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.

We can look high or we can look low in books or in journals, but the result is the same. The scientific literature has no answers to the question of the origin of the immune system.

Throughout history there have been many other examples, similar to that of Haeckel, Huxley and the cell, where a key piece of a particular scientific puzzle was beyond the understanding of the age.

Although Darwin was able to persuade much of the world that a modern eye could be produced gradually from a much simpler structure, he did not even attempt to explain how the simple light sensitive spot that was his starting point actually worked.

If you take away a rock from a pile of rocks you haven't changed much. It's still a heap of rocks - just a rock or two smaller. Take away a component from the mousetrap and it isn't a mousetrap any more.

For example, both humans and chimps have a broken copy of a gene that in other mammals helps make vitamin C. ... It's hard to imagine how there could be stronger evidence for common ancestry of chimps and humans. ... Despite some remaining puzzles, there's no reason to doubt that Darwin had this point right, that all creatures on earth are biological relatives.

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.