Reasons to Believe

Increasing the Torque on Intelligent Design

New Work Further Reveals Machine-Like Character of the Bacterial Flagellum

Some people are so well known they need no introduction. That's also the case for the bacterial flagellum. This protein complex, embedded in the cell wall of many different bacteria, has become the widely recognized symbol of intelligent design.

The flagellum looks like a whip and extends from the bacterial cell surface. Some bacteria have only a single flagellum, others possess several flagella. Rotation of the flagellum(a) allows the bacterial cell to navigate its environment in response to various chemical signals.

An ensemble of over 40 different kinds of proteins makes up the typical bacterial flagellum. These proteins function in concert as a literal rotary motor. The bacterial flagellum's components include a rotor, stator, drive shaft, bushing, universal joint, and propeller. The bacterial flagellum is essentially a molecular-sized electrical motor directly analogous to man-made rotary motors. The flow of positively charged hydrogen ions through the bacterial inner membrane powers the flagellum's rotation.

The Case for Intelligent Design: Irreducible Complexity

Most intelligent design theorists argue the flagellum provides evidence for intelligent design because it's irreducibly complex.

Biochemist Michael Behe first articulated the concept of irreducible complexity (IC) in his book Darwins's Black Box. According to Behe, IC describes "a single system composed of several well-matched, interacting parts that contribute to basic function, wherein removal of any one of the parts causes the system to effectively cease functioning."

Behe makes the case that irreducibly complex systems, like the bacterial flagellum, cannot be produced from a proto-system by the Darwinian process of slight, incremental, iterative change. Any proto-system lacking even one of the parts that contributes to "basic function" is nonfunctional. The same result occurs even if all the essential components are present, but do not interact with one another in a "just-so" fashion. If the proto-system doesn't have function, then natural selection can't operate on it to produce an improved system. Without function, natural selection has nothing to select. Irreducibly complex systems must come into existence complete and fully operational. This being the case, it's completely within the bounds of rational thought to conclude that such systems, like the flagellum, came into existence through intelligent agency.

The Case for Intelligent Design: The New Watchmaker Argument

In my book The Cell's Design, I take a different tact to make the case for intelligent design. Following after William Paley, I argue that biochemical systems share many features in common with objects and systems produced by human designers. And because of this we can take these features as evidence for intelligent design. In other words, if certain characteristics and features indicate that a structure or process is the product of a human mind, and we observe these same properties in biochemical systems, then by analogy it logically follows that life stems from the work of a mind as well.

My argument for intelligent design takes on the same form as Paley's famous Watchmaker argument for God's existence: just as a watch requires a watchmaker, life needs a creator. In the case of molecular motors, the startling similarity between the flagellum and man-made machinery can be taken as evidence that a divine mind created life. (For a more detailed discussion on biomolecular motors' impact on the Watchmaker argument listen to the podcast I recorded to accompany The Cell's Design.)

Even though I find Behe's use of irreducible complexity compelling, my preference is to use the Watchmaker analogy to make the case for intelligent design for a number of reasons. (I am going to focus on only one of the reasons in this article.) In my view, framing the case for intelligent design based on irreducible complexity makes for a stagnant argument. Once a system is established as irreducibly complex new insights into its operation are irrelevant, unless they demonstrate that the system isn't irreducibly complex. A system is either irreducibly complex or it isn't. In contrast, constructing an argument based on analogy, such as the Watchmaker, allows the case for biochemical intelligent design to gain strength as new discoveries are made.

Analogical Reasoning

Analogical thinking involves comparing instances. If similar enough, then one can conclude that the events, systems, or objects compared are the same in some way. If, however, the instances are significantly dissimilar, such a conclusion is unwarranted.

For example, if two systems, labeled A and B, are compared. If A possesses properties a, b, c, d, e… and z, and B possesses properties a, b, c, d, e…, it is reasonable to conclude that B possesses property z as well. This conclusion becomes more likely if the property z, somehow relates to properties a, b, c, d, e….

In the case of the Watchmaker analogy, because human machines are comprised of stators, rotors, drive shafts, bushings, etc (a, b, c, d, e…) and are the work of human designers (z) then it's reasonable to conclude that the bacterial flagellum, which possesses a stator, rotor, drive shaft, bushing, etc. (a, b, c, d, e...) are the work of a Divine Designer (z).

To properly reason from analogy several factors must be considered. The two most relevant to this discussion are: 

  • The number of similarities that are part of the analogy. The greater the number of similarities, the greater the cogency of the conclusion.
  • The number of events, objects, or systems that enter into the comparison. The greater the number of separate comparisons, the more probable the conclusion.

The importance of these two factors in analogical reasoning means that the more features of the bacterial flagellar motor (or any other particular molecular motor) that correspond to human machines, the more certain the conclusion that it originated from an intelligent Agent. And in turn, every time biochemists learn more about the bacterial flagellum, particularly if these new insights highlight its machine-like character, the stronger the case for intelligent design becomes.

New Discoveries Make the Case for Intelligent Design Stronger

For example, David Rogstad described the discovery of a clutch in the bacterial flagellum. This finding adds one more one more piece of common ground between the flagellum and man-made motors.

As another example, a team of biophysicists recently presented work that shows how the bacterial flagellum not only consists of components analogous to human inventions, but also functions like a machine. The researchers developed a mathematical model to account for experimental observations of the flagellar motor's behavior while operating. Specifically, they were trying to understand the motor's torque generating mechanism.

The stator of the flagellum is composed of a series of protein subunits that organize into a ring surrounding the rotor. The scientists discovered that during the rotor's movement (powered by interactions with the components of the stator) two time scales are important: one corresponding to the rotor's rotation and one corresponding to a waiting period during which the rotor interacts with components of the stator. These two time scales respond differently to the load. In general, researchers have observed that the greater the load, the slower the speed of the flagellum's rotation. It turns out that moving time is more affected by the load than the waiting time.

Additionally, the biophysicists studied how the number of stator components influenced the flagellum's rotation. For a near-zero load, the speed of rotation is independent of the number of stator components. At high loads, however, the greater the number of components, the greater the speed.

Because of the two time scales dictating its mechanism, the flagellum will rotate in a herky-jerky, step-wise manner. The researchers discovered that increasing the number of components in the stator will smooth out the rotation under both near-zero and high loads. Under near-zero loads, the smoother rotation stems from the increased step number per revolution. Under high loads the rotation becomes less rough because of the increased torque generated for each step.

Based on this new work, it's hard to escape the fact that the bacterial flagellum is structurally and operationally analogous to human machinery. As biochemists and biophysicists continue to learn more about the bacterial flagellum, its machine-like character becomes increasingly evident. And if analogies are used to make the case–so does the case for biochemical intelligent design.

Subjects: Biochemical Design

Dr. Fazale Rana

In 1999, I left my position in R&D at a Fortune 500 company to join Reasons to Believe because I felt the most important thing I could do as a scientist is to communicate to skeptics and believers alike the powerful scientific evidence—evidence that is being uncovered day after day—for God’s existence and the reliability of Scripture. Read more about Dr. Fazale Rana