Onset and early use of gestural communication in nonhuman great apes.

The early gesturing of six bonobos, eight chimpanzees, three gorillas, and eight orangutans was systematically documented using focal animal sampling. Apes' were observed during their first 20 months of life in an effort to investigate: (i) the onset of gesturing; (ii) the order in which signals of different sensory modalities appear; (iii) the extent to which infants make use of these modalities in their early signaling; and (iv) the behavioral contexts where signals are employed. Orangutans differed in important gestural characteristics to African ape species. Most notably, they showed the latest gestural onset and were more likely to use their early signals in food-related interactions. Tactile and visual signals appeared similarly early across all four species. In African apes, however, visual signaling gained prominence over time while tactile signaling decreased. These findings suggest that motor ability, which encourages independence from caregivers, is an important antecedent, among others, in gestural onset and development, a finding which warrants further investigation.