The evolutionary process and optimization

venus at ccwf.cc.utexas.edu venus at ccwf.cc.utexas.edu
Sat Nov 9 15:28:52 EST 1991


On first glance, evolution seems to be a process that optimizes structures
and functions in living organisms. Amazing efficiency and coherence are
usually common features in many biological processes and structures.
However, a more precise definition of optimal is required here.
The evolutionary process does not exactly resemble the process that, for
example, a stone in the bottom of a river undergoes. The stone has any
shape at first, but in the bottom of the river it starts hitting other
rocks and the water polishes it until it reaches the optimal shape of a sphere.
In other words, the spherical shape is the optimal intrinsic shape that
this process will eventually produce.
I wonder if what we call "optimal structures and functions" are just
observed phenomena in the naturally-ocurring (wild) type of any given
species. Is "Optimal" a qualification that only can be given to a structure
or function in relation to the  species' circumstances? Are there absolute
"optimal structures and functions" in living organisms, or rather just only
more or less successful features for that species?
An example of this phenomenon can be found in DNA polymerase III. It is the
enzyme in charge of replicating DNA in E.coli bacteria. According to Stryer
( Biochemistry, 3rd edition) the effeicient 3' to 5' exonuclease activity
of DNA-polymerase III makes it a highly precise enzyme. It even removes one
in ten correctly paired nucleotides! just to make sure that mistakes are
not inherited. Its proof-reading activity, coupled with additional repair
machanisms, produce an observed spontaneous mutation frequency of 10 to the
-10. Furthermore, some E.coli mutants have lower than normal spontaneous
mutation rates due to a higher than normal ratio of exonuclease to
polymerase activity in DNA polymerase III. Some other mutants have higher
spontaneous mutation frequency than that of the wild type.


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