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Index to Creationist Claims,  edited by Mark Isaak,    Copyright © 2006
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Claim CB200.2:

The biochemistry of blood clotting is irreducibly complex, indicating that it must have been designed.


Behe, Michael J. 1996. Darwin's Black Box, New York: The Free Press, pp. 74-97.


  1. The blood clotting systems appears to be put together by using whatever long polymeric bridges are handy. There are many examples of complicated systems made from components that have useful but completely different roles in different components. There is also evidence that the genes for blood clotting (indeed, the whole genome) duplicated twice in the course of its evolution (Davidson et al. 2003). The duplication of parts and co-opting of parts with different functions gets around the "challenge" of irreducible complexity evolving gradually.

  2. Blood clotting is not irreducibly complex. Some animals -- dolphins, for example -- get along fine without the Hagemann factor (Robinson et al. 1969), a component of the human blood clotting system which Behe includes in its "irreducible" complexity (Behe 1996, 84). Doolittle and Feng (1987) predicted that "lower" vertebrates would lack the "contact pathway" of blood clotting. Work on the genomes of the puffer fish and zebrafish have confirmed this (Yong and Doolittle 2003).

  3. Irreducible complexity is not an obstacle to evolution and doesn't imply design.


Acton, George, 1997. Behe and the blood clotting cascade.

Behe, M. and K. Miller. 2002. Transcript: American Museum of Natural History April 23, 2002 (Part 7).

Dunkelberg, Pete, 2003. Irreducible complexity demystified.

EvoWiki, 2004. Blood clotting.

Musgrave, Ian, 2005. Clotted rot for rotten clots.


  1. Davidson, C. J., E. G. Tuddenham, and J. H. McVey. 2003. 450 million years of hemostasis. Journal of Thrombosis and Haemostasis 1: 1478-1497.
  2. Robinson, A. J., M. Kropatkin, and P. M. Aggeler. 1969. Hagemann factor (factor XII) deficiency in marine mammals. Science 166: 1420-1422.

Further Reading:

Doolittle, Russell F., 1997. A delicate balance. Boston Review (Feb./Mar.),

Ussery, David, 1999. A biochemist's response to "The biochemical challenge to evolution". Bios 70: 40-45.
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created 2001-2-17, modified 2005-9-24