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

Abstract

Previously, through manipulative experiments we demonstrated the division of labor in hand usage in free-ranging bonnet macaques wherein we showed that unlike human handedness, the two hands in primates are specialized for different kinds of tasks (maneuvering in 3-d space versus physical strength). In an attempt to explore division of labor in other species, we reviwed the studies on handedness in capuchin monkeys, Cebus spp. and argued that the hand-usage patterns seen in those studies dovetail with the proposed idea of division of labor. Also,through our review we emphasised the need to consider forms and functions while studying laterality, proposed experimental designs that would facilitate studying manual asymmetries and qualified the scope of individual, population, or species comparisons. Further we specualted adaptive value of the division of labor and showed that it is associated with hand performance. Considering the problem of adaptive value in more detail, we mathematically modeled how an asymmetric element at lower level could instigate and govern asymmetries at the next higher level, then to other next higher level and so on; in the end lateralizing the whole system. We used the model to compare a symmetric (employing symmetric motor-action patterns) and an asymmetric (employing asymmetric motor-action patterns) system and showed that asymmetric system not only performed better as compared the symmetric system in terms of time optimization, but also provided greater advantage as the complexity of the task increased. Finally, we tested if the macaques were aware about the difference in maneuvering dexterity of their two hands using apparatus of the hand-performance differentiation task. However, the experimental setup could not provide sufficient evidence for the same.