Rotating axles have not evolved in animals not because they were complex, but because any part of an animal requires permanent connections with the other parts, not only for the supply with energy but also for the continuous repairing that is required by any living body, to avoid death.
Artificial machines rely on spare parts manufactured elsewhere, which are used by external agents to replace the worn out parts.
For an animal to have wheels, it would have to grow wheels in some part of the body, periodically, then use its limbs to detach the wheels and attach them on the axles, after removing the old wheels. This is something sufficiently complex to be extremely unlikely to appear from evolution.
Even this huge complication would be enough only for passive wheels. For active wheels there exists no suitable motor, as the rotational motors with ionic currents are suitable only for the size of a bacteria. All bigger living beings use contractile motors, which cannot be used for a rotation of unlimited angle. So active wheels would also need a different kind of motor, which can work without a solid connection between the 2 moving parts. The artificial motors of this kind use either electromagnetic forces or fluid expansion due to temperature or pressure variation. Both would be very difficult to evolve by a living being, though electric fish and bombardier beetles show some possible paths.
Artificial machines rely on spare parts manufactured elsewhere, which are used by external agents to replace the worn out parts.
For an animal to have wheels, it would have to grow wheels in some part of the body, periodically, then use its limbs to detach the wheels and attach them on the axles, after removing the old wheels. This is something sufficiently complex to be extremely unlikely to appear from evolution.
Even this huge complication would be enough only for passive wheels. For active wheels there exists no suitable motor, as the rotational motors with ionic currents are suitable only for the size of a bacteria. All bigger living beings use contractile motors, which cannot be used for a rotation of unlimited angle. So active wheels would also need a different kind of motor, which can work without a solid connection between the 2 moving parts. The artificial motors of this kind use either electromagnetic forces or fluid expansion due to temperature or pressure variation. Both would be very difficult to evolve by a living being, though electric fish and bombardier beetles show some possible paths.