Anyone who has ever chucked a tennis ball in the general vicinity of a border collie knows that some animals take play very seriously. The intense stare, the tremble of anticipation, the apparent joy with every bounce, all in pursuit of inedible prey that tastes like the backyard. Dogs are far from the only animals that devote considerable time and energy to play. Juvenile wasps wrestle with hive mates, otters toss rocks between their paws, and human children around the world go to great lengths to avoid make-believe lava on the living room floor.
When a dog chases a ball or a child adjudicates relationship disputes in doll-land, something important and meaningful is clearly happening in their minds, says Laura Schulz, a cognitive scientist at the Massachusetts Institute of Technology in Cambridge. “Play has a lot of peculiar and fascinating properties,” she says. “It’s totally fundamental to learning and human intelligence.”
Scientists take play seriously, too. For decades, psychologists, evolutionary biologists, and animal behaviorists, among others, have labored to understand the playful mind. They have given toys to octopuses, set up wrestling matches for rats, trained cameras on wild monkeys in the jungle and on semi-domesticated children on the playground. Their biggest question: What do these creatures get out of playtime? Clarifying the motivations and benefits of play could tell us much about behavior and cognitive development in people and other animals, Schulz says.
Answering this question, however, has proved surprisingly difficult. Some of the most obvious explanations haven’t held up to scientific scrutiny.
One hypothesis, for instance, is that play helps animals learn important skills. But experiments haven’t borne this out. A 2020 study of Asian small-clawed otters living in zoos and wildlife centers found that the most dedicated rock jugglers weren’t any better than their non-juggling friends at solving food puzzles that tested their dexterity, like extracting treats jammed inside a tennis ball or under a screw-top lid.
Researchers were surprised, but the otters were following a long-standing tradition of animals that don’t seem to learn much through play. Previous studies had found that kittens that grow up surrounded by cat toys aren’t especially successful hunters as adults, and playful juvenile meerkats aren’t any better as adults at managing territorial disputes.
As Schulz and a colleague write in the Annual Review of Developmental Psychology, even human children, arguably the most playful creatures in the world, don’t seem to reap any definitive long-term emotional or developmental benefits from pretend play, an elaborate and well-studied form of human play. Whether studies look at creativity, intelligence, or emotional control, the benefits of play remain elusive. “You can’t say that kids who play more are smarter or that kids who engage in more pretend play do better,” Schulz says. “None of that is true.”
Play is actually somewhat rare in the animal world — you’re unlikely to run across a playful rattlesnake, a recreating eagle, or a whimsical bullfrog — which only deepens the mystery of why it exists at all, says Sergio Pellis, a behavioral neuroscientist at the University of Lethbridge in Alberta, Canada, and coauthor of a 2010 book, The Playful Brain. Evolution normally encourages behaviors that help a species survive and propagate. It doesn’t favor fun for fun’s sake. Play “isn’t like eating or sex,” Pellis says. “We have to explain why it shows up in some lineages but not others.”
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