> However, there are at least two mechanisms for gradual assembly of
>a complex system.
> Sequential addition of parts as needed could produce a realtively
>complicated final product. For example, several tRNA genes are similar
>enough that they are believed to be mutated copies of one another. All
>living cells today require a full set of the genes to make proteins, but
>the genes suggest that some distant ancestor of all current life was
>getting by with only a few tRNAs and then added more by duplication and
>mutation of these genes.
> Another possibility is by taking existing parts and combining them
>into a new, more complicated system. Some time back, a biochemist (who I
>think is on this list) gave the example of the citric acid cycle. Certain
>bacteria use half of the cycle for one process and all but one enzyme of
>the other half for another process, with the last enzyme closely
>associated.
Its certainly the case for many systems, you can argue for mutation and
gradual adoption of other enzymes. Either design or evolution would work
for those. Behe's argument is that there are *some* cases (certainly not
all) where gradualism or adoption wouldn't work - where the system
absolutely needs all components working exactly as they are or there
would be absolute systemic failure (a couple of his examples are the
blood clotting cascade and the immune system).
><-- @
>><Jeffrey Lee: jlee@isisph.com @@ \
>>><Quality Systems Development @@@ \
>>>><Isis Pharmaceuticals, Inc. @@@@ \
>>>>><www.isip.com @@@@@___________\
>>Standard Disclaimers Apply: My views are my own unless they're not.