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Topic: Is "complexity" relative or absolute?
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Paul A. Nelson
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posted 28. March 2002 14:08
Edmund wrote:
Again, I was especially hoping that some of the IDC's out there would provide empirical evidence for the *limits* of natural selection, since those examples would be the most exciting.
I don't know if this is the sort of argument you're looking for, but it may be worth a look:
Siegfried Scherer, "Basic Functional States in the Evolution of Light-driven Cyclic Electron Transport," Journal of Theoretical Biology 104 (1984): 289-299.
Abstract: Current theories regarding the evolution of light-driven cyclic electron transport are reviewed and considered critically. The hypothetical evolutionary sequence leading to cyclic photosynthetic electron transport is divided into successive basic functional states in order to estimate the probability of changing from one basic functional state to another. Based on our present knowledge of molecular biology and biochemistry it is concluded that the evolution of light-driven cyclic electron transport remains an unsolved problem in theoretical biology. In order to clarify the situation, further experimental work in molecular evolution urgently is needed.
In the body of the paper, Scherer argues explicitly that, given our current understanding of natural selection (NS), NS is insufficient to construct light-driven cyclic electron transport. For instance, he writes, "...in this investigation no regulatory mechanisms have been considered, which are by no means less important than the new enzymes needed. An organism with unregulated biosynthetic pathways will be discarded quickly by natural selection. It seems impossible to decrease the number of proteins needed in each basic functional state investigated here." (p. 298)
Edmund, can you say if any of the cases mentioned by Drosera and Charlie D. represent the sort of example you had in mind? If so, could you pick one of them and develop the case in detail? A problem I see in this discussion is passing-of-ships-at-night: i.e., many design theorists will agree that the adaptive radiation of cichlid fishes (for instance) is best explained by ordinary population genetic mechanisms; but they might well disagree that a weakly-articulated plausibility argument for the origin of a protein complex (based on little more than sequence similarity) qualifies as a valid illustration of NS. Thus, choosing particular cases and carefully laying them out -- i.e., doing more than stringing together a list of PubMed cites, many of which may well be irrelevant to the issue at hand -- will be important. Thanks.
[ 28 March 2002, 14:19: Message edited by: Paul A. Nelson ]
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Moderator
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posted 28. March 2002 14:09
Dear edmund,
Participation in the Brainstorms forum requires a level of professionalism which includes granting your discussion partner respect. This is a big issue in my book. Your use of the term "IDC" exudes disrespect and disdain. I do not know of a single ID theorist who refers to him/her self as an "IDC" and therefore find the term derogatory. I would like you to make the appropriate change to your recent posts, and to avoid using such juvenile word choices in the future. This is warning one.
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Drosera
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posted 28. March 2002 15:13
Paul Nelson wrote,
quote:
[M]any design theorists will agree that the adaptive radiation of cichlid fishes (for instance) is best explained by ordinary population genetic mechanisms;
Cool...
quote:
but they might well disagree that a weakly-articulated plausibility argument for the origin of a protein complex (based on little more than sequence similarity) qualifies as a valid illustration of NS.
Au contraire...all of the given genetic examples were picked specifically because there has been a significant amount of work done on them in addition to mere sequence similarity searches, specifically looking at the role of natural selection *in these cases* *in these peer-reviewed articles*.
Now the "angle" the various papers take on studying natural selection is different, e.g. in Sdic scientists have reconstructed a detailed pathway for the origin of the new gene from the chimerization of two old genes, and have examined the decrease in diversity on the chromosome section containing this gene (~10 copies of this gene, actually).
In the case of the origin of nylon degradation, the process has been replicated several times in the lab, amplified via further selection, etc.
In the case of PCP degradation, my understanding is that scientists have looked in detail at the proposed ancestral and current pathways and enzymes, and considered how the former got to the latter.
Ditto for antifreeze proteins, detailed ancestors and pathways have been reconstructed.
This is not to denigrate sequence comparison studies, which I think are quite impressive on their own terms (and I have yet to see a coherant argument that anything other than regular-old mutation, selection, etc. are necessary to explain them, or why ID constitutes a better explanation), but what I'm trying to say is that scientists have looked at these particular genes (among others) in more detail, specifically investigating the role of natural selection in their origin.
Drosera
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Paul A. Nelson
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posted 28. March 2002 16:08
Drosera wrote:
scientists have looked at these particular genes (among others) in more detail, specifically investigating the role of natural selection in their origin.
OK. Then take one of the cases and spell it out in detail. Give a formal definition of the process of natural selection (NS) (I'd suggest John Endler, Natural Selection in the Wild [Princeton University Press, 1986], pp. 4-5), and show how the case in question satisfies the evidential requirements of NS.
Shouldn't be hard to do. Pick just one case that you think fundamentally challenges ID, explain why it does so, and give the NS details.
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Drosera
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posted 28. March 2002 16:58
Hi Paul,
Love to. Before I start though, could you please define what you mean by 'ID'?
Everyone seems to have a somewhat different meaning in their heads. For example, I gather from Mike Gene's posts that I've seen here and over at the Access Research Network (ARN) bulletin board that he would pretty much agree that all of the posted cases are examples of the action of natural processes like mutation & selection. This would appear to indicate that Mike Gene would concede that natural processes can, and regularly do, produce new genes with new functions, hence new information in at least the colloquial definition of information.
Other ID advocates, however, sometimes argue that mutation and selection cannot produce information. E.g. Spetner and perhaps Dembski although I have a heck of a time nailing down exactly what Dembski's arguments would say about the specific genes mentioned.
So, I'd be much obliged if you would draw for us your "line in the sand" where you would argue that natural processes cannot cross (or are stupdenously unlikely to cross) and ID is required. If you draw the line similar to Mike Gene, it may be that all of the examples I posted are on the "explainable by natural processes" side of the line already. This would however annull your comments about these examples being weak plausibility arguments, so I am expecting your line to give somewhat more territory to ID.
Thanks, I bring this up just so that we're all on the same page about 'ID' at in this discussion.
Drosera
[ 28 March 2002, 17:00: Message edited by: Drosera ]
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charlie d.
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posted 28. March 2002 17:03
quote:
Paul Nelson: Shouldn't be hard to do. Pick just one case that you think fundamentally challenges ID, explain why it does so, and give the NS details.
Actually, Paul, I think there are 2 issues here that tend to become confused, but shouldn’t. The first one is: is RM/NS a sufficiently powerful explanatory mechanism for the generation of biological novelty? This is what I think edmund was alluding to here:
quote:
what can evolution do, and how do we know it can do it? … I'll even make my challenge a little inflammatory: living organisms have a lot of characteristics which are classic "fingerprints" of natural selection. Unless IDC's can show conclusively that non-intelligent processes CAN'T construct systems equivalent to those in living organisms, I think natural selection gets the benefit of the doubt. So what hard, irrefutable evidence do we have of the limits of natural evolutionary processes?
Many of the examples that Drosera and I have mentioned (I would also add RNase evolution in colobine monkeys, discussed at length in Kirk’s Ka/Ks thread) indicate that random mutation and natural selection appear eminently capable of giving rise to new structures and new functions in the biological world.
In the absence of any falsification of these examples and their interpretation, or of any alternative testable mechanism with equal or better explanatory powers (which has not yet come from the ID camp) edmund would conclude that darwinian mechanisms based on RM/NS are the only current satisfactory explanation for the vast majority of biological evolution.
The second issue raised by edmund is more directly related to ID:
quote:
There has been a lot of discussion about "irreducible complexity", but to my knowledge it has not been shown rigorously that evolution cannot build systems which appear IC-- in fact, some evolutionists have proposed seemingly reasonable evolutionary paths to IC. Right now we seem lost in this subjective "gray area" where people argue that "it does/doesn't seem likely to me." Those arguments don't have much force.
That is, can RM/NS also account for IC systems? This is more tricky because evidence of NS is very hard to come by. There is however evidence for the gradual, progressive evolution of at least some IC systems, such as the complement cascade (see for instance: Smith et al, Immunopharmacology 42:107-20, 1999. Complement systems in invertebrates. The ancient alternative and lectin pathways), including how some apparently IC "steps" may have originated. New data also suggest reasonably solid evolutionary scenarios for the origin of the adaptive immune system from non-adaptive immune system components, via recruitment of transposon-like mechanisms (reviewed in Agrawal et al, Transposition mediated by RAG1 and RAG2 and its implications for the evolution of the immune system. Nature. 1998 394:744-51). So the question is: are these plausible, evidence-based evolutionary scenarios sufficient to nick ID’s IC/CSI armor, or do detailed evolutionary pathways need to be spelled out? Initially, it seemed that Behe and Dembski were claiming that IC/CSI were refractory to darwinian interpretations a priori, but more recently they seem to have retreated to the safer ground of asking for specific and complete explanatory mechanisms for evolutionary pathways leading to such systems.
Of course, as I have stressed in many of my posts, the real question for me is: independently of how RM/NS could have originated IC, how does ID propose it originated? Until some actual mechanism is proposed, there is no way of fairly comparing the explanatory powers of the 2 theoretical systems.
[ 28 March 2002, 17:06: Message edited by: charlie d. ]
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edmund
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posted 28. March 2002 17:25
To the moderator and the ID theorists on this BB:
I sincerely apologize for my use of the acronym "IDC", which apparently carries a derogatory connotation. I was unaware that this term was considered derogatory by ID theorists and it was not my intention to demean anyone by its use. I will refrain from using the term in the future.
Again, my apologies, and my thanks to the moderator for catching my faux pas.
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Paul A. Nelson
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posted 28. March 2002 17:45
Charlie wrote:
[1] Many of the examples that Drosera and I have mentioned (I would also add RNase evolution in colobine monkeys, discussed at length in Kirk’s Ka/Ks thread) indicate that random mutation and natural selection appear eminently capable of giving rise to new structures and new functions in the biological world.
[...]
[2] That is, can RM/NS also account for IC systems? This is more tricky because evidence of NS is very hard to come by.
Could you explain the apparent contradiction between the statements I've marked as [1] and [2]? Do we have evidence for the causal power of NS, or not? Does the phrase "evidence of NS is very hard to come by" refer only to the historical origin of IC systems? Please clarify.
Drosera, for the sake of discussion, let's us the best-articulated theory of design inferences (ID) currently available, namely, Dembski's. Let me know if you have a copy of No Free Lunch, and we'll take it from there. Thanks.
[ 28 March 2002, 17:49: Message edited by: Paul A. Nelson ]
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Drosera
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posted 28. March 2002 18:08
Hi Paul,
Yes, I have Dembski's No Free Lunch. I must admit I'm a bit confused about what it really says at numerous points, but we can go with that if you like.
Perhaps you could answer this question then as a modification of my previous one: if the scientists who wrote these articles on the evolutionary origin of novel genes by natural processes, e.g. the various examples we've posted in this thread, are correct... does this contradict Dembski's thesis or not?
The difficulty appears to be that Dembski has constructed a main argument:
1) Basically, natural processes (law+chance) cannot produce specified complexity, which means an improbable result which is specified. In biology specification denotes function, so (for example) all functional amino acid sequences longer than say ~120 amino acids would have CSI.
(Parenthetically, the potential tautology, improbable things are improbable, is very worrisome here however as it assumes what it is trying to prove. Several ICSID writers have mentioned this.)
And an emergency back-up argument:
2) But if it turns out that natural processes can produce something that definitely has CSI, e.g. new genes, then #1 isn't falsified like we would expect, but rather the CSI has come from some vague "underground" status, perhaps even the very laws of physics -- or something... This whole part of Dembski's argument is very obscure to me. Dembski's discussion of Turf-13, the only somewhat analogous case in his book to what we're discussing, only makes things more confusing in my opinion.
So, would examples of the origin of new genes with new functions, if they originated via basically the natural processes that scientists have published, contradict Dembski's thesis or not?
I can't tell for sure, myself. If they *would* contradict it then we have a reason to start discussing the examples.
Drosera
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charlie d.
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posted 28. March 2002 19:04
quote:
Paul:
Charlie wrote:
[1] Many of the examples that Drosera and I have mentioned (I would also add RNase evolution in colobine monkeys, discussed at length in Kirk’s Ka/Ks thread) indicate that random mutation and natural selection appear eminently capable of giving rise to new structures and new functions in the biological world.
[...]
[2] That is, can RM/NS also account for IC systems? This is more tricky because evidence of NS is very hard to come by.
Could you explain the apparent contradiction between the statements I've marked as [1] and [2]? Do we have evidence for the causal power of NS, or not? Does the phrase "evidence of NS is very hard to come by" refer only to the historical origin of IC systems? Please clarify.
Sure. No contradiction.
What I mean is that pathways relying entirely on RM/NS have been shown to be able to explain some cases of emergence of new biological adaptations such as, for instance, the ability of colobine monkeys to digest leaves (duplication/divergence of RNase 1 gene), the ability or arctic fish to avoid freezing (duplication and divergence of various proteins of unrelated function into molecular "antifreeze"), and so on. Some of these evolutionary pathways have been characterized molecularly in great detail, showing the adaptive role of individual mutations.
Of course, such extensive knowledge of each adaptive step is not common, either because of gaps in the molecular record or its interpretation in terms of adaptation, or because of ignorance of the details of past selective pressures. Nevertheless, most evolutionary pathways seem in principle reducible to linear, progressive series of events of the kind that RM/NS have been shown to provide an adequate mechanism for. Thus, until proof of the contrary, or better alternative mechanistic hypotheses, RM/NS are clearly the best available scientific explanation for the vast majority of biological novelties.
That said, in some cases we don't have any evidence whatsoever of what the evolutionary pathway may have been. Some cases, those that ID theorists call IC, certainly look particularly hard to explain. However, even in the absence of detailed knowledge about the role of NS, there is some evidence that step-wise molecular evolutionary processes may explain the emergence of at least some IC systems, such as complement and adaptive immunity, without too much difficulty.
Whether ID supporters would consider this sufficient evidence of the ability of darwinian mechanisms to generate IC, or what kind of additional evidence, if any, would suffice, you have to tell me.
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Jesse
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posted 28. March 2002 19:11
Drosera:
1) Basically, natural processes (law+chance) cannot produce specified complexity, which means an improbable result which is specified. In biology specification denotes function, so (for example) all functional amino acid sequences longer than say ~120 amino acids would have CSI.
Actually, I don't think there's any reason to think long functional amino acid sequences would necessarily possess high CSI. If the probability of a functional amino acid sequence evolving is fairly high (relative to the laws and initial conditions being considered) then such a sequence will possess low CSI, whether it is made up of 120 amino acids or 1000. Of course, as you say, Dembski does seem to have a sort of "backup argument" involving CSI being smuggled in somehow, so that even if something has low CSI relative to the laws of nature that may just show that the laws themselves were designed, or something.
[ 28 March 2002, 23:31: Message edited by: Jesse ]
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Mike Gene
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posted 28. March 2002 23:44
I asked three simple questions in response to Edmund's challenge (although this seems to be a topic change, Edmund, the author of the thread, invited the change).
I asked about the fingerprints of natural selection. Drosera gave us three. Then, in response to my question 3, he provided a laundry list of examples of, I suppose, the most impressive examples of RM&NS as the 'designer' (and Charlie added another).
Fingerprint #1: reduced diversity in regions of the chromosome undergoing selection in a population
Okay, but which example listed above has this fingerprint?
Fingerprint #2: novel features come from the modification of older features (and this can result in designs that have aspects that appear "dumb" to designers with foresight like us);
I don't buy this as a fingerprint. I originally warned that we should not confuse common descent/similarity with random mutation/natural selection. Evidence of similarity or descent is not evidence of the mechanism behind the descent. A fingerprint of descent is not a fingerprint of natural selection. However, I'll buy the "looks dumb" fingerprint, but I didn't see this fleshed out for any of the examples above.
Fingerprint #3: the "designs" of organisms will have the ultimate "purpose" of increasing reproduction of the genes of the organism (unlike human designs, which basically always have the purpose of performing a task for something else, usually the human designer).
I don't think this is a very useful fingerprint at all. Design is constrained by the laws of nature. And the laws of nature dictate that mutations will occur sooner or later. As such, any designer implementing a design that did not benefit the possessor of the design would not be a very good designer. Why? The original design would quickly decay away by mutation. That is, mutations that eliminated the function would quickly spread through the population that possessed the designed feature. Any designer intent on having his/her design be propagated across deep time would need to employ selection (or continually return to fix things). That selection is employed for such purposes does not mean selection is behind the source of the design.
This brings me to my second question. Both mutation and natural selection clearly exist. Finding evidence of their existence of hardly that remarkable. The question is not about the existence of natural selection and its involvement in biological history, but its causal role and responsibility for what we see today. That natural selection has been involved with evolution is no more remarkable than the fact that genetic drift has likewise been involved. But is anyone going to argue that it was genetic drift that formed the bacterial flagellum? Thus, finding fingerprints of its involvement is not all that impressive. Again, the question that matters is how has it been involved. Exactly what has it accomplished?
As I see it, there are really two very different questions here. The first question permeates the traditional debate, namely, is RM&NS sufficient for explaining the origin of systems with X-level complexity? If the answer is yes, we're supposed to adopt RM&NS as the explanation. If the answer is no, we're supposed to reject RM&NS as the explanation. Now, I can fully understand the logic of a negative answer, but I don't subscribe to the notion that we infer RM&NS as the cause if we can demonstrate it is probably sufficient to the task. The reason is very simple - we do not live in a reality where bioengineering and RM&NS cannot co-exist. In fact, thanks to our own recent advances in biotechnology, we now live in a reality where some organisms (such as Dolly) exist because of bioengineering and others do not. This pattern will only become more pronounced in the future. And since this is a forum that takes teleological causes seriously, it won't work to dismiss them with rhetoric.
Thus, the second question is not whether RM&NS are sufficient to the task. It is whether or not RM&NS was truly behind the task. It is a question of what happened, not what could have happened. This is why I inquired about the fingerprints. What fingerprints indicate that RM&NS were indeed behind the evolution of some biotic feature? What fingerprint tells us that RM&NS evolved the flagellum, for example?
Drosera claims I need a time machine. Historians don't need time machines. Instead, they propose explanations that attempt to incorporate all the facts and generate the most coherent account. They don't offer a historical scenario as the best explanation when it is nothing more than a philosophical appeal to something that could have possibly happened in the past. As I struggle to come up with ways to infer ID, I am not trying to argue that ID is a sufficient cause or that ID is a possible cause (as I think it rather clear this is already true). I am not arguing that ID could have happened (because it could have). Instead, I look for data that point to an actual ID event, clues best explained by ID as something that did indeed happen (not could have happened). Perhaps I am misguided in thinking that non-teleologists would seek out the same type of explanation for their views about our history.
Edmund wants someone to demonstrate the blind watchmaker can't make something. Yet when one's imagination is largely unconstrained, free to imagine and seriously propose unknown causes or vague just-so stories, that's a pretty safe demand to make of others. I prefer the approach as discussed by E.G. Leigh who wrote in TREE:
quote:
The primary problem with the synthesis is that its makers established natural selection as the director of adaptive evolution by eliminating competing explanations, not by providing evidence that natural selection among random' mutations could, or did, account for observed adaptation..... However, the failure to provide clinching evidence gives antidarwinians no reason to substitute natural selection for God in their view of the world. Neither have antidarwinians any vested interest in a mechanistic explanation of the origin and evolution of life; if we want them to accept one, it will have to be convincing.
In other words, if you think something like the flagellum arose by RM&NS, provide the evidence for this belief. What are the fingerprints that indicate RM&NS evolved the flagellum?
Nevertheless, if we are simply supposed to write history through generalization, then at least come up with the most impressive example of RM&NS as designer. Instead of a laundry list, pick the show case example. Describe the pre-designed state and the post-designed state (so we can get a feel for the 'complexity' being created) and where/how RM&NS went to work. Or use the AFGPs as an example and explain precisely how this translates as evidence for the evolutionary origin of the bacterial flagellum through RM&NS.
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edmund
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posted 29. March 2002 04:35
quote:
Fingerprint #3: the "designs" of organisms will have the ultimate "purpose" of increasing reproduction of the genes of the organism (unlike human designs, which basically always have the purpose of performing a task for something else, usually the human designer).
I don't think this is a very useful fingerprint at all. Design is constrained by the laws of nature. And the laws of nature dictate that mutations will occur sooner or later. As such, any designer implementing a design that did not benefit the possessor of the design would not be a very good designer. Why? The original design would quickly decay away by mutation. That is, mutations that eliminated the function would quickly spread through the population that possessed the designed feature. Any designer intent on having his/her design be propagated across deep time would need to employ selection (or continually return to fix things). That selection is employed for such purposes does not mean selection is behind the source of the design.
The fingerprint is not just "NS produces systems which serve to reproduce the organism's genes." It is "NS produces ONLY systems which serve to reproduce the organism's genes." If we discovered systems with any other complex, specified attributes, we could be sure that those attributes weren't put there by NS.
There are many possible examples. Naturalists used to think that small fruits grew up high and large fruits grew down low for the benefit of humans who then wouldn't be killed by falling fruit. (This pattern actually holds for much of Europe, but was dethroned by tropical botany.) Had that pattern held true, NS couldn't have explained it. Nor could it have explained the sort of "group selection" arguments which used to be prevalent, in which old or sick animals sacrifice themselves for the good of the species. There are a lot of patterns that we once thought existed in biology which NS couldn't possibly account for, but closer scrutiny has called many of these patterns into doubt.
It does seem that natural systems have those attributes which NS can generate (the tendency to reproduce the organism's genes) and lack those attributes which NS can't generate. This doesn't prove beyond all doubt that NS is responsible, but, if NS isn't, it is an eerie coincidence.
The idea that the designer would put NS-mimicking attributes into biological designs because only those attributes would be sustained by NS over time is an interesting one. Is it testable? I'm not sure what data would distinguish between "NS alone" and "NS-mimicking design preserved by NS"-- except to show that NS *couldn't* have fashioned a particular biological system.
PS to Paul Nelson: The article you cited is indeed the sort of thing I'm interested in-- especially if such examples form some sort of pattern from which we can get a more general idea of what sorts of systems seem intractable to NS.
[ 29 March 2002, 04:43: Message edited by: edmund ]
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Paul A. Nelson
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posted 29. March 2002 07:33
Charlie wrote:
Nevertheless, most evolutionary pathways seem in principle reducible to linear, progressive series of events of the kind that RM/NS have been shown to provide an adequate mechanism for.
This perception seems very much to depend on the convictions of the individual investigator -- remarkably so, in fact, to a degree that would be unusual in other sciences.
Stuart Kauffman, for instance, writes that neo-Darwinism "has always faced the danger of facile construction of 'just-so' stories plausibly postulating a use for a feature in the face of no possible tests at all. This truly has been one of the major problems in evolutionary biology....If selection alone is to account for the order we find and if we cannot genuinely determine that which is selected, then our account of the order in organisms stands in peril of weakening into a formal explanation whose validity can rarely be ascertained in concrete cases" (Origins of Order, pp. 17-18). It has been my experience in looking at natural selection explanations for complex features that those explanations devolve into long strings of suppositions -- "next we hypothesize that the following changes occurred" -- where the necessary variations, e.g., embryological or developmental, have never been observed.
This skepticism about the causal efficacy of RM & NS is, as you know, not restricted to ID theorists. "Many important evolutionary phenomena," write Gunther Wagner and colleagues, "do not result naturally from the current implementation of the Neo-Darwinian model" (Journal of Theoretical Biology, vol. 213 [2001]: 213-274; p. 242). Among such phenomena, Wagner et al. include "innovation" -- i.e., the origin of novel complex systems -- and say that the relationship of this puzzle "to the mechanistic theory of evolutionary change, as represented in population genetics, remains tense and unclear" (p. 242).
That's why I want to examine particular cases in detail. The devil (or God, if you like) is in the details. It is not at all obvious to me that the major episodes in the history of biological complexity can be explained by RM & NS.
To Drosera: you're still working at far too abstract a level. One cannot possibly answer your questions about whether a RM & NS hypothesis would, or would not, refute an ID analysis of the same data, without looking at particular cases.* Don't be bashful: pick a specific example from your list above and lay out the NS details. We don't need close exegesis of No Free Lunch for that.**
If RM & NS cause CSI, defined by Dembski's universal probability bound, then we should have plenty, or at least some, examples of that happening.
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*I don't think Dembski would agree that "the laws of physics" can construct biological complexity. If they could, the problem of abiogenesis would have been solved a long time ago.
**I looked at the passage you cited, and Dembski writes that "this [the origin of URF13] is still uncomfortably small, but well above the universal probability bound" (p. 219). I haven't seen the Cell paper, or any of the other data, on which this counterexample rests, however, so I might well disagree with Bill about its relevance. If you'd like, I'll track down the original paper and other relevant sources, and we can go into the nitty-gritty. Let me know.
[ 29 March 2002, 08:46: Message edited by: Paul A. Nelson ]
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charlie d.
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posted 29. March 2002 08:49
Paul:
I totally agree that we only have at best partial, at worst totally speculative models for the evolution of the majority of biological systems. Indeed, what I said just after the passage you quote is:
quote:
Nevertheless, most evolutionary pathways seem in principle reducible to linear, progressive series of events of the kind that RM/NS have been shown to provide an adequate mechanism for. Thus, until proof of the contrary, or better alternative mechanistic hypotheses, RM/NS are clearly the best available scientific explanation for the vast majority of biological novelties.
That is:
we know RM occurs
we know NS takes place
we know that together they can bring forth stepwise, progressive new adaptations in nature.
Therefore, in the absence of falsification or better alternative explanations, we would be crazy not to use RM/NS as our basic model for the evolution of all biological features which are reducible, at least in principle, to progressive pathways along a fitness axis (such as eyes and wings, for instance). At our current status of knowledge, I think it is heuristically just useless to argue that Darwinian evolution is not the way most change is brought forth in nature, since this is in any case the hypothesis tested every time data about a system do become available, and the more we learn, the more opportunities for falsification will abound.
Incidentally, this approach is used all the time in science: we built ourselves a good model of how stars work based on the laws of physics (as we currently know them), and on a limited number of careful astronomical measurements and observations, and as far as I know nobody seems to insist that we have to check equally carefully every star to avoid “just so” stories about how things work in the Crab Nebula.
[ 29 March 2002, 08:51: Message edited by: charlie d. ]
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