The early gesturing of six bonobos, eight chimpanzees, three gorillas, and eight 10 orangutans was systematically documented using focal animal sampling. Apes' were 11 observed during their first 20 months of life in an effort to investigate; i) the onset of 12 gesturing; ii) the order in which signals of different sensory modalities appear; iii) the 13 extent to which infants make use of these modalities in their early signaling; and, iv) the 14 behavioral contexts where signals are employed. Orangutans differed in important 15 gestural characteristics to African ape species. Most notably, they showed the latest 16 gestural onset and were more likely to use their early signals in food-related 17 interactions. Tactile and visual signals appeared similarly early across all four species. 18In African apes, however, visual signaling gained prominence over time, while tactile 19 signaling decreased. The current findings suggest that motor ability, which encourages 20 independence from caregivers, is an important antecedent, among others, in gestural 21 onset and development, a finding which warrants further investigation. 22 23

Contemporary research hypothesizes that biological inheritance and 16 ontogenetic factors shape the development of gestural communication in nonhuman 17 great apes. Little is known, however, about the specific role that mothers play in the 18 acquisition of their infants' gestures. We observed six bonobo (Pan paniscus) and four 19 chimpanzee (Pan troglodytes) mother-infant dyads and recorded their gesture types and 20 frequency. We analyzed all behavioral contexts in which gestures occurred as well as 21 the play context alone. Infants of both species were unlikely to share gestures with their 22 mother or unrelated adult females. Gestural sharing was, however, prevalent within age 23 groups. Within and across species, infant-infant and mother-mother groups were 24 homogenous regarding the types of gestures they shared; although there was individual 25 variation in the frequency of gesture use. Our findings provide limited evidence that 26