Why do animals like to play? Scientists have often used the word play simply to describe any behavior that does not have any apparent adaptive function. In The Animal Mind, James L. Gould and Carol Grant Gould describe play as an "apparently purposeless activity with no immediate adaptive goal, utilizing species-typical motor programs that are exaggerated in intensity or number of repetitions, or misordered compared to mature behaviour, or mixed together with behaviour appropriate to different contexts."
Writing in The American Naturalist in 1974, Robert Fagen provided a similar account for what constitutes play. When an animal exhibits an "active, oriented behavior whose structure is highly variable, which apparently lacks immediate purpose," according to Fagen, you might reasonably argue that the animal is playing.
The natural world is rife with such "purposeless activities," but might there be a deeper purpose to play than simple joy? It's one thing to figure out what sorts of activities qualify as play, but another to figure out what they're for. Find out the answers to these questions in my latest column at BBC Future: Why do animals like to play?
And, in case you've missed them, here are links to the previous pieces in my BBC Future column, Uniquely Human:
Image: Argo, a border terrier, displays a "play bow." Copyright the author.