  Structural and dynamical fingerprints of evolutionary optimization in
biological networks are still unclear. We here analyze the dynamics of genetic
regulatory networks responsible for the regulation of cell cycle and cell
differentiation in three organisms or cell types each, and show that they obey
a version of Hebb's rule which we term as coherence. More precisely, we find
that simultaneously expressed genes with a common target are less likely to
conflict at the attractors of the regulatory dynamics. We then investigate the
dependence of coherence on structural parameters, such as the mean number of
inputs per node and the activatory/repressory interaction ratio, as well as on
dynamically determined quantities, such as the basin size and the number of
expressed genes.
