The origins of the hierarchical complexity construct, as it is defined here, are in the work of Jean Piaget, whose model of mental representation delineates five developmental stages (and a varying number of sub-stages), These have been represented as the (1) reflexive, (2) sensorimotor, (3) symbolic or preoperational, (4) concrete, and (5) formal stages (Piaget & Inhelder, 1969). Each of these developmental stages is defined by a set of formal properties. In the Piagetian model, development from one form of thought to the subsequent form involves a process of hierarchical integration, in the sense that the actions of the earlier form become the content of the actions of the latter (Piaget, 1985). A number of researchers have described general developmental sequences that elaborate this notion of hierarchical integration (Baldwin, 1894; Case, 1991; Demetriou & Valanides, 1998; Fischer, 1980; Pascual-Leone & Goodman, 1979; Werner, 1948). Recently, for example, Noelting and Rousseau (2000) employed the notion of hierarchical integration to demonstrate that each Piagetian stage is composed of three levels — two substages and one consolidated stage — to form a hierarchy of 12 levels covering the period from early childhood to adulthood. The concept of hierarchical integration is also fundamental to several neo-Piagetian models of cognitive development, including those of Fischer (1980), who emphasizes the development of skill hierarchies in particular contexts; Pascual-Leone and Goodman (1979), who focus on the growth of mental attention and memory capacity; Case (1991), who describes the development of memory capacity and associated processing structures; and Demetriou & Valanides (1998), who describe hierarchical development in terms of processing functions.

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