The stable configurations resulting from BVSR processes can be seen as primitive elements: their stability distinguishes them from their variable background, and this distinction, defining a "boundary", is itself stable. The relations between these elements, extending outside the boundaries, will initially still undergo variation. A change of these relations can be interpreted as a recombination of the elements. Of all the different combinations of elements, some will be more stable, and hence will be selectively retained.
Such a higher-order configuration might now be called a system. The lower-level elements in this process play the role of building blocks: their stability provides the firmness needed to support the construction, while their variable connections allow several configurations to be tried out. The principle of "the whole is more than the sum of its parts" is implied by this systemic construction principle, since the system in the present conception is more than a mere configuration of parts, it is a stable configuration, and this entails a number of emergent constraints and properties (Heylighen, 1991). A stable system can now again function as a building block, and combine with other building blocks to a form an assembly of an even higher order, in a recursive way.
Simon (1962) has argued in his famous "The Architecture of Complexity" that such stable assemblies will tend to contain a relatively small number of building blocks, since the larger a specific assembly, the less probable that it would arise through blind variation. This leads to a hierarchical architecture, that can be represented by a tree.
Two extensions must be made to the Simon argument (cf. Heylighen, 1989). 1) If one takes into account autocatalytic growth, as when a small stable assembly makes it easier for other building blocks to join the assembly, the number of building blocks at a given level can become unlimited. 2) It is possible, though less probable, that a given building block would participate in several, overlapping stable assemblies; it suffices that its configuration would satisfy two (or more) selection criteria, determining stable systems. It is clear, however, that the more selection criteria a configuration would have to satisfy, the less likely that such a configuration would be discovered by blind variation. These two points lead us to generalize the tree structure of Simon's "nearly-decomposable" architecture to a loose or quasi-hierarchy (Joslyn, 1991), which in parts can be very flat, and where some nodes might have more than one mother node.
Reference: Heylighen F. (1992): "Principles
of Systems and Cybernetics: an evolutionary perspective", in:
Cybernetics and Systems '92, R. Trappl (ed.), (World Science, Singapore),