Compared with children, adults do not play as much, but social play in adulthood is considered a universal human characteristic. Playful activities contribute to the development of tolerance, cohesion, bonding, and cooperation. However, a study published in Cell Press Current Biology shows that some chimpanzees, just like humans, continue to play frequently throughout their lives and, in particular, before engaging in acts that require collective cooperation.
“We show that adult chimpanzees’ social play can promote a range of cooperative behaviors, from dyadic interactions to complex and risky activities that require coordination among several individuals,” says Liran Samuni of the German Primate Center in Göttingen, Germany, and of the Taï Chimpanzee Project in Côte d’Ivoire. “We identified a strong link between this positive social behavior, known for eliciting feelings of joy, and some of the most complex forms of cooperation observed in non-human species.”
Samuni and his colleagues have been studying three cohesive groups of chimpanzees living in the Taï Forest in Côte d’Ivoire. Although there had been no previous studies on play among wild adult chimpanzees, they recognized that adult males and females in these groups play together regularly. Their play often involves physical actions such as wrestling, nips, slaps, pulls, and chases. The positive nature of these interactions is highlighted through “play faces” and panting vocalizations, which researchers compare to human smiles and laughter.
“Although adult–to–adult social play was not a daily occurrence, it consistently emerged under specific conditions,” says Samuni.
To better understand how play operates in chimpanzee society, they studied play in 57 adult chimpanzees. The researchers found that adult chimpanzees were more likely to engage in social play before taking part in group activities, such as hunting monkeys or defending territory against hostile outsiders. The chimpanzees who played together were more likely to cooperate in these activities, indicating that play may signal cooperative motivation and reinforce collective cooperation.
When chimpanzees played only with one other individual, they frequently involved close social partners, illustrating the strong link between play, familiarity, and trust. Play also occurred more frequently during times of greater social tension, such as during competition for mates or after recent disputes, which suggests to the researchers that play may be a means of relieving tension and resolving conflicts.
The results obtained from the chimpanzees in this study may or may not reflect play in other chimpanzee populations. Samuni explains that this is due to chimpanzees being behaviorally diverse and flexible, with different populations exhibiting unique strategies and behaviors.
The prevalence of adult play in this particularly cohesive population may reinforce the notion that “societies characterized by cohesion and tolerance also exhibit higher frequencies of adult play,” says Samuni.
In future work, they would like to learn more about how Taï Forest chimpanzee play compares with that of other groups of chimpanzees. They are also curious to know whether the chimpanzees consciously decide to play as an intentional strategy to promote engagement, or whether the positive effects of play promote cooperation naturally, without the chimpanzees intending to do so.
