The following story is excerpted from TIME’s special edition, The Science of Childhood, which is available in stores, at the TIME Shop and at Amazon.
Nothing is as natural as a child at play. After a month of little more than eating and sleeping, infants begin to engage in play with their parents and the world around them. Left alone, young children will launch into imaginary play, inventing characters and stories. Put together with peers, children will almost instinctually organize games and activities. Play is so basic to childhood that it is seen even among children in the most dire conditions, in prisons and concentration camps. It is so important to the well-being of children that the United Nations recognizes it as a fundamental human right, on par with the rights to shelter and education. And until recently, American children—finally free from working in the fields or in a factory, as children long had— were allowed to play on their own. In his book Children at Play: An American History, writer Howard Chudacoff describes the first half of the 20th century as a “golden age” of children’s playtime.
Yet today, play is something of an endangered activity among American children. A 2011 article from the American Journal of Play notes that children’s free, unscheduled playtime has been declining steadily over the past half-century. When children do play, it’s more likely to be highly structured—think playdates and enrichment classes. Peter Gray, the author of that article and a psychology professor emeritus at Boston College, says the decline in free play is “at least partly because adults have exerted ever-increasing control over children’s activities,” which should sound familiar to many parents. As even elementary schools come under greater and greater pressure to have their students score well on standardized tests, recess time has been increasingly cut. In 1989, 96% of elementary schools had at least one recess period, yet just a decade later, one survey found that only 70% of even kindergarten classrooms had any recess periods at all.
Gray and other play experts believe these changes have had lasting and negative effects on children. He notes that over the same years that recess and playtime have declined, there have been rises in major depression, anxiety and the suicide rate. “If we love our children and want them to thrive, we must allow them more time and opportunity to play, not less,” Gray has written.
Parents and teachers cutting back on children’s playtime aren’t doing it to be mean— even if it might seem that way to children. They believe that in an increasingly competitive world, there’s less time for a kid to be a kid; that is, free, unstructured play doesn’t have the payoff that another lesson or test-prep class would. They’re restricting playtime because they want their children to thrive. And evolutionary biologists might have once backed them up. Play is, by definition, an activity that has little clear immediate function. That’s what separates it from work or education.
But scientists have learned that free play isn’t just something children like to do—it’s something they need to do. Play keeps kids physically active, all the more important at a time when some 20% of American children are obese—more than triple the percentage from the more play-friendly 1970s. (Early activity habits matter—a 2005 study in the American Journal of Preventive Medicine found that the most active 9-to-18-year-olds remained the most active later in life.) It also exercises their minds and their creativity. More than anything else, play teaches children how to work together and, at the same time, how to be alone. It teaches them how to be human.
Yet one of the best ways to understand why children play is to look at the behavior of young animals. Primates and many other animals play as juveniles, usually with a characteristic gait or signal that demonstrates to other animals that their activities—which can seem aggressive—aren’t meant to be taken seriously, just as children might smile as they play-fight. Play among animals is more conditional on the environment than it appears to be among children—during periods of drought and food scarcity, young animals will cease playing. But play does have a major impact on the brains of animals—and researchers believe it may have a similar impact on the brains of human children.
Rats and cats, like many animals, play with increasing frequency during their juvenile years, before peaking at puberty and, not unlike humans, declining as adults. The development of the cerebellum—the part of the brain that coordinates and regulates muscular activity—follows the same curve, growing rapidly during the juvenile period and then leveling off after puberty. Scientists have theorized that those two facts might be connected. In one experiment, carried out by Sergio Pellis, a neuroscientist at the University of Lethbridge in Alberta, researchers raised two sets of rats from birth, allowing one group to play with other juvenile rats while the other group was kept from playing but otherwise had normal interactions with adult rats. At puberty, the rats were euthanized and dissected. Rats raised in the environment without play showed a more immature pattern of neurons in the prefrontal cortex—the center of the brain in mammals—than did rats who had been allowed to play.
Pellis believes that playing while young helps an animal—and potentially a child— selectively prune the overabundance of cortical brain cells that exist at birth, aiding in the process of maturation. The brain rewires itself under the positive stress of play, as children figure out how to navigate the world and each other.
The apparent randomness of play may be its secret genius. Part of what sets humans apart from other animals is the range of creativity, flexibility and adaptation. That’s precisely what free play—play without the encircling structure of adults—helps promote. Children who can entertain themselves, or play with one another, are unconsciously learning how to adapt themselves to challenges they’ll face further down the road. This is especially true of the pretend play that is most characteristic of human children. (Rats, as far as we know, do not have imaginary friends.) Play, in this way, can be thought of as education by another name—which is another reason we should be concerned that free playtime is now being taken up by structured activities or screen time.
Play also has a vital social drive, as education experts Olivia Saracho and Bernard Spodek have described. Anyone who has observed a school playground knows that children can instantly organize themselves to play in groups. Playing together—and playing with parents—helps children learn to predict and respond to another’s shifting movements and to interpret their desires. It helps them learn how to work together in groups and to share, negotiate and resolve conflicts—especially if parents and other adults give children the space they need to work out problems on their own. Working with juvenile rats, neuroscientist Jaak Panksepp of Washington State University found that play actually changes the brain to make it more pro-social. Of the 1,200 neocortical genes that Panksepp looked at in one rat experiment, about one third of them showed significant changes in activity after just a half-hour of play.
The good news is that after years of cutting back on free playtime for children, smart schools and parents are beginning to understand the benefits of letting kids of all ages roam relatively free. In 2013 the American Academy of Pediatrics’ Council on School Health released a statement arguing that “safe and well-supervised recess offers cognitive, social, emotional, and physical benefits that may not be fully appreciated when a decision is made to diminish it.” At Texas Christian University, Debbie Rhea developed what she calls the LiiNK program, which stands for “Let’s inspire innovation ’n kids.” Children in kindergarten and first grade in the program, which has been tried out in a handful of schools in Texas, are sent out to recess as often as four times a day, in short bursts that add up to an hour. That ensures that the youngest children get more than enough free playtime while encouraging them to sit still when they are in the classroom, knowing a break isn’t too far away.
In an age of standardized testing and intense academic competition, it’s easy to believe that play is one more thing American children will have to do without. But free play encourages the development of the two skills that no robot can replace: creativity and teamwork. Just as the most imaginative and innovative leaders in business and politics needed time away from work to come up with some of their best ideas, so do children need time to play on their own, away from schools and screens and even adults. The payoff will be there down the line—and even more than that, it will be felt here and now. Because let’s not forget—play is fun. That’s the whole point.