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.
In addition, although most mutations have very little effect, often
a single mutation is enough to drastically change the action of the
product. This creates enormous flexibility in the system. As a result, it
is highly unlikely that the function of any biochemical systems could not
be performed by a very different system, and almost any biochemical system
could, with a few mutations, do something quite different.
In general, we don't have much data on the evolution of biochemical
systems. In part, this is because we're still discovering them and trying
to figure out how they work. Also, there is little incentive-the money in
biochemistry is for finding commercially useful substances, and the
humanitarian interest is in medicine or agriculture. Even within academia,
there is often separation if not tension between molecular biology and the
more traditional organism-level studies (where most of the evolutionary
research occurs, among other things). Probably most biochemists "believe
in evolution" without knowing much about it, and so don't see researching
it as necessary; likewise, those who "don't believe in macroevolution" may
not see much point in trying to research evolution. As a result, I think
it's risky to say that something did or did not occur in the evolution of
biochemical systems. The morphological evidence suggests that God has
largely created following the patterns of "natural" laws rather than by
setting them aside from time to time, so I'd expect molecular evolution to
also generally obey "natural" laws.
David Campbell
"Old Seashells"
Department of Geology
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315
919-962-0685
FAX 919-966-4519
"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug