The human designed rotary motor and the bacterial rotary motor share the same top-down design logic including many of same components in the same functional and spatial relationships. This connection is far stronger than the superficial similarities between human and natural bridges, pillars, or crosses. A major difference is that the latter are the result of natural processes creating configurations of matter directly driven by natural laws, and they do not need to meet tight constraints.
In contrast, human and biological engines represent configurations of materials which transcend their physical and chemical properties, and they must meet tight functional requirements in accordance with a top-down design logic in order to function. In addition, the configurations of atoms in both classes of motors require assembly processes which force pieces to form and fit together in ways which would never happen through purely natural processes.
Many biologists fully acknowledge the strong connection between the motors. For instance, Howard Berg described the flagellum as not simply similar to a human rotary motor, but he said it is a “rotary electric motor.” He even laid out the piece by piece comparisons:
Bacterial flagellar motor
The flagellar motor is a remarkably small rotary electric motor that drives a proximal hook ( flexible coupling ) and helical filament ( rigid propeller ). The motor components include a rod ( drive shaft ), L- and P-rings ( bushing ), MS-ring ( mounting plate ), and FliG, M, and N (circular arrays of subunits attached to the MS-ring that make up the cytoplasmic, or C-ring, also called the switch complex ). MotA and B act as force-generating elements ( pistons ), linked via MotB to the rigid framework of the cell wall. MotA engages FliG. Each force-generating element comprises four copies of MotA and two copies of MotB, which together constitute two transmembrane ion channels. The motors are powered by protons or sodium ions that flow through these channels from the outside to the inside of the cell, which, depending upon the configuration of the C-ring, drive the rod, hook, and filament CW or CCW. The chemotaxis signaling protein CheY–P (not shown) binds to FliM and N, enhancing CW rotation. At high loads, eight or more force-generating elements are active, each generating the same torque. The transport apparatus pumps rod, hook, and filament subunits into an axial pore, upon transfer from cytoplasmic chaperones via the ATPase complex. Other components (not shown) include FlgJ (rod cap, discarded upon rod completion), FlgD (hook cap, discarded upon hook completion), FliK (hook-length control protein), and FlgM (factor that blocks late-gene expression). It is commonly assumed that the MS- and C-rings rotate as a unit (as the rotor ), but this has yet to be shown experimentally. The MotA and MotB force-generating elements comprise the stator.