Social play by adult primates is linked to social style

Although about half of primate species play as adults with other adults, a team of international researchers has just unlocked a key factor in the reason why some don’t. The answer lies in the type of society in which the animals live.

“Despotic and moderately despotic species are markedly less likely to exhibit adult–adult play than tolerant ones,” according to the study recently published in Biology Letters.

Alumni Distinguished Service Professor Gordon Burghardt from the University of Tennessee, Knoxville, worked with scientists from University of Pisa and University of Turin in Italy as well as the University of Lethbridge in Canada on the study, based on a literature review that included 37 species of non-human primates. 

Play behavior is well documented in juveniles, but the new findings illuminate a long-time conundrum about the persistence of play in adults, according to Burghardt, an internationally renowned expert on animal behavior who wrote a book about the origins and evolution of play across animal species.

This research provides one of the most comprehensive analyses to date of adult play in primates. By bridging primatology, anthropology, and sociology, it opens a new perspective on how social systems shape behavior, not only in other species, but in humans.

The analysis found neither physical characteristics, such as size or sexual dimorphism, ecology, or evolutionary relatedness explained the patterns of play. Even closely related species diverge in their play behavior. For example, the study notes that bonobos engage in adult–adult play more frequently than chimpanzees.

The strongest predictor of adult behavior such as play wrestling and other social interactions is what researchers call “social style.” In tolerant species, where social bonds are flexible and cooperation is common, adult play occurs in over 90% of cases. In contrast, in despotic species characterized by rigid dominance hierarchies and high aggression, adult play is almost entirely absent.

The team defined tolerant societies as displaying reciprocal grooming, effective conflict resolution, and less rigid hierarchies. Despotic societies, by contrast, are marked by steep dominance gradients and tense social relationships.

The results suggest that play and tolerance reinforce each other in a “virtuous circle.” In tolerant groups, adult play becomes a strategic tool to negotiate complex relationships, build trust, and maintain group cohesion. In despotic systems, however, the risk of aggression makes play unstable, or even dangerous, effectively suppressing it.

Beyond the animal kingdom, the findings offer a revealing mirror for human societies. “We think these findings can help understand better human social, cultural, and political variation,” Burghardt said.

The researchers draw parallels with hunter-gatherer groups, where egalitarianism fosters humor and play as non-coercive tools of social regulation. By contrast, human authoritarian systems, comparable to despotic primate societies, tend to inhibit creative and cooperative behaviors that do not align with political goals.

The research was inspired by a series of workshops held at UT by the National Institute for Modeling Biological Systems (NIMbioS) on the evolution and function of play. 

“The ideas were developed over some years but only now were we able to collect enough solid data to rigorously test the hypothesis,” said Burghardt, who was a member in both UT’s Department of Psychology and Neuroscience and Department of Ecology and Evolutionary Biology.