Division of Labour:A Democratic Approach towards 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 analysing 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 revealed both the functional and adaptive significance of manual asymmetries respectively, and pointed towards the division of labour 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. manoeuvring 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. We then describe the division of labour 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.