with quadrupedal reaching. We did not find consistent relationships between an individual’s hand preference for different types of tasks. Population-level directional bias was not evident for any task for rhesus monkeys and was observed only in the bimanual task for chimpanzees. The majority of rhesus monkeys and chimpanzees showed significant lateral biases when reaching from a freestanding posture and when engaged in a coordinated bimanual task. We examined hand preference in 22 rhesus monkeys and 79 chimpanzees using unimanual reaching tasks varying in postural stability and in a coordinated bimanual task. Nonhuman primates afford unique comparative opportunities to evaluate potential routes for the evolution of handedness, as well as to uncover relationships between behavioral lateralization and underlying neural, genetic, and physiological correlates. In turn, they provide clues about both proximal and distal factors that shape the development and expression of association between motor asymmetries and underlying neural substrates. Investigations of behavioral lateralization in nonhuman primates yield important insights into brain–behavior relationships.
Further, whilst there was overall stability in hand preference across time periods, some individuals changed their preferred hand, suggesting there may be individual-level temporal instability of hand preference for certain tasks. These results suggest that posture stability may be important in affecting hand preference. Overall, the results indicate that simple reach elicits laterality at the individual level and is consistent across postures and stable over time, which is consistent with the literature. The findings of this study show temporal stability in simple reach, although only partial between-task consistency. The data showed no significant influence of posture on the strength of hand preference, which contrasts with previous research. Between-task consistency of hand preference was assessed by comparing simple reach and fish in hole, while temporal stability was assessed by comparing simple reach from two points in time: 20. Fish in hole was defined as inserting a stick into a hole in the wall with one hand and then extracting it with the same hand.
Simple reach was defined as extending a hand to grasp a small object, then flexing the limb in a continuous motion, and was examined in quadrupedal, sitting and climbing postures. We investigated hand preference in simple reach and fishing behaviours in a group of 19 chimpanzees at Chester Zoo in the UK. Research on chimpanzee hand preference requires careful examination of important factors such as between-task consistency, temporal stability and posture although few studies have investigated all of these factors in combination.
Studying hand preferences in chimpanzees can provide insights into the evolutionary origins of human hemispheric specialization.
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