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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Jon Garvey - #24765

August 6th 2010

@Daniel Mann - #24754

Special pleading is beneath you! To paraphrase your argument, “Although all the available evidence supports an age of life on earth in billions of years, that’s only because a worldwide conspiracy of scientists is excluding all Creationists from universities and suppressing the real evidence. These Creation Scientists, even though omnipresent on the Internet, influential in US politics and funded by some of the richest churches in the world, have been unable to come up with either watertight refutation of the prevailing science, nor a persuasive method that points to a young earth, because of the demonic nature of this conspiracy.”

That is no better an argument than saying Christianity would be proven untrue if only the Church hadn’t suppressed the real evidence for centuries. Or that the world’s goverments are all covering up the presence of Aliens on earth. Or that the Illuminati are taking over the world. Or that the US Government bombed the WTC to discredit Islam.

The evidence is all peer-reviewed, published and comprehensible to an intelligent adult.

Daniel Mann - #24769

August 6th 2010


The very NT mention of the Sabbath (often related to the six days of work – Luke 13:14) also endorses the Gen.1 account.

I too respect your civil and enquiring mind and hope that we can continue to connect in cyber-land. Here’s my blog:!

Daniel Mann - #24772

August 6th 2010


I don’t think you’re being fair. I’m not talking “conspiracy,” but I am invoking the power of our social and profession biases. In this regard, let me just quote from Karl Giberson’s “Saving Darwin”:

“How shocking it is today to acknowledge that virtually every educated person in the Western culture at the time …shared Haeckel’s [racist, eugenic] ideas. Countless atrocities around the globe were rationalized by the belief that superior races were improving the planet by exterminating defective elements…there can be little doubt that such viewpoints muted voices that would otherwise have been raised in protest.”

I think you’re placing too much hope in peer review, and I’m not the only one who has grave doubts about this institution.

Jon Garvey - #24781

August 6th 2010

@Daniel Mann - #24772

Well, maybe I was a little harsh - but the Creationists have not produced evidence, and you can’t argue a case on the basis that the evidence would probably be there if only it weren’t.

I don’t think a comparison of the ubiquity of Social Darwinism in the last century has much to contribute to an assessment of a myriad streams of physical evidence in the literature on earth chronology. But as we started this recent discussion on the relative “transparency” of Scripture and nature, it’s only fair to point out that in South Africa and the Southern states Christians found incontrovertible evidence in Scripture that the Hamitic races were cursed and therefore inferior. And that was being taught in an Evangelical Anglican seminary in SA to my friend a couple of decades ago, long after it had vanished from the scientific world.

Both show that society’s convenient presuppositions are easy to read into both science and theology.

Daniel Mann - #24782

August 6th 2010


Thanks for the apology. I too agree “that society’s convenient presuppositions are easy to read into both science and theology.” There’s no limit to the way we can misconstrue things.

However, I think that the potential for deception is even greater today because of the horrible imbalance in discovering new “findings” and reporting them, as I had mentioned. In additional to this, the universities and media are staunchly committed to evolution and to silencing anyone who breaks rank with them. And I fear that this will become even more rampant as the fear/love of God continues to disappear from our horizons.

You mention the failure of creationists to promote new scientific findings. Well, for one thing, they can’t get jobs in major universities. For another, no professional journals will publish their findings. Even some so-called Christian schools have contempt for them. Phillip Johnson claims that he’s received some of his worst receptions at Christian schools.

Jon Garvey - #24867

August 7th 2010

@Daniel Mann - #24782

Phillip Johnson is of course an ID lawyer rather than a creation scientist. I was at a meeting where he adressed national evangelical leaders, medics etc here in the UK and he got a respectful hearing. At an open meeting the next day, where he shared the platform with Andrew Snelling, he received some flack form ordinary churchgoers for *not* taking an unequivocal stance on the historicity of Genesis. Maybe that’s the kind of opposition he met in schools.

Alternatively, a few years down the line, the schools might be aware enough of the debate to see that ID has got into a difficult philosophical position by being founded on the basis of trying to use science to show what science cannot explain. It is a sophisticated God of the Gaps movement, which has already given up some of its earlier ground.

Snelling, by the way, only had opposition from a scientist present who was angrily accusing him of abusing the data in his publications. This was, of course, rather technical for a meeting of predominantly completely lay-persons, but I had the impression that Snelling rather resented being challenged in public debate. But that’s how science works.

Daniel Mann - #24878

August 7th 2010


I goofed. Yes, Johnson is ID and not a creationist.

I liked the way you put it: “to use science to show what science cannot explain.” Very concise, but, of course, I disagree. It’s not just that ID points to the limits of naturalism (not science), but also attempts to demonstrate that ID causation is more likely than natural, unintelligent causation to explain phenomena in question.

Instead, “naturalism of the gaps” is more appropriate. It tries to fill in the gaps where we do not find ID apparent. There is not one stitch of scientific evidence that phenomena occur because of natural law or causation!!

England, hmm! Where? What do you do?

Jon Garvey - #24883

August 7th 2010

@Daniel Mann - #24878

“There is not one stitch of scientific evidence that phenomena occur because of natural law or causation!!” That’s a little contentious - or did you mean “these” phenomena, ie those ID points out as opaque to science?

The problem is that everything in the natural realm starts as not-understood, and needs sometimes quite lengthy study (sometimes thousands of years) to join the ranks of the now-understood. As I and others have repeatedly stated, Scripture is happy to ascribe to God’s design even those things adequately understood at the time (ie they knew that “God feeds the ravens” means “God works things out so a rabbit dies close to where they’re foraging”). ID could have the same humble attitude, but (a) tends to say “Chance did everything except this especially complex bit, which only God could do” and (b) tends to get trumped by the unravelling of new “natural” mechanisms.

Personally I’d rather encourage reverent wonder by saying, “Wow, look at that!”

“England, where?” That blob just of the coast of Europe, actually ... no, I was a GP in Essex until I retired 2 years ago. But my daughter’s just down the road from you on Upper West Side.

Daniel Mann - #24886

August 7th 2010


I am making a more radical statement than ID. I’m proposing that there is absolutely no scientific evidence or even philosophical justification for naturalism. Yes, we all agree that things happen according to formula in predictable ways. But what is the foundation of these laws? Natural, independent and non-intelligent, or do they emanate from the mind of God. Philosophically and Biblically, I’d go with the latter:

•  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…

Sadly, naturalism had pulled off the greatest coup – it has convinced both layman and professional that it IS science and not an impoverished philosophy that forbids any mention of God in the classroom.

Please see for why supernationalism is a better paradigm than naturalism.

When you visit you daughter in NYC, please come for a meal, with your daughter of course!

Jon Garvey - #24929

August 7th 2010

@Daniel Mann - #24886

You’re stating a theological point that I don’t think helps us much (discussed in various blogs on the site).

Let’s suppose I’m an atheist. I see that the Universe acts very consistently, and can trace cause and effect back to the fundamental forces. I assume that’s all there is.

Suppose I’m a Christian (not too hard, that one). Again I see that the Universe acts consistently so it’s covenient to say that God works material things by principles he’s set up, so I call them “laws” by analogy with Mosaic law. At the same time I believe in miracles. So I could explain the situation in several ways, probably equally valid biblically:

God set up the Universe to operate quasi-autonomously, but so cleverly that events pan out as he wishes (every sparrow falling to the ground according to his will). Occasionally he manually
overrides nature to produce miracles.

Or the same, but does miracles cunningly using the “laws” (but who’s going to measure it?)

Or he makes everything happen each moment, “law” being just a statement of his usual habits.

Or he guides events by contingency within the laws (eg chaos/quantum mechanics).

One may be correct, but God’s not telling, so why worry?(...)

Jon Garvey - #24933

August 7th 2010

PS Arguably the book of Genesis was the basis on which the investigation of natural law became feasible. If you fancy some more turgid prose, I did a slightly tongue in cheek piece a while ago on the predicitive value of the creation account for science:

Daniel Mann - #24974

August 7th 2010


The question of naturalism vs. supernaturalism matters greatly. For one thing, since naturalism has won out, consideration of the supernaturalistic paradigm and causation have been ruled out of bounds. It would be like a detective looking for a murdered, but arbitrarily ruling out the possibility that the murdered is under six feet tall. Such a limitation might prevent him from finding the real murderer.

Furthermore, a lot of foolish research is going on and money wasted because the research is devoted to finding natural causes for things that it can’t possibly explain—life, the origin of DNA, the beginning of the Big Bang, consciousness…

Jon Garvey - #25106

August 8th 2010

@Daniel Mann - #24974

I’m not sure this is consistent - if your view is what might be called “hypersupernaturalism” (that is, God manages each individual event and natural law is a chimera) then *all* science is waste of money and time, because every result has to be interpreted, “God did it that way on this occasion, but who knows what’ll happen next time?”

If nobody investigates the “big questions” they’re also guaranteed to fail to come up with evidence that particular phenomena are impossible to explain scientifically - something the opposite of the ID programme. Not that such negative evidence is likely - absence of evidence is not evidence of absence. so unbelievers will remain.

It seems to me (in brief) that Scripture tells us that God has created a Universe separate from himself and made it fair game for us to investigate (from making fire to Big Bang cosmology) both for utility and to glorify his works.

Those things that are off-limits are what transcends the Universe, and cannot therefore be approached using created things like vision, human reason etc. That, in sum, is God. Information about him can *only* come from revelation (salvation events, prophecy, personal encounter). Deut 29.29.

Daniel Mann - #25111

August 8th 2010


Sorry. Evidently, I didn’t communicate clearly enough. Science is just as relevant to the supernaturalist as to the naturalist. However, while the naturalist believes that causation (Laws and forces) arises from independent, self-sustaining, undersigned, multiple forces, the supernaturalist recognizes that these must be intelligently created, sustained, and harmonized by a single intelligence.

Interestingly, these laws operate uniformly throughout the universe. Forces have a source, but when we move further from the source, its force diminishes. Not so with our laws of physics. How can naturalism explain this? Rather, it seems that the unchanging source of our laws, operating within the context of molecules-in-motion, must be transcendent.

Jon Garvey - #25112

August 8th 2010

@Daniel Mann - #25111

I’m not sure if I agree or not - I.m confused, or else we both are. Let’s work through…

(1) “Forces have a source.” Current science places the origin of all the fundamental forces in One Big Bang. Of course, that begs the question of its origin (cf my Three Creation Myths) but I’m not sure that’s what you mean.

(2) “The naturalist believes that causation arises from multiple independent forces.”  They’re actually trying to resolve them to one, but so far I believe 4 is the number, though there are hints that two might be interdependent. The values of those forces*appear* independent and fine-tuned to favour a user-friendly universe. The theory is they arose randomly early in the big bang, and because that stretches credulity it’s postulated (unprovably) that Multiverses exist, and we regard ours as loaded because only such universes prduce folks like us (Strong Anthropic Principle). To my mind, a rational God makes more sense.

(3) But I don’t think your “forces diminishing” argument holds good. Big Bang -> Universe -> governed by outcome of Bang. If a bomb causes shrapnel, it’s still shrapnel when it hits you. The ubiquity of physics/maths does negate polytheism though.

Daniel Mann - #25114

August 8th 2010


Just to regard #3—The shrapnel decreases in velocity as it travels further from its source. The same pertains to radio or TV waves. However, the laws of nature—gravity and other constants—exert the same force wherever we look in the universe. The very fact that these forces/laws are unchanging and uniform argues against them coming from a physical or energy source within this universe of molecules-in-motion, and should tend to cause us to look for a transcendent cause.

Jon Garvey - #25116

August 8th 2010

@Daniel Mann - #25114

I’m still not sure the analogy is valid. If a lump of shrapnel from a nuclear explosion in New Mexico drops harmlessly at my feet, I’m still not surprised if exploding a similar bomb in my living room kills me (and half the population).

You can imagine it as the Big Bang generating a bunch of hand grenades. Each one was “designed” and primed at source, but there’s no reason they still shouldn’t go off with a bang once they arrive here and you pull out the pin.

It is wonderful (and convenient) that the Universe is of a piece, but I don’t think it would give a scientist any philosophical problems. The fundamental forces are not energy per se - they’re the maths by which energy operates, and they’re built into matter/energy wherever it goes.

Put it this way - I don’t think the issue would persuade an honest scientist or philosopher that things didn’t add up. Whereas the actual values of the fundamental forces might - and have done, in not a few cases, such as Anthony Flew’s.

Daniel Mann - #25141

August 9th 2010


Evidently we’re kicking different soccer balls, perhaps even in different fields. I probably didn’t explain myself clearly enough.

Jon Garvey - #25149

August 9th 2010

As long as we’re not kicking hand grenades…

Rich - #28502

September 7th 2010

Jon (24883):

You wrote:

“ID could have the same humble attitude, but (a) tends to say “Chance did everything except this especially complex bit, which only God could do” and (b) tends to get trumped by the unravelling of new “natural” mechanisms.

“Personally I’d rather encourage reverent wonder by saying, “Wow, look at that!” “

If I had a dime for every time I’ve corrected (a), I’d be richer than Bill Gates.  ID does *not* say “Chance did everything except this especially complex bit, which only God could do”.  It has *never* said that.  Yet TE/EC people keep passing this off as a characterization of ID, *even after they are challenged and can’t find a single ID writer who says this*.  I wish TE/EC people would actually read ID material and get it straight before they criticize it.

On (b), I can’t think of a single example where any important ID claim has been unravelled by any new empirical discovery of science.  Can you?

On your third point, ID people say, “Wow! Look at that!” all the time.  And like the Psalmist and the author of Romans, they draw a rational inference from the “Wow!”.  They aren’t bound by a fideistic theology which has a built-in prejudice against design detection.

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