Fossil evidence indicates that early humans hunted and ate other animals, and this seems to suggest that our catching and throwing capabilities may well be rooted in our development as hunters and tool users. Hitting or catching a moving animal requires an ability to estimate its path in advance. These are the basic skills required for every game of catch and throw, but for our ancestors, they may have been requirements for survival.

Recent paleoanthropological studies suggest that our ancestors were walking erect four million years ago, long before we developed large brains. So it's just possible that our throwing abilities were already in use even at that early date, and that all possible trajectories for moving objects are already stored in our brains, waiting to be called up for use at any given moment.

Psychologists have observed that human babies as early as eight months of age already have expectations about the movements of objects within their field of view, which they cannot possibly have learned from experience, and which therefore must have been wired into their brains by the processes of evolution. And by the age of one year, human babies already have acquired some ability to catch and throw objects, an ability which improves with practice and neurological development.

Compared to catching a hard-hit line drive on the run, it would seem that catching the pop-up fly would be simple. But it isn't. It may be that, given enough time, the room for error in estimation of flight path actually increases; a player may think himself into an error. This is like trying to draw a straight line freehand. If you look where you want to draw the line and then just draw it there without concentrating, you will probably succeed in drawing a fairly straight line. If, on the other hand, you worry about how straight the line is, millimeter by millimeter, the task becomes impossible. Catching a ball may be easier when there's no time to think.

All aspects of baseball seem keyed to a balance of learned skills and inherent biological limits.

Charley Metro: "Now who designed baseball, whether it was [Abner] Doubleday or [Alexander] Cartwright or whoever it was, he was fantastic as an engineering genius because it takes you so long to run and so long to make the double play, and if it had been longer or shorter it would throw the game completely out of kilter."

The trade-off that baseball players make between these skills and limits make for an interesting and constantly changing game.