The Strengths and Weaknesses of - The Edge of Evolution


The discussion was instigated by the following response from Larry Moran to Michael Behe’s discussion of Moran’s criticisms that were published in Behe’s most recent book.
Is this a fair and accurate assessment of Behe’s argument in The Edge of Evolution ? Are there any responses that could be offered to defend that argument?


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Other than Behe’s own defenses of his book? Not much. Even the ‘positive’ reviews (which generally weren’t by scientists) tended to spend more time slinging mud at the negative reviewers than saying nice things about the book.

(Incidentally, EoE isn’t Behe’s most recent – he’s published Darwin Devolves and A Mousetrap for Darwin since that book – the latter is in fact is a collection of Behe’s previously-published defenses of his earlier books, and includes quite a bit of his defense of EoE.)


What following response? Did you neglect to put in a link?

Hi Alex
I think Larry’s argument slightly misrepresents Behe’s argument and as it stands is a straw man argument as Behe’s argument is not based on a specific function but any biological function requiring several coordinated mutations.

Behe simply tried to show the mathematical challenges of mutations, before a viable function, that required several mutations would take an extreme long time.

IMO his argument is valid and poses a severe challenge to the Darwinian mechanism…

That’s mistaken. Larry clearly agrees that the relevant factor is the number of mutations required for a function regardless of what specific function they perform, and that there actually is an “edge of evolution” where, IF the hypothetical function can only evolve through some specific and sufficiently large set of mutations, that function is too unlikely to evolve in the relevant amount of time. The hypothetical idea of an “edge” is not in dispute here.

There was some quibbling about what exactly the number of mutations required for chloroquine resistance are(and whether they are neutral or beneficial, and what the relevant population size and so on is), but that’s really not the main thing at issue with Behe’s “edge” argument. Even Behe actually agrees chloroquine resistance evolved after all.

But we all agree that we can conceive of situations where the numbers wouldn’t add up and there are hypothetical functions that are extremely unlikely to evolve in the relevant timescale.

It’s just that we know of no actual example of such a function where we know it was too unlikely to evolve. They all rely on the assumption that some extant function is a tiny isolated target, rather than just another contingent historical outcome. Behe has not been able to come up with any credible example of something that represents a target in this way.

The issue is when he generalizes the idea that since chloroquine resistance required X number of mutations and Y population size, therefore other things that require the same amount of mutations found in species with smaller populations and lower mutation rates couldn’t evolve.

But we know of no such example of things that require what chloroquine resistance requires, in species with smaller population sizes and lower mutation rates etc. So there is no known example of an adaptation that demonstrably lies beyond the edge.


The empirical evidence that he offers shows that the edge of evolution (the Darwinian mechanism) is a few coordinated mutations. Can you show a novel functional gene (with a unique sequence) forming without a few coordinated mutations? Can you show an alpha helix or a beta sheet forming without a few coordinated mutations?

Your prior claim was without strong purifying selection random change will move a sequence away from function.

Still not in dispute that there’s a hypothetical edge. What’s in dispute is that any known function lies beyond it.

I can definitely show you examples of new genes evolving, yes.

Clearly if this required too many specific mutations to occur, it wouldn’t have.


Does Behe think the evolution of chloroquine resistance required “coordinated mutations”?


There’s the key, Bill. Neither Behe nor you look for the vast majority of the relevant evidence.

The fact that Behe’s cherry-picked cases don’t even support his global conclusion is damning.

Can you show us the evidence that shows that any mutations must be coordinated?

Yes. It’s what many completely random peptide sequences do. Do you really not know something so basic?


Sure but in this case you are using bacteria as your experimental vehicle with smaller genomes and gene sets. Do you think that bacteria have as difficult a path to reproductive advantage as vertebrates?

@colewd tacking on to Rum’s comments …

It’s difficult to demonstrate that something is unlikely to evolve without first identifying what can or cannot evolve. IIUC Behe considers the case of “stepwise” mutations or simultaneous mutations, but not (to my knowledge) recominations or deletions, which greatly expands the possibilities.

I don’t know of ANY work done on identifying sequences which are functional yet cannot evolve. I agree with the “edge” in that there should exist such sequences, and that would seem to be a necessary step to establish a case for ID, Every sequence discussed in the ID literature is found in living creatures, but until we know what “not evolvable” means, those examples can only be speculation (at best).


Hi Dan
Behe is challenging the Darwinian mechanism which narrows the field. In his paper he assumes gene duplications are part of the process but his argument is targeting the mechanism of random mutation and natural selection. His examples are targeted at vertebrates and not single cellular organisms.

I agree that these expand the possibilities and I think recombination is certainly an important component of environmental adaptions.

According to his last book Behe believes that speciation is certainly within the edge but probability limited to the genus/family level.

More importantly, did it? Or are all of the allegedly coordinated mutations seen by themselves in the wild? What does the empirical evidence tell us?

And @colewd, kindly note that Behe’s quote-mining of a single review is neither empirical nor evidence.


And has he found any actual instances of speciation in which the new species was in a different genus/family than its parent species?


Hi Walter
He has made extrapolations from the genetic changes that are feasible from the Darwinian mechanism. An example is his examining the genetic changes between polar bears and brown bears where the differences in genes are close enough to be accounted for by standard population genetic models and selective pressure.

Obviously not. That is why it would be interesting to know whether, according to @colewd’s reading, Behe has claimed it did.

From the fact that you wrote that in response to @WalterKloover’s comment, one can assume you intended that as an answer to his question.

So it is puzzling that your comment did not answer his question at all.


I’ll take that as a no, he has not found any purported instance of speciation that goes beyond the edge of evolution.

Given that Behe seems to be the best qualified, most persistent advocate for the intelligent design intuition, and that his best argument is so ineffective, your choice to spend so much time pushing it seems like a waste of your time.


Hi Walter
Are you making an argument against evolutionary theory?

He has extrapolated against a model of change mostly based on population genetics. Are you claiming this is not a scientific process? This is admittedly fuzzy without strict definitions of species, genus and families. He may use the genus/family claim as a way to deal with the fuzziness.

This area of discussion (edge of evolution) is not Behe’s most interesting argument IMO.

A further point, that I think is not sufficiently appreciated, is that Behe has overtly admitted that he is unable to identify a single biological difference between humans and chimpanzees that lies beyond his alleged “edge of evolution”, nor which requires the creation of any “irreducibly complex” system or structure.

IOW, whatever role Behe might imagine the “intelligent designer” (i.e. God) has played in the evolution of life on earth, God’s intervention was not needed in order for human beings to evolve from a common ancestor with chimpanzees.

This should be a very significant finding for ID, and one has to wonder why Behe has not proclaimed it more loudly.

Just kidding. We all know exactly why he has kept this hush hush, and why no other ID’er has acknowledged it.


I would suggest that this provides no evidence that this “model of change” is valid, particularly given (i) the qualifier of “mostly based” and (ii) given he is using it to extrapolate (rather than merely interpolating) .

I don’t know about Walter, but given his extrapolation and the lack of mention of validation of his model (let alone peer review of it), I would be willing to (tentatively) assert that claim.

Formulating a model should be merely the start of a scientific process.

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