How come there are no wheels in nature?
Human inventors often turn to nature for inspiration, like in designing the wings of a plane.
But how come there are no wheels or motors in nature? Animals have electricity, so they could have a bone-based propeller with magnetic material that they rotate, right?
Perhaps the problem is that the wheel would have to be an independent, freely moving component, which would be too hard to service. Even if the organism could lick the propeller, the propeller would have to be a full-blown independent organism in order to do something with the nutrients.
Which leads me to the idea that nature isn't that modular. You can't pull out a liver and replace with another one without destroying the organism. Machines, you can power down, replace a part, and it's good to go.