December 14, 2006Link
To write about the natural history of games and play, I decided to consult an expert. The other day, as I was twirling my 5-year-old daughter around so that she could pretend she could fly with her fairy wings, I asked her why she likes to play.
Charlotte flew on in silence for a moment. I could tell my question seemed strange to her. "Everyone likes to play," she said. "Except for grown-ups."
I suppose the thought of not playing is just too absurd for a 5-year-old to take seriously. Play is a kind of lingua franca for children. Charlotte gets a bit shy when we visit friends, but if there's a child in the house who's ready to share a train set or a princess costume, she takes off in a sprint. I might as well have asked her why she eats or sleeps.
It's hard enough for a child to explain why she likes to play. So imagine trying to get a straight answer from an octopus. For centuries, naturalists have observed animals doing something that looks an awful lot like playing. Horses kick and dance. Dogs wrestle each other to the ground. Warblers toss rocks. And when scientists give octopuses Lego blocks, they seem to have a lot of fun batting them around with their tentacles. But it is a supreme challenge to determine if they are actually playing in the same way Charlotte does, or if we are just projecting our own experiences on an alien animal kingdom. In fact, many scientists who study animal behavior avoid the question of animal play, because it is just so hard to tell if they're having fun.
In his recent book, The Genesis of Animal Play, psychologist Gordon Burghardt argues that play is a distinctive distortion of other kinds of behavior. Play is not a means to an end, but an end in itself. Charlotte loves to wrestle with her younger sister Veronica, for example, but thankfully, she doesn't beat her senseless. Play occurs spontaneously, Burghardt argues, and it is rare in times of stress. And, last but not least, play is fun.
Human play certainly meets all these standards, but Burghardt proposes that many animals play as well. Along with the usual suspects, such as dogs and cats, he offers evidence of play in some unexpected species: turtles, fish and, yes, even octopuses.
With so many potentially playful creatures in the world, the question naturally arises: When and how did play evolve? Burghardt argues that it emerged independently several times in the evolution of animals. Birds, for example, are particularly playful, but they evolved from a common ancestor with alligators, snakes and other reptiles, none of whom show much evidence of play. Certain features seem to make animals prone to playfulness. If parents feed and protect their offspring, for example, young animals don't have to always be searching for food or hiding from predators. They've got free time to fill, in other words. It also helps to have a powerful brain that can produce actions that are more than just automatic reflexes. And play is encouraged by a high metabolism, which gives animals extra energy that they can burn off doing things that are not essential to their immediate survival.
Play may have first emerged in animals simply as a byproduct of their physiology. But it may have evolved into an opportunity for animals to increase their odds of survival and reproduction. Natural selection may have transformed play into a vital part of development in some animals. By playing, young animals can teach themselves about their physical environment. They can also try out complicated maneuvers that could serve them well later in life.
Play is also an opportunity for animals to bond. Rats, for example, like to rough-house with one another, releasing high-frequency chirps that may be a rodent version of laughter. Jans Panksepp of Washington State University found that he could get in on the fun by tickling the rats, which chirp in response. Studies on the brains of chirping rats indicate that chirping is accompanied by a surge in chemicals that create a feeling of pleasure. Playing together, it seems, just feels good to a rat. And the good feeling causes rats to stick together. Chirping rats tend to bond with other chirping rats and to avoid less playful ones.
These bonds can become a matter of life and death. Marc Bekoff, a psychologist at the University of Colorado, spent seven years following coyotes in Wyoming. Some yearling coyotes drifted away from their groups to live alone, while others stayed behind. Fewer than 20% of the stay-at-home coyotes died, while more than 55% of the drifters did. Together, coyotes may be able to find food and fight off rivals better than they can alone. Bekoff thinks that play has a crucial role in keeping coyote groups together. Young coyotes learn how to follow social rules that can prevent conflicts from escalating into all-out battle. They can bite, but not hard enough to hurt. Play also allows coyotes to tamp down the tensions in the coyote hierarchy. During play, dominant coyotes will roll on their backs in submission to lower coyotes.
The evolutionary roots of our own playfulness may run very deep. After all, rats and humans descend from a common ancestor that lived some 100 million years ago. Play certainly seems to tickle some of the same neural circuits in both species. About 60 million years ago, our earliest primate ancestors evolved. They became more and more social, spending their increasingly long lives in large groups. Our primate ancestors evolved exquisitely expressive faces and neural circuits dedicated to recognizing subtle clues in them. Play became even more important to primates as they learned these new social skills.
Kerrie Lewis, an anthropologist at Washington University in St. Louis, found that the brains of more playful primate species are different from those of less playful ones. Two key structures in their brain--the amygdala and the hypothalamus--are bigger. It may be no coincidence that these are also the two key brain structures that primates--ourselves included--use to recognize facial expressions and figure out how to respond to them.
Humans are a particularly playful species, even compared to other primates. Hominids have a longer childhood than other primates, offering more opportunity for play. Play may have allowed young hominids to learn survival skills, such as finding food and preparing it to eat. (Plato argued that play was the best sort of education.) Play also prepares children to live in an increasingly complex social world. Hominids evolved into highly cooperative hunters and food-gatherers and spread throughout the world. Only by learning social rules could hominid bands stick together. Our ancestors could also apply their growing powers of imagination and language to play as well. Along with good old rough-housing and stone-tossing came fairy wings and train sets.
Scientists have only just begun to explore the natural history of play, but it already seems clear that it's not just a puzzling way kids kill time. Play, Burghardt writes, "may lie at the core of who we are and how we came to be."
Copyright 2006 Carl Zimmer