  We use the formalism of 'Maximum Principle of Shannon's Entropy' to derive
the general power law distribution function, using what seems to be a
reasonable physical assumption, namely, the demand of a constant mean "internal
order" (Boltzmann Entropy) of a complex, self interacting, self organized
system. Since the Shannon entropy is equivalent to the Boltzmann's entropy
under equilibrium, non interacting conditions, we interpret this result as the
complex system making use of its intra-interactions and its non equilibrium in
order to keep the equilibrium Boltzmann's entropy constant on the average, thus
enabling it an advantage at surviving over less ordered systems, i.e. hinting
towards an "Evolution of Structure". We then demonstrate the formalism using a
toy model to explain the power laws observed in Cities' populations and show
how Zipf's law comes out as a natural special point of the model. We also
suggest further directions of theory.
