  Diverse biological networks exhibit universal features distinguished from
those of random networks, calling much attention to their origins and
implications. Here we propose a minimal evolution model of Boolean regulatory
networks, which evolve by selectively rewiring links towards enhancing
adaptability to a changing environment and stability against dynamical
perturbations. We find that sparse and heterogeneous connectivity patterns
emerge, which show qualitative agreement with real transcriptional regulatory
networks and metabolic networks. The characteristic scaling behavior of
stability reflects the balance between robustness and flexibility. The scaling
of fluctuation in the perturbation spread shows a dynamic crossover, which is
analyzed by investigating separately the stochasticity of internal dynamics and
the network structures different depending on the evolution pathways. Our study
delineates how the ambivalent pressure of evolution shapes biological networks,
which can be helpful for studying general complex systems interacting with
environments.
