The conditions of play—the generation of signals that enhance learning without an accompanying stress response—allow the brain to explore possibilities and to learn from them. Thus, a major function of play may well be to provide practice for real life. The use of a skill or other mental capacity builds up that ability. Evidence from animals suggests that this is the case for play, which usually reflects an animal’s more serious needs. Kittens play at pouncing on objects, a behavior that resembles the hunting they do later. Fawns don’t pounce much, but they do gambol around, a behavior that resembles escape.
So it’s possible that play is practice that prepares animals for the real activity later—when it matters. Researchers of early childhood development have applied the concept of play skill building in Tools of the Mind, a preschool program that uses complex play to get children to make elaborate plans and to exercise self-restraint—practice for the prefrontal cortex, which is involved in self-control. Even before that, the 19th-century kindergarten movement, which popularized the concept of preschool education, was based on the idea that songs, games, and other activities are a means for children to gain perceptual, cognitive, social, and emotional knowledge that prepares them for entering the world.
In mammals, play is necessary for forming normal social connections. Rats and cats raised in social isolation become incompetent in dealing with others of their kind and typically react with aggression. In our species, abnormal play as children often presages dysfunction in adults. A notable feature of psychopaths is that their childhoods lacked in play. Serial killers are often reported to have had abnormal play habits, keeping to themselves or engaging in particularly cruel forms of play. Sometimes such problems are associated with early-life head injury.
Play also transmits culture.8
Middle-class mothers in the United States encourage their infants to pay attention to objects and are likely to prompt them to play with toys such as blocks. Japanese mothers encourage their babies to engage in social interactions while playing—for example, suggesting that they feed or bow to their dolls. Communities that emphasize the development of independence place more importance on object play, while interdependent communities encourage social play.
There are some downsides to play, too. For one thing, though play by definition occurs in the absence of stressors or external threats, children aren’t always good at detecting threats, such as the hazards of fast-moving traffic; thus, play can be dangerous. This problem is not unique to people. In a study of baby seal mortality, 22 of 26 deaths happened when the pups played outside the sight or hearing of their parents. Play can distract people and other animals from recognizing danger. But even here, play may be practice for real life. Risk taking in children’s play may be an important developmental process. It tests boundaries and establishes what is safe and what is dangerous. In the United States, playground equipment has been made very safe, leading to the unanticipated problem that children lack experience with such distinctions, which may lead to trouble later in life.