Feedback Loops

            Central to a full understanding of dissipative systems, and especially those in symbiotic relationships, is the concept of system feedback (Stear, 1987). Complex systems with feedback loops that allow for self-renewal are called autopoietic structures.  One example of a simple, self-organizing system is a whirlpool. Another example is the red spot on the planet Jupiter. Other systems, such as the human body, can be extremely complex (Briggs and Peat, 1989).

            System feedback is a loop wherein information of some kind is fed back into the system. In this way, the system can respond to its environment. There are two main kinds of loops:  negative loops control and/or regulate; positive loops amplify. 

            A typical example of a feedback system is shown in Figure 2. Input into a system, together with an unknown quantity labeled disturbances, results in an output which is fed back into the system again.

Figure 2.  Components of a Simple Feedback System.

Figure 3.  Heater and Thermostat as a Simple Feedback System.  

            A simple feedback loop, consisting of a heater and a thermostat, is shown in Figure 3.  One square represents the heater and the other the thermostat. The heater kicks on, heating up a room. Heat, the output of the heater, serves as input to the thermostat. At a certain critical temperature, the thermostat tells the heater that the room is warm enough. The heater, receiving this feedback information through an electrical connection, shuts itself off. After a while, the thermostat notices that the room has cooled to a specific temperature, and notifies the heater. The heater kicks on again.  The information traveling from the heater to the thermostat and back again is a feedback loop.

            There are many such loops. When you are hungry, your stomach growls to let you know it wants to be fed, so you eat. Your stomach tells you that it is full, so you stop eating. The information that circles between your stomach and brain, and back again, is a feedback loop.

            The Autopoietic Paradox states that the more independent a system, the more feedback loops it requires (Briggs and Peat, 1989). This is a paradox because, by definition, an independent system does not require environmental feedback. However, the paradox holds because in real life, there truly are no closed or independent living systems. All living systems are open, and all living systems have feedback loops. A living system can only appear to be independent, by knowing exactly what is going on around it, and this implies the need for feedback loops. According to Stear (1987), all living systems are governed by feedback loops serving as regulatory processes.