 Irreducible complexity is supposedly something which could not have come through unbroken law (meaning law that has no special divine guidance), and especially not through the agency of natural selection. Critics claim that Behe shows a misunderstanding of the very nature and workings of natural selection. No one is denying that in natural processes there may well be parts which, if removed, would lead at once to the non-functioning of the systems in which they occur. The point however is not whether the parts now in place could not be removed without collapse, but whether they could have been put in place by natural selection. Consider an arched bridge, made from cut stone, without cement, held in place only by the force of the stones against each other. If you tried to build the bridge from scratch, upwards and then inwards, you would fail – the stones would keep falling to the ground, as indeed the whole bridge now would collapse were you to remove the center keystone or any surrounding it. Rather, what you must do is first build a supporting structure (possibly an earthen embankment), on which you will lay the stones of the bridge, until they are all in place. At which point you can remove the structure for it is no longer needed, and in fact is in the way. Likewise, one can imagine a biochemical sequential process with several stages, on the parts of which other processes piggyback as it were. Then the hitherto non-sequential parasitic processes link up and start functioning independently, the original sequence finally being removed by natural selection as redundant or inconveniently draining of resources.