Biological organisms have evolved in a changing environment, using
biochemical networks to implement survival strategies when conditions became
adverse. The role of networks as survival tools should therefore be
reflected in their topological structure, or in the positioning of various
types of genes within the network. However, before looking for hallmarks of
survival and evolution in networks, it is necessary to identify the very
strategies that organisms use to survive in a fluctuating environment.

Two key strategies are known to promote survival in a changing environment.
In responsive strategies, defense is activated after the environment becomes
adverse. By contrast, in preventive strategies defense is activated by
random phenotypic switching, before the environmental challenge. I will
illustrate how random phenotypic switching can aid survival in a changing
environment by a gene regulatory model system that we have recently
assembled.

Since only living organisms can evolve, survival in adverse conditions is a
prerequisite for evolution. Indeed, publicly available genome-scale data
seem to reveal a particular bipolar architecture of gene regulatory
networks, which consist of a set of highly conserved "core" genes with
stable expression, and a set of "peripheral", mutation-prone genes with
highly variable expression.