In his blog on intelligent design (Wednesday 2nd Nov 2005), Peter Williams takes me to task for producing an unbalanced issue of THINK on Intelligent Design, pointing out that ID proponent Michael Behe has “responded” to Orr’s demolition job (here) on Behe’s argument for intelligent design (which I published). Behe has indeed responded (here), but not effectively.
I have read Behe’s response and still think Orr nails Behe. Orr points out that many organisms are irreducibly complex in the sense that if you remove parts like brains, lungs etc. they cease to function. Yet such systems can evolve by natural selection, because parts that were inessential can become so, e.g. air sacs can develop into useful but not essential primitive lungs, and later these may become essential when the gills or whatever disappear. Clearly, this could happen on the natural selection theory. So natural selection has no particular problem regarding such irreducibly complex systems.
Here is the key response to this point from Behe.
Professor Orr has a mistaken notion of irreducible complexity. I thought I made that clear in my reply, but from his response I suppose I did not, so let me try again. I define irreducible complexity in Darwin’s Black Box as “a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.” Orr, however, uses the term loosely to mean something like “if you remove a part, the organism will die.” In his review he talks about lungs, saying “we grew thoroughly terrestrial and lungs, consequently, are no longer luxuries-they are essential.” The problem is, if you quickly dissect lungs from an animal, many parts of it will continue to work. The liver will work for a while, muscles will twitch, cells will metabolize until they run out of oxygen. Thus lungs are not absolutely required for the function of those other parts, not in the way that a spring is absolutely required for a standard mousetrap or nexin linkers are required for ciliary function. That’s the problem with using poorly chosen examples, especially at the whole-organ level. I am careful in my book (pp. 46-47) to say that you must look at molecular systems to see if Darwinism can explain their development. When you look at irreducibly complex molecular examples, it is clear that Darwinism has not and, I believe, cannot explain them. Orr’s main line of argument, therefore, simply misses the point.
This is surely confused. First, here again is Behe’s definition of an IC (irreducibly complex) system:
“a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning.”
But a living organism of the sort Orr describes does still qualify as IC, as it does effectively cease to function when dismantled. So doesn’t Orr’s example stands as an example of an IC system?
Behe’s point is that some parts of the organism will function for a while on their own when the system is dismantled. But this is irrelevant. The system pretty quickly ceases to function. So, by Behe’s own definition of IC, a living organism with lungs is irreducibly complex, isn’t it?
But of course, even if Orr’s specific example didn’t qualify as irreducibly complex (because Behe requires for irreducible complexity that the system immediately cease functioning – that very second – on removal of a part – it must not slowly wind-down over even a minute or two, as a human body does), Orr’s point would in any case remain valid. The point remains that natural selection allows that parts that are at one time inessential can become essential (even so essential that their removal results in immediate loss of function). So there’s no particular difficulty about an IC system evolving by natural selection.
KEY POINT: Why does Behe suppose IC systems cannot evolve by natural selection? Because they would have to evolve “in one go”. They cannot evolve by increments, by natural selection.
Orr explains how an IC system can evolve gradually, by natural selection.
So game over, not withstanding the irrelevencies raised by Behe.