Play and Sociality: A Comparative Study in Chimpanzees and Gorillas

Great apes live in complex social groups and have evolved sophisticated systems to communicate emotions and intentions. During social play, individuals acquire information and inter-individual communication serves to regulate and balance the sessions. Communication modality varies in primate species and is influenced by many factors, such as social system, rank, relationship quality between players, age and gender. During play, animals use both gestures and facial expressions to communicate their motivations. Gestures are considered intentional signals, whereas facial expressions can also be the result of an internal emotional state. Therefore, play is a perfect field to explore the dichotomy between emotionality and intentionality. To understand how signals are produced and used during the play session and how they are influenced by the species, we carried out a comparative study on play dynamics in chimpanzees (Pan troglodytes) and gorillas (Gorilla gorilla) . We investigated what parameters affect play modality in these two species that are characterized by strong differences in hierarchical organization and distribution of affiliative behaviours. Social play involving more than 2 players was more frequent in chimpanzees than in gorillas. The unbalanced play sessions characterized by a prevalence of one player over another occurred more often in chimpanzees than in gorillas, even though the probability of escalation was higher in gorillas than in chimpanzees. In gorillas, play asymmetry was positively affected by the number of players involved, which explains the low levels of polyadic play in this species. In conclusion, play dynamics seem to reflect social dynamics in the great apes showing different levels of cohesion and social support.