The development of social and spatial independence: Do bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) differ? (#909)
To model the behaviour of early hominoids, a bulk of research has been focusing on humans’ closest relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes). Interspecific comparisons proposed a distinct bonobo-chimpanzee dichotomy in social behaviour and development, e.g. concerning aspects such as social bonds, sexuality and agonistic interactions. However, recent reports of considerable inter-site variability of chimpanzee behaviour challenge this dichotomy. In addition, systematic quantitative comparisons of chimpanzee and bonobo behaviour in groups living in natural environments are still lacking. The aim of the present study was therefore to shed further light on this intriguing issue by studying the ontogeny of social and spatial independence in two bonobo (LuiKotale and Wamba, DRC) and two chimpanzee communities (Taï South, Côte d’Ivoire; Kanyawara, Uganda). We had two questions: First, do social interactions emerge at comparable time points in bonobos and chimpanzees? Second, does spatial independence develop similarly in bonobos and chimpanzees? To answer these questions, we investigated interaction rates and play behaviour as well as mother-infant body contact and proximity. The behaviour of twelve chimpanzee and twelve bonobo infants was recorded during 1200 and 600 hours of observation respectively, using a focal/time sampling protocol, which resulted in a total of 8562 sample points. Our results showed that conspecific interaction rates of bonobos increased compared to those of chimpanzees during the second year of life. In addition, bonobo infants showed a higher frequency of social play while chimpanzee infants engaged more often in solitary play involving objects. Concerning the development of spatial independence, bonobo infants stayed in closer proximity to their mothers than same-aged chimpanzee infants. The frequency of body contact did not differ between the species, but was influenced by mothers’ experience (i.e. parity). Overall, our findings provide substantial evidence that bonobos and chimpanzees differ in patterns related to social and spatial development. Results will be discussed in terms of hypotheses concerning self-domestication, social structure and tool use.