The physics of sociality: Investigating patterns of social resource distribution among the Pan species

Humans invest social resources in predictable "circles of friends," from intimate ties to acquaintances. Whether these concentric social bonding dynamics (CSBD) are uniquely human or shared with other primates is unclear. We applied the CSBD model to 24 groups of bonobos and chimpanzees (N = 284) to test for evolutionary continuity and potential age-related changes in social selectivity. Results show that both ape species distribute social resources in ways resembling humans, supporting shared socio-cognitive structuring within the hominoid lineage. Yet clear species differences emerged: bonobos distributed resources more evenly across group members, while chimpanzees concentrated them more selectively. Moreover, chimpanzees-but not bonobos-became increasingly selective with age, mirroring human patterns of intensified interactions with fewer partners in later life. These findings suggest that our closest living relatives structure their social networks in ways that parallel humans', while also pursuing species-specific strategies that reveal both shared evolutionary roots and divergent pathways of primate sociality.