The Flagellum is Not a Motor?

Continuing the discussion from Brian Miller: Co-option and Irreducible Complexity:

Really? For starters, the bacterial flagellum is not a rotary motor. Didn’t you know?

What is it that tells you the Flagellum has top-down design logic? What makes you think it is an engine?


The rather obvious response is that @bjmiller did not say that the bacterial flagellum is a rotary motor.

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Of course. Then I’d ask him to present the similarities and differences between a flagellum and a rotary engine. The differences would far out number the similarities. The differences would make the use of the analogy in the context of ID absurd.

It is also likely he would struggle to list the difference because he doesn’t know the difference, which would indicate he is falling prey to the idol of the marketplace. Perhaps you too are falling prey to the same idol.

@bjmiller posted a link. Perhaps a review is in order.

Bacterial flagellar motor

Please also see the “Where can i learn more?” section at the end of that article. It’s not as if IDists are making this stuff up. Do you really want to have a discussion about when is a motor “really” a motor?

Yes Mung, he did say it right here.

Reading before speaking is a rather important trait. You should try it sometime.


Very good advice indeed.

@mung, I’d have no objection to saying “the flagellum is roughly analogous to a rotary motor”, and then carefully noting the differences where it becomes important. I do object to saying “the flagellum is a rotary engine”, which is a totally absurd claim. The more you know about flagellum and rotary engines, the more absurd this claim looks.

Also the linked article does not argue that the flagellum is indistinguishable from an engineered rotary motor, just that it is analogous.

I reached the same initial conclusion as Mr. Horton on this. Mung, are you perhaps implying that “the bacterial rotary motor” is not semantically equivalent to “the bacterial flagellum is a rotary motor” because the former is merely an analogy not meant to be taken literally? (In other words, are you preferring that the correct punctuation convention would have placed quotation marks around “rotary motor” so as to discourage reading the phrase too technically??)

As to the best definition of the word motor, this topic is hugely at risk of equivocation fallacies unless everyone can agree on the same definition.

It’s all semantics in the end. For example, I found an article titled “The Sun, The Mighty Engine Of Our Solar System”. We already know that stars form naturally, so we have examples of engines forming naturally. Of course, we also have motor neurons and nobody thinks you can power a car or a boat with them. This is why replacing a scientific argument with semantics isn’t that convincing.


Yes, I’m very weary of arguments that depend upon semantics, especially equivocation fallacies.

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If ID-Creationists didn’t have their silly equivocation word games they’d have nothing to talk about at all.

Mr. Horton, another equivocation game for your list:

“Evolution is only a theory.”


This is to everyone posting here, not just Joshua… I just chose his quote (above) as an example. Doesn’t everyone agree upon this?? That the bacteria contain a chemical mechanism that looks and works similar to how an electric motor works, but that is more efficient than an electric motor and able to change directions more quickly?

Does anyone really believe that the bacteria literally contain tiny motors in their posteriors? It seems like there should be universal agreement on the facts… but that it is the interpretation of them that is open to discussion and subject to opinion. If I’m missing something, please let me know. It’s not obvious to me, but I’ve been told that I’m often lacking understanding. So, go easy on me.


An electric motor works as a rough analogy, and like all analogies it fails when we look at the specifics. We could also describe ocean currents as moving walkways or the Earth’s core as the engine of Earth’s geology. We use human designs as analogies for many natural processes because it offers a quick way of getting our ideas across to other people.

Bacteria don’t have motors like the ones humans design. There are no magnets or electrical currents in the bacterial flagellum, nor are there any metal parts. The only rough comparison is a rod that spins within a circular apparatus.


Right, and thanks. I appreciate this and understand it… I did so to begin with. But I still think that everyone understands this. It is not a metal motor that works by generating an opposing electromagnetic force that then turns the shaft… but it works like a motor. So when one refers, as in the link below, to a bacterial flagellar motor, this is all implicit in what’s said. As I asked earlier, it seems to me that the facts are plain. What varies is the interpretation of what those facts mean.

To say bacteria have motors would be incorrect. But one who refers to a flagellar motor is not implicitly incorrect… they have referred to the obvious. That the mechanism that turns the flagellum acts like a motor.

I’m just trying to understand the nature of this argument and I don’t get it.


Bacterial flagellar motor
Howard C. Berg
Departments of Molecular and Cellular
Biology and of Physics, Harvard University,
16 Divinity Avenue, Cambridge,
Massachusetts 02138, USA.
E-mail: (removed)

I’m just assuming that this person from Harvard believes that everyone reading this document will understand that the word motor is an analogy, not a technical term, in the same way that you know that I don’t actually have a hammer, anvil and stirrup in my ear.


The ID argument is that only designers can make motors, so finding a motor in bacteria is evidence that bacteria were designed. First, this argument begs the question by assuming all motors require a designer. Second, it creates a false equivalency between motors humans design and a flagellum. That’s the gist of it.


Thanks… that’s what I thought. It seemed that the war that was being waged was not over the word “motor” and its use, but rather you chess players were working a few moves ahead, fighting another battle instead.

I always appreciate your honesty! So, then, isn’t the disagreement over the opinion as to whether or not it (the “m-thing”) was designed or not? Not whether or not it can be called a motor?

So, this is a philosophical issue. The ID folks would absolutely disagree that point one begs the question. The would insist that it does not. Moreover, they would state that it is not a false equivalency at all. So, it just seems to me that arguing over whether or not one can use the word “motor” is merely moving the goalposts, or fighting an alternative war instead.

I’m not fighting the battle at all, I’m merely trying to understand what’s going on. As you say, the gist of it is whether or not the spinning portion of the bacteria that propels it through the water was designed or evolved naturally. So, given that, why argue about the label? It seems as though it is merely an end-around attempt at warding off the design argument (or potentially lending it credibility) to begin with.

(EDIT: And… I’ll probably stir up all of the hornets and then run away for a few hours, because you all intimidate the heck out of me. :slight_smile: )


The point is that the mechanism is does NOT work similarly to how an electric motor works, nor does it look similar to one. They are just not the same thing.

That appears to be the ID argument being made by some people, especially because they are often unwilling to explain it as an analogy or acknowledge where the analogy fails. See, for example, this thread. @bjmiller was building the rhetorical impression that the flagellum = motor, and when asked to clarify the distinction, there is no response. I don’t want to over-interpret a single example of silence, but this is a pattern that takes place over and over. If he is not equivocating the two, he could clear it up very quickly by explaining the dozens of disanalogies between rotary motors and flagellum. I’m doubtful he even knows what the differences are, so I’m not accusing him of dishonesty here. Rather this is just a case where shallow understanding of biology might be showing.

The “electric” part, however, does not even work well as an analogy beyond the most surface of levels. Electric motors and flagellum both harness charge differences to produce physical movement “somehow”, and that is about where the similarities end. The way they harness these charge differences could not be more different.

Great examples of differences, though there may be an “electrical” current involved, not of electrons, but of protons. Depending on how we define electrical, this could count as a current. Of course, how this current is made use of is totally different than in a human designed rotary motor.

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No that is not it, at least not for me. This problem is that the flagellum is not very much like a human designed motor. We can only used that analogy if we understand the differences as well as the similarities. It does not appear the people insisting on that analogy understand the differences.

I have no problem with the label. I have a problem with replacing the reality of what a flagellum is with the straw man of a “motor,” when a flagellum is no such thing.

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So, then, is the author of the noted article, Howard C. Berg, an ID proponent who is using the label in the title as ammunition? Or is he merely a scientist who is using the label generically, as I would or any other confused person would?

Biologists often make analogies like this. What they are doing there is totally legitimate. Berg would also be able to rattle off all the differences too, and would totally dispute the use of his analogy as evidence of ID. Analogies are important, but only if we insist on keeping them merely analogies, accutely aware of where they fail.

The problem with these analogies with ID is that they seem to avoid discussion, knowledge, and understanding of where and why the analogies fails. This is an example of an Idol of the Marketplace, a prototypical example of anti-scientific thinking (Idola fori - Wikipedia).

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