The number of types of classes, orders, families, and species
is increasing, and our results show that this observation is surprisingly
consistent with the increasing evolutionary speed from kernels to
plug-ins to I/Os to batteries.
We propose that the slow evolution of
the top components and fast evolution of the bottom components of
the hierarchy is a universal phenomenon in evolution, not only in the
gene regulatory networks, but also in protein interaction networks,
cell signaling networks, and metabolic networks