Hand usage in a colony of bonnet monkeys, Macaca radiata

Handedness and its possible inheritance have been studied in a colony of 69 Macaca radiata by observation of hand usage during daily feeding and foraging activities. Each animal was observed for the number of right- and left-handed actions made during two tasks:feeding and searching. Individual animals fell into one of three classes: significantly right-handed, significantly left-handed, and no significant preference. For analysis, handedness was considered as both a directional phenomenon (percentage right-handed usage) and a degree phenomenon (absolute deviation from 50:50 hand usage). Feeding and searching were significantly correlated for both direction and degree. Therefore, laterality for handedness does exist in this primate species. A developmental aspect to laterality was suggested by the positive correlation of degree with age. No mother-offspring correlations were found for either direction or degree and half-sibships were not more similar for either. Thus, there is no evidence for a genetic component to either direction or degree of handedness.