Irreducible complexity

Irreducible complexity (IC) is the argument that certain biological systems cannot evolve by successive small modifications to pre-existing functional systems through natural selection. Irreducible complexity is central to the creationist concept of intelligent design, but it is rejected by the scientific community, which regards intelligent design as pseudoscience. Irreducible complexity is one of two main arguments used by intelligent design proponents, the other being specified complexity.

Michael Behe, a professor of biochemistry at Lehigh University, first argued that irreducible complexity makes evolution through natural selection of random mutations impossible. However, evolutionary biologists have demonstrated how such systems can evolve. There are many examples documented through comparative genomics showing that complex molecular systems are formed by the addition of components as revealed by different temporal origins of their proteins.

In the 2005 Kitzmiller v. Dover Area School District trial, Behe gave testimony on the subject of irreducible complexity. The court found that "Professor Behe's claim for irreducible complexity has been refuted in peer-reviewed research papers and has been rejected by the scientific community at large."

Michael Behe defined irreducible complexity in natural selection in his book Darwin's Black Box:

A single system which is composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning.

A second definition given by Behe (his "evolutionary definition") is as follows:

An irreducibly complex evolutionary pathway is one that contains one or more unselected steps (that is, one or more necessary-but-unselected mutations). The degree of irreducible complexity is the number of unselected steps in the pathway.

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