The flagellum’s clutch means less design


Bacterial Flagellum

Daniel Kearns and colleagues have found that bacterial flagellum(pictured here courtesy of Access Research Network) has the equivalent of a clutch. The Discovery Institute wasted no time in proclaiming that this is more evidence for intelligent design.  In a June 30, 2008 post entitled More Similarities Between Flagellum and Human-designed Machines, Casey Luskin states:

It [flagellum] functions like a human-designed rotary engine that propels a bacterium through a liquid medium in the same way a propeller powers submarine through the ocean…. The flagellum is basically a rotary engine, with a motor, a rotor, a stator, a bearing, a u-joint, and a propeller. Now it turns out that the flagellum has a clutch.

Scientists have known for awhile that the flagellum stops moving in certain situations (i.e. the formation of a biofilm).  This gives us two choices:a brake or a clutch.  Either way, ID proponents would say that the new structure, either a brake or clutch, shows design as human-designed motors have both.  So this discovery does not bolster their argument.

The protein that acts like the clutch, EpsE, has some interesting properties that make it clear that it was not designed for this purpose; it evolved from a protein with another purpose.  For one, it looks like a protein that adds sugars to other proteins or lipids, but removing this ability from the protein does not effect its ability to act like a clutch.  It is part of a group of genes that are needed to make biofilms, not with flagellum genes.  Not exactly the way someone would design the system.

Bacteria swimming vs. motorboat

Bacterial Swimming

I also want to add a little about how the bacterial flagellum is used by bacteria to move in a particular direction.  Logically, if you were going to build a motor (like for a boat), wouldn’t you make it be able to run as long as you needed and in the direction you wanted?  This is not what you find with bacteria.  They go through two different phases, tumbling and straight swimming.  The bacteria swim for awhile in one direction and then turn off the motor and tumble. If they are swimming the direction they want, then they swim longer.  This is repeated unti they get where they are trying to go.  In the image below, I have drawn an example of bacteria (green path) compared to a motorboat(red path) trying to swim towards the red gradient.  If you ask me, this is a terribly inefficent (and unintelligent) way to move, but it does work.