Play is reported in humans, other primates, mammals, and birds. It is most commonly observed in juveniles, but persists into adulthood in many species. Play can be divided into three categories: locomotor play, object play, and social play. The frequency of these play types vary among species, with social play being the most common type overall. In adults, play may facilitate courtship/mating, allow unfamiliar individuals to engage in social assessment, and establish dominance relationships. In contrast, the phylogenetic inertia hypothesis suggests that play existed in the common ancestor of modern primates, and membership in this order is a major predictor of play behavior. This hypothesis, while shedding light on evolutionary origins, cannot explain the function of play in the common ancestor (Pellis 2009).
Play serves different functions in adults and juveniles. While adult-adult play is often focused on mating and social interactions, adult-juvenile play also occurs in humans and great apes. These interactions serve an important learning function for juveniles and also promote bonding and attachment. In human education, early formal instruction often takes the form of games that facilitate cooperative interaction, encourage creativity, and introduce life skills. Human adults manufacture toys that allow children to model child care, resource trading, chores, and physical skills. Mimicry is extensively involved in this learning process, but different human cultures approach the teaching role differently. In industrialized societies, overt instruction during play by a specially trained adult is common. In contrast, many traditional foraging societies avoid formal instruction. For example, the Mbendjele of the Congo consider overt teaching to be an offensive display of social power differences. Instead, Mbendjele children play by mimicing hut building, yam digging, and hunting behavior exhibited by elders as part of "Massana" ritual (Knight 2009).
Humans engage in extensive mating and non-mating related adult play. This pattern is mirrored in chimpanzees, while orangutans engage less frequently in mating play. There are no reported cases of non-mating play in Orangutans, while this is the only type that is observed in gorillas. Different macaque species exhibit different frequencies of adult play: M. mulatta play rarely and M. arctoides play fequently. Across primates, a surprising trend emerges in which adult play (mating and non-mating) occurs more fequently in more solitary species. Humans and chimpanzees provide dramatic exceptions, as do other social mammals like dogs and dolphins. Pellis hypothesizes that play originally developed as a communication device to address unfamiliarity among primates. Since then, it has been coopted for mating and recreational purposes(Pellis 2000). Chris Knight argues that life-long play encourages symbolic behavior that may have significantly contributed to the evolution of human language. Play may also harness "pretending" as a tool for deceptive mimicry (animal calls) that facilitated hunting success (Knight 1998).
Adult play is likely universal in human populations. Recreation activities vary widely among humans, comprising solitary and social pursuits.
Object play is reported to be common among carnivores and dolphins.
As well as words: Congo pygmy hunting, mimicry, and play, , The Cradle of Language, Volume 2: African Perspectives, p.232-252, (2009)
Adult-Adult Play in Primates: Comparative Analysis of Its Origin, Distribution and Evolution, , Ethology, Volume 106, p.1083-1104, (2000)
Ritual/speech coevolution: a solution to the problem of deception, , Approaches to the Evolution of Language, (1998)