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the final three-dimensional structure; the opposite might also happen and
neighbor amino acids in the protein chain may face completely different
moieties and be involved in distinct aspects of the structure or functionalities
of the protein. Finally, the most important fact about protein structure and
function is that the function of a particular protein is dictated by its unique
three-dimensional structure, which is ultimately dictated by the sequence of
the gene. Note, however, how far a protein is from its DNA sequence! Such is
the power of simple transformations and the beauty of emergence.
The expression trees of gene expression programming are also the prod-
ucts of simple transformations and the results are equally overwhelming. We
will also see that, in GEP, the expression trees also fold in particular ways,
bringing together elements distant in the gene, and separating others that
were close. We will also see that some expression trees have a quaternary
structure, being composed of smaller subunits (sub-expression trees) that are
linked together by different kinds of posttranslational interactions.
1.3 Adaptation and Evolution
Much of the diversity we see in the living world, results from the accumu-
lation of mutations (in the broad sense) in proteins. If we take any protein,
for instance, hemoglobin, and analyze its sequence among the individuals
of one population, we will see that there are numerous protein variants,
differing in one or several amino acids. Most of these variants work with
equal efficiency, but some of them may exhibit slight differences in func-
tion. In certain environments some of these variants are better adapted than
others and may confer some advantage to the individuals expressing them.
If we continue this investigation further and analyze the hemoglobin mol-
ecules from different species, we will see that there are, in this case, con-
siderable differences between their hemoglobins. Although these different
hemoglobins play exactly the same function, they seem wonderfully adapted
to the natural environment of the particular species. Indeed, the modifica-
tions that occur at the molecular level in proteins enable populations of
organisms to develop new abilities, adapt to new environments, and ulti-
mately become new species.
For populations to adapt in the long run, the individual organisms must be
selected to reproduce. In terms of evolution, the survival of a particular or-
ganism is only important if this organism leaves progeny. It is the
