  Assessing quantitatively the state and dynamics of a social system is a very
difficult problem. It is of great importance for both practical and theoretical
reasons such as establishing the efficiency of social action programs,
detecting possible community needs or allocating resources. In this paper we
propose a new general theoretical framework for the study of social complexity,
based on the relation of complexity and entropy in combination with
evolutionary dynamics to asses the dynamics of the system. Imposing the second
law of thermodynamics, we study the conditions under which cooperation emerges
and demonstrate that it depends of relative importance of local and global
fitness. As cooperation is a central concept in sustainability, this
thermodynamic-informational approach allows new insights and means to asses it
using the concept of Helmholtz free energy. Finally we introduce a new set of
equations that consider the more general case where the social system change
both in time and space, and relate our findings to sustainability.
