In fact, play can be scientifically proven to be useful. After carefully documenting the play behavior of the Alaskan grizzlies over more than fifteen years, the Fagens (..) found that the bears that played the most were the ones who survived best. This is true despite the fact that playing takes away time, attention, and energy from activities like eating, which seem at first glance to contribute more to the bears’ survival. The real question, then, is why and how play is useful.

One major theory is that play is simply practice for skills needed in the future. The idea is that when animals play-fight, they are practicing to fight or hunt for real later on. But it turns out that cats that are deprived of play-fighting can hunt just fine. What they can’t do — what they never learn to do — is to socialize successfully. Cats and other social mammals such as rats will, if seriously missing out on play, have an inability to clearly delineate friend from foe, miscue on social signaling, and either act excessively aggressive or retreat and not engage in more normal social patterns. In the give-and-take of mock combat, the cats are learning what Daniel Goleman calls emotional intelligence—the ability to perceive others’ emotional state, and to adopt an appropriate response.

“I believe that play teaches young animals to make sound judgments,” Bob Fagen told me that day in Alaska. “For instance, play-fighting may let a bear learn when it can trust another bear and, if things get too violent, when it needs to defend itself or flee. Play allows ‘pretend’ rehearsal for the challenges and ambiguities of life, a rehearsal in which life and death are not at stake.” Play lets animals learn about their environment and the rules of engagement with friend and foe. Playful interaction allows a penalty-free rehearsal of the normal give-and-take necessary in social groups.
(..)
Animals that play a lot quickly learn how to navigate their world and adapt to it. In short, they are smarter. Neuroscientist Sergio Pellis of the University of Lethbridge in Canada, and neuroscientist Andrew Iwaniuk and biologist John Nelson of Monash University in Melbourne, Australia, reported that there is a strong positive link between brain size and playfulness for mammals in general. For their study, which was the most extensive quantitative comparative study of juvenile play ever published, they measured brain size and tabulated play behavior in fifteen species of mammals that ranged from dogs to dolphins. They found that when they made allowances for differing body size, the species with larger brains (compared with body size) played a lot and the species with smaller brains played less. [T]he amount of play is correlated to the development of the brain’s frontal cortex, which is the important brain region responsible for much of what we call cognition: discriminating relevant from irrelevant information, monitoring and organizing our own thoughts and feelings, and planning for the future. In addition, the period of maximum play in each species is tied to the rate and size of growth of the cerebellum. This part of the brain lies in back of and below the main hemispheres, and contains more neurons than the whole rest of the brain. Its functions and connections were once thought to be primarily for coordination and motor control, but through new brain-imaging techniques researchers are finding that the cerebellum is responsible for key cognitive functions such as attention, language processing, sensing musical rhythm, and more.

Byers speculates that during play, the brain is making sense of itself through simulation and testing. Play activity is actually helping sculpt the brain. In play, most of the time we are able to try out things without threatening our physical or emotional well-being. We are safe precisely because we are just playing. For humans, creating such simulations of life may be play’s most valuable benefit. In play we can imagine and experience situations we have never encountered before and learn from them. We can create possibilities that have never existed but may in the future. We make new cognitive connections that find their way into our everyday lives. We can learn lessons and skills without being directly at risk.

//Stuart Brown, Christopher Vaughan, Play: How it Shapes the Brain, Opens the Imagination, and Invigorates the Soul