posted 19. September 2002 02:07                   

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Above, Dembski asked you to put your "hallmarks of evolution" on the table. You then listed three criteria. I found this encouraging. However, in light of your parsimony argument above, it's starting to look like your hallmarks have no teeth. Above, you seem to be arguing that you accept the evolution of the flagellum because of the evolution of blood clotting and the immune system. In other words, you don't need any hallmarks in the case of the flagellum. Instead, you appeal to philosophical arguments about parsimony.

As I see it, a rigorous hallmark would be used to score something as evolved or not. That is, biological features that fail to exhibit any of your hallmarks should not be scored as "evolved." But how can this be when the non-teleological approach begins by assuming every biotic feature arose through evolution? That is, since you already believe every biotic feature arose through evolution, and use parsimony arguments to justify extrapolating evolution here from evolution there, your hallmarks appear to be nothing more than window dressing that are applied, post-hoc, if they can be applied. Put simply, your hallmarks do not appear to have any scoring power since failure to find hallmarks does not dislodge or even weaken the evolution belief. It seems to me you are trying to draw from two different methodological approaches that don't mix very well - one approach scores and the other approach generalizes.

I do think the scoring approach is a better way to address a history full of contingency. Attempts to generalize end up smearing all biotic data into a blurry, homogenous whole, such that changing wing colors in moths becomes evidence for the Darwinian origin of the bacterial flagellum. I prefer the investigative method that scores; one that is open-ended, looking for the best explanation rather than merely looking for facts to support preconceptions. This is why your leading attempt to highlight hallmarks of flagellar evolution (motA-exbB homology) is much better than the philosophical arguments revolving around parsimony. That's why I will try to get to it in the next few busy days.

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Hey Mike,

I agree that it would be useful to formalize what we might call "relative likelihood reasoning" or some such thing, perhaps even with some attempt at scoring.

Perhaps it would be best to start another thread to do this. Briefly, several distinctions that would probably be useful in such an endeavor:

Positive evidence (evidence for some hypothesis) vs. negative evidence (evidence against some hypothesis), perhaps vs. "neutral" (e.g., perhaps no evidence either way).

Evidence for "it did happen this way" vs. evidence for "it could happen this way". E.g. the known Type III secretion systems, which are derived, are not particularly good evidence for "it did happen this way" but (IMO) are certainly evidence for "it could happen this way" ("it" = evolution of flagellum from a transport system).

A consideration of *expectation* of evidence, i.e. we can expect more evidence regarding the evolution of things that fossilize easily than we can for the evolution of things that fossilize poorly. E.g., chimps live in rainforests with acidic soils that dissolve bones so the lack of chimp fossils compared to hominid fossils is not particularly surprising.

(Along a similar vein, billions of years older = less expectation of evidence; this is an argument I advanced earlier regarding the flagellum vs. the immune system)

Another variation on the above would be length/amount of study. Short version that often causes woe to those of us interested in evolution: relevant to medicine = lots and lots of study (a plus in the case of the immune system, however); not relevant to medicine = take a hike. Bombadier beetles just aren't going to get quite the amount of attention that the immune system does.

There's probably more ("length of time since reasonably complete understanding of system"), but that's a start.

Obviously complete agreement might be difficult but perhaps it would be useful. Feel free to quote/use this in another thread if you are so inspired, Mike.

Thanks, nic

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Nic,

The formulation of some kind of "relative likelihood reasoning" sounds interesting, but my main point dealt with the tension created by using both the "hallmark" approach and the "parsimony" approach. It would seem to me that attempts to converge these different methods into a single approach merely end up weakening both. For example, if you were to find sufficient evolutionary hallmarks for biotic feature X, the "hallmarks" end up as nothing more than window dressing given that you already believed X evolved on the basis of parsimony. But if you don't find any hallmarks for biotic feature Y, the appeal to parsimony ends up looking like a dive down the escape hatch (to rescue the pre-existing belief that Y evolved). Put simply, by bringing parsimony into the picture, your "hallmarks" end up looking more like apologetic devices than investigative tools. Personally, I'd jettison the "parsimony" appeals, as they tend to collapse into a philosophical argument and merely undercut your hallmarks.

This problem is then amplified when some of the qualifications as part of your "relative likelihood reasoning" are put into play. For example:

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Along a similar vein, billions of years older = less expectation of evidence; this is an argument I advanced earlier regarding the flagellum vs. the immune system
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Is this yet another apologetic move or a true investigative concern? It's hard to tell. If it is the latter, it would seem to me that non-teleologists should rigorously define some type of temporal evidential threshold, where we would not expect to find any evidence for evolution prior to this threshold. Then, appeals to ancient events would have some teeth. As it stands, the "it's too old" argument comes across as more of an excuse that gets applied in an "escape hatch" manner (creating now two escape hatches). But is the "it's too old" argument truly valid? Does it always apply? For example, which is older - the origin of mitochondria or the origin of Broca's speech center, avian lungs, and the bat's wing? It would seem to me that the evolutionary origin of the latter three, while much more recent than the origin of mitochondria, are less well "evidenced." Or, if we turn to the flagellum itself, recall that Ken Miller and many others argue the evolutionary origin of the Krebs cycle is well-evidenced. Yet the Krebs is found in both archaea and eubacteria (unlike eubacterial-specific flagellum we discuss), clearly indicating it to be older than the bacterial flagellum (from the traditional viewpoint, that is). If you can find evidence for the evolutionary origin of the Krebs, complaining that the evolutionary origin of the flagellum was too old clearly comes across as a rationalization and excuse.

Perhaps my perceptions are flawed here, but this is how this all ends up looking from where I sit:

You think the Krebs Cycle evolved and there is evidence of this evolution.

The Krebs Cycle is older than the bacterial flagellum.

We can't expect to find evidence for the evolutionary origin of the flagellum because it is too old.

Ah, but we have evidence for the evolutionary origin of the flagellum (i.e., ExbB-to be addressed soon).

Ah, but if we didn't have this evidence, we'd have to conclude the flagellum evolved because the immune system evolved.

Like I said before, I'll try to deal with your hallmark for the flagellum. In the meantime, it would be nice to see you explain why it is the capabilities of chance alone are very very limited.

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posted 19. September 2002 12:29                   

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But for now, the main point, as I see it, is whether it is a good investigative idea to mix the "identify the hallmark and infer" method with the "parsimony mandates extrapolation" method. As I mentioned above, mixing both approaches ends up turning them both into apologetic devices.

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Two more things. First, it seems clear to me that one is going to have to rely on intuition in trying to determine where and when the listed dynamics come into play (and to what degree they come into play). I'm encouraged to see that Nic is beginning to understand that intuition is more than something to be ridiculed.

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Secondly, a similar approach could likewise be developed for the expectations about the designer and ID. For example, those critical of ID demand that we must be able to watch the designer designing before anyone can take ID seriously. How reasonable is that?

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