  Darwinian evolution gives rise not only to the adaptation to the environment
but also to the enhancement of the robustness against mutation. Suppose more
than one phenotypes share the same fitness value. We expect that some
phenotypes are hardly selected as a consequence of the selection bias for
mutational robustness. We investigated this phenotype selection for a model of
gene regulatory networks (GRNs). We constructed the randomly generated set of
GRNs using the multicanonical Monte Carlo method and compared it to the
outcomes of evolutionary simulations. The results suggest that the mutationally
least robust phenotype is suppressed in evolution.
