Animals

Play is loosely defined by scientists as vigorous movements performed by the young for no immediate benefit, but which often have counterparts in serious adult behavior. Play may be solitary, as in the studying of and pouncing on a swaying blade of grass by a leopard cub, or social, as when wolf pack-mates romp and nip at one another. It is a common activity among most mammals, especially those most intelligent and social, such as primates, dolphins and carnivores. Invertebrates, fish and reptiles lack play behavior, but it has been observed among birds such as ravens.
Play requires huge amounts of extra energy, and it cuts into food-gathering time. Furthermore, it often exposes the young to predators while at the same time involving potentially dangerous activities. Despite its high costs, mammals continue to play, in part because it teaches them essential skills for survival. For example, young gibbons swing from branches — a critical adult skill — even after falling to the forest floor.
Sometimes play enables adults to display better parenting skills. Monkeys and apes, for instance, show more attention and patience with their offspring when they have had experience as juveniles playing with their younger siblings.