  Expression level is known to be a strong determinant of a protein's rate of
evolution. But the converse can also be true: evolutionary dynamics can affect
expression levels of proteins. Having implications in both directions fosters
the possibility of a feedback loop, where higher expressed systems are more
likely to improve and be expressed even higher, while those that are expressed
less are eventually lost to drift. Using a minimal model to study this in the
context of a changing environment, we demonstrate that one unexpected
consequence of such a feedback loop is that a slow switch to a new environment
can allow genotypes to reach higher fitness sooner than a direct exposure to
it.
