Reassuring body contact promotes social tolerance in bonobos and chimpanzees

Social tolerance underpins cooperation in humans and other social animals, but its proximate drivers in short-term, competitive contexts remain poorly understood. Reassurance behaviours may enable individuals to pre-empt conflict and signal benign intent, facilitating social tolerance. We tested whether reassuring body contact during anticipation of a collective feeding event promotes cofeeding tolerance in our closest primate relatives. Using a controlled cofeeding paradigm across five semi-wild bonobo and chimpanzee groups (n = 116 individuals), we quantified pre-feeding affiliative contact and measured access to a restricted, depleting food zone. In both species, increased affiliative body contact enhanced subsequent cofeeding tolerance in most groups. Bonobo female-female pairs and chimpanzee male-male pairs engaged in more pre-feeding reassurance than other-sex pairings, aligning with species-specific predictions. However, these trends were only clear for socially tolerant groups. Likewise, vulnerable chimpanzee-specific kissing behaviours were more prevalent in a tolerant group. Our results reveal that reassuring contact may function as a flexible, short-term mechanism to mitigate contest competition and promote group-level tolerance. By identifying a proximate behavioural tool for managing competition in our closest cousins, our findings demonstrate the important role that friendly social behaviours play in negotiating the trade-off between competition and cooperation, as is essential to our own species' survival.