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In a complex adaptive system, behavior emerges that is not easily predicted from the component parts of the system and various input stimuli. Information flows into a system in a changing external environment, prompting a response in the form of self-organization. Information flows back into the environment, allowing both positive and negative feedback mechanisms to contribute to the system's next round of response. In this unit, we consider examples of complex adaptive systems in biology from the molecular level to the behavior of whole organisms, colonies of organisms, and the human brain. A much broader range of systems display this behavior, however, including the stock market and flow of immigrants across the semi-permeable U.S. land border. (Unit: 9)