Hierarchical complexity, as defined by James G. Miller in Living Systems Theory, is the number of levels of organization or higher-order representing structures, or HORS, which create order and meaning out of a chaotic or complex system. HORS generally consist of dynamic feedback loops and enhance the organization’s adaptability and overall flexibility, thus allowing for higher levels of complexity and the dynamic coalescence of purposeful action in pursuit of emergent goals. Hierarchical complexity is understood to be a key factor in the complexity, adaptability, and robustness of organizational and natural systems.

See also: complexity science, emergence, evolutionary computing, evolution