International Encyclopedia of Systems and Cybernetics

The ability of a system to select a satisfactory response to any stimulus.

Systems must constantly be able to select a convenient response, either to a variation in their environment, or some internal perturbation evoked by such a variation (directly or not).

The first condition to do that is to dispose of a suitable choice of possible responses (Requisite variety law)

If this condition is fulfilled, the choice still must take place. This is where selectivity enters.

According to H. SIMON, there are two basic kinds of selective processes:

"1. Various paths are tried out, the consequences of following them are noted, and this information is used to guide further search".

Of this first process, SIMON gives the following example: "… in organic evolution various complexes come into being, at least evanescently,and those that are stable provide new building blocks for further construction. It is this information about stable configurations, and not free energy or neguentropy from the sun (Note: which is, in any case, the prime mover) that guides the process of evolution and provides the selectivity that is essential to account for its rapidity"

"2. The second source of selectivity in problem solving is previous experience. We see this particularly clearly when the problem to be solved is similar to one that has been solved before. Then, by simply trying again the paths that led to earlier solution, or their analogues, trial and error search is greatly reduced or altogether eliminated".

"The closest analogue (in organic evolution) is reproduction. Once we reach the level of self-reproducing systems, a complex system, when it has once be achieved, can be multiplied indefinitely" (1965, p. 68).