The Widespread Nature of Play in the Animal Kingdom: Defining Play and Its Criteria

Play is not limited to mammals and birds but may be widespread in the entire animal kingdom./nThe definition of play is not a simple issue and requires a generic definition to cover all types of play and species, including phenomena that are not traditionally considered play and in species once thought unable to play such as fish./nFive criteria for identifying play were developed and are now widely adopted./nPlay has been identified and recorded in invertebrates.