Abstract

Studying the similarities and differences in socio-communicative behavior between chimpanzees and bonobos is critical to increasing our understanding of the evolution of human sociality and communication. Both species rely heavily on the use of vocalizations during communicative interactions, although the form and function of these signals may vary between the two ape species. For example, bonobo vocalizations seem to be structurally more complex than those produced by chimpanzees, and calls seem to be directed to individuals not in immediate physical proximity. Both species, however, make use of communicative signals from different modalities concurrently, particularly vocalizations and manual gestures. However, this multimodal communication is more commonly observed in chimpanzees when compared to bonobos, who more frequently use vocalizations exclusively, without signals from additional modalities. In addition, there are a number of marked differences in social characteristics between the two species. Though both species exhibit fission–fusion behavior, chimpanzees do so more often, potentially as a result of their habitat profile and foraging strategies. Differences also exist in terms of dominance and aggression. Chimpanzees live in largely patriarchal societies with strong male–male bonds, whereas bonobos tend to be matriarchal with strong female–female bonds. These differences in communicative and social characteristics are thought to be linked to the ecology of the respective habitats of the two apes and their strategies for resource exploitation. In all likelihood, similarities in feeding ecology played a crucial role in selecting for the advanced cognitive abilities of both species—e.g., producing meaningful communicative signals, regulating competition and group cohesion, and making and utilizing tools to aid in foraging. Similarly, differences in their respective habitats may have led to selection for characteristics resulting in the behavioral differences observed today between the two species. Therefore, a clearer understanding of the similarities and differences between the two species most closely related to humans will provide valuable information into our own evolution by elucidating those characteristics shared among humans and our ape ancestors and those derived in the hominin lineage.