"Ecological understanding must be ecological."
Gregory Bateson

Cities, like natural ecologies, emerge through recursive procedures. They are the cumulative result of countless individual operations repeated over time with slight variation. Difference is produced incrementally, as an effect of repetition and feedback. As an urbanistic model, an "artificial ecology" implies a complex interplay of agents, objects and process, where time is a key variable. There are ecologies of waste, development, pollution or leisure, not to mention war, politics or terrorism. Ecologies are by definition incompatible with fixed categories. What architecture might learn from ecology is a more flexible form of practice itself: a series of working concepts flexible enough to accommodate the wildly improbable demands of the contemporary city.