From: FMAJ1019@aol.com <FMAJ1019@aol.com>
[...]
>A classification of possible routes of Darwinian evolution. Richard H.
>Thornhill1 and David W. Ussery. Published in The Journal of Theoretical
>Biology, 203: 111-116, 2000.
>
>"Possible routes of Darwinian evolution can be classified into four
>fundamental categories, as outlined below."
[...]
I think it's unwise to place too much reliance on this paper by Thornhill
and Ussery. Their definition of irreducible complexity seems to me to be
just as problematic as Behe's. I've yet to see any definition of IC which
defines the meaning of "parts" or "components" in an adequate way.
If you can select the components freely, as Behe allows, then almost any
system can be considered IC. For example, I can consider the human body to
consist of two components: the skeleton and the soft tissue. These
components are well-matched and interacting, and removal of either of them
causes the body to effectively cease functioning, so by Behe's definition,
the human body is IC. And a similar line of argument can be applied to
almost any functional system.
Thornhill and Ussery attempt to save the concept of IC by introducing the
idea of "functionally indivisible components". But I don't think their
definition of functional indivisibility is adequate. Here's what I wrote in
an email to Dave Ussery:
[quote]
I am, however, having difficulty understanding your paper "A classification
of possible routes of Darwinian evolution." In particular, I find your
definition of "functionally indivisible" to be confusing, and would be
grateful for some clarification. The definition given in your paper is as
follows:
"Functional indivisibility: The quality of a component of a structure such
that there is at least one alteration to it which would render the whole
structure absolutely non-functional. This term was implied but not used by
Behe (1996a, pp. 45, 142)."
The corollorary of this is that a functionally *divisible* component is one
to which no possible alteration would render the whole structure
non-functional. You subsequently mention, as an example of functionally
divisible components, the increments of giraffe neck length. Yet it seems
clear to me that there are plenty of alterations in such increments which
could render the giraffe non-functional (i.e. dead!)--for example the
absence of any aesophagus from such an increment.
[end quote]
Ussery and Thornhill were unable to resolve this problem for me, and said
that they themselves were now uncertain about their definitions.
I've attempted to think of a more useful definition of IC, but without
success. I now doubt whether a useful definition of IC is even possible.
Richard Wein (Tich)
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