Why did it take so long to invent the wheel?

To most of us, wheels seem pretty intuitive. You've probably known from an early age, for example, that circular or rounded things roll more easily than boxy or angular things. Knowing this, it's hard to imagine that our earliest ancestors did not come to similar realizations on their own — and yet, the first wheels… » 3/07/12 7:40am 3/07/12 7:40am