ABSTRACT
Human development is marked by extended immaturity, necessitating extended care throughout infancy and childhood, facilitating advanced cognitive, social, and cultural skill acquisition. Parallels of extended development are also present in our closest living relatives, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes), which differ markedly in their social systems. Bonobos live in more tolerant, female-bonded societies, while societies of chimpanzees are more hierarchical, and male-dominated. These differences in social ecology may thus also shape the pace and nature of early behavioural development.

However, systematic, quantitative comparisons of developmental patterns of bonobos and chimpanzees are very limited, and results are conflicting. Hence, this study addressed this crucial gap by systematically examining behavioural development in bonobo and chimpanzee infants living in two populations (Kokolopori community, Kokolopori Bonobo Reserve, DRC, N = 21; Ngogo community, Kibale National Park, Uganda, N = 22) in their natural environments. We specifically focused on infants aged 0–5.5 years and investigated behavioural markers of independence (travel, feeding, grooming) and spatial independence.

Our results showed similar developmental trajectories but marked species differences concerning specific social and spatial patterns. While chimpanzee infants exhibited prolonged dorsal riding, bonobo infants travelled independently more often and maintained greater distances from their mothers. In addition, age, sibling presence and maternal parity, but not sex, influenced behavioural patterns.

These findings highlight the importance of systematic comparative developmental research across great ape populations for understanding both species-specific adaptations and the broader evolutionary foundations of extended development in the human lineage.