Triadic and collaborative play by gorillas in social games with objects.

Interaction with others over objects has until recently been thought lacking in the social play of non-human great apes, in contrast to that of children; even now, only bonobos have been observed to engage in social play involving objects. Human children's triadic interactions with objects involve joint attention, showing and giving, communication that maintains interaction, and sharing of emotions and experiences. We question assertions that chimpanzees, and non-human great apes in general, lack the key characteristics of children's collaborative play. Here, we show that zoo gorillas play games that are both triadic and collaborative. These games were videotaped at the San Francisco Zoo in five different years and involved five different pairings of gorillas. The context was in most cases playfully competitive, involving objects such as balls, bags and leather pieces as foci of joint attention; the ostensible goal in most games was to gain or keep possession of a particular object. In some episodes, roles as possessor or pursuer of an object were exchanged many times; in others, one gorilla retained possession of an object but encouraged pursuit from a partner. Through gaze and gesture, gorillas invited others to: share interest in and attention to objects; share patterns of play; and re-engage after breaks in play. Sometimes, gorillas would assist others in their efforts to engage in collaborative play: older gorillas encouraged younger partners by 'self-handicapping' their own actions. Collaborative games may occur later in the ontogeny of gorillas than in humans, and depend on the challenges and artifacts available in a particular group's habitat.