Joined: Oct. 2007
"Direct Darwinian pathway" is Behe's term for a multi-step process in which every step is "add a new part to the system". This is all well and good, but it's worth noting that evolutionary changes aren't limited to just adding new parts; in addition, an evolutionary change can also (a) remove an existing part, and (b) modify an existing part. Therefore, there are any number of Darwinian pathways which include at least one step other than "add a new part to the system" -- which means there are any number of Darwinian pathways which do not fit Behe's definition for "direct Darwinian pathways"
|Quote (inquiry @ Dec. 10 2009,13:39)|
|There exists within the cell highly complex machines. These molecular machines are made up of multiple parts that perform a specific function. If any part of the system is tampered with it no longer can perform the original function. This is known as the irreducible core. Can natural selection account for such irreducibly complex machines? In direct Darwinian pathways natural selection improves upon a system through the evolutionary process, yet the function of the system remains the same throughout the process. However, the irreducible core for the cell is quite complex. The function of the cell is dependent upon its complex components. In order for a direct Darwinian pathway to be a viable option the complexity of the cell came about by the evolution of simpler systems that had the same function. But if you any of the parts of the cell are missing it can no longer serve its function. Therefore, there could not be prior simpler systems that performed the same function. Natural selection supposedly starts to work on a simple organism, yet nothing more simplified could perform the same function as this complex system. The only option would be for the complex system to come to be all at once. An alternative to a direct pathway is an indirect pathway whereby the system and the function itself evolve over time. As far as I know there is no empirical evidence to support such a claim.|
Personally, I think Behe is right that his "direct Darwinian pathways" aren't capable of generating an irreducibly complex structure. Where he and I differ is that he thinks this restriction on "direct Darwinian pathways" applies to any and every Darwinian pathway whatsoever, direct or otherwise, and I call bullshit on that.
Now, Behe has already acknowledged that very simple Irreducibly Complex systems can arise by chance, no Designer needed. So let's look at a hypothetical IC system with only two parts, A and B. Since this system is IC, both of these parts are required for the system to do its job; if either part A or part B should be broken or absent, the system don't do its job. So this simple, two-part system chugs along, doing its job, until a mutation adds a new part, C, to it. At this point, part C is something the system can take or leave; the presence of part C might be helpful, but its absence won't hurt anything, either. And so our three-part system chugs along, doing its job with part C as a helpful-but-unnecessary attachment... until a new mutation hits part A, modifying part A in such a way that now part A needs part C in order to do its job. This modification of part A has rendered part C a necessary component of the system; at this point, what had formerly been a two-part IC system is now a three-part IC system. And there's nothing to keep new parts D, E, F, G, etc, from being incorporated into this IC system, with each new part being incorporated by an add-a-new-part/modify-an-existing-part tango.
Again: For Behe, a direct Darwinian pathway consists entirely of "add a new part" steps, so the scenario I just outlined, which includes a "modify an existing part" step, is not what Behe would call a direct Darwinian pathway! Therefore, everything Behe says about direct Darwinian pathways does not apply to the scenario I just outlined.
If Behe, or anybody else, wants to argue that evolution cannot produce IC systems, fine: All they have to do is figure out what's going to prevent mutations from modifying biological systems in such a way that parts of those systems get 'promoted' from helpful-but-unnecessary to required-in-order-to-function-at-all.