Division of Labor: A Democratic Approach to Understanding Manual Asymmetries in Non-Human Primates

A consequence of the ‘gold rush’ like hunch for human-like handedness in non-human primates has been that researchers have been continually analyzing observations at the level of the population, ignoring the analysis at the level of an individual and, consequently, have potentially missed revelations on the forms and functions of manual asymmetries. Recently, consecutive studies on manual asymmetries in bonnet macaques, Macaca radiata [Mangalam et al., 2014a; Mangalam et al., 2014b] revealed both the functional and the adaptive significance of manual asymmetries respectively, and pointed towards the division of labor as being the general principle underlying the observed hand-usage patterns. We review the studies on manual asymmetries in capuchin monkeys, Cebus spp. and argue that the observed hand-usage patterns might reflect specialization of the two hands for accomplishing tasks that require different dexterity types (i.e., maneuvering in three dimensional space or physical strength). To this end, we do a step-by-step analysis of the various tasks used in the studies on manual asymmetries in capuchin monkeys, wherein we: (a) analyze the different manual tasks that have been used to study manual asymmetries in non-human primates on the basis of the attributes such as the number of hands required to solve a given task (i.e., unimanual, pseudo unimanual, or bimanual) and the spatiotemporal progression of manual actions (i.e., sequential or concurrent). (b) Determine the forms and functions of manual asymmetries that these tasks can potentially elicit within the broader scope of the behavioral repertoire of an individual, a population, or a species. (c) Qualify the scope of the inter-individual, -population, or -species comparisons. We then describe the division of labor as a general principle underlying manual asymmetries in non-human primates, and propose experimental designs that would elaborate the forms and functions of manual asymmetries in non-human primates, and the associated adaptive value.