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.

As can be seen even by this limited number of examples proteins carry out amazingly diverse functions.

In Darwin's time all of biology was a black box: not only the cell, or the eye, or digestion, or immunity, but every biological structure and function because, ultimately, no one could explain how biological processes occurred.

Biology has progressed tremendously due to the model that Darwin put forth. But the black boxes Darwin accepted are now being opened, and our view of the world is again being shaken.

In the abstract, it might be tempting to imagine that irreducible complexity simply requires multiple simultaneous mutations - that evolution might be far chancier than we thought, but still possible. Such an appeal to brute luck can never be refuted... Luck is metaphysical speculation; scientific explanations invoke causes.

The first point one has to get straight in discussions like this, is that ID is not the opposite of evolution. Rather, it is the opposite of Darwinism, which says life evolved by an utterly unguided, undirected mechanism. If god directed the process of evolution, or rigged the universe to produce complex life, then that is not Darwinism - it is intelligent design.

It was only about sixty years ago that the expansion of the universe was first observed.