Some reasons why biology has problems making wheels:The Mad Hatter wrote:There's no reason a creature can't evolve a wheel operating on an axis, we simply just can't picture how it would work.
http://en.wikipedia.org/wiki/Rotation_i ... locomotion
Perhaps the most significant is growing a wheel. If it is free to rotate on an axle it is very difficult to keep the tissue that grows the wheel supplied. It can't be like bone or antler, which need blood supply to grow.