By J.B. Ruhl
Post 2: What is a Complex Adaptive System?
July 21, 2006
Complexity theory is the foundation for the study of complex adaptive systems (CAS). A CAS is a heterogeneous collection of interacting agents that evolves over time at the macroscopic system scale. Any agent in the system interacts with one or more other agents in any “move” of the system according to rules. Some or all of the agents in the system also base their decisions about what to do in the next move based on the macroscopic state (macrostate) of the system or on conditions exogenous to the system having some impact on it.
So far, pretty straightforward. It gets interesting, however, as we tinker with the number of agents, their heterogeneity, the number and tightness of couplings between them, and the rules of each move. The upshot is that, although all the agents are basing moves according to strict rules of interaction and response, it can become impossible to predict the evolutionary path of the system very far into the future. Complexity theory describes a number of attributes that account for this property of CAS behavior, which I will cover in the next two posts. For deep background reading on this topic, the classics are At Home in the Universe by Stuart Kauffman, and Hidden Order by John Holland.
Next: What attributes of a complex adaptive system make it complex and unpredictable?