How Target Animacy Affects Manual Laterality in Hylobatidae: The First Evidence in Northern White-Cheeked Gibbons (Nomascus leucogenys)

Abstract

Our study presents the first evidence on how target animacy impacts on manual laterality in the Hylobatidae and contributes to filling the knowledge gap between monkeys and great apes in primate evolution of emotional lateralization. Eleven captive individuals of northern white-cheeked gibbons (Nomascus leucogenys) were chosen as focal subjects. There were significantly more ambipreferent individuals than left/right-handed individuals for both inanimate (χ2(1, n = 11) = 7.364, p = 0.007) and animate (χ2(1, n = 11) = 4.455, p = 0.035) targets, meaning no significant group-level hand preference. The right hand was more frequently used than the left hand for inanimate targets whereas the left hand was more frequently used than the right hand for animate targets, although the interaction between target animacy and hand use was not significant (proportion: F1, 10 = 0.283, p = 0.607; rate: F1, 10 = 0.228, p = 0.643). Our findings in N. leucogenys could not fully support either the tool use theory or the right hemisphere hypothesis.