In a message dated 9/16/2000 8:25:31 AM Pacific Daylight Time,
ccogan@telepath.com writes:
<< At 12:59 AM 09/16/2000, you wrote:
>http://www.cs.colorado.edu/~lindsay/creation/evolve_irreducible.html
>
>Scenario #1: reduction of function
>Scenario #2: loss of scaffolding
>Scenario #3: duplication
Chris
I would add:
Scenario #4: "sideways" evolution from some other equally complex, but not
*irreducibly* complex, structure.
>>
That could be another route. I am presently reading a paper:
"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. "
They address the potential pathways evolution can take. One of them is:
There are two ways by which irreducibly complex structures of functionally
indivisible components could result from adoption:
(i) Generation of an irreducibly complex structure by the joining of two or
more non-irreducibly complex structures of functionally
indivisible components. A possible example is the V(D)J joining mechanism in
the immune systems of jawed vertebrates, as the most primitive
version of this may have been formed by the insertion of a transposon into
the gene for a membrane-spanning receptor (Agrawal et al., 1998; Hiom
et al., 1998; Plasterk, 1998). The receptor, which probably had a function in
the non-adaptive defence system of jawless vertebrates, may not have
been irreducibly complex. The product of the transposon, which had the
non-defence-related function of transposing the transposon itself, was very
simple, consisting solely of two transposases, and may not have been
irreducibly complex. However, the insertion gave rise to irreducibly complex
split antigen-receptor genes, and thus ultimately to the highly advantageous
variable immune system.
(ii) Supply of an existing irreducibly complex structure of functionally
indivisible components. The structure would have evolved previously
by either redundancy elimination or the joining of two or more
non-irreducibly complex structures of functionally indivisible components.
Undulipodia may be accessible by Darwinian evolution in this manner, as their
two main hypothesised origins are from ectosymbionts (Szathmary,
1987) and spindle tubules (McQuade, 1977; Cavalier-Smith, 1978, 1982).
However, the most detailed published hypothetical pathway for the
transformation of ectosymbionts into undulipodia was actually one of parallel
direct Darwinian evolution. In this scheme, the connection between
tubulin microtubules and dynein arms, which Behe suggested to be irreducibly
complex, was absent at the initiation of the mutualist relationship
between the eukaryote and the microtubule-containing spirochete, and its
origin was explained, albeit incompletely, as part of the transformation
from rotational to undulipodial motility (Szathmary, 1987).
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