Quote Originally Posted by mklotz View Post
[Actually, it's the axle, not the wheel that is the big invention. The ancients were using wheel-like rollers to move heavy loads long before somebody hit on the idea of attaching roller slabs to a stick and placing a load on it.]
This is a great point about the axle.

I think there had to be isolated instances of Mesoamerican use of carts or barrows of some sort, even if their use wasn't commonplace, or they weren't formally "invented". It just doesn't seem enough of a cognitive leap from a roller to a wheel that nobody would figure it out.