Since natural selection requires a function to select, an irreducibly complex biological system, if there is such a thing, would have to arise as an integrated unit for natural selection to have anything to act on.

Although Professor Behe is adamant in his definition of irreducible complexity when he says a precursor 'missing a part is by definition nonfunctional' what he obviously means is that it will not function in the same way the system functions when all the parts are present. Dover Area School District the first direct challenge brought in United States federal courts to an attempt to mandate the teaching of intelligent design on First Amendment grounds Behe was called as a primary witness for the defense and asked to support the idea that intelligent design was legitimate science.

Michael J. He currently serves as professor of biochemistry at Lehigh University in Pennsylvania and as a senior fellow of the Discovery Institute's Center for Science and Culture. Behe is best known for his argument for irreducible complexity which asserts that some biochemical structures are too complex to be adequately explained by known evolutionary mechanisms and are therefore more probably the result of intelligent design.