The wheel is considered to be man's greatest invention. With the wheel came movement. I will argue however that the humble ball is actually man's greatest invention. The ball is one of the world's most emotionally satisfying objects and the most sustainable. Only balls with holes in them, unable to be inflated ever again, end up in landfills.

Ever wonder why we love the ball so much? The ball is our childhood friend. As children we learn to discover the world using our instincts and impulses. The ball is round and round is a signal that something is touchable, safe, not dangerous. The ball is non-threatening. The ball is safe to hold and its behavior is predictable. If you throw it, bounce it or kick it, a perfectly round ball will move in its intended direction -- up, down, in a direct line. The curved roundness of a ball signaled comfort to us when we were children, a knowingness based on maternal familiarity and a preference that is also seen in our childhood love for round characters such as Barney or the Teletubbies. (Compare this to the toys and games older children prefer which tend to take on the realistic features and qualities of adulthood.)

Without the ball, I propose that the wheel could not have been invented. Not because I think the roundness of the ball inspired the wheel, but because without the ball what would man have bounced against the wall while he was thinking about the wheel? The ball surely predated the wheel because man's most important need, outside of food of course, is for play. Without play, new lands would not have been conquered. And without play, the human race would have surely died out. How can this be? How can play be that important? I believe that play is one of the most critical behavioral experiences in which all living creatures engage.

What is play? Play is the pirates we fight in our front yard with broomsticks and cardboard daggers. Play is the hiding spot in the closet where we're certain that we'll never be found. Play is the pink lipstick we put on our brothers.

But if play is only thought of as an activity for children then how can I argue that play is critical to the life experience of all humans? Because not only is play the method through which children learn the world, but adults use play in the same way. We shy away from calling it play, choosing instead to let psychobabble and complicated terms stand in for a very short and simple four letter word.

Play is how adults gauge friend or foe, play is how we understand if our crush is interested, play is how battles are fought and won and, of course, play is how we test our own personal strengths and weaknesses. The difference between adult play and child play is only in its consequences. Children play freely, children see possibility where there may not be any, and children don't let rules or convention stand in the way of the next better idea. This play freedom is what adults tend to lose when they grow up.

Neuroscience underscores what every good parent knows intuitively: play is key to healthy intellectual, emotional and social development -- as important as sleep, rest and food in developing "imagination, dexterity, and physical, cognitive and emotional strength." Our curiosity and fearlessness help us learn about the world, each other and ourselves. But as we age, we, sadly, push playfulness aside.

One of my favorite books showcases the best offices around the world in which to work. Not surprisingly many of them belong to technology companies. Technology companies understand that play walks hand-in-hand with innovative thinking. A ping-pong table, an Air-Stream reinvented as a meet-and-greet room, a graffiti wall that invites new ideas with its rows of markers on string. And they are right.

Play in its many forms: physical play, object play, transformative play, social play, imaginative play and creative play, is inseparable from mankind's greatest discoveries and quite possibly from the very spark that caused you to be here today.

As we age we minimize the role of play in our lives. We watch our children play. We are entertained by others through movies and TV. And it's unfortunate. Think how wonderful the world could be if we all reminded ourselves of the real power free play has in our lives. The next time you look at the lowly ball that you kick out of the way, rushing out the door, you should consider stopping to pick it up, instead, to say thank you. Or bring it with you.