Animals in Translation (19 page)

That fits in with the fact that all human children do less and less roughhouse play as they grow up and their frontal lobes mature. Probably the more dominant your frontal lobes, the more “serious” and nonplayful you are. Stimulants increase frontal lobe functioning, so naturally they would decrease play, too. As a matter of fact, some parents whose hyperactive children (ADHD, for attention deficit hyperactivity disorder) take Ritalin or other stimulants complain that their kids lose too much of their playfulness, and when you give a stimulant to a young animal it plays less, too. So play is definitely not a neocortical function.

There are other chemicals that decrease play, including the stress hormones and oxytocin. We also know that lots of opioids are released during play. But none of this adds up to a clear picture of the brain biology of play, and behavior studies don't tell us why animals play, either. But the fact that they all play at just about the same age relative to brain development tells us that play may be important to brain growth and/or to socialization.

Two researchers, John Byers at the University of Idaho and Curt Walker at Dixie State College of Utah, have developed an interesting theory about
locomotor play.
Locomotor play is the pretend chasing and jumping-and-spinning play a young animal does when it's alone. (If you want to see locomotor play, watch a goat. They are the biggest jumpers and spinners ever.) Drs. Byers and Walker think the purpose of locomotor play might be to help grow good connections among the cells in the
cerebellum,
²⁷
which is the small, round “ball” down at the bottom of the brain that handles posture, balance, and coordination.
²⁸
Their research shows that in mice, rats, and cats, locomotor play begins when the cerebellum starts to form lots of new connections (or
synapses
) between its cells, and peaks at the same time synaptic growth peaks. So mice start locomotor play at around fifteen days after birth and hit their play peak from four to ten days later; cats begin locomotor play around four weeks after birth, and reach their play peaks at around twelve weeks. In both mice and cats, the peak point of brain growth is also the peak point of locomotor play.

Since the cerebellum handles physical coordination, it makes sense that a young animal or human might spend a lot of time leaping, running, and chasing during the period that his cerebellum is forming new connections. The locomotor play period also coincides with the period when muscle fibers are turning into either
fast-twitch
or
slow-twitch
fibers. (Fast-twitch fibers give you the kind of short-lasting blasts of power you need for sprinting; slow-twitch fibers give you the long-lasting, endurance strength you need to run a marathon. Your heart would have to have slow-twitch fibers, or you'd be dead.)

So far this finding is only a correlation, and we don't know from a correlation whether it's the locomotor play that's causing the cerebellar development, or the cerebellar development that's causing the locomotor play, or both, or neither. Researchers will have to run controlled experiments to answer those questions. But my guess is play probably does help brain development. That makes me worry about all the computer games kids play today. I don't know whether the overall amount of locomotor play American children do has gone down, but if it has that's probably not good. When I was a child we didn't have game systems or computers or cable TV; we had two recesses a day at school instead of just one; and the only time of the week when kids could watch cartoons was Saturday morning. To me it seems like we probably did more locomotor play if only because we didn't have anything else to do. If locomotor play is important to developing the brain, I wonder whether children today are getting enough of it.

This is a bigger question than just whether or not kids grow up to be well-coordinated adults. Physical movement is probably the basis of a huge amount of academic, social, and emotional intelligence. A lot of major psychologists, including Jean Piaget, the Swiss psychologist who mapped out the stages of children's cognitive development, have said that movement is basic to learning, and I agree. My drafting students who've never learned to draw
physically,
holding a pencil in their hand and moving it across a piece of paper, can't draw at all on the computer. You have to learn to draw by hand first and then move to the computer. Virtual drawing isn't a substitute for the real thing. I've seen this over and over again. Piaget said children learn by physically manipulating objects and seeing how they work.
That's
movement.
So if kids aren't getting as much locomotor play now as they did in the past, that could be a problem not just for coordination but for learning.

Physical movement is probably what caused the brain to evolve in the first place, as a matter of fact. Dr. Rodolfo Llinas, a neuroscientist at NYU who wrote
I of the Vortex: From Neurons to Self,
says the brain evolved because creatures needed a brain to help them move around without knocking into things.
²⁹
He gives the sea squirt as the ultimate example of what having a brain is all about. The sea squirt is a primitive organism with about three hundred brain cells that starts out looking something like a tadpole, and ends up looking a little bit like a turnip. For the first day of its life it swims around until it finds a permanent spot to latch on to. Once it finds its spot, it doesn't move again for the rest of its life.

Here's the interesting part: while it is swimming it has a primitive nervous system, but once it becomes attached to an object it eats up its own brain. It also eats its own tail and tail muscles. Basically the sea squirt begins life as a kind of tadpole, with a tadpole-like brain, and then turns into an oyster-class creature. Since the sea squirt isn't going to move ever again, it doesn't need a brain.

Dr. Llinas's theory is that we have brains so we can move. If we didn't move we wouldn't need brains and we wouldn't have them. So I won't be surprised if Dr. Byers and Dr. Walker are right that one of the primary purposes of play is to develop the brain.

A
NIMAL
R
OUGHHOUSING

No one knows exactly why young animals and humans play with their friends and siblings, either. We do know social play always means roughhousing, which has led a lot of behaviorists to reason that play fighting must teach animals how to win a fight when they're grown up. On the face of it that always sounded logical, because young males usually do more play fighting than young females, the same way adult males do more real fighting than adult females. Behaviorists figured the play fights were practice for the real thing.

But when researchers tried to establish a direct connection between
roughhouse play and adult fighting in squirrel monkeys they didn't find any connection. The squirrel monkeys who played the most didn't win more fights as adults, and the monkeys who
won
the most play fights when they were young didn't necessarily win the most real fights when they were grown up. There was no correlation one way or the other. That doesn't disprove the hypothesis, but it doesn't support it, either.

Another interesting fact: play fighting is nothing like real fighting. A lot of the moves that happen in real fighting never happen at all in play fighting, and the ones that do, happen in a different sequence.

We also know that the brain circuits for aggression are separate from the brain circuits for play. Testosterone, which can increase aggression, either has no effect on play fighting or actually reduces it. Sometimes roughhousing play will
turn into
a real fight, but inside the brain rough play and real aggression are two different things.

The other piece of evidence that play fighting isn't about learning how to win is the fact that all animals both win
and
lose their play fights. No young animal ever wins all his play fights; if he did, nobody would play with him. When a juvenile animal is bigger, stronger, older, and more dominant than the younger animal he is play fighting with, the bigger animal will roll over on his back and lose on purpose a certain amount of the time. That's called
self-handicapping,
and all animals do it, maybe because if they didn't do it their smaller friends would stop playing with them. This is also called
role reversal,
because the winner and the loser reverse roles.

Role reversal is such a basic part of roughhouse play that animals do it when they play games like tug-of-war, too. A friend told me a story about her mixed-breed dog, when he was a year old and fully grown, playing with the four-month-old Labrador puppy next door. The new puppy was about a third his size, but Labradors are fearless and up for anything so she wasn't fazed by his size. The two dogs liked to play tug-of-war with a rope toy my friend had out on his terrace, but of course my friend's dog was so huge compared to the puppy that it was no contest. If he used all his strength he'd end up just whipping the puppy around the terrace like a Frisbee.

But that's not what happened. Pretty soon my friend noticed that
the puppy was “winning” some of the tugs. First my friend's mutt would pull the puppy backward across the terrace, then the puppy would pull
him
backward a way. My friend said her dog was “keeping the puppy in the game,” and I'm sure she's right.

Some behaviorists say that the fact that all animals self-handicap might mean that the purpose of play fighting isn't to teach animals how to win but to teach them how to win
and
lose. All animals probably need to know both the dominant and the subordinate role, because no animal starts out on top, and no animal who lives to old age ends up on top, either. Even a male who is going to end up as the alpha starts out young and vulnerable. He has to know how to do proper subordinate behaviors.

P
LAY AND
S
URPRISE

Marek Spinka, an animal researcher in the Czech Republic, has created a general hypothesis of play in animals. His theory is that play teaches a young animal how to handle novelty and surprise, such as the shock of being knocked off balance or a surprise attack.

If Dr. Spinka is right, that would explain why play fighting is so different from real fighting, because a play fight has to be constantly surprising to teach the young fighters to respond to novelty. Dr. Spinka's theory also goes along with self-handicapping, since changing roles in the middle of a play fight means that the animals put themselves in roles they don't normally have. A normally dominant young animal puts himself in the subordinate role, and a normally subordinate young animal puts himself in the dominant role. That's a novel situation.

Dr. Spinka's theory is probably related to Dr. Llinas's research on the brain and movement. Dr. Llinas says that a brain has to do three things to allow its owner to move: it has to set goals (where do I want to move to?), it has to make predictions (if I move this way will I crash into that tree?), and it has to rapidly process tons of incoming sensory data to make sure its predictions are coming true and its owner is getting where he wants to go in one piece.

All of that is a pretty good description of what happens in almost any kind of play in young animals, whether it's locomotor or social
or
object play,
which is playing with any kind of object, like a ball or a stick. One time I watched Red Dog playing with a plastic bag in the field next to Mark's house. It was a windy day, and she would pick up the bag, carry it upwind to the fence, then put it down on the ground where the wind would catch it and blow it across the field to the other side. She'd chase the bag the whole way across the field and then, when she got to the fence, she'd catch the bag and bring it back to the upwind side where she could put it back down so the game could start all over again. It's hard to see any reason for that game other than the fun of setting goals (I'm going to chase that bag across the field and catch it), making predictions (which way do I have to move to catch that bag?), and rapidly processing a lot of incoming sensory data from her race across the field. When you watch a young animal doing object play it really does look like they've
got
to be developing their basic brain functions in some way.

Social play has all of the same qualities. Mark likes to play a “go fishing” game with Red Dog where he takes a bullwhip and flips the tip out and lets Red Dog grab on to it. Then he says, “Oh, I'm going to reel in a big one!” That's a social game, and it's pure locomotion. When you look at what young animals do when they're playing, and put that together with the fact that animals do the most physical play while the cerebellum is forming connections, I think we'll probably find out that play is an important way that a young animal develops its brain's ability to guide active movement.

C
URIOUSLY
A
FRAID

So far, research is showing that the primal core emotions—
rage, prey chase drive, fear,
and
curiosity/interest/anticipation
—are handled by separate circuits in the brain. That doesn't mean that more than one circuit can't be turned on at the same time, or that one emotion can't trigger another.

A friend of mine tells a story about her six-month-old mixed-breed dog's reaction to her husband when he came home from a two-month research trip overseas. When the dog saw her husband he was overcome by terror and joy at the same time. He hit the floor in fear, crying and screaming, and at the same time he kept lifting his
eyes up to the husband and frantically wagging his tail in greeting. Then he'd jerk his head back down and carry on screaming and cowering, all the while creeping along the floor
on his belly
toward the husband. My friend said it was exactly like the dog thought he was seeing a ghost. He was terrified and overjoyed in the same moment, seeing someone he thought he would never see again.