Science and the Sacred

Science and the Sacred

One Step at a Time


The diagram above shows the complex process of the human blood-clotting cascade, which requires the interaction of at least a dozen different proteins to properly work. The system is so complex that intelligent design proponents argue that it cannot be explained simply by natural selection (it is irreducibly complex).

On the surface, that argument seems to offer a strong challenge to evolutionary theory. After all, if even one of the needed proteins in the cascade is missing, the whole system falls apart. How could it have evolved over time, then, if each protein is necessary for the system to work? Wouldn’t earlier versions have been useless and therefore not favored by natural selection?


However, in the case of the human blood-clotting cascade, recent evidence has shown that the system arose gradually over time, thanks to gene duplication. As Francis Collins notes in The Language of God, most of the components of the clotting cascade are related to each other at the amino acid sequence level. These similarities can be shown to reflect ancient gene duplications. Such duplications would have left a functioning version of the protein to serve its original purpose while at the same time allowing a new copy to gradually evolve to perform a new function. Over time, these small steps could converge into the complex system present in the human blood-clotting cascade.


Admittedly, we cannot precisely say the exact order of how the human blood-clotting cascade evolved. However, there is a difference between something being unknown and something being impossible.

Stay tuned to our blog and the BioLogos Web site in the coming weeks as we discuss in more detail the concept of irreducible complexity.


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posted August 13, 2009 at 10:58 am

One Step At A Time

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posted April 28, 2011 at 3:29 pm

Sigh….If one part is missing, the system DOES NOT FALL APART and it is not an immediately lethal condition.

I submit the genetic disease Hemophilia. Hemophilia (lack of factor 8 or 9) is well documented in history and medicine. It is, by itself, not a leathal disease.

In addition, almost every factor has been described as missing in various disease states. I personally have met people lacking foctors 7,8,9, proteins C and S along with people with von Willebrants disease (missing or dysfunctional factor XIII).

These factors are proteins that act as enzymes, or catalysts (for the more chemically minded) that speed up reactions immensely. Fibrinogen will spontaneously convert to fibrin ( it is energetically favorable), but will do so much more slowly than in the presence of thrombin.

As mentioned these diseases are not lethal, but they, for the most part, do shorten an individuals lifespan. Therefore, having a completely functioning cascade therefore provides _an evolutionary advantage_.

This also strikes down the argument that this is too complex to be evolutionarily derived. Rather this is a finely tuned, layered approach to a problem. One can see how the layers were added in a sequential fashion with each mutation providing a better balance of pro and anti-coagulant effects and thus making each organism more successful than their counterpart who lacked that extra step.

See for some more information

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