Reciprocating Bill
Posts: 4265
Joined: Oct. 2006
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| Quote (Ftk @ Oct. 07 2007,02:24) | As a layperson, this is an area in which considering the “standards of argumentation“ of the scientific community really make little sense to me. If Behe’s arguments in regard to IC are refuted merely because scientists may have a scenario that might possibly aid in further clues about the evolution of the immune system or said molecular machine, then it seems to me that Darwinian evolution is unfalsifiable in this regard.
Behe’s personal opinion, after years of contemplation and research, is that the IC of the flagellum “cannot be attained solely by means of natural selection” (along with the other mechanisms of evolution). That is the conclusion that he has come to, but I’ve never heard him share his opinion as an absolute...
In the discussion about the stacks of books, from what I understand, some of you were saying that what Behe meant was that there were “NO” possible evolutionary pathways for the evolution of the immune system, yet this is never what I believed him to be suggesting. |
This is the heart of the issue, and in my opinion you are not quite characterizing Behe's position accurately.
As you know, Behe's argument in Darwin's Black Box revolved around the logic of "irreducible complexity." To paraphrase his argument: "within the black box of cell biology we find biological structures of such complexity that they could not have been assembled gradually, stepwise, by natural selection. Those systems are entirely non-functional until fully assembled; because intermediate steps are non-functional they cannot have conferred adaptive advantage, and therefore could not have been selected for. Hence natural selection is incapable of assembling such irreducibly complex structures."
In short, Behe's main assertion was that, at least for these few irreducibly complex structures, there are NO POSSIBLE evolutionary pathways that may be traversed solely by means of mutation and selection.
This is essentially a claim about the logic of selection. Behe did not argue merely that we have yet to empirically demonstrate the existence of such evolutionary pathways; he argued that pathways paved to these structures by natural selection cannot exist. Therefore Behe himself set the bar for the refutation of his assertion: to show that he is wrong, one need only show that one or more such pathways could exist utilizing only the resources of natural selection. It was the strength of Behe's claims that dictated that this is sufficient for their refutation. Plausible evolutionary pathways have indeed been described for structures Behe characterized as irreducibly complex (e.g. bacterial flagella) based upon known phenomena that Behe ignored, such as scaffolding and exaptation (cooption). Behe's image of "parts being assembled" has also been shown to omit important elements of the model proposed by natural selection. He may dispute that these pathways would actually work, but he doesn't get to decide that. The scientific community does.
Of course, this isn't the evidentiary standard ordinarily applied within science, which calls for empirical predictions of sufficient power that the generating model can be disconfirmed. No scientist is satisfied with the mere demonstration that such pathways are possible. We'd like to know which actually occurred in history. Hence much work needs to be done, and is being done. However, Behe himself set the bar in this way. The thesis of DBB has been judged by the standard he specified, and found wanting.
[Edit] Behe's original definition of irreducible complexity, from DBB: "By irreducibly complex I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. (p. 39)"
Now you have heard him express his opinion as an absolute.
[minor edits for clarity and rhetorical flair.]
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Myth: Something that never was true, and always will be.
"The truth will set you free. But not until it is finished with you."
- David Foster Wallace
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