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Bacterial Flagellum: Appearances Can be Deceiving

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July 29, 2010 Tags: Design

Today's entry was written by Kathryn Applegate. You can read more about what we believe here.

If any symbol captures the spirit of the Intelligent Design movement, the bacterial flagellum is it. Beautiful artistic renderings so frequently adorn ID books, blogs, and videos that ID critic Ken Miller has called it the “‘poster-child’ of the modern anti-evolution movement.”

For many decades, the exquisite structure and function of the bacterial flagellum was unappreciated outside the scientific community. We can thank ID leader Michael Behe for changing that. His 1996 book Darwin’s Black Box introduced the world to the flagellum and at the same time exalted it an impassable obstacle to Darwin’s theory of evolution. Behe used the flagellum to illustrate his principle of irreducible complexity—the idea that some features of life are too complex to have developed gradually. These features, Behe argued, are best explained as the product of a Mind.

Today we’ll take a brief look at the flagellum and see why it remains such a powerful icon for the ID movement. In future posts we’ll consider whether the biology of the flagellum makes more sense in light of an evolutionary or a design paradigm.

What is the bacterial flagellum?

Bacteria typically live in aqueous (watery) environments and need to swim to find food and evade enemies. To accomplish this feat, they use a truly marvelous apparatus, the flagellum.

Bacterial flagella are long, whip-like tails protruding from a base tethered in the cell wall. The base contains a rotary motor powered by an electrochemical gradient: a mismatch in the concentration of hydrogen ions across the membrane provides the energy needed to power the motor. The strength of the gradient controls the speed of rotation; typically the propeller tail spins in the range of several hundred to a thousand RPM. As a result, bacteria can travel up to 60 cell lengths per second! The shape of the propeller and the ability of the rotor to change directions allow the bacterium to either swim in a precise direction or randomly tumble to reorient when needed. The number and arrangement of flagella can vary dramatically by species, yielding great diversity in the way bacteria get around, but the basic unit is the same.

While the cartoon above makes the flagellum look simple enough, in reality the machine is quite complicated. Just like an outboard motor, the flagellum has a rotating element (rotor) and a stationary element (stator) embedded in the cell wall and membrane. These elements are connected to the flexible filament by a hook (see cartoon at left). The parts list for these three components includes about 40 different proteins.

A powerful analogy

Why do some argue that the bacterial flagellum is the product of intelligent design rather than evolution? For starters, it looks like something known to be designed—the outboard motor. ID proponents like Behe are not alone in recognizing the parallel. In 1998, structural biologist David DeRosier marveled, “more so than other motors, the flagellum resembles a machine designed by a human.”

The resemblance is so striking, we find it difficult to resist extending the analogy to how the flagellum originated. We know that all outboard motors are designed by intelligent engineers; the parts are carefully crafted to work together for an intended purpose. The bacterial flagellum also has many well-matched components. Together they perform the same job as the outboard motor—swimming. Since the flagellum wasn’t designed by human engineers, it seems only reasonable to infer that it was designed by Someone Else.

But appearances can be deceiving. Look carefully at the photograph below:

It’s beautiful, isn’t it? A light wind blows playfully, rustling the tall grass. The red rocks in the distance radiate heat from the day. I’d love to be there to watch the clouds unfurl in all the majesty of a prairie sunset.

The only problem is, the place doesn’t exist. This piece of art is not a digitally altered photo, or even a realistic-looking painting. It’s a real scene in miniature, created by 26-year-old artist Matthew Albanese out of faux fur (for the grass), cotton wool (clouds) and tile grout (rocks).

Don’t believe me? If you watched Albanese in action, you would immediately understand how he created this amazing image. Check out his studio setup for making realistic cloud images from a suspended tuft of cotton:

What does this have to do with the bacterial flagellum?

The example above illustrates how deceptive appearances can be. The landscape in the photograph appears to be entirely natural, but every detail is meticulously designed. In contrast, the bacterial flagellum looks entirely unnatural. It seems much too complicated to have arisen through random mutation and natural selection. Yet as we will see in future posts, even the most iconic irreducibly complex system, the bacterial flagellum, can be understood in light of these evolutionary processes.

It’s worth pointing out that understanding the creative process magnifies, rather than diminishes, the work of the artist. I don’t imagine many people fly into a rage when they learn how Matthew Albanese creates his beautiful photographs. Rather than feel deceived, they feel amazed! In the same way, when we see how God created all the marvelous forms of life through an extended dance of natural processes—his laws—the appropriate reaction is not dismay, but worship.

Kathryn Applegate is Program Director at The BioLogos Foundation. She received her PhD in computational cell biology at The Scripps Research Institute in La Jolla, Calif. At Scripps, she developed computer vision software tools for analyzing the cell's infrastructure, the cytoskeleton.

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Marshall - #23899

July 29th 2010


I’m having trouble understanding your position – whether God is out of the picture now (Deist God) or is directing things.

God created and sustains natural processes. Both what nature does and what happens without natural causation (the resurrection, etc.) is part of what God is doing. Nature does not work apart from God, and God is not limited to the natural.

However, it would seem that your position is telling the atheist that he does have an excuse for not believing.

What I have said is that whether someone accepts a particular ID argument does not determine whether they accept the revelation Romans 1 speaks of.

However, it would seem that from your perspective the heavens would only declare that there are physical laws out there – origin unknown!

I wrote, “I believe God created the natural processes that scientists study.” I do not believe nature provides a complete revelation of God, but it does point to some of his attributes. This revelation has been understood in some sense since the beginning of humanity (Romans 1:20); it is not something new uncovered by the ID movement (or by TEs, for that matter).

Gregory - #23900

July 29th 2010

“Intelligent Design and Neo-Darwinian evolution are human constructs and not worth debating. / I would rather expend hot air on a more relevant issue like ,..... whether one should should favor the Yankees or the Red Sox.” - conrad

Though conrad might rather give his hot air to the human constructs and performances of baseball, America´s national pastime, there are others for whom ID and NDE are pastimes instead.

“TEs…or, perhaps, evolutionary creationists, or better yet, why not BioLogians?” - Biophilos

How then would one distinguish between a ´biologist´ and a ´Biologian´?

The -logos is of course already present in the word ´bio-logy.´ The Logos that is referred to in Collins´ term is of course that of the Abrahamic faiths, right?

Indeed, a big question: if not TE or CE, then what could a supporter of the (at least to me still rather vague) idea ´Bio-Logos´ be called?

nedbrek - #23901

July 29th 2010

What I find odd is this belief in “natural laws” apart from God.  As if they have some existence in and of themselves.

I believe the natural laws are our understanding (models) of how God works in the world.  Gravity, the strong and weak nuclear forces are all applications of “God holding all things together” (Heb 1:3).

Marshall - #23903

July 29th 2010

Hi nedbrek,

Do you think that someone posting here holds to that “odd” view? I think I’ve been quite clear that I don’t, and I haven’t noticed anyone else here going down that road. I’m curious what prompted that comment.

nedbrek - #23906

July 29th 2010

Hello Marshall, you said “we discovered that the natural, mindless force of gravity is largely responsible for the orbits of planets rather than God’s direct, supernatural action.”

I would say that it is God’s direct, supernatural action.  Because God is consistent and orderly, that action can be modeled as g = GMm/r^2

unapologetic catholic - #23913

July 29th 2010

“I would say that it is God’s direct, supernatural action.  Because God is consistent and orderly, that action can be modeled as g = GMm/r^2”

So God’s consisent and orderly laws of genetics and DNA replication as studied though evolution, and His consistent and orderly laws relating to the half life of radioactive isotopes also present no problem to you, correct?

Marshall - #23915

July 29th 2010

Hi nedbrek,

Thanks for quoting what you were referring to. From what you wrote, I think you’re describing a position quite similar to something Chesterton wrote in Orthodoxy, and one that resonates with me:

But perhaps God is strong enough to exult in monotony. It is possible that God says every morning, “Do it again” to the sun; and every evening, “Do it again” to the moon. It may not be automatic necessity that makes all daisies alike; it may be that God makes every daisy separately, but has never got tired of making them. It may be that He has the eternal appetite of infancy; for we have sinned and grown old, and our Father is younger than we. The repetition in Nature may not be a mere recurrence; it may be a theatrical encore.

In this view, the natural forces and processes that science studies are not entities unto themselves, but merely the ways God chooses to typically work. In science we see God’s normal working, while still allowing that there may be “grace notes” that don’t fit these patterns where God chooses to work outside of the normal pattern. (cont.)

Marshall - #23917

July 29th 2010

(cont.) I appreciate Chesterton’s cautious “may” in the last line: I don’t know that this is how it is, but it’s an interesting idea. Yet, the end result for science is the same as if God created natural processes that have a real existence of their own in the same way (no more, no less) as we do.

Regardless of how one gets there, I think we’re both agreed that God provides our daily bread, causes the rain to fall on the righteous and the wicked, and formed each of us in our mother’s womb, even though all of those also have natural explanations. In this case, it really comes down to semantics. To you, “supernatural” may indicate that God is involved (so even things that have natural explanations are called supernatural), whereas to me, “supernatural” is a contrast to natural, and both are part of God’s toolkit.

conrad - #23922

July 29th 2010


I would like to see your list.
I have me own list but you may have some i overlook.

I think the Bible’s repeatedly scooping the scientists is impressive.

A world “without form” describes the Planck Epoch BUT WHO ELSE EVER DREAMED OF SUCH A STRANGE PHASE ?
No other culture’s “creation myths” even get close to describing a truly unusual event,... which later is confirmed to have been a real event.

conrad - #23962

July 30th 2010

And Dan,
  The currently hot topic that I think may have been first published by Genesis is cosmic inflation.

Last night when most of you were sleeping i spent about 90 minutes watching Alan Guth the MIT genius-type guy explain cosmic inflation [which he is famous for introducing].

I am trying to understand if this is the same as the “expansion” on the second day of creation. 
There is a lot of similarity.

Now they say Guth’s initial theory does not hold up but there definitely seems to be SOME KIND of inflation/ expansion/ sky formation,..... that occurred early in the Creation period.
The translators were not kind to the Bible when they used the word “firmament” and then took a meaning of that word indicating solid glass dome-like structure.
But I have a Rabbi friend who says “empty expanse” is a better fit.

IT SOUNDS VERY MUCH LIKE COSMIC INFLATION,... but unfortunately Guth and the other cosmologists do not have THEIR scenario completely worked out.

It is difficult to compare two vague unsettled accounts.

But if the Bible has described cosmic inflation on the heels of describing the Big Bang and Planck’s era,.. IT IS TRULY REMARKABLE.

penman - #24014

July 30th 2010

If I may add a thought…

The trouble with citing Romans 1:18ff as proving ID is that Paul doesn’t say we CAN detect theistic design in the universe. He says that we DO know God as Creator. There’s a difference.

Romans 1:20 have been clearly perceived
Romans 1:21 although they knew God
Romans 1:32   they know God’s decree

These feed back into v.18, “suppress the truth” - a truth they know.

Belief in the Creator doesn’t depend on detecting intelligently designed mechanisms here & there. It’s more basic than that: what Calvin called “a sense of divinity”. That surely is Paul’s point in Rom.1.

Blaise Pascal said that the problem with philosophical arguments for God’s existence is that they demand such close attention, that even if they convince, an hour later we’ve forgotten why & have to work through it again.

So, while I wouldn’t rule out arguments from (e.g.) irreducible complexity, I really can’t think that’s what Paul has in mind in Rom.1. I think he’s talking about an actual consciousness of God that is possessed by humans per se, not the end product of a complex chain of reasoning which will go over the heads of many people.

Bilbo - #24018

July 30th 2010

Hi Kathryn,

Looking forward to your evolutionary explanation of the bacterial flagellum.  I hope it is less speculative than your evolutionary explanation of the antibody diversity system.

Bilbo - #24021

July 30th 2010

By the way, I think your speculative scenario for how the antibody diversity system arose could be tested:  randomly place a RAG transposon in the genomes of animals that don’t have an antibody diversity system, and then observe the results.  Is anybody trying this?

Bilbo - #24024

July 30th 2010

And are you saying that Matthew Albanese had to “meticulously design” his artwork (as opposed to making it come about randomly like a Jackson Pollack painting), but that God did not need to meticulously design the flagellum?  If not, what exactly is your point in using his artwork as an example?

Daniel Mann - #24025

July 30th 2010

1.  TIME IS NOT ETERNAL: 2 Tim. 1:9 who has saved us and called us to a holy life—not because of anything we have done but because of his own purpose and grace. This grace was given us in Christ Jesus before the beginning of time,

2.  A BEGINNING: Genesis 1:1 “In the beginning God created the heavens and the earth.” (Contra the steady-state theory that had ruled science).

3.  BUILDING BLOCKS AREN’T VISIBLE: Hebrews 11:3 By faith we understand that the universe was formed at God’s command, so that what is seen was not made out of what was visible.

4.  LAWS: Jeremiah 33:25 This is what the LORD says: ‘If I have not established my covenant with day and night and the fixed laws of heaven and earth, (Also Job 38:33)

5.  WATER CYCLE: Job 36:27 “He draws up the drops of water, which distill as rain to the streams.” (Also Amos 9:6)

6.  DINOSAURS?? Psalm 74:14 It was you who crushed the heads of Leviathan and gave him as food to the creatures of the desert. (Isa 27:1; 51:9; Jer. 51:34; Eze 29:3)

7.  INNUMERABLE STARS: Jeremiah 33:22 I will make the descendants of David my servant and the Levites who minister before me as countless as the stars of the sky…

Daniel Mann - #24026

July 30th 2010

8.  COSMIC EXPANSION, ROUND EARTH: Isaiah 40:22 He sits enthroned above the circle of the earth, and its people are like grasshoppers. He stretches out the heavens like a canopy, and spreads them out like a tent to live in.  (42:5)

9.  STARS AS GUIDES: Genesis 1:14 lights in the expanse of the sky… [would] serve as signs to mark seasons and days and years.”

10.  COUNTLESS STARS:  Jeremiah 33:22 states, “I will make the descendants of David my servant and the Levites who minister before me as countless as the stars of the sky and as measureless as the sand on the seashore. ” (Also Job 11:7-8; 22:12)

11.  THE EARTH DOES NOT SIT ON A PEDESTAL: Job 26:7 He spreads out the northern skies over empty space; he suspends the earth over nothing.

12.  STRESS NEGATIVELY IMPACTS HEALTH: Proverbs 17:22 A cheerful heart is good medicine, but a crushed spirit dries up the bones.

13.  UNHEALTHY EXCREMENT: Deut. 23:12-13 Designate a place outside the camp where you can go to relieve yourself. 13As part of your equipment have something to dig with, and when you relieve yourself, dig a hole and cover up your excrement.

14.  FOSSIL FINDS IN THE MOUNTAINS: Psalm 104:6 …the waters stood above the mountains.

Daniel Mann - #24029

July 30th 2010


It’s not the chaos or even the size of the universe that points so unmistakably to God, but the glorious design. Without the design, there would be no requirement to believe in the Designer as Romans 1 demands. Yes, you’re right that it also points to His more personal characteristics, but these can not be conveyed if creation didn’t also convey His design and purpose thru that design. It’s not either-or; it’s both!

Daniel Mann - #24032

July 30th 2010


I agree with you wholeheartedly that the governing laws are supernatural—flowing from and maintained by the mind of God, so that they work harmoniously and uniformly. Here’s why I think that this hypothesis is far more reasonable than the naturalistic one:

nedbrek - #24036

July 30th 2010

un ac: “So God’s consisent and orderly laws of genetics and DNA replication as studied though evolution, and His consistent and orderly laws relating to the half life of radioactive isotopes also present no problem to you, correct?”

Sure, today.  But we cannot use the processes of today to infer backwards to a beginning (especially in light of the changes due to the Flood).  That is way too close to 2 Peter 3:4 for me (and those who say it say the same things).

conrad - #24043

July 30th 2010

Wow Dan those are good.
But #6 about the dinosaurs is really a good example.

I remember when Luis Alvarez made that discovery of the iridium layer.
We weren’t quite ready for the Garden of Eden when T.Rex was around.

I love your list.
I’m collecting things like that.
Someday I want to publish it somewhere.
Maybe we could pool efforts here.

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