A core principle of differential emotions theory (DET) is that emotions operate as systems (Izard, 1971; Izard et al., 1965). An emotion is a complex system in the sense that it emerges from interactions of constituent neurohormonal, motoric, and experiential processes. Although personenvironment transactions play a role in the development of healthy emotions, the potential for each component of each discrete emotion system self-organized in phylogeny and emerged as an evolutionary adaptation. Individual emotions also coassemble with other emotions to form contingent emotion patterns that stabilize over repetitions and time. Thus, discrete emotions are both the product and stuff of system organization. The systems are self-organizing in the sense that recursive interactions among component processes generate emergent properties.

This system perspective of DET fits well with the general emphasis of dynamic systems (DS) theories of development on the self-organization of the structure of behavior. Both DS theories of development and DET have the central theoretical goal of understanding organization and pattern in complex systems, without recourse to some deus ex machina (Izard, 1977; Smith and Thelen, 1993; Thelen, 1989). For both theories, structure and complexity emerge from constituent processes to yield behavioral performances that vary among individuals and within individuals over time. Understanding the individual variation is a main theoretical concern of both DET and DS theories of development.