Other species play, but none play for as much of their lives as humans do, or as imaginatively, or with as much protection from the family circle. Human children are unique in using play to explore hypothetical situations rather than to rehearse actual challenges they’ll face later. Kittens may pretend to be cats fighting, but they will not pretend to be children; children, by contrast, will readily pretend to be cats or kittens — and then to be Hannah Montana, followed by Spider-Man saving the day.
And in doing so, they develop some of humanity’s most consequential faculties. They learn the art, pleasure and power of hypothesis — of imagining new possibilities. And serious students of play believe that this helps make the species great.
The idea that play contributes to human success goes back at least a century. But in the last 25 years or so, researchers like Elizabeth S. Spelke, Brian Sutton-Smith, Jaak Panksepp and Alison Gopnik have developed this notion more richly and tied it more closely to both neuroscience and human evolution. They see play as essential not just to individual development, but to humanity’s unusual ability to inhabit, exploit and change the environment.
Dr. Gopnik, author of “The Scientist in the Crib” and “The Philosophical Baby,” and a professor of psychology at the University of California, Berkeley, has been studying the ways that children learn to assess their environment through play. Lately she has focused on the distinction between “exploring” new environments and “exploiting” them. When we’re quite young, we are more willing to explore, she finds; adults are more inclined to exploit.
To exploit, one leans heavily on lessons (and often unconscious rules) learned earlier — so-called prior biases. These biases are useful to adults because they save time and reduce error: By going to the restaurant you know is good, instead of the new place across town, you increase the chance that you’ll enjoy the evening.
Most adults are slow to set such biases aside; young children fling them away like bad fruit.
Dr. Gopnik shows this brilliantly with a game she invented with the psychologist David Sobel (her student, now a professor at Brown). In the game, which has the fetching name Blickets, players try to figure out what it is that makes an otherwise undistinguished clay figure a blicket. In some scenarios you can win even if you’re applying a prior bias. In others you can’t.
Last summer I joined Dr. Gopnik behind a wall of one-way glass to watch her lab manager, Sophie Bridgers, play the game with an extremely alert 4-year-old, Esther.
Seated at a child-size table, Esther leaned forward on her elbows to watch as Ms. Bridgers brought out a small bin of clay shapes and told her that some of them were blickets but most were not.
“You cannot tell which ones are blickets by looking at them. But the ones that are blickets have blicketness inside. And luckily,” Ms. Bridgers went on, holding up a box with a red plastic top, “I have my machine. Blicketness makes my machine turn on and play music.”
It’s a ruse, of course. The box responds not to the clay shapes but to a switch under the table controlled by Ms. Bridgers.
Now came the challenge. The game can be played by either of two rules, called “and” and “or.” The “or” version is easier: When a blicket is placed atop the machine, it will light the machine up whether placed there by itself or with other pieces. It is either a blicket or it isn’t; it doesn’t depend on the presence of any other object.
In the “and” trial, however, a blicket reveals its blicketness only if both it and another blicket are placed on the machine; and it will light up the box even if it and the other blicket are accompanied by a non-blicket. It can be harder than it sounds, and this is the game that Esther played.
First, Ms. Bridgers put each of three clay shapes on the box individually — rectangle, then triangle, then a bridge. None activated the machine. Then she put them on the box in three successive combinations.
1. Rectangle and triangle: No response.
2. Rectangle and bridge: Machine lighted up and played a tune!
3. Triangle and bridge: No response.
Ms. Bridgers then picked up each piece in turn and asked Esther whether it was a blicket. I had been indulging my adult (and journalistic) prior bias for recorded observation by filling several pages with notes and diagrams, and I started flipping frantically through my notebook.
I was still looking when Esther, having given maybe three seconds’ thought to the matter, correctly identified all three. The rectangle? “A blicket,” she said. Triangle? A shake of the head: No. Bridge? “A blicket.” A 4-year-old had instantly discerned a rule that I recognized only after Dr. Gopnik explained it to me.
Esther, along with most other 4- and 5-year-olds tested, bested not just me but most of 88 California undergraduates who took the “and” test. We educated grown-ups failed because our prior biases dictated that we play the game by the more common and efficient “or” rule.
“Or” rules apply far more often in actual life, when a thing’s essence seldom depends on another object’s presence. An arrow’s utility may depend on a bow, but its identity as an arrow does not. Since the “or” rule is more likely correct and simpler to use, I grabbed it and clung.
Esther, however, quickly ditched the “or” rule and hit upon the far less likely “and” rule. Such low-probability hypotheses often fail. But children, like adventurous scientists in a lab, will try these wild ideas anyway, because even if they fail, they often produce interesting results.
Esther and her twin brother, Benny (who played another version of the game), generated low-probability hypotheses as fast as I could breathe. “Maybe if you turn it over and put it on the other end!” “Let’s put all three on!” They were hypothesis machines. Their mother, Wendy Wolfson (who is a science writer), told me they’re like this all the time. “It’s like living with a pair of especially inquisitive otters.”
Alas, Dr. Gopnik said, this trait peaks around 4 or 5. After that, we gradually take less interest in seeing what happens and more in getting it right.
Yet this playlike spirit of speculation and exploration does stay with us, both as individuals and as a species. Studies suggest that free, self-directed play in safe environments enhances resilience, creativity, flexibility, social understanding, emotional and cognitive control, and resistance to stress, depression and anxiety. And we continue to explore as adults, even if not so freely. That’s how we got to the Internet, the moon, and Dr. Gopnik’s lab.
Finally, in the long game of evolution, Dr. Gopnik and some of her fellow scientists hypothesize that humans’ extended period of imaginative play, along with the traits it develops, has helped select for the big brain and rich neural networks that characterize Homo sapiens. This may strike you either as a low-probability or a high-probability hypothesis. But it certainly seems worth playing with.