Sense and respond has been used in control theory for several decades, primarily in closed systems such as refineries where comparisons are made between measurements and desired values, and system settings are adjusted to narrow the gap between the two. Since at least the early 1980s, sense and respond has also been used to describe the behavior of certain open systems called complex adaptive systems, or CAS. These are chemical, biological, ecological and cybernetic systems for which the functions, rules and strategies of the system emerge. Hurricanes, butterfly migrations, and chemical clocks are examples. The Santa Fe Institute has been a leader in studying such systems, and described sense and respond behavior as an iterative Sense–Interpret-Decide-Act cycle. Continued iteration through