Physical touch before a tense moment can keep the peace. That is the finding of a new study led by Durham University in the UK, which analyzed the reassuring body contact behaviors of bonobos and chimpanzees, the two ape species most closely related to humans.
The study, published in Proceedings of the Royal Society B: Biological Sciences, tested whether reassuring body contact such as embracing, touching, and kissing improved social tolerance between individuals in competitive situations. Researchers filmed 116 individuals across five semi-wild groups during a controlled five-minute window before food was released into a shared, restricted space. The setup was designed to mimic the social tension of natural resource competition, such as the kind that occurs around fruiting trees.
The results showed that individuals who engaged in more reassuring touch before those feeding events subsequently spent more time co-feeding alongside others. That finding points to a direct connection between pre-competition physical contact and peaceful resource sharing. Researchers recorded who touched whom, in what way, and how much time each individual then spent feeding near others. They also tracked aggression events before, during, and after the feeding windows.
The patterns were not identical across the two species. Within bonobos, the strongest effect appeared among female-female pairs, which is consistent with the central role female alliances play in bonobo society. In chimpanzees, the effect was strongest among male-male pairs, reflecting the importance of male bonds in that species' social structure. In both species, the effects were clearest in the more socially tolerant groups, suggesting that alliance relationships reinforced by reassurance before feeding may function to maintain a tolerant social climate.
The researchers also documented a striking behavior in chimpanzees. Males, in particular, engaged in high rates of what the team described as risky intimate contact, including placing fingers or hands in each other's mouths. These acts of physical vulnerability appeared considerably more often in the more tolerant groups, suggesting the behavior may function as a signal of trust between individuals.
The close similarity between bonobo and chimpanzee reassurance behaviors led the team to conclude that the practice likely has a common evolutionary origin. The researchers believe it dates back at least 6 million years, to the common ancestor shared by humans and these two ape relatives.
According to the researchers, this means friendly touch may function as a flexible, short-term tool to manage social tension and competition, maintain social relationships, and preserve group harmony. That conclusion carries implications beyond the study of apes, pointing toward a possible evolutionary basis for the role of physical touch in human social life as well.
