Hmmm, didn't think of that.
Perhaps what i should have said is that nature never evolved any stator-rotator systems. This includes wheels, rotors, propellers, motors and in fact anything which requires roller bearings and seals to work.
Even here there are some single cell examples of chemically driven rotating motors.
http://www.allaboutthejourney.org/mi...-organisms.htm
The so-called "bacterial flagellum" is what propels a bacterium through its microscopic world. The bacterial flagellum consists of about 40 different protein parts, including a stator, rotor, drive shaft, U-joint, and propeller. Through 21st century magnification technology, we now understand that a simple bacterium has a microscopic outboard motor! The individual parts come into focus when magnified 50,000 times using electron micrographs. These microscopic motors can run at 100,000 rpm. Nevertheless, they can stop on a microscopic dime. In fact, it takes only a quarter turn for them to stop, shift gears and start spinning 100,000 rpm in the other direction! The flagellar motor is water-cooled and hardwired into a sensory mechanism that allows the bacterium to get feedback from its environment!
http://en.wikipedia.org/wiki/Flagellum