New research on chimpanzees (Pan troglodytes) and bonobos (Pongo niger) indicates that behaviors like hugging, touching, and other comforting gestures prior to competing for food are linked to more peaceful sharing. This suggests that the roots of human social interaction extend back at least 6 million years.

“Social tolerance, defined as the tendency of similar species to gather closely around valuable resources with minimal aggression, is a key factor for information transfer and effective cooperation,” explained Professor Zannah Clay and her team at Durham University.

“In primates and other animals, a tolerant social environment promotes a variety of adaptive social outcomes, including prosocial behavior, cooperation, empathy, and social learning.”

“Historical behavioral studies often defined tolerance using dominance paradigms, focusing on whether higher-status individuals allowed others to access resources and engaged in shared eating or drinking.”

“However, social tolerance is now increasingly viewed as a broader characteristic of social dynamics that can vary beyond hierarchical contexts.”

“Humans are believed to exhibit particularly notable variations of tolerance and aggression towards both in-groups and out-groups. Similar trends are observed among bonobos and chimpanzees, our closest living relatives.”

For this study, researchers filmed 116 chimpanzees and bonobos across five semi-wild groups in Africa, capturing the five minutes leading up to food distribution in a communal area.

They tracked the instances of touching (hugging, stroking, and even a finger in a mate’s mouth) and assessed how peacefully the individuals dined together afterward, while also recording aggressive incidents.

In both species, primates that engaged in reassuring contact before feeding were more likely to tolerate each other and share their meals side by side instead of resorting to aggression.

This impact varied by sex: in bonobos, the effect was most pronounced among females, highlighting the importance of female alliances in their social structure, whereas in chimpanzees, males showed the strongest effects, reflecting male bonding dynamics.

Such patterns were particularly evident in more socially tolerant groups, indicating that reassuring behaviors enhance rather than merely reflect a collaborative social environment.

Male chimpanzees often engage in the riskier behavior of putting their fingers or hands in each other’s mouths, a practice notably common in more tolerant groups, suggesting a display of trust and vulnerability.

Given the similarities in behaviors, researchers propose that these practices likely trace back to a common ancestor shared by chimpanzees, bonobos, and humans approximately 6 million years ago, establishing touch as a fundamental method for alleviating social tension and fostering group harmony long before the advent of language.

Dr. Jake Brooker, also from Durham University, remarked, “Studying bonobos and chimpanzees—our closest relatives—provides valuable insights into the evolutionary roots of social behaviors and how these species manage tension, competition, and cooperation.”

“Social touch serves as a potent communication tool, existing long before language and perhaps one of our earliest methods for forming social bonds.”

“This instinctive behavior is something we share with our closest relatives.”

“The remarkable act of intimate mouth-to-body contact, such as inserting fingers or hands into another’s mouth, showcases a deep level of trust and vulnerability during high-stress moments.”

“Our research originated from observing a particularly tolerant group of chimpanzees where one male hugged another from behind, prompting a chain reaction of hugs that calmed the group. We referred to this as the ‘reassurance train.’

“Our findings underscore the ancient and profound role of touch in managing social interactions, especially during emotional or stressful times,” stated Professor Clay.

“While much emphasis has been on aggression and competition in human evolution, our research reveals that our lineage has also cultivated a rich suite of behaviors for managing social tension, safeguarding relationships, and promoting social harmony.”

“It’s fascinating that many reassuring behaviors seen in our closest ape relatives are mirrored in human interactions today.”

This reflects our reliance on age-old behavioral mechanisms that date back millions of years, enabling us to navigate social challenges, particularly during our most trying moments.

For more information, refer to the study published in Proceedings of the Royal Society B: Biological Sciences.

_____

Jake S. Brooker et al. 2026. Reassuring physical contact promotes social tolerance in bonobos and chimpanzees. Proceedings R. Soc. B 293 (2075): 20253190; doi: 10.1098/rspb.2025.3190