Index to Creationist Claims,  edited by Mark Isaak,    Copyright © 2007

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Claim CB200:

Source:

Response:

1. Irreducible complexity can evolve. It is defined as a system that loses its function if any one part is removed, so it only indicates that the system did not evolve by the addition of single parts with no change in function. That still leaves several evolutionary mechanisms:
   
   
   • deletion of parts
   • addition of multiple parts; for example, duplication of much or all of the system (Pennisi 2001)
   • change of function
   • addition of a second function to a part (Aharoni et al. 2004)
   • gradual modification of parts
   
   All of these mechanisms have been observed in genetic mutations. In particular, deletions and gene duplications are fairly common (Dujon et al. 2004; Hooper and Berg 2003; Lynch and Conery 2000), and together they make irreducible complexity not only possible but expected. In fact, it was predicted by Nobel-prize-winning geneticist Hermann Muller almost a century ago (Muller 1918, 463-464). Muller referred to it as interlocking complexity (Muller 1939).
   
   Evolutionary origins of some irreducibly complex systems have been described in some detail. For example, the evolution of the Krebs citric acid cycle has been well studied (Meléndez-Hevia et al. 1996), and the evolution of an "irreducible" system of a hormone-receptor system has been elucidated (Bridgham et al. 2006). Irreducibility is no obstacle to their formation.
   
   
2. Even if irreducible complexity did prohibit Darwinian evolution, the conclusion of design does not follow. Other processes might have produced it. Irreducible complexity is an example of a failed argument from incredulity.
   
   
3. Irreducible complexity is poorly defined. It is defined in terms of parts, but it is far from obvious what a "part" is. Logically, the parts should be individual atoms, because they are the level of organization that does not get subdivided further in biochemistry, and they are the smallest level that biochemists consider in their analysis. Behe, however, considered sets of molecules to be individual parts, and he gave no indication of how he made his determinations.
   
   
4. Systems that have been considered irreducibly complex might not be. For example:
   • The mousetrap that Behe used as an example of irreducible complexity can be simplified by bending the holding arm slightly and removing the latch.
   • The bacterial flagellum is not irreducibly complex because it can lose many parts and still function, either as a simpler flagellum or a secretion system. Many proteins of the eukaryotic flagellum (also called a cilium or undulipodium) are known to be dispensable, because functional swimming flagella that lack these proteins are known to exist.
   • In spite of the complexity of Behe's protein transport example, there are other proteins for which no transport is necessary (see Ussery 1999 for references).
   • The immune system example that Behe includes is not irreducibly complex because the antibodies that mark invading cells for destruction might themselves hinder the function of those cells, allowing the system to function (albeit not as well) without the destroyer molecules of the complement system.

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