limited. Modular networks can evolve by rewiring the modules. This
rewiring capability property tends to make modular networks more
evolvable (Hartwell et al., 1999; Sun and Deem, 2007). A hierarchical
network is an advanced modular network. In hierarchical networks,
some modules are key modules that may relate to the core function
and be resistant to mutation. Other modules are periphery modules
that may be more likely affected by the environmental changes
(Ravasz et al., 2002). Peripheral modules evolve rapidly and allow the
organism to survive in a changing environment.