Play behavior is more highly developed in mammals than in other classes. Mammals have distinct, separate behavior for play but most of the actions can be modified into prey capture, escape or fighting later in life. Young animals play more than older ones and their motivation appears to be entertainment.

Play is most important in species that take a long time to mature. It can sometimes be observed in group behavior in juveniles, adolescent and adult peer group relationships. Playing youngsters may involve members from every level of the hierarchy as well as their own siblings and cohort members. Play encompasses mock situations that serve to train the young, develop survival skills and provide practice in different behaviors. A single behavior may be repeated or there may be a switch from - attack to defense, from fighting to prey killing, or from attack to fleeing. Often a characteristic exuberance is evident and play behavior often shares species-specific characteristics.

General physical fitness is promoted by play behavior. The young acquire species-specific action patterns and improve actions requiring accurate coordination. A young animal that does not learn to use these effectively may be unable to escape predators or catch food. Play enlarges the individual's experience. As a communal activity it provides a reason for young animals to seek the company of others while their mother is absent. For example puppies deprived of contact with other dogs when they are 3-10 weeks old will not develop normal social responses.

Play is a true activity in its own right and the internal motivating factors, which affect it, change with age. The internal stimulus to play diminishes in intensity with age, although adults do play. (The black-backed jackal uses play to determine strength and social status without fighting). Adults will play with babies and predators playing with prey learn by practice.