The Adaptive Value of Complex Socio-Communicative Behavior

Human spoken language represents the most elaborate communication system, however the selection pressures leading to its emergence are still uncertain. Unlike humans, bonobos and chimpanzees do not have language. However, bonobos may have been subjected to similar selection pressures as early hominins, subsequent to their phylogenetic split from chimpanzees roughly 1.5 million years ago. The current study investigated the similarities and differences in sociality and communicative production between bonobos and chimpanzees in captive settings, using 9, 10-minute focal follows for each individual. Analyses revealed a significant positive correlation between social proximity score and total communicative signals produced, as well as a significant positive correlation between the proportion of time spent playing and total communicative signals produced, for both bonobos and chimpanzees. Additionally, a significant negative correlation was found between the proportion of time spent grooming and total communicative signals produced. Furthermore, a MANOVA indicated a significant species differences in overall communicative production and social proximity score. Specifically, bonobos produced significantly more signals and spent more time in close proximity to conspecifics than chimpanzees. These data are consistent with previous findings that bonobos travel in larger social groups, have greater flexibility in their communicative production, and have the largest communicative repertoires of all non-human ape species. The multifaceted relationship between sociality and communication, and species differences in socio-communicative behavior observed in bonobos and chimpanzees, can provide insight into the evolutionary origins of human spoken language and complex social behavior