The NEJM review has schematics of the factors, showing the many homologies of domains. The 5 proteases are each composed of a single peptide chain which is almost exactly the same length in all, and the point at which the chain is cut in the activation process is in exactly the same relative position in all 5. Eight defined domains or motifs, e.g. the serine protease domain, are located in exactly the same positions in 4 of the 5 protease factors. In other words, at this low level of detail all four are 100% homologous.
Same length-doesn't mean same sequence. If you have four sentences are the same lenghth...they are not by that definition the same.
The current scheme of the clotting system raises questions about Behe's concept of an "irreducibly complex system", which obviously rests on a reliably objective way to define the "system". Yet Behe flatly declares that the clotting system is irreducibly complex. One wonders *which* "clotting system" he's talking about
He's talking about both, he mentions it in the book, didn't you read it? LOL...puts into doubt the desire of the author to be honest.
Behe's approach of using the earlier nomenclature for the clotting factors is gratuitously forbidding to people unfamiliar with the subject. It has the effect of telling them that a moderately complex system is totally impenetrable, rather than that it is approachable and comprehsnsible. It's as annoying as watching someone try to present arithmetic to schoolchildren using Roman numeral notation.
The author assumes that the cascade is reducible to begin with. And false analogy-bringing up the Roman numeral analogy.
This immediately suggests to someone with an exposure to introductory molecular biology an explanatory mechanism (gene duplication) and this in turn predicts a huge number of other homologies. Some known or predicted homologies include:
You cannot call on gene duplication-because two copies of one gene is just that-two copies of the same gene! That doesn't give rise to a different gene...and he seems to ignore the regulatory system and control systems....
"Knowledge of homology is certainly very useful, can give us a good idea of the path of descent, and can constrain our hypotheses. Nonetheless, knowledge of the sequence, structure, and function of relevant proteins is by itself insufficient to justify a claim that evolution of a particular complex system occurred by natural selection. Gene duplication is not a Darwinian explanation because duplication points only to common descent, not to the mechanism of evolution."
Behe incorrectly implies that the homologies are few in number and confined to primary structure. He dismisses the vast amount of homology data by saying that it has to be meaningless, since the system is obviously "irreducibly complex" and that homology data is useless for telling us how the system arose. This is really no different from a Creationist rejecting all sequence homology data for evolution on the a priori grounds that it's illegitimate to compare different "kinds".
Behe is not a creationist, he's a theistic evolutionist. And Behe is not bringing in a priori decision like creationists (the earth is 10000 years old group)-he began his career believing there were answers to complex systems...but found out later that there was no answer to how things evolve. Thus, this book.
"For example, if the digestive enzyme precursor trypsinogen were mistargeted to the bloodstream, the potential for disaster would be very large. In the pancreas, misactivation of trypsinogen is prevented by the presence of trypsin inhibitor. In Miller's scenario one cannot plausibly suppose there to be a trypsin inhibitor fortuitously circulating in the plasma. If the mistargeted enzyme were accidentally activated, it would most likely cause generalized damage in the absence of a regulatory mechanism. It would not be a viable evolutionary intermediate." This answers the thing below as well...pretty sure
It's puzzling why Behe leaves out the obvious homology with the serine protease digestive enzymes. Standard texts such as that of Lubert Stryer have stressed this point. Surely someone with Behe's academic credentials knows about this material. The effect of Behe's presentation after using Stryer is like reading a discussion of the Shroud of Turin that totaly omits any mention of the radiocarbon dating studies.
His conclusion that "nobody knows how it arose" is highly reminiscent of the standard ending of a tabloid piece on sensational "discoveries". The ending is never that a new theory of space-time dislocation is being developed to explain the B-52 on the moon. It's that "scientists are baffled". It's reasonable to suppose that Behe is writing for a National Enquirer audience, since he's left behind anyone who knows something about the details of the clotting system or what Doolittle is talking about. It's highly disingenuous of him to violate norms of presentation to a scientific audience and protest when serious scientists reject his work. In one admittedly personal view, it is doing a deep disservice to a National Enquirer audience to write an account of science for them that encourages National Enquirer attitudes, and that is what Behe has done.[/quote]
There is no science behind anything anyone has said-it's storytelling. So, Behe is not wrong in saying nobody knows...science involves experimentation, remember? This was a crappy response, could have been better, but kinda pre-occuppied...will respond to other one, but read the in defense of the blood clotting mechanism link...
http://www.arn.org/docs/behe/mb_indefen ... ascade.htm
