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 - #24433

August 3rd 2010

There are several things that warrant unpacking here - so little space, so little time…

DNA containing contingency plans - I’m not sure that would make much sense to a biologist, but would imply that after the fall, selective pressure caused evolution: sounds a bit Lamarckian to me.

You define the understanding of “good” in Genesis 1 as “no death” - that’s circular. It’s more likely to mean “fit for purpose” in the context.

Isaiah 65 (it’s a wolf, not a lion, with the lamb) does not say there’s a return to the original earth, but that the new heavens and the new earth will make the old forgotten. If he is talking about a literal return, v20 suggests accursed people dying before 100 years and the rest “living out their years”.

Can we prove from the Bible that what was true in Eden was true in the outside world? It was God’s special space. Their punishment, after all, was to be excluded from it to a world where life would be a struggle.

“Survival of the fittest” means those most suited, not those most violent. I worked in a lab once where the cutest rabbit was the one that survived. God made it clear to Adam that for him “fittest” meant obeying his clear command.

Daniel Mann - #24446

August 3rd 2010


I’m not maintaining that there’s a “return to the original earth,” but merely that the idyllic quality of Eden. Therefore, we read about the “restoration of all things” (Acts 3:21). Wesee it pictured in Revelation:

•  Rev. 22:2-3…. On each side of the river stood the tree of life, bearing twelve crops of fruit, yielding its fruit every month. And the leaves of the tree are for the healing of the nations. No longer will there be any curse.

The Edenic imagery acknowledges that Eden was an ideal state, not a Darwinian struggle, and that God would fulfill aspects of His original plan. Jesus, as the second Adam, accomplished this:

•  1 Cor. 15:21-22 “For since death came through a man, the resurrection of the dead comes also through a man. For as in Adam all die, so in Christ all will be made alive.”

Death didn’t result from God’s messy plan but from sin. Humanity didn’t die because that was just God’s way of doing business, but because of us! Likewise, Jesus didn’t come to correct the sin and death of God’s imperfect, bloody plan, but the effects of the Fall. Therefore the “very good” initial state did not include death.

Do you deny Satan and demonic forces?

Scanman - #24462

August 3rd 2010

Mike Gene,

You said…“Interesting.  One thing to ponder is that “environmental pressures” tend to largely be the output of other living things.  For example, bacteria and viruses are ubiquitous and constitute a major component of our “environment.”  Evolution has occurred in the context of a biosphere and not on the surface of a sterile planet”

I say…
But where does God’s omniscience play into the scheme of Theistic Evolution? If God takes any sort of guiding role in what survives to reproduce, then wouldn’t you call that ‘Intelligent Design’?


Jon Garvey - #24469

August 4th 2010


You seem to have a tendency to shift ground rapidly - why should I deny demonic forces when my arguments have been that you’ve dealt inadequately with Scripture and indeed have tacitly added greatly to it to explain the world we live in (that is, a complete redesign of the animal world to accommodate death, on which Scripture is silent, and which you vaguely explain as “it was already in the DNA”.

You cited Isa 65 (altered) as evidence for a return to the original world of animals and man at peace, but then deny you’re suggesting there will be areturn to the original earth. That chapter clearly, as we’d agree, refers to the final state, and clearly contains Edenic imagery and yet clearly contains figurative elements since it includes human death, which we’d agree to be absent from the new heavens/new earth scenario. To rest a herbivorous future, still less a herbivorous past, on a wolf and a lamb is to conclude too much.

The Revelation and 1 Corinthians passages both refer to the human realm. The latter refers to all who are “in Adam”, ie humanity and all “in Christ”, the saints. If it meant the animal world, we’d be expecting a general resurrection of animals, which is hardly orthodox! (...)

Jon Garvey - #24470

August 4th 2010

(...) I think at root you have *assumed* that the Bible means “all death whatsoever” when it refers to death, and I would argue that careful exegesis does not support that - indeed, it extricates one from all kinds of spiritual somersaults.

Incidentally I see on another blog here a professional church historian noting that including animal death in the original state of the world is hardly new, being assumed by theologians as venerable as Augustine and Thomas Aquinas.

Apologies for typos on previous entry.

penman - #24471

August 4th 2010

Trevor K:


Evolution on the other hand proposes that that information is newly created - something that goes against all knowledge of the DNA structure to date>


Now, I’m not a professional scientist, but as an interested layman I’ve studied some of the issues. I don’t think we may just airbrush away the view that evolution can produce new genetic information. Here are a few sources that argue the point (I’m not competent to comment but the sources don’t seem to be talking obvious nonsense) -

Examples of Beneficial Mutations and Natural Selection (on

Your own view that there are broad “kinds” with a DNA plan capable of much variation but within limits (no new kinds developing) is, I assume, a possible scientific hypothesis. But I still don’t think that’s what Gen.1 says. All I see is God creating “all kinds of animals”, where “kind” is an ancient-near-eastern common-sense observation of horses, sheep, goats, etc. There’s no science here: just a celebration of abundance.

penman - #24473

August 4th 2010

Daniel Mann:



Well, Daniel, I would say I’m not overly interested in Darwin. His writings are not some scientific equivalent of a Holy Book. I’m interested in the history of our planet & its life. You’ll be interested to know that I’ve been “pursuing inquiries” pretty relentlessly for some four years solid, after becoming fed up with the ignorance & misrepresentations of young earth literature (to which I was exposed in my church). To date, my inquiries have convinced me ever more deeply of two things:

1 - The reality of geological “deep time”, the origins of biodiversity in common descent with modification, & natural selection as a basic mechanism of change;
2 - The fact that I don’t have to give up the essence of any catholic, creedal doctrine to believe the above, but can stand firmly in the 2000 year tradition of Bible-based orthodox faith. (I’d say a good parallel is the way Christians were forced by scientific discovery in the 17th century to give up a geocentric for a heliocentric view of the solar system. All the posturing about heliocentrism denying the Bible turned out to be massively misguided…)

Daniel Mann - #24474

August 4th 2010


Once again, I think that there’s a great deal of evidence of a Fall from an ideal state and a future restoration to something similar. I asked you about the Devil because there’s a lot of NT evidence that the Devil was in Eden relative to the Fall (Rev. 12:7-9; Rom. 16:20; 1 John 1:8; John 8:44).

As far as death suddenly coming to even the animal world:

•  Romans 8:20-21 For the creation was SUBJECTED TO FRUSTRATION, not by its own choice, but by the will of the ONE who subjected it, in hope that the creation itself will be LIBERATED FROM ITS BONDAGE to decay and brought into the glorious freedom of the children of God.

“Creation” didn’t come in Darwinian form. Instead, it had been subsequently “subjected” to “decay” (death).

In summary, there is just too much Biblical evidence for a Fall from something idyllic to a heavenly restoration. (Acts 3:21)

Daniel Mann - #24476

August 4th 2010


The reason that the Church had been geocentric was that the science of the day had been geocentric. The church had been taken captive by the “science” of their day. I suspect that, in some respects, the church is even now being taken captive by the modern scientific consensus.

Jon Garvey - #24479

August 4th 2010


I don’t have a problem with Satan in Eden, because Scripture makes the connection - however it does raise questions about exactly how materialistically to take the Eden account. Genesis simply says “the serpent” as the most subtle of the wild animals - and modern serpents crawl on their bellies as per the curse. But they’re not very subtle nowadays. Not many Christians eradicate snakes on sight as Satanic. Later Scriptural use varies:  John the Baptist applied “seed of serpents” to the Jewish leaders (satanically influenced humans). Isaiah uses the child and the (ordinary) adder as an Eden allusion. Revelation refers to “that ancient serpent” as Satan the spiritual being. There are all kinds of metaphorical uses going on throughout, and work is needed to understand them.

To conclude things like, “There was only one snake in Eden. I talked and had legs in Eden, got taken over by a fallen angel Satan, and was cursed to leglessness and enmity with man as a result. The fall robbed it of speech and intelligence, but we are now correct to speak of evil men as his offspring, and Satan as cursed but not legless.” Some of those things may be true, but only if one accepts metaphor at some level. (...)

nedbrek - #24482

August 4th 2010

penman, I encourage you to have more confidence that God can speak to us clearly through His word in the Bible - and less confidence in men.

All of the experiments showing beneficial mutations show that mutations can happen very quickly - yet, these mutations always result in the same sort of organism.  It has never been shown that a prokaryote can become a eukaryote, or an asexual organism can become sexual (like a paramecium from an amoeba).

You are asked to take on faith that small changes over time can result in large changes - yet experiments show hard boundaries on variations.

Jon Garvey - #24483

August 4th 2010

(...) I was working on the Romans 8 passage only last week, and though I’ve by no means drawn extensive conclusions I realised what unthinking assumptions I’ve always made about the text. For example, I’ve always assumed it refers to “creation” as “the material cosmos”. And yet look at its meaning in Col 1.23 and Mk 16.15.

Similarly “decay” seems to suggest thermodynamic or death issues, but actually the Greek is the same word used in the Septuagint of Genesis 6.11 (“corruption”), which is the human corruption of sin rather than the death imposed by God on the creation as a result of the fall.

“Frustration” relates back to the “vanity” of Ecclesiastes, which is in itself a commentary on the futility of human affairs because of sin and death.

“Liberty” is used by Paul elsewhere only of Christian freedom from the law.

What, exactly, would it mean for the non-human creation to “wait in eager expectation” for the Sons of God to be revealed? Is nature sentient? If I take the passage as referring to nature, I have to take it figuratively. If I take it to mean creation in the human sense, I can take it literally. I certainly can’t take the meaning for granted, as I did before.

Jon Garvey - #24485

August 4th 2010

@nedbrek - #24482

You’re hardly being fair on the scientists - I never heard of evolution proposing that paramecium evolved in one step from amoeba - that would be like a badger evolving into a sea urchin.

But I’m not clear where the Bible says clearly that species are immutable - indeed Daniel Mann seems to concur in the actuality of a massive change in the species after the fall to encompass carvivorous species in every phylum (even amoeba): filter-feeding whales, parasitic wasps, pitcher plants, anteaters, woodpeckers, spiders.. and badgers and sea urchins of course.

Daniel Mann - #24493

August 4th 2010


Granted – there are interpretive difficulties and figurative elements in the first several chapters of Genesis. However, this shouldn’t become an argument to dismiss their historicity or “materiality.”

Whenever the NT quotes or eludes to these chapters, it’s never to suggest that they are figurative, but rather historical. For example, Jesus’ teaching on marriage:

Matthew 19:4-6 “Haven’t you read,” he replied, “that at the beginning the Creator ‘made them male and female (Gen 1),’ and said, ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh’ (Gen 2)? So they are no longer two, but one. Therefore what God has joined together, let man not separate.”

Daniel Mann - #24516

August 4th 2010

Ok, let’s take your suggestions for a test-drive. Below, I plugged them into Romans in parentheses to see if they make sense:
•  Romans 8:20-21 For the creation was subjected to frustration [“futility of human affairs because of sin and death’], not by its own choice, but by the will of the one who subjected it, in hope that the creation itself will be liberated [“from the law”] from its bondage to decay [“the human corruption of sin”] and brought into the glorious freedom of the children of God.

1.  “Frustration” works better than “futility of human affairs because of sin and death.” Perhaps we can now make a case that our “human affairs” have corrupted the planet, but this case could hardly have been Paul’s point. Instead, it seems that he argues that all creation (perhaps also the cosmos) was affected by the Fall. Besides, it was God who did the subjecting and not “human affairs.”


Daniel Mann - #24517

August 4th 2010

2.  Liberation “from the law” has nothing to do with this context. Rather, it’s a matter of liberation from “decay.” You have it this way: “creation itself will be liberated [“from the law”] from its bondage to “the human corruption of sin.” Creation needs no liberation from the law. The rest of the sentence is incoherent.

But even if you are right, you are still unable to wiggle away from the Fall. Even according to your reconstruction, creation is seen as fallen from a more perfect state, and will return to “freedom.”

Jon Garvey - #24525

August 4th 2010

@Daniel Mann - #24493

So, you say that early Genesis is history with figurative elements. The question is what hermeneutical principles are used to decide which is which. In the Isaiah passage we’ve discussed we’d agree it’s talking of future historical (post-historical?) events, but with figurative elements including a new creation with human death, infants, vineyards at all latitudes and pet adders.It would help to define “historical” and “figurative”.

As regards “materiality” that could mean “about the real world” or “giving a physical account of the world”, which is different. But John Walton’s book on Genesis has shown how blinkered our assumptions can be on that: I agree with the reviewer who said every Bible student should stop whatever they’re doing and read it, because it completely redefines the discussion.

Regarding the idea that “figurative” and “factual” are opposed, here’s a link to a humble piece I’ve attempted recently to show what a false and dangerous division it is:

Jon Garvey - #24527

August 4th 2010

@Daniel Mann - #24516-7

Why would I want to “wiggle away” from the fall? That was the serpent’s job. I’m trying to see what God’s word really teaches about its nature.

A second test drive on Romans 8: previous context is the contrast between human life in the Spirit and in the flesh.

For the whole of creation (κτισις)[humanity to which the gospel has been preached, Col 1.23] was subjected to vanity (ματαιοτητι)[cf Ecclesiastes], not by its own choice, but by the will of the one who subjected it [through the curse on Adam and his line, ch 5], in hope that this creation itself will be liberated from its bondage to corruption (φθορας) [Gen 6.12, Rom 1.23, 2 Pet 1.4] and brought into the glorious freedom (ελευθεριαν) of the children of God [Rom 6.18, 6.22, 8.2, Gal 5.1].

Follow-up context is God’s purpose in hardening the Jews so both they and the Gentiles will be saved. In my reconstruction mankind [taken generally rather than comprehensively, as Scripture habitually does] is liberated so that the ground is no longer cursed because of him. Scripture teaches an entire re-creation (and coming together) of heaven and earth that no mind has conceived, but that doesn’t mean Romans 8 teaches it.

penman - #24552

August 5th 2010


> I have confidence that God not only can, but does, speak clearly in His Word about things that are necessary for our salvation. That’s the Protestant view of “clarity” in Scripture. Eg the Westminster Confession - “All things in Scripture are not alike plain in themselves, nor alike clear unto all; yet those things which are necessary to be known, believed, and observed for salvation, are so clearly propounded, and opened in some place of Scripture or other, that not only the learned, but the unlearned, in a due use of the ordinary means, may attain unto a sufficient understanding of them.” Unless we argue that young earth creationism is necessary for salvation, it isn’t covered by what the Bible “clearly” teaches. It’s by no means clear to me that the Bible teaches the distinctive beliefs of young earth-ism, or even some of the distinctives of old earth creationism (eg fixity of “kinds”, however defined). I understand your scientific doubts about the mechanisms of evolution. But the general theory (common descent with modification) seems well established to me.
penman - #24556

August 5th 2010

Daniel Mann
“The reason that the Church had been geocentric was that the science of the day had been geocentric. The church had been taken captive by the “science” of their day. I suspect that, in some respects, the church is even now being taken captive by the modern scientific consensus.”

I don’t think that’s a good analogy. The analogy is that theologians defended geocentricity by appealing to what the Bible clearly & literally teaches, against a finally triumphant consensus among practicing scientists that heliocentrism was the better theory. In the process, theologians made themselves look like closeted ignoramuses (or should that be ignorami?) & enemies of hard-won knowledge.

I forbear out of charity & courtesy to make present day applications.

In my neck of the woods, “the church” is certainly not “being taken captive by the modern scientific consensus”. It is vilifying everyone who even sympathizes with it, & using unChristian tactics to destroy reputations.

Having said that, I don’t actually think that the church, qua church, should be preaching any scientific theory of origins as “things most surely believed among us”. It should be preaching the faith of Christ, & giving space to discuss the science.

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