From Creation Evolution Headlines

Flagellum Is a Gear-Driven Motor of Motors

“That’s an outboard motor! That’s designed.”

That was biochemist Michael Behe’s reaction when he saw crude electron micrographs of the bacterial flagellum in the 1990s. When he presented the flagellum as one icon of intelligent design in his book Darwin’s Black Box in 1996, most people looking at a drawing of it had a similar reaction. Behe argued that the flagellum was “irreducibly complex”— a term he coined to convey why some biological devices defy evolution. All the essential parts had to work or nothing worked. Irreducible complexity (IC) precluded step-wise evolution by natural selection, which could only work (if at all) by one small step at a time.

The Darwinians dug in, though, claiming that this rapidly-spinning motor evolved by “co-option” of other protein parts and in no way threatened the “scientific” theory of natural selection. Some claimed it evolved from another protein pump, the Type III Secretion System (TTSS), because it used some of the same protein parts. This begged the question, however, of what the TTSS evolved from. By the time of the Dover Trial in 2005, the pro-evolution side had convinced Pennsylvania judge John E. Jones that the flagellum had an evolutionary explanation.

Behe testified at the Dover trial, but Judge Jones ruled against the Pennsylvania school district that was trying to allow students to hear evidence for intelligent design. The ACLU and Darwinian scientists at the trial convinced the judge (who had no experience with intelligent design theory), that the ID proponents were trying to sneak religion into public school science classrooms.

His ruling claimed that ID was religious because it could not meet the criteria of science (see articles at Science & Culture Today here and here). Yet the Design Inference is common to many sciences (see examples here, here, and here). It simply infers whether a phenomenon shows marks of foresight and intention instead of being explicable by natural law or chance. We all use the design inference every day. It’s not religious.

It should be noted that Judge Jones’s ruling set no legal precedent and had no jurisdiction outside that school district in Dover, Pennsylvania, despite the plaintiffs’ attempt to portray the ruling as the “death of intelligent design” – watch this video.

That Was Then

A new paper in PNAS ramps up the case for irreducible complexity by an order of magnitude. The flagellum, seen under increasing magnification, turns out to be a “motor of motors.” Not only that, it has gears! The authors makes this stunning announcement: “The bacterial flagellar motor is driven by the first set of enmeshed gearwheels that has been described in any living cell.” They even measured the gear ratio: “Torque-generating stator unit and flagellar motor rotor act like intermeshed gearwheels with ~6.2 gear ratio.”

Torque-generating units of the bacterial flagellar motor are rotary motors (Hosu et al., PNAS, published online 10 Dec 2025).

For several reasons, this new paper could vindicate Behe and shame the Darwinists and lawyers who tried to destroy intelligent design science back in 2005. Consider:

• The three authors are physicists on the faculty of Harvard University.
• The paper makes no mention of evolution or any attempt to explain the origin of the flagellum.
• What they discovered is almost more astonishing than the initial evidence that convinced Behe of intelligent design: the flagellum is a gear-driven system of rotary motors!

Today we will introduce this paper to a wider audience and to ID scientists or creation scientists who may wish to investigate the details further. For starters, here’s the Significance statement:

Bacteria swim by rotating rigid helical flagellar filaments. Here, we find that the torque-generating unit that drives flagellar rotation is itself a rotary motor. Each torque-generating unit is a heteromeric macromolecular machine—a pentamer of MotA subunits that surround a dimer of proton-conducting MotB subunits. Torque is generated as the MotA spins around MotB. The MotA pentamer interacts with rotor of the flagellar motor in a manner resembling intermeshing gearwheels. The bacterial flagellar motor is driven by the first set of enmeshed gearwheels that has been described in any living cell.

Their discovery begins to explain how the flagellum generates torque using principles of physics, how it achieves such astonishing speed, and how it can reverse direction in a quarter-turn, as was known back in 2002 when Illustra Media published Unlocking the Mystery of Life. The method these authors used opens the door to approach other rotary molecular machines like ATP synthase using principles of physics. They clearly had no need of natural selection or other evolutionary concepts in their work.

The bacterial flagellar motor (BFM) is a proton-powered rotary engine (1–3). Cryoelectron microscopy has revealed the structure of the rotor at the flagellar base (Fig. 1A) and the structure and stoichiometry of the torque-generating stator unit (Fig. 1B) (5, 7, 8). The rotor has a central rod with rings for each layer of the cell envelope. Outside the cell, the rod connects to the flagellar filament by a flexible hook. Inside the cell, the rod connects to the MS-ring, in turn attached to the C-ring, the wheel that is mechanically powered by surrounding stator units.

Using clever experiments and measurements, the authors determined that electrostatic interactions generate torque that turn the motors in the stator, which in turn mesh with the rotor to cause rotation. The spacing between the electrostatic charges is precise enough to maximize torque. Moreover, the stator motors can quickly jump from inside to outside a ring to switch from clockwise to counterclockwise rotation, allowing the bacterium to quickly change direction.

Because the C-ring interacts directly with the torque-generating stator unit, the C-ring represents the cytoplasmic gearwheel that rotates the flagellum.

The paper contains images and movies of the flagellum’s mode of operation.

This paper could turn out to be the final bombshell that obliterates any attempt to Darwinize the flagellum. If the flagellum displayed irreducible complexity then, how much more does it now? How would the ACLU, Ken Miller, and the other “victors” dancing on the tomb of intelligent design in Dover explain a “set of enmeshed gearwheels” at the basis of one of the most efficient molecular machines known to biology? The efficiency of the flagellar motor was already known to approach 100%. Some versions of the flagellum can rotate at 100,000 RPM!

Recall that bacteria were assumed to be more “primitive” and lower on the evolutionary scale than eukaryotic microbes. Yet here is a paragon of irreducibly complex engineering design found to be common in many bacteria. Some “peritrichous” bacteria, like E. coli, possess multiple flagella on their exteriors that work in cooperation with each other. Don’t forget that every living organism running on ATP has another rotary motor a tenth the size and no less wondrous, ATP synthase.

Our purpose here is to get this paper seen and known by ID supporters and critics, rather than to analyze it in detail today. It seems poised to revolutionize the study of molecular machines and revitalize the argument for irreducible complexity with evidence that may be strong enough to convince critics of ID to stop and ponder, “That’s an outboard motor. That’s designed.”