"I strongly disagree with David Tyler's admission that the
critics' task is to show that systems are not irreducibly
complex. Behe's critics must show that irreducible complexity
can arise via normal evolutionary processes."
Thanks Terry for your contributions on this topic. I restrict
my response to the above two sentences - allowing Del Ratzsch's
post to address the exaptation issue.
I think this difference may be to do with terminology. I have
viewed the phrase "irreducible complexity" as an oxymoron for
philosophical naturalists and methodological naturalists. If the
systems "can arise via normal evolutionary processes", then IMO
they are not irreducibly complex!
I would express things this way: by showing that "irreducible
complexity can arise via normal evolutionary processes", Behe's
critics will demonstrate that the "systems are not irreducibly
complex".
I don't think I'm much out of step with Behe on this, as on page
230 of his book, he writes: "To reach a strong presumption of
nondesign will require the demonstration that a system is not
irreducibly complex or does not have much specificity between its
components".
Best wishes,
David J. Tyler.