Adult Play

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
No Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
MOCA Domain: 
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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).


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
25,000 thousand years ago
Probable Appearance: 
25,000 thousand years ago
Definite Appearance: 
100 thousand years ago
Background Information: 

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).

The Human Difference: 

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).

Universality in Human Populations: 

Adult play is likely universal in human populations. Recreation activities vary widely among humans, comprising solitary and social pursuits.

Occurrence in Other Animals: 

Object play is reported to be common among carnivores and dolphins.

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Moral Sense Speculative


  1. As well as words: Congo pygmy hunting, mimicry, and play, Lewis, J. , The Cradle of Language, Volume 2: African Perspectives, p.232-252, (2009)
  2. Adult-Adult Play in Primates: Comparative Analysis of Its Origin, Distribution and Evolution, Pellis, S. M., and Iwaniuk A. , Ethology, Volume 106, p.1083-1104, (2000)
  3. Ritual/speech coevolution: a solution to the problem of deception, Knight, C. , Approaches to the Evolution of Language, (1998)