traderdrew writes:
Neither the constitutive nor the inducible evolved strains grew on lactose in the absence of IPTG. (Hall 1982b)
I might not be getting the idea here, but doesn't this say that neither of the strains were capable of growing on lactose in the absence of IPTG? That is to say, both the original and the evolved strains lacked this capability?
This would indicate to me that we can ignore the significance of this third mutation when examining the point that this example provides. The bacteria developed the ability to metabolize lactose, a seemingly irreducibly complex system. They did not develop the ability to transfer the lactose through their cell membrane, a different matter altogether. The argument is not that cells can arbitrarily develop any quality that is required to live in an environment on demand; for instance neither strain would survive without a petri dish, but it makes no sense to consider this lack a mark for irreducible complexity.
In any case, the question is not if this particular bacterial strain could spontaneously develop the ability to metabolize lactose after devastating genetic damage. The point is that genetic alteration in a specific area does not make the system come tumbling down. The irreducible complexity argument suggests that knocking out one part of the system would prohibit everything from functioning properly, and thus there is no way to develop into such a system gradually. Not only is this argument inherently flawed (it may have been supported by other mechanisms which were selected out as they no longer contributed to survival) but arbitrarily including other lacking factors makes the comparison pointless. It is like arguing that a car is irreducibly complex because if you remove the pistons it cannot climb walls; it never could climb walls, so be frikkin' impressed when it develops pistons out of the blue and leave it at that.