The Stone Bridge example and IC

Dr. Swamidass, without a clear example, it is difficult for me to understand what Muller’s point is. I thought the stone bridge was meant to be such an example. You say that it is not. And now you say you have provided two examples to illustrate Muller’s argument. What exactly are those two examples?

I was going to move on to Orr’s argument, but you say that you really want to hear from Behe, not from me. Since Behe already had an extended exchange with Orr that can be found in his list of articles, you have heard from Behe. How do you think Behe’s response failed?

And by the way, the article you cited calls the stone bridge an example of the Mullerian two step process:

“A clear example of the Mullerian two-step is given by a stone bridge. Consider a crude “precursor bridge” made of three stones. This bridge spans the area needed to be crossed and is thus functional. For step one of the Mullerian two-step, a part is added: a flat stone on top, covering all precursor stones. Whether this improves the functionality of the bridge is irrelevant — it may or may not, the bridge still functions. For step two of the Mullerian two-step, the middle stone is removed. Voilá, we have an irreducibly complex bridge, since the last step made the top-stone necessary for the function.”

So you may not think the stone bridge is an example. But the article you cite thinks it is.

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Let’s use lungs as an example. Terrestrial vertebrates (e.g. reptiles, mammals, birds) can’t live without them which makes them necessary. However, there are species that have both gills and lungs (e.g. lungfish). They are able to extract oxygen from water, but are also able to extract oxygen from air if they find themselves in brackish water that is depeleted in oxygen. In the case of these fish, lungs are a benefit but not a requirement. When fish evolved to be land creatures they lost their gills. This resulted in a situation where lungs are now necessary.

This is an example of a Mullerian two step. Add lungs, which are beneficial. Later, make them necessary.


Hi TA, in that example, Behe would say that lungs and gills are very complex multi-systems, and wouldn’t qualify as counterexamples to IC, which considers single systems.

Perhaps he would. But it would be a dodge.


The ameba-bacteria obligate symbiosis is an excellent example to work out that shows why this is a dodge. Also, @Biblo, have you read these two linked critiques yet?

These articles have it spot on. No mention of these or rebuttal of them from Behe that I have found. Have you?


I have a feeling that nothing you show Behe would be considered a counterexample. He would find some excuse as to why each example does not count.

Nonetheless, lungs are still an example of the Mullerian Two Step which is ultimately what you were asking for.


Yes, TA, thanks for the example.

No, it is not a dodge. Behe’s point is that before we can answer the question of whether Darwinian evolution can account for the evolution of things like lungs and gills, we first need to answer the question of whether it can account for the evolution of “simple” molecular machines. If it has problems accounting for those, why assume it can account for more complex systems.

Make up your mind, Dr. Swamidass. Do you want me to try to answer your challenges, or do you just want to hear from Behe?

I’m wondering if there could be ANY single system examples of IC. All living things we know of are multisystems. Bacterial flagella are beneficial, but not necessary. Blood clotting is beneficial for a creature IF it has already developed a circulatory system, but not before. Even the flagellum itself is a multisystem, and most of the component protein have multiple roles within the cell.

Nothing evolves in isolation. Restricting the definition of IC to single systems is sort of like asking why evolution has not produced a Crockoduck.

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I want to hear from Behe. On another thread if you’d like to make your own case from IC, not speaking for or defending him, that might have value. This means you would have to make the case with logic and evidence, answering criticize consistently, without appealing to Behe’s authority. It would not be about whether or not we understand Behe, but whether or not you are making a coherent case. Is that what you want to do?

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That’s just an excuse. The only reason Behe excludes macroscopic adaptations is because we have a fossil record for those changes.

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Not true, TA. Behe argued for common descent in his second book. He does not reject evolution. He rejects the idea that it all happened via random mutations. But the question is how to decide that question. He hopes that it can be decided by analyzing the possibilities at the molecular level. This means considering “simple” molecular machines.

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The basic IC argument applies to any system, be it at the molecular level or at the macroscopic level.

The idea is that such a system can’t evolve through a pathway where the individual parts would have a selective advantage. Instead, the whole system has to appear at once if it is going to evolve through random mutations and selection. That is the argument.

Therefore, finding macroscopic IC systems that do have function without some of the parts or predecessors that have different functions counters the argument. There are examples in the fossil record, such as the evolution of the irreducibly complex mammalian middle ear evolves two of the required parts from bones in the reptilian lower jaw.

What Behe’s argument boils down to is an argument from ignorance. Behe can’t think of an indirect pathway by which these systems can evolve, therefore they didn’t. This is why he sticks to molecular systems because he doesn’t have to worry about transitional forms being dug up.

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Dr. Swamidass, I am a layperson. So I rely on experts to try to help me sift through the evidence. It helps me when Behe publicly debates the experts. He has done this in the past. From what I can tell, Behe usually carries the day. However, I could be mistaken about that. What would help is if an expert, such as yourself, were to evaluate Behe’s debates. For example, you could read through the debate he had with Moran in 2014 and offer your opinion. Or you could read through the debate he had with Miller in 2015 and do the same. Or his debate with Thornton (2012, I think) and do the same. That would be very helpful.

And I hope Behe eventually engages with you publicly. I would look forward to reading both sides.

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TA, it’s not just that Behe can’t think of intermediate forms. Nobody can think of intermediate forms. Or so he argues. If the theory is that such systems evolved by random mutation, then one should be able to offer a plausible pathway by which it could have happened. If nobody can, then why insist that it happened that way? It makes Darwinian evolution into a religion, instead of a science.

To belabor a point already made on these threads: Do you believe that Lewis and Clark’s expedition traveled from St. Louis to the Pacific Ocean and back? Nobody knows the exact path and daily day-by-day progress (although their log notes were quite impressive and come close). And as you said, at best one may only be able to offer “plausible pathways by which it could have happened.” Yet, no doubt our understanding of such will improve as the discoveries are made and the evolutionary processes better understood.

Is something utterly false in science until the piles of evidence reach a certain height? How many excellent hypotheses in science were far less well attested a century ago than they are now? Did that make those hypotheses “religion instead of science” until they reached a level that suddenly became science?

Meanwhile, Darwinian evolution hasn’t been the standard in a very long time. It was never a religion. It was a step along the way of continually clearer understandings of evolutionary processes. There is much yet to be understood—but that doesn’t make evolutionary biology a religion. Not even close.

It would be far easier to argue that various of Behe’s claims are closer to “religion”. (I put religion in quotation marks because I’m using the word in this context more like you are using it, even though I don’t normally use it that way. As an academic, I’m more prone to apply the word religion in its religious studies definition of that which involves reverence towards that which is transcendent.)

That’s what makes it an argument from ignorance.

I don’t see why this is true. It is entirely possible for systems to evolve and us humans being ignorant of how it evolved.

Behe is also shifting the burden of proof. It isn’t enough to challenge evolution. Behe needs to offer positive evidence for his own claims. For example, Behe needs to show us the generation before these IC systems appeared and the generation after these same systems appeared. He then needs to show all of the genetic changes that resulted in the emergence of this system, and then show how these changes were guided.

We tend to think that IC systems evolved because of all the other evidence that supports evolution.

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I assume that we can offer plausible pathways that Lewis and Clark used. If we couldn’t, then I think it would be reasonable to doubt that they did indeed make such a trip.

If we insist that Darwinian evolution, or random evolution, or non-intelligently guided evolution, happened, when we aren’t able to posit plausible pathways, then I think we have reason to doubt it. To insist that we accept it regardless is to make it into something other than science. Call it religion or superstitution, or whatever term you prefer. Just not science.

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