International Encyclopedia of Systems and Cybernetics

Coexistence in a complex system of a number of subsystems of different types.

Any complex system must carry out a variety of functions in order to maintain its activity. If complexity results of the complementary association of numerous components, these components need necessarily be of different kinds. This may be observed easily in human as well as in biological systems.

Heterogeneity is a sine qua non condition of complexity because it allows the emergence of synergies and increases enormously the system's variety, which thus becomes polyvalent, its capacity of useful interaction with its environment being as a result, vastly enhanced.

Heterogeneity expresses itself at various levels in most (if not all) complex systems: the specialized components are generally themselves complex systems. J.G. MILLER did demonstrated this in a very thorough manner in his "Living Systems" (1978).

A. ANGYAL used the expression "unitas multiplex" which makes perfectly clear the idea of a complex multiplicity within a whole, but it never became of common use (1969, p.27).

Heterogeneity grows by differentiation processes, as for example:

- MARUYAMA's deviation-amplifying mutual causal process;

- BENARD's dissipative structuration;

- von FOERSTER and ATLAN's order from noise;

- PRIGOGINE's bifurcations originated by giant fluctuations in systems far away from equilibrium.

Its development needs a source of energy and an internal variety sufficiently wide to be moderately constrained. Unrestricted heterogeneity would lead back to homogeneity and to the systems demise. Excess of constraints would finally block it, which is another road to destruction.

Heterogeneity also presents a temporal dimension: The different parts or subsystems transform themselves along different rhythms and cycles in time, while these rhythms and cycles combine to produce a global and generally very intricated behavior.

Finally, space heterogeneity as an environmental condition favoured the appearance of heterogeneous systems. According to the German biophysicist H. KUHN:" The driving force for the self-organization of matter is seen in a specific environmental structure to be found on the surface of the earth. By this structure, which is periodic in time and heterogeneous in space, evolution is initiated and driven towards a continuously increasing degree of complexity correlated to a continuous expansion of the accessible living space" (1976, p.68).

According to S.R. REICE: "Spatial heterogeneity and disturbance are interdependent. Disturbance creates patches, but patchiness modifies and sets the extent of the disturbance - that is, the disturbance responds to the underlying heterogeneity of the environment. Different patch types generate different frequencies and degrees of disturbance and provide numerous opportunities for recruitment" (1994, p.434).

The whole subject is closely related to percolation and criticality phenomena in composite systems: avalanches, flicker noise, etc.

In a different meaning, M. MARUYAMA widely researched heterogeneity in cultures and states: "In any society, at any time there is heterogeneity of logics among individuals. It is possible to find individuals of any logical type in any culture at any time… Cultural differences consist in the way some logical type becomes dominant and influences individuals of other types. Beneath the homogeneous surface of a culture, there are all individual logical types, hidden, camouflaged or transformed" (1994, p.3).

As observed by MARUYAMA, heterogeneity is in some societies and cultures considered positive, and in others, negative. He argues that heterogeneity could "mean interaction for mutual benefit", a view held in some African Cultures, as the MALINKE of Western Africa.

The use of the term "heterogeneous" seems subject to some misunderstandings. M. BUNGE writes: "There are no heterogeneous systems (e.g. systems composed of people and values, or books and theories)" (1993, p.214)

This should be correct if we would give to "heterogeneous" the meaning of "foreign to", or "not coherent with", or "without structural and functional relations". An hypothetical living being, constructed from elements and organs from different and unrelated animals would be heterogeneous in this sense… but could not function, nor survive.