International Encyclopedia of Systems and Cybernetics

Anomalous variation of the environment which impairs the correct working of the system or of one of its parts.

Any viable system is adapted to a specific environment, according to its perceptive abilities, to the internal organization that it obtained from former systems, to the learning processes it underwent, and its ability to use its internal variety or reserves through its regulation devices.

The environment may fluctuate within some limits without endangering the system, but these limits correspond, of course to the limits of the systems possibilities of adaptation.

A similar idea was enounced under the guise of the "Law of Requisite Variety" by ASHBY.

I. PRIGOGINE states that "dynamical systems have no way to forget perturbations" (1985, p.7). A recent example of this has been the destruction of Comet SHUMAKER-LEVY 9 after having its orbit perturbed by Jupiter.

A. LIONI gives an interesting example of the way an exogenous perturbation may convert itself in an endogenous one: In a public bus line, when a unit is delayed by an environmental incident, the delay tends to extend itself because in the mean time more passengers have accumulated on the next stops. As a result the next units in the line crowd up with fewer and fewer passengers and the exogenous perturbation finally generates a global endogenous perturbation (2000, p. 149)

→ Collective behavior; Delay amplification; Queuing theory