A reply to Rob's post on Irreducible Complexity
As you say, this is interesting, but also about ten year old news. The Internet abounds with replies. As it would be completely useless for me to try to approach the matter in all the biochemical detail it deserves, I will stay on a more general level (and even hope everyone listening in approves).
An irreducible complex system is defined as a system that loses its function if any one part is removed, so that the system under consideration could not have evolved by the addition of its components. It would have no function until it was complete, and therefore have no selective advantage for the organism in its intermediate stages.
This concept however is flawed, for it it only allows the system to evolve by adding single parts, with no change in function. This ignores other known evolutionary mechanisms like:
Therefore, even if an irreducibly complex system were identified (we are still waiting for the first one), this would only invalidate evolution in the hobbled version stipulated by the definition.
Irreducible Complexity, or something very much like it, is rather a prediction of evolutionary theory, of course allowing all possible mechanisms by which evolution operates. The reasoning is as follows: a system may develop overlapping functionality, where parts serve more functions and a function is served by diverse parts. This is well-known in biochemistry. In the course of evolution some of these systems might become streamlined, when unnecessary parts, and functions better served by other parts, might get lost, and the result would be irreducibly complex for the system so streamlined.
M. Behe is aware of this criticism and has acknowledged it, but considers that the greatest problem is not how the systems get streamlined, but how they arise in the first place. Some years ago he announced that he would tackle this problem next, presumably he is still at it. In the meantime, he feels justified to have his book reprinted, despite all legitimate criticisms, or without addressing those criticisms.
Of course the problem how the flagellum could evolve is still relevant for Biology. That a flagellum absolutely needs all the protein parts Behe claims it needs is not true. Much simpler flagella are known to function well in other bacteria. Besides, a subset of the components of the flagellum can function as an excretion system, more concretely: as a kind of needle by which toxins are excreted in other cells. This means that simpler versions of the flagellum could have functioned as such a system, before the flagellum acquired its motor function. Since many of the proteins in the bacterial flagellum are similar to each other or to proteins for other functions (40 of the 42 flagellar proteins in the flagellum Behe considers can also serve in other functions), evolutionary pathways can be hypothesized which account for the evolution of the flagellum. If the flagellum were truly IR in the sense Behe uses the word, such hypotheses would not be possible.
I have a personal experience reading Darwin's Black Box, by Michael Behe. When I read it I was completely flummoxed by the complexity of the blood clotting system as Behe described it. When I read up on the subject however, it soon became clear that at least part of the complexity was due to Behe's presentation, because other writers were able to present the same material in a much more lucid way. Not that I now know all the ins and outs of the vertebrate blood clotting mechanism, far from it, but at least I get an idea what they are talking about. The other authors also mentioned things Behe apparently forgot to mention, like the great similarity between many of the factors cooperating in the blood clotting system, and the redundancy in this system, that Behe represented as irreducibly-complex-no-part-can-be-missed. By this time I felt so cheated by Behe that I returned the book posthaste to the library.
I really loved the comparison with nanotechnology though, although my conclusion is a bit different. Compared with the nanotechnology in nature, as in the flagellum, our attempts at nanotechnology are just pitiful. It just shows that evolution is much smarter than we are.
Regards,
Karel
As you say, this is interesting, but also about ten year old news. The Internet abounds with replies. As it would be completely useless for me to try to approach the matter in all the biochemical detail it deserves, I will stay on a more general level (and even hope everyone listening in approves).
An irreducible complex system is defined as a system that loses its function if any one part is removed, so that the system under consideration could not have evolved by the addition of its components. It would have no function until it was complete, and therefore have no selective advantage for the organism in its intermediate stages.
This concept however is flawed, for it it only allows the system to evolve by adding single parts, with no change in function. This ignores other known evolutionary mechanisms like:
- a part gets deleted;
- a part is copied, resulting in multiple parts;
- a part gets a different function;
- a part acquires an extra function;
- a parts gets modified.
Therefore, even if an irreducibly complex system were identified (we are still waiting for the first one), this would only invalidate evolution in the hobbled version stipulated by the definition.
Irreducible Complexity, or something very much like it, is rather a prediction of evolutionary theory, of course allowing all possible mechanisms by which evolution operates. The reasoning is as follows: a system may develop overlapping functionality, where parts serve more functions and a function is served by diverse parts. This is well-known in biochemistry. In the course of evolution some of these systems might become streamlined, when unnecessary parts, and functions better served by other parts, might get lost, and the result would be irreducibly complex for the system so streamlined.
M. Behe is aware of this criticism and has acknowledged it, but considers that the greatest problem is not how the systems get streamlined, but how they arise in the first place. Some years ago he announced that he would tackle this problem next, presumably he is still at it. In the meantime, he feels justified to have his book reprinted, despite all legitimate criticisms, or without addressing those criticisms.
Of course the problem how the flagellum could evolve is still relevant for Biology. That a flagellum absolutely needs all the protein parts Behe claims it needs is not true. Much simpler flagella are known to function well in other bacteria. Besides, a subset of the components of the flagellum can function as an excretion system, more concretely: as a kind of needle by which toxins are excreted in other cells. This means that simpler versions of the flagellum could have functioned as such a system, before the flagellum acquired its motor function. Since many of the proteins in the bacterial flagellum are similar to each other or to proteins for other functions (40 of the 42 flagellar proteins in the flagellum Behe considers can also serve in other functions), evolutionary pathways can be hypothesized which account for the evolution of the flagellum. If the flagellum were truly IR in the sense Behe uses the word, such hypotheses would not be possible.
I have a personal experience reading Darwin's Black Box, by Michael Behe. When I read it I was completely flummoxed by the complexity of the blood clotting system as Behe described it. When I read up on the subject however, it soon became clear that at least part of the complexity was due to Behe's presentation, because other writers were able to present the same material in a much more lucid way. Not that I now know all the ins and outs of the vertebrate blood clotting mechanism, far from it, but at least I get an idea what they are talking about. The other authors also mentioned things Behe apparently forgot to mention, like the great similarity between many of the factors cooperating in the blood clotting system, and the redundancy in this system, that Behe represented as irreducibly-complex-no-part-can-be-missed. By this time I felt so cheated by Behe that I returned the book posthaste to the library.
I really loved the comparison with nanotechnology though, although my conclusion is a bit different. Compared with the nanotechnology in nature, as in the flagellum, our attempts at nanotechnology are just pitiful. It just shows that evolution is much smarter than we are.
Regards,
Karel
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