The simplest form of a wheel is a wooden log. The prototypes were readily available and supplied by nature. Now to make an actual wheel, with spokes and mostly

The simplest form of a wheel is a wooden log. The prototypes were readily available and supplied by nature. Now to make an actual wheel, with spokes and mostly 'hollow' inside and to put it on an axle - would have required better tools, so the wheel was probably created/invented quite naturally alongside the advances in metallurgy.