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Index to Creationist Claims,  edited by Mark Isaak,    Copyright © 2007
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Claim CB200:

Some biochemical systems are irreducibly complex, meaning that the removal of any one part of the system destroys the system's function. Irreducible complexity rules out the possibility of a system having evolved, so it must be designed.


Behe, Michael J. 1996. Darwin's Black Box, New York: The Free Press.


  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:

    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:


TalkOrigins Archive. n.d. Irreducible complexity and Michael Behe.


  1. Aharoni, A., L. Gaidukov, O. Khersonsky, S. McQ. Gould, C. Roodveldt and D. S. Tawfik. 2004. The 'evolvability' of promiscuous protein functions. Nature Genetics [Epub Nov. 28 ahead of print]
  2. Bridgham, Jamie T., Sean M. Carroll and Joseph W. Thornton. 2006. Evolution of hormone-receptor complexity by molecular exploitation. Science 312: 97-101. See also Adami, Christopher. 2006. Reducible complexity. Science 312: 61-63.
  3. Dujon, B. et al. 2004. Genome evolution in yeasts. Nature 430: 35-44.
  4. Hooper, S. D. and O. G. Berg. 2003. On the nature of gene innovation: Duplication patterns in microbial genomes. Molecular Biololgy and Evolution 20(6): 945-954.
  5. Lynch, M. and J. S. Conery. 2000. The evolutionary fate and consequences of duplicate genes. Science 290: 1151-1155. See also Pennisi, E., 2000. Twinned genes live life in the fast lane. Science 290: 1065-1066.
  6. Meléndez-Hevia, Enrique, Thomas G. Waddell and Marta Cascante. 1996. The puzzle of the Krebs citric acid cycle: Assembling the pieces of chemically feasible reactions, and opportunism in the design of metabolic pathways during evolution. Journal of Molecular Evolution 43(3): 293-303.
  7. Muller, Hermann J. 1918. Genetic variability, twin hybrids and constant hybrids, in a case of balanced lethal factors. Genetics 3: 422-499.
  8. Muller, H. J. 1939. Reversibility in evolution considered from the standpoint of genetics. Biological Reviews of the Cambridge Philosophical Society 14: 261-280.
  9. Pennisi, Elizabeth. 2001. Genome duplications: The stuff of evolution? Science 294: 2458-2460.
  10. Ussery, David. 1999. A biochemist's response to "The biochemical challenge to evolution". Bios 70: 40-45.

Further Reading:

Gray, Terry M.. 1999. Complexity--yes! Irreducible--maybe! Unexplainable--no! A creationist criticism of irreducible complexity.

Lindsay, Don. 1996. Review: "Darwin's black box, the biochemical challenge to evolution" by Michael Behe.

Miller, K. 1999. Finding Darwin's God. Harper-Collins, chap. 5.

Shanks, N. and K. H. Joplin. 1999. Redundant complexity: A analysis of intelligent design in biochemistry. Philosophy of Science 66: 268-298.

Ussery, David. 1999. (see above)
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created 2001-2-17, modified 2007-7-19