Human social systems are open systems interacting with their environments through the exchange of matter, energy, and information deriving both from the system itself and from the environment. The behaviour of such systems is typically purposive and directed toward a goal. Such systems, including subsystems such as individuals and groups within them, interact as communication systems in the form of a dynamic that tends to lead to a steady state situation whose disruption they resist. Within relatively narrow limits they are capable of adjusting and adapting to their environments, as well as changing them. Such systems are characterized by functional unity, namely a condition in which all parts work together with a certain degree of harmony or internal consistency, and without producing persistent conflicts which cannot be resolved or regulated.